Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Reexamination Certificate
2001-04-02
2002-12-31
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
C342S194000, C342S027000
Reexamination Certificate
active
06501414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to detecting anomalies in microwave penetrable material and, more particularly, to the use of multiple reflections obtained at each of multiple positions in the microwave penetrable material for determining such anomalies. Anomalies of this type include but are not limited to plastic land mines, underground plastic pipes, liquid/foam interfaces, interfaces between geological materials, voids, and the like, which may be found in microwave penetrable environments that may camouflage such anomalies to a high degree.
2. Description of Prior Art
On average, every twenty minutes someone in the world loses a limb to a landmine. Many landmines are made of plastic.
Ground probing radar (GPR) has been used with some success in detecting underground metallic objects, but systems for detecting plastic or nonferrous objects are unreliable and have very little real world detection success for small objects. The environment of the ground provides an effective mask that makes it difficult to distinguish plastic and nonferrous materials electromagnetically. For instance, false detections caused by rocks, tree roots, air pockets, soil inhomogeneity, and miscellaneous buried objects are often a problem. Another problem is the apparent disappearance of a mine at some frequencies caused by either a permittivity match with the surrounding soil or an unfavorable complex addition of reflected energy at the receiver. Additional problems arise from high moisture content in the soil or a layer of water above the mine or plastic object.
Electromagnetic induction techniques generally work well for metallic objects. However, the amount of metal in plastic mines is often very small (only the fuse element, or none at all). This makes detection of plastic mines difficult or impossible. Plastic or PVC pipe cannot be detected in this way.
Infrared detection is another technique commonly used for mine detection. Because there is generally a difference in the heating/cooling rate of the mine as compared to the soil, at certain times of the day a surface spot above the mine can be detected because of a slight temperature difference. However, this technique fails when the day
ight temperature changes are minimal and when the mine is buried more than a few inches deep.
Other techniques such as superconducting magnetic field gradiometers, nuclear magnetic resonance imaging, and thermal neutron activation have been used with some success, but all have been shown to be deficient in one respect or another for detecting small plastic land mines. In addition, the equipment using these techniques is heavy, costly, and not amenable for field use in many environments.
Patents related to this area show many attempts to solve the above problems.
U.S. Pat. No. 5,867,117, issued Feb. 2, 1999, to Gogineni et al., discloses an apparatus and method for detecting an object and determining the range of the object. A transmitter, coupled to an antenna, transmits a frequency-modulated probe signal at each of a number of center frequency intervals or steps. A receiver, coupled to the antenna when operating in a monostatic mode or, alternatively, to a separate antenna when operating in a bistatic mode, receives a return signal from a target object resulting from the probe signal. Magnitude and phase information corresponding to the object are measured and stored in a memory at each of the center frequency steps. The range to the object is determined using the magnitude and phase information stored in the memory. The present invention provides for high-resolution probing and object detection in short-range applications. The present invention has a wide range of applications including high-resolution probing of geophysical surfaces and ground-penetration applications. The invention may also be used to measure the relative permittivity of materials.
U.S. Pat. No. 5,592,170, issued Jan. 7, 1997, to Price et al., discloses a frequency-agile, narrow-instantaneous bandwidth radar system that detects objects, and discriminates between different types of objects, from a safe stand-off distance. Transmit circuitry transmits a train of continuous wave signals in a multitude of stepped operating frequencies that illuminates the target area. Return signals from the target area are received through at least a pair of spaced-apart receive antennas. Signal receive/processing circuitry coupled to the spaced-apart receive antennas selectively combines and processes the return signals to identify variations in the received signals indicative of the presence of a specific type of object. At each of the stepped frequencies, the system noise and the clutter of the signals is reduced by averaging and smoothing the incoming data, and the cross-power spectrum at each frequency is calculated. Using the information of the power spectra of all frequencies, the Mahalanobis distance is defined and the presence and classification of a target is determined. Using the information of the cross-power spectra of all frequencies, the location of the mine is determined by the azimuth angle and echo time.
U.S. Pat. No. 4,240,027, issued Dec. 16, 1980, to Larsen et al., discloses a method for electromagnetic analysis of cellular or cell ghost physiology and pharmacology without disrupting the physical integrity of the cell membrane is described. The method utilizes the technique of multi-frequency automatic network analysis and signal processing to derive complex permittivities from the error corrected complex reflection coefficient of cell containing samples at each measured frequency. Complex permittivity at each frequency is then related to the dispersion in dielectric conductivity (a term which includes ohmic and non-ohmic losses) thereby measuring the ion permeability barrier and transport functions of the cell membrane and ion distribution inside of and outside of the cell membrane. The method measures the complex reflection coefficient of a capacitive termination containing a cellular sample as high frequencies are applied. Meaningful data can be developed in the range of frequencies of from 100 KHz to 100 MHz depending upon the exact nature of the cells and the automatic network analyzer used.
U.S. Pat. No. 5,557,277, issued Sep. 17, 1996, to Tricoles et al., discloses a method for imaging substances leaking from underground structures using continuous-wave signals that includes the steps of translating an antenna array over the ground, transmitting a continuous-wave signal into the ground at an array of points, detecting the amplitude and phase of the reflected signal at each point, transforming the reflectance values into the frequency domain, propagating this reflectance spectrum to a predetermined depth, and transforming the propagated spectrum into an image in the spatial domain at that depth. An image representing the underground structure containing the substance may be overlayed on the calculated image to detect differences that represent leakage. Successive images of the same area may be produced over a period of time and the differences compared to determine the rate of leakage.
U.S. Pat. No. 5,819,859, issued Oct. 13, 1998, to Stump et al., discloses an apparatus and method for locating an underground object or structure by employment of a radar-like probe and detection technique. The underground structure is provided with a device which generates a specific signature signal in response to a probe signal transmitted from above the ground. Cooperative action between the probe signal transmitter at ground level and the signature signal generating device provided on the underground object provides for accurate detection of the subsurface object, despite the presence of a large background noise signal. The depth and, if desired, orientation of the underground object may also be determined using the signature signal generated by the signature signal generating device mounted to the underground object. Orientation information may be may be encoded on the signature signa
Arndt G. Dickey
Byerly Kent A.
Carl James R.
Ngo Phong H.
Stolarczyk Larry G.
Andrea Brian K
Barr Hardie R.
Cate James M.
Tarcza Thomas H.
The United States of America as represented by the United States
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