Abstract: A piezoelectric ceramic composite material useful for use in underwater transducers or hydrophones, including an elastic organic matrix, and piezoelectric ceramic powder dispersed in the substrate and having a composition:Pb.sub.1-x TiO.sub.3-xwherein x is a number of 0.005 to 0.12.

Abstract: A piezoelectric ceramic composite material useful for use in underwater transducers or hydrophones, including an elastic organic matrix, and piezoelectric ceramic powder dispersed in the matrix and having the following chemical formula:Pb.sub.1+x TiO.sub.3+xwherein x is a number greater than 0.

Abstract: Piezoelectric type liquid level sensor for detecting whether the level of various liquids such as oil of an internal combustion engine, a generator or the like is a predetermined value or higher or not, and method of making the sensor. The sensor is arranged to eliminate the influence of the weight of the lead wires on the vibration element and to facilitate its assembly. The sensor may be provided with a damper member for increasing the sensitivity.

Abstract: An underwater acoustic wave transmitting and receiving unit having excellent characteristics for both transmitting and receiving and providing stable characteristics over long operating periods. A plate-shaped polarized piezoelectric resonator is provided formed of at least one plate made of a complex of fluorosilicon rubber and lead titanate. The resonator is sealed in a rubber casing filled with an insulating liquid matching the water around the casing in acoustic impedance.

Abstract: An ultrasonic wave transmitter and an ultrasonic wave receiver are disposed in a tank in any positional relation to each other so long as the wave transmission and wave reception surface do not face each other to check whether the liquid level in the tank is above a predetermined level. When both the wave transmitter and wave receiver are submerged in the liquid in the tank, a wave radiated from the wave transmitter can be received by the wave receiver because of the facts that the directivity angle of the wave from the transmitter is large in the liquid and the wave propagates through the liquid without attenuation. When the liquid level decreases and becomes lower than either of the wave transmitters or wave receiver that is at an upper level, a wave from the transmitter can no longer be received by the receiver. This principle is utilized for the liquid level detection.

Abstract: A sensor for detecting the level of oil in the crankcase of an internal combustion engine. The sensor has a generally tubular body and at one end a thin metal plate to which is bonded the piezo-electric element. The plate, and hence the piezo-electric element, are oriented in the crankcase such that they are generally perpendicular to the level of the oil within the crankcase.

Abstract: A device for detecting knocking in individual cylinders of a multicylinder engines comprises a movable vibration sensor, an ignition pulse detector, a control circuit and a control console. The ignition pulse detector is a clip for the ignition cable of the specified which can detect propagation of the high-voltage ignition signal therethrough without damage the insulation. The signal from the vibration sensor is checked for a threshold amplitude at a frequency indicative of knocking. If the threshold is exceeded and the ignition detector simultaneously detects an ignition pulse for the specified cylinder, the control circuit outputs a signal to operate an indicator on the console. The console also includes a selector for adjusting the knocking amplitude threshold.