Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Reexamination Certificate
2001-03-28
2003-02-18
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
C342S118000, C342S175000, C342S194000
Reexamination Certificate
active
06522285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to non-invasive methods and systems for probing the earth, and more specifically to radars that can image and detect objects and other anomalies in the ground.
2. Description of the Prior Art
Many valuable and/or dangerous objects are buried in the ground, and digging them up to see what is there is often not possible or practical. Ground-penetrating radars have been developed as a way to “see” what is underground. But conventional methods and equipment have only provided crude hints of things very near the surface.
Michael D. Bashforth, et al., describe a wide band stepped frequency ground penetrating radar in U.S. Pat. No. 5,499,029, issued Mar. 12, 1996. Such relates to attempts to increase the average signal power and to preserving phase information so digital signal processing can extract more information about objects in the soil. The radar transmitter steps in frequency from 100 MHz to 1,000 MHz, and data is taken at 2.0 MHz step intervals. Both in-phase and quadrature data are collected for over 900 samples. The received signals are combined with samples from the transmitter to detect any phase shifting that may have been caused by objects in the ground, e.g., landmines and waste containers.
An earlier technology is described in U.S. Pat. No. 5,325,095, issued Jun. 28, 1994, to Kenneth G. Vadnais, et al. Such discloses a prior art stepped-frequency ground penetrating radar with a less-capable phase locked loop device.
The present inventors, Larry Stolarczyk and Gerald Stolarczyk, describe the measuring of the thickness of ground deposit layers with a microstrip antenna, in U.S. Pat. No. 5,072,172, issued Dec. 10, 1991. Interpolation tables are used to lookup the layer thickness values corresponding to antenna conductance and resonance measurements. Such resonant microstrip patch antenna (RMPA) and their resulting measurements are used to guide coal-seam drum-cutter equipment for more efficient mining of natural deposit ores. The RMPA driving-point impedance (S
11
) changes significantly when a solid, gas, or liquid layer thickness overlying the RMPA varies.
The RMPA can be swept above a soil surface to find buried landmines, utilities, and other shallow-buried objects. These objects don't necessarily need to be made of metal to be found. What is needed is that the dielectric constants of the objects and the medias they are buried in must differ, e.g., for contrast.
Calibrating the RMPA sensor establishes the RMPA driving-point impedance relationship to a layer-measurement value. In prior art mining applications, layers of various thickness needed to be cut with a mining machine so the RMPA impedance at each layer thickness can be recorded. But such prior art calibration procedures proved to be difficult in practice. A better approach is needed that has an independent means of measuring layer thickness that can be run concurrent to any driving-point impedance measurements.
U.S. Pat. No. 5,769,503, issued Jun. 23 1998 to Stolarczyk, et al., describes mounting such RMPA on a rotating drum or arm of a coal, trona, or potash mining machine. A ground-penetrating-radar transmitting antenna and a receiving antenna can be mounted on a cutting drum to detect deeply buried objects and anomalous geology just ahead of the mining. A radar frequency downconverter is used so low-cost yet-accurate measurement electronics can be built. A first phase-locked loop (PLL) is operated at the resonant frequency of the patch antenna or at each sequentially stepped radar frequency. A second PLL is offset from the first PLL by an intermediate frequency (IF) and is called a tracking PLL. The measurement speed can be delayed by the sequential way in which the PLL's lock on to signals, so a solution to that delay is described.
The calibration curves represent an analytical function that has been reconstructed from a set of discrete I and Q data points measured at each height (H). The discrete sensor height calibration data can be used to construct two different polynomials with the independent variable being the physical layer thickness or height (H). The physical height (H) is independently measured with acoustic height measurement electronics during the calibration process or by other means, such as an inclinometer on the boom of a mining machine. The two calibration polynomials are,
I
(
H
)=
Re H=b
n
H
n
+b
n-1
H
n-1
+. . . +b
1
H+b
O
(1A)
and
Q
(
H
)=
Im H=a
n
H
n
+a
n-1
H
n-1
+. . . +a
1
H+a
O
(1B)
U.S. Pat. No. 5,325,095 describes a modulator that sequentially creates in-phase (I) and quadrature phase (Q) shifts in a frequency source signal. The frequency source signal is sequentially shifted by 0° or 180°(in-phase), then by 90°or 270°(quadrature) in passing through the phase modulator to the radar transmit antenna. The electronic circuits employ isolators. Isolators and quadrature modulator transmitters are costly and difficult to build with wide bandwidth. The receiver section of the radar receives the reflected signals from the target and uses a single frequency conversion design to transpose the received radar signal frequency to a lower frequency range where the I and Q signal measurements are sequentially made at each frequency in the stepped-frequency radar method that has become one of the standard ground penetrating radar practices. The I and Q signals contain the antenna sensor information. As is well known in the art, the sensor information is processed in a Fourier transform to transform frequency domain information to time domain information. The time domain information is used to determine the time (t
O
) for the signal energy to travel to and return back to the radar. By knowing the velocity (V) in a dielectric natural media such as coal
v
=
c
ϵ
c
where c is the speed of light, &egr;
c
is the relative dielectric constant of coal (about 6). The distance to the reflective target is
d
=
c
2
ϵ
c
t
o
.
The relative dielectric constant must therefore be known to accurately to determine distance.
The velocity formula is made more complex whenever the natural media layer is not coal, trona, or some other high-resistivity liquid or solid. The velocity of radio waves generally depends on the frequency and resistivity of the natural medium. It is therefore preferable to simultaneously measure the in-situ dielectric constant, e.g., when using radar to measure depths. Stepped-frequency radars have separate transmitting and receiving antennas, and are circularly polarized antennae. But printed circuit antennas radiate front and back. To counter this, U.S. Pat. No. 5,325,095, teaches the placement of radar-energy absorbing material on one side of the printed circuit board to reduce the back lobe.
The antenna pattern is directed only to one side of the printed circuit antenna. Such antennas are preferably oppositely polarized so that they can be operated in continuous wave (CW) mode and in close proximity to each other. The transmitter and receiver sections operate concurrently. The radar return signals from the target will typically be repolarized opposite to the transmitted signal. The reflected wave can thus be readily measured by the receiving antenna and associated electronics. But not all the reflected signals will be oppositely polarized. An electromagnetic wave traveling in a first media and into a second media is reflected at the interface.
Electromagnetic wave reflection occurs at the interface of two different dielectric medias, and the reflection coefficient can be expressed in Equation (2) as,
Γ
=
E
s
E
p
=
ϵ
1
-
ϵ
2
ϵ
2
+
ϵ
1
;
σ
ωϵ
<<
1
(
2
)
where, E
s
is the reflected electric field component of the electromagnetic wave, a vector; E
p
is the incident electric field component of the electromagnetic wave, a vector; &egr;
1
is the relative dielectric constant of the first me
Stolarczyk Gerald L.
Stolarczyk Larry G.
Gregory Bernarr E.
Main Richard B.
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