Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1998-06-25
2001-08-28
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S642000, C324S632000
Reexamination Certificate
active
06281688
ABSTRACT:
GOVERNMENT INTEREST STATEMENT
The invention described herein may be manufactured, licensed, and used by or for governmental purposes without the payment of any royalties thereon.
I. BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for and a method of monitoring a number of geophysical and other physical variables by way of the refractive index or, indirectly, the dielectric constant of materials. Specifically, it related to monitoring of such properties as soil and pavement moisture content; the moisture content of bulk food products such as grains and beans; liquid levels in storage tanks; interface levels between water and floating layers of oil or other petroleum products; the thickness of ice layers; the frozen/unfrozen interface in partially frozen ground; the location of liquid and gas leaks on roofs, in landfill liners, geosynthetic membranes, and pipelines; and the location of electrical short circuits, open circuits, and impedance discontinuities in cables. The detection technique is based on the reflection of frequency-modulated continuous waves during their propagation along transmission line probes embedded in the material being tested.
2. Prior Art
The frequency-modulated continuous wave technique has been used in radar system applications wherein electromagnetic waves are transmitted into space from antennas. Applications employing transmission lines have been disclosed in the inventor's previous application directed to the detection of water-sediment interfaces around bridge piers and pilings (Ser. No. 08965483, filed Nov. 6, 1997) and another application relating to the detection of frazil ice on underwater gratings (Ser. No. 08871624, filed Jun. 9, 1997).
II. SUMMARY OF INVENTION
This invention relates to apparatus for the monitoring, both locally and remotely, of physical variables related to the refractive index of materials such as moisture content, air/liquid interfaces, oil/water interfaces, and ice/water interfaces. It is applicable to measurements of soil and pavement moisture content, the moisture content of bulk food products, liquid levels in storage tanks, interface levels between water and floating layers of oil or other petroleum products, the thickness of ice layers, the frozen/unfrozen interface in partially frozen ground, the location of liquid and gas leaks on roofs, electrical short circuits, open circuits, and impedance discontinuities in cables.
The apparatus comprises a transmission line probe, inserted into the material being monitored, means for generating a frequency-modulated continuous voltage wave signal, means for detecting frequency differences between frequency-modulated voltage signals. The interpretation of frequency difference signals involves the solution of equations interrelating the refractive indices of materials the distance from the proximal end of the transmission line probe to the location of discontinuities in refractive index, and to the length of the probe.
In the frequency-modulated continuous wave method of this invention, a transmission line probe is inserted into the medium whose properties are being monitored and a frequency-modulated continuous wave is applied to the proximal end of the probe. The wave propagates along the transmission line probe at the speed equal to the speed of light divided by the refractive index. The refractive index is equal to the square root of the dielectric constant of the material in which the probe is embedded. Reflected waves will be generated at points along the probe where discontinuities in refractive index occur, and at the distal end of the probe.
The frequency of the continuous wave signal is modulated, i.e., the frequency is altered with respect to time. Preferably, the frequency increases or decreases linearly with time form a low frequency to a high frequency, the difference between these frequencies being referred to as bandwidth. Non-linear frequency modulation patterns may be used but linear variation of frequency with time is preferred.
Mixing the input wave signal with reflected wave signal produces frequency sum and frequency difference signals which are related to the distance traveled by the waves to a refractive index discontinuity, or to the end of the probe, and to the refractive indexes of the materials surrounding the probe. Frequency sum signal components are filtered out by a low-pass network; only frequency difference signal components are amplified and utilized. Refractive indices are empirically correlated with moisture content, ice content, liquid-liquid interface level, the location of liquid or gas leaks, and the location of electrical short circuits or breaks in electrical cables.
The frequency differences signals may be recorded locally or transmitted by wireless means to remote monitoring/data recording equipment.
REFERENCES:
patent: 4737791 (1988-04-01), Jean
patent: 4807471 (1989-02-01), Cournane
patent: 4847623 (1989-07-01), Jean
Deb Anjan K
MacEvoy John
Metjahic Safet
The United States of America as represented by the Secretary of
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