Radio-frequency Absorber Research Articles

Case Report of a Fire Accident When Using a Radiofrequency Absorber (Accusorb MRI) during an MRI Examination

Case Report of a Fire Accident When Using a Radiofrequency Absorber (Accusorb MRI) during an MRI Examination

A Study on Design and Microwave Characteristics of a RF/IR Multispectral Absorber

In this paper, a design for a radio frequency(RF) and infrared(IR) absorber with metasurfaces is discussed in microwave frequency bands. The RF absorber includes double layers of metasurfaces to operate in S- and X-bands. Effects of sheet resistance of the metasurfaces and thicknesses of dielectric supporting layers on reflection responses are investigated. An IR stealth layer incorporates an array of conductive grids with slits to reflect IR signals but to transmit RF signals and visible rays. Periodicity of the grids and slits is studied for transmission responses in the X-band and a surface area ratio. Reflection responses of the RF/IR multispectral absorber are found to be lower than -10 dB and -16 dB in the S- and X-bands, respectively, from full-wave simulation. Finally, the RF/IR multispectral absorber is fabricated and its reflection responses are measured to verify designed performance.

Resonant cavity method based on RF measurement and simulation for measuring complex permittivity or permeability of RF absorbing materials

Accurate measurement of complex permittivity and/or permeability of radio-frequency (RF) absorbing materials is essential to predict the performances of higher-order-mode damping in damped accelerating cavities or in vacuum chambers. We propose an improved resonant cavity method that can be used as a complement to the widely used Nicolson–Ross–Weir method for measuring the RF characteristics of materials. The conventional resonant cavity method is based on the cavity perturbation theory. However, the measurements are inaccurate when losses in the materials are large. The improved method we propose determines the complex permittivity or permeability of materials from the measured resonant frequencies and Q factors based on eigenmode simulations. Because the reliability on the eigenmode calculation for RF cavities with lossy materials has become sufficiently reliable, determination of complex permittivity and permeability can be achieved using such a simulation software. We demonstrate this method using ferrite HF70 (TDK Corp.), which is useful for RF absorbers in damped accelerating cavities or in vacuum chambers.

A Switchable Metamaterial Absorber for Fine-Tuning of the Coherence Bandwidth in a Reverberation Chamber

Since wireless communication technology has been widely applied in our daily lives, wireless devices exhibit explosive growth. A reliable, efficient, and repeatable over-the-air (OTA) testing method is vital for the research and development of wireless devices. Due to the particular advantages of the reverberation chamber ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> ), it has become a popular facility to perform OTA tests nowadays. In the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> -based OTA tests, loading the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> with radio frequency (RF) absorbers is a standardized procedure to control the frequency selectivity of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> channel according to the cellular telecommunications industry association (CTIA). However, this procedure involves iterative manual calibrations and, therefore, is tedious and time-consuming. Moreover, it may be difficult to tune the coherence bandwidth (CBW) to a desired value accurately given fixed RF absorbers. In this work, a locally switchable metamaterial absorber (MA) is proposed for fine-tuning of the CBW of the channel in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> . It is experimentally verified that the CBW can be easily controlled by switching on and off of the absorbing/reflection units of the MA. The proposed MA can provide fine-tuning of the CBW in an efficient and convenient manner.

Beam Splitting Planar Inverted F Antenna For 5G Communication

A planar inverted-F antenna with symmetrical split beams and loaded with radio frequency absorbers (here Eccosorb MCS) for 5G communication is proposed. The multi-beam antennas reduce the requirement of number of antennas and provide wide coverage. But they require a complex system such as a phased array or MIMO antennas. On the other hand, multi-beam antennas do not have such requirements. In this work, we propose a PIFA antenna which achieves multi-beam behaviour by six slabs of absorbers placed periodically between the PIFA patch and substrate to split the beams into two directions at +26°. The proposed antenna obtains a frequency band of 24.2- 25.7 GHz and achieves a high gain of approximately 10 dB at +26°. The performance of the proposed antenna is suitable for G communication. All simulations of the antenna are carried out using Ansys HFSS. The design was validated by simulations and later confirmed with measurements.&#x0D;

Validation of a Method for Predicting Anechoic Chamber Performance: A Technique That Uses Polynomial Approximations for RF Absorber Reflectivity

Indoor antenna ranges must have the walls, floor, and ceiling treated with a radio-frequency (RF) absorber. The normal incidence performance of the absorber is usually provided by the manufacturer of the material—but the bistatic or off angle performance must also be known. Recently, a polynomial approximation was introduce.

Low-Frequency Model for Radio-Frequency Absorbers.

A simple model is developed to characterize the behavior of radio-frequency absorbers at low frequency. The absorber is represented by a flat, homogeneous, isotropic slab of lossy material, with effective constitutive parameters. These parameters are determined by a fit to measured data. Excellent fits are obtained in the two applications considered. The model is intended for use in the characterization of absorber-lined chambers at low frequency. It could also be used to predict the low-frequency performance of partially loaded shielded enclosures.