Electricity: measuring and testing – Of geophysical surface or subsurface in situ – With radiant energy or nonconductive-type transmitter
Reexamination Certificate
2000-09-28
2003-09-30
Le, N. (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
With radiant energy or nonconductive-type transmitter
C324S239000
Reexamination Certificate
active
06628118
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to transmitting and receiving electromagnetic energy through or across materials that have previously been barriers to the penetration and passage of this type of energy. Specifically, the present invention relates to a method and apparatus for transmitting electromagnetic energy into or across ferromagnetic materials, paramagnetic metals or other electrically conductive materials that are magnetically permeable. These materials are barriers through which electromagnetic energy typically cannot penetrate into or pass through.
The invention also relates to a method and apparatus that can concentrate the magnetic flux field lines penetrating into a small volume region of the barrier material. This reduces the power required to fully or partially saturate the selected region of the barrier material.
Further, the invention relates to a method and apparatus that bends magnetic flux lines as they penetrate through such barrier material. This bending is a result of the changed permeability of the barrier material. This magnetic flux bending can be used to focus the magnetic flux as it penetrates through the barrier material into the matter or objects on the other side of the barrier. More specifically, the controlled focusing of the magnetic flux partially counteracts the normal rapid geometric spreading of the flux field. In turn, concentrating the magnetic flux allows distant sensing of or focusing upon objects using much less power than would otherwise be required.
The invention relates to a method and apparatus comprising at least one electromagnet or permanent magnet capable of at least partially. saturating a volume region of barrier material. The apparatus also comprises one or more transmitter magnets having means to simultaneously create oscillating magnetic flux lines penetrating into the saturated or partially saturated volume region of the barrier material. The device also contains means for receiving electromagnetic signals from or across the area of saturation. The apparatus may also include means to vary in a controlled manner the frequencies of the oscillating magnetic flux field.
The degree or level of saturation of the volume area of the barrier region may be controlled to create magnetic lenses that focus the flux field lines. More particularly, the present invention relates to a method of studying the properties or characteristics of a barrier material fully or partially saturated with magnetic flux. This is performed by detecting and measuring the magnetic flux field induced by electric current (eddy currents) generated by the passage of the transmitted oscillating magnetic signal permeating into or through the affected volume region of the barrier material. The method and apparatus of the invention do not require physical contact with the barrier material for the detection or study of the properties of the barrier material or objects on the opposite of the barrier material. The apparatus may be stationary and the barrier material being studied being moved in relation to the stationary apparatus, or the apparatus may be moving across a surface of stationary barrier material. The invention also pertains to an apparatus that can be used to determine or measure the electrical characteristics or electrical properties of such objects existing behind or on the opposite side of the barrier material.
2. Description of Related Art
There are many examples of the use of electromagnetic (EM) energy for sensing and measurement. However, materials that are electrically conductive and are magnetically permeable act as barriers to the use of EM energy for sensing and measurement. (These barriers are hereinafter termed “Barrier Materials” or “EM Barriers”.) Magnetic permeability is the ability of a material to absorb magnetic energy. The limitation in sensing or measurement by electromagnetic energy through EM Barriers has prevented utilization of EM energy for sensing or measuring through carbon steel tanks, pipelines, well casings and the like.
There has long been a need for a device that can make Barrier Materials transparent or semi transparent to EM energy. Also, there has been a need for a device that can make Barrier Materials transparent or semi-transparent for a sufficiently broad spectrum of EM wave frequencies. This would permit EM energy to be used to obtain useful measurements of the electromagnetic properties of electrically conductive matter or objects (hereinafter “Objects”) existing within or on the opposite side of the EM Barrier.
It is well known that ferromagnetic and paramagnetic materials are electrically conductive. It is also well known that magnetic energy is dissipated by both conductive and ferromagnetic or paramagnetic material. The absorption of magnetic energy is due to the molecules of such material responding to the magnetic component of EM energy. It is this molecular response that consumes or absorbs magnetic energy. The higher the permeability, the greater the capacity to absorb EM energy. Ferromagnetic carbon steel casing has a permeability of about 2,000 to 10,000 webers/amp, depending on the specific chemical structure of the material.
On the other hand, non-ferromagnetic metals such as aluminum, copper, and stainless steel do not absorb magnetic energy from permanent magnets or electromagnets generated by direct current. They have a permeability of one (1) but are also highly conductive of electric energy. Air also has a permeability of 1 but is significantly less conductive. Transmitting an EM wave through aluminum, therefore, is much different than transmitting an EM wave through air. Since aluminum is an excellent electrical conductor, part of the EM wave is readily dissipated. In the near field to a low impedance transmitter antenna (i.e., within 5 wavelengths of the transmitter antenna), the magnetic field predominates. The fact that the magnetic field predominates allows the magnetic signal to penetrate a non-ferromagnetic material, e.g., aluminum. All oscillating EM signals through aluminum will experience attenuation or damping because the electrical conductivity of the aluminum generates eddy currents that dissipate the EM wave.
The situation changes dramatically when aluminum is replaced by a ferromagnetic material, e.g., carbon steel. The much higher carbon steel permeability readily dissipates even the near magnetic field.
The inspection or detection of material properties, including but not limited to location, thickness, corrosion, defects, cracks or anomalies, has required the use of Gamma rays, X-rays, conducting a DC electric current through the EM Barrier Material, use of acoustic devices or other work intensive methods.
Gamma rays require a radioactive source and provide limited penetration. It requires cumbersome equipment and safety precautions. The use of X-rays requires use of relative high electrical power, as well as cumbersome equipment and safety precautions. The evaluation of the data collected from gamma ray and X-ray devices requires the viewing and interpretation of the photos or data by specially trained personnel. Many gamma ray and X-ray devices and methods are also not easily adapted to a continuous recording of data during ongoing industrial operations.
The use of electric current or acoustic signal passing through Barrier Material requires the material to be physically contacted. This requires the insulation coating or other covering matter to be wholly or partially removed. It also impedes the prompt or continuous measurement of the material in an ongoing industrial or otherwise uncontrolled environment. These methods or devices also have limited reliability or sensitivity.
Conducting DC currents through the barrier material, of course, requires contact with the Barrier Material and provides limited data. The present invention allows detection of properties and defects at greater distances from the target of the study. The present invention also allows more detailed description of the EM Barrier properties and
Aurora Reena
Em-Tech Sensors LLC
Le N.
McEwing David
LandOfFree
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