Ultrasonic contactless measurement with micromembranes

Abstract

The resonance frequency of appropriately structured micromembranes is dependent on some parameters of the membrane itself and on the medium surrounding it. Two parameters, the temperature and strain, have been investigated in detail. The resonance frequency of mechanical vibrations of a membrane tightened across a frame depends among others on the internal mechanical tensile stress of this membrane. When the materials of membrane and frame are of different thermal expansion coefficients, the internal mechanical stress and thus the resonance frequency of the membrane and frame can be deduced from the resonance frequency. When microstructures are applied to a freely tightened membrane, it is subdivided into many equal micromembranes. When the parameters for manufacture and design of the membrane are appropriately chosen, the resonance frequency will be within the range of some megahertz so that it can be measured with the aid of ultrasonic methods. The sample principle applies to the detection of strain at the measuring point owing to the vibration of the internal tensile stress of the micromembrane. Ultrasonic contactless measurement of strain and temperature was experimentally verified based on these principles. >