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The principle of ultrasound: Difference between revisions
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More of on reflection – it occurs only when the acoustic impedance of one media is different from acoustic impedance of the second media at the boundary. If the ultrasound hits the reflector at 90 degrees (normal incidence), then depending on the impedances at the boundary the % reflection = ((Z2 - Z1) / (Z2 + Z1))^2. Then transmission is 1 - % reflection. Physics of oblique incidence is complex and reflection/transmission may or may not occur. We do know that the incident intensity is equal to the sum of the transmitted and reflected intensities. | More of on reflection – it occurs only when the acoustic impedance of one media is different from acoustic impedance of the second media at the boundary. If the ultrasound hits the reflector at 90 degrees (normal incidence), then depending on the impedances at the boundary the % reflection = ((Z2 - Z1) / (Z2 + Z1))^2. Then transmission is 1 - % reflection. Physics of oblique incidence is complex and reflection/transmission may or may not occur. We do know that the incident intensity is equal to the sum of the transmitted and reflected intensities. | ||
[[File:PhysicsUltrasound_Fig18.svg|thumb|left|400px| Fig. 18]] | |||
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'''Refraction''' is simply transmission of the ultrasound with a bend. This occurs when we have an oblique incidence and different propagation speed from one media to the next. The physics of the refraction is described by Snell’s law. Sine (transmission angle)/sine (incident angle) = propagation speed 2/ propagation speed 1. | '''Refraction''' is simply transmission of the ultrasound with a bend. This occurs when we have an oblique incidence and different propagation speed from one media to the next. The physics of the refraction is described by Snell’s law. Sine (transmission angle)/sine (incident angle) = propagation speed 2/ propagation speed 1. | ||