A Radiating Near-Field 24 GHz Radar Stethoscope

A prototype 24 GHz radar stethoscope has been developed for the diagnosis of heart sounds when direct contact with the skin is contraindicated. It is shown that a vibration sensing, bi-static radar operating in the near-field has a sensitivity maximum at a non-zero range and that maximum is proportional to the square of the radar operating frequency. By placing the instrument in the near-field, close to, but not touching the skin, a 20 dB sensitivity increase can be demonstrated. The transmitter antenna has a hot spot in the near-field which further increases the stethoscope's sensitivity. The instrument is a modified, Doppler radar based, commercial RF motion detector that transmits very low RF power. When used as a stethoscope it is shown to pose no radiation hazard to the patient or medical personnel. An example is given to illustrate that the non-contact radar stethoscope has an audio output that is comparable in characteristics and quality to a conventional, skin-contact, acoustic stethoscope.