WO2002013311A1

WO2002013311A1 - Electromagnetic absorber material, method for the production thereof and method for the production of shielding devices thereof

Info

Publication number: WO2002013311A1
Application number: PCT/EP2001/009154
Authority: WO
Inventors: Josef Kuchler; Jan-Thomas KÜHNERT; Klaus Kupfer; Stefan Rossmayer; Wolfgang SCHÖPS; Hans-Werner Zier
Original assignee: Hermsdorfer Institut Für Technische Karamik E.V.; Colfirmit Rajasil Gmbh & Co. Kg
Priority date: 2000-08-10
Filing date: 2001-08-08
Publication date: 2002-02-14
Also published as: CZ20021624A3; EP1307944A1; PL353917A1

Abstract

The invention relates to a method for effectively decreasing electromagnetic radiation by means of active absorbing material in a broad frequency band, preferably from 100 MHz - 10 GHz, wherein said material combines the desired shielding properties with the heat insulating properties of a porous material in addition to providing a favourable ratio between density and resistance. The inventive method is characterised by an absorber granulate which consists of a highly porous glass and/or ceramic granulate which is coated or filled with ferrite and/or an electrically conductive material.

Description

ELECTROMAGNETIC ABSORBER MATERIAL, METHOD FOR THE PRODUCTION THEREOF AND SHIELDING DEVICES

The invention relates to an electromagnetic absorber material, a process for its production and a process for the production of shielding devices, such as absorber walls, absorber linings or absorber housings, including electromagnetic field-free, so-called anechoic measuring chambers, using this absorber material.

The invention is aimed both at creating as field-free conditions as possible for carrying out particularly precise and / or particularly sensitive electrical measurements and also at protecting the population and, in particular, the workers in the commercial use of alternating electromagnetic fields from possible harmful effects thereof.

From the discussion about the term "electrosmog", the sensitization of the population to the technically induced enrichment of the natural environment with electromagnetic radiation can be seen. Both the legislature and the professional associations have reacted by issuing or tightening limit values for the maximum power density of a radiation source. Examples include the 26th BImSchV (Ordinance on Electromagnetic Fields) and the regulation DIN VDE 0848 (Safety in Electromagnetic Fields). The limit values set for the protection of the population in the 26th BImSchV are based on international recommendations, such as those of the International Commission for Protection against Non-Ionizing Radiation (ICNIRP) or the World Health Organization (WHO). These recommendations are revised again and again as soon as new scientific results are available. The most recent ICNIRP publication in April 1998 confirmed the values on which the 26th BImSchV is based. Table 1 shows the limit values for high-frequency fields permissible for the general population in accordance with DIN VDE 0848.

Table 1 Limits for the general population

The division into electrical and magnetic field components made in this regulation is due to the considerable effort involved in measuring the specific absorption rate (SAR [W / kg]). The SAR is the globally recognized basic parameter for thermal effects, since the radiation power absorbed by the body is decisive for the biological effect of HF radiation.

According to current findings, SAR values of 1 - 4 W / kg (averaged over the whole body) lead to an increase in body temperature of 1 ° C in 30 minutes. A total body SAR limit of 0.4 W / kg was set to protect occupationally exposed persons and a value of 0.08 W / kg for the general population.

The problem with these limit values or precautionary values is that the decree alone suggests a hazard to the population or sensitizes them to a long-term effect that may not yet be reliably proven. This is reinforced by the purely technical discussion, i.e. the exclusive reference to the thermal effects. Current or already published studies by WHO, ICNIRP and IEGMP to influence the brain waves, in particular through the use of mobile phones, due to their frequency and modulation, allow the so-called athermal effects to come to the fore. For this reason and in anticipation of positive results from studies currently taking place in the sense of influencing the human body, the development of an absorber granulate to protect the resident population is imperative. For the absorption of electromagnetic waves, mainly ferrites and / or conductive substances are available in different mixtures and matrices. For example, Ferrite Domen Co. in Russia offers various ferrites as microwave absorbers in powder form, which have a useful frequency of 1 to max. Have 40 GHz. The company Spectro Dynamic Systems in the USA sells silver-coated cenospheres for HF absorption, which are to be used as fillers for paints and resin systems for the production of surface coatings. In one exemplary embodiment, the damping power is specified as 60 dB from 100 MHz -10 GHz for a film of 5 mm thickness. The TDK company offers a range of radio wave absorbers with a reflection attenuation greater than 20 dB, covering the entire range from 0.03 to 40 GHz. Another absorber is sold by Emerson & Cuming Microwave Products, Inc. under the name ECCOSORB®MCS for the frequency range 1 to 8 GHz with an attenuation of 6 - 63 dB / cm.

The published patent application DE 199 49 631 A1 describes a composite absorber for electromagnetic waves, a ferrite powder with a dielectric constant not higher than 4.9 being dispersed in a conventional resin, shaped as a pyramid-shaped absorber and connected to a ferrite plate. The composition of the ferrite plate with the main components Fe ₂ θ ₃ , NiO, ZnO and CuO as well as the resin-bound, pyramid-shaped absorber with the main components Fe ₂ θ ₃ , NiO and ZnO is given. The attenuation to be achieved is specified in the frequency range from 100 MHz to 10 GHz with at least 20 dB.

In the published patent application DE 195 25 636 AI, a wall covering for the absorption of electromagnetic waves is described, which enables broadband reflection through the composite of a ferrite plate with a resistance material facing the wall. No measured values for the reflection attenuation achieved are mentioned.

US Pat. No. 5,323,160 describes the production of an absorber by combining two soft ferrites (Mn-Zn, Ni-Zn) with a varying layer thickness. In any case, these layers are applied to a metal as a carrier. The measured values result in an attenuation of at least 20 dB in the range from 200 MHz to 1 GHz. A broadband absorber is named in US Pat. No. 5,446,459, which consists of a sintered ferrite and a CuO-Fe ₂ θ ₃ spinel ferrite. An absorption is measured using the HP 8510 A network analyzer using a coaxial measuring line. Frequency ranges with an attenuation greater than 20 dB are specified for different compositions. These are between min. 98 MHz and max. 950 MHz.

The published patent application EP 0 858 982 AI describes a composition for an absorber and its production method. It is a mixture of Fe ₂ 0 ₃ , NiO, ZnO and CuO, which is ground, shaped and sintered. The absorption rate is measured using the Holaday HI-400 RF measuring system at different distances from a mobile phone. Absorption rates are given in percent.

The published patent application DE 199 11 304 AI describes a paint or film for electromagnetic shielding in a wide frequency range. For this purpose, a ferrite powder is mixed with a conductive powder and processed into foils or paints with the aid of a spreadable binder. The measured attenuation values are given as> 30 dB / mm.

The state of the art described above suffers from the defect that only the aspect of electromagnetic shielding is taken into account, in part using complex methods and expensive materials, regardless of the applicability of these technologies in construction.

The invention has for its object to effectively reduce the electromagnetic radiation by means of an absorber material in a broad frequency band, preferably from 100 MHz to 10 GHz, this material having the desired shielding properties with the thermal insulation properties of a porous material and with its favorable ratio between density and Combine strength.

This object is achieved by the invention described in the claims.

The advantages of the invention are demonstrated by the subsequent comparison of the characteristic values of the mortar Ml (conventional compact mortar) and M2 (with a nem conventional lightweight aggregate in the form of expanded glass granulate without an electromagnetic shielding effect (filled mortar) with the characteristic values of the mortars M3.1, M3.2, M3.2 (coated expanded glass granulate) and M4 (filled expanded glass granulate) produced according to the invention

The invention is described in more detail below using various exemplary embodiments:

First 4 exemplary embodiments for producing a coated expanded glass granulate according to claim 1 are listed:

The expanded glass granulate used is characterized by a porosity of approximately 82% and a density of approximately 430 kg / m.

example 1

2.5 l expanded glass granulate with a grain size of 0.25 mm ... 0.50 mm or a grain size of 0.5 mm ... 1.0 mm were placed in each case. The suspension for coating consisted of 1500 g ferrite powder, 375 g binder solution and 1350 g water. This suspension was sprayed onto the granules in the fluidized bed using a two-component nozzle. The granules obtained were then treated to solidify the binder at 200 ° C. for 16 hours.

Example 2

2.5 l expanded glass granulate with a grain size of 0.25 mm ... 0.50 mm or a grain size of 0.5 mm ... 1.0 mm were placed in each case. The suspension for coating consisted of 1085 g ferrite powder, 315 g graphite, 375 g binder solution and 1300 g water. This suspension was sprayed onto the granules in the fluidized bed using a two-component nozzle. The granules obtained were then treated to solidify the binder at 200 ° C. for 16 hours.

Example 3

In each case, 2 l expanded glass granulate with a grain size of 0.25 mm ... 0.50 mm or a grain size of 0.5 mm ... 1.0 mm were placed on the plate of a plate granulator TP 10 from Eirich. A mixture of 600 g of carbon powder and 400 g of ferrite powder was premixed with an MTI mixer and alternated with the surface moistening of the granules with about 600 g of binder solution applied to the granules. The granules obtained were then treated to solidify the binder at 200 ° C. for 16 hours.

Example 4

In each case, 2 l of expanded glass granules with a grain size of 0.25 mm ... 0.50 mm or a grain size of 0.5 mm ... 1.0 mm were placed on the plate. 1000 g of carbon powder was applied to the granules alternating with the surface moistening of the granules with the binder solution. The granules obtained were then treated to solidify the binder at 200 ° C. for 16 hours.

In the following, further exemplary embodiments 5 to 7 for producing a filled expanded glass granulate according to claim 2 are listed.

Table 2 Starting mixtures for the production of filled expanded glass granules (in parts by mass):

These mixtures were granulated with a binder and blowing agent, dried and expanded at a temperature higher than the softening temperature of the glass used.

In comparison to the bulk density of the quartz sand used with 1200 - 1500 kg / m ³ , the following bulk densities result as an example:

Table 3 Bulk densities of the filled expanded glass granules (in kg / m ³ )

To test the effectiveness of the invention according to claims 1 and 2 and the subordinate claims, four mortar offsets were produced.

Ml: Mortar with quartz sand up to 1 mm as a dense aggregate (designated in the following composition table with [1])

M2: compared to Ml mortar, the quartz sand fraction 0.25 mm ... 0.50 mm is replaced by the same volume of uncoated expanded glass granulate and the same grain fraction (as characterized above) (designated in the composition table below with [2])

M3.1: analogous to M2, but with expanded glass granules coated with Mn-Zn ferrite according to Example 1 (designated in the following composition table with [3])

M3.2: analogous to M2, but with both Mn-Zn ferrite and

Carbon according to Example 3 coated expanded glass granules (designated in the following composition table with [4]).

M3.3: analogous to M2, but with expanded glass granules coated with carbon according to Example 4 (designated [5] in the composition table below).

M4: analogous to M2, but with expanded glass granulate filled with carbon and ferrite according to Example 5 (designated [6] in the composition table below). Table 4 Composition of the mortar (data in g)

Surcharge types: [1] quartz sands,

[2] expanded glass,

[3] coated expanded glass according to Example 1,

[4] coated expanded glass according to Example 3,

[5] coated expanded glass according to Example 4,

[6] filled expanded glass according to Example 5.

The measurements were carried out with the help of an HP 8510 A network analyzer and a 16/100 coaxial cable. The shielding attenuation S shown here is made up of the proportions of the absorption A and the reflection R additively.

The representation of the curve of the measurement results of the mortar mixtures can be seen in FIGS. 1 and 2.

Claims

claims

1. Electromagnetic absorber granulate, preferably for a frequency range from 100 MHz to 10 GHz, characterized in that it consists of a highly porous glass and / or ceramic granulate which is coated with ferrite and / or an electrically conductive material.

2. Electromagnetic absorber granulate, preferably for a frequency range from 100 MHz to 10 GHz, characterized in that it consists of a highly porous glass and / or ceramic granulate which is filled with ferrite and / or an electrically conductive material.

3. absorber granules according to claim 1 or 2, characterized in that the electrically conductive material is metal and / or carbon.

4. Coated absorber granules according to claim 1 or 3, characterized in that the granule size between 0.2 and 5 mm and the thickness of the coating with ferrite and / or electrically good conductive material is between 10 microns and 300 microns.

5. Coated absorber granules according to claim 4, characterized in that the thickness of the coating with ferrite and / or highly electrically conductive material is between 100 microns and 300 microns, with the restriction that the thickness of the coating is less than 30% of the diameter of the uncoated granules.

6. Absorber granules according to one of the preceding claims, characterized in that the ferrite is a Mn-Zn, Ni-Zn, a Ba and / or Sr ferrite, an Sc-, Co- or Ti-substituted hexaferrite with a garnet structure ,

7. absorber granules according to one of the preceding claims, characterized by a combination of carbon with a ferrite, preferably a Ni-Zn or Ba ferrite, the mass ratio of carbon to ferrite being greater than 0.225.

8. A method for producing a coated absorber granulate according to claim 1 or a subordinate claim, characterized in that the ferrite and / or the electrically highly conductive material is finely ground and applied with a binder as a suspension on the glass and / or ceramic granulate.

9. The method according to claim 8, characterized in that the suspension is applied to the granules after the fluidized bed, mixed granulation, plate granulation or after the dip coating process.

10. A method for producing a filled absorber granulate according to claim 2 or a subordinate claim, characterized in that a raw granulate is produced from glass powder, a blowing agent, ferrite and / or electrically conductive powder with the addition of a binder, dried and solidified in a thermal process and is inflated.

11. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that it is applied as plaster to masonry with an organic and / or inorganic binder.

12. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that it is used as an organic and / or inorganic binder

Layer is applied to supports and / or plates preferably serving as walls.

13. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that it is processed as a filler in an organic and / or inorganic matrix to give molded parts.

14. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that the processing into molded parts preferably for absorber housings takes place by spraying into a hollow mold.

15. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that the processing is preferably carried out to form absorber linings by extrusion.

16. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that the processing preferably takes place to form absorber linings by rolling.

17. A method for producing shielding devices using the absorber granules according to one of claims 1 to 10, characterized in that the processing is preferably carried out to form absorber linings by film casting.