Medical Devices - Infrared light boosts pacemakers

Aug. 1, 1999
OSAKA-At the engineering depart ment of Osaka University, Satoshi Kawata and colleagues have used near-infrared (NIR) light to produce electricity for implanted microdevices such as heart pacemakers and artificial inner ears.

OSAKA-At the engineering department of Osaka University, Satoshi Kawata and colleagues have used near-infrared (NIR) light to produce electricity for implanted microdevices such as heart pacemakers and artificial inner ears.

Until now, the source of electricity for such devices has been either an implanted battery or high-frequency electromagnetic induction. The first method requires periodic surgery to exchange the battery, which, for a pacemaker, means approximately every 10 years. The second method requires ensuring that electromagnetic noise from other electronic devices does not cause problems.

The Osaka researchers have developed a method for producing electricity that starts with an 810-nm semiconductor laser, the light from which is easily transmitted a short distance through the body. A single-crystal silicon solar cell inside the implanted microdevice converts the NIR light to electricity.

In its experiment, the group tested this approach on a pacemakerwhich also contained a backup electrical source. To test the viability of sending energy through live flesh, the re searchers implanted the light-receiving solar cell 2 mm below the skin of a marmot. Then they directed a 30-mW, 810-nm semiconductor laser onto the cell and measured the power output of the pacemaker. The pacemaker produced regular output and with a pulse that did not waver, even when the light source was turned off and the backup energy source took over. A supercapacitor condenser was included in the implanted instrument. In the test case, only two hours of charging were required for a full day of continuous operation.

The group also is researching the use of NIR light to transmit sound to artificial inner ears. Microphone signals modulate the semiconductor light, which is transmitted to the implanted instrument. This light is reconverted to electrical signals and, as a result, external sounds can be heard.

Courtesy of O plus E magazine, Tokyo

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