Ultrasonic interferometer

Pandey et al. have used ultrasonic velocity measurement to study compatibility of EPDM and acrylonitrile-butadiene rubber (NBR) blends at various blend ratios and in the presence of compa-tibilizers, namely chloro-sulfonated polyethylene (CSM) and chlorinated polyethylene (CM) [22]. They used an ultrasonic interferometer to measure sound velocity in solutions of the mbbers and then-blends. A plot of ultrasonic velocity versus composition of the blends is given in Eigure 11.1. Whereas the solution of the neat blends exhibits a wavy curve (with rise and fall), the curves for blends with compatibihzers (CSM and CM) are hnear. They resemble the curves for free energy change versus composition, where sinusoidal curves in the middle represent immiscibility and upper and lower curves stand for miscibihty. Similar curves are obtained for solutions containing 2 and 5 wt% of the blends. These results were confirmed by measurements with atomic force microscopy (AEM) and dynamic mechanical analysis as shown in Eigures 11.2 and 11.3. Substantial earher work on binary and ternary blends, particularly using EPDM and nitrile mbber, has been reported. 

Figure 6. Ultrasonic interferometer. C.w. ultrasound is generated by the transducer, and the amplitude of the received signal is measured as the distance between the reflector plate and transducer is varied.

Saito 7) measured the sound velocity in well-characterized CA solutions with a Pierce type ultrasonic interferometer with high accuracy and determined s. Figure 26 shows the relation between s,, of CA whole polymer solutions and e of the solvent at 25 °C 7). While the dependence of Sq on e differs depending on < F>, s, , except for C A(2.46)-acetone increases with increasing polarity of the solvent in a similar manner as the chemical shifts of the O-acetyl and hydroxyl groups. In Fig. 27, the effects of on Sq for CA-DMAc and CA-dimethylsulfoxide (DMSO) solutions at 25 °C are shown. In both systems, Sq has a maximum at F 2.5 7). 

A review of the common methods of measuring acoustic absorption and dispersion is presented by Cottrell and McCoubrey [9], The ultrasonic interferometer, the absorption tube, the condenser transducer, and the reverberation chamber are the standard types of apparatus. 

Vibrationai and Rotational Excitation in Gaseous Coiiisions 2. The Ultrasonic Interferometer... 

Among the first polyatomic molecules in which rotational relaxation was investigated is methane. Kelly [278], employing an ultrasonic interferometer, concluded that for this gas as 314°K, Zr = Mtt 15 collisions. More recent ultrasonic data obtained by Hill and Winter [279] provide apparent rotational relaxation times for CH4 and C2H4 as a function of temperature. Their results are given in Table 3.5. The increase in Zr with increasing temperature... 

Measurement of the velocity of sound in helium has been described by Gammon and Douslin. They studied the gas in the ranges — 175 to 150 °C and 10 to 150 bar using an ultrasonic interferometer operating at 2.5 MHz. 

Continuous wave methods are the most accurate means of making ultrasonic measurements. Even so, they are used less frequently than pulse methods because measurements are more time consuming and laborious to carry out, are more difficult to automate, and the measurement cell requires a high degree of precision engineering. These techniques therefore tend to be used in specialized research laboratories where accurate measurements are important. Continuous wave ultrasound is utilized in a variety of different techniques, but the most commonly used is the interferometer [10,11]. 

A simple interferometer is illustrated in figure 6. The same basic components can be used for a c.w. experiment as for a pulsed experiment, i.e., a signal generator, a transducer, a measurement cell and an oscilloscope. Nevertheless, there function and arrangement are slightly different. The sample is contained in the measurement cell, between an ultrasonic transducer and a reflector plate which moves vertically through the sample. 

Measurements of sound velocity at ultrasonic frequencies are usually made by an acoustic interferometer. An example of this apparatus11 is shown in Fig. 2. An optically flat piezo-quartz crystal is set into oscillation by an appropriate electrical circuit, which is coupled to an accurate means of measuring electrical power consumption. A reflector, consisting of a bronze piston with an optically flat head parallel to the oscillating face of the quartz, is moved slowly towards or away from the quartz by a micrometer screw. The electrical power consumption shows successive fluctuations as the distance between quartz and reflector varies between positions of resonance and non-resonance of the gas column. Measurement of the distance between resonance positions gives a value for A/2, and if /... 

Figure 3.11 An acoustic interferometer of the type used in the author s laboratory (from Nethery [104]). A X-cut quartz crystal, 100-600 KHz B crystal support mount and aligning screws. Optical flat E is attached to a movable reflector D for generation of ultrasonic standing waves. Invar rod F position is read from precision micrometer slide L.

Ultrasonic-laser instruments can use short-pulse lasers (a few nanoseconds long) to generate ultrasound and long-pulse (tens of microseconds long) or continuous lasers, coupled to an optical interferometer for the detection of US (I.e. the corresponding mechanical displacements) [22]. 

The detectors oommonly used in laser ultrasonics include various types of interferometers, which are sensitive to the displacement or velocity of the surface, and of knife-edge e.g. photoelectromotive force reoeivers) detectors, which are sensitive to the tilt of the sample surface [27]. 

Due to their high sensitivity to strain, temperature variation, vibration, and acoustic waves, embedded extrinsic Fabry-Perot interferometric optical fiber sensors have been developed to detect delamination, based on changes in the acoustic properties of the materials before and after delamination [41]. Impact events and corrosion cracking generate ultrasonic waves, which can be characterized using elliptical core fiber sensors [40]. The in-line Fabry-Perot interferometer seems well suited for the local detection of shear waves and the characterization of impact-induced damage. 

Fig. 1.35 Poisson s ratio measured by the (filled circle) LUFP (laser ultrasonics coupled with a Fabry-Perot interferometer) method and (plus sign) laser ultrasonic pulse technique using SiC as a standard [9]. With kind permission of Wiley and Sons...

The frequency dependence of 33 over a frequency range of more flian eight decades can be obtained by utilizing two methods, namely, a step-response and an interferometric technique (Zhang et al. 2004). The step-response measurement is based on the quasistatic method utilizing the direct piezoelectric effect and employs, for data evaluation, a Fourier analysis of the temporal electrical response to fire appUcation of a pressure step. This method yields useful data in the frequency range from 10 Hz to several Hz. For frequencies from 1 Hz to 300 kHz, an interferometer can be utilized. In addition, acoustic method can also be used to obtain the frequency dependence of 33 in audio and ultrasonic ranges. 

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