Ultrasonic absorption and velocity dispersion measurements in thin adhesive layers

This paper presents a new technique for the measurement of plane wave absorption and propagation velocity as functions of frequency in thin layers of adhesive polymer. The adhesive layer thickness can be in the range 0.05–2 mm and the frequency range of measurement from d.c. up to 30 MHz, although 100 MHz is achievable in principle. The technique is based on the use of acoustically thick transducers to generate and receive very wide bandwidth pulses, and signal processing of received data to calculate absorption and velocity as functions of frequency. Preliminary results are presented.