Parker K J
J Acoust Soc Am. 1985 Feb;77(2):719-25. doi: 10.1121/1.392340.
The absorption coefficient of a material can be determined by measuring the heating which occurs as a result of ultrasonic irradiation. When narrow focused beams are used to heat a sample, or when the available volume of a material is restricted to small dimensions, then the effect of heat conduction to surrounding unheated regions becomes significant, complicating the relation between measured temperatures and acoustic parameters. In this paper new analytical expressions, which account for radial and axial heat flow in a medium, are derived for the case of Gaussian-shaped ultrasonic beam patterns in thin or semi-infinite absorbing materials. Solutions are given for temperature histories resulting from an ultrasonic impulse (pulse decay method) or a step input (rate of heating method). The use of these equations in absorption measurements is discussed, and experimental results are given. These expressions provide flexibility in choice of laboratory ultrasonic parameters, and the results are especially useful for many biomedical measurements where the volume of tissue available is restricted.
材料的吸收系数可通过测量超声辐照产生的热来确定。当使用窄聚焦光束加热样品时，或者当材料的可用体积限制在小尺寸时，热传导到周围未加热区域的影响就会变得显著，从而使测量温度与声学参数之间的关系变得复杂。本文针对薄或半无限吸收材料中高斯形超声束模式的情况，推导了考虑介质中径向和轴向热流的新解析表达式。给出了超声脉冲（脉冲衰减法）或阶跃输入（加热速率法）产生的温度历史的解。讨论了这些方程在吸收测量中的应用，并给出了实验结果。这些表达式为实验室超声参数的选择提供了灵活性，其结果对于许多可用组织体积受限的生物医学测量尤为有用。
