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A laser interferometer to measure fetal heart activity.

The function, some specifications and preliminary results of a new device, a so-called laser microphone for detection of fetal heart activity, are presented. The fundamental principle of the new transducer is based on a Michaelson interferometer. Though the device was built only to discover whether it is possible to detect vibration of the maternal abdomen due to fetal heart activity, the results showed much more than that. The findings suggested the construction of a comparable based on a laser diode.