Passive ultrasonic sensors, methods and systems for their use

摘要

Passive acoustic sensors having at least two flat parallel acoustically reflecting surfaces. At least one reflecting surface is on a member which is movable such that the distance between the reflecting surfaces varies as a function of a physical variable to be determined. Preferably, the sensor is made such that the intensity of a first portion of incident acoustic waves which is reflected from one reflecting surface is equal or substantially similar to the intensity of a second portion of the incident acoustic waves which is reflected from the other reflecting surface. The first portion and the second portion interfere to form a returning acoustic signal having one or more maximally attenuated frequencies which is correlated with the value of the physical variable. The internal acoustic signal is received and processed to determine the value of the physical variable from one or more of the maximal attenuation frequencies. Methods and systems for using the passive sensors are disclosed.