Ultrasound Pulse-echo

FIGURE 60.4. Ultrasound pulse-echo pattern obtained at 10 MHz in a polystyrene disk 3 mm thick. The interval between successive reflections indicates the velocity of the longitudinal wave, and the ratio of intensity of any two successive reflections the attenuation. The horizontal scale is 2.00 xs/division. in this material the (longitudinal) speed of sound is 2.14 km/s, the acoustic impedance is 2.25 MRayls (units of 10 kg/(cm -s) and the attenuation coefficient is ca. 12 db/cm. See text below for the calculation [57]. 

Then, the weld depths penetration are controlled in a pulse-echo configuration because the weld bead (of width 2 mm) disturbs the detection when the pump and the probe beams are shifted of 2.2 mm. The results are presented in figure 8 (identical experimental parameters as in figure 7). The slow propagation velocities for gold-nickel alloy involve that the thermal component does not overlap the ultrasonic components, in particular for the echo due to the interaction with a lack of weld penetration. The acoustic response (V shape) is still well observed both for the slot of height 1.7 mm and for a weld depth penetration of 0.8 mm (lack of weld penetration of 1.7 mm), even with the weld bead. This is hopeful with regard to the difficulties encountered by conventional ultrasound in the case of the weld depths penetration. 

In this paper we propose a multivariable regression approach for estimating ultrasound attenuation in composite materials by means of pulse-echo measurements, thus overcoming the problems with limited access that is the main drawback of through-transmission testing. 

The result from the work shows that we can obtain good approximations of the attenuation values using pulse echo ultrasound. This indicates that it will be possible to replace the through-transmission technique by a pulse echo technique. 

For example, an echo detected 13 ]ls after the ultrasound pulse represents a boundary 10 cm away from the source. 

The resolution in an ultrasound image is, among other things, related to the duration of the ultrasound pulse, ie, the shorter the pulse the better the resolution. Imaging may not be performed when the pulse duration is longer than the time to receive an echo. The shorter the ultrasound pulse the more difficult it is to discern it from noise, and the poorer the SNR of the image. As the pulse duration is decreased, the power of the ultrasound pulse is typically increased to compensate for the poorer SNR. 

Medical Ultrasound Many of us have first seen our unborn children or grandchildren thanks to medical ultrasound technology. This application is somewhat related to sonar in that both use pulse echo methods to send and receive signals. However, in this short-range application, transducer arraj can be designed to form images. 

Essentially all imaging from medical ultrasound to non-destructive testing relies upon the same pulse-echo type of approach but with considerably refined electronic hardware. The refinements enable the equipment not only to detect reflections of the sound wave from the hard, metallic surface of a submarine in water but also much more subtle changes in the media through which sound passes (e. g. those between different tissue structures in the body). It is high frequency ultrasound (in the range 2 to 10 MHz) which is used primarily in this type of application because by using these... 

Sonar and imaging technologies are based on sending out ultrasound pulses and receiving the echoes. The resolution capabilities depend upon the emitted pulses being sharp, and the sharper the pulse the more Fourier components it has. Therefore, for a transducer to emit and detect a sharp pulse it must be able to respond to a wide frequency range - that is it must have the broad band characteristic associated with low mechanical Q. The very lossy nature of the polymer phase endows the composite with this (Q < 10). 

Essentially, all imaging from medical ultrasound to non-destructive testing relies on the same pulse-echo type of approach, but with considerably refined electronic hardware. 

Ultrasound through-transmission ultrasound ( ITU) or pulse echo (PE) ultrasound is the primary method for the acceptance of composite laminate materials using an automated scanning system with water-coupled piezoelectric transducers and acceptance standards. Many variations are applicable depending on the material, configuration, thickness, and sensitivity requirements. 

Piezoelectric transducers are key components in medical ultrasound imaging and are used both as the acoustic source and the detector (pulse-echo teclmique). The uses for ultrasound are numerous and include examination of the fetus in the mother s womb as shown in Figure 31.22 and high-resolution imaging of intravascular structures. PZT is the ceramic of choice for this application mainly because it has a high k and is inexpensive compared to some of the other options such as polymer piezoelectrics. 

X = wave length of ultrasound, A = crystal size) perpendicular to the beam axis and a quarter of the pulse length along the beam axis. Taking typical values of A 10mm for conventional probes, A = 6mm for a SAFT probe, R = 100 mm and X 1 mm the lateral resolutions of the conventional pulse echo technique and SAFT are 10 mm and 1.5 mm respectively. Thus SAFT substantially Improves the lateral resolution of ultrasonics. SAFT therefore finds applications In... 

After fabrication, ail the panels were interrogated by pulse echo ultrasound (10 MHz) and film X-ray. There was no indication of any delamination and no gross porosity regions were noted in the panels. In addition, each panel had two tensile bars extract for witness testing at room temperature. All samples tested failed above a 0.3% strain to failure requirement. Hence, all panels were accepted into the testing effort. Samples were cut out of the accepted plates and holes where drilled in diameters of 2.286 and 4.572 mm at the center of the lecimens forming 20% of the width of the specimen. 

Image formation in medical ultrasound is accomplished by a pulse-echo mechanism in which a thin ultrasound beam is transmitted and the echoes generated by the interaction of that beam with scat-... 

Hunt, J. W., Arditi, M., and Foster, F. S. (1983), Ultrasound transducers for pulse-echo medical imaging, IEEE Trans. Biomed. Eng., 30 453-481. 

Both methods use the pulse-echo technique. A pulse is sent into the sample, where it is reflected by the front and back surfaces of the material and returned at reduced amplitude to the transducer, while the waveforms are monitored on a recording oscilloscope. From the timing and amplimde of the reflected waves the sound speed and attenuation of the material may be determined. Successive reflections provide additional information on both these properties. A typical ultrasound pattern obtained using the direct-coupled transducer method is shown in Fig. 60.4. 

After fabrication, all the panels were interrogated by pulse echo ultrasound (10 MHz) and film X-ray. There was no indication of any deiamination and no gross porosity was noted in the panels. In addition, each panel had 2 tensile bars extracted for witness testing at room... 

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