Abstract: A noise-reducing resonant chamber sound pick-up for electronic stethoscopes is claimed. It consists of a resonating chamber (24) which acoustically preamplifies the selected frequencies of heart sounds, 50-150 hz, and bruits of breath or blood, 150-500 hz, while rejecting ambient sounds. A skin contact (34) has elastic foam support (14), whose rigidity is varied by varying the applied pressure, in order to select the preamplified band of sounds. The other side of the resonating chamber contains a sound transducer (10) largely encased in heavy malleable metal (12) that absorbs sound not coming from the chamber. A damping vent hole (26) shapes the band of preamplified sounds. The resulting superior signal-to-noise ratio permits two, small chambers to be used in a stereophonic chest piece little larger than that of a conventional stethoscope, with better amplification enabling examination through clothing or surgical dressing even in heavy persons.

Abstract: A microwave detector (10) is provided for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations. A biased ferrite (26, 28) produces a magnetization field flux that links a B-dot loop (16, 20). The magnetic field of the microwave pulse participates in the formation of the magnetization field flux. High-frequency insensitive means (18, 22) are provided for measuring electric voltage or current induced in the B-dot loop. The recorded output of the detector is proportional to the time derivative of the square of the envelope shape of the microwave pulse.