In 1880 the remarkable French physicist Пьер Кюри and his brother Jacques opened, that at tension or compression in certain directions of some crystals, not having a center of symmetry, on their surfaces the electric charges of opposite signs are revealed. This phenomenon got the name of p'ezo effect. In 1881 there is other French physicist, Gabriel Lippman, from the cleanly theoretical considering supposed that in piezoelectric crystals must be observed also and reverse effect. Really, soon the brothers of Curie confirmed this prediction experimentally. They discovered that the sizes of crystal of quartz change under the action of electric-field. Posterior researches showed that direct and reverse p'ezo effects are observed at many semiconductor matters of crystalline structure, adopted by p'ezo electricians. All ferroelectrics at a temperature below than temperature of Curie are at the same time by p'ezo electricians.
P'ezo electricians got different applications in science and technique. First from them behaves to times of the first world war. The prominent French physicist Paul Langeven, creating a device for finding out the German submarine boats, used a quartz emitter. The variable difference of potentials of high-purity compelled to vibrate quartz plate which sent longitudinal ultrasonic waves in water. At meeting with an obstacle, in particular with a submarine boat, waves were reflected and perceived by a receiver, in the quartz plate of which as a result of action of the reflected waves variable electromotive force became excited.
In the technique of our days the various are widely used on the device and setting ultrasonic options. A basic element of ultrasonic device is an emitter, sending high-frequency waves in surrounding space.
There are various types of emitters the construction of which is based on different physical principles. Among them пьезоизлучатели, able to generate the most high-frequency vibrations is most widespread. For making of piezoelectric emitters a quartz, titanatum of barium and phosphate of ammonium, is mostly used, which a round or rectangular plate is definitely cut out from. On opposite parties of plate metallic electrodes which high-frequency and comparatively high electric tension is tricked into to are inflicted. So, for example, for creation of powerful ultrasonic stream it is necessary on the electrodes of quartz plate to give tension, arriving at ten of thousands volt. At the same terms an emitter from titanatum of barium requires less tensions considerably.
At a serve on the surface of p'ezo of variable electric tension of frequency of V he changes the sizes so much one time, frequency of V of change of tension is which. In other words, under act of variable tension a p'ezo hesitates and radiates waves in surrounding space. Depending on frequency of vibrations these waves can be perceived by a human ear. Frequencies a from 20 to 20 LTD. of hertzs behave to audio frequencies. Bodies, hesitating withby frequencies higher 20 000 hertzs, send ultrasonic waves in space. Thus, giving variable tension of different frequencies on the electrodes of p'ezo, it is possible to get different waves, since infrasonic ending ultrasonic.
The vibrations of p'ezo become especially intensive, when frequency of electric tension coincides with his eigenfrequency. In this case there is resonance. Taking advantage of him, it is possible to build the emitters of high intensity.