Absolute Measurement of Ultrasonic Intensity in the Nearfield

提出了一种近场超声强度绝对测量的新方法。为此提出了三种理论：第一，提出了一种新的活塞源近场速度势解。根据新的理论，瑞利表面积分，给出了一个圆形活塞源的速度势，减少到无穷级数的球谐函数时，适当地选择坐标。该理论的优点是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。迄今为止，球在近场中的声散射还没有解析计算过.最后，本文计算了弹性球在任意圆活塞声源近场中的声辐射压力，并与实验进行了比较.理论与实验结果基本一致。结果表明，可以通过测量放置在圆形活塞源上的球体的辐射声压来确定其近场声强的绝对值，铍和熔融石英由于其辐射声压的频率特性平坦，最适合作为圆形活塞源的球体材料。

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.