Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1998-09-24
2001-07-31
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S239000, C340S551000, C340S572100
Reexamination Certificate
active
06268723
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to magnetic field generation and detection systems, and is particularly directed to a new and improved magnetic field excitation and receiver coil or transducer configuration that is operative to produce an electrical output representative of a differential combination of responses from a plurality of magnetic fields impinging thereon. These fields include the excitation field, a response magnetic field generated from an object-tagged transponder and other (noise source) magnetic fields. The receiver coils are connected in opposite polarity, so that energy from the excitation coil and relatively distant sources is canceled, while producing a useful net output for the field produced by a nearby (object-tagged) transponder.
BACKGROUND OF THE INVENTION
The use of magnetic fields for communications and the powering of short-range wireless (e.g., object detection) systems is becoming widespread in a variety of industries and technologies. Many of these systems produce large signal levels at the source (or reader) to power transducers (or tags) at short range and look for relatively small return signals from transducers. Most of these systems find application in very benign electromagnetic environments, such as, but not limited to retail outlets and filling stations.
In one type of system, the transducers may be configured as relatively simple resonators which are detected by their resonate response due to an exciting magnetic field. In a second type of system, the tag may contain transponder circuitry that is powered-up by an incident field and responds by modulating that field or generates an independent electromagnetic response. As these types of systems become more capable in range, simultaneous reading of multiple transducers, more capable transducers, etc. will be required.
Where application of such systems includes severe electromagnetic environments, such as those produced by machinery and processes (e.g., welding, induction heating, dielectric heating, industrial lighting and large electric motors) employed in heavy industry, the ability to overcome environmental interference becomes a fundamental requirement. All of these tools, when sized for heavy industry, produce significant field levels and broadband electromagnetic noise that can interfere with and even disable reader/transponder systems using magnetic fields.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a magnetic field excitation and detection coil arrangement that is configured to produce an electrical output signal representative of a differential combination of responses from a plurality of magnetic fields impinging thereon. Such incident magnetic fields may include the field emitted from the excitation coil, a response magnetic field emitted from an object-tagged transponder being interrogated by the excitation coil, and other magnetic fields from extraneous sources, such as industrial equipment or machinery. This differential combination of the responses from the detection coils will contain only the desired signal (e.g., response from an object-tagged transponder), as the excitation field and other far away fields cancel and therefore produces a net output signal level that is available to a downstream signal processor.
In a first embodiment of the invention, which may be employed in a wand-configured, or a compact, hand-portable device, an magnetic field excitation coil is wound around a generally cylindrically configured rod of high magnetic permeability material, such as a ferromagnetic rod, which provides shaping of the generated magnetic field along the rod axis, and assists in producing higher field levels over a larger area. A receiver coil arrangement comprises a pair of cylindrically wound electrically identical receive coils that are coaxial with and spaced apart equidistant from and in close proximity with opposite ends of the excitation coil. In addition, the receive coils are connected such that their winding directions are opposite to one another.
When the excitation coil is energized, a magnetic field is emitted from the ferrite core. Since magnetic field strength is proportional to the inverse of the distance from a very close proximity magnetic field source, and since the receive coils are equidistant from the excitation coil, as for relatively distant sources, the received magnetic field energy at both receiver coils will be effectively the same. As a result, since the receiver coils are connected in opposite polarity, energy from the excitation coil and relatively distant sources is canceled, which serves to protect sensitive receiver electronics from the large potentials and transients that may be produced by the excitation coil. It also prevents interference with nearby (object-tagged) transponder responses.
When the magnetic field generated by the excitation coil is used to elicit a response from a nearby object (e.g., a magnetic field generated from a tag-embedded transponder of the type described in the above-referenced continuation-in-part application), the response magnetic field will be received by the two receive coils at different amplitude levels due to the lateral displacement of the coils along the ferrite core axis, thereby producing a net signal amplitude for a transponder response field.
In a second embodiment, a large area excitation—response coil arrangement of the coils provides doorway and conveyor belt coverage. In this embodiment, the size of the excitation coil may be on the order of the area to be monitored for one or more object-tagged transponders. As in the first embodiment, a pair of receiver coils are displaced laterally on the same axis as the excitation coil. Because increased area coverage requires the used of very large sized coils, lateral displacement therebetween must also increase in order to minimize loss of the desired signals in the composite output. To overcome this potential drawback, each receiver coil may be implemented as a plurality smaller coils connected in an array and placed in parallel planes, that are equidistant from the excitation coil.
REFERENCES:
patent: 5034689 (1991-07-01), Inoue et al.
patent: 5726628 (1998-03-01), Yoo
Belcher Donald K.
Boyd Robert W.
Hash Ronald J.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Snow Walter E.
Wherenet Corporation
LandOfFree
Magnetic field emission and differential receiver coil... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic field emission and differential receiver coil..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic field emission and differential receiver coil... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2482336