Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N5/00—Details of television systems
  • H04N5/64—Constructional details of receivers, e.g. cabinets or dust covers
  • H04N5/65—Holding-devices for protective discs or for picture masks
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/86—Vessels; Containers; Vacuum locks
  • H01J29/867—Means associated with the outside of the vessel for shielding, e.g. magnetic shields
  • H01J29/868—Screens covering the input or output face of the vessel, e.g. transparent anti-static coatings, X-ray absorbing layers

Definitions

• This invention relates to an improved electro ⁇ magnetic interference (EMI) /radio frequency interference (RFI) shield.
• EMI electro ⁇ magnetic interference
• RFID radio frequency interference
• cathode ray tubes are located in close proximity to sensitive navigational receivers, for example when a depth finder display, radar display or other display is located adjacent to LORAN as often occurs on personal and com ⁇ flashal boats and aircraft.
• the LORAN signal is relatively weak and easily overwhelmed by the EMI from the CRT.
• An alternative is to physically contain the offending interference at its source. While it is possible to shield most areas of interference-emitting devices by enclosing them in a conductive shield such as a wire mesh shield or metal box, shielding the display surface itself where visual clarity is important can be more difficult.
• wire mesh based shields have been proposed for the display surfaces. While these generally work acceptably with monochrome systems, with color displays, which employ a dot matrix style of display, wire mesh can seriously degrade signal patterns by creating moire patterns. This interference can also lead to color shifts.
• Glass panel shields with transparent metal coat ⁇ ings have been proposed as well. These materials have a transparent, substrate with a layer of metal on one surface. They have numerous failings. For one, the panels are extremely costly and difficult to work with because of their glass construction. For another, such panels tend to be thick and heavy.
• EMI/RFI filters for use in front of visual display terminals.
• These filters are multilayer composites. Beginning with the outer layer, that is the layer closest to the viewer or furthest from the display surface, the composite has a diffuse nonglare hard-coat. This hard-coat is a transpar ⁇ ent, scratch resistant surface generally from about 3 to 10 microns in thickness.
• the next layer is a sheet of plastic having a thickness of from about 1 to about 50 mils. This plastic may be flat or may be shaped and thermally formed as needed to conform to the face of the display device.
• the next innermost layer itself comprises a stack of dielectric and metal layers.
• This can be in a dielectric-metal-dielectric configuration or can include more than one metal layer sandwiched between dielectrics.
• the thickness of these layers can be expressed in terms of their electrical resistivity. (Thinner layers have higher resistivity and thicker layers have lower resistivity. )
• the metal layers should have a resistance of 20 ohms or less.
• These metal layers are electrically connected to grounding sources . This connection generally occurs on substantially the circumference of the shield.
• the shields are further characterized by their optical transparency in combination with the above noted conductivity. Typical transparencies are 25% or greater over the visual range.
• this invention provides a kit for consumer application of the above described shields .
• This kit comprises: (a) a cut-to-size sheet of transpar ⁇ ent conductive film which is user-tailored to the size and shape of the cathode ray display face; and (b) a conduc ⁇ tive tape which is affixed around the circumference of the sheet and then electrically connected to ground.
• Fig. 1 is a perspective partially cut away view illustrating the placement of a shield of this invention in front of a visual display screen
• Fig. 2 is an expanded scale cross sectional scale view of a shield of this invention.
• Fig. 3 is an expanded scale cross sectional view of the filter material illustrating its various layers;
• Fig. 4 is a story. board in six views showing one way of using the invention.
• the present invention provides an EMI/RFI shield which combines high visual trans ittance with high electrical conductivity and concomitant high shielding efficiency.
• This shielding efficiency is high enough to prevent transmission of interference between closely placed CRTs and sensitive receivers.
• a shield of this inven ⁇ tion 10 is shown positioned in front of a cathode ray tube 11.
• Shield 10 can be flat or formed to conform to the face of tube 11. This forming generally is a three dimensional forming.
• Shield 10 includes a transparent center portion 12 and grounding connectors 13, 13a, 13b, and 13c. These grounding connectors preferably es ⁇ sentially completely surround the transparent region of the shield 10 (that is, provide 360° grounding).
• the back region of the CRT and the remainder of the display unit would be surrounded by a grounding shield as well. For brevity this is not shown in Figure 1.
• the shield 10 includes at minimum a diffuse nonglare hard-coat 21, a transparent plastic substrate 22, and an electrically conductive metal-metal oxide layer 23. Also shown in Figure 2 is a grounding conductor 24, electrically con- nected to conductor layer 23, and in turn electrically connected to conductor 25 which goes to ground; 24 and 25 are functionally identical to conductor 13 in Figure 1.
• Diffuse hard-coat 21 is provided to enhance resistance to abrasion. Generally, in use this layer is accessible to the operator of the display terminal and can be touched with hands and the like. Therefore, the dif ⁇ fuse hard-coat serves an important function by minimizing damage by the operator. Diffuse hard-coat 21 can, for example, be a cured silica hard-coat or an acrylic-based hard-coat. These types of hard-coats present a relatively mat finish. This serves to reduce specular reflections off of the outer surface of the shield to levels of 0.1 or lower, by scattering ambient light. They also serve to reduce fingerprinting when the panel is touched.
• the amount of antireflective hard-coat should be in the range of from about 0.5 to about 20 mils, preferably from about 1 to about 10 mils, and more preferably from about 1.5 to about 8 mils.
• typical hard-coats include the Dyalex material sold by MPV and applied by the process of Rollcoating and the Marnot material sold by Terra and ap ⁇ plied by the process of Rollcoating.
• the shield 10 has a flexible plastic substrate 22.
• This can be formed of plasticized polymer such as poly(carbonate) , poly(ester), poly(olefin) , poly(ether sulfone) , or the like.
• Poly(carbonate) and the poly(ester) poly(ethylene terphthalate) (PET) are preferred plastic substrates because of their toughness and resistivity to chemicals and the like.
• Plastic substrate 22 has a thickness of from about 1 to about 50 mils. If desired it can be thicker. Preferably the substrate has a thickness of from about 2 to about 25 mils and more preferably from about 5 to about 20 mils.
• Substrate 21 can be clear or it can be tinted or pigmented.
• This tinting can be carried out by in- corporating the color or pigment in the plastic substrate itself or by applying the color as a layer on the plastic .
• the transmission over the visual range desired for the shields of this invention can be achieved when the plastic substrate has transmittance values of between 30% and 100%. Generally, it has been found that when the transmittance values are below about 30% this in combina ⁇ tion with the diminished transmittance imparted by the conductive metal layer leads to an unacceptably low overall transmittance.
• plastic substrate 22 When the plastic substrate is treated to reduce its transmittance this is more commonly done to yield a transmittance of from about 35 to about 95% and preferably from about 40 to about 80%.
• Absorbance can be imparted to plastic substrate 22 by any of the methods known in the art for reducing light transmittance, including, without limitation, pigmenting or dyeing substrate 22, applying a pigment or dye overcoat, impart ⁇ ing circular polarizing properties to the plastic layer, or the like.
• pigmenting the plastic substrate is the gener- ally preferred method of reducing transmittance.
• the inner surface of substrate 22 carries a transparent electrically conductive layer 23.
• Layer 23 is itself made up of more than one layer, as is shown in more detail in Figure 3.
• 21 is the diffuse hard- coat
• 22 is the plastic substrate
• layer 23 includes dielectric layer 31, metal layer 32, and dielectric layer 33.
• This form of conductor offers significant advantages over a conventional metallic conductor such as a metallic screen or the like in that it cannot generate interfering moire patterns and has significant optical transparency.
• This multilayer stack has a total thickness of from about 500 angstroms to about 2,000 angstroms.
• the metal layer 32 is formed of a conductive metal and is from about 50 angstroms to about 500 angstroms in thickness. Representative metals include silver, gold, copper, nickel, mixtures thereof, and the like.
• the dielectric layers are independently selected and are generally from about 100 angstroms to 1,000 angstroms in thickness.
• Representative dielectrics include metal oxides such as titanium dioxide, lead oxide, tin oxide, bismuth oxide, zirconium oxide, iron oxide, indium oxide, and the like, as well as metal sulfides such as zinc sulfide.
• These dielectric-metal-dielectric sandwiches can be also characterized by having transmittances of from about 30% to about 80%, and especially from about 40% to about 80%.
• An important characteristic of the metal layer which directly relates to its performance as an EMI/RFI shield is its substantial electric conductivity.
• This layer should have a conductivity as measured by resist- ance, of less than 20 ohms per square, preferably it has a conductivity of 15 ohms or less per square, and more preferably has a conductivity of 12 ohms per square to 0.5 ohms per square.
• Conductive layer 23 is again joined to conductor 24 for grounding.
• This connection can be carried out by the use of conductive ink buss bars, by metal contacts, or the like.
• Conductive adhesive tape is a preferred conduc ⁇ tor.
• conductor 24 is shown contact ⁇ ing dielectric layer 33.
• the conductive layers are made up of continuous layers. Such layers can be laid down by sputter deposit and vacuum deposit techniques. From our experience, magnetron sputtering, as shown in S. Schiller, U. Heisig and K.
• the process for preparing the RFI/EMI shields of the present invention typically has the following steps .
• the hard-coat is applied first primarily for economy reasons. This is a relatively low cost material, so subsequent wastage is not as harmful as might be the case with more expensive steps.
• the dielectric-metal-dielectric layers are laid down. This can be done on a commercial scale in magnetron sputterers using various electrodes to lay down the various layers either one after another in a single pass, or by sequential passes through the sputtering apparatus. In this apparatus, the plastic substrate is generally fed as hard-coated roll stock.
• the hard-coated and conductive layer coated roll stock is then removed, cut into sheets corresponding to the size of the shields desired, and the sheets are then thermoformed to conform to the shape of the display tube. If the display tube is basically a flat panel, this shaping may only involve trimming the shield material to proper size.
• the shield can be thermoformed using conventional processes. These can include matched metal die pressing at effective thermofor ing temperatures, such as from about 110 to about 150 C in the case of carbonates, or from about 175 to about 250 C in the case of polyesters. Other conventional processes include vacuum forming and pressure forming wherein the plastic substrate with attached layers is drawn or pressed into a mold by pressure or vacuum.
• An advantage of the shields of the present invention is their ability to be shaped to conform to display surfaces after the hard-coat and conductive shielding layer have been applied without disturbing or disrupting either of these layers. This allows for relatively inexpensive fabrication and permits a lower cost product to be achieved.
• the shields of this invention can be in ⁇ corporated in devices as OEM components or they can be provided as aftermarket "add-ons". In a typical aftermarket application, the shield is employed as shown in Figure 4. In Figure 4(a) the first step is shown. The user removes the front cover or bezel frame in front of the CRT screen.
• the second step is shown in which the user measures the length (A) and width (B) of the display area plus the area under the bezel or cover.
• the shield material is trimmed to size to fit the (A) and (B) dimensions.
• the shield as sold preferably carries a peel-off protective layer over the metallic conductive layer. This is peeled off in step 4 ( Figure 4(d)) being careful not to handle the exposed conductive layer with the fingers . This is best done by wearing cotton gloves or touching only the regions which will be under the bezel.
• step 5 ( Figure 4(e)) conduc ⁇ tive adhesive tape is applied to the perimeter of the shield. This can be done by cutting A and B length pieces or by folding the tape around the shield.
• step 6 the shield is mounted in front of the CRT display so that the conductive side is facing the display.
• the conductive tape perimeter is grounded to the chassis of the display or to another ground. This is easily done using additional conductive tape. Thereafter the bezel or cover plate is reinstalled.
• the shields of the present invention will be further described by the following examples. These are provided to illustrate embodiments of the invention, but are not to be construed as limiting the scope of the invention.
• EXAMPLE 1 An EMI/RFI shield in accord with the present invention is prepared as follows:
• polyester (poly(ethylene terphthalate) ) roll stock is coated on one side with an acrylic diffuse nonglare hard-coat; the hard-coat is approximately 5 microns in thickness.
• the polyester has a nominal thick ⁇ ness of 15 mils.
• This material is then loaded into a magnetron sputterer and a three layer stack of dielectric, metal and dielectric is laid down.
• the dielectric layers each have a thickness of about 300-600 angstroms.
• the metal which is primarily silver has a thickness of about 100 angstroms, and the other dielectric layer is similar to the first.
• This conductive stack has a resistance of about 10 ohms per square.
• the conductive stack has a visual light transmittance of about 60%.
• the plastic substrate has neutral grey pigmenting, which gives it a visual transmittance of 40 to 50%, giving an overall transmittance level of 25 to 30%.
• the product so formed is removed from the magnetron sputterer, cut into sheets, and the sheets are then thermoformed and trimmed to conform to the face of a cathode ray tube by a pressure forming process.
• Silver ink buss bars are painted on the conductive layers and these are in turn adhered to copper mesh electrode sur ⁇ rounding essentially all 360 of the periphery of the shield.
• a conductive adhesive tape is ap ⁇ plied to the edge of the conductive layer.
• this shield does not have any mesh lines or the like which can interfere with the visual image transmitted through the shield.
• this shield When this shield is grounded via the conductor surrounding its periphery, it provides effective EMI/RFI shielding so as to prevent emissions of such radiation from the cathode ray tube.
• Example 1 is repeated with the following changes.
• the shield is designed for use in front of a flat panel display. Accordingly, the shield itself has a flat cross section and does not have the thermoforming called for in Example 1.
• Example 3 The production of Example 2 is repeated with one change; instead of a neutral grey tinted polyester, an untinted polyester is used. This yields an overall transmittance of about 60% while retaining the excellent shielding characteristics of the material of Examples 1 and 2.

Landscapes

• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)

Applications Claiming Priority (4)

Publications (2)

Family

ID=26808723

Family Applications (1)

Country Status (4)

Families Citing this family (5)

Citations (1)

Family Cites Families (3)

• 1988
  • 1988-10-20 WO PCT/US1988/003695 patent/WO1989004099A1/fr not_active Application Discontinuation
  • 1988-10-20 JP JP50936588A patent/JPH03503221A/ja active Pending
  • 1988-10-20 EP EP19880910261 patent/EP0383825A4/en not_active Withdrawn
  • 1988-10-20 AU AU27212/88A patent/AU2721288A/en not_active Abandoned

Patent Citations (1)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events