Wave propagation measurements pulses

Shear Wave Propagation. A pulse shearometer (Rank Bros.) was used to measure the propagation velocity of a shear wave through the weak gels formed by the solutions of HMHEC in dilute NaCl. The polymer concentration range studied was 0.5-2.0%. With this apparatus, the frequency of the shear wave is approximately 1200 rad s" and the strain is <10 . At this strain, n pst systems behave in a linear viscoelastic fashion, and the wave-rigidity modulus, G is... 

FIG.8-2. Apparatus for longitudinal bulk wave propagation measurements, by echoing longitudinal pulses through a liquid with and without a polymeric sample in the path. (Nolle and Mowry.p ... 

For a strong primary shock wave, the reflected rarefaction wave propagates into water that has already been set in motion. Consequently, the rarefaction wave arrives earlier than predicted from the acoustic approximation, which ignores the particle velocity. Thus the pressure cutoff is not instantaneous. This effect typically gives a pulse shape shown by the solid line for Point A of Fig 33. The shallower the point at which pressure measurements are made, the sooner the primary shock pulse is truncated and the shorter its duration (see Fig 33, Point B). At shallow enough locations, the rarefaction wave interacts with the shock front and reduces the peak pressure (see Fig 33, Points C and D). The region in which the peak pressure is reduced is known as the anomalous region ... 

The sonic speed used was longitudinal wave speed, measured using a pulse propagation meter (Model 4, H. M. Morgan Co., Cambridge, Mass.). Pulse frequency was 8-10 kHz. Transverse wave velocity was calculated from longitudinal wave velocity using the approximation... 

The effective P may be determined with the electron beam apparatus. When the sample (slab geometry) is thick enough to absorb all of the incident electrons, a compressive stress wave propagates from the irradiated region into the sample bulk. A transducer, located just beyond the deposition depth, may be used to record the stress pulse. Alternatively, the displacement or velocity of the rear surface of sample may be observed optically and used to infer the initial pressure distribution from the experimentally measured stress history. Knowledge of the energy-deposition profile then permits the determination of the Gruneisen coefficient. 

Inevitably, the conjunction of frequency-dependent visco-elastic properties and wave propagation leads to consideration of visco-elastic wave dispersion and its influence on conventional wave-based measurements, such as those involving resonance phenomena and pulse propagation techniques. 

O.G. Martinsen and S. Grimnes, Bioimpedance and Bioelectricity Basics. Academic Press, 2011. K.S. Matthys, J. Alastruey, J. Peiro, et al, Pulse wave propagation in a model human arterial network Assessment of 1-D numerical simulations against in vitro measurements, Journal of biomechanics, vol. 40, no. 15, pp. 3476-3486, 2007. 

The experimental set-up we used is shown in Fig. 2, A synchronously pumped mode-locked and cavity-dvunped dye laser, which can be timed to the D or Dj line of Cs, generates pulses of about 20 ps duration at a pulse rate of U MHz and peak powers of several hundred watt. They are split into linearly polarized pump pulses and stronger circularly polarized probe pulses, which pass an optical delay line. Both beams are focussed into a common interaction region where they act on the Cs vapor, which is contained in a cell at room temperature. The radiated wave propagating in pump pulse direction is detected by a photomultiplier, which measures the transmitted average intensity behind a crossed polarizer as a function of the delay time. 

The dynamic elastic modulus is determined by measuring the wave propagation velocity of ultrasonic pulses in the material. It is a nondestructive method, based on the dependence between the elastic modulus and the velocity of the propagation of the sonic or ultrasonic waves (mechanical vibrations). The method is very precise. The apparatus is not complicated, and it is possible to measure the dynamic elastic modulus at high temperatures. It is measured according to the standards ASTM C 1198-01 [53] and ISO 3312 1987 [54], and the elastic modulus of carbon materials is measured according to ASTM standard C747 [55]. 

Acoustic Measurements. Measurement of the propagation of ultrasonic acoustic waves has been found useful for determining the viscoelastic properties of thin films of adhesives. In this method, the specimen is clamped between transmitting and receiving transducers. The change in pulse shape between successive reverberation of the pulse is dependent on the viscoelastic properties of the transmitting material. Modulus values can be calculated (267,268). 

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