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.