Pulse-echo

In Lakestani (10) modelling work performed within the PISC III project is validated against experiments. Figure 1 shows the pulse echo response from the lower edge of a 10 mm vertical strip-like crack at centre depth 55 mm. The probe has the size 20 mm by 22 ram, is of SV type with angle 45 and has centre frequency 2.2 MHz and an assumed bandwidth of 2 MHz. The calibration is perfomed by a side-drilled hole of diameter 9.5 mm and centre depth 60 mm (the... 

In service inspections of French nuclear Pressure Water Reactor (PWR) vessels are carried out automatically in complete immersion from the inside by means of ultrasonic focused probes working in the pulse echo mode. Concern has been expressed about the capabilities of performing non destructive evaluation of the Outer Surface Defects (OSD), i.e. defects located in the vicinity of the outer surface of the inspected components. OSD are insonified by both a "direct" field that passes through the inner surface (water/steel) of the component containing the defect and a "secondary" field reflected from the outer surface. Consequently, the Bscan images, containing the signatures of such defects, are complicated and their interpretation is a difficult task. 

There have been numerous efforts to inspect specimens by ultrasonic reflectivity (or pulse-echo) measurements. In these inspections ultrasonic reflectivity is often used to observe changes in the acoustical impedance, and from this observation to localize defects in the specimen. However, the term defect is related to any discontinuity within the specimen and, consequently, more information is needed than only ultrasonic reflectivity to define the discontinuity as a defect. This information may be provided by three-dimensional ultrasonic reflection tomography and a priori knowledge about the specimen (e.g., the specimen fabrication process, its design, the intended purpose and the material). A more comprehensive review of defect characterization and related nondestructive evaluation (NDE) methods is provided elsewhere [1]. 

This paper deals with the control of weld depth penetration for cylinders in gold-nickel alloy and tantalum. After introducing the experimental set-up and the samples description, the study and the optimization of the testing are presented for single-sided measurements either in a pulse-echo configuration or when the pump and the probe laser beams are shifted (influence of a thermal phenomenon), and for different kind of laser impact (a line or a circular spot). First, the ultrasonic system is used to detect and to size a flat bottom hole in an aluminium plate. Indeed, when the width of the hole is reduced, its shape is nearly similar to the one of a slot. Then, the optimization is accomplished for... 

Fig. 4 Testing configurations of the pump-probe system (a) pulse-echo configuration, (b) split...

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. 

Fig. 8 B-scan views of the artificial slot of height 1.7 mm (left image) and of the lack of weld penetration 1.7 mm (right image) in a pulse-echo configuration for gold-nickel alloy.

Fig. 6. Test with one segment of 6 sector transducer in pulse-echo mode on aluminium plate, (a) no defect (b) defect simulated with mercury droplet (c) defect position.

Accurate modelling of the field radiated by ultrasonic transducers is an essential step forward considering the final goal of the complete simulation of pulse echo experiments. 

Ultrasonic Testing of Concrete with Fast Imaging Pulse-Echo-Technique. 

Due to the outer circumference of the silo, about 25 meters, a non- or rarely destructive testing method was needed for the localization. Because the building was still in use, it was only accessable from the exterior side. We chose the ultrasonic pulse-echo-technique as an appropriate way of doing the testing. 

Krause, M. et altera Comparison of Pulse-Echo-Methods for Testing Concrete, In NDT E International 1997, Vol. 30, pp. 195-204... 

Hillger, W. Inspection of Concrete by Ultrasonic-Pulse-Echo-Technique, In Proceedings of the European Conference on Non Destructive Testing, Nice 1994, pp. II59-II63... 

Our solution for this inspection problem is a special ultrasonic system consisting of a special probe and a modified pulse-echo ultrasonic instrument. 

The PS-4 ultrasonic examination system provides many new features, which allows the operator to perform several inspections simultaneously. Both pulse-echo and time-of-flight-diffraction technique can be applied together with storage of digital A-scan data at the same time. 

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. 

Based on the observation above, we maintain that it is of great interest to be able to replace TT measurements by pulse-echo, PE, measurements. The PE technique does not have the above... 

During the attenuation measurements. Transducer 1 was excited with a narrowband tone burst with center frequency 18 MHz, see Figure 1 for a schematic setup. The amplitude of the sound pressure was measured at Tranducer 2 by means of an amplitude peak detector. A reference amplitude, Are/, was measured outside the object as shown at the right hand side of Figure 1. The object was scanned in the j y-plane and for every position, (x, y), the attenuation, a x, y), was calculated as the quotient (in db) between the amplitude at Transducer 2, A[x, y), and Are/, i.e., a(x,y) = lOlogm Pulse echo measurements and preprocessing... 

Ultrasonic techniques are an obvious choice for measuring the wall thickness. In the pulse-echo method times between echoes from the outer and inner surface of the tube can be measured and the wall thickness may be calculated, when the ultrasonic velocity of the material is known. In the prototype a computer should capture the measuring data as well as calculate and pre.sent the results. First some fundamental questions was considered and verified by experiments concerning ultrasonic technique (Table I), equipment, transducers and demands for guidance of the tube. 

The common civil engineering seismic testing techniques work on the principles of ultrasonic through transmission (UPV), transient stress wave propagation and reflection (Impact Echo), Ultrasonic Pulse Echo (UPE) and Spectral Analysis of Surface Waves (SASW). 

As the spins precess in the equatorial plane, they also undergo random relaxation processes that disturb their movement and prevent them from coming together fiilly realigned. The longer the time i between the pulses the more spins lose coherence and consequently the weaker the echo. The decay rate of the two-pulse echo amplitude is described by the phase memory time, which is the time span during which a spin can remember its position in the dephased pattern after the first MW pulse. Tyy is related to the homogeneous linewidth of the individual spin packets and is usually only a few microseconds, even at low temperatures. 

The characteristic time of the tliree-pulse echo decay as a fimction of the waiting time T is much longer than the phase memory time T- (which governs the decay of a two-pulse echo as a function of x), since tlie phase infomiation is stored along the z-axis where it can only decay via spin-lattice relaxation processes or via spin diffusion. 

In electron-spin-echo-detected EPR spectroscopy, spectral infomiation may, in principle, be obtained from a Fourier transfomiation of the second half of the echo shape, since it represents the FID of the refocused magnetizations, however, now recorded with much reduced deadtime problems. For the inhomogeneously broadened EPR lines considered here, however, the FID and therefore also the spin echo, show little structure. For this reason, the amplitude of tire echo is used as the main source of infomiation in ESE experiments. Recording the intensity of the two-pulse or tliree-pulse echo amplitude as a function of the external magnetic field defines electron-spm-echo- (ESE-)... 

In electron spin echo relaxation studies, the two-pulse echo amplitude, as a fiinction of tire pulse separation time T, gives a measure of the phase memory relaxation time from which can be extracted if Jj-effects are taken into consideration. Problems may arise from spectral diflfrision due to incomplete excitation of the EPR spectrum. In this case some of the transverse magnetization may leak into adjacent parts of the spectrum that have not been excited by the MW pulses. Spectral diflfrision effects can be suppressed by using the Carr-Purcell-Meiboom-Gill pulse sequence, which is also well known in NMR. The experiment involves using a sequence of n-pulses separated by 2r and can be denoted as [7i/2-(x-7i-T-echo) J. A series of echoes separated by lx is generated and the decay in their amplitudes is characterized by Ty. ... 

The stimulated (tln-ee-pulse) echo decay may also be modulated, but only by the nuclear frequencies (0,2 and... 

Passino S A, Nagasawa Y, Joo T and Fleming G R 1997 Three-pulse echo peak shift studies of polar solvation dynamics J. Phys. Chem. A 101 725-31... 

Ultrasonics. The most widely used nondestmctive test method for explosion-welded composites is ultrasonic inspection. Pulse-echo procedures (ASTM A435) are appHcable for inspection of explosion-welded composites used in pressure appHcations. 

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