方板阶梯辐射体辐射声场的计算及测试

The sound field radiated from the stepped square plate radiator

研究了一种同相弯曲振动方板阶梯辐射体。以边长50 mm的方形平板为例,材料为钢,厚度为6mm。其第四阶本征振型的频率为19332 Hz,用同频率的纵振换能器激励其中心,会出现节线与边长成45°夹角的响应（本征振型中无）。为了获得辐射体辐射声场的高指向性,在四个板角与四条节线围成的等腰直角三角形区域加阶梯,可将平板辐射体改进成阶梯辐射体。计算得到阶梯辐射体的指向性比平板辐射体的指向性尖锐,与方板活塞辐射体的指向性相似。实验测试辐射体指向性与计算结果基本一致。进一步计算发现,方板阶梯辐射体与线性尺寸相同的矩形、圆盘阶梯辐射体比较,其频率低,指向性同样尖锐,可望应用于超声测距、料位测试中。

A type of in-phase stepped square radiator in bending vibration is studied in this work. Taking a fiat square steel plate as an example, side length and thickness are 50 mm and 6 ram. The frequency of fourth order intrinsic mode is 19332 Hz. The fiat square plate driven by a longitudinal vibration transducer with the same resonant frequency at its center is able to create a bending vibration mode, whose four nodal lines locate at 45° angle with each side （there＇s no such mode shape in its intrinsic eigenvibration）. In order to get a highly directional sound, the surrounded areas of the four isosceles triangles formed by each nodal line and each right triangle are modified to be raised ones, the fiat square plate radiator is modified a stepped radiator, so that the surface elements vibrating in phase and phase cancellation can be avoided. The calculated radiation pattern of the stepped radiator is better than that of the flat one, whose configuration is similar to that of the theoretical piston one. The measured vibrational mode shape of the stepped radiator is in good agreement with the calculated one. The result of further calculation shows the frequency of itself is lower and its direetivity is still shaper by comparison of the square plate stepped radiator and the same linear dimension of rectangular or circular stepped radiator, so it is expected to be used in ultrasound distance measurement and level measurement in stock.