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Energy reflected, acoustic impedance

Detonation, Shock Impedance and Acoustic Impedance in. Acoustic impedance is the ratio between sound pressure and particle velocity. A sound wave, on reaching a boundary between two media, has part of its energy reflected at the boundary and part transmitted into the 2nd medium. The relationships depend on the values of the acoustic impedance in the two media. Swenson (Ref 2) showed that ... [Pg.518]

For the convenience of the reader, the values of the sonic characteristics of representative and frequently encountered materials are listed in Table 1. Energy which is not transferred is reflected. Maximum transfer takes place when the acoustic impedance of all materials are equal When the angle of incidence is normal to the. interface, the fraction of the reflected incident energy is found as follows ... [Pg.47]

Consider first the signal labeled As discussed in the previous section, for the incident sound energy to penetrate the outer surface of the coating without reflection, the material used must have an acoustic impedance close to that of water. Materials having impedance values near that of water include many common rubbers. For example, arbitrarily selecting four commercial rubber samples from stock, we found the particular natural rubber sample had a surface reflectivity of 24 dB (6% reflective), the urethane sample measured 20 dB (10% reflective), and both the neoprene and nitrile rubbers were 12 dB (25% reflective). If lower reflectivity were required, the impedance of any of these rubbers could be altered simply by adding low density or low sound speed filler material. [Pg.214]

These three quantities are not totally independent. The W2/Wx ratio depends on the generator and gives its energetic efficiency. The WK/W2 ratio depends on the efficiency of the coupling between the emitter and the sonicated medium. Due to different acoustic impedance, not all of the energy output from the transducer is transmitted to the medium, and part is reflected at the emitter/medium interface [1] and this is degraded into heat in the transducer. This will depend of course on the nature of the irradiated medium (density, viscosity, gas content,...) and on the experimental conditions (temperature, external pressure), but it will also depend on the mass and almost certainly on the geometry of the reactor. [Pg.5]

The best imbedding liquid was found to be castor oil for measurements in water. Castor oil has an acoustic impedance close to that of water (so that the percentage of incident sound energy reflected at the interface is small) and a rather high absorbtion coefficient. The probe is placed in such way that the direction of propagation of the sound wave is perpendicular to the thermocouple wires. The response of the probe follows the pattern described above (see Figure 7). According to the authors, this type of probe is extremely useful because (i) it is small in size, (ii) it has a low input electrical impedance, and (iii) it is not sensitive to stray radio frequency fields. [Pg.18]

The bounding interface between the external and middle ear is the tympanic membrane. Pressure variations across the membrane move three ossicles, the malleus (hammer) connected to the membrane, the incus (anvil), and the stapes (stirrup) whose footplate is a piston-Hke structure fitting into the oval window, an opening to the fluid-filled cavities of the inner ear. Ligaments and muscles suspend the middle-ear ossicles so that they move freely. If sound reaches fluids of the inner ear directly, 99.9% of the energy is reflected [Wever and Lawrence, 1954], a 30-dB loss due to the mismatch in acoustic impedance between air and inner-ear fluids. Properties of the external meatus, middle-ear cavity, tympanic membrane, and middle-ear ossicles shape the responsiveness of a species to different frequencies. [Pg.75]

Acoustic impedance is an important parameter. When an acoustic wave passes from one medium to another, some of the energy is transmitted and some is reflected. The acoustic impedance controls the ratio of transmitted to reflected energy. In acoustic emission, monitoring the acoustic impedance explains the need for an acoustic coupling agent between the sensor and the surface on which it is mounted. Without this the detected signal will be very low, as most of the energy will be internally reflected at the wall. [Pg.3890]

The reflection factor depends on the product of density p and wave velocity V, which is called the acoustic impedance of a material. It is easy to see that if material 2 is identical to material 1, theoretically, all of the energy is transmitted. It is difficult to completely understand... [Pg.434]

The specific acoustic impedance, Z, is the resistance of a medium to the propagation of a sound wave. It can be defined as the ratio of acoustic pressure to the so-called particle velocity at a single frequency (McClements, 1997). At an interface, the proportion of wave energy transmitted or reflected depends on the difference in impedance between the two media. Consequently, this difference determines the coupling between emitting surface and the treated medium. If the impedance difference is large, the proportion of energy reflected will be important and the ultrasound effects will be mainly localized at the interface. However, if the... [Pg.271]

Figure 6.31 General scheme for through-transmission ultrasonic non-destructive testing. An ultrasonic signal is sent from the transmitter to the receiver through the bonded component. If the received signal, 4r, is very small compared to the transmitted signal, 4t, then it may be concluded that most of the energy has been reflected by an area of low acoustic impedance, i.e. a void may be present [138]. Figure 6.31 General scheme for through-transmission ultrasonic non-destructive testing. An ultrasonic signal is sent from the transmitter to the receiver through the bonded component. If the received signal, 4r, is very small compared to the transmitted signal, 4t, then it may be concluded that most of the energy has been reflected by an area of low acoustic impedance, i.e. a void may be present [138].
When selective layers are deposited, the whole structure must be treated as a multiple resonator in which the reflection and/or refraction of the acoustic energy occurs at each interface. For example, when a polymer film is deposited on top of the gold electrode of the QCM, it is the polymer-Au interface with which we are concerned. When the mass loading of multiple structures becomes too high, the effect of the impedance mismatches becomes significant and the crystal ceases to oscillate. Even approximate treatment of the multiple resonator is difficult because densities, as well as thicknesses and shear moduli, of the individual layers must be known. [Pg.74]

The other important consideration concerns the transmission of ultrasound (and other forms of energy) from one medium to another and the importance of impedance matching . When wave energy is transferred from one medium to another then a part is transmitted and the rest reflected. The ratio of reflected to transmitted energies depends on the characteristic impedances of the two media and the transmission is total if these are matched. In the case of acoustic waves the specific impedance (Z) of a medium is given by the product of the density p and the velocity of sound v. that is... [Pg.374]

The oscillating resonator surface may be considered as a source for shear waves that are radiated into the contacting film. The upper film surface reflects these radiated shear waves downward, so that the mechanical impedance seen at the quartz surface is dependent upon the phase shift and attenuation undergone by the wave in propagating across the film. When the film is rubbery, significant phase shift across the film occurs. Consequently, the coupling of acoustic energy into the film depends upon thin-fllm interference. [Pg.69]

Part II of the book deals with lesser known aspects of US for the analytical chemists such as its use as an energy source for detection purposes. Thus, ultrasound-based detection techniques viz. US spectrometry in its various modes including ultrasound attenuation, ultrasonic velocity, resonant ultrasound, laser-generated, ultrasound reflection and acoustic wave impedance spectroscopies) are dealt with in Chapter 9. Finally, Chapter 10 is devoted to seleoted applioations of US spectrometry — mostly non-analytical applications from whioh, however, analytical chemists can derive new, interesting analytical uses for ultrasound-based deteotion techniques. [Pg.32]

Sound absorbers are usually employed for modilying the sound reverberation in a room, suppressing undesired sound reflections from remote walls (echoes), and reducing the acoustical energy density and, hence, the sound pressure level in noisy rooms. There are two standard methods of measuring absorption coefficients. One is for measuring normal incidence absorption coefficients in an impedance tube and the other is for measuring random incidence absorption coefficients in a reverberation room (Bies and Hansen, 2009). [Pg.107]


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See also in sourсe #XX -- [ Pg.240 ]




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Acoustic energy

Acoustic reflectance

Acoustic reflection

Acoustical impedances

Impedance, acoustic

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