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2014-08-20 PIER Vol. 148, 233-243, 2014. doi:10.2528/PIER14062703

Multiband Frequency Reconfigurable 4G Handset Antenna with MIMO Capability

Janne Ilvonen, Risto Valkonen, Jari Holopainen, and Ville Viikari

A novel frequency reconfigurable 4G Multiple-Input Multiple-Output (MIMO) handset antenna is presented and verified with experimental results. Frequency tuning is used to minimize the antenna volume and to compensate for the losses related to user-originated impedance detuning. Both antenna elements are independently frequency reconfigurable and can cover most of the LTE-A bands. The study compares the losses of CMOS- and MEMS-based digitally tunable capacitors (DTC). In addition, two prototypes with total antenna volumes of 1170 and 3900 mm3 have been studied. The results show that the larger antenna structure operates with an efficiency better than 49% across the frequencies of 698-960 MHz and better than 56% across the frequencies of 1430-2690 MHz, when a MEMS-based DTC is used. In addition, a new method is introduced to estimate the suitability of the antenna geometry for frequency tunable antennas.

2014-08-20 PIER Vol. 148, 223-231, 2014. doi:10.2528/PIER14071705

Investigation of Wireless Power Transfer Using Planarized, Capacitor-Loaded Coupled Loops

Chenchen Jimmy Li and Hao Ling

A capacitor-loaded coupled loop structure is investigated for wireless power transfer at 6.78 MHz for a target transmission distance of 1 m. It is shown that the optimal configuration for this structure occurs when the coupled loops are coplanar. Therefore, by converting thick wires into wide strips, a planarized configuration can be achieved. Simulation results are verified in measurement, which shows a 60% overall power transfer efficiency at 1 m. The contribution of different loss mechanisms is examined. Next, power transfer efficiency in the presence of dielectric materials is investigated in simulation and measurement. Additionally, tuning capabilities that arise from the implementation of variable capacitors are shown. Finally, design space exploration is performed to examine design tradeoffs.

2014-08-20 PIER Vol. 148, 209-221, 2014. doi:10.2528/PIER14032405

A Differential DPSM Based Modeling Applied to Eddy Current Imaging Problems

Thierry Bore, Pierre-Yves Joubert, and Dominique Placko

This paper deals with an innovative implementation of a semi-analytical modeling method, called the Distributed Points Source Method (DPSM), in the case of an eddy current problem. The DPSM has already shown great potentialities for the versatile and computationally efficient modeling of complex electrostatic, electromagnetic or ultrasonic problems. In this paper, we report a new implementation of the DPSM, called differential DPSM, which shows interesting prospects for the modeling of complex eddy current problems such as met in the non-destructive imaging of metallic parts. In this paper, the used eddy current imaging device is firstly presented. It is composed of an eddy current (EC) inducer and a magneto optical set-up used to translate the magnetic field distribution appearing at the surface of the imaged part, into a recordable optical image. In this study, the device is implemented for the time-harmonics (900 Hz) imaging of a two-layer aluminum based assembly, featuring surface-breaking and buried defects. Then, the basics of the time-harmonics DPSM modeling are recalled, and the differential approach is presented. It is implemented for the modeling of the interactions of the eddy current imaging device with the considered flawed assembly in the same operating conditions as the experimental implementation. The comparison between experimental and computed data obtained for millimetric surface and buried defects is presented in the form of complex magnetic cartographies and Lissajous plots. The obtained results show good agreement and open the way to the modeling of complex EC problems. Furthermore, the low computational complexity of the differential DPSM modelings makes it promising to consider for the solving of EC inverse problems.

2014-08-19 PIER Vol. 148, 193-207, 2014. doi:10.2528/PIER14061207

Human Body as Antenna and its Effect on Human Body Communications

Behailu Kibret, Assefa K. Teshome, and Daniel Lai

Human body communication (HBC) is a promising wireless technology that uses the human body as part of the communication channel. HBC operates in the near-field of the high frequency (HF) band and in the lower frequencies of the very high frequency (VHF) band, where the electromagnetic field has the tendency to be confined inside the human body. Electromagnetic interference poses a serious reliability issue in HBC; consequently, it has been given increasing attention in regard to adapting techniques to curtail its degrading effect. Nevertheless, there is a gap in knowledge on the mechanism of HBC interference that is prompted when the human body is exposed to electromagnetic fields as well as the effect of the human body as an antenna on HBC. This paper narrows the gap by introducing the mechanisms of HBC interference caused by electromagnetic field exposure of human body. We derived analytic expressions for induced total axial current in the body and associated fields in the vicinity of the body when an imperfectly conducting cylindrical antenna model of the human body is illuminated by a vertically polarized plane wave within the 1-200 MHz frequency range. Also, fields in the vicinity of the human body model from an on-body HBC transmitter are calculated. Furthermore, conducted electromagnetic interference on externally embedded HBC receivers is also addressed. The results show that the maximum HBC gain near 50 MHz is due to whole-body resonance, and the maximum at 80 MHz is due to the resonance of the arm. Similarly, the results also suggest that the magnitude of induced axial current in the body due to electromagnetic field exposure of human body is higher near 50 MHz.

2014-08-15 PIER Vol. 148, 183-191, 2014. doi:10.2528/PIER14050308

Microwave Resonators for Weak Light Detection at Telecom Wavelength

Pin-Jia Zhou, Yiwen Wang, Qiang Wei, and Lian-Fu Wei

We report the experimental measurements of weak light signal at 1550 nm wavelength with a high-quality factor microwave coplanar waveguide (CPW) resonators. The quality factor of this niobium λ/4 CPW resonator is measured as Q = 7.4×105 at ultra-low temperature (20 mK). With this device, we developed a technique to implement the proper fiber-resonator coupling, and realized the desirable weak light detection at telecommunication wavelength with 35 pW resolution by probing the shift of resonance frequency (f0). We found that the resonator shift increases with the increasing light power (from 11.7 pW to 9.77 nW), similar to the effects of increasing the system temperature (from 20 mK to 800 mK). The observed blue shifts of f0 (with the increasing of either the temperature and the applied light powers) are thoroughly deviated from the usual Mattis-Bardeen theory prediction, and could be explained by the effects relating to the two-level system existed on surface of the CPW device.

2014-08-08 PIER Vol. 148, 171-182, 2014. doi:10.2528/PIER14071201

A General Solution to Wireless Power Transfer Between Two Circular Loop

Ada S. Y. Poon

Wireless power transmision has been analytically studied in near-field coupling systems based on the small-antenna and near-field approximations, and in microwave power beaming systems based on the far-field approximation. This paper attempts to provide a general solution based on full-wave analysis to wireless power transmission between two circular loops. The solution applies to arbitrary transmit and receive loop radii, transmission range, orientation and alignment of the loops, and dielectric properties in a homogeneous isotropic medium. The power link is modeled as a two-port network and the efficiency based on simultaneous conjugate matching is used as the performance metric. The self and mutual admittances are analytically solved by expressing the current on the loops in Fourier series and the fields in vector spherical wave functions, and by the use of vector addition theorem to relate the coupling between the loops. The general solution is then applied to draw new insights such as the optimal carrier frequency between symmetric loops and impact of higher order modes on the power transfer efficiency between asymmetric loops.

2014-08-08 PIER Vol. 148, 159-170, 2014. doi:10.2528/PIER14052608

Mixed Finite Element Method for 2D Vector Maxwell's Eigenvalue Problem in Anisotropic Media

Wei Jiang, Na Liu, Yifa Tang, and Qing Huo Liu

It is well known tha the conventional edge element method in solving vector Maxwell's eigenvalue problem will lead to the presence of nonphysical zero eigenvalues. This paper uses the mixed finite element method to suppress the presence of these nonphysical zero eigenvalues for 2D vector Maxwell's eigenvalue problem in anisotropic media. We introduce a Lagrangian multiplier to deal with the constraint of divergence-free condition. Our method is based on employing the first-order edge element basis functions to expand the electric field and linear nodal element basis functions to expand the Lagrangian multiplier. Our numerical experiments show that this method can successfully remove all nonphysical zero and nonzero eigenvalues. We verify that when the cavity has a connected perfect electric boundary, then there is no physical zero eigenvalue. Otherwise, the number of physical zero eigenvalues is one less than the number of disconnected perfect electric boundaries.

2014-08-07 PIER Vol. 148, 151-158, 2014. doi:10.2528/PIER14070603

Energy Transfer for Implantable Electronics in the Electromagnetic Midfield (Invited Paper)

John S. Ho and Ada S. Y. Poon

The wireless transfer of electromagnetic energy into the human body could power medical devices and enable new ways to treat various disorders. To control energy transfer, metal structures are used to generate and manipulate radio-frequency electromagnetic fields. Most systems for transfer across the biological tissue operate in the quasi-static limit, but operation beyond this regime could afford new powering capabilities. This review discusses some recent developments in the design and implementation of systems operating in the electromagnetic midfield, where transfer exploits wave-like fields in the body.

2014-07-24 PIER Vol. 148, 141-150, 2014. doi:10.2528/PIER14051301

Inhomogeneous Microwave Lens Based on Periodically Loaded Transmission Lines

Joni Vehmas, Pekka Alitalo, and Sergei Tretyakov

A new design for a low-reflection inhomogeneous microwave lens based on periodically loaded one-dimensional transmission lines is proposed and experimentally tested. The inhomogeneous effective refractive index of this flat-profile lens is achieved by loading the transmission lines comprising the lens with different inductive elements.

2014-07-24 PIER Vol. 148, 129-139, 2014. doi:10.2528/PIER14050905

Robust Cylindrical Plasmonic Nano-Antennas for Light-Matter Interaction

Kaushal Choonee and Richard R. A. Syms

A cylindrical metallic plasmonic nano-antenna consisting of a shell supporting a disk, named capped shell, is proposed and studied by frequency domain finite element analysis. This new topology is shown to be weakly dependent on the radius of the structure and is therefore suitable for fabrication by parallel processes such as island lithography which generates a pseudo-random array with a distribution of diameters. Furthermore, compared to similar resonators such as rods, disks and shells, the capped shell generates a larger volume with high fields, and is hence useful as a nano-antenna for light-matter interaction.

2014-07-21 PIER Vol. 148, 113-128, 2014. doi:10.2528/PIER14062904

Lattice Maxwell's Equations (Invited Paper)

Fernando Lisboa Teixeira

We discuss the ab initio rendering of four-dimensional (4-d) spacetime of Maxwell's equations on random (irregular) lattices. This rendering is based on casting Maxwell's equations in the framework of the exterior calculus of differential forms, and a translation thereof to a simplicial complex whereby fields and causative sources are represented as differential p-forms and paired with the oriented p-dimensional geometrical objects that comprise the set of spacetime lattice cells (simplices). We pay particular attention to the case of simplicial spacetime lattices because these can serve as building blocks of lattices made of more generic cells (polygons). The generalized Stokes' theorem is used to construct discrete calculus operations on the lattice based upon combinatorial relations depending solely on the connectivity and relative orientation among simplices. This rendering provides a natural factorization of (lattice) 4-d spacetime Maxwell's equations into a metric-free part and a metric-dependent part. The latter is encoded by discrete Hodge star operators which are built using Whitney forms, i.e., canonical interpolants for discrete differential forms. The derivation of Whitney forms is illustrated here using a geometrical construction based on the concept of barycentric coordinates to represent a point on a simplex, and the generalization thereof to represent higher-dimensional objects (lines, areas, volumes, and hypervolumes) in 4-d. We stress the role of the primal lattice, the barycentric dual lattice, and the barycentric decomposition lattice in achieving a complete description of the lattice theory. Lattice Maxwell's equations based on the exterior calculus of differential forms and on the use of Whitney forms as field interpolants inherits the symplectic structure and discrete analogues of conservation laws present in the continuum theory, such as energy and charge conservation. This framework also provides precise localization rules for the degrees of freedom associated with the different fields and sources on the lattice, and design principles for constructing consistent numerical solution methods that are free from spurious modes, spectral pollution, and (unconditional) numerical instabilities. We also brie y consider the relationship between lattice 4-d Maxwell's equations and some incarnations of discretization schemes for Maxwell's equations in (3+1)-d, such as finite-differences and finite-elements.

2014-07-21 PIER Vol. 148, 83-112, 2014. doi:10.2528/PIER14063009

Differential Forms and Electromagnetic Field Theory (Invited Paper)

Karl Warnick and Peter H. Russer

Mathematical frameworks for representing fields and waves and expressing Maxwell's equations of electromagnetism include vector calculus, differential forms, dyadics, bivectors, tensors, quaternions, and Clifford algebras. Vector notation is by far the most widely used, particularly in applications. Of the more sophisticated notations, differential forms stand out as being close enough to vectors that most practitioners can readily understand the notation, yet at the same time offering unique visualization tools and graphical insight into the behavior of fields and waves. We survey recent papers and book on differential forms and review the basic concepts, notation, graphical representations, and key applications of the differential forms notation to Maxwell's equations and electromagnetic field theory.

2014-07-21 PIER Vol. 148, 73-82, 2014. doi:10.2528/PIER14063001

Hybrid Simulation of Maxwell-Schrodinger Equations for Multi-Physics Problems Characterized by Anharmonic Electrostatic Potential (Invited Paper)

Takashi Takeuchi, Shinichiro Ohnuki, and Tokuei Sako

A novel hybrid simulation based on the coupled Maxwell-Schrödinger equations has been utilized to investigate, accurately, the dynamics of electron confined in a one-dimensional potential and subjected to time-dependent electromagnetic fields. A detailed comparison has been made for the computational results between the Maxwell-Schrödinger and conventional Maxwell-Newton approaches, for two distinct cases, namely, characterized by harmonic and anharmonic electrostatic confining potentials. The results obtained by the two approaches agree very well for the harmonic potential while disagree quantitatively for the anharmonic potential. This clearly indicates that the Maxwell-Schrödinger scheme is indispensable to multi-physics simulation particularly when the anharmonicity effect plays an essential role.

2014-07-14 PIER Vol. 148, 63-71, 2014. doi:10.2528/PIER14043003

A Printed Vivaldi Antenna with Improved Radiation Patterns by Using Two Pairs of Eye-Shaped Slots for UWB Applications

Kun Ma, Zhiqin Zhao, Jiangniu Wu, Sani Mubarak Ellis, and Zai-Ping Nie

In this paper, a printed Vivaldi antenna with two pairs of eye-shaped slots is proposed for UWB applications. By using two pairs of eye-shaped slots, the side lobe levels of the radiation pattern are reduced, and the antenna gain is improved at low frequencies. To illustrate the effectiveness of the proposed design, a prototype of the proposed antenna is fabricated and measured. Experimental results show that the proposed antenna presents a measured impedance bandwidth, defined by |S11| < -10 dB, from 3 to 12.8 GHz with a compact size (36 mm×36 mm). Good unidirectional radiation characteristics with a front-to-back ratio better than 10 dB are also achieved. The measured gain is better than 3.7 dBi in the operating frequency band. In addition, the measured group delay of the proposed antenna is around 1.2 ns with a variation less than ± 0.5 ns.

2014-07-14 PIER Vol. 148, 55-61, 2014. doi:10.2528/PIER14030405

Snowfall Detectability of NASA's CloudSat : the First Cross-Investigation of its 2c-Snow-Profile Product and National Multi-Sensor Mosaic QPE (NMQ) Snowfall Data

Qing Cao, Yang Hong, Sheng Chen, Jonathan J. Gourley, Jian Zhang, and Pierre E. Kirstetter

This study investigates snowfall detectability and snowfall rate estimation with NASA's CloudSat through the first evaluation of its newly released 2C-16 SNOW-PROFILE products using the National Mosaic and Multisensor QPE System (NMQ) snowfall products. The primary focus is on the detection and estimation of 18 surface snowfall. The results show that the CloudSat product has good detectability of light snow (snow water equivalent less than 1 mm/h) but degrades in moderate and heavy snow (heavier than 1 mm/h). The analysis suggests that the new 2C-SNOW-PROFILE algorithm is insufficient in correcting signal losses due to attenuation. Its underestimation is well correlated to snowfall intensity. Issues of sensitivity and data sampling with ground radars, which may affect the interpretation of the results, are also discussed. This evaluation of the new 2C-SNOW-PROFILE algorithm provides guidance for applications of the product and identifies particular error sources that can be addressed in future versions of the CloudSat snowfall algorithm.

2014-07-01 PIER Vol. 148, 41-53, 2014. doi:10.2528/PIER14022607

Novel Short Tapered Leaky Wave Antennas with Complementary Split Ring Resonantor for Back Lobe Suppression

Jie-Huang Huang, Chien-Rung Huang, and Christina F. Jou

Two novel short tapered leaky wave antenna (LWA) designs with a complementary split ring resonator (CSRR) structure are proposed in this paper. The CSRR structure is positioned at 1/4λg away from the open-end edge of the LWA. For one of the antenna designs, the CSRR is placed at the ground plane; for the other one, the CSRR is placed on the antenna plane. The reflected wave caused by the open-end edge of the LWA is cancelled by the reflected wave caused by the CSRR, thus, the back lobe can be effectively suppressed. The length of these two short tapered LWAs with CSRR design is only 1.2λg at 4.3 GHz. According to the measurement results, the impedance bandwidth is 650 MHz for 7 dB return loss, which covers the range from 4.3 GHz to 4.95 GHz. The back lobe can be suppressed effectively about more than 12 dB at the whole operating frequency band. The scanning range of the main beam is about 34˚, which covers the scanning angle from 10˚to 44˚.

2014-06-27 PIER Vol. 148, 31-39, 2014. doi:10.2528/PIER14031103

An Efficient Dual-Circularly Polarized Rectenna for RF Energy Harvesting in the 2.45 GHz ISM Band

Walid Haboubi, Hakim Takhedmit, Jean-Daniel Lan Sun Luk, Salah-Eddine Adami, Bruno Allard, Francois Costa, Christian Vollaire, Odile Picon, and Laurent Cirio

This paper reports a 2.45 GHz, low power dual circularly polarized (DCP) and dual access rectenna. It contains two dc-recombined rectifiers and a cross-slot coupled square patch antenna fed by a microstrip line. A judicious dc recombination scheme allows to minimize the RF power imbalance between accesses caused by multipath effects and consequently arbitrary polarized incident waves. The proposed rectenna is then able to harvest linearly polarized, right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) electromagnetic waves, with nearly stable performances. The rectenna has been optimized at -15 dBm per access and dedicated to remote and contactless supply low consumption sensors. It has been experimentally tested with very low power densities from 0.057 μW/cm2 (Erms=0.46 V/m) to 2.3 μW/cm2 (Erms=2.95 V/m). At 1.49 μW/cm2 (-15 dBm on each rectifier), the structure exhibits an output dc voltage and a global efficiency of 189 mV and 37.7%, respectively when the azimuthal angle (Φ) of the incident field is equal to 0°. Due to the nearly constant total gain of the DCP antenna and an appropriate dc recombination of the two rectifiers, the global efficiency slightly varies between 37.7% and 41.4% when the azimuthal angle (Φ) varies between -90 and 90°.

2014-06-21 PIER Vol. 148, 23-30, 2014. doi:10.2528/PIER14050204

Circular Polarized Patch Antenna Generating Orbital Angular Momentum

Mirko Barbuto, Fabrizio Trotta, Filiberto Bilotti, and Alessandro Toscano

The recent extension of the orbital angular momentum (OAM) concept from optical to microwave frequencies has led some researchers to explore how well established antenna techniques can be used to radiate a non-zero OAM electromagnetic field. In this frame, the aim of the present paper is to propose a new approach to generate a non-zero OAM field through a single patch antenna. Using the cavity model, we first analyze the radiated field by a standard circular patch and show that a circular polarized (CP) TMnm mode excited by using two coaxial cables generates an electromagnetic field with an OAM of order ±(n-1). Then, in order to obtain a simpler structure with a single feed, we design an elliptical patch antenna working on the right-handed (RH) CP TM21 mode. Using full-wave simulations and experiments on a fabricated prototype, we show that the proposed antenna effectively radiates an electromagnetic field with a first order OAM. Such results prove that properly designed patch antennas can be used as compact and low-cost generators of electromagnetic fields carrying OAM.

2014-06-20 PIER Vol. 148, 15-22, 2014. doi:10.2528/PIER14050902

Antenna Pattern Retrieval from Reflection Coefficient Measurements with Reflective Loads

Zhou Du, Ville Viikari, Juha Ala-Laurinaho, Aleksi Tamminen, and Antti V. Räisänen

This paper presents a new method for antenna pattern retrieval from reflection coefficient measurements. A reflective load with known reflective properties is placed close to the aperture of the antenna under test. The reflection coefficient of the antenna is measured at the antenna feed with multiple different reflective loads. The antenna pattern is then solved from the measurements with an inversion method. This paper derives and verifies the analytical foundations needed to implement the method, and demonstrates the method both by simulations and experiments for a pyramidal horn antenna at 30 GHz.

2014-06-15 PIER Vol. 148, 1-14, 2014. doi:10.2528/PIER14012306

Analysis of Moving Human Micro-Doppler Signature in Forest Environments

Jose Miguel Garcia-Rubia, Ozlem Kilic, Vinh Dang, Quang M. Nguyen, and Nghia Tran

Automatic detection of human motion is important for security and surveillance applications. Compared to other sensors, radar sensors present advantages for human motion detection and identification because of their all-weather and day-and-night capabilities, as well as the fact that they detect targets at a long range. This is particularly advantageous in the case of remote and highly cluttered radar scenes. The objective of this paper is to investigate human motion in highly cluttered forest medium to observe the characteristics of the received Doppler signature from the scene. For this purpose we attempt to develop an accurate model accounting for the key contributions to the Doppler signature for the human motion in a forest environment. Analytical techniques are combined with full wave numerical methods such as Method of Moments (MoM) enhanced with Fast Multipole Method (FMM) to achieve a realistic representation of the signature from the scene. Mutual interactions between the forest and the human as well as the attenuation due to the vegetation are accounted for. Due to the large problem size, parallel programming techniques that utilize a Graphics Processing Unit (GPU) based cluster are used.