ELECTROMAGNETIC WAVES ABSORBING MATERIAL

Abstract

The present invention relates to an electromagnetic millimetre wave absorber material, preferably having a volume resistivity of more than 1 Ω cm, containing solid particles having an aspect ratio (length:diameter) of at least 5 of a first electrically conductive material, particles having an aspect ratio (length:diameter) of less than 5 of a second electrically conductive material and an electrically non-conductive polymer, wherein the absorber material is capable of absorbing electromagnetic waves in a frequency region of 60 GHz or more. The invention also relates to its use and method for absorbing as well as a sensor apparatus comprising said absorber material.

Claims

1. An electromagnetic millimetre wave absorber material containing solid particles having an aspect ratio (length:diameter) of at least 5 of a first electrically conductive material, particles having an aspect ratio (length:diameter) of less than 5 of a second electrically conductive material and an electrically non-conductive polymer, wherein the absorber material is capable of absorbing electromagnetic waves in a frequency region of 60 GHz or more.

2. The absorber material of claim 1, wherein the solid particles having an aspect ratio (length:diameter) of at least 5 of the first electrically conductive material are solid fibre particles having an acicular or cylindrical shape or a turned chip like shape.

3. The absorber material of claim 1, wherein the particles having an aspect ratio (length:diameter) of less than 5 of a second electrically conductive material are non-fibrous particles having a spherical or lamellar shape.

4. The absorber material of claim 1, wherein the electrically non-conductive polymer is a thermoplast, a thermoplastic elastomer, a thermoset, or a vitrimer.

5. The absorber material of claim 1, wherein the particles of the first and second electrically conductive material are homogenously distributed in the absorber material.

6. The absorber material of claim 1, wherein the absorber material is subject to injection molding, thermoforming, compression molding, or 3D printing.

7. The absorber material of claim 1, wherein an amount of the particles of the first and second electrically conductive material is from 0.05 wt.-% to 24.95 wt.-% based on the total amount of the absorber material.

8. The absorber material of claim 1, wherein an amount of the particles of the second electrically conductive material is from 0.05 wt.-% to 15 wt.-% based on the total amount of the absorber material.

9. The absorber material of claim 1, wherein the first or the second or the first and the second electrically conductive material are carbon or a metal.

10. The absorber material of claim 9, wherein the metal is zinc, nickel, copper, tin, cobalt, manganese, iron, magnesium, lead, chromium, bismuth, silver, gold, aluminum, titanium, palladium, platinum, tantalum, or an alloy thereof.

11. The absorber material of claim 1, wherein the first and the second electrically conductive material is the same.

12. The absorber material of claim 1, wherein at least one of the following prerequisites is fulfilled: the first and the second electrically conductive material is carbon; the first electrically conductive material is iron or steel and the second conductive material is carbon; the particles of the second electrically conductive material are carbon black; the iron or iron alloy material is stainless steel; the particles of the first electrically conductive material have a length of from 0.01 to 100 mm; the particles of the first electrically conductive material have a diameter of from 0.1 μm to 100 μm.

13. The absorber material of claim 1, wherein the absorber material additionally contains one or more additives.

14. An electronic device containing a radar absorber in form of a radar absorber part or a radar absorbing housing, the radar absorber comprising at least an absorber material of claim 1, wherein the at least one absorber material is comprised in the electronic device in the radar absorber; at least one transmission area, transmissible for electromagnetic millimeter waves in a frequency region of 60 GHz or more; and a sensor capable of detecting and optionally emitting electromagnetic millimeter waves in a frequency region of 60 GHz or more through the transmission area.

15. (canceled)

16. A method of absorbing electromagnetic millimeter waves in a frequency region of 60 GHz or more, the method comprising irradiating an absorber material of claim 1 with electromagnetic millimeter waves in a frequency region of 60 GHz or more.

17. The absorber material of claim 1 having a volume resistivity of more than 1 Ωcm.

Description

[0141] The following examples and FIGURE explain the invention in further details without limiting the invention to these.

[0142] In the FIGURE the following is shown:

[0143] FIG. 1 shows the stainless-steel fibers in example C4

EXAMPLES

Materials

[0144] Poly(butylene terephthalate) (PBT, Ultradur® B2550 NAT and B4500 NAT) were obtained from BASF SE. Carbon fibers (aspect ratio >5) were obtained from Toho Tenax. Black pearls 880 (aspect ratio <5) were obtained from Cabot corporation and special black 4 (aspect ratio <5) was obtained from Orion Engineered Carbon. The stainless-steel fiber (stainless steel 1.4113) with a broad length distribution including particles with aspect ratio >5) was obtained from Deutsche Metallfaserwerk. Glass fibers were obtained from 3B.

Measurement of the Interaction with Electromagnetic Waves

[0145] The experimental setup for the characterization of the absorbers in the range 60-90 GHz is as follows.

[0146] A vectoral network analyzer Keysight N5222A (10 MHz-26.5 GHz), two Keysight T/R mm head modules N5256AW12, 60-90 GHz and as a sample holder a swisstol2 corrugated waveguide WR12+, 55-90 GHz. The calibration of the corrugated waveguide (cw) is done by doing a thru and short measurement. For the thru measurements the flanges of the cw are connected, for the short measurement, a metal plate is inserted between the flanges. The field distribution of the cw is described in: IEEE Transactions on Microwave Theory and Techniques 58, 11 (2010), 2772.

[0147] After the calibration, the sample (minimum diameter 2 cm) is inserted between the flanges of the cw and the S11 (reflection) and S21 (transmission) parameters are measured in the range 60-90 GHz (amplitude and phase). From the measured S11 and S22 parameters, the absorption A of the sample was calculated as follows: A (%)=100−S11(%)−S21(%).

[0148] From the measured parameters, the dielectric parameters ε′ (dielectric permittivity) and ε″ (dielectric loss factor) of the sample material is calculated at each frequency point using the swissto12 materials measurement software.

Preparation of the Comparative Example C4

[0149] Poly(butylene terephthalate) (PBT, Ultradur® B4500 NAT) was obtained from BASF SE and dried to a water content below 0.04 wt %. The PBT was fed into to extruder (ZE25) with a barrel temperature of 270° C. and an output of 15 kg/h. Steel fibers were added directly in the melt in zone 4 of the extruder to prevent excessive shearing of the fibers. Material was granulated and dried to a water content below 0.04 wt %. The samples for the electromagnetic analysis (60×60×1.5 mm) were injection molded using 260° C. for melt temperature, 60° C. for mold temperature.

[0150] The composition of the examples containing carbon fibers (I1-2) and the comparative example (C0-C3) have been stated in Table 1 (a and b). In Table 2 materials containing metal fibers (I3-4) and comparative examples (C4) are shown.

TABLE-US-00002 TABLE 1a Compositions of the comparative examples with carbon fibers comparative examples C0 C1 C2 C3 PBT resin % 100 79.5 39.5 29.5 (Ultradur B2550 NAT) Glass fiber (average diam. 10 % 20 20 20 μm with epoxysilane sizing) Carbon black batch (20% % 40 50 carbon black Black-Pearls 880-in PBT) Carbon fiber batch (15% % carbon fibers-in PBT) Lubricant (C16-C18 fatty % 0.5 0.5 0.5 esters of pentaerythritol) radar absorption at 77 GHz % 6 8 58 69 for 2 mm thick samples Dielectric permittivity at 2.97 3.35 5.15 6.15 77 GHz tensile E-modulus MPa 2500 7000 7800 8000 tensile strength MPa 57 117 117 116 elongation at break % 35 3.5 2.4 2.0

TABLE-US-00003 TABLE 2b Compositions of the examples with carbon fibers inventive examples I1 I2 PBT resin (Ultradur B2550 NAT) % 38,5 37,5 Glass fiber (average diam. 10μm with % 20 20 epoxysilane sizing) Carbon black batch (20% carbon % 40 40 black Black - Pearls 880 - in PBT) Carbon fiber batch (15% carbon fibers % 1 2 - - in PBT) Lubricant (C16-C18 fatty esters of % 0.5 0.5 pentaerythritol) radar absorption at 77 GHz for 2 mm % 66 73 thick samples Dielectric permittivity at 77 GHz 6,52 7,46 tensile E-modulus MPa 7950 8050 tensile strength MPa 116 116 elongation at break % 2,4 2,4

TABLE-US-00004 TABLE 2 Compositions of the examples and comparative examples containing metal fibers comparative examples Inventive examples C0 C4 I3 I4 PBT resin (Ultradur B4500 NAT) % 99.5 93.5 91.5 89.5 Lubricant (C16-C18 fatty esters of pentaerythritol) % 0.5 0.5 0.5 0.5 carbon black batch (25% carbon black Special black 4 - in PBT) % 2 4 Stainless steel fiber % 6 6 6 Radar absorption at 77 GHz for 1,5 mm samples % 4 78 82 87 Dielectric permittivity at 77 GHz 2,97 4,77 4,40 4,06