Basic principles of ultrasonic secondary responses in ultrasound-based detection techniques

Basic principles of ultrasonic secondary responses in ultrasound-based detection techniques 

As stated above, US secondary responses are obtained under speoific conditions such as resonance, are derived from primary responses suoh as impedanoe or are a fraction of the overall primary response e.g. absorption, refleotion). Measurements made under resonanoe conditions are the basis for resonance ultrasonic spectroscopy (RUS), also known as high-resolution ultrasonic spectroscopy — the latter name was given by the leading manufacturer of RUS instruments. The importanoe of this teohnique warrants disoussion of its basic principles below. 

The US resonance phenomenon for the case of a plane parallel-type resonator consists of exoitation by one of the piezotransducers of the ultrasonic wave traveiiing in the direction of the second piezotransducer. Upon reflection by the second piezotransducer, the wave comes back and is reflected again. At the frequencies corresponding to a whole number of half wavelength between the piezotransducers, resonance occurs and increases the amplitude of the signal at the second piezotransducer. 

The principles behind resonance US measurements differ depending on the liquid or solid nature of the sample. 

Resonant US in liquids. Measurements of ultrasonic resonance in liquids involve using a resonator cell comprising two major elements, namely a resonator chamber, where acoustic resonance forms and two transducers (usually piezoelectric), which excite and detect ultrasonic vibrations. 

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