Standard Article


  1. John H. Cantrell

Published Online: 15 MAR 2011

DOI: 10.1002/3527600434.eap548.pub2

Encyclopedia of Applied Physics

Encyclopedia of Applied Physics

How to Cite

Cantrell, J. H. 2011. Ultrasonics. Encyclopedia of Applied Physics. 195–242.

Author Information

  1. University of Tennessee, NASA Langley Research Center, Hampton, VA, USA

Publication History

  1. Published Online: 15 MAR 2011


The fundamental physical and technical principles of ultrasound in solids and fluids are developed with an emphasis on the underlying relationship with thermodynamics. The development of concepts relevant for understanding the technical and analytical applications of ultrasound is stressed throughout the article. The notions of stress (pressure), strain, and elastic constants are introduced via the thermodynamic state functions. The basic wave equations are obtained and solved for various modes of wave propagation in unbounded propagation media. The introduction of bounded media with appropriate boundary conditions leads variously to the consideration of wave reflection and refraction, resonance phenomena, surface waves, and guided waves. Ultrasonic attenuation is introduced as a manifestation of wave scattering, diffraction, and energy absorption. The effects of relaxation processes in solids, liquids, and gases on the ultrasonic wave velocity and attenuation are considered from the perspective of irreversible thermodynamics. The origin of wave dispersion is addressed and discussed in the context of its influence on ultrasonic measurement parameters and techniques. Both contacting and noncontacting means of generating and detecting ultrasound are reviewed. Representative pulse, continuous wave, and optical techniques for measuring ultrasonic velocity and attenuation are summarized. Applications of ultrasound are emphasized and discussed at appropriate places throughout the article as the subject is developed. The article concludes with an extended review of industrial, medical, microscopical, and underwater applications.


  • attenuation;
  • piezoelectric transducers;
  • Lagrangian strains;
  • monochromatic wave;
  • refraction;
  • propagation medium;
  • velocity