Mike makes light of sensing sound

 作者:单佛     |      日期:2019-03-08 03:03:07
By Paul Marks PATIENTS undergoing body scans cannot usually communicate with the outside world because metal parts in microphones distort the electromagnetic field generated by the scanner. But a new microphone that uses light rather than electricity to sense sound waves could overcome the problem, allowing patients to talk to the radiographer while the scan is taking place. “You can’t have any metal in the scanner as the strong field would be perturbed by it,” says Wolfgang Niehoff, research director for the German audio company Sennheiser. Niehoff’s answer to the problem is a microphone made entirely of glass and plastic. An LED sends light down a glass optical fibre, which guides it onto a polymer membrane that acts as the microphone’s diaphragm. Light reflected from this membrane enters a second optical fibre. Sound waves striking the membrane cause variations in the intensity of the light reaching the second fibre. This light passes to a photodiode, which generates an electrical signal proportional to the intensity of the light it receives, and which can be amplified. Niehoff is working with the University of Frankfurt, medical equipment maker Siemens and fibre-optic experts at Phone-Or, an Israeli company, to turn a prototype into a product. The microphone could also be used in environments containing flammable vapour, where a metallic microphone might generate sparks in an electromagnetic field,