Wireless breakthrough sees implants shrink in size

A new technique to power medical implants wirelessly could see them shrink to sub-millimetre sizes in the future if an approach described in Physical Review Letters pays off.

Researchers at Stanford University propose a new design that will allow wireless power transfer to sub-millimetre devices. According to the research there will enough power to drive a pacemaker.

Existing devices such as cochlear implants that are powered by radio-frequency electromagnetic fields remain bulky because they require a receiver coil a few centimetres across.

Ada Poon and colleagues at Stanford University in California looked for a way to reduce the size of the receiver, ideally so that implants need to be no bigger than a millimetre or so.

This battery-free approach could work in situations where “a device turns on when activated by an external source but is otherwise dormant.” Said Poon.

She added: “These might include stimulators for treating neurological disorders, sensors that are powered during read-out, or locomotive drug-delivery systems that are inside the body for a short time.”

Poon’s team has shown that, despite the issue of tissue absorption, radiating modes can after all be used to boost power transfer—which makes it less necessary to match the size of the source and receiver.

Poon said: “Previously this problem with high frequencies has been considered insurmountable.”

But she and her colleagues have found that there is a “sweet spot” at which the waves can penetrate deeply enough into the tissue to transfer a significant amount of power.

They added as the source frequency increases, the strength of the interaction between the receiver and the magnetic field increases—but so does tissue absorption.

Anil Kumar, a specialist in wireless biomedical technology at the University of Utah said: “This work definitely provides food for thought.”

However he added: “The tissue model used in the authors’ simulation is still too simplistic to represent, say, a chest cavity.”

Poon claims their approach of identifying optimal source fields might be used to design better optical antennas for capturing light, for example in solar energy conversion.