Safe design of portable med-tech

How big a trend is miniaturisation in medical technology?

“As with many other areas of electronic design, it is no understatement to say that miniaturisation is massive in medical devices. This is, in part, due to the advancement of various technologies such as semiconductors, sensors and imaging technology, which means it’s possible to design effective functionality into smaller footprints. It is worth noting, however, that miniaturisation in medical technology doesn’t strictly mean shrinking devices into handheld electronics; it also covers a general rise in the portability of medical equipment. There are six main categories of medical devices - implantable, wearable, handheld, portable, transportable and stationary - and all bar the latter are subject to this trend for miniaturisation.

“While most people will instinctively associate the phrase medical technology with larger pieces of equipment, such as ventilators or anaesthesia machines, these devices have shrunk in the past couple of decades. This shrinkage allows design engineers to incorporate portability into these devices, so that healthcare staff can relocate equipment as needed. Overall, it makes delivery of care easier for healthcare professionals.

“Alongside portability of larger medical devices, the increasing sophistication of portable computing has given rise to greater use of medical carts in hospitals. Medical carts are often overlooked when we think of important equipment in a hospital. However, they are necessary to ensure that medical practitioners can deliver the best possible care to patients in a timely and efficient manner.

“Portability has also become a key consideration of electronic medical devices due to the rise of the home healthcare market, which has gone from strength-to-strength in the past few years. Although it does include things such as apps for smartphones and other consumer electronics, it also includes other medical electronic devices for everything ranging from blood pressure monitoring to pulse oximetry. As lifespans get longer and we are faced with an ageing population that requires medical treatment, home healthcare is becoming increasingly important.”

What are the challenges presented to design engineers by this trend?

“Unfortunately, technology advances at different rates. So, while semiconductor technology has made it possible to design increasingly powerful and energy efficient devices in shrinking sizes, advances in battery cells have not developed at the same speed or in the same way.

“The challenge here for design engineers working on portable medical electronics is to balance compact and sleeker designs with effective power. Battery manufacturers assist in this process by developing increasingly slimline, compact smart batteries that can deliver suitable performance. However, the best course of action is for design engineers to incorporate batteries into the early design concept by working directly with battery manufacturers.

“There is no such thing as a universal battery in medical applications; the requirements, such as the voltage, energy density and cycle life, will vary on an application-by-application basis. It’s only by working directly with battery experts at the earliest opportunity that the right battery can be specified.

“In line with the previous point about in-hospital portability of larger equipment, undoubtedly, a challenge for designers of medical carts is the increasing complexity of design. In many ways, the effective design of a medical cart can be as vital as that of conventional medical equipment.

“However, medical carts have traditionally used sealed lead acid (SLA) batteries as a power source. These batteries are heavy, require regular costly maintenance and perform poorly when working in regular discharge cycles. If medical cart designers are to effectively embrace the trend for lightweight carts, then the power supply itself must change. Lithium iron phosphate (LiFePO4) batteries are up to three times lighter than SLAs of the same energy density, which allows the overall cart to have better manoeuvrability and a more compact design. Crucially, LiFePO4 batteries also overcome the traditional lifespan problems encountered with SLAs.

“Accutronics’ parent company, Ultralife Corporation, has developed a rechargeable Lithium Iron Phosphate (LiFePO4) battery called the URB12400-U1-SMB. This battery includes Ultralife’s SMART CIRCUIT battery management electronics, to provide the user with accurate run-time information in addition to a balancing and protection system that maximises both safety and performance.”

How do you recommend that design engineers approach portable power supplies?

“The single most important step that design engineers can take when designing portable or handheld electronics that will require a battery is to incorporate it into the design at the earliest convenience. This will often mean working directly with a bespoke battery manufacturer, who can help ensure that a project has the best power solution possible. It’s an important consideration across all electronic design projects, but especially in critical applications such as medical electronics.

“All too often, we are approached by design engineers that have their product design effectively finalised and need a battery that will fit the existing design, which usually requires a bespoke solution. However, the space requirements of many portable electronic designs unavoidably places limitations on the energy density of any power solution. In applications where reliable performance and power is imperative, design engineers must work with battery manufacturers as soon as possible, as we can then advise on what is feasible, within the confines of the proposed design, and both parties can work together to develop a solution that ticks all the right boxes.

“Overall, it’s advantageous for design engineers and device manufacturers to work with battery specialists who can ensure that the right solution is selected. Although it’s a component that, despite its importance, is often still an afterthought for many, there are a lot of variables that need to be considered in battery selection. Variables such as battery chemistry, discharge profiles and the long-term effects of ageing, as well as charge rate, are all problems that continue to perplex many manufacturers.”