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Ultrasonics, science of sound waves with frequencies above those that humans can hear (above 20,000 cycles per second). Modern piezoelectric techniques generate ultrasonic waves with frequencies above 24,000 cycles per second. These exhibit the normal wave properties of reflection, refraction, and diffraction, and are used to clean fine machine parts and, in medicine, to examine internal organs non-surgically.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Transcendentalism to United Church of Christ