Abstract: In a sensor device which detects pressure variations owing to displacements of a body surface of a subject by respiration through variations of the output impedance of a piezoelectric vibrator, the pressure variations can be more efficiently transmitted to the piezoelectric vibrator. The sensor device, attached to a subject's body surface, comprises a contact piece contacting the body surface; a displacement-signal convertor which converts the displacements of the body surface into electrical signals; and an outputting device which outputs the electrical signals to an external unit; the sensor device is clamped between the body surface of the subject and an upper edge portion of a subject's bottom garment, and the contact piece is arranged in one side surface of a housing, and a stopping member which can be attached with the upper edge portion of the bottom garment in the other side surface of the housing.

Abstract: In a sensor device which detects pressure variations owing to displacements of a body surface of a subject by respiration through variations of the output impedance of a piezoelectric vibrator, the pressure variations owing to displacements can be more efficiently transmitted to the piezoelectric vibrator. The sensor device, attached to a subject's body surface and detecting displacements of the body surface accompanying respiration of the subject, comprises a contact piece having a contact surface which contacts the body surface when the sensor device is attached to the body surface; a displacement-signal convertor which is connected with the contact piece and converts the displacements of the body surface into electrical signals; and an outputting device which outputs the electrical signals to an external unit; wherein the contact surface of the contact piece is a curved surface projecting outward in a direction from its periphery to its center.

Abstract: A method of monitoring variation in either or both respiration and heartbeat of an animal comprising the steps of vibrating a piezoelectric vibrator by continuously or intermittently applying an AC voltage of a frequency corresponding to a natural resonance frequency of the vibrator to the piezoelectric vibrator under such condition that the vibrator is placed directly or indirectly in contact with the surface of the animal's body; collecting a current generated by the vibrator under vibration; and calculating an impedance of the vibrator from a value of the current and a value of the AC voltage applied to the vibrator so as to continuously or intermittently detect variation of the impedance by lapse of time is effective to monitor variation of respiration and/or heartbeat of animals including humans who are in sleep or under exercise and take a variety of positions with high sensitivity.

Abstract: A thin porous piezoelectric Pb(Zr,Ti)O.sub.3 ceramic sheet having a thickness of 0.05 to 2 mm which is favorably employable for manufacturing a piezoelectric transducer has small pores essentially all of which have a size of less than 25 .mu.m in which pores having a size of 5 to 25 .mu.m have a mean pore size of 1/10 to 1/1,000 based on the thickness of the ceramic sheet, and which shows a ratio of apparent density to true density in the range of 5/10 to 9/10.