Erdem Ofli

Effects of Hand Phantom on Mobile Phone Antenna Performance

With the continuous trend to smaller mobile devices with more functionality and more wireless bands, the possible insufficient over-the-air (OTA) becomes a growing concern for service providers. In addition to reduced radiation efficiency by smaller antennas in smaller phones, the head and in particular the hand may further impair radiation performance. The aim of this paper is to investigate the influence of the various parameters of the hand upon the OTA performance criteria to support the standardization process of the hand phantom and to provide the tools for optimization of handheld transmitters. The results reveal the following order of significance for small variations in hand parameters: 1) position of index finger; 2) distance between phone case and palm; 3) position of the other fingers; 4) size of the hand; 5) dielectric parameters; 6) wrist length and tilt. Some configurations may lead to a slight increase of the peak spatial SAR in the head. OTA assessment without the hand does not provide a good measure of phone performance in real life. However, good reproducibility of evaluations requires a precise definition of the hand, in particular its geometry and the phone position within the hand.

Novel E-plane filters and diplexers with elliptic response for millimeter-wave applications

A new class of E-plane filters based on cross-coupled resonators or over-moded cavities is introduced. The filters exhibit pseudoelliptic transfer functions with steep attenuation slopes. The metal inserts and separating wall between waveguide sections can be fabricated using electro-deposition techniques with the accuracy required for millimeter-wave applications. The filters are mass-producible, are much shorter than traditional E-plane filters, and have less insertion loss. Based on this new type of E-plane filter, highly compact diplexer structures are designed. A comparison between prototype filters and design prediction shows excellent agreement.

Influence of the Hand on the Specific Absorption Rate in the Head

The influence of the users hand holding a mobile phone to the ear on the peak spatial-average Specific Absorption Rate (psSAR) averaged over any 1 g and 10 g of tissue in the head is investigated. This study is motivated by recent reports that found substantial increases in psSAR by the presence of the hand in some cases. Current measurement standards prescribe the measurement of SAR in a head phantom without a hand present. The mechanisms of interaction between the hand and mobile phone models are studied. Simulations and measurements at 900 and 1800 MHz have been conducted to complement the understanding of the hand grip parameters leading to higher SAR in the head. Numerical simulations were conducted on four mobile phone models, and parameters such as the palm-phone distance and hand position were varied. Measurements of 46 commercial mobile phones were made, and the maximum psSAR with different hand positions and palm-phone distances was recorded. Both simulations and measurements have found increases in the psSAR in the head of at least 2.5 dB due to the presence of the hand. Furthermore, the psSAR is sensitive to the hand grip, i.e., the variations can exceed 3 dB.

Effects of hand phantom and different use patterns on mobile phone antenna radiation performance

The effects of hand phantom on mobile phone antenna performance were investigated in this paper. The studied parameters of hand phantom include homogeneity of hand phantom, dielectric properties of hand phantom material, hand and wrist size, and different use patterns. The study confirms that positioning of the mobile phone in the hand phantom is the largest hand-related uncertainty component for OTA performance testing.

User's hand effect on the Specific Absorption Rate in the head

This study is an investigation of the influence of the users hand on the radiated performance of a mobile phone, particularly the peak spatial averaged Specific Absorption Rate (psSAR) averaged over 1 g and 10 g in the head of the user. Recent studies found that the psSAR in the head can be increased by the presence of the hand in some cases. In this study, simulations are performed at 900 and 1800 MHz on different mobile phone models, and the psSAR in the head is recorded with and without a hand holding the mobile phone. Numerical simulations were conducted on four mobile phone models, and hand models were posed in different locations and grips to find the condition with the highest psSAR. Simulations show that the psSAR with the hand can be up to about 2.5 dB higher than without the hand. The psSAR is sensitive to the hand grip, with more than 3 dB variation possible, depending on the hand location and palm distance.

SAr and efficiency performance of mobile phone antenna with different user hand positions

The effects of hand positions on the mobile phone antenna performance in terms of OTA parameters and peak spatial SAR were studied with a commercial mobile phone model. Different hand positions cause significant change in both OTA performance and SAR values. It was also found that the hand phantom may have positive effect on the mobile phone antenna performance at GSM band. However, higher SAR value is obtained compared to that without hand in DCS band. The OTA performance of mobile phones can be strongly impaired by the hand and therefore tests without the hand will not provide meaningful assessments of the performance under real-life conditions. However, the hand geometry as well as the exact position of the phone inside the hand must be very precisely defined in order to obtain highly reproducible results in future OTA measurements.

Analysis of the hand effect on head SAR with generic and CAD phone models using FDTD

The assessment methodology and procedures of the peak-spatial SAR in the head are defined in IEEE 1528 [1]. In the current version of the standard, the users hand is not included for obtaining conservative SAR results. However, recent studies have demonstrated that the hand can increase the SAR in the head in some cases [2]. In other words, the SAR measurement without considering the effect of the users hand may not always be the most conservative estimation. It is a great challenge to study the effect of the hand in terms of SAR, since mobile phones and the hand have very complicated geometries and are in the reactive near-field of the antenna. The objective of this paper is to conduct a multi-variable study of the effect of the hand on the SAR in the head with generic phone models and generic hand and head phantoms.

Mechanisms of RF Electromagnetic Field Absorption in Human Hands and Fingers

The absorption of electromagnetic fields in the hand is investigated over the 900-3700-MHz frequency range. This enables the determination of the envelope of the peak spatial specific absorption rate in the hand. It also provides a basis for deriving measurement procedures for evaluating compliance of wireless devices with specific absorption rate limits in the hands. Both plane waves and dipole antennas are used to investigate the patterns of RF absorption in hand and finger tissue models for far- and near-field exposures. The results demonstrate that absorption enhancements are found in the hand that are not present in a standardized flat phantom. Enhancements of several decibels are observed, depending on the model parameters. A method to conservatively estimate the exposure in the hand based on flat phantom measurements is proposed.

A Novel Approach for Mobile Device Design: GA-Based Distributed Optimization to Comply with OTA, SAR, and HAC Standards

The objective of this study was to investigate the cost and time effectiveness of virtual prototyping when applied to the optimization of antenna system design for mobile phones, compared to traditional development approaches. For the proposed evaluation, an enhanced commercial FDTD-based electromagnetic simulation platform, powered with GPU hardware acceleration and distributed network parallelization, was applied. Advanced genetic algorithms (GAs) were used to obtain robust antenna designs, targeting a multi-goal optimum within a minimum number of simulations. Various antenna structures, including folded monopoles, planar-inverted F, and folded-inverted-conformal antennas were considered. An optimized structure was developed in less than 24 hours, indicating the superiority of virtual prototyping over traditional design and optimization procedures for reducing costs, improving quality, and, particularly, in reducing development time.

Hand phantom models for the assessment of SAR in the head from cellular telephones

A methodology for assessing the SAR in the head in the presence of the hand has been developed and investigated. A standardized hand phantom, developed for radiated power and receiver performance, has been adopted for SAR measurements. The results indicate that the inclusion of the hand phantom increases the measurement uncertainty, but within reasonable limits.