Ultrasonic coefficient

The development of active ceramic-polymer composites was undertaken for underwater hydrophones having hydrostatic piezoelectric coefficients larger than those of the commonly used lead zirconate titanate (PZT) ceramics (60—70). It has been demonstrated that certain composite hydrophone materials are two to three orders of magnitude more sensitive than PZT ceramics while satisfying such other requirements as pressure dependency of sensitivity. The idea of composite ferroelectrics has been extended to other appHcations such as ultrasonic transducers for acoustic imaging, thermistors having both negative and positive temperature coefficients of resistance, and active sound absorbers. 

Ultrasonic Spectroscopy. Information on size distribution maybe obtained from the attenuation of sound waves traveling through a particle dispersion. Two distinct approaches are being used to extract particle size data from the attenuation spectmm an empirical approach based on the Bouguer-Lambert-Beerlaw (63) and a more fundamental or first-principle approach (64—66). The first-principle approach implies that no caHbration is required, but certain physical constants of both phases, ie, speed of sound, density, thermal coefficient of expansion, heat capacity, thermal conductivity. 

Part AM This part lists permitted individual constnic tion materials, apphcable specifications, special requirements, design stress-intensity vafues, and other property information. Of particular importance are the ultrasonic-test and tou ness requirements. Among the properties for which data are included are thermal conduc tivity and diffusivity, coefficient of theiTnal expansion, modulus of elasticity, and yield strength. The design stress-intensity values include a safety factor of 3 on ultimate strength at temperature or 1.5 on yield strength at temperature. 

Requires high energy and long ultrasonic exposure because of low coefficient of friction. 

Bulk viscosity, rj, is evaluated from the ultrasonic absorption coefficient a and shear viscosity ri by "... 

Here p is the solution density, v the sound velocity, ctp the coefficient of thermal expansion, Cp the specific heat, and F the concentration dependence of the equilibrium, r = [LS] -f- [HS] . The measurement of ultrasonic relaxation thus enables the determination of both the relaxation time x and the... 

The viscosity coefficients at dislocation cores can be measured either from direct observations of dislocation motion, or from ultrasonic measurements of internal friction. Some directly measured viscosities for pure metals are given in Table 4.1. Viscosities can also be measured indirectly from internal friction studies. There is consistency between the two types of measurement, and they are all quite small, being 1-10% of the viscosities of liquid metals at their melting points. It may be concluded that hardnesses (flow stresses) of pure... 

Matthews and Riley [99] preconcentrated iodide by co-precipitation with chloride ions. This is achieved by adding 0.23 g silver nitrate per 500 ml of seawater sample. Treatment of the precipitate with aqueous bromine and ultrasonic agitation promote recovery of iodide as iodate which is caused to react with excess iodide under acid conditions, yielding I3. This is determined either spectrophotometrically or by photometric titration with sodium thiosulfate. Photometric titration gave a recovery of 99.0 0.4% and a coefficient of variation of 0.4% compared with 98.5 0.6% and 0.8%, respectively, for the spectrophotometric procedure. 

The sound absorption coefficient, a, is increased when the dynamics of the chemical system are of the same order of magnitude as the frequency of the sound wave,41 and experimentally this quantity is measured as a function of frequency of the ultrasonic sound wave (Fig. 4). When the frequency of the sound wave is of the same order as the frequency for the relaxation process, effects due to relaxation of the equilibrium give rise to characteristic changes in the quantity a//2, where a is the sound absorption coefficient measured at frequency /40 The variation of a with frequency, /, has an inflection point at the relaxation frequency of the system, fr, which is related to 1/t, where r is the relaxation time (1/t = 27i/r).40,41 The expression relating the quantity... 

Tsukahara, Y., Takeuchi, E Hayashi, E., and Tani, Y. (1984). A new method of measuring surface layer-thickness using dips in angular dependence of reflection coefficients. IEEE 1984 Ultrasonics Symposium, pp. 992-6. IEEE, New York. [214] Tsukahara, Y Nakaso, N., Kushibiki, J., and Chubachi, N. (1989a). An acoustic micrometer and its application to layer thickness measurements. IEEE Trans. UFFC 36, 326-31. [213-215]... 

The spiked filters were placed in a 50-mL beaker with the spiked side up and 1 mL of water was added. The beaker was shaken so that all of the filter area had been washed by the water. One mL of the reduction-buffer solution without the sodium hydrosulfite was added to the filter and water. The beaker was shaken a second time. The filter was then turned over (spiked side down) and the beaker placed in an ultrasonic bath for 15 minutes. At the end of this period, the solution in the beaker was colored. A 1-mL aliquot of this solution was transferred to a 4-mL vial. One mL of a freshly prepared solution of 100-mg sodium hydrosulfite in 10-mL phosphate reduction buffer was then added to the vial. The vial was then capped and shaken several times during the course of an hour. During this time, the original color of the solution disappeared or changed to a different color, depending on the dye present. This solution was then injected into the liquid chromatograph. A 10-yL aliquot was used, giving a measurement limit of 0.38 ng benzidine/yL. The analytical reproducibility at this limit was 10% coefficient of variation (CV). 

It seems to me that we can scarcely progress in our understanding of the structural and kinetic effects of the H-bond without knowing the AG and AH terms involved, so I intend to discuss some methods of determining them. The references will provide simple examples of the methods mentioned. The most significant AG and AH values are those evaluated from equilibrium measurements in the gas phase—either by classical vapour density measurements, the second virial coefficient [1], or from, spectroscopic, specific heat or thermal conductance [2], or ultrasonic absorptions [3]. All these methods essentially measure departures from the ideal gas laws. The second virial coefficient provides a measure of the equilibrium constant for the formation of collision dimers in the vapour as was emphasized by Dr. Rowlinson in the discussion, this factor is particularly significant as only the monomer-dimer interaction contributes to it. 

Holland, R. Representation of dielectric, elastic, and piezoelectric losses by complex coefficients. IEEE Trans. Sonics and Ultrasonics, SU-14, No. 1, 18 (1967). 

Perturbation of a chemical equilibrium by ultrasound results in absorption of the sound. Ultrasonic methods determine the absorption coefficient, a (neper cm-1), as a function of frequency. In the absence of chemical relaxation the background absorption, B, increases with the square of the frequency f (hertz) that is, a/f2 is constant. For a single relaxation process the absorption increases with decreasing frequency, passing through an inflection point at the frequency at (radians sec-1 = 2nf) which is the inverse of the relaxation time, t (seconds), of the chemical equilibrium [Eq. (6) and Fig. 3]. 

The ultrasonic absorption coefficient of urease has been measured (5S) md found to increase in the presence of urea. 

In practice ultrasound is usually propagated through materials in the form of pulses rather than continuous sinusoidal waves. Pulses contain a spectrum of frequencies, and so if they are used to test materials that have frequency dependent properties the measured velocity and attenuation coefficient will be average values. This problem can be overcome by using Fourier Transform analysis of pulses to determine the frequency dependence of the ultrasonic properties. 

Here A is the amplitude of the wave, and x is the distance traveled. The attenuation coefficient is determined by measuring the dependence of the amplitude of an ultrasonic wave on distance and fitting the measurements to the above equation. The attenuation is often given in units of decibels per meter (dB nr1) where 1 Np = 8.686 dB. 

The impedance is practically important because it determines the proportion of an ultrasonic wave which is reflected from a boundary between materials. When a plane ultrasonic wave is incident on a plane interface between two materials of different acoustic impedance it is partly reflected and partly transmitted (Figure 3). The ratios of the amplitudes of the transmitted (At) and reflected (Ar) waves to that of the incident wave (Aj) are called the transmission (T) and reflection coefficients (R), respectively. 

The greater the difference in acoustic impedance between the two materials the greater the fraction of ultrasound reflected. This has important consequences for the design and interpretation of ultrasonic experiments. For example, to optimize the transmission of ultrasound from one material to another it is necessary to chose two materials with similar acoustic impedance. To optimize the reflection coefficient materials with very different acoustic impedance should be used. The acoustic impedance of a material is often determined by measuring the fraction of ultrasound reflected from its surface. 

Each echo has traveled a distance twice the cell length d further than the previous echo and so the velocity can be calculated by measuring the time delay t between successive echoes c = 2d/t. The cell length is determined accurately by calibration with a material of known ultrasonic velocity, e.g. distilled water 2d = cw.tw (where the subscripts refer to water). The attenuation coefficient is determined by measuring the amplitudes of successive echoes A = A0e-2cxd, and comparing them to the values determined for a calibration material. A number of sources of errors have to be taken into account if accurate measurements are to be made, e.g., diffraction and reflection (see below). 

---