The Pitch Position Deviation Of Radiation Effects On The Ladder Disc Sound Field

In the field of high power ultrasound radiation to the air medium, the acoustic radiator is widely used which is composed of the longitudinal vibration sandwich piezoelectric transducer and the flexural vibration circular plate, the advantage is combined with high efficiency and power of the longitudinal vibration transducer and big radiation area of the circular plate, it is conducive to radiate the ultrasonic energy to medium. Especially the stepped circular plate have been proposed in the later, its height of the step is equal to a half wavelength of the radiation medium. which is effectively avoid acoustic field destructive interference caused by the opposite phase to further improve the acoustic field directivity and the radiation efficiency.The sharp degree of acoustic field directivity pattern indicates whether the energy of acoustic field is concentrated, the radiation impedance determines the radiation efficiency is high or low, so it is particularly important to study the acoustic field directivity pattern and the radiation impedance. The frequency and substrate thickness of the stepped circular plate are related to the directivity pattern and the radiation impedance. The center of the stepped circular plate is drove by longitudinal vibration transducer, the frequency of the transducer is equal to the frequency of the stepped circular plate, the position of nodal circular is coincide with the pre-designed position of the stepped circular plate. But in practice, there is a little contact area between the transducer and the stepped circular plate, it is difficult to in resonant state in the work because of mechanical processing, assembly and so on. There is little deviation of the frequency between two, the stepped circular plate is not in the resonance state, the position of nodal circular is deviation of the step position, it has certain influence of radiation acoustic field especially the acoustic field directivity pattern. Under the condition of little effect about directivity, how much is transducer frequency range with different vibration area corresponding to the longitudinal vibration. taking a central convex stepped circular plate for example, and the effect on the radiated acoustic field is calculated due to the deviation of the nodal circular position from the frequency, the radius of stepped circular plate, the radius of nodal circular, displacement distribution and so on. the main work is as follows: 1Based on the acoustic radiation theories of the flexural vibration circular plate and the flexural vibration stepped circular plate, the acoustic field directivity pattern and the radiation impedance of the stepped circular plate in the air medium are calculated and compared with different frequencies, different substrate thickness of a single nodal circular wite the free boundary.2Using the finite element methed, the nodal circular of the stepped circular plate and the resonance frequency under the certain driving area are calculated with different driving frequency. Taking a nodal circular is smaller than the position of the stepped for example, the expression of radiated acoustic pressure is derived by the principle of superposition in the acoustic field.3Under the condition of that there is a little contact area between the longitudinal vibration transducer and the stepped circular plate, and the effect on the directivity pattern is calculated due to the deviation of the nodal circular location from the stepped one. The results showed that the frequency of the transducer is not equal to the frequency of the stepped circular plate will lead to more or less deviations between the nodal circular position and the stepped position, these will lead to the directivity pattern and the radiated efficiency will have be reduced to a certain degree.4Driving frequency under the different driving area is calculated with little effect on the directivity pattern(the little deviation of nodal circular from the stepped). The results show that:the greater the driving area is, the higher the frequency of the transducer should close to the frequency of the stepped circular plate.