Using simulation to optimize heat management prior to building prototypes and speed up development

Making blood sugar tracking more accessible

Advances in medicine have made diabetes an eminently treatable disease, allowing patients to live normal lives. However, managing diabetes requires constant monitoring of blood sugar levels to ensure food and insulin are taken at the right time. One common method for doing this is by inserting a test strip with a small amount of the user’s blood into a glucometer that gives an instant reading on current blood sugar levels.

Although extremely accurate, for a long time these devices were only available to medical professionals. Further, they needed to be plugged into a power source rather than running on batteries. To make life easier for diabetics, the devices needed to be portable and readily available.

B&W Engineering, a specialist in medical technology headquartered in Stuttgart, Germany, set out to create a portable, wireless and rechargeable device that would be just as accurate. The aim was to make it as small as possible while keeping it affordable enough to enable all patients to take advantage of it. B&W Engineering called on Siemens Digital Industries Software and its Simcenter™ STAR-CCM+™ software and NX™ software to help them achieve their goal.

Managing heat dissipation

Andre Gasko, simulation engineer at B&W Engineering, explains that it was important to eliminate a charging port to make the device as waterproof as possible and thus safer to carry around. Wireless or induction charging consists of a transmitter coil inside a charging station and a receiver coil inside the blood sugar measuring device. These coils generate heat so they must be managed carefully. They must comply with the medical electrical equipment standard of the International Electrotechnical Commission (IEC 60601-1), which is a requirement for commercializing such products in many countries. The standard requires the maximum temperature on the surface to not exceed 60 Celsius (°C) if the touching time is between 10 seconds and 1 minute. However, this is not a problem as the coils do not generate enough heat to reach this level. However, there are stricter temperature requirements to ensure the accuracy of each test.

To operate the device, the user extracts a small amount of blood from the finger via a pin prick onto a test strip. The strip contains chemical components that mix with the blood before it is inserted into the device where electric tension is applied.

The device calculates the resistance that calibrates the blood sugar level. If the temperature of the testing region is not between 34°C and 45°C, this will accelerate or decelerate the chemical process, leading to unreliable results.

Therefore, it was crucial to position the receiver coil where it would have minimal influence on the temperature of the testing region while minimizing charging time.

Finite element model analysis

B&W Engineering used NX to design the device and Simcenter STAR-CCM+ to carry out all the necessary electromagnetic and thermal simulations to prove it operates efficiently.

Simcenter and NX are part of the Siemens Xcelerator business platform of software, hardware and services.

“One advantage of Simcenter STAR-CCM+ is that it comes with existing models that we can use,” says Gasko. “We measured the performance of the induction charging system using the finite element harmonic electromagnetic model while the ohmic heat model was activated. This allowed us to calculate the induced current in the receiver coil and the amount of heating power produced on both coils.”

The heating power was then used in a separate simulation with a complete model of the device and charging pad to calculate the effect on the device temperature. The primary sources of heat generation are the coils and the battery during recharging, but the calculations also included other electrical components producing heat such as the voltage regulator and capacitors.

“The cooling strategy was to insulate the testing region by adding more plastic material, similar to the device housing, to the wall thickness of the testing region,” says Gasko. “We also needed a method to heat up the testing region if the ambient temperatures were too low. So we inserted two electric resistors that are activated if the temperature falls below 34°C.”

Combining harmonic electromagnetic calculations with CFD simulations

“Simcenter STAR-CCM+ gave us great insights into the induction properties of the device,” says Gasko. “It enabled us to see exactly what was happening internally and determine the ideal size and power. We wanted the device to be as small as possible for portability, but this means more dense electronics inside and less surface area and fewer openings for heat dissipation. Without simulation, we would have had to build many prototypes to assess this – a costly and time-consuming process.”

“Thanks to Simcenter STAR-CCM+, we could optimize heat management before building prototypes, allowing us to bring the device to the market faster while also reducing development costs. Defining the size and power requirements early in the design process also enabled us to better identify the right suppliers for manufacture. Otherwise, there would have been a trial-and-error approach – again taking more money and time.”

Gasko also points to seamless integration as a significant benefit. “The finite element model is more accurate but takes much longer to calculate,” he says. “Therefore, using it for the complete device simulation would have been impractical. But because Simcenter STAR-CCM+ enables us to conduct both finite element and CFD simulations, it was easy to carry out both for optimum efficiency.

“As far as I know, there is no other software capable of performing harmonic electromagnetic calculations and CFD simulations simultaneously. Using Simcenter STAR-CCM+ makes integrating additional modules relatively straightforward and delivers the expected results when comparing test data from previous projects.”

Saving time now and in the future

Using Simcenter STAR-CCM+ has reduced development time by approximately 30 percent compared to previous projects, says Gasko. “In our experience, the testing phase for a prototype, depending on its complexity, may be up to two months. However, simulations typically take two weeks and cost six times less,” he explains. “This is not only because we don’t need to build so many prototypes, but also because we can re-use simulation templates from previous projects rather than having to start from scratch every time. Of course, we still need to carry out final testing on a prototype, but by replacing much of the testing with simulation we can significantly speed up development time. This is only possible due to the high level of confidence we have in the simulation results.”

Gasko is confident that these techniques will be extremely valuable for the medical technology industry. “Wireless charging is the future of many medical devices,” he says. “It allows surfaces to be cleaned and disinfected more effectively than when traditional sockets are in place. It also offers the potential to make devices waterproof and to be more durable and portable.”

“I see Simcenter STAR-CCM+ as being a vital tool in the development of these products, as well as helping us meet our goal of minimizing energy losses during charging to make them even more efficient.”