Absolute Measurement of Ultrasonic Intensity in the Nearfield

提出了一种新的近场超声强度绝对测量方法。为此，提出了三种理论：首先，给出了圆形活塞源近场速度势的一种新解。根据新的理论，当坐标选择适当时，给出圆形活塞源的速度势的瑞利面积分可归结为无穷级数的球谐函数。该理论的优点在于它既不包含近似，也不包含数值积分。其次，利用该理论计算了近场中球体的超声散射。到目前为止，还没有对球体在近场中的声散射进行解析计算。最后，计算了位于任意圆形活塞声源近场的弹性球体的声辐射压力，并将各种理论与实验进行了比较。理论和实验之间有很好的一致性。结果表明，可以通过测量球体上的声辐射压强来确定圆形活塞声源近场声强的绝对值。结果表明，铍和熔融二氧化硅由于其辐射压强的频率特性平坦，最适合球体材料。

A new method has been developed for the absolute measurement of ultrasonic intensity in the nearfield. Three theories have been presented for this purpose.In the first place, a new solution for the velocity potential in the nearfield of a circular piston source has been developed. According to the new theory, the Rayleigh surface integral, giving the velocity potential for a circular piston source, reduces to an infinite series of spherical harmonics when the coordinates are suitably chosen. The theory has the advantages that it includes neither approximations nor numerical integrations.Secondly, ultrasonic scattering by a sphere placed in the nearfield has been calculated by use of the above theory. So far sound scattering by a sphere in the nearfield had never been calculated analytically.Finally, the acoustic radiation pressure has been calculated for an elastic sphere placed in the nearfield of any circular piston source.Each theory has been compared with experiments. Excellant agreement has been observed between theory and experiment. The results compel the conclusion that we can determine the absolute value of acoustic intensity in the nearfield of circular piston source by measuring the acoustic radiation pressure on a sphere placed there.It has been found that beryllium and fused silica are most suitable for the sphere material because of flatness in their frequency characteristics of radiation pressure.