The Excitation Source Area Of ​​the Vibration Characteristics Of Disk And Ladder Tray

In the process of studying the effects of driving area on the vibration characteristics of circular plate and stepped circular plate, external exciting source refer to the longitudinal vibration transducer. The main problems are the high absorption and the low acoustic impedance of the air medium when strong power ultrasonic wave generate and propagate in gases. In order to obtain high efficient transmission of ultrasonic energy in gases, it requires the radiator has directivity and achieve a good impedance match with the gases. A compound transducer consisting of a longitudinal vibration transducer and a thin radiator has a wide range of applications in practice. It combines advantages of large radiation surface and low radiation impedance of thin plate in flexural vibration and high efficient of longitudinal vibrator. The compound transducer is mainly used for thickness measuring, level gauging and distance measuring in gases.The plate in flexural vibration will produce one or several nodal circle as the role of excitation source. Because the vibration phase on the two sides of nodal circle in contrast, the sound field generates destructive interference and a part of acoustic radiation cancel out, which lead to low radiation efficiency and bad directivity. In order to solve above problems, measures of adopting stepped plate and perforated plate to make the radiating surface vibrating in phase so as to obtain the characteristic of high efficiency, good directivity and long distance transmission of transducer in gases.The longitudinal transducer is linked with the center of the radiator through the mechanical amplifier, the contact area between the radiator and the mechanical amplifier is very small, which usually be regarded as point excitation in previous researches. In practice, especially in high power applications, the contact area can't be neglected, the size of contact area has an impact on the vibration characteristics of the radiator. In this paper, for this problem of the practical application, the effects of driving area on the vibration characteristics of circular plate and stepped circular plate is studied, research results as following:1,The effects of the exciting area on the location of nodal circle on the circular plateAccording to resonant frequency expression of the thin circular plate in flexural vibration with free boundary, the fundamental frequency of the flexural plate with a certain size can be obtained. Design the size of longitudinal vibration transducer, Satisfy the frequency of excitation source equal to the fundamental frequency of the flexural plate. The longitudinal vibration transducer with different exciting area driving the centre of thin circle plate, the radius of nodal circle on the plate can be obtained in different modes of flexural vibration. When the driving radius keeps invariant, the higher the frequency of flexural vibration mode, the greater the radius of the nodal circle, one driving area can produce many different flexural modes of the plate, however, there is one resonant mode of longitudinal-flexural vibration in which the frequency of the system is closer to that of the longitudinal transducer. In these resonant modes, as the driving area increases, the radius of nodal circle reduces and ultimately vanishes. Further study shows that the disappearance of nodal circle is related to the ratio of exciting area and plate area.2,The effects of the exciting area on the radiated sound field of flexural plateIn the resonant modes of longitudinal-flexural vibration, when the exciting area increases to a certain value, the plate changes from flexural vibration to vibrating in phase. Compare the radiated sound field of two different vibration, we can find that when the plate vibrating in phase, the value of axial sound pressure is not zero, show stronger directivity.3,Different driving areas correspond the position of nodal circle on the stepped plateThe radius of nodal circle on the stepped plate is calculated by finite element method when the longitudinal vibration transducer with different exciting area driving the centre of the stepped plate. The frequency equation of stepped plate is studied in the situation of the location of nodal circle and the stepped position are not strictly coincided. Through programming and solving frequency equation, the radius of nodal circle, stepped radius and radius of stepped plate are calculated numerically.The results show that the value of stepped radius through numerical calculation is a little greater than design values by finite element method; the radius of stepped plate through numerical calculation is basically consisting with the design values by finite element method; the nodal circle radius by finite element method simulation is slightly less than the value through numerical calculation.The results of analysis can provide theoretical guidance for utilizing plate radiator efficiently in practical power applications.