Based Spectral Analysis Method Of Ultrasonic Cavitation Characteristics Of Experimental Research

Ultrasonic cavitation is a unique physical phenomenon when ultrasonic acts on the liquid medium. It is the main power in practical application for ultrasonic. Since 1990s, the study of ultrasonic cavitation is coming into a new stage of development with security requirements posed such as ultrasonic dosage for medical use, the rapid risen ultrasonic medicine and phonochemistry. At the same time, the application study has been a major concern with the development of high-technology industry, the accurate and perfect observation technology and the need of protection of public health. Because of the incomplete cavitation theory and the complexity of cavitation fields, the measurement of cavitation in the reactor has not been resolved and the method to accurately describe cavitation has not been found. This causes it is difficult to judge and make use of cavitation. In this paper, the cavitation noise in the reactor is measured based on experimental methodology in order to present the more quantitative and more practicable measurement methods of cavitation fields.In this paper, spectrum analysis methods are adopted to study the cavitation fields, then chooses the hydrophone and the microphone as measuring instrument to measure the cavitation noise of the cylindrical and the rectangular reactor in the water and in the air, and to the cavitation noise data which obtained has made the power spectrum and the cepstrum analysis, finally to the result which obtained has carried on the analysis and the comparison. By the massive experimental study, the following work has been done and the responding conclusions are drawn:(1) The simple lowpassis designed and made, and the frequency response of it are analyzed and measured.(2) Randomicity and periodicity are the characteristics of pressure waveforms of ultrasonic cavitation noise signal, so to analysis the metrical data needs to apply random signal process theory. Moreover, it is necessary to acquire a long time data in order to enhance the results repetition and ensure that the time interval is equal to integral times of the period in order to reduce error.(3) Cavitation noise signal of the cylindrical and the rectangular reactor has been measured by the hydrophone and the microphone, and the data which measured to the hydrophone and the microphone has carried on power spectrum processing with the MATLAB procedure. The results indicate, the scopes of fundamental wave, subharmonics and harmonics in the power spectrogram are different with the input electric power increasing; under the same input electric power and the sme reactor conditions, the scope of harmonics and subharmonics in the power spectrogram of the transducer with nominal frequency 20kHz, 25kHz are bigger than that of the 45 kHz; under the same input electric power and the same frequency of transducer conditions, the scope of harmonics and subharmonics in the power spectrogram of the reactor with basal diameter 10cm and 12cm is bigger that of the reactor with basal diameter 11cm; under the same input electric power and the same frequency of transducer conditions, the scope of fundamental wave, subharmonics, harmonics scope in power spectrogram of the cylindrical and rectangular reactor with same basal area are different; the fundamental wave, subharmonics, harmonics scope in power spectrogram of the identical reactor are the similar when the transducers are stuck to the different positions. The power spectrogram of the microphone is similar to that of the hydrophone, but sometimes there is certain difference because of the ambient noise, reactor oneself whistles and the different sensitivity of microphone and the hydrophone. On the whole, cavitation noises in the water and the air are similar.(4) Cepstrum analysis is generally a certain modification of signal spectrum analysis. As the result of this analysis the so-called cepstrum is obtained, enabling the detection of periodicality in the frequency spectrum. The data which measured to the hydrophone and the microphone has carried on cepstrum processing with the MATLAB procedure. The result indicated, Some viewpoints of the cepstrum analysis and the power spectrum is similar, But the data which measured to make the cepstrum analysis, the cepstrum analysis proved, the existence of irregularities, hardly visible in the power spectrum. For example, these frequencies arrange into a sequence of fractional parts of the ultrasonic wave frequency, and the conducted cepstrum analysis proved the existence of regularities in the power spectrum.