Abstract
This chapter discusses ultrasound in liquids only, and to compressional waves; viscosity effects and shear waves are neglected. The restricted treatment discussed in the chapter can cover only the most essential facts for the application to kinetics. For performing ultrasonic measurements, suitable transducers must convert electrical into sound energy and reverse. These transducers can be classified into several groups: (1) electrostatic; (2) magnetostrietive, e.g. Ni-wires; (3) piezoelectric, e.g., crystalline quartz, barium titanate and other ferroelectrics, and also evaporated or sputtered thin films; (4) optical effects, Debye-Sears, for detection only. The frequency range reached by acoustical measurements ranges at present from a few kHz to more than 2 GHz. This presentation deals with methods for a range from about 50 kHz to 100 MHz— that is, (time constants from 3 microseconds down to 1.5 nanoseconds), which is of special importance for biochemical investigations. Until now ultrasonic techniques have been indispensable for the evaluation of many very fast chemical reactions, especially because the almost universal temperature-jump method does not reach time constants much shorter than 1 sec. It appears desirable to have several ultrasonic methods operating at one place; ultrasonic spectroscopy, which is still in the developmental stage, requires the coverage of a wide frequency range in a single instrument.