Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Reexamination Certificate
2002-10-11
2004-08-31
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
C324S220000, C324S329000
Reexamination Certificate
active
06784666
ABSTRACT:
BACKGROUND ART
The invention relates to a probe for detecting a dielectric medium defined by a face and comprising at least one transmitter/receiver antenna located near the face, a signal processor for receiving signals from the antenna and generating data representative of the structure of the dielectric medium, and a dielectric material located between the at least one transmitter/receiver antenna and the boundary surface.
In particular, although not exclusively, the invention relates to a probe for detecting voids in the soil around a pipe, such as e.g. a sewer pipe.
By the term “detected”, it is in the above sense to be understood that the dielectric face and the dielectric medium are inspected, measured, analysed and described, the latter by means of e.g. data and/or images.
It is well known that voids can be formed around a sewer pipe. Formation of voids typically arise by sediment being washed into a leaky pipe because this pipe is functioning as drain. In connection with heavy rain, the water pressure in the pipe will often exceed the water pressure in the surrounding sediment whereby water is flowing out of the pipe. On its way back into the pipe, the water will bring along sediment.
A void, once formed, is in time likely to grow resulting in the fact that depressions are formed in the overlying ground. If the ground surface is covered with asphalt or concrete, the void can gradually assume a substantial size before the damage really appears.
Furthermore, the voids are often popular habitats and breeding grounds for rats. However, the rats are not efficiently exterminated without knowledge of the existence and location of the voids.
The voids are difficult and often impossible to reveal by detection from the ground surface. The problem cannot be solved by means of a video camera guided through the pipe either. By means of a video camera, it is possible to observe the inside of the pipe but not areas outside the pipe. For example, a bad and leaking joint cannot always be seen with a video camera.
Instead, these voids are therefore attempted to be revealed and localized by detection from within the pipe using probes designed for this specific purpose.
Such a probe is known from EP 0 816 872 A1. In this case, a number of antennas are placed along the periphery of the probe. A signal processor is furthermore part of the probe for generating three-dimensional images of the signals from the antennas.
The known probe operates with a radar which is able to transmit signals through the wall of the pipe. On its way through the pipe, the probe is thus emitting radar signals into the surrounding soil at short time intervals and detecting the returned radar signals. The signal processor converts the signals into data representative of the structure in the soil around the location in the pipe where the probe or rather its antennas are at a given moment.
If the soil around the pipe is homogeneous and without other objects, the data recorded during the travel of the probe through the pipe will assume an even and regular character. Conversely, deviations are signs that there are voids or objects in the soil of divergent electric properties (permittivity). Normally, the voids and objects can be distinguished from one another on the diversity of the data.
The known probe makes use of several closely set antennas. Thereby, the advantage is obtained in that it is only necessary to guide the probe through the pipe one time in order to at least essentially detect abnormal conditions in the ground around the pipe.
However, the number of antennas is limited by the modest space left when many antennas in this way must be placed closely next to each other along the periphery of the probe. This is especially a problem in case of small pipe dimensions.
Another disadvantage is that it is not possible freely to choose the location of the measuring profile or the closeness between the profiles by means of this probe. Moreover, the measurements are limited to only be able to take place along the pipe as the probe cannot be made to rotate in the pipe on a given location for example in order to check a joint and possible corrosion in the top and/or bottom of the pipe.
Theoretically, the antennas can be located in direct contact with the wall of the pipe. However, since a pipe normally does not have the precise same inside diameter in all cross sections, such a positioning is however not always possible in practice.
However, it is possible to compensate for the varying and imprecise inside diameter of a given pipe by letting the antennas be spring-loaded and dragging them along the inside face of the pipe. Since pipes of e.g. concrete often have a rough and uneven inside face, this solution is only suitable for minor inspections where the inevitable wearing of the antennas is not of great importance.
In practice, there must therefore be a gap conventionally filled with air between the transmitter/receiver antennas and the inside face of the pipe. However, the existence of such a gap reduces the effect of the signals penetrating into the ground around the pipe. Another detrimental effect is that undesirable reflections from the wall of the pipe are generated in addition to the desired reflections.
A preferred antenna type would be a high-frequency shielded dipole antenna. These antennas are normally arranged for direct connection with the base, that is the distance between the medium being checked and the antenna must be as short as possible. Even if the antenna is spring-loaded, it will be necessary to have a certain distance between the antenna and e.g. the inside face of the sewer pipe due to oval pipes, staggered joints etc. as the probe otherwise could get stuck too frequently.
However, an increased distance between the inside face of the sewer pipe and the antenna increases the surface reflections. Apart from a smaller effect in the part of the signal penetrating the pipe and into the ground, it also has the effect of reflections being generated inside the pipe from the probe and the inside face of the pipe. These undesired reflections can be removed during subsequent signal processing to some extent but they still degrade the final measuring results.
GB 2 166 599 A discloses an electromagnetic detector system for detecting the layers surrounding a horizontal borehole. Above an antenna which is part of the system, a dielectric material is located with a dielectric constant mainly corresponding to the dielectric constant of the surrounding layers.
U.S. Pat. No. 5,138,263 discloses a drill string for measuring the electric properties of an earth formation surrounding the borehole. For this purpose, a transmitting antenna is used for generating electromagnetic waves and at least two receiving antennas for receiving the reflected electromagnetic waves. The antennas are covered by an elastomeric layer which is located in a groove in the drill string. The layer is serving for protecting the antennas against shocks and abrasive contaminants.
In both of these patent documents, transmission of the signals takes place via a gap between the respective probe and the boundary surface resulting in the aforesaid disadvantages.
Furthermore, German Patent Publication DE 40 17 238 A1 discloses a method and a device for detecting e.g. a concrete pipe and its surroundings. In this case, an antenna is located rotatably on a shaft mounted on a vehicle only shown schematically. It is mentioned that the axis of the shaft coincides with the axis of the pipe but the publication does not mention any means for achieving this. By means of the arrangement shown only schematically in the drawing, it is however not possible to obtain a fairly regular, constant distance between the antenna and the inside face of the pipe, and the antenna must therefore be located at an adequate distance from the inside face of the pipe.
The present invention now provides a device and method that overcomes the problems of the prior art.
SUMMARY OF THE INVENTION
The present invention provides a system that provides an improved connection between t
Patidar Jay
Winston & Strawn LLP
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