Introduction to Holography, 2nd Edition

22 Acoustic Holography

DOI: 10.1201/9781003155416-26

22.1 Introduction

Acoustic holography has many important applications because acoustic and ultrasound waves can readily penetrate materials which are opaque to visible light, including various kinds of biological tissue. Acoustic frequencies normally range from the audible below about 20 KHz to ultrasonic (from 20 kHz to several GHz). In solar seismology, frequencies of a few mHz are used.

The velocity v of a compressive, longitudinal acoustic wave in a medium of bulk elastic modulus of elasticity C and density ρ is given by

$$v=\sqrt{{\displaystyle \frac{C}{\rho }}}$$

For dry air at 20^°C, this works out at 343 ms⁻¹, and the wavelength can range from about 7 m at 50 Hz to about 0.33 μm at 1 GHz. In addition to compressive acoustic ...