Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Using radiant energy
Reexamination Certificate
1999-10-07
2001-09-11
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Using radiant energy
C324S754120
Reexamination Certificate
active
06288530
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for measuring the resonance frequency of an electric circuit with no undesirable influences or disturbances on the circuit. According to the measurement of the present invention, the resonance frequency, an important parameter for evaluating the circuit, can be determined with low disturbance and high accuracy, so that the present invention greatly contributes to the information/communication and electronics industries.
This application is based on Patent Applications No. Hei 10-287736 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Generally, a resonance circuit of an electric circuit is designed based on calculated results of the reactance and capacitance of the circuit. However, in most cases, the practical resonance frequency is different from the design value due to the dispersion of characteristics of each element included in the circuit, or to floating capacitance.
Conventionally, an electrically-systemized method has been employed for measuring the resonance frequency, in which a frequency-sweep electromagnetic wave is applied to the resonance section in the target electric circuit, and related reflection or the electric field induced in the resonance section is then measured using a coil. Therefore, the measuring apparatus electrically influences the measured section, and the measured frequency may be different from the real value.
SUMMARY OF THE INVENTION
In consideration of these circumstances, the present invention has an objective to provide a method and apparatus for measuring the resonance frequency of an electric circuit with low disturbance and high accuracy.
Therefore, the present invention provides a method of measuring the resonance frequency of an electric circuit having a resonance section, the method using an electrooptic crystal, whose refractive index changes according to the strength of an applied electric field, as a sensor for detecting a change of an electric field, and the method comprising the steps of:
applying a frequency-sweep electromagnetic wave to the resonance section of the electric circuit from an external device, so as to induce a current flowing in the resonance section;
measuring a change of the refractive index of the electrooptic crystal in the form of a corresponding change of light intensity;
detecting the change of the strength of the electric field with reference to the measured change of the refractive index, and determining the resonance frequency of the electric circuit based on the maximum value of the strength of the electric field.
In the above method, any one of an oxide of a trigonal crystal, a compound semiconductor of a cubic crystal system, and a single crystal oxide of a cubic crystal system may be used as the electrooptic crystal.
The present invention also provides an apparatus for measuring the resonance frequency of an electric circuit having a resonance section, comprising:
frequency sweep means for generating a frequency sweep signal;
electromagnetic wave supply means, to which the frequency sweep signal is supplied from the frequency sweep means, for generating and externally applying a frequency-sweep electromagnetic wave to the resonance section of the electric circuit, so as to induce a current flowing in the resonance section;
electric field strength measuring means having and using an electrooptic crystal, whose refractive index changes according to the strength of an electric field generated by the induced current, as a sensor for detecting the electric field;
data processing means for determining the resonance frequency of the electric circuit based on the maximum value of the measured strength of the electric field; and
display means for image-displaying the resonance frequency obtained by the data processing means.
According to the present invention, the resonance frequency of an electric circuit is measured using an optic effect so that highly accurate measurement can be performed. In addition, a frequency-sweep electromagnetic wave is applied to the resonance section from an external device; thus, the resonance frequency can be measured with a very simple system arrangement. Furthermore, a very small crystal which is subject to the Pockels effect (an electrooptic effect) is used, thereby performing the measurement with no influence on the electric circuit (to be measured) as a dielectric conductor.
Consequently, the resonance frequency, an important parameter of the electric circuit, can be determined with low disturbance and high accuracy.
REFERENCES:
patent: 4394617 (1983-07-01), Wampler
patent: 5034683 (1991-07-01), Takahashi et al.
patent: WO 96/00905 (1996-01-01), None
“A Technique for Detecting Resonance”, R.E. Laferty, IEEE Transactions on Instrumentation and Measurement, vol. 37, No. 2, Jun. 1988, p. 326.*
K. Tsuru, et al. “Measurement of the Resonance Frequency of Contactless IC Cards Using an EOS Probe,”Technical Report IEICE, CS99-33, RCS99-25, pp. 1-5, Jun., 1999.
K. Tsuru, et al., “Measurement of the Resonance Frequency of Contactless IC Cards Using an Electro-Optic-Sampling Probe,” SBMO/IEEE IMOC'99, pp. 1-3, Aug., 1999.
Lafferty, R. E., “A Technique for Detecting Resonance,” I.E.E.E. Transactions on Instrumentation and Measurement, New York, vol. 37, No. 2, (Jun. 1988), p. 326.
Murata Koushi
Nakajima Hideki
Suzuki Naobumi
Tsuru Koji
Brown Glenn W.
Burns Doane Swecker & Mathis
Deb Anjan K
Nippon and Telegraph and Telephone Corp.
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