Analysis of the specific absorption rate in handset antennas with slotted ground planes

The study of the interaction between human head and handset antennas should be taken into account since all the mobile phones have to guarantee a biological compatibility. This research analyzes several antennas with different slotted ground planes in terms of free space and also in terms of human head interaction. The main objective is to compare the measured bandwidth and efficiency in free space and the impact on measured SAR (Specific Absorption Rate) of such antennas as a function of the slot configuration and the antenna/slot location. Results show that slots may be useful to increase bandwidth and efficiency while keeping a similar SAR compared to the non-slotted ground plane. Changing the antenna and the slot location is a good way to achieve a significant SAR reduction.Peer ReviewedPostprint (published version

Balanced antennas for mobile handset applications. Simulation and Measurement of Balanced Antennas for Mobile Handsets, investigating Specific Absorption Rate when operated near the human body, and a Coplanar Waveguide alternative to the Balanced Feed.

The main objectives of this research are to investigate and design low profile antennas for mobile handsets applications using the balanced concept. These antennas are considered to cover a wide range of wireless standards such as: DCS (1710¿1880 MHz), PCS (1850¿1990 MHz), UMTS (1920¿2170 MHz), WLAN (2400¿2500 MHz and 5000 ¿ 5800 MHz) and UWB frequency bands. Various antennas are implemented based on built-in planar dipole with a folded arm structure. The performance of several designed antennas in terms of input return loss, radiation patterns, radiation efficiency and power gain are presented and several remarkable results are obtained. The measurements confirm the theoretical design concept and show reasonable agreement with computations. The stability performance of the proposed antenna is also evaluated by analysing the current distribution on the mobile phone ground plane. The specific absorption rate (SAR) performance of the antenna is also studied experimentally by measuring antenna near field exposure. The measurement results are correlated with the calculated ones. A new dual-band balanced antenna using coplanar waveguide structure is also proposed, discussed and tested; this is intended to eliminate the balanced feed network. The predicted and measured results show good agreement, confirming good impedance bandwidth characteristics and excellent dual-band performance. In addition, a hybrid method to model the human body interaction with a dual band balanced antenna structure covering the 2.4 GHz and 5.2 GHz bands is presented. Results for several test cases of antenna locations on the body are presented and discussed. The near and far fields were incorporated to provide a full understanding of the impact on human tissue. The cumulative distribution function of the radiation efficiency and absorbed power are also evaluated.UK Engineering and Physical Sciences Research Council (EPSRC

Multilayered broadband antenna for compact embedded implantable medical devices: design and characterization

Design and characterization of a multilayered compact implantable broadband antenna for wireless biotelemetry applications is presented in this paper. The main features of this novel design are miniaturized size, structure that allows integration of electronic circuits of the implantable medical device inside the antenna, and enhanced bandwidth that mitigates possible frequency detuning caused by heterogeneity of biological tissues. Using electromagnetic simulations based on the finite-difference timedomain method, the antenna geometry was optimized to operate in the 401-406 MHz Medical Device Radio communications service band. The proposed design was simulated implanted in a muscle tissue cuboid phantom and implanted in the arm, head, and chest of a high-resolution whole-body anatomical numerical model of an adult human male. The antenna was fabricated using low-temperature co-fired ceramic technology. Measurements validated simulation results for the antenna implanted in muscle tissue cuboid phantom. The proposed compact antenna, with dimensions of 14 mm × 16 mm × 2 mm, presented a −10 dB bandwidth of 103 MHz and 92 MHz for simulations and measurements, respectively. The proposed antenna allows integration of electronic circuit up to 10 mm × 10 mm × 0.5 mm. Specific absorption rate distributions, antenna input power, radiation pattern and the transmission channel between the proposed antenna and a half-wavelength dipole were evaluated

Characterization and Enhancement of Antenna System Performance in Compact MIMO Terminals

Co-band multiple-antenna implementation in compact user terminals is necessary for harvesting the full potential of diversity and multiple-input multiple-output (MIMO) technology in cellular communication systems. The recent worldwide deployment of Long Term Evolution (LTE), which requires the use of MIMO technology in the downlink, adds to the urgency of achieving both practical and optimal multiple-antenna systems in user terminals. Contrary to conventional understanding, an optimal multiple-antenna implementation does not only involve the design and placement of antenna elements in the terminals, but extends beyond the antenna elements and common antenna parameters to comprise interactions with the near field user and the propagation environment. Moreover, these interactions are non-static, which implies that the multiple-antenna system must adapt to the prevailing overall communication channel in order to assure the highest performance gains. This doctoral thesis aims to address several key issues in optimal multiple-antenna system design for compact multi-band MIMO terminals, with the first half (Papers I to III) focusing on the performance characterization of such terminals in the presence of user interaction and propagation channel, under the challenging constraint that the terminals are compact. The second half of the thesis (Papers IV to VI) considers two performance enhancement approaches suitable for compact MIMO terminals in realistic usage conditions. In particular, the potential benefits of harmonizing compact multiple-antenna systems with the propagation channel and user influence are determined with respect to reconfigurability in antenna patterns and impedance matching circuits. In Paper I, the diversity performance of internal multiple antennas with multi-band coverage in a mock-up with the size of a typical mobile handset is investigated in different user interaction scenarios. For comparison, a second mock-up with only one multi-band antenna is also evaluated in the same user cases. An ideal uniform propagation environment is assumed. The performance at frequency bands below and above 1 GHz are presented and analyzed in detail. Paper II extends the study in Paper I by evaluating the single-input multiple-output (SIMO) and MIMO capacity performance of the same antenna prototypes under the same user interaction scenarios and propagation environment. In Paper III, the impacts of gain imbalance and antenna separation on the throughput performance of a dual-dipole configuration are studied at frequencies below and above 1 GHz in a repeatable dynamic multi-path environment, using a live HSPA network. Since the compactness of a user terminal has implications on the antenna separation and gain imbalance of the multiple antennas, the focus is to gain knowledge on how these two factors affect the end user experience in practice. In Paper IV, three simple dual-antenna topologies implemented in compact smart phone prototypes of identical form factors are evaluated in MIMO channel measurements in noise-limited and interference-limited urban scenarios. Each dual-antenna topology is intentionally designed to provide a distinct set of antenna patterns. The goal is to investigate the potential of antenna system design as one of the key performance differentiators in real terminal implementations. Paper V extends the work in Paper IV by introducing user interaction to the same MIMO channel measurement setup. Furthermore, the focus of this paper is on the evaluation of both the average and local channel performances and their potential enhancements. Finally, Paper VI ascertains the potential capacity gains of applying uncoupled adaptive matching to a compact dual-antenna terminal in an indoor office environment, under a realistic user scenario. The performance gains are evaluated by means of extensive MIMO channel measurements at frequency bands below and above 1 GHz

Performance characteristics on patch antenna with sar reduction using artificial magnetic conductor (amc) for wban applications

Great advances have been made in the area of wireless body area networks (WBANs) of improving wireless communication technology since the invention. These advances range in refining, size reduction and shape, gain improvement, more efficiency and combination of the requirements for applications which include health monitoring, military and personal navigation entertainment. Several types of antennas have been developed for WBANs and they have achieved narrow bandwidth, decrease gain, low radiation efficiency, a high specific absorption rate (SAR) value, high front-to-back ratio (FBR) and structural complexity. However, it is necessary to achieve better performance antenna for less impact of frequency detuning, by improving FBR, high radiation efficiency and reduce SAR for WBAN application. Conventional patch antennas are adopted since they can be low weight, low profile and easy to integrate with the device. Having these unique characteristics, patch antenna has shown to have clear advantages for WBAN applications. Since an antenna is placed a close to the human body with its curvatures and complexities, the antenna performance must be taking into account the structural, mismatch, and losses caused by the body, while simultaneously sustaining optimum performance. This work proposes to design, analysis and optimization of low-profile antenna integrated with Artificial Magnetic Conductor (AMC) for WBAN applications. Multilayer model of the adult human body at the frequency band of the proposed antenna is used, which helps to study the effects of the human on the antenna performance. The results showed that the presence of human head affects the antenna performance in terms of radiation pattern, efficiency and S11 and SAR values on the body parts. To further improve the performance of the proposed antenna design, several techniques have been developed in reducing SAR value with low complexity using AMC to realize broadside radiation for on /off body communication. AMC structure and miniaturized reflector reduce the back radiation and the impact of frequency detuning due to high losses of human body and the two proposed techniques are mounted on human head phantom. In addition, AMC improved FBR by 15.3 dB with enhanced of gain 7.61 dBi and radiation efficiency more than 88 %. The AMC have achieved 93.7 % reduction of the initial SAR value while metal reflector achieved a reduction of 77.7 %. Then, the antenna is fabricated and measured to validate the concept. Thus, the proposed antenna with AMC structure was designed and fabricated using two different materials for far-field radiation pattern measurements. The measured and simulated results reveals that proposed antenna with AMC array shows good impedance matching and far-field radiation pattern .Therefore, the proposed antenna is a potential candidate for WBAN

Design and characterisation of wideband antennas for microwave imaging applications

Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are well known equipments used to generate images to aid in diagnostic procedure. However, the imaging equipments have some limitations whereby the equipments are very expensive and therefore, they are not always accessible in many medical centres. Besides, the equipments are bulky and less mobility. Moreover, existing CT cannot be used frequently on the human body because the scanner exposes patients to more radiations of ionised frequency. The limitations of the equipment create a need to design an alternative imaging method which is relatively low cost, small in size, has high mobility, and non-ionise frequency. This research is to design an antenna for microwave imaging, namely corrugated u-slot antenna at 1.17-5.13 GHz with the reference of S11 less than -10 dB. Two corrugated u-slot antennas; namely antenna 1 and antenna 2 are placed on a mirror side of skull phantom to examine their ability to detect an object inside the skull. VeroClear-RGD810 skull phantom containing water is used, and the obtained results are verified using ZCorp zp-150 skull phantom which has approximately similar permittivity. Both the antennas are tested to detect the object which is located at 40 mm and 80 mm from the respective examined antenna. An Inverse Fast Fourier Transform (IFFT) technique is used to analyse the time domain reflection pulse according to the dielectric properties difference, as the electromagnetic wave propagates through the skull. The results show that the antenna 1 is able to detect the object faster than the antenna 2 for both skulls, due to inconsistent thickness of the phantoms. Furthermore, the antennas are fabricated in adjacent to measure decomposition and superposition specific absorption rate (SAR) in Specific Anthropomorphic Mannequin (SAM) head phantom at 1800 MHz and 2600 MHz. The maximum allowable SAR in head is 2 W/kg at 10 g contiguous tissue which is referred to International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline. Based on the measured results, superposition SAR of the antenna can reach up to ±12% of the maximum decomposition SAR. This research forms a significant contribution to medical engineering field in designing a corrugated u-slot antenna that serves to detect an abnormality inside human head at 1.17-5.13 GHz. The designed antenna satisfies the SAR standard, which is required in microwave imaging applications

Design and characterisation of wideband antennas for microwave imaging applications

Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) are well known equipments used to generate images to aid in diagnostic procedure. However, the imaging equipments have some limitations whereby the equipments are very expensive and therefore, they are not always accessible in many medical centres. Besides, the equipments are bulky and less mobility. Moreover, existing CT cannot be used frequently on the human body because the scanner exposes patients to more radiations of ionised frequency. The limitations of the equipment create a need to design an alternative imaging method which is relatively low cost, small in size, has high mobility, and non-ionise frequency. This research is to design an antenna for microwave imaging, namely corrugated u-slot antenna at 1.17-5.13 GHz with the reference of S11 less than -10 dB. Two corrugated u-slot antennas; namely antenna 1 and antenna 2 are placed on a mirror side of skull phantom to examine their ability to detect an object inside the skull. VeroClear-RGD810 skull phantom containing water is used, and the obtained results are verified using ZCorp zp-150 skull phantom which has approximately similar permittivity. Both the antennas are tested to detect the object which is located at 40 mm and 80 mm from the respective examined antenna. An Inverse Fast Fourier Transform (IFFT) technique is used to analyse the time domain reflection pulse according to the dielectric properties difference, as the electromagnetic wave propagates through the skull. The results show that the antenna 1 is able to detect the object faster than the antenna 2 for both skulls, due to inconsistent thickness of the phantoms. Furthermore, the antennas are fabricated in adjacent to measure decomposition and superposition specific absorption rate (SAR) in Specific Anthropomorphic Mannequin (SAM) head phantom at 1800 MHz and 2600 MHz. The maximum allowable SAR in head is 2 W/kg at 10 g contiguous tissue which is referred to International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline. Based on the measured results, superposition SAR of the antenna can reach up to ±12% of the maximum decomposition SAR. This research forms a significant contribution to medical engineering field in designing a corrugated u-slot antenna that serves to detect an abnormality inside human head at 1.17-5.13 GHz. The designed antenna satisfies the SAR standard, which is required in microwave imaging applications

방사 무선전력전송을 위한 무지향성 안테나 및 전송 효율 한계에 대한 연구

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 남상욱.본 논문에는 방사하는 전자파를 이용한 무선 전력 전송에 대해 집중적으로 연구를 진행하였다. 보다 구체적으로는, 무지향성 안테나의 분석과 설계, 자유공간과 손실매질에서의 최적 송신 전류 분포, 전송 효율의 한계에 대한 연구를 기술하였다. 추가적으로, 전자파의 인체 영향에 대한 비교 및 이론적인 최적 전류 분포의 효과적 구현에 대한 연구를 진행하였다. 본 연구에서는 방사형 무선전력전송을 전원을 공급 유무에 따라 수동형과 능동형 무선전력전송으로 구분하고, 수동형 방사 무선전력전송부터 능동형 방사 무선전력전송까지의 연구를 순차적으로 기술하였다. 먼저, 수동형 방사 무선전력전송 연구에서는 전자파 에너지 하베스팅용 안테나에 대한 분석 및 설계에 대한 연구를 진행하였다. 수동 방사 무선전력전송의 상황을 고려하여 등방성 패턴, 전기적으로 작은 크기, 높은 효율 특성을 나타내는 안테나를 제안하였다. 전기적으로 소형이면서 등방성 패턴을 방사하는 SRR이 기본 구조로 활용되었다. SRR에 대한 이론적 분석을 진행하였고, 시뮬레이션 결과와 잘 맞는 것을 확인하였다. 분석에 기초하여 FSRR 안테나를 설계하였고, 측정을 통해 제안한 아이디어를 검증하였다. 수신 파워의 크기를 향상시키기 위해, 이중 대역 및 확장된 대역에서 동작하는 FSRR 안테나를 추가로 설계하였다. 제안된 구조는 선행연구와 비교하였을 때, 상대적으로 우수한 성능을 보여주었다. 한편 수동형 방사 무선 전력전송의 경우, 주변의 낮은 전력 밀도로 인해 수신 전력이 매우 낮은 한계점이 존재한다. 따라서, 송신 타워를 이용해 모바일 안테나로 무선 전력을 전송할 수 있는 능동형 방사 무선전력전송에 대한 후속 연구를 진행하였다. 능동형 방사 무선전력전송에서는, 송신 타워를 활용하여 모바일 기기에 효과적으로 무선전력전송을 수행하는 방법에 대한 연구를 진행하였다. 본 연구에서는 방사형 무선전력전송의 효율을 최대화 하는 송신 전류분포와 주어진 면적을 활용할 때 얻을 수 있는 최대 한계 효율을 이론적으로 도출하였다. 본 연구의 결과를 통해, 기존의 방식으로는 파악할 수 없었던 중거리 무선전력전송 효율의 최대 한계치와 송신 전류분포의 최적 형태를 파악할 수 있다. 연구의 결론에 따르면, 수신하는 안테나의 송신 방사 패턴이 효율을 결정함에 있어 중요한 역할을 하였다. 제안한 이론을 실제 안테나에 적용하여 선행연구와 비교를 하였고, 선행 연구로 파악할 수 없는 이론적 한계 효율을 도출하였다. 제안한 연구를 일반적인 상황으로 확장하기 위해 손실 매질 내부에서의 무선전력전송에 대한 추가 연구를 진행하였다. 손실 매질이 있는 경우에서도 최적 전류 분포와 효율의 최대 한계치를 도출하였다. 최적 송신 전류를 활용하여, 실제 안테나 어레이를 구현하고 인체 팬텀에 미치는 영향을 파악해보았다. 마지막으로, 앞서 도출한 이론적인 전류분포를 실제 안테나로 구현하는 방법에 대해 연구를 진행하였다. 선행 연구를 참고하여, 이상적인 전류분포를 thinned 배열로 구현하는 두가지 방법을 제안하였다. 이론적인 전류 분포에 유전 알고리즘을 활용한 방법과, density tapering을 응용한 방법을 적용하였다. 두 방법 모두 동일한 개수의 균등 어레이에 비해 성능이 개선되는 결과를 보였다. 특히 density tapering을 이용하면 같은 개수 및 같은 면적의 격자구조보다 비용, 무게, 효율 등에서 장점이 있으며, 수신기의 위치가 변할 때에도 더 높은 효율로 송신이 가능하다.In this thesis, research on the radiative-wireless power transmission (R-WPT) using radiated electromagnetic(EM) fields is presented. More specifically, the analysis and design of quasi-isotropic antennas, the analytical study on the optimal transmitting current, and the efficiency bounds are described. In addition, research on the comparison of the EM effects on the human phantom, and the effective implementation of the optimal current distribution are conducted. The research is described sequentially from the passive R-WPT to active R-WPT, which indicate the absence or presence of the power supplying base station. First, research is conducted on the analysis and design of the passive R-WPT antenna. Considering the ambient environment, an antenna with quasi-isotropic pattern, electrically small size, and high efficiency is proposed. A split-ring resonator (SRR) that radiate quasi-isotropic pattern with electrically small size is used as a basic structure. The analysis on the SRR is well matched with the simulation results. Based on the analysis, folded split-ring resonator (FSRR) is proposed and designed for the passive R-WPT antennas, and verified through the measurement. A dualband and wideband FSRR that can harvest more ambient power is designed as an extended work. The proposed antennas are compared with recent studies showing superior performances. On the other hand, the receiving power of the passive R-WPT is very low due to low power density of ambient field, a study on the active R-WPT, which can transfer wireless powers from the base station to the mobile antenna, is conducted as a next step. In the active R-WPT, a study on the way to effectively transfer wireless power to the mobile devices by using a transmitting tower is described. The optimal current distribution of the transmitting surface, and maximum power transfer efficiency (PTE) bounds when the transmitting area is limited are analytically derived. Through the results, it is possible to figure out the maximum efficiency bounds for the mid-range R-WPT and the optimal shape of transmission current distribution that could not be found by the conventional method. The results indicate that the optimum current distribution on the transmitting surface and the maximum efficiency of radiative WPT depend on the radiating field pattern of the mobile antenna. To generalize the proposed theory, an additional analysis in lossy environment is carried out. The optimal transmitting current and efficiency bound in lossy media is found for a couple of examples. The results are compared with the previous works to verify the proposed theory. Based on the results in lossy media, the EM effects on the human body is investigated. Lastly, research on the effective implementation of the theoretical current distribution as practical antenna arrays is described. Based on the previous research, two techniques that can effectively realize the ideal current are proposed in designing a thinned array. An optimization using genetic algorithm, and deterministic density tapering are applied to sample the theoretical current distribution. As a results, the proposed thinned arrays show improved performance compared to the same number of densely arranged regular arrays. In particular, the use of density tapering has advantages in cost, weight, efficiency than the same number of the regular array. In addition, it is possible to transmit wireless power with better efficiency even when the position of the receiver changes.Chapter 1. Introduction 1 1.1. Classification of Wireless Power Transmission 1 1.2. Separation of Regions 3 1.3. Passive and Active Radiative-Wireless Power Transmission 6 1.4. References 14 Chapter 2. Passive: RF Energy Harvesting Antenna 18 2.1. Motivation 18 2.2. Analytical Study on RF Energy Harvesting Antenna 19 2.2.1. Previous Research 19 2.2.2. Analysis on Split-Ring Resonator 21 2.2.3. Analysis on the Symmetric Folded Split-Ring Resonator 25 2.2.4. Analysis on the Asymmetric Folded Split-Ring Resonator 30 2.3. Design of RF Energy Harvesting Antenna 34 2.3.1. Antenna Design 37 2.3.2 Results and Discussion 44 2.4. Design of RF Energy Harvesting Antenna with Dual-band Operation 45 2.4.1. Motivation 45 2.4.2 Antenna Design 45 2.4.3. Results and Discussion 48 2.5. RF Energy Harvesting Antenna with Wide-band Operation 53 2.5.1. Motivation 53 2.5.2 Antenna Design 54 2.5.3. Results and Discussion 57 2.6. Conclusion 65 2.7. References 69 Chapter 3. Active: Radiative-WPT in Lossless Medium 73 3.1. Motivation 73 3.2. Previous Research 73 3.3. Theoretical Approach 77 3.3.1. Power Transfer Efficiency 77 3.3.2. Optimum Transmitting Current 80 3.3.3. Minimizing Transmitting Area 84 3.4. Numerical Examples 86 3.3.1. Dipole Antenna 88 3.3.2. Patch Antenna 90 3.3.3. Horn Antenna 91 3.5. Results and Discussion 93 3.5. Conclusion 98 3.6. References 99 Chapter 4. Active: Radiative-WPT in Lossy Media 103 4.1. Motivation 103 4.2. Previous Research 103 4.3. Theoretical Approach 106 4.3.1. Problem Formulation 108 4.3.2. Maximum Power Transfer Efficiency 110 4.4. Practical Examples 114 4.4.1. Planar Inverted-F Antenna 116 4.4.2. Half-Mode Cavity-Backed Antenna 120 4.5. Electromagnetic Human Exposure in Radiative WPT System 125 4.5.1. Motivation 125 4.5.2. Simulation Results 126 4.6. Conclusion 132 4.7. References 134 Chapter 5. Active: Implementation of Optimal Transmitting Current Distribution 138 5.1. Motivation 138 5.2. Theoretical Approach 139 5.2.1. Radiation Pattern Matching 139 5.2.2. Optimal Excitation Coefficient 141 5.2.3. Thinning of Transmitting Array 141 5.3. Implementation of the Optimal Current Sheet 145 5.3.1. Array Thinning using Genetic Algorithm 145 5.3.2. Results and Discussions 148 5.3.3. Array Thinning using Density Tapering 151 5.3.4. Results and Discussions 154 5.4. Conclusion 158 5.5. References 159Docto