Patent Number: 048250902
Section: summary

BACKGROUND OF THE INVENTION The present invention relates generally to a device for shielding electromagnetic radiation emanating from electronic devices and electrical power sources. More particularly, the present invention relates to a shielding membrane that absorbs undesirable radiation emitted by cathode ray tubes, power sources and other electronic equipment systems. In recent years, there has been a growing concern that extensive exposure to electromagnetic radiation and large electrostatic fields may have adverse implications to a person's health. With the continually increasing use of video display terminals and power supplies, there has been extensive research studying the effects of radiation and fields generated by such devices. During an international conference on "Working With Display Units" held in Stockholm, Sweden in May, 1986, evidence was presented showing a correlation between adverse health effects and extensive exposure to non-ionizing radiation emissions from the video display terminals. Additionally, some studies have shown that low frequency emissions from power lines located over residential areas have adverse health effects on people living in the region. In addition to health concerns, such emissions may appear as noise to surrounding electronic equipment, thereby degrading the performance of neighboring equipment. Additionally, it has been shown that equipment can be readily constructed to detect radiation emitted from various computers and that the nature of data being worked with can be deciphered from an analysis of that radiation. Therefore, data security, particularly in the environment of embassies, banks and the like, has become a major concern. Therefore, there is a need for a device capable of effectively absorbing electromagnetic and RFI radiation as well as static electricity buildups. In response to such concerns, there have been numerous devices developed for absorbing electromagnetic radiation. For example, in Japanese Patent Application No. 55-91870, an electromagnetic wave absorber is disclosed comprised of a plurality of foamed polystyrol members sandwiched between a metallic plate and a front surface having a plurality of pyramidal shaped foam surfaces created from the same material as the wave absorbing members. The polystyrol members serve as radiation absorbing media. However, the metallic layer reflects radiation incident thereon. Thus, even though a large thickness of wave absorbing members is used, there will be substantial reflection back through the sandwiched materials towards the radiation source. Unfortunately, such reflected radiation can have adverse effects on the operation of the electronic equipment. Particularly, such radiation may be picked up by the equipment as noise thereby adversely affecting performance. Therefore, it is extremely important to absorb most of the radiation within the shielding membrane. Japanese Patent Application No. 55-29599 discloses an alternative embodiment of a wave absorber that comprises a plurality of triangular pyramid shape ferrite members disposed over ferrite plates that are backed with a metal plate. While such a device would effectively absorb some frequencies, its reliance upon wave length matching principles (due to its ferrite composition), restricts its usefulness to limited frequency ranges. Therefore, there is a need for a shielding membrane that is easy to fabricate with inexpensive material, effectively absorbs a substantial percentage of the electromagnetic radiation incident thereupon over a wide frequency range, while passing virtually none of the radiation and reflecting only a small percentage of the radiation back into the region from which it originated. SUMMARY OF THE INVENTION Accordingly, it is a primary objective of the present invention to provide a shielding membrane capable of absorbing a substantial percentage of the electromagnetic and RFI radiation incident thereupon. Another object of the invention is to provide a housing suitable for shielding users from radiation emitted by electronic appliances. Another object of the present invention is to provide a shielding membrane that minimizes reflections back to a radiation source. Another object of the invention is to provide a shielding membrane with a low radiation transmissivity. To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a shielding membrane is provided for shielding radiation from an electromagnetic radiation source. The shielding membrane has an incident surface facing the radiation source and a base surface facing away from the radiation source. The shielding membrane includes means for minimizing reflection of radiation directed onto the incident surface of the shielding membrane. Means is also provided for grounding some of the low frequency electrical components of the radiation. A conductive deflection layer, formed of a multiplicity of spaced-apart metallic deflection pads adapted to deflect incident radiation thereabout, is stacked behind the low frequency grounding means. A conductive absorption funneling layer is positioned spaced apart behind the deflection layer in a confronting relationship. The absorption funneling layer includes a multiplicity of apertures for passing radiation deflected about the deflection pads. A reflecting plate is placed near the base side of the absorption funneling layer. The low frequency grounding means, the deflection layer, the absorption funneling layer and the reflecting plate are each spaced apart and grounded to facilitate absorption of various components of the incident radiation. The gaps between these conductive layers are filled by spacers that are formed of an absorbing media to maximize radiation absorption. Preferably the spacers are formed of a high density porous foam. The low frequency grounding means preferably includes a conductive mesh. The reflection minimizing means preferably includes a waveguide barrier having a multiplicity of protrusions facing the radiation emitting source. The protrusions are preferably pyramidal in shape and the waveguide barrier is preferably formed of a high density porous foam. The apertures in the absorption funneling layer preferably have the same geometry as the deflection pads on the deflection layer. In a preferred method of construction, the apertures in the absorption funneling layer are stamped from a metallic foil and the cutout foil materials are used to form the deflection pads in the deflection layer. Such a shielding membrane may be used to shield video display terminals, power supply stations, electronic equipment and the like. Additionally the walls of buildings and/or rooms, ships, aircraft, and other vehicles that require data and detection security could be constructed to incorporate such a shielding device.