Ultrasonic waves are longitudinal waves that require a medium and consist of areas of compression and rarefaction with frequencies over 20kHz. They are used therapeutically between 500,000-3,000,000 cycles per second, with 1,000,000 Hertz most widely used. Ultrasonic waves are produced by applying a potential difference across a crystal such as quartz, causing it to vibrate at ultra-high frequencies determined by how the crystal is cut, generating ultrasonic waves by setting particles in motion.
2. Nature of ultrasonic waves
Longitudinal waves
Consist of to and fro movement
Require medium to travel
Areas of compression alternate with areas of rarefaction
Have frequencies of more than 20kHz
Frequency of waves for therapeutic purpose is between 500,000 and
3,000,000 cycles per sec
1,000,000 hertz is the most widely used frequency
3. Production of Ultrasounds
Principles of production:
Produced by vibration of matter , but no mechanical device is can
vibrate with sufficiently high frequency to produce ultrasonic waves .
One method is through vibration of crystal of quartz or some similar
material
4. Application of P.D across a suitable crystal causes distortion of the
crystal and this is followed by a series of changes in shape, the
frequency of which is determined by the way in which the crystal is
cut.
It is this oscillaton of the crystal that sets the particle of matter in
motion and produces the ultra sonic waves.
