The electromagnetic interaction between the antenna and the human head is reduced with metamaterials. Preliminary study of SAR reduction with metamaterials is performed by the finite-difference time-domain method with lossy Drude model. It is found that the specific absorption rate (SAR) in the head can be reduced by placing the metamaterials between the antenna and the head. The antenna performances and radiation pattern with metamaterials are analyzed. A comparative study with other SAR reduction techniques is also provided. The metamaterials can be obtained by arranging split ring resonators (SRRs) periodically. In this research, we design the SRRs operated at 900 and 1800 MHz bands. The design procedure will be described. Numerical results of the SAR values in a muscle cube with the presence of SRRs are shown to validate the effect of SAR reduction. These results can provide helpful information in designing the mobile communication equipments for safety compliance.Index Terms-Metamaterials, lossy drude model, specific absorption rate (SAR), split ring resonators (SRRs).

We present a novel reconfigurable quadri-polarization diversity aperture-coupled patch antenna which can provide four polarization states. By controlling the dc bias voltage of the pin-diodes on the feeding network, we can reconfigure the proposed antenna to provide a pair of orthogonal linear polarizations and a pair of orthogonal circular polarizations. Numerical and experimental results validate our design. This novel antenna provides potential polarization diversity features for wireless local area networks and multiple-input multiple-output systems.

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This paper proposes a compact zeroth-order resonant (ZOR) antenna with improved gain and efficiency. The proposed CRLH unit cell is based on the coplanar waveguide (CPW) structure. The proposed ZOR antenna is designed for a 2.45 GHz frequency band, and it has the characteristic of monopolar radiation. Shunt inductance is implemented by microstrip short-circuit stubs, and a metal-isolator-metal (MIM) capacitator provides series capacitance, where a large capacitance can be achieved in a small footprint. The proposed antenna comprises two interleaving composite right-/lefthanded CRLH unit cells, where the size of one unit cell is measured at only 0.12λ 0 × 0.098λ 0. Because the field is loosely confined within the CPW-based unit cell, a good antenna peak gain of 2.03 dBi, and a radiation efficiency of over 68% is achieved when fabricated on a thin substrate. The proposed antenna did not require an additional matching network, reducing the total antenna footprint. This paper presents antenna parameters such as the return loss, radiation pattern, antenna gain, and radiation efficiency to validate the proposed design, which achieved good simulation results.

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