Medical devices: Where wireless charging has real impact

April 21, 2015 // By Bill Schweber, EDN
Wireless charging of personal devices such as smartphones, laptops, and tablets is a hot topic. Several standards are competing to make it possible to just place the device on a table's surface or charging pad, and sit back while energy is transferred without the need to connect to a discrete, physical cable.

While this might seem a nice but not critical feature at home or office where you have your usual charger and connector already set up, it is a different story in a public place where you need the appropriate charger connector (USB, iPhone, and others), and the cord/connector are subject to extensive use, abuse, and even vandalism. Anytime you can seal the interface between unit A and unit B, that's good in terms of public access, reliability, and options for mischief.

 

Picture, above ; Not just a simple air or vacuum path: this model of the layered tissue structure between the skin surface and a 2-mm micro implant located 5 cm deep inside the human chest wall shows some of the challenges in wireless charging of in-body devices (from Physics Today, American Institute of Physics).

Wireless charging still faces some challenges, but there has been lots of progress in standardisation (admittedly with several competing standards), availability of needed ICs and other components, defining physical form factors, and other aspects. It’s hard to say if it will catch on and have long-term success, as there are associated costs with respect to components, size, and charging time. If it doesn't work out, the traditional technique of connecting a charger via a cable assembly is still a viable and well-established fall-back alternative.

But there are situations where practical wireless charging would bring real benefits: implanted medical devices. In many cases, the battery's size is a limiting factor in use, since it needs to power the device for several years. In some cases, such as brain stimulators, the battery is actually sited in the patient's chest, with wires running between the two locations—obviously, not a desirable situation, but there is no choice.

Why not use wireless charging for medical implants? It has been done, but with mixed results. There are several obstacles: the distance of between one and as much as five cm,