Generation and Detection of Sound with Frequencies Above 1 GHz (Hypersound)

Abstract

More recently it has become possible to produce and detect sound with frequencies far above 1 GHz. This relatively new field of acoustics is frequently called ‘microwave acoustics’, another frequently used name is ‘hypersound’. At first glance this linguistic separation from the range of ‘normal’ ultrasound seems even more arbitrary than the fixing of the lower frequency limit of ultrasonics at 20 kHz. Some justification for it, however, may be seen in the fact that with sound of very high frequencies, quantum effects become noticeable which are not observed in lower frequency ranges and which give access to fundamentally different methods of sound generation and detection. These methods are referred to as ‘incoherent methods’ which means that the sound produced is incoherent. The choice of name may be understood by comparing optical and acoustical sources of radiation.