Acoustics

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Ultrasonic

High intensity ultrasound applications utilize half wavelength transducers with resonant frequencies between 18 kHz and 45 kHz. Large blocks of transducer material is needed to generate high intensities which is makes manufacturing difficult and is economically impractical. Also, since half wavelength transducers have the highest stress amplitude in the center the end sections act as inert masses. The end sections are often replaced with metal plates possessing a much higher mechanical quality factor giving the composite transducer a higher mechanical quality factor than a single-piece transducer.

The overall electro-acoustic efficiency is:

             Qm0 = unloaded mechanical quality factor
             QE  = electric quality factor
             QL  = quality factor due to the acoustic load alone

The second term on the right hand side is the dielectric loss and the third term is the mechanical loss.

Efficiency is maximized when:

then: $\eta_{max} = 1 - \frac{2}{k_{eff} \sqrt{Q_E Q_{m0}}} \qquad \left ( k_{eff} \sqrt{Q_E Q_{m0}} \ll 1 \right )$

The maximum ultrasonic efficiency is described by: $I_{\mathrm{w}max} = \frac{1}{2} ( \omega_5 u_l )_{max}^2 \ \rho_{m\mathrm{w}} \nu_{\mathrm{w}} ( W / m^2)$

Applications of ultrasonic transducers include:

 Welding of plastics
 Atomization of liquids
 Ultrasonic drilling
 Ultrasonic cleaning
 Ultrasonic foils in the paper machine wet end for more uniform fibre distribution
 Ultrasound
 Non-destructive testing
 etc.