Pulse echo method

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

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. 

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. 

Chemical relaxation methods are widely used to study the kinetics of fast chemical reactions in solution. In particular, ultrasonic absorption techniques have been used to investigate fast exchange processes with relaxation times in the range 0.3 xs to 0.3 ns. The longer end of this time range has become accessible in recent years through the use of cylindrical resonator methods [1] which have lowered the frequency range covered by fictional pulse echo methods. 

The microstructures of the consolidated and deformed samples were characterized by X-ray diffraction, optical and electron microscopy (SEM and TEM). The samples for mechanical testing have been prepared by spark erosion. The linear thermal expansion was determined by using a thermomechanical system (TMA). The temperature-dependent elastic moduli have been measured by the resonance frequency and the pulse-echo method. The bulk moduli were determined by synchrotron radiation diffraction using a high-pressure diamond-die cell at HASYLAB. The compression and creep tests were performed with computer-controlled tensile testing and creep machines. 

Acoustic attenuation in an aerogel until now was solely determined by acoustooptical techniques. The pulse-echo method proved not to be suitable for this purpose because of millimeter-sized inhomogeneities generally present in the material. 

Fig. 2. Electronics block diagram for pulse-echo-method sound-velocity measurements. Frequency divider is used to provide phase-coherent pulses for a pulse-superposition method for sound-velocity-change measurements, due to changing temperature in the present case.

Anisotropy (elastic-constant variations with direction) can be determined on a single specimen with the pulse-echo method. 

Elastic constants (E and v) were determined by ultrasonic pulse-echo method using a 200 MHz ultrasonic pulser-receiver (Panametrics 5900 PR, USA) and bulk density was determined by Archimedes method. Crystalline phases were identified by X-ray diffraction (XRD) analysis and the microstructural and iiactogn hic analyses were perfomied using a scanning electron microscope (SEM) (JMS 6300, Jeol, Japan) coupled with an energy dispersive spectroscope (EDS) (Noram, USA). 

The elastic modulus, measured using the pulse echo method, was about 180 GPa, and the fracture strength determined by the three-point flexure test was about 800 MPa in the grain-alignment direction. This strength, which is relatively high for the large porosity of 25%, is almost equivalent to that of commercially available... 

The ultrasonic scanning microscope operates according to the pulse-echo method to produce an image of the surface and immediate subsurface volume of a flat ground or polished specimen. 

Conventional ultrasonic methods include the pulse-echo, the pulse-transmission and the pulse-resonance techniques [104]. Depending on the incidence of the piezo transducer with respect to the structural surface as well as on their design, P-waves, S-waves or a combination of both can be generated within the structure. P-waves are best suited for the inspection of thick components, for through-the-thickness damage detection, and are quite effective for the detection of anomalies along the sound path. By the pulse-echo method, detects are detected in form of additional echoes. In the pulse-transmission method wave dispersion and attenuation due to diffused damage in the material indicate possible defects [103]. 

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