Ultrasonic horn is a device used to pass ultrasound into a liquid medium. It basically consists of a transducer, a device which consists of a piezoelectric material, cut properly and sandwiched between metal electrodes. When alternating electrical current passes through the metal electrodes, it causes the piezoelectric material to expand and contract because of the piezoelectric effect of the quartz material. This mechanical contractions and expansions are transferred to a metal rod attached to the piezoelectric crystal.
The dimensions of the metal rod (called as extender) and its shape depends upon the node and antinode formation of the passing ultrasonic wave that is created due to continuous expansion and contraction of the piezoelectric material. Thus ultrasound is generated due to continuous expansion and contraction of the quartz material. There is also another way of producing ultrasound. It is called magnetostrictive effect. In this effect, there is a magnetostrictive material which changes its shape in changing magnetic field. Thus when a magnetostrictive material is placed in changing magnetic field, continuous expansion and contraction of the material takes place. This can be transferred as ultrasonic waves into liquid medium. The frequency of the ultrasound generated by these sonic horns range from a few Hz (cycles/sec) to several megahertz. When the ultrasound produced is in the region of 16 kHz up to 1000 kHz, it is called power ultrasound and is used to produce ultrasonic cavitation in the liquid medium.
Commercial ultrasonic horns provide power ranging from a few watts to several thousand watts with the frequency of the ultrasound in the range of 20 kHz to 40 kHz. When the ultrasound produced is in the frequency region above 1000 kHz, it is called medical ultrasound and is used for medical applications and diagnostic purposes.
Ultrasonic welding horns are used in manufacturing to assemble parts made from thermoplastics, non-woven materials, and some metal applications. The most common frequencies used range from 15 kHz to 40 kHz (although some go up to 70 kHz). Ultrasonic welding horns are typically machined from bulk titanium, aluminium or powdered metals.