Non-intrusive fiber optic electromagnetic field probe apparatus and associated methods

Claim 1

A field probe apparatus for measuring relatively weak RF electromagnetic fields generated within shielded enclosures and operative to minimumly disturb said fields, comprising: a sensing conductor means adapted to be inserted into said enclosure to provide a signal indicative of electromagnetic field strength; amplifier means having an input coupled to said conductor means and operative to provide a voltage to current conversion gain at an output; a light emitting device coupled to said amplifier output to provide a light signal according to the signal produced on said sensing conductor means; and an optical fiber cable having a first end positioned to receive said light signal from said emitting device to transport said light signal to a second end of said fiber, wherein said amplifier means includes a source of operating potential, transistor means having main electrodes coupled to said source of operating potential and a control electrode coupled to said sensing conductor means, and further circuit elements coupled to said transistor means and having output terminals for providing a current output to said light emitting device, said light emitting device being a light emitting diode (LED) having its anode and cathode coupled to said output terminals of said amplifier means, and said transistor means and other coupled circuit elements thereof having a very high input impedance at said control electrode and providing a very high voltage-to-current gain at said output terminals, such that relatively weak RF electromagnetic fields sensed by said sensing conductor means result in a current output sufficient to drive said LED, wherein said light emitted by said LED varies according to the signal provided by said sensing conductor means for applying said light signal to said first end of said optical fiber cable.

Claim 15

A method of measuring relatively weak RF electromagnetic fields inside a shielded enclosure with minimum disturbance to said fields in said enclosure, comprising the steps of: inserting a probe tip into said enclosure, said probe tip consisting of a piece of wire, one end of which is coupled to a very high input impedance amplifier to provide an output current of very high voltage-to-current gain proportional to a voltage signal provided by the wire, wherein said probe is mounted external to said enclosure whose internal field is being measured; placing a light emitting device in series with said output current to provide a light signal indicative of said current; transmitting said light signal via a fiber optic cable to a remote location; and monitoring said transmitted signal at said remote location to determine the nature of said monitored fields.

Claim 16

A method of measuring relatively weak RF electromagnetic fields inside a shielded enclosure with minimum disturbance to said fields in said enclosure, comprising the steps of: inserting a probe tip into said enclosure, said probe tip consisting of a piece of wire, one end of which is coupled to a very high input impedance amplifier to provide an output current of very high voltage-to-current gain proportional to a voltage signal provided by the wire, wherein said probe is mounted external to said enclosure whose internal field is being measured; placing a light emitting device in series with said output current to provide a light signal indicative of said current; transmitting said light signal via a fiber optic cable to a remote location; and monitoring said transmitted signal at said remote location to determine the nature of said monitored fields.