NDTnet 1998 Aug, Vol.3 No.8

Abstract

In the last years interest to application of microwave methods for the testing of internal structure of concrete building designs has much increased [1]. In a greater part of such investigations impulse radars are used. It is known, that such radars have a resolution in a concrete about few cm, that complicates the testing by the given method the concrete walls of small thickness. In the given work an opportunity of application a step-frequency microwaves for the testing the concrete walls structure, in particular for the determination the geometrical thickness of a wall and depth of inhomogeneties, is considered.

In [2] we presented the method of separate determination of inhomogeneities depth and dielectric properties of testing object by numerical processing the dependences of frequencies at maximums of received signals from displacement along the border of the object under testing. However, when the testing object is a wall, the reflection from the second border always present, that complicates the detection inhomogeneties in the wall and determination its depth. In a given work is described the updating of the method [2], allowing to determine the depth of inhomogeneties and thickness of a wall. For this purpose during scanning the antenna along a surface of the wall the average dependence of amplitude with frequency is determined. Obviously, that this dependence is connected with thickness of the given site of a wall. Then this average dependence is subtracted from frequency dependencies of received signal in every spatial point and transformed by such way spatial - frequent distribution is used by method, described in [2]. As a result we can calculate geometrical depth of inhomogeneties (for example, fixture). Then from comparison the oscillation periods of average frequency dependence and a sample of transformed distribution in a point above inhomogeneties the geometrical wall thickness on a site of scanning can calculated.

The effectivnes of proposed method was tested on experimental data, received with the help of portable continious wave radar. The operating frequency was controlled by computer and can changes in a range 2-4 GHz. Measurements were made on concrete blocks 500x350x150 mm size with the metal fixture and air cylindrical cavities insight it. The spatial interval of samples was 5 mm. The present results show the efficiency of a proposed method for testing a concrete walls in a case of one side measurements.

1. J.H.Bungey. The future for NDT in civil engineering Proc. Int. Conf. " Non-Destructive Testing in Civil Engineering. ", Liverpool, 8-11 April 1997: 69-76.

2. Deshchenko G.N., Kovalchuk A.A. The computing method of high-resolution determination the inhomogeneities depth in dielectric objects. Proc. Int. Conf. " Computer methods and inverse problems in NDT and diagnostics ", Minsk, 21-24 November 1995: 201-204.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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