Measurements were performed with different plate

When pi was divided by p30 ( Fig. 3b), the calculated transmission ratio JNJ-26481585 approximately constant at 30 ± 3%. Therefore, the relative transmission of sound pressure through the plate is independent of the distance of the plate from the transducer surface.
Since the distance of the plate to the transducer does not influence the transmission ratio, the results for the following experiments will be for a transmission plate fixed at 25 mm distance from the transducer unless otherwise stated.
3.2. Frequency and plate thickness effect on sound pressure transmission
Fig. 4(a) and (b) show the sound pressure transmission ratio calculated using Eq. (8) through a steel transmission plate for selected ultrasound frequencies and transmission plate thicknesses. In general, the measurements show that the transmission ratio declines with distance from the transducer surface (transmission plate fixed at 25 mm from the transducer), indicating that the sound is attenuated with distance. The attenuation of sound energy in water follows an exponential decay [16], and occurs even in the absence of a steel plate (Fig. 4(b)).