Acoustic Intensifier

a device for increasing sound intensity. The two types are the focusing and wave-guide acoustic intensifiers.

Focusing acoustic intensifiers are usually made as a system of mirrors or as spherical or cylindrical focusing ultrasonic radiators (see Figure 1). The latter are most frequently made from a piezoelectric ceramic, with oscillations at the fundamental resonance frequency normal to the surface. Cylindrical magnetostriction radiators are also used. Focusing acoustic intensifiers are used both in the laboratory and in industry, chiefly in apparatus for the technological application of ultrasound, such as ultrasonic cleaning, dispersion, and production of aerosols. Up to 90 percent of the radiated sound energy is concentrated in the focal point of focusing acoustic intensifiers. Since the dimensions of an acoustic intensifier must be large compared to the wavelength to produce good focusing, this type is mainly used in the high range of ultransonic frequencies (10³ hertz [Hz] and higher). Concentrators can produce sound with an intensity of up to 10³–10⁴ watts per sq cm.

Figure 1. Focusing spherical radiator made from a piezoelectric ceramic with oscillations normal to the surface

Wave-guide acoustic intensifiers (sometimes called mechanical transformers) are a section of a nonuniform (narrowing) wave guide in which the energy is concentrated as a result of the reduction in cross section. Extensive use is made of resonance wave-guide acoustic intensifiers in the form of metal rods a half-wavelength long with a cross section that varies smoothly according to a definite law or by steps (Figure 2). Such acoustic intensifiers can provide an amplitude gain of a factor of 10–15 and make possible the production of oscillation amplitudes up to 50 microns in the frequency range around 10⁴ Hz. They are used in ultrasonic machine tools for mechanical working, in ultrasonic welding equipment, and in ultrasonic surgical instruments.

Figure 2. Resonance wave-guide acoustic intensifiers: (1) conical, (2) exponential, (3) stepped; (ξ) distribution of vibration amplitudes