Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-01-13
2001-02-13
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S598000, C342S179000, C367S013000, C324S344000
Reexamination Certificate
active
06186006
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for nondestructive, three-dimensional detection of structural elements in structures, especially those made of concrete or similar materials.
A method of this kind is known from DE-A-43 20 473 according to which the echo signals from the far field of a single ultrasonic test head can be detected. The amplitudes and travel times of the echo signals can be stored together with the position of the ultrasonic test head in a memory unit as travel time-location curves with the corresponding amplitude values. From the totality of the travel time-location curves, by means of a filter device that has an image-producing device located upstream of it, selectable portions of the stored location curves can be filtered out.
In ultrasonic test methods, sound waves are regularly emitted in the lower frequency range and the multiple reflections of sound waves between a transmitting and/or receiving point and the object to be measured are utilized as the measured parameter. This produces significant peaks in frequency graphs from which the distance to the object can be calculated, if the speed of the waves is known. In the publication “Schickert, G. (editor): Papers and Reports of the International Symposium on Nondestructive Testing in Construction, Report Volume 21, Berlin: DGZfP 1991, pp. 488-504; Wüstenberg H., Possibilities and Concepts for Ultrasonic Test Heads, Especially for Construction,” regarding the use of ultrasonic echo methods on structures made of concrete, the use of an artificial aperture was proposed. The goal is to eliminate the problems that result from the use of large-area ultrasonic heads by moving small comparatively simply constructed test heads and processing the signals accordingly. For this purpose, an illuminating test head was coupled to the underside of a concrete block and a shadow caused by refraction was produced by means of a bore. As a result of numerical storage of the sound signals recorded with amplitude and phase and of reconstruction using the algorithms of holography, the approximate size of the disturbing object could be determined. However, it is disadvantageous that significant phase errors can be produced due to the non-constant coupling, so that evaluation based on phase-sensitive scanning is unreliable.
In addition, electromagnetic radar methods are employed based on the idea that layers with different dielectric properties are present in the material to be tested. A method of this kind is known from the publication “Symposium on Nondestructive Testing in Construction, Feb. 27, 1991 to Mar. 1, 1991 in Berlin, Report Volume 21, Part 2, pp. 537-544; Author: Dipl.-Ing. C. Florher, Hochtief, Frankfurt/Main; Dipl.-Ing. B. Bernhardt, Berlin, The Locations of Stress Reinforcements Beneath Multilayer Reinforced Concrete Reinforcements.” Using an antenna, pulses were transmitted and received primarily in the frequency range between 900 MHz and 2 GHz. The depth information was obtained from the travel-time measurement of the reflected signals, with the propagation rate being calculated from the speed of light in a vacuum divided by the root of the average dielectric constant of the material being investigated. Typical values for the dielectric constant for example are 7 for concrete, 4 for brick, 81 for water, and infinity for iron. Since the value of the dielectric constant is also dependent on moisture, evaluation requires an expert and experienced specialist. In the radar method an antenna is moved continuously, and accordingly a manipulator is used in the ultrasonic test method that is based on the principle of the synthetic aperture. On the basis of these common features, a depth-dependent representation of the object under investigation is made possible by arranging the recorded amplitudes in series. From the different travel times of the signals as well as the dielectric constants of the materials, the depth position of the imaged object is estimated, but the accuracy of the location depends largely on the moisture content of the material or on cavities filled with water, among other factors.
In addition, from the publication “Acoustical Imaging, Vol. 19, edited by Helmut Ermert and Hans-Peter Harjes, Plenum Press, New York and London; Authors: Schmitz, V.; Müller W.; Schafer G.; Synthetic Aperture Focusing Technique—State of the Art” an imaging method is known called “synthetic aperture focusing technique, or SAFT. This imaging method makes it possible to calculate the respective spatial image of an area under investigation.
Finally, a method for measuring the thickness of dielectric objects is known from SU-A-1 364 868. According to this method, electromagnetic waves and sound waves are directed alternatively at the object and the thickness of the object is calculated as a function of the reflected energy.
SUMMARY OF THE INVENTION
Taking its departure from this technology, the goal of the invention is to improve the method of the species recited at the outset in such fashion that the accuracy of the location of structures is improved. The results will largely be independent of ambient variables and boundary conditions. Furthermore, the method can be implemented at an cost that is as low as possible.
The method according to the invention for nondestructive three-dimensional detection of structural elements is used primarily for testing structures and monitoring structures. It permits optimum determination of the thickness of walls and foundations or of cavities in prestressing cuts. Furthermore, the exact position of prestressing elements, prestressing cuts, and other structural elements can be determined. In addition, with the method according to the invention, the location and classification of material inhomogeneities can advantageously be performed. especially the fine cracks caused by corrosion of reinforcing rods.
Using the method according to the invention, the area to be investigated is scanned areawise both by radar and sound, with the high-frequency travel-time dependent data being recorded at each point. By means of an ultrasonic imaging method, especially the synthetic aperture focusing technique, hereinafter called SAFT, which is a three-dimensional method, an image of a common volume range is generated. Optionally, any layer thicknesses and optionally these same layers in any direction can be displayed. These layers can be shown both parallel to the measured surface and also perpendicular to the measured surface. Advantageously, local calibration of the respective volume ranges is performed with the aid of “fingerprints.” Moreover, in volume reconstruction using the special integration method described, the signal
oise ratio is improved. The data are linked with one another in any sectional planes desired, and a quantitative analysis of the volume range is performed on the basis of the precisely located link. In this way, unknown materials can be identified from a knowledge of dielectric constants and moisture distribution.
REFERENCES:
patent: 5495576 (1996-02-01), Ritchey
patent: 5805098 (1998-09-01), McCorkle
patent: 61791 (1984-04-01), None
patent: 201382 (1987-09-01), None
patent: 242186 (1992-08-01), None
Krause Martin
Maierhofer Christiane
Schmitz Volker
Wiggen-Hauser Herbert
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Fayyaz Nashmiya
Fraunhofer-Gesellschaft zur Foerderung der Angewandten Forschung
Williams Hezron
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