Harvesting light and heat energy from the body with a hybrid device

Rechargeable batteries are increasingly more common in neural implants, removing the need for multiple surgeries to replace a depleted battery. Alternative strategies are being developed for replenishing the energy of the battery. The most established method of energy delivery is via radio waves. Recent shift toward the use of higher frequencies in the 0.1-1 GHz band made the rectenna (receiving antenna) extremely small. This allowed the implant to fit within an injectable needle for a minimally invasive delivery at a location near a peripheral nerve. In order to eliminate the need for coupling the implant with an external charging device, methods are being developed for harvesting the energy from the human body. These methods utilize the energy of light (visible or infrared), heat, or vibration.  Harvesting of visible light can be done most efficiently in the retina, while infrared light can penetrate the skin and be used for transcutaneous powering of the implants. In the body, amount of energy available for harvesting is rather limited, so that multiple forms of energy – such as light and heat, or light and vibrations – can be used simultaneously in order to collect a sufficient amount for practical use. This can be achieved by combining different kinds of energy transducers. In pursuit of this approach, Fujitsu Laboratories has developed a new hybrid harvesting device that captures energy from either light or heat in a single device. Their device is manufactured from inexpensive organic materials, keeping the production costs low. The device contains two types of semiconductor materials – P-type and N-type semiconductors – allowing it to function as a photovoltaic cell or thermoelectric generator. Importantly, their hybrid device can be fabricated on flexible substrate for easy accommodation into different implant shapes.  The company is currently refining the technology to increase its performance, and aims to commercialize it by around 2015.

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