Detection acoustic

For completeness, we include in this brief survey a schematic diagram of the photoacoustic method (Fig. I4.2e), which has been discussed in Section 11.7. Absorption of chopped light by the particles gives rise to periodic heating which is detected acoustically. Scattered light does not contribute to the signal. 

Xiang and Sabatier [149] used a scanning laser Doppler vibrometer (LDV) to detect acoustic-to-seismic surface motion. This technique exploits airborne acoustic waves penetrating the ground and causing seismic motion. When an anti-personnel landmine... 

Budanov A.V., Kustov A.I., Migel I.A. (2004) The Study of Changes of Physical - Mechanical Properties of Materials in a Condensed State under Hydrogen influence using Fault Detection Acoustic Microscopy Methods. // Hydrogen materials science..., Science Series, II. Mathematics, Physics..., v. 72, 203-215. 

As indicated above, for solids it is possible to transfer energy between nuclear spins and the lattice via phonons generated within the sample. Kastler [4] and Altershulter [5-7] proposed that it should also be possible to utilize this path in reverse, with applied phonons (ultrasound) causing a nuclear spin system to experience a net absorption of energy, and result in detectable acoustic nuclear magnetic resonance (ANMR) spectra. 

The viscosity sensor uses a microacoustic sensor device [11], in which the piezoelectric effect in a crystal is used to excite (and detect) acoustic vibrations. For microacoustic liquid sensing, special wavetypes are used in order to avoid unwanted radiation losses due to the excitation of compressional waves in the liquid. This... 

Kramer and co-workers (7) reported that acoustic emission occurred in polystyrene immersed in diflFerent swelling liquids only when the crazes ruptured but not during their formation and growth. As long as the bridging by filamental elements is still intact, the deformation at the craze tip and in the craze is still so slow that no acoustic bursts are generated. It is the final fracture of these elements which is abrupt enough to cause the emission of a detectable acoustic burst. 

Photoacoustic calorimetry is another widely used technique to study the thermochemistry of organic systems in solution [127-129]. Light is used to initiate a reaction of interest, and the heat liberated from the reaction is detected acoustically. From the amplitude of the photoacoustic signal and the solution transmittance, the enthalpies of reaction and bond dissociation enthalpies can be derived. 

H. Nakajima, T. Shoji, M. Kikuchi, H. Nitsuma, M. Shindo, Detecting acoustic emission during cyclic crack growth in simulated BWR environments, in S.J. Hudak, R.J. Bucci (Eds.), Fatigue Crack Growth Measurement and Data Analysis, ASTM STP 738, ASTM International, West Conshohocken, PA, 1981, pp. 139—162. 

In an experimental study of explosive vaporization of the bubble on a microheater, by detecting acoustic emissions during explosive vaporization process of the bubble, the bubble volume and the bubble expansion velocity and acceleraticm was reconstructed [17]. The vapor pressure inside the bubble was also calculated using the Rayleigh-Plesset equation. 

This is an indicator system that produces and detects acoustical vibrations in metal surfaces. It is useful for bond inspection of aluminum honeycomb materials. No acoustic coupling is required. 

Figure 11.1.2 shows the measuring method of the cracking load [ 7]. A silicon nitride flat plate and a silicon nitride ball were used as test materials. The cracking load was decided by detecting acoustic emissions while gradually adding a load to the test pieces. Three kinds of balls, 5/32, 5/16 and 3/8 in., were used in this test. 

Sensors based on laser interferometers are being developed to detect acoustic signals for surveillance. A buried sensor can detect the sound of footsteps from as far away as 30 feet. 

Piezoelectrics have been the sensing and broadcasting element of underwater acoustics since its inception. Passive sensors are designed to detect acoustic signals by converting pressure waves or vibrations into electrical signals. Ignoring temperature, bias stress, and electrostrictive effects, Eqs. (3.18) and (3.20) reduce to ... 

Dielectric, NMR and low frequency dynamic mechanical studies indicate that the transition detected acoustically at 193 K can be ascribed to the onset of oscillatory motion of the phenyl group. Transitions observed at 383 K and 373 K are attributed to the glass transition and this assignment has been confirmed by dilatometry measurements. The observation of two transitions leads to the suggestion that clustering occurs in the solid phase. The lower temperature transition would therefore correspond to the onset of collective motions of polymer chains in the amorphous regions. The low temperature dependence of the modulus between 373 K and 383 K is believed to be... 

If one considers the acoustic energy form, a sensor for this example would be a microphone, which is able to detect acoustic wave inputs and provide an electrical signal output in accordance. In contrast, a sound speaker works as an actuator. This concept is generalized in Fig. 11.1. 

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