The Method Of Radiating Sound Field Of A Disk And Attenuating Non-resonant Mode Interference

Directivity as an important parameter to describe the performance of a radiator,has been widely applied in many fields at present.The vibration plane or the radiating plane of the vibration system is in a variety of forms,which are commonly focused on its directivity.The flexural vibration radiator has many important applications for radiating high power ultrasonic into air,and people have a keen interest in this kind of radiator.The phase on two sides of the vibration line of the flexural vibration radiant flat plat is opposite,resulting in the radiation field in the distributional space vibrates and destructive interference,it will cause acoustic energy waste and no sharp directivity.In order to avoid phase cancellation,Gallego and others converted radiator plate surface into a stepwise radiation flat surface.According to the frequency equation to design the stepped plates,it contains some variables such as:the number of steps,based thickness,and frequency.There are many design schemes for the stepped plate at a given frequency.For example,frequency is 20kHz,basal thickness is 5mm,the number of steps can be one,two or more.Which directivity is better in these schemes?The stepped plate with sharp directivity is the best choice,because the sharp degree of the acoustic field directivity determines whether the sound field energy is concentrated.What’s the relationship between the number of the steps of stepped plates and directivity?To this problem,this paper designed fours stepped plates with one to four steps,frequency is 20kHz,the basal thickness is 5mm.Using the method of numerical and superposition,the directivity of the stepped plates with two and more steps car calculated.Radiation plates are often energized by some other vibrational modes when resonating at high frequencies,which can interfere with resonant modes as well as lead to some problems like phase confusion and low efficiency.In the Design of the radiation plate,we should try to pull the distance of the resonant frequency and the adjacent frequency,weakening the effect of mode coupling.Using the finite element calculation,this paper found grooving the back face of plate radiator can stretch the intervals between the resonant frequency and the adjacent frequency.as well as explored the best position of grooving and the best geometry size.In this paper,the main work and research results are as follows:(1)The directivity of plates with one to four steps of same frequency and base thickness are calculated in this paper,it shows that,with the increase of the number of the steps(it means the plate with greater radius),the directivity is sharper;.(2)The directivity of the stepped plates with same base thickness and material are calculated,with the increase of frequency,directivity of main lobe are becoming more acute;the stepped plates with same frequency and base thickness,but materials are different,the directivity of the stepped plates is almost the same.The same frequency and the thickness of the base,so the consistent geometric structure,which is also the main cause of directivity;The directivity of stepped plates with the same frequency and material,but different thickness of the base,the main flap becomes increasingly sharp as well as the side lobe becomes narrower and sharper with the increase in the thickness of the base.(3)Processing of one to four stepped plates and one flat plate,and then making an experiment that the results are in good agreement with the theoretical results,which shows the theoretical calculation is correct.(4)Working at the resonant frequency under high-power state,unwanted modes of the plate may be excited.These unwanted modes may give rise to modal interactions and a range of nonlinear phenomena.In order to avoid or to palliate such problem,in this paper,the profile of the back face of the plates(including a flat plate,two plates with one step and two steps)are modified by grooving their back faces.By following this procedure using finite element(FE)modeling,it is possible to increase the separation between the closer modes in the treated cases.The best grooved position,width and thickness are investigated in this paper.It shows that grooved position near the secondary maximize displacement direction of the plates,and 2 mm in width and depth is the best solution.