Applications of polymers and molecular magnets - low frequency electromagnetic shielding and resonators/absorbers

Background

With the rapid advances and broad implementation of computer and telecommunication technologies there is increased interest in shielding of electromagnetic radiation, especially in the radio and microwave frequency ranges. The usual shielding techniques focus on the use of standard metals and their composites, which have disadvantage due to limited mechanical flexibility, heavy weight, corrosion, and difficulty of tuning the shielding efficiency. Conducting polymers are promising materials for shielding electromagnetic radiation and reducing or elimination of electromagnetic interference (EMI) because of their relatively high conductivity and dielectric constant and ease of control of these properties through chemical processing [1].

Together with the conductive polymers one could use polymeric magnets. The inherent low densities and high molecular masses of molecule/polymer-based magnets mean that bulk applications relying on high magnetic moments either on a mass or volume basis are unlikely. In contrast, other uses such as for inductors (for example, as the core material in transformers) that guide magnetic fields and for magnetic shielding of low-frequency magnetic fields are feasible. The high permeability to mass ratio make this class of soft (low coercive fields) magnetic materials potentially attractive for lightweight transformers, generators and/or motors as well as dc and low frequency shielding applications [2].

Recent Advances

Recently we reported the high shielding efficiency (SE) of highly conducting doped polyaniline, polypyrrole, and polyacetylene in comparison with that of copper [1].Very thin conductive polymer samples have high and weakly temperature dependent shielding efficiencies. The easy tuning of intrinsic properties by chemical processing suggests that such polymers, especially polyaniline, are good candidates for low frequency shielding applications.

Also, the potential for our room-temperature V(TCNE)x y(solvent) polymeric magnet in the area of electromagnetic shielding has been established 3]. (V(TCNE)x y(solvent) [4] is magnetic at room temperature, its extrapolated Tc being about 400 K (125 oC), above its decomposition temperature of 350 K.) The V(TCNE)x y(solvent) magnet also has the attributes of low power loss and flexible low-temperature processing -key technological advantages.

Publications

C.Y. Lee. H.G. Song, K.S. Jang, E.J. Oh, A.J. Epstein, and J. Joo, Electromagnetic Interference Shielding Efficiency of Polyaniline Mixtures and Multilayer Films, Synthetic Metals 102, 1346-1349 (1999).

J. Joo, C.Y. Lee, H.G. Song, J.-W. Kim, K.S. Jang, E.J. Oh, and A.J. Epstein, Enhancement of Electromagnetic Interference Shielding Efficiency of Polyaniline Through Mixture and Chemical Doping, Molecular Crystals, Liquid Crystals 316, 367-370 (1998).

J. Joo, E-J Oh, and A.J. Epstein, Electromagnetic Interference Shielding Capability of Conducting Polymers in Far-Field and Near-Field Regions, Molecular Electronics & Devices, 107-118 (1995).

R.S. Kohlman, Y.G. Min, A.G. MacDiarmid and A.J. Epstein, Tunability of High Frequency Shielding in Electronic Polymers,  Proc. Soc. of Plastics Engineers Annual Technical Conference (ANTEC 1996), 1412-1416, Indianapolis, IN 5-9 May 1996.

J. Joo, A.G. MacDiarmid and A.J. Epstein, Control of Dielectric Response of Polyanilines:  Applications to EMI Shielding, Proc. Annual Technical Conference of Soc. of Plastics Engineers 2, 1672-1677, Boston, MA  7-11 May 1995.

J. Joo and A.J. Epstein, EMI Shielding Capability of Intrinsically Conducting Polymers,  Proc. Conference on Plastics for Portable Electronics, Las Vegas, NV, 5-6 January 1995, 140-149 (1995).

Created by Darren Gebler and Mihai Girtu. Maintained by John Rohrbacher. Last updated 5/23/00.