Ultrasonic longitudinal wave

T. Leon-Salamanca and D. E. Bray, "Ultrasonic Measurement Of Residual Stress In Steels Using Critically Refracted Longitudinal Waves (L j )," R j". NDE 6(4) 1995 (in press). 

UFM detection is obtained by measuring the cantilever deflection as the ultrasound amplitude is modulated (Fig. 13.3). The ultrasonic excitation from a longitudinal wave transducer fixed to the bottom of the sample causes normal vibration of its surface. As the ultrasonic amplitude is increased, contact is eventually broken at the pull-off point (aI = hi), giving a discontinuity in the time-averaged displacement. We refer to this ultrasonic amplitude as the threshold amplitude, and the corresponding inflection in the displacement... 

There are two distinct types of ultrasonic waves the most commonly used in fats characterization are longitudinal waves (Fig. lA) where deformations occur in the direction of propagation of the wave. It is also possible to generate shear waves with deformations normal to the direction of propagation (Fig. IB). Shear waves do not travel macroscopic distances in fluids so it is often impossible to make good measurements in foods. Throughout this work I will exclusively focus on longitudinal waves. 

Fig. 2 Temperature dependences of ultrasonic attenuation for longitudinal waves propagating in ZnSe V along the [110] axis, measured at 270 MHz open circles), 156 MHz (filledcircles), and 52 MHz triangles). A a = a (T) - a (To), To = 16 K. The plot for 52 MHz is shifted downward by 0.7 dB for clarity. Concentration of the dopand = 5.6 X lO cm After Fig. 3 in [3]...

The ultrasonic longitudinal and shear wave speeds were measured at room temperature for two fully oxidized samples of Ba2YCu307, as described above. From these values and the measured mass density, a longitudinal modulus,, and a shear modulus, Cs, can be calculated from Equation 3. The ordinary isotropic elastic moduli are related to these two moduli by ... 

ANL s ultrasonic viscometer is a nonintrusive in-line device that measures both fluid density and viscosity. The design of the viscometer is based on a technique that measures acoustic and shear impedance. The technique was first applied by Moore and McSkimin (1970) to measure dynamic shear properties of solvents and polystyrene solutions. The reflections of incident ultrasonic shear (1-10 MHz) and longitudinal waves (1 MHz), launched toward the surfaces of two transducer wedges that are in contact with the fluid, are measured. The reflection coefficients, along with the speed of sound in the fluid, are used to calculate fluid density and viscosity. Oblique incidence was commonly used because of better sensitivity, but mode-converted waves often occur in wedges that do not exhibit perfect crystal structure and lack well-polished surfaces. For practical applications, we use the normal-incidence arrangement. 

Ultrasonic Nebulizers. Ultrasound can be used to break up a liquid mass into smaller particles. In the ultrasonic nebulizer, an ultrasonic generator drives a piezoelectric crystal at a frequency between 200 kHz and 10 MHz. The surface of the liquid sample will breakdown into an aerosol when the longitudinal wave propagates from the surface of the crystal toward the liquid-air interface. The wavelength of the surface wave is given by the following equation ... 

A beam of ultrasonic waves generated by a transducer is directed on to the surface of the polymer which is immersed in a suitable liquid, for example water or silicone oil. Two refracted beams are produced, the higher velocity beam corresponding to a compressional or longitudinal wave, the other to a transverse or shear wave. There is also a reflected... 

Figure 14.1 Schematic diagram of the experimental setup for ultrasonic measurements by the immersion method. P, pulser Tl, transmitting transducer T2, receiving transducer S, sample a, incident ultrasonic beam b, refracted beam of longitudinal wave c, refracted beam of transverse wave d, transmitted beams. Sample and transducers immersed in silicone oil within the tank (LT). AT, attenuator AM, wide band amplifier CRO, oscilloscope CTR, time interval counter Si, triggering signal for CRO and start signal for the counter S2, signal viewed on CRO and stop signal for the counter. (Adapted from [4] by permission of Elsevier Science Ltd.)...

Figure 14.2 Schematic diagram showing incident and transmitted ultrasonic waves. For clarity, only the longitudinal wave in the sample is shown.

Sound consists of longitudinal pressure waves, i.e., the particles of the medium are displaced parallel to the propagation axis (in transverse waves such as ripples on a water surface, the oscillating displacement of the liquid particles is perpendicular to the propagation axis). In a liquid, an ultrasonic wave induces the local displacement (e) of the particles, i.e., the oscillation around an equilibrium position. We will now consider a longitudinal wave obeying the central relationship (Eq. 3) which applies to the propagation of a one-dimensional linear wave ... 

Ultrasonic Attonuation. The frequency range of this technique is of the order of 1 MHz. The attenuation a of the longitudinal waves is related to the longitudinal loss modulus M" by M" = 2apu lco, and the longitudinal storage modulus M by M = pu, where p is the density and u is the ultrasonic velocity. For an example of the use of this techniques, see References 151 and 152. 

The contact resonance frequencies are excited by an ultrasonic transducer, which emits longitudinal waves or shear waves into the sample. Figure 2 displays the normalized contact resonance spectra of the first (Fig. 2a) and second (Fig. 2b) flexural mode measured on fused quartz, silicon, and sapphire. The spring constant... 

---