Communications: electrical – Continuously variable indicating – Condition responsive
Reexamination Certificate
1998-03-11
2001-05-01
Horabik, Michael (Department: 2735)
Communications: electrical
Continuously variable indicating
Condition responsive
C340S545300, C340S870180, C324S260000
Reexamination Certificate
active
06225917
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the problem of accurately measuring electromagnetic fields. More specifically, the present invention provides an electromagnetic field probe which accurately measures electromagnetic fields while reducing the interaction of the probe with the field.
Currently, the most commonly used types of electromagnetic field probes interact with the field they are attempting to measure to an undesirable degree. This is largely due to the fact that electrically conductive lines are employed to transmit the detected signal from the probe to the instrumentation. It is well known that such electrically conductive lines generate their own electromagnetic fields and also interact with and alter the field being measured, thereby adversely affecting the accuracy of the measurement.
In addition, currently available probes lack sophistication in that they are only able to measure the amplitude of the field. The frequency content of the field, an obviously important field parameter, is not measured.
Both of these problems have been addressed to some degree by recent, experimental, optically-based technology. Unfortunately, other limitations continue to make commercial viability for such technology problematic. Not only do optically-based probes tend to be very expensive initially, they are also mechanically fragile resulting in a high cost for maintenance and repair.
It is therefore desirable to provide an electromagnetic field probe which reduces the effects on the field to be measured by the probe itself and its cables. It is also desirable for such a probe to provide information about a measured field beyond its amplitude.
SUMMARY OF THE INVENTION
According to the present invention, an electromagnetic probe is provided which avoids the use of electrically conductive transmission lines to transmit information about a measured field from the probe to its accompanying instrumentation. The probe of the present invention includes conversion circuitry for converting the signal received from the probe's sensing element(s) from an electrical modality to, for example, an acoustic or optical modality. The converted signal is then transmitted via the appropriate medium to the measurement instrumentation where it is converted back to an electrical modality and analyzed for information regarding the measured field. The effect on the measured field of the transmission of the converted signal to the instrumentation is negligible because the frequency content of the converted signal and any fields generated by the transmission are significantly different from unconverted sensing signal.
According to various embodiments, the quality and fidelity of the transmitted converted signal may be enhanced according to any of a variety of analog and digital signal processing techniques. For example, a wide variety of encoding schemes may be employed with the present invention to encode the converted signal. Alternatively, a wide variety of modulation schemes may be employed to enhance the fidelity of the transmitted signal. For example, the converted signal may be used to modulate a carrier.
According to other embodiments of the invention, manipulation of the sensor output using various techniques facilitates reliable and accurate determination of field parameters. According to one specific embodiment in which the field of interest has a modulation in the audio frequency band, the sensor output is rectified resulting in a signal in the audio frequency band. The rectified signal is transmitted to a transceiver which converts the electrical signal to an acoustic signal for transmission to the probe's instrumentation. According to more specific embodiments, the rectified sensor output may be amplified, encoded, or used to modulate a carrier before being converted and transmitted as an acoustic signal.
According to another specific embodiment, an RF field of known frequency and amplitude is added to the field of interest. The probe's sensor generates a mixed signal representative of the combined fields. This heterodyning produces several field components including a difference component which corresponds to the difference between the frequencies of the two fields. Using the known frequency of the second field, the frequency of the field being measured may be derived.
According to yet another embodiment, a second transceiver receives the converted signal and converts it back to its first modality for use in generating a reference signal for the purpose of calibrating the loss in the transmission medium. The signal is then reconverted to the second modality for transmission to the instrumentation via the transmission medium.
Thus, the present invention provides a probe for measuring an electromagnetic field. A sensing element senses the electromagnetic field and generates a sensing signal indicative thereof. The sensing signal is characterized by a first modality. First conversion circuitry coupled to the sensing element converts the sensing signal to a second modality. A transmission medium coupled to the first conversion circuitry transmits the sensing signal in the second modality. Measurement circuitry coupled to the transmission medium receives the sensing signal in the second modality and generates measurement data corresponding to the electromagnetic field.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
REFERENCES:
patent: 4788545 (1988-11-01), Farque
patent: 4891641 (1990-01-01), Gard et al.
patent: 5363095 (1994-11-01), Normann et al.
patent: 5675674 (1997-10-01), Weis
Safety Considerations for Human Exposure to EMF's from Mobile Telecommunication Equipment (MTE) in the Frequency Range 30 MHz—6 GHz; Apr. 30, 1996; European Committee for Electrotechnical Standardization, SECRETARIAT SC 211/B, WGMTE96/4; pp. 39-44.
Edwards, Jr. Timothy
Horabik Michael
Siemens Information and Communication Networks Inc.
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