Ultrasound piezo-electric crystal

Transducers contain a piezo-electric crystal that vibrates when an electric current is passed through it, producing an ultrasound beam which propagates through the soft tissues. Reflection or refraction of the ultrasound beam may occur when it reaches a soft tissue interface of different acoustic impedance. The reflected ultrasound beams then return to the transducer where they are converted to electrical currents and subsequently to form an image. When there is a large difference in impedance, for example at a hone-soft tissue interface, a bright echo is produced. 

Ultrasound is a high frequency, mechanical vibration consisting of alternate waves of compression and rarefaction (Kremkau 1997 McDicken 1991). The waves are generated by piezo-electric crystals shaped into a transducer which focuses the ultrasound waves into a beam. Commonly used frequencies for the liver are 5.0 or 3.5 MHz corresponding to wavelengths in tissue of 0.3 and 0.5 mm respectively, and this is the theoretical best spatial resolution that can be achieved. 

Ultrasonic nebulizers may divide into the liquid couplet and vertical crystal systems. Ultrasound is produced by the piezo-electric effect on certain crystals. The crystal vibrations are then transmitted to the solution to be nebulized. 

In 1880, Pierre Curie and his brother Jacques made the first observation of the piezo-dectric effeU. What they found was that some crystals, e.g. quartz, are deformed mechanically when an electrical voltage is applied to them. An AC electric potential might thus cause vibration. This made possible the generation and reception of ultrasound (a sound with such a high frequency, more than 15 000 Hz = 15 kHz, so that the human ear cannot hear it). For technical and medical uses of ultrasound, still... 

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