ABSTRACT
This chapter deals with four quite different techniques, which have in common the fact that the transduction mechanism is very loosely coupled to the sample, if at all. Two of them, laser ultrasonics and electromagnetic acoustic transducers, are in a mature phase, while capacitive micromachined ultrasonic transducer and resonant ultrasound spectroscopy are still developing. Laser ultrasonics comprises the generation and/or detection of ultrasonic waves by laser techniques. Historically, practical interest in the use of lasers and optical effects of ultrasound was for visualization of ultrasonic fields. The basic generation mechanism is quite simple to describe. An incident high-power laser beam is partially absorbed in a surface region of the sample. Crystal lattices are discrete atomic structures, so they exhibit dispersion at sufficiently high frequencies.
