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Selective Radio Frequency Shielding


OBJECTIVE: Investigate the feasibility for selective radio frequency (RF) shielding that will have the capability to block unwanted frequencies and pass only select narrow bandwidth frequencies. DESCRIPTION: The Air Force Research Laboratory (AFRL) has made significant contributions to Electronics and Photonics for Air Force Systems. Through both in-house research and a recently completed contractual effort, very effective, composite/polymer-based, non-conductive, high thermal conductivity, radio frequency (RF) and electromagnetic interference (EMI) shielding has been demonstrated.[1,2] Non-conductive, high thermal conductivity, RF/EMI shielding allows microelectronic circuits and sensors to be RF/EMI shielded without electrical shorting by simply coating or spraying the material directly onto the circuit. High thermal conductivity has the potential to remove heat from the circuit, thus, increasing circuit lifetime. Being able to coat the circuit with RF/EMI shielding material also provides shielding between wires within the circuit as well, which becomes more crucial as processing and data rate speeds increase. The material can also potentially be used as a casing for external wires for RF/EMI shielding. Composite materials, such as the polymer-matrices containing conductive fillers developed in AFRL, have proven very attractive for shielding RF/EMI due to their high shielding efficiency and seamlessness, processability, flexibility,light-weight and low-cost. It has been shown that a thin layer of this new composite-based (typically ~30 - 50 m) can block RF/EMI radiations up to 60 dB effectively over an RF frequency range of KHz to tens of GHz, exhibiting excellent RF/EMI shielding effectiveness. A wide selection of metal and graphite nanoparticle/nanopowder fillers have been tested for their performance in RF/EMI shielding effectiveness. Among them, silver and carbon-based nanoparticles/nanopowders have demonstrated the best performance to date and can be easily rendered non-conductive, while preserving effective RF/EMI shielding. The purpose of this effort is to determine if new materials can be developed to be radio frequency selective materials. To possess the capability to effectively block unwanted radio frequencies, while allowing desired radio frequencies to pass, enhancing the capabilities of current Air Force C4ISR systems. The basic idea is to ultimately design ultra-narrow-band RF filters which can be an RF counterpart to optical filters which block out certain wavelengths while allowing others to pass. For mobile platforms, such selective filtering is essential, as certain communication data from sensors, GPS, etc. needs to be transmitted and received, while the entire platform is shielded from RF and cannot be detected. PHASE I: Process candidate selective radio frequency shielding materials for specific C4ISR device/devices and characterize these materials to show their suitability. The demonstrated characteristics of these materials will help determine whether to proceed onto Phase II. PHASE II: Select RF component to fabricate and test RF devices using the selective radio frequency shielding materials developed during Phase I and compare them with any currently implemented devices. Also, continue with materials development by optimizing the selective radio frequency materials developed during Phase I, and/or processing new selective radio frequency materials in order to optimize the performance of the device/devices under development. PHASE III: Integrate RF component fabricated in Phase II onto the selected airborne platform, and conduct field testing to evaluate RF shielding performance. REFERENCES: 1. D. Zang and J. Grote,"DNA-Based Nanoparticle Composite Materials for EMI Shielding", SPIE Proceedings, 8259, DOI: 10.1117/12.905284 (2012). 2. D. Zang,"Biotronic Sensors for Cost, Size, Weight and Power, and Enhanced Bandwidth (C-SWaP-B) - DNA-Based EMI Shielding Materials (DESM)", Air Force Research Laboratory Technical Report, AFRL-RX-WP-TR-2012-XXXX, (2012).
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