Measuring scanning acoustic microscope with a harmonic sounding signal

A concept of a scanning acoustic microscope with a harmonic sounding signal for measuring the parameters of local homogeneous regions of flat samples is proposed. The distinctive feature of the device is the utilization of th e Doppler effect that occurs in the sounding wave reflected from the sample surface when the sample is uniformly moved relative to the focusing ultras onic transducer of the microscope. It is theoretically demonstrated that th e spectrum of the received signal is determined by the product of the refle ction coefficient and the transfer function of the transducer. The errors o f the measurement technique are considered, and the sources of signal disto rtions are analyzed. High sensitivity of the measurement results to the err ors of the scanning system is demonstrated. The developed measuring microsc ope is described, in which an acoustic interferometer is used to provide th e necessary precision of the scanning coordinate measurement. The microscop e transfer function is measured for the frequency of the sounding signal 65 MHz, and the values of density and bulk wave velocities are determined for a homogeneous sample by the measured phase of the reflection coefficient u sing the technique of nonlinear estimation of parameters. With fused quartz used as an example, it is shown that the measurement error is 7.2% for den sity and 2.3 and 0.7% for the velocities of longitudinal and transverse wav es, respectively. In addition, the velocity of a leaky surface wave (SAW) i s determined by two methods. One method is based on measuring the position of the inflexion point for the experimental phase of the reflection coeffic ient, and the other is based on calculating the SAW velocity corresponding to the measured values of density and hulk wave velocities. The errors of t hese methods are found to be equal to 0.42 and 0.17%, respectively. (C) 200 0 MAIK "Nauka/Interperiodica".