ELECTROMAGNETIC WAVEGUIDE WITH AN EMI SHIELDING GASKET

Abstract

The present invention relates to an electromagnetic waveguide comprising an electromagnetic interference shielding gasket which includes a self-supporting body of non-woven carbon nanotubes adapted to incorporate one or more apertures and to the electromagnetic interference shielding gasket per se.

Claims

1. An electromagnetic waveguide comprising: a first waveguide section; a second waveguide section; a first flange mounted on an end of the first waveguide section; a second flange mounted on an end of the second waveguide section, wherein the first flange is connected to the second flange; and an EMI shielding gasket mounted between the first flange and the second flange, wherein the EMI shielding gasket includes a self-supporting body of non-woven carbon nanotubes adapted to incorporate one or more apertures.

2. An electromagnetic waveguide as claimed in claim 1 wherein the self-supporting body of non-woven carbon nanotubes is coated.

3. An electromagnetic waveguide as claimed in claim 1 wherein the coating is a partial coating.

4. An electromagnetic waveguide as claimed in claim 2, wherein the coating impregnates the self-supporting body of non-woven carbon nanotubes.

5. An electromagnetic waveguide as claimed in claim 1 wherein the self-supporting body of non-woven carbon nanotubes is coated with a polymer.

6. An electromagnetic waveguide as claimed in claim 5 wherein the polymer is a non-conductive polymer.

7. An electromagnetic waveguide as claimed in claim 6 wherein the non-conductive polymer is a fluoropolymer.

8. An electromagnetic waveguide as claimed in claim 6 wherein the non-conductive polymer is polyvinylidene difluoride (PVDF) or a copolymer or terpolymer thereof.

9. An electromagnetic waveguide as claimed in claim 5 wherein the polymer is a conductive polymer.

10. An electromagnetic waveguide as claimed in claim 5 wherein the polymer is polyvinylpyrrolidone (PVP).

11. An electromagnetic waveguide as claimed in claim 1 wherein the areal density of the self-supporting body of non-woven carbon nanotubes is 60 gsm or less.

12. An electromagnetic waveguide as claimed in claim 1 wherein the areal density of the self-supporting body of non-woven carbon nanotubes is 20gsm or less.

13. An electromagnetic waveguide as claimed in claim 1 wherein the surface of the self-supporting body of non-woven carbon nanotubes is non-uniform.

14. An electromagnetic waveguide as claimed in claim 1 wherein the thickness of the self-supporting body of non-woven carbon nanotubes is subject to variation by up to 20%.

15. An electromagnetic waveguide as claimed in claim 1 obtainable or obtained from a process comprising: (a) introducing a flow of metal catalyst or metal catalyst precursor into a temperature-controlled flow-through reactor; (b) introducing a flow of a source of carbon into the temperature-controlled flow-through reactor; (c) exposing the metal catalyst or metal catalyst precursor and source of carbon to temperature zones sufficient to generate particulate metal catalyst and to produce carbon nanotubes; (d) displacing the carbon nanotubes as a continuous discharge through a discharge outlet of the temperature-controlled flow-through reactor; (e) collecting the continuous discharge in the form of a self-supporting body of non-woven carbon nanotubes; and (f) adapting the self-supporting body of non-woven carbon nanotubes to incorporate one or more apertures.

16. An EMI shielding gasket as defined in claim 1.

Description

[0093] The present invention will now be described in a non-limitative sense with reference to the accompanying Figures in which:

[0094] FIGS. 1 to 32 are attenuation plots demonstrating the shielding performance of representative embodiments of EMI shielding gaskets according to the invention;

[0095] FIGS. 33 and 34 show SEM images of uncoated and coated CNT materials;

[0096] FIG. 36 shows a comparison of tensile stress and strain (%) for uncoated and coated CNT materials;

[0097] FIG. 37 shows a comparison of fracture energy for uncoated and coated CNT materials;

[0098] FIGS. 38 and 39 show the test set-up for Example 3 described below; and

[0099] FIGS. 40 to 47 show the shielding performance for various gasket materials measured using the test set-up.

EXAMPLE 1

[0100] The shielding performance of representative embodiments of EMI shielding gaskets according to the invention was assessed at high frequency by measuring attenuation relative to free-space or to a polythene (PE) spacer.

Experimental

[0101] Measurements were made using a horn antenna positioned to the side of a waveguide flange at a fixed distance. A signal source produced a test signal. The following flanges (Flann Microwave Limited) and frequencies were used: [0102] WR-112 10 GHz [0103] WR-42 26.5 GHz [0104] WR-19 50 GHz.

[0105] WR-112 is a choke flange which has a better performance metal-to-metal than a standard flange. For WR-112, the source was enclosed in a screen box.

[0106] For WR-42 and WR-19, the sources were in the waveguide.

[0107] The termination in each case was a waveguide load. The test method was based on IEEE Std 299: 2006 and the test equipment is listed in Table 1.

TABLE-US-00001 TABLE 1 Item Model Manu- No. No. Description facturer H058 861D 40-60 GHz Horn Antenna Alpha 25 dBi E204 45821H 26-40 GHz Horn Antenna Hughes 20 dBi E329 8349B 2-20 GHz Amplifier Agilent E296-4 11970U 40-60 GHz mixer Agilent E366 WBH224S 1.7-24 GHz horn antenna Q-par E777 MG3695B 50 GHz signal Anritsu generator E755 N9030B PXA Spectrum Analyser Keysight E853 — Cable 2.4/2.92 mm E933 321B WR-112 Load Narda Calstron E934 U910A WR-42 load Fmi E935 2217 WR-19 load HP H024 ESG-0015 250 kHz-15 GHz Signal ERA Instruments Generator

[0108] The CNT materials used to prepare the EMI shielding gaskets of the invention are available from TorTech with the following catalogue numbers: [0109] C-322-H3 20 gsm [0110] C-340-H3B 30 gsm [0111] C-254-H2A 60 gsm.

[0112] The CNT material was laser cut according to standard techniques to incorporate apertures and the desired configuration of the EMI shielding gasket. Tests were carried out on uncoated EMI shielding gaskets made from the CNT materials and on PVDF coated EMI shielding gaskets made from the CNT materials. The PVDF coated EMI shielding gaskets were prepared by dissolving PVDF pellets (Sigma Aldrich) in acetone (15% w/w) and applying the solution to the surface of an uncoated EMI shielding gasket. The acetone was allowed to evaporate to leave a PVDF coating.

[0113] A silicone elastomer containing nickel and graphite (CEM-NC001-0-0.3 80H 600 gsm) was used as a reference material.

Results

[0114] Attenuation plots are provided in FIGS. 1 to 32. For each of the waveguide types, the results are tabulated below. In the attenuation plots and Tables, the following abbreviations are used:

“PVDF” is a PVDF coated EMI shielding gasket
“ASIS” is an uncoated EMI shielding gasket
‘Direct’ is a waveguide with no gasket (ie metal-to-metal contact between waveguide flanges)
“PE70” is a polyethene spacer
“NiGrSi” is a gasket made from the reference material.

TABLE-US-00002 TABLE 2 10 GHz 322-H3 322-H3 Open 20 gsm 20 gsm WG PE70 Direct PVDF A PVDF B NiGrSi −10.9 −54.5 −106.5 −107.0 −112.1 −105.4 340-H3 340-H3 340-H3 30 gsm 30 gsm 30 gsm PVDF A PVDF B PVDF C −106.0 −103.7 −106.0 322-H3 asis A 322-H3 asis B −107.0 −112.1 340-H3 asis A 340-H3 asis B −112.2 −110.5

TABLE-US-00003 TABLE 3 26.5 GHz 340-H3B 340-H3B 340-H3B Open 30 gsm 30 gsm 30 gsm WG PE70 Direct PVDF A PVDF B PVDF C −39.1 −44.5 −80.7 −98.5 −98.5 −97.4 340-H3B 340-H3B 340-H3B 30 gsm 30 gsm 30 gsm asis A asis B asis C −95.8 −96.5 −99.4 254-H2A 254-H2A 254-H2A 60 gsm 60 gsm 60 gsm asis A asis B asis C −98.6 −98.8 −98.7 322-H3B 322-H3B 322-H3B 20 gsm 20 gsm 20 gsm asis A asis B asis C −99.3 −96.8 322-H3B 322-H3B 322-H3B 20 gsm 20 gsm 20 gsm PVDF A PVDF B PVDF C −98.6 −100.1 −102.5 NiGrSi −98.4

TABLE-US-00004 TABLE 4 50 GHz 322-H3 322-H3 322-H3 322-H3 Open 20 gsm 20 gsm 20 gsm 20 gsm WG PE70 Direct PVDF A PVDF B asis A asis B −32.8 −49.4 −93.6 −94.7 −93.0 −93.0 −93.0 340-H3 340-H3 340-H3 340-H3 30 gsm 30 gsm 30 gsm 30 gsm NiGrSi PVDF A PVDF B asis A asis B −93.0 −93.9 −86.7 −94.0 −93.4

Conclusions

[0115] The results indicate generally that EMI shielding gaskets made from the CNT materials provide an improvement in attenuation over those made from the reference material. The gasket made from the CNT material with the lowest areal density (20 gsm) was surprisingly better than the EMI shielding gaskets made from the other CNT materials (30 gsm and 60 gsm). The PVDF coated EMI shielding gaskets unexpectedly outperformed the other gaskets.

EXAMPLE 2

[0116] Various properties of coated CNT material were measured using standard techniques.

[0117] FIGS. 33 and 34 show respectively an SEM image of each face of a CNT material (20 gsm) coated with PVP. FIG. 35 shows an SEM image of a CNT material coated with 10 wt % PVDF.

[0118] FIG. 36 shows a comparison of tensile stress and strain (%) for an uncoated CNT material (60 gsm), a CNT material (60 gsm) coated with PVP, an uncoated CNT material (20 gsm) and a CNT material (20 gsm) coated with PVP.

[0119] FIG. 37 shows a comparison of fracture energy for the uncoated CNT material (60 gsm), the CNT material (60 gsm) coated with PVP, the uncoated CNT material (20 gsm) and the CNT material (20 gsm) coated with PVP.

EXAMPLE 3

Experimental

[0120] The test equipment used for measurement is as follows:

TABLE-US-00005 RN Model Manu- No. No. Description facturer E366 WBH224S 1.7-24 GHz Horn Antenna Qpar E777 MG3695B 50 GHz Signal Generator Anritsu H301 45821H 24-40 GHz Horn Antenna Hughes H302 DP241 6-40(50)GHz DP Horn Fmi H304 83050A 2 GHz-50 GHz amplifier Agilent H305 87421A power Supply Agilent E755 N9030B PXA 3 Hz-50 GHz Spectrum Keysight Analyser E759 MX6-10-NH 75-110 GHz x6 Multiplier MMW Group E781 MX4-10-NH 50-75 GHz x4 Multiplier MMW Group E296-5 11970V 50-75 GHz Mixer HP E296-6 11970W 75-110 GHz Mixer HP E503 25240-20 20 dB std. gain horn fmi 50-75 G 0410 2524-20 20 dB std. gain horn fmi 50-75 G E579 27240-20 20 dB std. gain horn fmi 75-110 G 0411 2724-20 20 dB std. gain horn fmi 75-110 G
The test enclosure used for the tests was fabricated by Shielding Solutions Ltd based on design input from RN Electronics Ltd. It was specifically configured for testing the shielding effectiveness of materials at high frequencies (>5 GHz).

Test Method:

[0121] Based on IEEE 299: 2006

Test Standard:

[0122] IEEE 299: 2006

Test Items:

[0123] Gasket samples

Location:

[0124] Test area A

Sample Plan:

[0125] Measure at fixed distance of 30 cm, 25-100 GHz

Test Requirements:

[0126] Measurement of non-woven CNT mat 25-100 GHz [0127] Effectiveness of the material relative to free-space.

[0128] The main objective of the test was to compare and assess the shielding performance of a number of gasket materials at high frequencies. These types of material are typically employed for shielding small scale electronic enclosures and the aim of the test was to evaluate the suitability of each material for use in devices operating at these high frequencies. The materials are listed below (CNT Materials manufactured by TorTech).

MFS-NCRS001 Nickel over copper plated metallised polyester ripstop fabric

C-267-H3B CNT mat 11 gsm

C-279-H3B CNT mat 30 gsm

C-279-H3B o CNT mat 30 gsm

C-302-H2 60 gsm

C-314-H2 PCU 900NM 19 gsm

C-283-H3 36 gsm

[0129] C-283-H3 100% epoxy circle
Optiveil 20444A Cu+Ni coated carbon veil 20 gsm
Aluminium foil 40u 108 gsm (For reference at 25-50 GHz)
Ground aluminium disc 10 mm thick (for reference at 50-100 GHz)

[0130] Each gasket disc was placed centrally over a 40 mm diameter hole in the front face of a test enclosure (see FIG. 38) with the frequency source inside (see FIG. 39). The gasket was held in place by a 50 mm diameter 10 mm thick Tufnell disc. The gasket was compressed using a single toggle clamp that was electrically insulated from the disc. This ensured that the only electrical connection between the disc and the enclosure was provided by the gasket. All of the gasket samples were subject to identical test procedures.

Results

[0131] The results of screening attenuation in dB relative to free-space and accompanying plot for each gasket type measured through a 50 mm round aperture in the test jig/screened box are shown in FIGS. 40-47.

[0132] The CNT materials also showed promise for use as an EMI shielding gasket material evidenced by how well they self-terminated on the aluminium surface of the enclosure aperture.