Higher harmonics of finite amplitude ultrasonic waves in solids

Abstract

Absolute measurements of the amplitude of the first four harmonicof 30-MHz finite amplitude ultrasonic waves are reported for fused silica samples of various lengths and for aluminum single crystals with different amounts of cold work. The harmonically distorted motion of the end of the sample is detected by a capacity microphone and the individual harmonics are then selected and amplified by a heterodyne receiver with flat frequency response from 30 to 250 MHz. The fused silica data are found to be in excellent agreement with a model of Fubini, originally developed for gases, which for solids depends on the second- and third-order elastic constants but none of the higher constants. A discussion is presented of the reasons for the insensitivity of the measurements to the values of the fourth- and higher-order elastic constants. Agreement with the model of Fubinin is not observed in single crystal aluminum. The quantitative differences are not fully consistent with existing models for dislocation contributions to harmonic generation.Subject Classification: [43]25.15, [43]25.20; [43]35.26; [43]25.25.