EMC-Compatible Shielding

This book is aimed at engineers, scientists, students, researchers and practical professionals. Electromagnetic compatibility (EMC) has been developing since its beginnings in the 1950s to 1960s as a result of the pulse problems in automation/control engineering.

In the research and development (R&D) of novel RF materials for housing technology and in materials development, the description of the manifold resistive, dielectric and magnetic material properties is of interest [43]. The aim of this R&D project is to improve the EMC properties of packages. An increased shielding loss with simultaneous smoothing of the internal field amplifier resonances is to be achieved. Electronics should function safely in metal housings without internal field excesses. For this purpose, new RF ferrite materials are to be developed. The focus of this research project is on the exact formulation of the interaction of EMC interference energy with the ferrite material, the development of an RF ferrite material and the testing of the EMC properties of the RF materials and the new types of housings.

The aim of this work is the deposition of thin ferritic layers as absorber material for EMC applications [43]. Initially, the work concentrates on NiZn ferrite layers. Fundamental investigations on the suitability of ferrite layers were realized.

For radar materials starting in the X- or Ku-band (new designation H-, I-, J-band), further effects have to be considered. In addition to the EMC effects discussed so far, the radar effects of linear and non-linear extinction must be considered integrally.

The test setup in Fig. 5.1 has a total dynamic range of 50 dB. This high sensitivity was realized by two preamplifiers.

A distinction is made between near-field and far-field shield attenuation. The shielding attenuation also differs according to the type of field: electrostatic shielding, magnetostatic shielding, alternating electric field shielding, alternating magnetic field shielding and electromagnetic wave field attenuation [46]. A shielding wall consists of two interfaces. The electromagnetic wave field is reflected at interface 1 (outer surface of a shielding wall). The radiation passing through this interface is partially absorbed and reflected at interface 2. The reflected part of the wave is now absorbed again and partly reflected at the interface 1. Thus, only a part of the source radiation enters the interior of the housing and is further reflected.

By combining conductive polymers with one or more suitable ferroelectric and ferromagnetic materials, synergy effects of the two groups of materials can be expected through additional absorption mechanisms. When choosing the ferroelectric, it should be noted that the greatest dielectric loss is to be expected near the Curie temperature. Suitable mixtures of ferroelectrics with different Curie temperatures must therefore be investigated. In addition to the composition of the ferroelectric, the dependence of shielding effectiveness and dielectric losses on such influencing variables as grain size, size of the ferroelectric domains, textures, etc. must be investigated. Furthermore, the interactions between the conductive particles in the polymer and the ferroelectric particles regarding the absorption of high-frequency electromagnetic fields are to be investigated theoretically and experimentally from the point of view of material physics. The possibilities of further synergy effects through ferromagnetic materials are to be considered in the work.

Metal housings of amplifier circuits can, depending on the geometry and design of the circuit, favour the emergence of higher modes inside the housing. This can cause undesirable natural vibrations (oscillations) in the amplifier at higher frequencies and thus considerably worsen the noise characteristics in the useful frequency range.

New housing materials will be modelled, synthesised and analysed. The aim of these new housings is to improve shielding effectiveness and smooth the internal RF field strengths if electronics with RF sources are present in the housing systems.

In the following chapter, the application of the newly developed nanoferrite layer as an absorbing intermediate layer on a test PCB structure is discussed. A simple strip resonator couples out higher frequency harmonics, which are generated by a simple oscillator component (Figs. 10.1 and 10.2).

Experiments on the effectiveness of a laboratory storage of ferrite particles (grain size D₅₀ = 50 μm) have shown a well measurable absorption effect of 4 dB.

There should not be complete surfaces as shielding surfaces. The mesh wire as a damping fabric should be considered as a transparent window in a housing wall. Through such a wire mesh, a display shall be viewed and the interfering harmonics shall be damped.

For the new EMC problems of information technology, electronics, control engineering and industrial electronics, there are no effectively usable EMC suppression ferrite materials on the market. Metals have clear disadvantages in terms of resonances, i.e. shielding loss.

References: [56, 63].