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Where a, in cm-¹, is the absorption coefficient for the medium at a particular frequency. The table below gives some typical absorption coefficients. The intensity is proportional to the square of the amplitude, and its dependence on depth is 1 = loe-2 -2ax

Where a, in cm-¹, is the absorption coefficient for the medium at a particular frequency. The table below gives some typical absorption coefficients. The intensity is proportional to the square of the amplitude, and its dependence on depth is 1 = loe-2 -2ax

University Physics Volume 1
University Physics Volume 1
18th Edition
ISBN:9781938168277
Author:William Moebs, Samuel J. Ling, Jeff Sanny
Publisher:William Moebs, Samuel J. Ling, Jeff Sanny
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What is the attenuation of sound intensity by 1 cm of muscle and fat?

When a sound wave passes through tissue, there is some energy loss due to frictional effects. The absorption of energy in the tissue causes a reduction in the amplitude of the sound wave. The amplitude A at a depth x cm in a medium is related to the initial amplitude Ao (x = 0) by the exponential equation A = A₂e-ax. Where a, in cm³¹, is the absorption coefficient for the medium at a particular frequency. The table below gives some typical absorption coefficients. The intensity is proportional to the square of the amplitude, and its dependence on depth is I = = loe-2ax 1
Transcribed Image Text:When a sound wave passes through tissue, there is some energy loss due to frictional effects. The absorption of energy in the tissue causes a reduction in the amplitude of the sound wave. The amplitude A at a depth x cm in a medium is related to the initial amplitude Ao (x = 0) by the exponential equation A = A₂e-ax. Where a, in cm³¹, is the absorption coefficient for the medium at a particular frequency. The table below gives some typical absorption coefficients. The intensity is proportional to the square of the amplitude, and its dependence on depth is I = = loe-2ax 1
Where I is the incident intensity at x = 0 and I is the intensity at a depth x in the absorber. Material Frequency (MHz) Muscle 1 Fat 0,8 Brain (on average) 1 Bone (human skull) 0,6 0,8 a (cm-¹) 0,13 0,05 0,11 0,4 0,9 1,7 3,2 4,2 5,3 7,8 2,5 x 10-4 Half - Value Thickness (cm) 2,7 6,9 3,2 0,95 0,34 1,2 0,21 1,6 0,11 1,8 0,08 2,25 0,06 3,5 0,045 Water 1 1,4 × 10³ Table 1: Absorption Coefficients and Half-Value Thickness for various Substances The half-value thickness (HVT) is the tissue thickness needed to decrease lo tolo. Table 1 gives the typical HVTs for different tissues. Note the high adsorption in the human skull and that the absorption increases as the frequency of the sound increase. This increasing absorption with frequency also occurs for other body tissues and limits the maximum frequencies that can be used clinically.
Transcribed Image Text:Where I is the incident intensity at x = 0 and I is the intensity at a depth x in the absorber. Material Frequency (MHz) Muscle 1 Fat 0,8 Brain (on average) 1 Bone (human skull) 0,6 0,8 a (cm-¹) 0,13 0,05 0,11 0,4 0,9 1,7 3,2 4,2 5,3 7,8 2,5 x 10-4 Half - Value Thickness (cm) 2,7 6,9 3,2 0,95 0,34 1,2 0,21 1,6 0,11 1,8 0,08 2,25 0,06 3,5 0,045 Water 1 1,4 × 10³ Table 1: Absorption Coefficients and Half-Value Thickness for various Substances The half-value thickness (HVT) is the tissue thickness needed to decrease lo tolo. Table 1 gives the typical HVTs for different tissues. Note the high adsorption in the human skull and that the absorption increases as the frequency of the sound increase. This increasing absorption with frequency also occurs for other body tissues and limits the maximum frequencies that can be used clinically.
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