Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Reexamination Certificate
1999-10-07
2001-06-12
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
C342S196000
Reexamination Certificate
active
06246354
ABSTRACT:
BACKGROUND OF THE INVENTOR
1. Field of the Invention
The present invention relates to a method of determining a relative permittivity of concrete, in particular in dependence on its moisture content and according to which a radar wave is emitted into a concrete mass, and a reflected radar signal, which is generated in the concrete mass and, in particular, from foreign bodies contained in the concrete mass, is electronically processed and is subjected to an evaluation. The present invention also relates to use of the method of determining of the permittivity for depth scaling of the radar data, in particular, for determining presence of foreign bodies in the used constructional material with an electromagnetic sensor.
2. Description of the Prior Act
In the field of non-destructive material testing in the microwave frequency region, different methods of determining of the permittivity of an inspected medium are known. In this field, the inspection of concrete dependent on its composition and/or moisture content is of a particular interest.
In the article of Bungey et al. “The influence of concrete composition upon radar test results,” “Non-Destructive Testing in Civil Engineering,” The British Institute of Non-Destructive Testing, INSINT, vol. 39, No. 7, 1997, pp. 4874-478 (Bungey) among others, determination of dielectric properties of concrete by laboratory measurements is described. To this end, preliminary prepared concrete samples are placed inside of a large volume microwave conduit oncluded at one end with a predetermined load resistance, and their permittivities or dielectric constants and conductivities arc determined.
In the article of Padartz, et al., “Coupling Effects of Radar Antennae on Concrete”, Non-Destructive Testing in Civil Engineering, The British Institute of Non-Destructive Testing, NDT-CE '97, vol. 1, pp. 237-245 (Padartz), placing of plate-shaped concrete samples between a radar transmitter and a radar receiver (please see
FIG. 1
a
) and the determination of the propagation or the frequency-dependent shifting of a spectral density of a receiving signal are described.
Determination of an appropriate moisture content on an inspected bottom surface with GPR (Ground Penetrating Radar) during geodesic works is described in an article of Berktold et al., “Subsurface Moisture Determination With the Ground Wave of GPR”, R. G. Plumb GPR '98, University of Kansas (Berktold). Here, the difference in propagation of reflections of an emitted radar wave from two known reflectors located at different depths (please see
FIG. 1
b
) is evaluated with an algorithm.
Finally, a method of an iterative migration according to which a determined value of a dielectric constant or permittivity &egr;
r
is obtained with a focused migrated profile of recorded radar data is described in an article of Fisher et al., “Examples of Reverse-Time Migration of Single-Channel, Ground-penetrating Radar Profiles”, Geophysics, vol. 57, No. 4, 1992, pp. 577-586.
However, the use of the known methods for the determination of the moisture content by determining a relative permittivity in practice, e.g., on a constructional site, is connected with certain difficulties. This is because additional measurements are required, which is associated with increased costs, or as, e.g., with the method described in Berktold, the knowledge of the structure or the texture or the surface layer is required. With the method of Padaratz, a two-side access to the inspected samples for the transmission measurement is needed.
Accordingly, an object of the present invention is to provide a method of determining the constitution and/or the moisture content of concrete by determining the relative permittivity of the concrete which would not require any preliminary knowledge about the inspected material, provision of samples and/or additional separate measurements.
SUMMARY OF THE INVENTION
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a method including providing a radar apparatus to be positioned on a concrete mass and having a transmitting antenna for emitting a radar wave into the concrete mass and a receiving antenna for detecting a cross-signal generated by the radar wave emitted into the concrete mass by the transmitting antenna, electronically processing the cross-signal, and determining the relative permittivity by determining, with an algorithm, a frequency-dependent amplitude shifting in a spectrum of a section of the cross-signal within a predetermined time slot.
The present invention proceeds from a basic idea that it should be possible to emit, with an electromagnetic sensor properly positioned, a radar pulse into a predetermined medium, in particular, concrete via a transmitting antenna, and to obtain a satisfactory information about the permittivity of the inspected medium only from a cross-signal detected by a receiving antenna, which is spaced from the transmitting antenna, with the cross-signal being generated by the radar wave emitted by the transmitting antenna.
It was particularly important to develop a method and a sensor for detecting foreign bodies in the constructional material, in particular, in concrete. E.g., if fissures were formed in a concrete wall by a drilling hammer, it is, of course, important to determine at what depth from the surface, e.g., of a concrete wall, possible foreign bodies, e.g., reinforced steel, tubular conduits, and the like are located. If a radar measurement is used, in order to be able to effect a depth scaling of the available radar data, it is important to know the propagation velocity of the electromagnetic waves in the inspected medium. This velocity is determined from an equation
V
=
Co
ϵr
,
where Ps &egr;
r
is determined by the method according to the present invention, and Co is the speed of light in the air, i.e., Co=3.10
8
m/sec. Together with the determination of the time (t) of propagation, the depth (s) at which the foreign body is located in the concrete wall beneath its limiting surface in the region of a possible fissure or in the surface region covered by the electromagnetic sensor, is determined from the equation
s=vt
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments when read with reference to the accompanying drawings.
REFERENCES:
patent: 5420589 (1995-05-01), Wells et al.
patent: 5952561 (1999-09-01), Jaselskis et al.
patent: 3132573A (1983-03-01), None
“Multitarget detection/tracking for monostatic ground penetrating radar: application to pavement profiling”, Spagnolini, U.; Rampa, V., Geoscience and Remote Sensing, IEEE Transactions on, vol.: 37 Issue: 1 Part: 2, Jan. 1999, pp.: 383-394.
Liedtke Stefan
Tichy Stefan
Brown & Wood LLP
Hilti Aktiengesellschaft
Sotomayor John B.
LandOfFree
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