Acoustic methods of acoustical power determination
 
  1. A method of irradiated power estimation by determination of a horn oscillation amplitude by a vibrometer results in mistakable results because appearance of cavitation bubbles leads to considerable decreasing of acoustical impedance (rc), r is media density, c is media sound speed. This event is due to decreasing of sound speed in bubbly liquid that can be even smaller then sound speed in the gas. For example, sound speed in cavitating water falls down to two orders of magnitude (from 1500 m/s in pure water to 15-50 m/s!) At cavitation, the acoustic impedance of media is changed significantly and stochastically both in space and in time and also considerable sound speed dispersion takes place. Besides, one can measure the amplitude from the front of the horn only by this method, but the energy irradiated in other directions is determined laboriously.
  2. Computation of the irradiated specific power I is done by the formula:
    I = kU/(rc),
    where conversion coefficient k depends on the type of transducer, U is the voltage on the transducer. Note that k is undetermined in principle (because value of acoustical power is unknown) and varies in a wide range for every irradiator.
  3. Application of piezoelectric or magnetostrictive sensitive elements and thermoelectric method based on the absorption of sound and heating of a calibrated sticky drop, gives some relative parameters in one point (relative method).
  4. Optical measurements (interference and semi shadow methods), based on the measurement of refraction index, need a determined configuration of acoustical parameters. At cavitation, the distribution of acoustical parameters in a liquid is stochastic one and these methods are, obviously, inapplicable (relative method).
  5. Measurement of the radiation pressure in a small liquid volume gives wrong results at presence of multiple reflections of ultrasonic waves. Note, that methods 2-5 need precise determination of rc value and have the same drawback as method 1 considered above (relative method). Consequently, by using of these methods one cannot determine correctly the irradiated acoustical power and moreover the absorbed one as well.