Acoustic Impedance Measurement by Reflection of an Ultrasonic Impulse on a Specimen Through a Coupling Layer

Abstmcr-A new method to measure the acoustic impedance of a solid medium which presents only one plane surface is described. This method is based on the resonance of the liquid coupling layer between the transducer and the medium investigated. First, the resonance of the layer is studied, and from its relative amplitude the acoustic impedance of the medium can be deduced. Second, the influence of the lack of parallelism of the coupling layer is determined, and a model is proposed to explain the experimental results. From the observation of the resonance when the transducer is inclined, it is possible to adjust correctly the parallelism of the layer so the acoustic impedance of the medium can be obtained with an accuracy varying between 4 and 8 percent.