This paper proposes a new mobile handset antenna structure to reduce the value of the speciflc absorption rate (SAR). The antenna is based on the PIFA structure and operates at dual-bands of 0.9GHz and 1.8GHz. The chassis current is reduced using a metallic shim-layer inserted between the patch and chassis. This shim-layer is connected to the handset chassis through posts whose number and positions are determined using optimization techniques. Sidewalls are attached to increase the gain of the antenna and reduce the radiation towards human head. Simulations in the cheek mode show that the SAR reduction factor (SRF) of the proposed structure averaged over 10-g is more than 75% at 0.9GHz and 46% at 1.8GHz. The SRF values obtained using simulations and measurements are found to be better than 51% and 76% at 0.9GHz and 1.8GHz, respectively.

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A New Low SAR Antenna Structure for Wireless Handset Applications

This paper reviews the different methods employed in the last years for the development of low specific absorption rate (SAR) antennas inside portable terminals of mobile phone systems. Specifically, auxiliary antenna elements, ferrite loading, EBG/AMC surfaces and metamaterials techniques will be examined. From the recent information about the possible health effects of electromagnetic radiation on humans, it is apparent that the SAR reduction techniques have to be improved in order to create practical implementations that allow an extensive use of low SAR mobile phone terminals. Satisfying the bandwidth, efficiency, size and cost requirements of a low SAR solution for the new mobile terminals has not been completely possible so far. Each low SAR technique has limitations and that prevents an extensive use in the mobile terminals available in the market. From the methods reviewed the EBG and metamaterial techniques appear as feasible low SAR options that need more study to improve the size and bandwidth parameters that limits their use.

State of the art methods for low SAR antenna implementation

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Risto Valkonen Name of the doctoral dissertation Impedance matching and tuning of non-resonant mobile terminal antennas Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 40/2013 Field of research Radio Engineering Manuscript submitted 25 October 2012 Date of the defence 15 March 2013 Permission to publish granted (date) 8 January 2013 Language English Monograph Article dissertation (summary + original articles)

Impedance matching and tuning of non-resonant mobile terminal antennas

In this paper, we consider energy detection based spectrum sensing for narrowband signals in a wideband cognitive radio system using OFDM. The effect of fast Fourier transform (FFT) size on detecting narrowband signals is analyzed, and appropriate FFT size is suggested to improve the probability of detection. In order to reduce complexity, an improved spectrum sensing scheme is proposed to improve the detection probability without increasing the implementation complexity. Simulations are performed to verify the presented schemes.

Energy detection of narrowband signals in cognitive radio systems

A method to reduce the specific absorption rate(SAR) of the antenna for WiMAX mobile communication is proposed in this paper. The SAR reduction is achieved by miniaturizing the physical size of the antenna for the given resonance frequency by devising a metamaterial-composite right- and left-handed(CRLH) configuration-based radiator much smaller than the quarter-guided wavelength adopted a lot in the conventional planar inverted F antenna(PIFA) or modified monopole antenna. The proposed antenna is placed near the head-phantom and its SAR is evaluated by the full-wave simulations(SEMCAD X), where the metamaterial-inspired antenna is shown to have the lower value than a modified monopole as the reference in terms of the SAR.

A Metamaterial-Based Handset Antenna with the SAR Reduction

In order to reduce the spatial peak specific absorption rate (SAR) in a human head due to a portable telephone, we have proposed attaching a ferrite sheet to the portable telephone. In this paper, the mechanism of SAR reduction is reviewed and then the effects of the attachment location and size, and the material properties of ferrite sheet on the SAR reduction are investigated by using the finite-difference time-domain (FDTD) method in conjunction with a detailed human head model. Their effects on the antenna radiation efficiency are also given. The results lead to a guide to choosing and designing a ferrite sheet with the maximum SAR reducing effect for portable telephones.

T. Takagi

Papers

Effects of ferrite sheet attachment to portable telephone in reducing electromagnetic absorption in human head