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Materials for Shielding Microwave Radiations

Polymer based shielding materials that can block electromagnetic radiations have been developed at IISc. 

Developed in the Materials Engineering Department at IISc, these materials are “composites” – materials made from two or more components with very different properties. “Polymer based composites are promising materials for shielding electromagnetic radiation because of suitable properties, which can be easily controlled by using different manufacturing methods”, says the author Suryasarathi Bose.

Shielding means not allowing electromagnetic waves to pass through. Electrical waves are blocked when the shield is made of a material having high conductivity. Magnetic waves, on the other hand, are blocked only by absorption.

The main composite used in this study is a combination of poly(vinylidene fluoride), an insulating polymer and carbon nanotubes, which can conduct electricity (called PVDF/CNT composites). The shielding effectiveness of neat PVDF is extremely low because it is insulating in nature. Addition of CNT improves conductivity and thus the shielding effectiveness. Shielding effectiveness in fact increases with increased percentage of CNT in the composites. PVDF with 3 wt% CNT gives shielding effectiveness of 31dB.

To this primary composite, the researchers added two different materials. One was a combination of nanoparticles of graphene oxide and barium titanate, to get the material PVDF/CNT/BT-GO composites. These materials increased the “dielectric constant”, or the ability to store charge. This increased the ability of the material to attenuate electromagnetic radiation. Another material added was cobalt nanowires which was synthesized in Dr. Chandan Srivastava’s laboratory, with magnetic properties which resulted in PVDF/CNT/CoNW: a material with high “permeability”, the ability to support formation of a magnetic field.

The shielding effectiveness of PVDF/CNT/BT-GO is better than that of PVDF/CNT. However, PVDF/CNT/CoNW has the best shielding effectiveness value of 35dB.

Nascent PVDF is a thermal insulator, and prevents heat transfer. But the composites PVDF/CNT/BT-GO and PVDF/CNT/CoNW showed good thermal conductivity. This is desirable because components inside the electronic devices generate heat that needs to be dissipated efficiently to keep the components working reliably.

The researchers also observed that even though very less amount of nanoparticles were used, the materials had a very high shielding effectiveness. In earlier studies, higher concentration of nanoparticles was needed to generate materials with high shielding effectiveness.

“Polymer based composites are easy to fabricate, process, modify etc in comparison to the conventional shielding materials like metallic/graphite sheets. Furthermore, the process we employed for designing the composites is an industrially viable technique. These materials are lightweight, flexible and cost-effective which make them promising in the near future” said Suryasarathi Bose.

These materials specifically shield microwave radiations. Apart from the near-ubiquitous microwave ovens we all use for heating, microwaves are also used in radars, in radio astronomy, wireless LAN networks and some mobile phone networks. A lightweight, cost effective and efficient shield will be very useful indeed.

About the authors

Maya Sharma and Mahander Pratap Singh are students in Materials Engineering Department, Indian Institute of Science, Bangalore. Suryasarathi Bose is an Assistant Professor in Materials Engineering Department, Indian Institute of Science, Bangalore. Chandan Srivastava is an Assistant Professor in Materials Engineering Department, Indian Institute of Science, Bangalore. Giridhar Madras is a Professor in Department of Chemical Engineering, Indian Institute of Science, Bangalore.

Contact: Suryasarathi Bose https://sites.google.com/site/polymerprocessinggroup/

Tel: +91-80-22933407 Fax: +91-80-23600472
Email: sbose@materials.iisc.ernet.in

The paper appeared online in the journal of ACS Applied Materials and Interfaces, published by the American Chemical Society.