Ultrasound is commonly acquired through mechanical, piezoelectric or magnetostrictive transducers. A simple example of mechanical oscillator is a well-known whistle. It sounds excited by the fact that the air jet is broken on the inside edge of the whistle cavity. Recurring vortices excite vibrations of the column of air which is in the cavity of the whistle. The dimensions of the cavity determine the natural frequency of the column of air, and hence the frequency of the emitted sound.
The smaller size of the cavity, the higher the sound. By reducing the size of the cavity, we can ensure that the whistle will start making sounds of high frequency – ultrasound. Sirens are based on another principle: the motor rotates the disk (rotor) with openings at the edges. The fixed disc (stator) also has holes somewhat smaller in diameter than a rotor indent. A jet of compressed air supplied to the siren, periodically interrupted by a rotating disk. As a result, the outlets of the fixed plate there are periodic air pressure change, generating a powerful ultrasound.
In electromechanical emitters ultrasound is produced as a result of transformation of an alternating electric current oscillations corresponding frequency mechanical vibrations of the radiator. Piezoelectric transducer apparatus based on piezoelectric effect. Crystals of a number of substances (quartz, tourmaline, barium titanate, and so on. D.) have a remarkable property. If one plate is cut in a certain way, then the compression or tension of such a plate on its surface electric charges will have positive and negative sides (thus forming piezoelectric effect, reversible by its nature). If the cover plate on both sides is made of the metal electrode (e.g., aluminum foil) and attached to the AC voltage source, the plate is alternately compressed, then stretched. These oscillations of the plate surface excite ultrasonic waves in the medium. Using piezoelectric transducers, it is possible to obtain a relatively small intensity of ultrasound.
Some ferromagnetic metals (nickel, iron, cobalt and others.) and their alloys have the property to expand or shrink under the influence of the magnetic field. This phenomenon is called magnetostriction, is used to obtain high-intensity ultrasound in a magnetostrictive radiator.
The simplest magnetostrictive transducer – is, for example, nickel rod inserted into the coil, which surface energises an alternating current, which results into emergence of alternating magnetic field in the stroke rod and its variations are periodically compressed or expanded, performing mechanical vibrations.
The industrial use
The incredible power of ultrasound is successfully applied in a wide array of industries – from large machinery assembling enterprises to medicine and air decontamination. The industrial enterprises oftentimes integrate ultrasound cleaning into their pipelines to speed up the processing procedures. The largest ultrasound-focused businesses, like UK-based Hilsonic, offer a comprehensive line-up of high-tech ultrasonic cleaners for a variety of purposes (despite the relatively high cost of the equipment, it almost inevitably pays for itself in the long run). (more…)