Electric lamp and discharge devices – With magnetic device – With envelope
Reexamination Certificate
1998-10-08
2001-10-02
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With magnetic device
With envelope
C131S313000, C131S255000, C131S255000, C315S248000, C315S344000
Reexamination Certificate
active
06297583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates in general to inductively driven electrodeless gas discharge lamps and, in particular, to electromagnetic shielding of radio frequency interference emitted from the drive coils used to energize such lamps.
2. Description of the Related Art
Inductively driven electrodeless gas discharge lamps utilize a solenoidal coil driven with alternating current to produce a plasma discharge within the lamp envelope. Alternating current flow through the coil generates a time-varying magnetic field that impinges upon the ionizable gas fill within the lamp, causing it to produce the plasma discharge. The gas fill can be an inert or other rare earth gas, such as neon, which produces a visible discharge when excited by the magnetic field.
Often, these lamps are driven at radio frequencies resulting in strong magnetic and electric fields that radiate well beyond the lamp envelope. In many applications, these radiated fields can detrimentally effect the operation of nearby circuits and sensors. For example, when used in automotive applications, the drive coils used to energize these lamps could detrimentally influence such things as engine sensors and the vehicle's electronic compass. Accordingly, it is well known to shield the electromagnetic radiation emanating from the drive coil. Although electric and magnetic field shielding is most effectively accomplished with a grounded, electrically conductive, ferromagnetic enclosure, such an arrangement is not practical since it would also shield the light transmitted by the lamp, making the entire assembly useless for its intended purpose.
Consequently, shielding is typically accomplished using a conductive screen or wire mesh that extends over all or a portion of the lamp envelope. See, for example, U.S. Pat. No. 5,397,966 to Vrionis et al. One problem with the use of a wire mesh for shielding purposes is that it can cause a significant reduction in the light output from the lamp due to the large total area covered by the wire making up the mesh. Vrionis et al. also disclose a shield made up of a plurality of electrically conductive fingers that extend generally in the direction of the axis of the induction coil. This arrangement of conductive fingers helps reduce any detrimental effect that the shield has on the efficiency of the lamp operation; however, it is believed that it also results in a correspondingly reduced effectiveness of the magnetic shielding effect.
SUMMARY OF THE INVENTION
The invention provides an electrodeless gas discharge lamp assembly which provides good electric and magnetic field shielding while minimizing its impact on the light output of the lamp. The lamp assembly includes a gas discharge lamp having a sealed envelope containing an ionizable gas fill, an inductive drive coil disposed about the lamp envelope, and a shield disposed over an end portion of the lamp envelope. The shield has a number of turns of electrically conductive material, such as wire, with each of the turns being disposed generally coaxially about the central, longitudinal axis of the drive coil. The turns are shorted together via a number of electrical conductors that are angularly disposed about the axis. These electrical conductors extend generally perpendicularly to the turns, either axially or radially, or both, relative to the longitudinal axis about which they are disposed. When connected in circuit, the electrical conductors are grounded. This arrangement provides good r.f. electric field and magnetic field shielding and permits the use of relatively few turns at a relatively large spacing of the turns so as to minimize the interference of the shield on the amount of light emitted from the lamp.
In one embodiment, the turns of the shield together comprise a continuous electrical path extending in a spiral helix about the end portion of the lamp. Each turn is shorted to each of the other turns at ninety degree intervals about their central, longitudinal axis. In another embodiment, each turn comprises a single loop, with some or all of the loops being shorted together via the electrical conductors.
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Bodem, Jr. Jack D.
Kohne Robert L.
Federal-Mogul World Wide Inc.
Gerike Matthew John
Patel Nimeshkumar D.
Reising Ethington, Barnes, Kisselle, Learman & McCulloch, P.C.
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