Sound Field Analysis In The Ultrasonic Cleaning Tank Excited By The Weighted Multi-frequency Signal

Ultrasonic cleaning is a branch of power ultrasound in various industries. It is composed of ultrasonic signal generator, ultrasonic transducer and the cleaning tank, and has the advantages of favorable cleaning effect, high-efficiency, low-cost, and automation. The transducer is bonded in the tank and excited by the signal generator with a proper frequency so that the system can work at the best situation. There are many factors contributes to the washing effect, especially the acoustic field plays a decisive role in the working. According to the superposition principle of acoustic wave and the theory of wave acoustics, we design a multi-frequency synthetic signal within a narrowband to excite the transducer system depending on the wave superposition with noninterference and the characteristics of diffusive field. The even index of the field is related to the band width of the signal. To overcome the shortcoming, this paper propose a method to make a composite signal with a proper weighting which against to the resonance properties to make sure the active power of different frequencies are identical. The specific work includes the following aspects:1 According to the working mechanism of ultrasonic cleaning, the factors that affect the cleaning effect are analyzed. Depending on the superposition principle of acoustic wave and the theory of wave acoustics, we proposed a way to improve the uniformity of the sound field in the tank. The research results shows that the uniformity of sound field in the tank is related to the superposition of abundant normal modes in single frequency and superposition with noninterference in multi-frequency. The uniformity of the sound field in the tank is decided by the number of normal modes in a sound field, the superposition non coherent acoustic wave and the application of band wide signal.2 Depending on the relationship between the sound pressure amplitude expression of the sound field in the tank and the sound pressure of the non coherent acoustic wave superposition, an expression for the sound pressure in the longitudinal direction of the acoustic field is given. According to the resonance characteristics of the system, the system resonance bandwidth Af_s is used as the reference, the degree of inhomogeneity of the corresponding sound field is analyzed in the case of bandwidth ?f< ?f_s, ?f= ?f_s, ?f> ?f_s. The experiment and simulation results show that compared with the single frequency signal excitation, using narrow band signal with uniform amplitude to excite the ultrasonic transducer system can improve the sound field uniformity in the rectangular space. The effect of synthetic signal to improve the uniformity of sound field is related to the bandwidth of the excitation signal and it is not simply monotonic. The optimal bandwidth ? fopt depends on the resonant characteristics of the system and it is about half of the resonant bandwidth ? f_s.3 Based on the effect of resonance characteristics of transducer system on the uniformity of sound field, we proposed a method that replace the synthesis signal with uniform amplitude by a composite signal with a proper weighting in exciting the transducer system. We compare the two kinds signal in the case of bandwidth ?f<-?f_s, ?f=?f_s, ?f>?f_s by measuring and analyzing the acoustic field in the vertical and horizontal directions with dying method and hydrophone. The experimental results show that, in terms of the of uniformity of sound field, while the influence of bandwidth variation on the sound pressure distribution is weakened after the signal is modified but the sound pressure amplitude is decreased and the uniformity of sound field is better.