Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
1998-05-04
2001-07-03
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Parameter related to the reproduction or fidelity of a...
C324S623000, C324S639000, C174S034000, C343S703000
Reexamination Certificate
active
06255830
ABSTRACT:
This invention relates to methods of measuring the effectiveness of electromagnetic shielding and to electromagnetic field generators for use in testing shielding effectiveness.
Generally, all circuits emit electromagnetic energy generated by components such as clocks and integrated circuits. Although careful design methodologies are used to keep such radiation to a minimum, there will always be leakage due to uncontrollable parameters. Once all known techniques have been used to reduce noise at the PCB (printed circuit board) level, any remaining leakage may be eliminated by physically shielding the circuitry.
In most designs, metal enclosures are used to form a Faraday cage around the noisy electronics. A perfect shield is not possible, and therefore all metal enclosures have a certain amount of shielding which they are able to provide. The SE (shielding effectiveness) of an enclosure is defined as the amount of shielding (in dB) that the enclosure provides. The SE is the difference between the maximum emission levels of an electromagnetic field generator in free space and the maximum emission levels of the same electromagnetic field generator located within the enclosure.
Typically, the shielding effectiveness of an enclosure for electronic circuitry is measured by passing a cable to an antenna within the enclosure and feeding noise signals through the cable to the antenna from an external signal generator.
One problem is that the cable itself can contribute to the electromagnetic radiation and give rise to erroneous results.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome problems associated with the use of cables and external signal generators.
According to a broad aspect, the invention provides a method of testing the effectiveness of electromagnetic shielding provided by an enclosure comprising: with a self-contained source of electromagnetic radiation placed entirely within said enclosure, the source comprising a clock pulse generator, a source antenna and a battery, making a first measurement of the radiation received by a measurement antenna located outside the enclosure; making a second measurement of the radiation received by the measurement antenna when the enclosure is removed; and comparing the first and second measurements.
According to a second broad aspect, the invention provides a method of testing the effectiveness of electromagnetic shielding provided by an enclosure comprising: with a self-contained source of electromagnetic radiation placed entirely within said enclosure, the source generating a signal having frequency content at a fundamental frequency and a plurality of harmonic frequencies, making a first series of measurements of radiation received from said source, one for each of the fundamental frequency and a finite number of the harmonic frequencies; making a corresponding second series of measurements of radiation received from said source when the enclosure is removed, one for each of the fundamental frequency and said finite number of harmonic frequencies; and comparing the first series of measurements with the second series of measurements.
According to a third broad aspect, the invention provides an apparatus comprising: a battery connected to a voltage regulator for producing a regulated voltage supply; a high frequency clock powered by said regulated voltage supply for producing a clock output signal; and at least one source antenna having an input connected to receive said clock output signal for generating an electromagnetic field.
According to a fourth broad aspect, the invention provides an apparatus for determining a shielding effectiveness provided by an enclosure comprising: a self-contained battery powered source of electromagnetic radiation comprising a clock pulse generator, a source antenna and a battery; a spectrum analyzer; a measurement antenna connected to the spectrum analyzer; wherein a first measurement is made of radiation received by the measurement antenna of radiation emanating from the source when located within the enclosure, a second measurement is made of radiation received by the measurement antenna of radiation emanating from the source when the enclosure is removed, and a comparison between the first and second measurements is made to determine the shielding effectiveness of the enclosure.
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The use of steel sheet for the construction of shielded rooms. A.M. Intrator, AIEE Transactions, vol. 72 Part I, Nov. 1953, pp. 599-605.*
ASTM D4935-99: Standard Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials.*
J.P. Muccioli et al, Integrated Circuit Radiated Emissions Diagnostic Procedure 1MHz to 1000MHz, Magnetic Field-Loop Probe, Jan. 31, 1995, pp. 1-23, Electromagnetic Compatibility Measurement Procedures for Integrated Circuits.
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Arcari Gianluca
Rollin Jacques J.
Wong Gary
Deb Anjan K
Nguyen Vinh P.
Nortel Networks Limited
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