Noncontact MMG Sensor Based on the Optical Feedback Effect in a Laser Diode

An optical interferometric MMG sensor is presented. It uses the feedback effect in a laser diode to measure the vibration generated by the MMG at the skin surface. Its key features are noncontact measurement, high sensitivity, and extended bandwidth toward low frequencies (≈1 Hz). Furthermore, as it is able to recover with a good accuracy the shape of vibrations ranging from 1 μm peak-to-peak, the MMG is expressed in the physiological unit (micrometer) rather than the sensor dependent unit. The MMG measurement conditions are reviewed through a clinical protocol, including the perturbation causes. This probe is compared with a classical microphone based sensor, and thereby the influence of the coupling between the muscle and a contact sensor is demonstrated. © 1998 Society of Photo-Optical Instrumentation Engineers.