Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1996-06-27
1999-02-02
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340572, G08B 13187
Patent
active
058670980
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a transponder for a detection system, which comprises a transmitter, for the production of a magnetic alternating field having a predetermined frequency, and a receiver, the transponder comprising a signal element made of soft magnetic material and the receiver being provided with a detector which detects the higher harmonics of the frequency of the alternating field, which harmonics are generated by placing the transponder in the magnetic alternating field, in which the signal element has a curved shape. A transponder of this type is disclosed in U.S. Pat. No. 4,074,249.
The known detection system comprises a transmitter which is composed of an alternating voltage generator and a coil unit connected thereto in order to generate a magnetic alternating field having a predetermined frequency. In addition, the detection system comprises a receiver, the receiving coil unit of which is placed opposite the transmitting coil unit of the transmitter. The receiving coil unit is connected to a detector of the receiver, which is set up to detect higher harmonics of the frequency of the alternating field. The known transponder for use in the known system comprises a carrier of insulating plastic material, on which a curved strip made of soft magnetic material is fixed.
When the transponder is located in the magnetic alternating field, it will be influenced by said field in such a way that harmonics of the frequency of the alternating field are generated, which harmonics are detected by the detector as an indication of the presence of the transponder in the magnetic alternating field.
The curved signal element used in the above known system provides a relatively good signal response over a wide range of orientation of the plane of the signal element in comparison to a straight element, but has the disadvantage that the detection is still direction-sensitive perpendicular to the abovementioned plane.
When the signal wire is positioned with its longitudinal direction perpendicular to the lines of force of the magnetic alternating field, no higher harmonics of the frequency of the alternating field are generated, or the amplitudes of said higher harmonics are too small to enable them to be detected. The detection system therefore works reliably only when the signal carrier has a specific orientation with respect to the magnetic alternating field.
SUMMARY OF THE INVENTION
The aim of the invention is to provide a transponder of the type mentioned in the preamble, with which the abovementioned disadvantage is avoided and as minimal as possible dimensions are possible while sufficient signal is still produced.
This aim is achieved according to the invention in that the signal element has a shape of a closed or open circle.
One skilled in the art would expect that by using a closed loop for the signal element the slightly direction-insensitive result in the plane of the signal element will be eliminated.
However, it has been found surprisingly that as a result of the circular shape of the signal element of the invention the detection of the presence of said signal is direction-insensitive in any direction with respect to the generated magnetic field.
The known elongated signal elements in the form of a straight or slightly curved strip have to be of a minimum length in order to be able to achieve reliable detection. The invention has the advantage that the maximum length of the transponder can be smaller because of a kind of unexpected resonance effect.
In addition, the invention has the advantage that the pattern of the frequency spectrum of the signal received by the receiver is constant as a function of the distance away from the aerial. Only the amplitude of the harmonics becomes proportionally smaller as the distance increases.
By application of the invention, a greater port width can also be used, that is to say the transmitting and receiving coil units can be placed a greater distance apart without the reliability of the detection becoming unacceptable.
The invent
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patent: 4825197 (1989-04-01), Church et al.
patent: 4829288 (1989-05-01), Eisenbeis
patent: 4849736 (1989-07-01), Cordery
patent: 4967184 (1990-10-01), Regelsberger
patent: 5182544 (1993-01-01), Aquilera et al.
patent: 5406264 (1995-04-01), Plonsky et al.
Angel Willem
Batterink Henri
De Nood Cornelis Simon Adriaan
Dutch A&A Trading B.V.
Swann Glen
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