Velocity, acoustic coupling fluid 29 32

The coefficients k are given in Table 3.3 with T in °C. The polynomial expansion is useful in analysis programs to calculate the velocity from the temperature. The attenuation in water decreases with temperature, but the rate of decrease is less at higher temperatures. The attenuation and velocity are plotted against temperature in Fig. 3.1. For practical operation of an acoustic microscope with water as the coupling fluid, the smallest lens radius for routine operation is 40 pm (focal length 46pm). With water at 60°C a lens... 

If the density pc of the cell is known, then the acoustic velocity in the cell can be immediately deduced, since vc = Zc/pc. Since determination of acoustic velocity by this method depends on the measurement of relative amplitudes, the amplifiers and their gain controls must be accurately calibrated. The combination of reflection and transmission coefficients on the right-hand side of (9.4) can be expressed in terms of the acoustic impedances of the coupling fluid, the cell, and the substrate. 

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