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Several significant effects of ultrasonic treatment on human serum cholinesterase and aminopeptidase isoenzymes and on other serum proteins have been found by starch gel electrophoresis. The selective activation of one cholinesterase isoenzyme is especially striking. These effects must be considered when ultrasonic treatment is used for the extraction of intracellular enzymes. When the effects are appreciated, ultrasonics should provide a valuable tool for isoenzyme research.

Several interesting phenomena involving the interaction of ultrasonic waves and electrons have been observed in piezo-electric semiconductors. These include the processes of ultrasonic amplification and nonlinear harmonic generation, which are manifestations of the action of electrons on ultrasonic waves. The reaction upon the electrons as a result of their strong coupling to ultrasonic waves is manifested by the phenomena of current saturation and current oscillations in amplifying semiconductor crystals. We discuss the principle of acoustoelectric amplification and the role it plays in these effects. The difference between the amplification process and the Cerenkov emission of sound waves is emphasized. The generation of harmonics of the sound wave due to the nonlinear transport properties of the electrons is reviewed. Various models of current saturation are considered, including an elementary treatment of the role of acoustoelectric fields. A discussion is given of the possibility of propagating collective sound waves under amplifying conditions and the role that this may play in the current oscillations in cadmium sulphide.

Publisher Summary A useful technique for investigating the physical properties of materials in the solid state is to measure the characteristics of the propagation of mechanical waves in the solid. These characteristics are the velocities of propagation and the spatial or temporal rates of absorption of energy from the mechanical wave. Data on the attenuation of mechanical waves have been interpreted over a range from 70 Gc sec -1 , in quartz at low temperatures, to frequencies corresponding to the time required for geological processes to take place. This chapter discusses the exploitation of this technique in the elucidation of the physical properties of semi-conductors. Particular emphasis is placed on the 1 to 200 Mc sec -1 frequency range. The term “ultrasonic” is used to describe mechanical waves of frequency greater than 1 Mc sec -1 ; waves of frequency greater than 500 Mc sec -l have been described in the literature as hypersonic and microwave ultrasonic. The usefulness of the ultrasonic technique is demonstrated in discussions of a wide variety of experiments in which ultrasonic is the research tool. This chapter discusses the classical analysis, including elasticity theory, wave propagation, scattering, and diffraction. Measurement and laboratory techniques are then discussed briefly. This chapter discusses the interpretation of experiments on a variety of semiconductors, both piezoelectric and nonpiezoelectric.