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Fundamentals of Acoustics

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Fundamentals of Acoustics

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    1. Fundamentals of Acoustics Transmission from one fluid to another :oblique incidence

    3. Applying the condition of continuity of pressure at the boundary z=0 yields

    4. Law of reflection:

    5. From the equation (3-7-10), we obtain

    9. The totally reflected

    10. The angle of transmission is again real but greater than the angle of incidence

    11. In this case , the transmitted wave assume a very peculiar form, the reflection coefficient is a complex

    12. 530 10.9 0.52a 180 0.4 0 IRI530 10.9 0.52a 180 0.4 0 IRI

    13. Transmission through a layer: Normal incidence Assume that a layer of uniform thickness L lies between two dissimilar fluids and that a plane wave is normally incident on its boundary, as suggested in following Fig.

    15. When an incident signal in fluid I arrives at the boundary between fluids I and II, some of the energy is reflected and some is transmitted into the second fluid. The portion of the wave transmitted will proceed through fluid II to interact with the boundary between fluids II and III, where again some of the energy is reflected and some transmitted. The reflected wave proceeds back to the boundary between fluids I and II, and the whole process is repeated.

    16. From the wave equation and the equation of motion, we obtain( neglect the time factor):

    17. At x=0, two boundary conditions

    19. Define the reflection coefficient of the layer

    20. Where Z21 is the input impedance of the layer. The boundary between fluid I and fluid II corresponds to an impedance . Then the form of the pressure reflection coefficient Note : Z21 has both real and imaginary components

    25. (1) When medium 3 is the same as medium 1, we have Z3=Z1, and

    30. Maximum transmission of plane acoustic waves from water into steel is required. What should be the optimum characteristic impedance of the material to be placed between the water and the steel? If the thickness of the layer of material to be used is 0.02m and the frequency of sound transmitted is 1000Hz, find the speed of sound in the material and the density of the material.

    31. The sound intensity transmission coefficient for transmission through three media at normal incidence is given by

    32. For maximum transmission of acoustic intensity, If

    33. Hence, Z2=8.35*106 MKS rayls Therefore 100% transmission of sound occurs only for bands of frequencies centered about the particular frequencies for which

    34. Homework Textbook P277 3-17, 3-18

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