Influence Of Different Incentive Modes On Rectangular Sound Field Uniformity

High power ultrasonic equipment generally consists of ultrasonic generator and ultrasonic transducer. Sine signal of a particular frequency or pulse signal is generated by the signal generator to incentive transducer system keep working at resonance condition. The distribution of sound field plays an important role in the application effect during in all kinds of high power ultrasound applications. Using the acoustic incoherence and the characteristics of diffuse sound field, a narrow-band multi-frequency synthetic signal of continuous frequencies is designed to incentive the system work, according to the sound wave superposition and the theory of wave acoustics, and rectangular acoustic field distribution was analyzed by combining with experimental study under different incentives. The main contents are as follows:1 Sound field distribution of rectangular space is analyzed under the single frequency wave and multi-frequencies irrelevant sound waves, according to the theories of wave acoustics and sound wave superposition principle. The result shows that:the sound field is superimposed by superposition of a large number of normal mode vibrations of single signals and multi-frequencies irrelevant sound waves, in addition, the higher frequencies, the more normal modes, and the sound field becomes more uniform.2 Based on the characteristics of the continuous and uniform spectrum of white noise, a new white noise signal is designed, which is filtered by band-pass filter to incentive the multi-element system maintains a long-term stable work. The Matlab software programming is used to generate a signal, which signal is introduced into function generator through a third party software UltraWave to come to analysis. The results show that:white noise signal which is filtered cannot drive the corresponding system work, due to too lower amplitude. Therefore, multi-frequency synthetic signal of a continuous sinusoidal superposition is further proposed and determined as the excitation signal of system.3 The resonant characteristics of rectangular ultrasonic transducer system are measured and analyzed under the small signal and large signal models, so as to accurately design the synthetic signal bandwidth. The results show that:the resonant characteristics of system are different under two kinds of incentive modes, mainly in two aspects:with the frequency increasing, the resonant bandwidth gets wider; the resonance frequency fs and resonance bandwidth Δfs become larger when the system is driven at the large signal mode. According to the actual work needs of high powers ultrasound system, the resonance frequency and resonance bandwidth are chosen as the standard to design synthetic signal parameter.4 The synthetic signal bandwidths are designed respectively under conditions of Δf<Δfs, Δf=Δfs and Δf>Δfs, according to resonance bandwidth Δfs which are measured under large signals, electrical parameter and sound field distribution of dyeing method are used to compared and analyzed sine signal and synthetic signals at the same time. The results show that:the performance of system is better on the whole, when the scope of synthetic signal bandwidth is designed in Δf<Δfs, and the system is more stable in high frequencies; the active power and the electric efficiency which are corresponding to electric parameters present a trend of slight decrease, in addition, this is more obvious in low frequencies, but sound field uniformities are all obviously improved. However, when the bandwidth is designed in Δf≥Δfs, the effect is not good as Δf<Δfs. The comprehensive analysis point out that all aspects of system performance is best, when the best bandwidth Δf of synthetic signal is designed at half of resonance bandwidth Δfs.5 Selecting sine signal and the best bandwidth synthetic signal as the test signal to incentive rectangular transducer system, sound fields of rectangular grooves are measured and analyzed through the glossy paper dyeing method and relative sound pressure relative measurement of hydrophone. The results indicate that:in terms of sound field uniformity, acoustic field of high frequency is better than low frequency, and multi-frequencies synthetic signal is better than sine signal. The average effect of the sound pressure measuring points is presented that the relative sound pressure of synthetic signal is greater than sine signal, it indirectly explains electro-acoustic efficiency of synthetic signal is better than sine signal.