DC to DC converter design – Don’t blow your fuse (and other lessons)

June 30th 2021

Finlay Knops-Mckim

Consultant Electronics Engineer

With a vast range of off-the-shelf and feature-rich control ICs available, the selection and design of DC to DC converters is a superficially simple process.

But even with these highly integrated parts and design resources there are still many common pitfalls that can lead to Electromagnetic Compatibility (EMC) or thermal nightmares, blowing budgets, timescales, and the occasional fuse in the process.

I’ll share a few of the most common “gotchas” that electronics engineers will contend with early in their careers. We’ll dodge the complex calculations here, but there are excellent resources such as “The Art of Electronics” that can provide a deeper mathematical explanation of the issues at hand.

Medical device or arc furnace? Context is key

You wouldn’t use a trailer truck to commute to work, nor would you use the family car to ship potatoes to a supermarket. Both are vehicles but, clearly, they operate in different contexts so have different strengths and weaknesses.

The same logic applies to switch-mode converters and controllers. A quick glance at the cover page of any switcher datasheet will often reveal potential use cases. This is not just marketing: if a switcher is intended for industrial machinery or large server farms, it is quite likely that its EMC performance faces different limits to those marketed at consumer or healthcare devices. For example, while higher noise limits in industrial settings liberate chip designers to focus more on power efficiency by maximizing switching speed and slew rate, this can also increase emissions.

Excessive switcher noise can lead to poor performance of analogue circuitry, and in severe cases can interfere with the function of nearby devices. So, while those efficiency figures might be tempting, using the switcher in a compact medical device could lead to months of work to achieve compliance in EMC test chambers.

Lesson: Use parts in the context for which they are designed. Parts targeted at industrial applications may lead to issues if used in consumer or medical devices.

The heat must go somewhere

So, you’ve found a very neat five-amp switcher with a 3x3mm footprint that is 90% efficient? Sounds perfect for your space-constrained, high-power design. Except you’ve just plugged it in, and it cuts out after ten seconds at load. This is less than ideal. The problem is that, even at 90% efficiency, the switching losses at 5A are enough to make a 3×3 chip quite toasty – so much so that the thermal cut-out is operating. You might have been fine if you had a large copper flood to take the heat away, but this is a space constrained design so of course you don’t.

Lesson: Always consider the thermal design of a high-power system. Even if a small switcher is electrically capable of high currents, it may require substantial heatsinking that wipes out any size or efficiency benefits.

Evaluation modules are there to help

Datasheets are an important resource for correctly integrating a switcher design into a larger electronic system, but they are also a company’s marketing collateral, and can mask certain “gotchas” in product performance.

They do not guarantee that your design or use-case will play nicely with the chosen parts. Evaluation modules (EVMs) provide a less theoretical way of confirming that a part is fit for purpose, and further provide a “best case” performance benchmark given exactly the right implementation.

Taking an EVM along when performing pre-compliance EMC tests is a quick way to confirm that the chosen part is not going to be an emissions nightmare in the final design, and similarly if the EVM overheats, your design probably will as well.

Lesson: Buy in an EVM for your chosen switcher part and perform a set of tests that represent the final use case. If you have problems at this stage, it’s fair to say you should pick a different part or modify your design to mitigate the issues.

Saturation current is not standardized

If your switcher’s primary inductor becomes saturated, the efficiency of the system will rapidly plummet, and it will likely lose regulation or overheat. Most switcher manufacturers helpfully include the necessary inductor current calculations to enable you to make the correct part choice; however, the inductor datasheets can themselves be misleading.

Saturation current is universally defined as the current at which inductance decreases by a certain percentage, but different manufacturers use different percentages. Wurth often take a 20% inductance drop to mean saturation, but other manufacturers may use a 50% or even 80% drop.

Careful consideration must be given to peak inductor current, not just expected output current. High efficiency switcher designs typically look to minimize switching time and thereby losses, but this inherently drives up peak inductor current (and also EMC emissions!)

Lesson: When specifying an inductor, check what inductance drop the saturation current parameter refers to. If 80%, then you need to design more current headroom into your system to maintain correct regulation. Pay attention to peak currents!

Switchers aren’t always best

Switchers are more efficient than linear regulators, so does that mean they should be used wherever possible? Not quite.

Look at the efficiency curves on the datasheet. See that bit where the efficiency curve falls off a cliff at low loads? If your mobile widget, for example, needs a 3V0 rail derived from a 3V7 LiPo, and spends most of its time in a micro-power sleep mode, your switcher will likely burn more power than an LDO in those periods when the load is not drawing much current. If you then add in inductor switching losses and quiescent current, you could end up throwing a lot more power away through trying to use an “efficient” switcher than by using an “inefficient” linear regulator.

Lesson: When designing power supplies for very low power devices, consider if a switcher is honestly the best option. Even low power optimized designs (such as Analog Devices Micropower ICs) may still yield worse results overall than a carefully specified LDO in a low power application, so a system level power budget analysis is a must.

Keep it (the high current path) simple

Switchers create circulating paths of rapidly switching high currents as part of normal operation. If you don’t carefully implement these paths, then the system is likely to radiate or couple excess noise to other parts of the system, causing yet more EMC issues.

If possible, design the converter on a single layer to avoid layer transitions by vias, and with short, low impedance paths between the diode, inductor, and capacitors on the output side, with similarly low impedance paths between the input capacitors and switch FET. The ground path between all these components should also be robust and low impedance. If using a four-layer board, placing a ground plane under the switcher can suppress coupling to other parts of the circuit, but make sure to follow layout guidelines for the particular part, as coupling between traces and ground can be relevant to operation and performance!

Lesson: Keep the entire switcher design compact, and keep the ground return path short and on the same layer if possible. Ground planes and careful splits can be useful for reducing coupling of the circulating currents into other parts of the system.

This is far from an exhaustive list of all possible design considerations for DC to DC converters, but hopefully it gives you some useful guidelines on what to look out for when embarking on a new power supply design, particularly for those at the start of their engineering career.

Here at CDP we employ a talented range of engineers across all disciplines who solve problems like these on a daily basis. If you are interested in joining our team, check out our vacancies in Cambridge, UK or Raleigh, N.C. USA.

If on the other hand you are experiencing these sorts of issues at your company, please do reach out to CDP to see how our business can help yours.

Women in innovation: Science and Engineering

May 6th 2021

Women play a crucial role in innovation and business success at CDP. We’re proud of the critical contribution made by our women colleagues, who lead in diverse areas of innovation including design, research, science, technology, engineering, and human factors.

In this second instalment of our Women in Innovation series, three of our STEM professionals discuss women, leadership, and their role in science and engineering. Caroline Zakrzewski, Alejandra Sánchez and María FM Balson reflect on their work and their career journeys. They aim to share a positive message and empower the next generation of women and girls in STEM (Science, Technology, Engineering and Mathematics). We believe their experiences and journeys can help and inspire many others.

Caroline Zakrzewski

Drug Delivery Devices Scientist

How did you become a scientist?

I always knew that I would be a scientist. It wasn’t clear to me immediately what that looked like, but I also knew that I wanted to help people and improve the quality of their lives – to make a lasting difference. I spent some time in hospital as an adolescent and that experience inspired me to focus on healthcare. I embarked on a master’s degree in chemistry and the synthetic organic chemistry that provided a foundation to many traditional drugs. Having started out analyzing drugs that came out of devices, I then got distracted by the devices themselves – how they worked and how they were made. After a while I backed up what I was learning at work with a master’s degree in pharmaceutical engineering that looked at drug and device manufacture in an industrial setting. It’s one of the great things about science that the tools you are given to harness and focus your curiosity can be applied to so many different areas – you don’t need to decide your whole career at the outset. I’ve had many different jobs that I’ve loved, including this one, and that feeling when I see the devices that I’ve helped to design, test, industrialize, and manufacture on the market and in the hands of real patients never gets old.

How does being a scientist help you make sense of the world?

Science is around us every day, helping with our understanding of the world, from flat pack furniture construction to the perfect recipe for banana bread. In the last year, the healthcare sector has made the news more than ever before as we’ve seen population statistics, data modelling, diagnostic devices, and vaccine development becoming front page news. This has been fascinating for me and it’s helped me to be objective about the current situation, but in equal measure it’s frustrating as much of the media fails to understand the details of what they’re reporting.

Does the world need more women in science?

Yes. I’m a great believer in the power of diversity and representation to drive effective innovation. At CDP we use the experiences of our colleagues across different markets – healthcare, consumer, and industry, to generate solutions to the issues our clients bring to us. Women make up half of the population and it’s important that their voices are considered in product development and particularly in healthcare at all levels. With the benefit to the user foremost in our minds, diverse inputs provide a more widely applicable and robust solution. Without this, healthcare needs of major groups, such as women, are side-lined and left wanting. If you want to make a difference to people’s lives, to find solutions to problems that you see in the world and to be part of a great team doing the same, then science has a career for you.

Alejandra Sánchez

Associate Biomedical Engineer

How did you become a scientist?

I think science chose me. Somehow, I was driven by different events to the point where I find myself today. At least I didn’t have a “conscious plan” to be where I am, but I can definitely say I’ve had decisive role models along the way – family and teachers – that have inspired me, stimulating my curiosity and passion for biology and innovation. Science gives me a deeper understanding of everyday life. It also represents the key element that steers my knowledge into engineered solutions that can ultimately be part of a marketed product in somebody’s hands. I think the best feeling is knowing that my work makes a difference. I also believe science breaks borders and boundaries, you can work in any country you want, the language of science gives you the ability to further understand people from different cultures and backgrounds. This opens so many doors!

Is work/life balance important for gender equality?

Work/life balance is still one of the many unanswered questions regarding gender equality. In my experience – including roles in Argentina and the UK – I’ve always been part of a warm and supportive workforce and life balance hasn’t been a personal issue. However, I’m aware that many leadership positions are not seen as attractive to women, for a number of reasons. For some, the nature of those roles is simply incompatible with non-professional responsibilities, such as caring for children or elderly relatives, which historically have been seen as female responsibilities. Nowadays, these personal responsibilities are better shared among men and women; however, I do think this should be properly addressed if we’re serious about achieving gender equality.

How can we foster the next generation of women leaders in science?

Education is the key. Diversity of thought provides space for creativity and innovation; this is what we need at all levels, from board and senior level executives on down, to better understand a problem and tackle it for optimal results. I’d love to see a greater promotion of inspirational women in STEM to much wider audiences. Everyone in a STEM class at school should be taught of the outstanding women that made a difference in these fields, thus encouraging young girls into following this incredible path. We should also get more companies into schools to show how creative and exciting the industry is and capture young minds.

How can women and girls start a career in science/STEM? Why is this important for the world?

STEM careers are often referred to as the jobs of the future, responsible for driving innovation, inclusive growth, and sustainable development. However, gender disparity in this space remains alarming. Until recently, different myths have been spread by word of mouth and even in academia, arguing first that women were biologically less capable and now that they’re simply less interested in STEM. I’m happy to say that both have been proven wrong, by scholars at Harvard University (for more information access the study and the science article from Slate), and that there is nothing about STEM that precludes female participation. Understanding how crucial it is to take part in STEM fields now, will allow us to take action and play a part in building our tomorrow.

María FM Balson

Consultant Biomedical Engineer

How did you become an engineer?

I’m extremely lucky: I’ve had a broad education, parents who fed and encouraged my curiosity, and excellent teachers. I have always loved languages, philosophy, and the sciences. If I could, I would study everything. I cannot, so I chose engineering.

I really like that von Kármán quote: “Scientists study the world as it is, engineers create the world that never has been”. I love that idea and, honestly, I think I won the lottery. In my job, I get to be a scientist whenever I encounter a new problem – I have to learn as much as I can about it, as quickly as possible – and then I put on my (metaphorical) engineering hat and work with extremely talented people to solve that problem.

I’m particularly interested in applying engineering principles to the solution of problems in biology and medicine, whether that is designing medical devices, modelling healthcare interventions, or improving access to contraception. Also, I have a terrible soft spot for Excel and Python, so if those are involved, even better.

What do you think of the assumptions and stereotypes connected to women in engineering?

Professor Tim Minshall sums it up really well in this TED talk: too often, when people think of engineering, they think “men, hammers, spanners, boots”. This, while sometimes true, is a very narrow and outdated view of engineering, which is a rich and evolving field as broad and diverse as any academic discipline. At its heart, engineering is the application of scientific principles to the solution of problems in any and all areas of life, from feeding the world’s growing population to reversing climate change.

Now, more than ever, we need STEM professionals. We need a larger and more diverse talent pool. We need to attract more women and minorities, then train them and retain them. This is a complex endeavour, and requires work on many fronts. One of these is outreach: engaging with the wider community to change their perception of science and engineering, from “hard, boring, and not for me” to “exciting, accessible, and world-changing”. I’m heartened to see all the great outreach that happens in Cambridge, coming from both the University and the local technology firms. I urge all STEM professionals to get involved in these types of activities and to continue expanding their reach into underserved areas. It’s not always easy and can be disheartening at times, but it really is worth it.

What can we do to empower women in STEM?

What a great question, and how difficult to answer! The first thing, as ever, is recognizing that there is an issue and that it needs to be fixed: we need more STEM talent urgently, we need a more diverse workforce, and there are barriers preventing women and other underrepresented groups from joining and advancing in the profession.

Many people (often men, but not always) are unaware of the extent of the issue and cost of ignoring it – they do not realize that inequality is holding us all back. It leads to missed opportunities and carries a very real social and economic cost. Therefore, the first step is education: educating ourselves and others on the value of diversity and the importance of working towards an equitable workplace and society.

Next comes the difficult task of untangling the problem: gender inequality is a very complex issue, deeply tied into cultural expectations, societal norms and economic incentives. And it’s a vicious circle: inequality breeds inequality. For example, women earn less than men on average, so they are more likely to take extended leave for childcare than male partners (to minimize lost earnings) and so they miss out on experience, raises, and promotion, which then widens the income gap even further.

Thankfully, a lot of great research has been done into the roots and ramifications of the problem, as well as concrete steps we can all take to address it. I hope to explore some of these in a future blog, but for now, I’ll leave you with a book recommendation: Women Don’t Ask, by Linda Babcock and Sara Laschever.

If you missed the first blog in our Women in Innovation series, you can find that here.

Making it last: Why testing is vital to product sustainability

March 25th 2021

Jonathan Wilkins

Mark Buckingham

How long do we expect a product to last? Many sophisticated technology products, such as phones and tablets, are routinely replaced after a few years as specifications evolve rapidly. But what about a chair or a toaster? There are a huge range of products that we only replace when they wear out, but how long will this take, and how do we decide when minor changes add up to justify a replacement? When we prepare new product designs, how do we test to predict whether the lifetime will be months, years, or decades?

The challenges of biomaterials

Many consumer products contain large quantities of plastics derived from crude oil. But there’s increasing consumer interest in products made from bio-based materials derived from plant matter. While bio-based plastics are renewable, many are recent innovations. There may be a temptation for designers to make a direct substitution between a well-established plastic derived from crude oil and a bio-based plastic. Yet the two materials are unlikely to behave on a “like for like” basis. Because of limited service experience, there’s often a lack of data or understanding of how new types of plastics degrade and age over time. As a result, long-term testing and lifetime predictions of bio-based materials is a particularly relevant topic and can begin right at the start of a design project, while still in the materials selection phase.

Designing for the long term

We want newly designed products to have a long service life and to withstand normal rough handling. If we buy a shiny new phone, bike, or car, we expect it to start looking slightly rough and worn after a while, but we don’t want it to break or change color too soon. How do we check for this? We need to think about how the product will be used and how it might fail.

We can look at this challenge in terms of material selection. How do products age under different applications? What types of rough handling will a product need to withstand, and will the result be sudden failure or a gradual loss of properties? How will subtle changes in the appearance of the product over time affect its suitability for continued use? Does it matter if it becomes less glossy or even changes in color? Is it easy to keep clean? Do certain design elements require local reinforcement to prevent early failures at potential weak points? It’s easy to overlook these questions when an existing product is redesigned, particularly if a change in material is proposed.

Even when changing the grade of the same plastic material, such as polypropylene, small variations in the amount or type of fillers and other additives, or the length of the polymer chains, can modify its behavior. We can’t look up a single set of properties for polypropylene as there are a huge number of grades with different characteristics. The impact of even a small change may be to move a design from rugged to marginal, with a substantially increased chance of failure. It’s vital to select specific tests in order to evaluate the risks for a particular application.

Better, or just different?

There are many perfectly sensible drivers for changing materials, including cost or weight reduction, improvement in properties or sustainability. In each case we seek to improve, but have we unwittingly introduced a new way in which the product might fail? If the appearance or feel of the product has changed, might it be used differently? If it appears to be stiffer and more rugged, is it OK for me to push it harder? Have we considered how to test the product design to take all possible failure modes into account? If the customer could misunderstand how to use the product there’s an increased chance of unanticipated rough handling.

If we design a product to have a long lifetime, we also need to take customer preferences into account. Until recently, there were drivers to replace products simply because they look a little old and tired. But much greater awareness of environmental issues has encouraged customers to continue to use well-liked older products until they fail, and to consider repairing them to enhance their useful life. Whatever nature can create, nature can also degrade. So, if we consider replacing a synthetic plastic with a natural material, then it may be biodegradable under the conditions of use and so it may fail in new and unexpected ways.

Mechanical performance testing is always a good place to start. As well as testing the finished product, additional trials on small pieces, or “coupons”, of the component materials will highlight any changes in properties after environmental aging. For many regulated applications, such as medical, food packaging or toys, there are specific mandatory tests, for example measuring levels of extractable or leachable materials. But in a novel design it’s often other, non-mandated tests that show up how a particular product might fail. It’s then the responsibility of the designer to investigate and mitigate the possible failure modes in a new product. Key tests will show up early signs of wear, damage or other aging and it may not be necessary to test the item to destruction.

Taking it outside

If a product is to be used outdoors or at high or low temperatures, the risk of failure must be checked over a wide range of conditions. Artificial weathering environments with water spray and UV light mean we can quickly predict the impact of many years of outdoor exposure. As well as possible changes in mechanical performance, the stability of color and other aspects of appearance can also be tested. For example, we expect the paint on a car to begin to degrade only after many years.

Specific environments will put additional stresses on some types of materials. The salt in a marine environment or the sand in a desert may cause wear much more quickly. Beneath the hood of a gas-powered vehicle, the components will be exposed to high temperatures and oil, fuel, and other fluids. Materials used in aircraft, high voltage systems and nuclear power stations also need to perform reliably in very specific ways.

Standing the test of time

Long-term subtle changes can be difficult to detect. For example, many plastics undergo creep when subjected to loads and specialized test regimes are needed to detect when substitution with a stiffer material is necessary. Exposure to fluids can also cause long-term changes, particularly when plastics slowly absorb the fluid and become softened and distorted.

If a product is designed to last for decades, for example if it’s installed within a building, then we need to carry out accelerated aging evaluation to test how its properties will perform over this period. One response is to apply the rule that the rates of chemical changes increase with temperature in a predictable, mathematical way.

By storing samples in ovens at a range of elevated temperatures and testing them periodically, we can build a picture of how the same material will perform over decades at room temperature. This methodology is often termed the Arrhenius approach. For example, it may allow us to predict behavior after 10 years at 20°C in only around six months, by accelerating the testing at 60°C. We can even immerse the accelerated test samples in fluids if we want to simulate use in wet conditions, for example in food or beverage applications.

A route through the maze

With appropriate experience in design, material selection and evaluation, it’s possible to devise a new product and to put together a suitable test plan. The data generated can be applied to provide confidence that a new design or a change of material will lead to a product with a long lifetime. After all, when we like a pair of shoes, we want them to wear out slowly, and there’s no reason why the same can’t apply to our favorite products.

Women in innovation: Design & Research

December 16th 2020

In this first interview of Women in Innovation series, we talked to four of our leaders working in the design and research field. Thanks to Nicki, Martha, Millie and Clodagh for sharing their stories.

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Nicki Sutton | Senior Innovation Consultant

My primary role is generating insights for innovation and design through immersive and exploratory research. That insight or opportunity specification forms the basis for early-stage concept generation and it’s always important for the researchers to be in the room when that happens. It means they represent the users, customers or wider stakeholders and ensure that their needs are being translated correctly into design and design attributes.

Does being a female researcher give you different perspectives from a male researcher in the same position?

Honestly, and speaking just personally, I don’t think so. I believe any good researcher should be able to cross divides such as gender, age, culture, etc., to empathize with the challenges that individual groups can face. Of course, some subject matters are quite gender based, where one gender may have a very different experience from the other, or not have the experience all! For example, at CDP, we’ve worked on condoms, sex toys, body hair removal and femcare, however we’ve always had mixed gender teams on those projects. Perhaps the women were a little further up the experience curve on some of the insight, but I don’t think the guys were held back!

Have any female mentors supported you through your career?

Not really. My university courses and the companies I’ve worked for during most of my career have been mainly male dominated environments. Since joining CDP I’ve been among the most senior women employee-owners and so there has not really been much scope for female mentorship. However, I do get inspired by the work of other women in the company – in the ‘front end innovation’ team and the wider organization. I see some of the younger women – researchers, strategists, designers, engineers – and I’m in awe of their sheer talent and confidence! I definitely think that our education system, at both school/college and university level, better prepares you for life in the commercial world compared to when I was passing through it!

Do you have any design heroes that you look up to?

As someone who sits at the insight end of design, I couldn’t possibly answer this question without mentioning Clay Christensen; the founding father of disruptive innovation and Jobs to be Done (JTBD). Indirectly, he has been as influential on my career as anyone. JTBD has been at the center of my work for the last 13 years. It’s now a mainstream innovation perspective, but it was still in its relative infancy when I was introduced to it. Focusing on the jobs that people want to get done in their lives as the input to design and innovation seems very obvious now, but when jobs thinking arrived, we lived in a very product-centric research world. Companies believed that users and consumers were too difficult to understand – saying one thing and doing another – so they just didn’t bother with research or research was ‘market research’ into products already launched. Today we live in a different world of design and innovation. One in which jobs, not products, are the driving force of progress.

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Martha Hodgson | Market & Design Insights Research Consultant

My passion is design research: gaining an in-depth understanding of the stakeholder, whether that’s the end user, the commercial sponsor or the key decision maker who sits within a supply chain. Uncovering and understanding unmet needs are at the heart of creating meaningful and effective innovation.

Does being a female designer give you different perspectives from a male designer in the same position?

Being a female can help in understanding some specific contexts -for example, femcare– but I believe what makes a good design researcher is your ability to semi-detach yourself personally and empathize with the context and end-user audience that you are designing for.

Do you think being female has any relevance to how you approach your work?

I think I approach design differently to any other women or men because of the unique journey I have taken to get to where I am today. My approach at work is shaped by my empathy and my understanding of others. I also believe that starting my career as a designer has shaped the innovator I am today and enables me to help improve lives through innovation. It provided me with a way of looking at the world, asking the right questions, interpreting what I see and hear, and making new connections that have led to uncovering new opportunities. It is the combination of characteristics, values, skills and capabilities that is each of our differentiators.

Have any female mentors supported you through your career?

Yes, I’ve had incredible women mentors, and at the same time, I’ve also had excellent men mentors. I consider myself very lucky to have different role models throughout my life and career, and there have always been strong female leaders in the places where I have worked.

Do you have any design heroes that you look up to?

No ‘heroes’ as such! I admire many examples of achievement in many forms where someone has been driven by passion, gumption, determination and a lot of hard work! I follow a group called The Female Lead on LinkedIn, which I find very inspirational – it showcases and celebrates female success, and the many forms it can take.

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Millie Ashton | Industrial Designer

Ever since I was a small child I’ve had a passion for design – I’ve spent many hours designing Lego houses, ceramic animals and 3D printed plant pots to name a few examples. Being able to turn a nebulous idea into a tangible 3D object never fails to excite me, and the fact that I’ve been able to pursue a career in it makes me feel extremely lucky. I’m grateful that my role provides me with the opportunity to help people and bring joy to them through my designs. There’s great satisfaction in creating solutions that have the potential to improve people’s everyday lives.

Does being a female designer give you different perspectives from a male designer in the same position?

I’d like to think that there aren’t many disparities between men and women in our perspectives or design approach. However, it’s difficult to deny that being a woman means you naturally have a perspective that just over half the world’s population doesn’t have – this is invaluable and allows me to use that empathy to tackle problem solving. We take pride in creating design that is centered around user insight, which is key to producing a successful solution for all gender identities. As a woman, I can come up with ideas and new ways of thinking that my male counterparts may not have, and challenge society’s norm of designing for the average adult male.

Do you think being female has any relevance to how you approach your work?

Yes, at CDP I always try to bring a fresh mindset and perspective to problems. As one of the youngest designers in the design team, I enjoy challenging and questioning design norms, as well as keeping a finger on the latest product trends. As the only female member of the Industrial Design team, I try to bring female insight into the products we design and ensure we’ve considered how other genders might use the product differently. I also feel it’s essential to design for future generations, considering how a product’s life cycle will impact the planet in years to come.

Have any female mentors supported you through your career?

Throughout my education and career, many of my peers and lecturers have been male. I didn’t have a female mentor at university, but I wish there had been more female role models to look up to. It has been refreshing at CDP to witness more women joining the company and being promoted into senior positions and hopefully female mentorship in design is something that will continue to be improved upon in time, as more women take up roles in the design industry.

What would you want to say to the design industry or anyone thinking of working in design?

My biggest tip would be this: don’t be afraid of failure or rejection. What you may think is a stupid or crazy idea might turn out to be ingenious. If you love designing things, don’t let self-doubt get in your way – passion often leads to success, and saying yes to new opportunities is vital when starting out. Never stop learning or assume you know everything, and ensure you get as much design related work experience or internships as you can, to figure out your niche.

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Clodagh Hogan | Human Factors and Usability Engineer

My background is in pharmaceutical chemistry, but I moved into the medical device design world so that I could bring my hands-on design skills and scientific background to people-centered design. I’ve always loved being able to turn an idea into a physical object and working in design allows you to be creative every day.

Does being a female designer give you different perspectives from a male designer in the same position?

No. How I approach a design challenge is based on my mindset, creativity, experience and style of problem solving. I work with multiple designers and we all have different perspectives and different skillsets, but this is down to the fact we are different people, not that we are different genders. If men were asked to list the benefits of being a man in design, it wouldn’t be something that I’d want to read and I’d take it as a negative dig towards women. I believe in equality, which means we must recognize that different people have different skills and that gender doesn’t really play a role in it at all.

Based on your experience, what are the top challenges you have faced as a woman working in innovation?

The biggest challenge I face as a woman in innovation is this assumption that I face challenges because I am a woman. I am lucky to be at an early stage in my career while things are actively changing, and it will only get better as time goes on, but change cannot happen overnight. In the near future, I hope that questions like this are no longer asked because we will be living in a world where people no longer assume that women face challenges just because they are women.

Do you have any design heroes that you look up to?

I don’t have any one specific design hero, but there are many graphic designers, illustrators, typographers, UX designers and product designers that I spend a lot of my spare time following and getting both motivation and inspiration from.

What would you say to the design industry and future woman and men that would like to work in design?

I would say that if you are interested in design, then pursue it and don’t let whether you are male or female get in your way. If you are a woman starting out, you will see that there is an imbalance. More women are taking up careers and education in design and STEM now, but it will take time for there to be balance. Know that you are starting your career during an exciting shift and that you are part of this important movement.

We hope to use these ideas and perspectives to inspire other women and girls to pursue a career in design and innovation. Our women designers add enormous value to our projects and team, and we believe it’s essential to celebrate this diversity. In our next blog we’ll share more stories of Women in Innovation, here at CDP.

Six strategies that accelerated innovation in 2020

December 3rd 2020

In so many ways, 2020 has not been the easiest of years in which to do business. But nonetheless, design technology company Cambridge Design Partnership is taking on more staff, opening new offices and gaining blue chip clients. Here, founding partner Mike Cane reveals six strategies the firm is employing to accelerate their innovation programs in this most challenging of times.

1. Finding ways to work faster

Although the COVID-19 pandemic has thrown up many unforeseen challenges, it has also provided a pressing need to hone our innovation approach this year, writes Cambridge Design Partnership founding partner Mike Cane. Our specialist knowledge of medical tech and diagnostics has seen us taking on large-scale, fast track projects to help tackle the pandemic, both in diagnostics and treatment for the disease. We are also delighted to have undertaken a significant amount of pro-bono work during the crisis, working on everything from PPE to ventilators, to help support the NHS and defeat the virus. All of these projects had urgent timescales not normally associated with complex healthcare programs, which has meant we have had to organise ourselves differently.

This huge demand to accelerate development timescales, without compromising performance and safety, has led us to refine our procedures and approaches to allow us to deliver these projects on time.

2. Market knowledge

We plan to celebrate CDP’s 25th anniversary in 2021 by hiring our 250th employee owner. This consistent organic growth has been the result of our focus on three key industry markets where innovation is particularly important to our clients’ success. This has driven us to develop in-depth knowledge and expertise in our customers’ industries, which creates a more fertile environment in which to develop the very best possible products for them.

3. A holistic approach

Here at CDP we purposely take a holistic approach to our work, with the aim of providing an end-to-end service from a clean sheet to product launch and post-market support. While our clients often come to us when they are already at some point along the new product development journey, this perspective allows us to be aware of how the task at hand contributes to the overall success of their venture. This allows us to plan projects more effectively and to add value beyond our immediate role.

Some clients do come to us for the very first strategic discussions and market research. We can then take their ideas through design and testing right up to launch and manufacture. This seamless approach enables them to avoid the pitfalls that result from changing teams at key stages in the development process.

4. Building expertise

Over the years, we have built up a wide range of technical expertise and as a result we increasingly have teams with in-depth technical specialists, such as medical robotics engineers. As the scale of our business grows, we can offer our colleagues exciting opportunities to work at the cutting edge of technology with some of the world’s largest companies. At the core of what we do is science and engineering, so we are always keen to hear from mechanical engineers, electronic engineers and software engineers, particularly those with experience of working in the regulated medical sector. We also have opportunities for people with manufacturing expertise, as we now offer our clients short-run manufacture in our own labs, as well as the know-how to take new products right up to the point of market launch and transfer to high-volume manufacture.

5. Combining local with remote

Today, our largest geographic market is the US, with assignments carried out by both our team in Raleigh, North Carolina and also at our HQ in Cambridge. Making sure we have team members close by our clients helps make sure we work closely in partnership. Also, given the shortage of engineering talent in the UK, especially in software engineering, it’s useful to be able to recruit from two pools of talent. All this means that our American operation is more important to us than ever and, as a result, we’ve recently invested in a new and larger R&D facility in Raleigh.

6. Facilities, people and performance

As well as our new office in the US, we are also investing in a state-of-the-art new facility in the UK that will be ready next year. This will significantly expand and upgrade our laboratories and workshops, as well as providing specialist facilities such as state of the art market research infrastructure, multi-technology 3D printing, optics, power electronics and manufacturing process development labs.

Among the many reasons for CDP’s consistent innovation performance is, I believe, our strong Employee Ownership culture and our innovation focused management team. We are now coming up to three years into full employee ownership, meaning that every staff member, or Employee Owners as we call them, has a real voice and stake in CDP’s approach and success. Our senior management team is 12 partners, each working in a different sector of the business, all focused on optimising our innovation projects. Even as we have grown, we have maintained our belief in a flat hierarchy, with Employee Owners fully empowered to create great new products

In conclusion…

Here at CDP, by far the most important thing we do is to put the success of our clients’ innovation projects at the centre of our business development planning. This means as well as developing new products, we are also developing our organisation, facilities and processes to provide the best possible support to our customers throughout the whole innovation process, helping them to launch the most competitive new products. As 2020 draws to a close, we’re optimistically looking to the future.

Crankl: from the bike shed to the operating theater, how CDP created a novel surgical tool

September 8th 2020

Matt Brady

It is important to start each innovation journey with the broadest possible mindset because this opens the door to all sorts of different solutions that might exist outside one team’s experiences. A great example of this philosophy in action was the design of a surgical torque wrench that we developed recently.

The story starts with one of our engineers who was a cycling enthusiast. He saw an unmet need amongst cyclists who owned ‘high end’ carbon fiber bikes for a simple torque wrench to stop them over tightening screws and damaging their bike frame. So, in his spare time, he came up with a simple, plastic, single piece wrench design that indicates the right torque every time. He publicized his idea on a trends website, but unexpectedly he received messages from surgeons who were also bike enthusiasts.

It turned out that orthopedic surgeons were frustrated by the tools they had to make sure that screws used to fix fractures and implants were not over tightened. Plates are commonly used to support fractured bones and over tightening the screws can break the screw, damage the bone or make the screws difficult to remove, under tightening can allow the fixation to become loose.

A torque wrench is a tool that indicates or limits the torque applied to a screw. They are used across all engineering sectors and surgeons have similar devices adapted for the operating theater. However, the inherent cost and complexity of these tools mean that they must be reused, which in turn creates additional processing complexity and cost for the hospital. Before each procedure, they must be thoroughly sterilized and tested, which is time consuming and open to error.

Single use medical devices have seen increasing adoption since their early introduction in the 1960s, initially for their ability to displace durable devices with their requirement for costly reprocessing, calibration, adjustment etc. Over time their potential to deliver when sterility and performance are paramount has become increasingly prominent, as they can be manufactured to tight quality standards and tested, packed and sterilized in controlled factory conditions where economies of scale make this cost-effective. Following pressures towards sustainability and ever-reducing costs the trend is swinging back again – with devices leveraging the benefits of single-use style designs, but with more robust materials and designs to allow a limited number of reprocessing and re-use cycles (multiple-use devices).

What was needed here was a single or multi-use wrench, that was accurate, easy to use and did not require maintenance.

The plastic construction of the bike wrench showed us that a single, low cost, plastic molding could be used as the active element in a basic torque wrench. However, the surgical version would need to be more accurate & repeatable, have different settings for different screws, and be more usable in the surgical environment – with a form factor that allows single handed use, and haptic feedback indicating when the correct torque is reached.

The design team reviewed the original bike torque wrench design and analyzed where it could be improved and adapted for surgery. The original bike wrench had a beam that buckled when the right torque was achieved but this phenomenon was influenced by several parameters that could result in lower accuracy. Together with a more compact form factor that better suited surgery, a new design was envisaged that only relied on bending, so should be more repeatable. It also provided better haptic feedback to the surgeon.

The design was modelled in 3D CAD and underwent FEA simulation to better understand how it would perform. This allowed the first round of optimization to get as close as possible to the desired performance. To allow the ergonomics and ‘feel’ to be evaluated, a first model was made using 3D printing. The Crankl surgical torque wrench was born.

When the wrench was assembled, the team were pleased that they had got close to a design that would meet the surgeon’s requirements. But 3D printed materials perform differently to the injection molded plastic that would be used in the final design, so another step was needed to verify the system would work. The team needed to have real injection molded parts in the correct material to test.

Moving to ‘production intent’ manufactured parts is a big step in all medical device developments. Medical devices have to meet strict standards to be placed on the market and CDP’s experienced device development and quality engineering teams ensure that this happens, in line with our ISO13485 certified quality system and device development process. This means that at the end of development all the correct processes and documentation will have been completed to support a submission under the EU Medical Devices Regulations and / or to the FDA, as appropriate to market need.

Obtaining molded parts is usually an expensive and time-consuming step because mold tools have to be designed and manufactured. These are complex and take time to make, and errors can occur that can affect performance and the validity of the test results – requiring a further iteration. For this reason, CDP has developed a “rapid digital molding” approach which uses 3D printing to very quickly make mold tools into which target polymers can be injected – rapidly creating production-intent parts.

The systems approach to formulation and product design

July 21st 2020

Mark Buckingham

Today’s liquid and paste formulations, from washing up liquid to shampoo to toothpaste are complex structured fluids or solids which are designed to meet the demanding needs of consumers. It is tempting to regard the formulation or recipe as the main challenge. However, these complex formulations behave very differently in the range of environments they experience across their lifetime, such as manufacturing, filling, distribution, storage and consumer use – sometimes leading to unexpected failures. Should we adapt the formulation to work with the process/packaging or vice versa or both?

Seeing the Wood for the Trees

We take a systems approach to designing and developing new formulations. Put simply one must consider the interactions between manufacturing process, formulation, distribution chain, application device or packaging, regulations (monographs, storage requirements etc…) as well as consumer habits and usage requirements. This has long been the goal of all product development groups but reality is often different.

Often there is a focus on only some of these parameters, for example the formulation, packaging, regulatory and consumer attributes, and then a huge effort is subsequently spent trying to adjust the manufacturing and distribution chains to accommodate the product – incurring unnecessary cost and time delays to new product introduction. This has a huge and often neglected economic impact, from personal experience this can add as much as 5% to the total delivered cost of the product.

Putting the Toothpaste back into the Tube

Many real-life examples exist of these manufacturing issues. These include a shampoo product, where the manufacturing line speed had to be turned down to prevent issues with filling bottles, such as dripping, mounding and air entrapment. Another was the high level of product rejects due to incomplete sealing of toothpaste tubes caused by the formulation stringing during filling. A third was the eventual upgrade, at a significant cost, of filling lines to accurately dose out a structured fluid and prevent periodic under-filling.

These solutions were a consequence of an incomplete understanding of how to design a recipe to cope with manufacturing and filling where there are quite extreme forces and shear rates involved. Recent advances in rheological equipment and methods, coupled with Computational Fluid Dynamic modelling now enable formulators to simulate these conditions and explore strategies to reduce or eliminate these issues. We have reached a tipping point where formulators can now actively design complex fluids to be easily prepared, as well as fulfil their other design criteria thus potentially avoiding unnecessary costs.

Delivering the Optimum Four-season Solution

Many companies are exploring new e-Commerce business models with products being distributed directly to the consumer, bypassing large parts of their centralised distribution network. This presents an interesting challenge to ensure products and packaging are designed to survive shipping and still deliver the intended consumer use experience. To help solve this puzzle it is important to obtain real-world data of what actually happens to your package before it reaches the consumer. Does it freeze in the middle of winter in Canada, or bake during the height of summer in Florida? Does it experience massive pressure swings as part of air freight causing packs to burst open? How often does the temperature cycle from high to low and back again, and how much vibration or shock loading does your pack receive?

All of these considerations can have a drastic impact on the integrity of your product and brand image and affect consumer acceptance. It is important to put together a testing protocol to verify that the formulation and packaging solution are sufficient to cope with any extreme conditions. We have experience fitting customised tracking sensors inside packaging and if necessary inside the pack itself. This enables real shipping or usage experiments to be run and high quality data collected to guide product design and stability requirements.

Putting it All Together

At CDP we have access to tools and techniques which can be used to explore important design spaces for formulated products, to avoid unnecessary costs and exploit new ways of doing business. Our broad combination of experience in Chemistry, Consumer Insights, Materials Science, Packaging design, Modelling & Simulation, Digital Systems, Manufacturing Technology and other areas can help you to take more control over your design space and specifications.

We do not specialise in just one area, instead we have experience in how all these aspects can work together across several industries, so that we can adapt and combine approaches from entirely different applications.

The recipe may be at the heart of the product, but it must work with the package and the process to provide the best possible customer experience.

Testing times: adapting user insights research for a new era

May 21st 2020

Ben Kelsey

Andres Barrera

As COVID-19 related distancing threatens established methods of engaging with consumers and patients, Ben Kelsey and Andres Barrera reflect on how to support innovation projects with ‘hygienic’ user research tools and techniques!

The ability to travel and observe how people live in their cultural context is a privilege, and an asset to a researcher’s toolkit. It enables us to elicit the insights that can develop new commercial strategies, and it allows our design and technical teams to create the new products and experiences that deliver critical benefits. So, a global pandemic would, at least on the face of it, seem a high barrier to the ‘day job’.

However, to preserve the global economy, businesses must and will adapt, therefore products and services must also evolve and reinvent themselves for this new environment. The emotional rollercoaster that many families are currently experiencing will certainly influence their behaviour, and understanding this may offer a valuable insights into potential long-term changes in habits and attitudes that will provide innovation opportunities in the future.

Our broad tool-kit and research expertise has developed over the last ten years to include both physical and remote insights capture and validation methods. The challenge is knowing the right tools to use and having the experience to deploy them to maximise results. No one tool is perfect for every task because the research objectives and budgets can vary significantly, but the starting point is that there is much to be gained, and little to be lost, by a learning engagement with your future potential customers.

As long as travelling to users’ houses is prohibited by the need for social distancing, traditional ethnography is impractical. However, online ethnography can go some way to replace it. Users can self-facilitate their interview, creating a series of short recordings on their smartphones across a series of scenarios which have been pre-defined by the moderator. This enables researchers to gain a valuable visual, narrated snapshot of respondents’ lifestyle, behaviour, shopping environments and product usage.

Today, it is estimated 3.5 billion people around the world have a Smart Phone¹. So these digital methodologies can access populations and user groups with greater ease and speed than face-to-face methods including ‘hard to reach’ populations in a way that was not previously possible. Furthermore, remote research allows the moderator and the observers to gather the insights captured within the participant’s natural environment; allowing the participant to be more relaxed and more instinctive behaviour to be observed, with sessions scheduled around the participants’ daily routine. At a practical level this can enable recruitment of wide diversity, both by geography and consumer segments, typically at a lower cost that physical field observations.

Our research and insights team is made up of a variety of subject matter expert backgrounds, including psychology and anthropology, science, and design. The objective of our work, whether for consumer or healthcare markets is always to creater a better, and more intuitive experience. Human Factors and Usability trials are another research activity that has been impacted by COVID-19, and this service has also benefitted from a creative approach and constantly expanding tool-kit to ensure client’s critical path healthcare development programmes remain on course as we switch to remote methods.

How we run online remote usability testing

There are three key questions we ask partipants which measure product desirability and usability:

“Does it fit in with the way I do things?”

One way we explore this is by gaining feedback on product workflow using storyboards or demonstration videos and animations which can be shared online. These tools are great for communicating assumptions and quickly learning whether they resonate with users and reflect how they do things. Study material can be shared prior to the session or presented to the participant during it.

“Can I understand how to use it?”

Gaining feedback on visual design and the hierarchy of information helps to validate mental models embodied in the design. This can be done using images, walkthroughs and interaction simulations to explore specific user interface features, i.e., interpretation, legibility, navigation, etc.

Each step of the user experience can be explored with the participant to determine their understanding of the device state and asked what they would do next.

“Am I able to physically use it?”

We can obtain richer feedback on physical interactions by posting test packs to the study participants. These might include, for example, handling models or low-fidelity prototypes, and briefing materials, which can be used in a range of ways – both moderated and unmoderated, depending on objectives.

3D printing is a great tool for this. We can print and finish a ‘looks-like’ model, and a 3D-printed headset allows them to video the encounter with their phone. We have also, as a matter of course, been including a personal hygiene pack and instructional information on measures to minimise virus contamination risks.

Participants are encouraged to ‘think out loud’ and walk through the overall experience with the device. This footage is then used by the research team to ask follow-up questions via video calls, to better understand use challenges or frustrations.

Heuristic analysis

Some tools avoid the need for usability testing with real users at all. One is heuristic analysis; an evaluation method which draws upon the collective knowledge and experience of a team of expert interaction designers and usability engineers to evaluate a device or concept against a set of pre-agreed criteria. This can also be expanded to consider capability loss or through exercises such as “walk-in-my-shoes” or using capability loss simulations. It provides a powerful empathetic solution when the target users are hard-to-reach, rare patient groups or are part of a niche consumer population.

Data logging

An approach we have pioneered at CDP is the use of data loggers hidden in prototype products, a service we call diialog. This allows a subject to receive a prototype device or packaging sample and naturally engage with it in their day to day routine in trials lasting up to a month, when it is eventually returned. At this point we download the stored data and analyse it to understand how the subject actually used the product.

This digital technology has been deployed successfully on research devices ranging from drug delivery systems to vacuum cleaners, both in concert with, and without a written diary.

As experienced researchers, we all know that there is no perfect single test method – but when faced with very diverse innovation challenges, the starting point is always collaborating closely with our clients to fully understand their objectives, and a broad and evolving toolkit to call upon! As an end-to-end innovation partner, we understand the importance of asking the right questions in order to uncover the right evidence to craft the right solution that is both desirable and safe for the user.

With a return to widespread physical in-home research some way off, you may be wondering how you are going to maintain your NPD critical path; whether you are in the early ‘explore’ phase of an innovation programme, or needing a decisive validation test result, if this feels like your current situation we would warmly encourage you to get in touch for a chat about your current research challenges, and some of the latest options that may be open to you.

References:

1. https://www.statista.com/statistics/330695/number-of-smartphone-users-worldwide/

CDP collaboration on pen-injector technology with the Stevanato Group

April 28th 2020

Uri Baruch

Cambridge Design Partnership (CDP), a UK and US based leading technology and product design partner, and the Stevanato Group, a leading producer of glass primary packaging and provider of integrated capabilities for combination products, today announced a collaboration agreement for the development of a new pen-injector based on the Axis-D technology and intellectual property (IP) licensed exclusively from Haselmeier in 2019.

The collaboration between CDP and the Stevanato Group strongly supports the expansion of the Stevanato group’s portfolio of devices for patients suffering from diabetes.

The agreement leverages the mutual strengths: on one side, CDP’s leading design and development expertise in drug delivery and on the other, the Stevanato Group’s extensive experience in glass containers, tooling, injection moulding, device assembly, and its global commercial network.

CDP and the Stevanato Group will be able to offer innovative drug delivery solutions to pharmaceutical customers working together from the first concept right through design development, scale-up, regulatory submission, and commercial-scale production in all global markets.

“We are delighted to be announcing this partnership,” says Uri Baruch, CDP’s Head of Drug Delivery. “The Stevanato Group is well established in the device field as a leading supplier of cartridges and assembly equipment for pen-injectors. It is a pleasure to extend our existing working relationship with them for their pen-injector and to address the needs of patients.”

“Our R&D team – with the active support of CDP, an established player in the design and development of drug delivery devices – will offer a competitive pen-injector platform and some customization options,” comments Paolo Patri, Chief Technology Officer at the Stevanato Group. “With the resources and experience of both companies, we will provide diabetic patients with a product that is easy-to-use, aesthetically appealing, and cost-effective.”

This new collaboration is one of the programmes behind the recent, substantial growth of CDP’s team of healthcare-focused designers and engineers in both Cambridge (UK) and Raleigh, NC (USA) facilities. “This is another strong vote of confidence in CDP. We look forward to this being the first of many end-to-end projects that we can collaborate on in this new partnership”, says Uri Baruch.

About Cambridge Design Partnership: Cambridge Design Partnership is an employee-owned technology and product design partner, located in Cambridge (UK) and Raleigh, North Carolina (US), focused on helping clients grow their business. Over more than 20 years, some of the world’s largest and most innovative companies have trusted CDP with their most important product development programs. CDP provide an integrated and holistic product development capability through a highly qualified team, well equipped development labs and ISO 13485/9001 approved methods. This encompasses research and strategy, design, technology and digital innovation, product development and regulatory and manufacturing support. CDP experts are able to take combination products through a full design cycle and submission, enabling customers to launch products that are user-centric and commercially effective. For more information, please visit our site.

For further information and media enquiries, please contact: media@cambridge-design.com or call 01223 264428

About the Stevanato Group: Established in 1949, the Stevanato Group is the world’s largest, privately-owned designer and producer of glass primary packaging for the pharmaceutical industry. From its outset, the Group has developed its own glass converting technology to ensure the highest standards of quality. The Group comprises a wide set of capabilities dedicated to serving the biopharmaceutical and diagnostic industries: from glass containers with its historical brand Ompi, to high-precision plastic diagnostic and medical components, to contract manufacturing for drug delivery devices, to vision inspection systems, assembly, and packaging equipment. The Group also provides analytical and testing services to study container closure integrity and integration into drug delivery devices, streamlining the drug development process. Thanks to its unique approach as a one-stop-shop, the Stevanato Group can offer an unprecedented set of solutions to biopharma companies for a faster time to market and a reduced total cost of ownership. For more information, please visit Stevanato Group.

For all enquiries, please contact Steven Kaufman

COVID-19 Modelling

April 3rd 2020

Dr Karla Sanchez

Head of Biomedical Engineering

Alison Hart

Maria Fernandez-Martos Balson

Models are everywhere – anyone who has played a computer game has encountered a model, but in a pandemic, mathematical models are vital for understanding the dynamics of transmission, disease progression, healthcare needs and the overall outcome on the population.

Recent real world events have shown that critical decisions are being taken based on model data. Many people are still uncertain of how models work which can lead to them being met either with undue suspicion or absolute faith. In reality models are incredibly powerful, as you can test different courses of action quickly so an optimised response can be formulated, but their limitations need to be understood.

What is modelling?

Here we try and explain the basic principles of models, how mathematical models can help and what their limitations are.

Mathematical modelling involves making a mathematical representation of a system where the expected outcome of changing various parameters can be calculated. This means you can examine the outcomes of many scenarios using the same model. For example, the models reported on recently look at the spread of Covid-19 with different levels of social distancing and other interventions such as school closures. A model of a complex system is usually a collection of many separate models, each a breakdown of a different part of the system. For example, the first thing to consider when modelling the spread of disease is infection. You need to know certain things such as;

how likely is the infection to spread person to person with each contact?
how often do people come into contact with each other?

These values are called parameters and can be changed depending on the situation. The equations behind epidemiological models for the spread of infection are well established, but the parameters will vary between countries depending on things like the breakdown of age and population density. Crucially, epidemiological models rely on data. Sourcing these parameters is all part of modelling and assumptions have to be made.

For recent UK modelling this data came from a number of diverse sources. Census data could give a good indication of the age and distribution of households, data on social connections broken down by type (work, school, home) and age came from a BBC citizen science project. Even knowing this, data on class sizes, commute distance and company size were then needed to create a virtual population to simulate the spread of the disease.

Models can also show where collected data may be inaccurate. Recent models monitoring the situation in Spain found that the number of COVID-19 deaths reported appears to be significantly underestimated, given existing data on the expected seasonal number of deaths in a normal year and data on the total number of deaths recorded in the past few weeks (by any cause).

Simple demo of infection model.

This is a very simple model purely looking at infection. When ‘infected’ balls come into contact with others susceptible to the disease there is a probability that the other balls will become infected. There is no death rate, everybody recovers and is then immune. The speed of the balls represents the number of social contacts. The probability of infection, the proximity for infection, the length of the infection all need to be set. Even in this toy model many assumptions have been made.

What changed with the recent modelling?

Having modelled infection and the population, the outcome needs to be considered. What proportion will recover and develop immunity? What proportion of people will become hospitalised? Of them, crucially, how many will need intensive care and specialist equipment like ventilators. All these parameters depend on the disease itself. Unfortunately, Covid-19 is practically unknown, researchers have had only a few months to study it. That means there has been a degree of uncertainty with the parameters fed into the models.

One widely reported model that looked at the impact on the UK population was led by Imperial College London. Having updated their models with better information from Italy on the proportion of patients requiring intensive care beds, it found that the UK’s National Health Service would not be able to cope without further action, which led to the recent dramatic change in government policy.

In the report, the team presents a pandemic curve for different degrees of potential government intervention. The different measures that they considered the impacts of were: no intervention, household isolation, social distancing, and school closures. With no intervention, the model predicted a need for hospitalisation thirty times what the current UK healthcare system can manage. Only by combining all of the measures would the healthcare system not be overwhelmed.

This is one of the graphs from the Imperial paper [1]. The vertical axis shows the number of critical care beds needed through time in each scenario. The blue region shows the time period on the horizontal axis where various social distancing is applied. The horizontal red lines show the maximum number of NHS critical care beds available. The various lines, explained in the key, show the difference between doing nothing, applying some social distancing and with full school and university closures. This graph shows that without all measures being taken the number of available beds would be exceeded.

What happens next? What about the large peak when the measures are withdrawn?

We need time. Time to get better testing, time to find new treatments and more ventilators. The current model suggests the current restrictions should keep the number of cases at a manageable level for the next few months.

The Imperial model makes important assumptions. Firstly, it assumes that measures put in place to control the spread of the virus are all lifted at the same time, which is neither realistic nor advisable. Secondly, it assumes that recurrences of the outbreak after the initial lift of restrictions continue for an indefinite period. In reality, this may not happen due to people acquiring immunity or the availability of a vaccine. Finally, it doesn’t account for infected cases that have gone undetected or for tools such as contact tracing, which can help break the chain of transmission. All of this will affect the number of people who become infected once the measures are lifted.

A competing model by Oxford University followed the publication of Imperial’s model. This model stated that under-detection of cases could be high, indicating that a significant part of the UK population could have already contracted the virus. This caused a big media response, however, given the data available it seems an unexpected conclusion to draw, as epidemiologist Adam Kucharski pointed out.

The Imperial model has since been refined and other competing models have been published, but the consensus remains.

It’s important to remember that the model is only based on what we know now. Models are continuously updated. Research teams are now focusing on measuring the impact and preparedness of healthcare systems by predicting the number of hospital beds, ventilators and testing kits needed based on what the models are telling us. They are also looking at the big question of the length of time needed before lifting restrictions and how to prevent a second wave of the outbreak, and models will help us to understand this better.

So in a few months the situation will have changed, the model will be updated with more information and the curve may look very different. Data should start to emerge to confirm level of immunity gained from recovering from the disease. More hospitals are currently being built and there is a national effort to produce more ventilators. Doctors have already identified the response that causes some patients to develop severe symptoms while most have a mild version, which may make it possible to screen people to detect who is most vulnerable or identify better treatments.

Given the rate of learning in the last 3 months the picture may be very different when more accurate assumptions are fed into the models.

Once a vaccine has been developed, we may require modelling for rolling it out to best effect, as well as monitoring changes in the virus. This will feed into the ongoing body of research for this pandemic and will help us prepare for future pandemics.

While models are not always accurate, they help build a consensus of understanding that informs policy and helps save lives. Taking the right measures at the right time is key in the fight against Covid-19 and through modelling we can make the best-informed decisions possible from the data available.

References

[1] https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-NPI-modelling-16-03-2020.pdf
[2] https://www.gov.uk/government/groups/scientific-advisory-group-for-emergencies-sage-coronavirus-covid-19-response