Toda M
Meas. Specialties Inc., Wayne, PA, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2008 Jul;55(7):1653-9. doi: 10.1109/TUFFC.2008.841.
This paper investigates acoustic wave radiation from cylindrical polyvinylidene fluoride (PVDF) film mounted inside a concentric wall with a small air gap. In such a structure, propagation is allowed only in the gap between the film and the wall surface, and the wave propagates in the axial direction of the cylinder. The radiation impedance of the cylindrical transducer inside the concentric wall has been calculated using a one-dimensional propagation model. After calculating the mechanical impedance of the cylindrical PVDF film, the generated acoustic wave has been calculated as a function of frequency with various air gaps between the PVDF film and the wall. It has been found that the excited acoustic wave becomes stronger for a narrower air gap and shows a maximum at a specific air gap. This phenomenon has been explained as the match between the transducer impedance and the radiation impedance of the air gap. When the gap is too small, the radiation impedance exceeds the transducer's mechanical impedance, the acoustic wave radiation decreases with the decreasing gap, and the resonance frequency increases due to loading by the imaginary part of the excessive radiation impedance. All these theoretical results have been experimentally confirmed.
本文研究了安装在具有小空气间隙的同心壁内的圆柱形聚偏二氟乙烯（PVDF）薄膜的声波辐射。在这种结构中，传播仅允许在薄膜与壁面之间的间隙中进行，并且波沿圆柱体的轴向传播。使用一维传播模型计算了同心壁内圆柱形换能器的辐射阻抗。在计算出圆柱形PVDF薄膜的机械阻抗之后，已计算出所产生的声波作为频率的函数，该频率是PVDF薄膜与壁之间具有各种空气间隙的情况。已经发现，对于更窄的空气间隙，激发的声波会变强，并且在特定的空气间隙处显示出最大值。这种现象已被解释为换能器阻抗与空气间隙的辐射阻抗之间的匹配。当间隙太小时，辐射阻抗超过换能器的机械阻抗，声波辐射随着间隙的减小而减小，并且由于过量辐射阻抗的虚部加载而使共振频率增加。所有这些理论结果均已通过实验得到证实。
