Ultrasound is sound above the conventional upper limit of human hearing, approximately . In a crystal, ultrasonic travel-time measurements determine long-wavelength elastic wave speeds, which are the small-wavevector slopes of the corresponding acoustic phonon branches.
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Ultrasound is a medical imaging technique that uses high-frequency sound waves to create images of structures within the body. It is commonly used in various fields of medicine for diagnostic purposes, as well as for therapeutic applications. ### Key Aspects of Ultrasound: 1. **How it Works**: - An ultrasound device, known as a transducer, emits sound waves at frequencies higher than the audible range for humans (usually above 20 kHz).