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Experimental forms of two different types of engine oil viscosity sensors have been tested that use uniformly poled disks of piezoelectric PZT ceramic. In both cases, the disks were used to form electromechanical resonators functioning as the frequency-controlling element in a transistor oscillator circuit. The simpler type of sensor used only one disk, vibrating in a radial-longitudinal mode of vibration. In this mode, a disk 2.54 cm in diameter and 0.127 cm thick had a resonant frequency of approximately 90 kHz. The second type of sensor used two such disks bonded together by a conducting epoxy, with poling directions oriented in opposite directions. This composite resonator vibrated in a radially-symmetrical, flexural mode of vibration, with the lowest resonant frequency at approximately 20 kHz. The presence of tangential components of motion on the major faces of both resonators made them sensitive to the viscosity of fluids in which they were immersed.

Cavitation thresholds of 5W30 and 10W30 oils were measured in laboratory experiments using electrically-driven disks of piezoelectric ceramic as sources of mechanical excitation. The technique allows the mechanical-wave power density at which cavitation begins to be observed and calculated from electrical quantities and the volume of the oil sample being tested. Both cavitation turn-on and turn-off thresholds have been measured as functions of temperature and frequency. The temperatures ranged from 20 to 100°C and the frequencies ranged from 50 kHz to 4 MHz. The experiments have shown these oils can be made to undergo cavitation at surprisingly low thresholds.