| 摘要 |
PURPOSE:To obtain the resonance frequency only of fundamental vibration by removing sub-resonance generated by cavity resonance, by providing a sound absorbing material in the housing of a sensor. CONSTITUTION:A sensor is fixed to an engine by mounting the screw part 3 integrally formed to the lower part of a housing 1 to the screw hole of the engine and the vibration of the engine is transmitted to a vibration plate 4 through the screw part 3, the main body of the housing 1 and the projection 2 provided to the inner bottom part of the housing 1. As a result, the vibration plate 4 is integrated with a piezoelectric element 5 to generate mechanical flexural oscillation and the electric signal corresponding to vibration is generated between the electrodes provided to the piezoelectric element 5. When a porous sound absorbing material is provided to the gas between the inner bottom surface of the housing 1 and the vibration plate 4, an incident sound wave enters the hole of the sound absorbing material 12 or the gap and, when said sonic wave is further ready to propagate through a material, the energy thereof is lost by flow resistance caused by viscosity to the vibratory flow of air. Therefore, subresonance due to cavity resonance is removed and the resonance frequency only of the fundamental vibration of a vibration detecting body can be obtained.
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