21 December 2012 1530-1730 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

From the effective medium theory, the periodic structures with sub-wavelength elements can be viewed as homogeneous metamaterials, for example, left-handed materials, zero-index materials, epsilon-negative medium, mu-negative medium, anisotropic metamaterials, and chiral medium. Some unusual electromagnetic properties have been found with homogeneous metamaterials, such as the negative refraction and perfect imaging. However, inhomogeneous metamaterials which are composed of non-periodic structures can provide much more freedom to control electromagnetic waves. In this presentation, I will mainly focus on the experimental verification to the control of electromagnetic waves using inhomogeneous metamaterials in the microwave frequency. There are three approaches to design inhomogeneous metamaterials: the geometrical optics method (gradient-index metamaterials), the quasi-conformal mapping (all-dielectric metamaterials), and the transformation optics (anisotropic metamaterials). We have designed, fabricated, and measured a couple of inhomogeneous metamaterial devices in the microwave frequencies, including the two-dimensional (2D) and three-dimensional (3D) ground-plane cloaks, gradient random surface, electromagnetic black hole, 3D flattened Luneburg lens, and the illusion-optics devices.

20 December 2012 1530-1730 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

Metamaterials have attracted great attentions due to their ability to control electro- magnetic waves and the unusual properties. This presentation will be focused on the application of metamaterials in microwave antennas, exploring better performance and/or new features of antennas. Three types of metamaterial antennas are presented: zero-index material antennas, small patch antennas for wireless communications, and metamaterial lens antennas.
We propose and experimentally demonstrate two kinds of anisotropic zero-index materials (AZIMs) in the Cartesian and cylindrical coordinates, respectively. The Cartesian AZIMs (such as z component of permittivity or permeability tensor equals zero) are shown to generate perfectly plane waves in the z direction, resulting in high-directivity antennas. We make two-dimensional (2D) and three-dimensional (3D) experiments to verify such new features. On the contrary, the radially AZIMs (radial component of permittivity or permeability tensor in the cylindrical coordinate equals zero) will always produce omnidirectional radiations regardless the numbers and positions of sources inside AZIM. We also show experimentally the powerful ability of AZIM to reach high-efficiency spatial power combination for the omnidirectional radiations.
We experimentally demonstrate efficient methods to improve the bandwidth and radiation efficiency of patch antennas and reduce the coupling among patch antenna array using metamaterials, which are important to the wireless communications (e.g., MIMO systems).
We present two kinds of metamaterial lens antennas. First, we demonstrate a series of 3D broadband, low loss, dual polarization, and high-directivity planar lens antennas which are realized using gradient-index metamaterials, which have excellent features and superior performance than traditional antennas (horns or Rotman lenses). Second, we propose and realize a 3D Luneburg lens with flattened focal surface using the transformation optics. The novel 3D lens has great advantages to the conventional uniform-material lens and spherical Luneburg lens with no aberration, zero focal distance, a flattened focal surface, and the ability to form images at extremely large angles. It can be directly used as a high-gain antenna to radiate or receive narrow beams in large scanning angles for dual polarizations.

12 December 2012 1100-1200 hrs @ Seminar Room E5-02-32, ECE, National University of Singapore

This talk will review our recent work on plasmonic and metamaterial nanophotonics devices, including plasmonic waveguides, couplers, antennas, and high performance absorbers. In particular, light absorption can be significantly enhanced through plasmonic resonances. Such light absorbers can be designed to be highly polarization sensitive or insensitive, as shown in our experiments. The absorption peak wavelength can be tuned by many methods, while the bandwidth of absorption can also be manipulated to be either broadband or narrow-band. Furthermore, the heat generated by the light absorption, i.e., the photothermal effect, can be utilized to fabricate micro- or nano- metallic structures, or manipulate nanoparticles. The collective heating effects of nanoparticle clusters can even provide applications in, e.g., nanoscale rulers, and many others.

21 November 2012 1030-1200 hrs @ Seminar Room E5-02-32, ECE, National University of Singapore

The linear PAs for advanced system, such as 4G and beyond, should handle signals with high PAPR. For amplification of the signals, the efficiency of the PAs is degraded significantly due to the operation at a low power region. To improve efficiency of the PAs, advanced design architectures are developed. These architectures are based on a highly efficient amplifier and try to maintain the high efficiency at a low power level. The representative architectures are Doherty amplifier, LINC, ET technique, class-S amplifier, and some digital PAs.
Doherty is the main force in mobile infrastructure PA and can provide a high efficiency for the amplification of signal with a high PAPR. There is a significant progress in the broad banding but the bandwidth is still limited. Recently, the performance of the LINC PA is improved significantly by increasing the power combining efficiency. The distortion is cancelled successfully using DPD technique.
ET is the most popular architecture for the handset application since this PA is very flexible, suitable to the multimode and multiband operation, together with high efficiency. This technique can be applied easily to a low-high mode PA, also. One variation of the technique is average power tracking (APT) amplifier, controlling VDC according to the average power level using a buck DC-DC converter.
As transistors are scaled down with higher speed, the digitally configured circuit can be applied for the RF signal amplification. The digital circuit can be very flexible and can be used for multimode/multiband application but the performance is not up to the expectation, yet. For the digital amplification, the I-Q modulated signal is normally up-converted to a polar signal. The amplitude information is digitized at the base band speed or the RF frequency and is applied to the digital PA. The digital bit can be amplified by the thermo-coded cells, which is a digital amplifier.  The digitizing can be done using sigma-delta modulator and the digitized bit can be applied to a PA, either as an input or as a bias voltage. The resulting amplifier is a class-S PA. I-Q modulated signal can be directly up-converted as a digital form using sampling technique and is applied to the thermo code cells. These digitally configured PAs are actively studied for handset application and will progress continuously.
These various advanced architectures for the next generation PA will be introduced in this talk.

The electromagnetic field scattering by arbitrarily shaped objects can be obtained by finding the solution of an integral equation. The integral equation is discretized by the standard method of moments (MoM). If the resultant matrix equation is solved by Gaussian elimination, it requires O(N^3) floating-point operations to solve N linear equations, or O(N^2) operations per iteration for iterative solvers.  With the fast multipole method (FMM) and the multilevel fast multipole algorithm (MLFMA), the complexity of matrix-vector multiply in iterative solves is reduced to O(N^1.5) or O(NlogN). The FMM and MLFMA also require less memory, and hence, can solve a larger problem on a small computer. MLFMA has been applied to the electromagnetic simulation of scattering and radiation from objects such aircraft and tanks with antennas, penetrable material scatterer, and rough surface.

In the last several decades, periodic structures have gained intensive interests and attentions of researchers. They can find a variety of applications in the area of electromagnetics. The integral equation approaches are developed to analyze the wave propagation in periodic structures. Firstly, an integral equation approach is developed to analyze the two-dimensional (2-D) scattering from multilayered periodic array. The proposed approach is capable of handling scattering from the array filled with different media in different layers. Combining the equivalence principle algorithm and connection scheme (EPACS), it can be avoided to find and evaluate the multilayered periodic Green's functions. For 2^N identical layers, the elimination of the unknowns between top and bottom surfaces can be accelerated using the logarithm algorithm. More importantly, based on EPACS, an approach is proposed to effectively handle the semi-infinitely layered case.

The existing Wi-Fi products are single-ship radio devices that operate in 2.4-GHz & 5.2-GHz bands, and can support data rate up to 70Mbps over a distance of 100 meters, and The existing WirelessHD products are also single-chip devices that operate at 60 GHz, which can enable high data rate up to Gbps over a distance about 10 meters. Due to having the ability to share with the existing IEEE 802.11 standard MAC layer, the IEEE 802.11.ad standard will make the future Wi-Fi mobile products to switch among 2.4 GHz, 5.2 GHz and 60 GHz freely and seamlessly. So, integration of a dual-band WLAN antenna and a 60GHz antenna in a package for a single-chip tri-band radio device is worthwhile developing for various types of portable terminals (palm top, handset, and etc.). In this talk, tri-band antennas in package for single-chip WLAN/60-GHz radio will be presented. Patch array antenna, cavity array antenna and grid array antenna for 60 HGz desings will be disscussed and compared. The dual-band monopole WLAN antenna will also be designed.

Tapered slot-line antenna (TSA) is a well known printed end-fire antenna with traveling wave feature. In order to further improve its performances and extend its functions, several techniques with patents were developed in SEU, and summarized in this article. Here include: grating-loaded TSA for gain enhancement, CPW-feeding TSA for bandwidth broadening, asymmetric TSA structure for beam shaping, coupled TSA with hybrid network for mono-pulse beam forming. Both conceptual illumination and simulated/measured results are described.

Based on a review of the family of conventional printed air-fed array antennas such as Fresnel-Zone-Plate (FZP) antennas, reflectarray (RA), transmitarray (TA), and Fabry-Perot resonator (FPR) antennas, a new structure is proposed and named as a Compound air-fed array (CAFA) antenna. It may be considered as a combination of RA and TA, also be understood as a phase-compensated FPR. After a physical explanation in principle, the CAFA antennas for different design targets: for high gain, or broad bandwidth, or thin profile, are presented in comparison, they have obvious merits and also some restrictions in performances.

30 August 2012 1400-1530 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

My talk discusses the following topics on millimeter-wave high-gain high-efficiency planar waveguide slot array antennas using low-loss transmission lines paying attentions to the simplified structures and the fabrication costs.
1. Losses of copper-clad dielectric substrates in the millimeter-wave band.
2. Losses of transmission lines in the millimeter-wave band.
3. Losses of a post-wall waveguide slot array antenna in the millimeter-wave band..
4. Transitions to post-wall waveguides (SIW) tolerable for fabrication error.
5. Slot array antenna on a rectangular waveguide with air-layer insertion for loss reduction.
6. Corporate-feed hollow-waveguide slot array antennas by diffusion bonding of laminated metal plates.
For instance, as for Topic 5, the measured transmission loss is reduced to 17% by inserting an air layer in the half along the height in a single-mode rectangular waveguide of LTCC with the dielectric constant of 6.6 in the 60GHz band. As for Topic 6, the overall estimated conductor loss is 0.26dB by assuming the copper conductivity of 5.8x107S/m in a plate-laminated waveguide corporate-feed 16x16-element slot array with 33.0dBi gain in the 60GHz band. The antennas can be extended to submillimeter waves around 350GHz.

With the development of satellite navigation technology, many countries have started to build their own satellite navigation systems. Nowadays, satellite navigation systems are intensively used. The American GPS and the Russian GLONASS are already operating world-wide. The Chinese Compass system has also provided a partial service. Future satellite navigation receivers will be provide multimode operation utilizing different satellite navigation systems to improve their positioning accuracy and reliability, so the design of terminal antenna for multimode satellite navigation systems is practically desirable.
A multimode satellite navigation receiver is required to cover several frequency bands for GPS, GLONASS, GALILEO and COMPASS systems. Each GNSS system has several frequency bands. The challenges in the design of a multiband receiver antenna come from two requirements – the antenna needs to provide right-hand circular polarization with a low axial ratio and also maintain a low VSWR over multiple frequency bands. In this talk several designs of dual band and tri-band GNSS antennas will be covered and their operating principles will be discussed.

30 August 2012 1030-1200 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

Millimeter-wave technologies are growing in sensing and communication applications. Automotive-radar systems are the first driving application of millimeter-wave technologies. The successful growth of the automotive radar contributes the cost reduction of millimeter-wave devices. The successive millimeter-wave applications are desired in these days. High-speed wireless communication systems using millimeter-wave signals are gradually growing in Japan. For example, HD video transmission can be achieved without data compression by Giga-bit wireless communication using millimeter-wave. Various standard-setting organizations, Wireless HD, IEEE802.15.3c, IEEE802.11ad, WiGig, are founded to progress the millimeter-wave communication systems. High gain antennas can be designed in the millimeter-wave band even though the physical size of the antenna is small. Beam-scanning function is attractive to detect the target in sensing systems and to cover wide area with high gain in communication systems. Three “LOWs”; low loss, low cost and low profile are important features in choosing the feeding system of high gain antennas. There are no perfect antennas for any uses. We always have to select feeding systems with distinct advantages depending on the specification. How many millimeter-wave antennas should be prepared to cover all applications? Two types of millimeter-wave antennas can cover most applications; microstrip array antennas and slotted waveguide antennas since they both have completely opposite advantages and compensate each other. Therefore, we have tried development of various designs of these two antennas. This lecture presents the distinct features of the planar antennas. The designs and the principles of the antennas are explained. The key technologies of the high-gain planar array antennas for use in the millimeter-wave band are presented in the seminar.

30 August 2012 0900-1030 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

Recent developments in wireless communication systems have been accelerating development of low-profile wideband antennas. In response to this trend, techniques for realizing wideband operation, including dual frequency band, multi-frequency band, and extremely wide frequency band operation, have been receiving considerable attention. This seminar presents recent progress in low-profile wideband antennas, which are categorized as either natural or metamaterial (MTM) antennas. The natural antennas are based on the right-handed material property and MTM antennas are based on the right- and left-handed material properties. The outline of this seminar is composed of three chapters. Chapter 1 describes fundamental concepts for realizing wideband antennas. Chapter 2 summarizes the analysis methods for natural and MTM wideband antennas, including the IEM (integral equation method) and MTM transmission line theory. Chapter 3 presents the antenna characteristics of several representative wide-band natural and MTM antennas. These antennas belong to four categories: (1) card-type antennas, (2) base station antennas, (3) flush-mount antennas, and (4) tilted beam antennas. Unique characteristics of these antennas are presented and discussed.

In this seminar, Prof. Dou Wenbin will introduce Southeast University, College of Information Science and Engineering (former Department of Radio Engineering) and the State Key Laboratory of Millimetre Waves. The presentation will provide details on the accurate measurement of complex permittivity of dielectric material based on Quasi-optical open cavity technique at millimetre waves, as well as introduce the measurement of complex permittivity of material at microwaves using strip line technique. Finally some work on antennas, radomes and imaging will be presented.

Traveling-wave antenna is one kind of commonly used antenna. To know its radiation mechanism is helpful in the design of new structure traveling-wave antennas. This talk plans to give some new explanations for the radiation mechanism of the traveling-wave structures. Novel MIM CRLH transmission line leaky-wave antenna, straight-slotted leaky-wave substrate integrated waveguide (SIW), and periodic leaky-wave structures with finite length are used as examples. In our investigation, it is found that the far-field of the traveling wave structure is mainly determined by some special sections on the structure, we called these special sections the Effective Radiation Sections (ERSs), while the radiations from the rest sections of the structure can be cancelled and have little contribution to the total far fields. Based on the theory of ERS, an approach for suppressing the side lobe level and generating radiation null region in the radiation pattern of the leaky-wave antenna is proposed. This approach can also give lower cross polarization level of the traveling wave antenna. In addition, the near field constitution of the periodic leaky-wave structure is studied using the spatial harmonic expansion (mode expansion) method. The influence of the bound modes on the far field of the periodic structure with finite length is discussed. It is proven that the radiation fields of the periodic leaky-wave structures with finite length can be calculated by the summation of the far fields generated by the corresponding ERSs for different spatial harmonics.

Dr. Shuang Zhang, School of Physics & Astronomy, University of Birmingham, UK

2 July 2012 1100-1200 hrs @ ECE Conference Room E4-05-39, National University of Singapore

Metamaterials are artificial photonic materials that show unconventional electromagnetic properties arising from their structural effect. Symmetry, coupling and interference between different excitation processes play important roles in introducing novel functionalities. Examples include a new type of Mobius symmetry, gigantic chirality that breaks mirror symmetry, and plasmon induced transparency that mimicks the electromagnetic induced transparency (EIT) in atomic systems. In this talk, I will present a number of functional metamaterials and plasmonic devices, passive or active, based on the mechanism of coupling and symmetry, including a chirality switching metamaterial, a plasmonic demultiplexer with continuum mediated anti-Hermitian coupling, and a metamaterial with interference induced asymmetric transmission.

Prof. Edward Kai-Ning Yung, Department of Electronic Engineering, City University of Hong Kong

Spoilt by the convenience provided by mobile phones, the public is now addicted to wireless systems. Pulled by market demands and pushed by technological advancements, fixed-wire links are being replaced by wireless ones of various formats and of different frequencies. The ubiquitous wireless system has drastically changed our daily lives as it facilitates us to do anything anywhere anytime. However, it also subjects us to a non-ionizing radiation 24 hours in a day, seven days in a week. Simply put, we, especially our brains, are vulnerable to the illumination of a strong electromagnetic field. It must be accurately accessed; otherwise, further developments of wireless systems could be banned by law. To this end, the present study aims to find the penetration of electromagnetic waves in our brain due to an antenna in proximity.
Wave penetration into a brain is a hot topic and many new observations are found in recent literature. In general, brain tissues are treated as lossy dielectric materials and their characteristics are measured accordingly. It is found that the conductivities and the permittivities of some animal in vivo and in vitro decline 18% and 9%, respectively. Moreover, it is observed that the billions of neurons in a brain exhibit a sizable dipole moment. Thus, it is postulated that a brain is bi-anisotropic, similar to a snail, a jellyfish, and many invertebrates.
Analytically, there exists no rigorous method for finding the wave scattered from and wave penetration into a heterogeneous bi-anisotropic body of arbitrary shape. One of the difficulties is derivation of the relevant dyadic Green’s function in a lossy bi-anisotropic medium. To this end, a new yet analytically rigorous method has been developed for solving the aforementioned problem. It works because the Maxwell’s equations in the complex medium are merely manipulated without solving the wave equations.

The advancement of electromagnetic engineering has been driving the need to develop efficient time domain techniques for transient analysis of transmission, propagation and reception of electromagnetic pulses. This presentation addresses one method based on numerical inversion of Laplace transform (NILT), which overcomes the restrictions in previous approaches, leads to good accuracy in both late and early time, and has a simple algorithm, short calculation time, small required memory size and readily controlled error. To our knowledge, this would be the first time that systematically treats the theory of NILT and its application in the transient analysis of electromagnetic waves. This talk highlights how to overcome the restriction that numerical inversion of Laplace transform has high demands on image functions, and places the emphasis on how to extend and apply this method to a variety of cases. The correctness and effectiveness of this work are validated through the comparisons between our results and those published in the literature. Meanwhile, the results that cannot be achieved with the previous approaches are also provided. Moreover, this talk presents some applications of the new technique in diverse engineering fields, including ultra wideband technology, electromagnetic compatibility and material science.

Countries with substantial coastal regions require greatly enhanced systems to monitor activity occurring within their Exclusive Economic Zones (EEZ). According to the United Nations Convention on the Law of the Sea (UNCLOS) of 1992, participating countries have extensive rights of exploitation within the EEZ, which extends up to 200 nautical miles (nm) from shore.  Activity will include isolated or grouped, moving and/or anchored surface targets and low-flying aircraft. The targets may be military/commercial, friend/foe, small/large. Beside the economic benefits, a participating country carries responsibilities such as prevention of smuggling, terrorism and piracy; the effective management and protection of off-shore fisheries; search and rescue, vessel traffic services, pollutant control as well as meteorological and oceanographic data collection.
Traditional land-based microwave radars are limited to line-of-sight, which means a maximum range of 50-60km even with an elevated radar platform. The EEZ can be covered by microwave radar in a patrol aircraft, but requires three to five aircraft (well above 20,000ft) with many hours on station. Satellites have neither the spatial nor the temporal resolution to provide this surveillance in real-time. Sky wave high frequency (HF) radars can be used for this purpose, but they need large installations, are expensive and detection of surface targets is still limited. Optimum sensor for EEZ surveillance seems to be the Surface Wave HF radar.
This seminar is about modeling and simulation strategies and challenges in integrated maritime surveillance systems based on High Frequency Surface Wave Radars (HFSWR). Topics to be covered include fundamental radar concepts, HFSWR signal characteristics (signal, noise, clutter, interference, etc.), Surface wave propagation modeling and mixed-path effects, Transmit/Receive Antenna systems and beam forming/steering, Target reflectivity and RCS prediction/reduction, and Stochastic modeling.

This seminar discusses modeling and simulation strategies as well as computer tools in teaching/studying Electromagnetic Engineering (EME). EME is multidisciplinary and extends from electrical, electronics, and electromechanical to computer engineering, biomedical engineering to chemistry. This necessitates multiphysics modeling of electromagnetic fields as well as novel computer simulation approaches. Engineers speak with numbers and numbers are obtained either via measurements or computations. This necessitates review of fundamental concepts such as accuracy, precision, resolution, error, and uncertainty. Then, modeling and simulation concepts, strategies and challenges in EME will be discussed. Problem definition in terms of physical requirements, deterministic and stochastic approaches, conceptual/analytical modeling, discretization and numerical modeling, simulation, validation, verification, and calibration are presented. Finally, several user-friendly virtual tools which are very effective in teaching lectures like not only Antennas and Radiowave Propagation, but also others like EM Wave Theory, Transmission Lines, Microstrip Circuit Design, Radar Cross-Section Prediction, etc. Canonical tests and examples will be included to illustrate range of validity, parameter optimization, and time and frequency domain comparisons.

This talk introduces research on wireless communications and microwave technologies at Shanghai University, China.  For wireless communications, we focus on the use of 2.4-GHz ISM band in City Metro Networks. I show that RF interferences between wireless data communication systems and the variety of existing users of this band become a critical issue. To solve the EMC and security problems, many approaches have been adopted in China where Shanghai University has played a leading role and offered valuable suggestions. For microwave technologies, Shanghai University has long been recognized as a Centre of Excellence in China.  I briefly touch on miniaturization of microstrip antennas, wireless power transmission, invisibility techniques, radio frequency device and integrate circuits.

Since 2002, research on artificial compound materials with exotic electromagnetic properties - socalled metamaterials - has skyrocketed worldwide. This presentation will offer an overview of recent research activities at the Institute of High Performance Computing in Singapore, centered on transformation optics with emphasis on wideband transient cloaking and on imaging using metamaterials. Super-resolution imaging involves the interaction of electromagnetic waves with objects that have dimensions similar to, or smaller than the wavelength. That is precisely the hallmark of microwave technology. It suggests that microwave concepts and design approaches may be helpful not only in the description and modeling of the
superlens behavior, but can provide useful tools for designing and realizing the superlens, notably the metamaterial itself. We present some interesting results and insights yielded by the microwave perspective, including waveguide, circuit and filter representations of the superlens. In this context we will also critically revisit the physics of negative refractive index, demonstrate key applications, and discuss fundamental limitations.

Prof. Kai Fong Lee, Dean Emeritus, School of Engineering and Professor Emeritus, Electrical Engineering, University of Mississippi

Microstrip patch antennas have become favorites of antenna designers.  Depending on the application, it is desirable for the antenna under design to be circularly polarized or multi-band.  A simple way of achieving these characteristics is by means of cutting suitable slots on the patch.  This talk presents some of the recent work by the author and his collaborators on this method.  After an overview of single-feed circularly polarized patch antennas, the use of slots in enhancing the performance of these antennas is described, followed by a design which achieves polarization reconfigurability. The talk concludes with a technique of designing dual and triple band linearly polarized patch antennas.

10 April 2012 1030-1130 hrs @ Meeting Room S2-B1 (S2-B2b-75), School of EEE, Nanyang Technological University

As a major remote sensing sensor, Synthetic aperture radar (SAR) can produce high resolution images from a moving platform, such as an airplane or a satellite, and is being widely used in many civilian and military applications. The main advantage of SAR is that images of the illuminated area can be obtained independent of time-of-day or weather conditions (e.g., fog, cloud level, rain, and snow). Compressive sensing (CS) is a new developing novel theory that enables perfect recovery of signals and data from what appear to be highly sub-Nyquist-rate samples. It offers the possibility to effectively reduce data size, complexity, weight, power consumption and costs of SAR systems. As an example, a novel spaceborne SAR wide-swath imaging approach based on Poisson disk-like nonuniform sampling and compressive sensing is used to illustrate the CS-SAR application and some processing issues are discussed in details.

The marine controlled-source electromagnetic (CSEM) technology has attracted much attention for its capability in directly detecting thin hydrocarbon reservoirs. The approach is based on comparing the electric field amplitude as a function of the source-receiver offset with a similar measurement for a non-hydrocarbon bearing reservoir. The presence of hydrocarbon raises the amplitude of the measured electric field indicating the existence and to some degree determining the horizontal extent of the hydrocarbon zone; however with this approach it is difficult to know the reservoir's depth and shape. A more rigorous approach to address this type of application is the full nonlinear inversion. In this presentation we present two rigorous nonlinear inversion algorithms.

The first method is the so-called pixel-based inversion (PBI). In this approach the investigation domain is subdivided into pixels, and by using an optimization process the conductivity distribution of the investigated domain is reconstructed. The optimization process uses the Gauss-Newton minimization method augmented with various types of regularization. This PBI approach has demonstrated its ability to retrieve reasonably good conductivity images. However, the reconstructed boundaries and conductivity values of the imaged anomalies are still not adequately resolved. Nevertheless, the PBI approach can provide some useful information on the location, the shape and the conductivity of the hydrocarbon reservoir.

The second method is the so-called model-based inversion algorithm (MBI), which uses a priori information on the geometry to reduce the number of unknown parameters and to improve the quality of the reconstructed conductivity image. This PIA approach can be also used to refine the conductivity image that we obtained using the PBI algorithm. The PIA also adopts the Gauss-Newton minimization method. The parameters that govern the location and the shape of an anomaly include the depth and the location of the user-defined nodes for the boundary of the region. The unknown parameter that describes the physical property of the region is the conductivity.

We will show some inversion results of synthetic and field data to illustrate the PBI and MBI approaches. We further show that by combining both inversion algorithms we arrive at a better interpretation of the controlled-source electromagnetic data. This work is a joint work with T.M. Habashy, M. Li, and G. Pan.

The proposed seminar will focus onto the non-destructive evaluation of conductive layered structures in the eddy current (diffusive) realm. Here this means that proper coil probes are placed in air above the structure under testing, eddy currents are generated within it and diffuse in it, defects (cracks, voids) affect their distribution pattern, and consequently anomalous magnetic fields outside it appear, whose measurement should yield pertinent information on the defects (variations of impedances of probes might be the quantity of interest as well). If one wishes to fully understand the observed electromagnetic phenomena, obviously to be able to decipher the observed signals so as to get the sought information on the defects causing them, and possibly to design better probes in order to achieve more effective inspections, one has to develop fast and robust simulation tools of such phenomena. That issue will be discussed in some depth during the exposé. This will involve (after introduction of the challenges faced and some illustrations of them) a description of the pertinent vector integral field formulations employed and associated dyadic Green functions as needed, and effective ways to deal with them. A number of synthetic and experimental results will be proposed as examples. One will then put forth a number of still open questions, with, time permitting, a glimpse also to fast imaging methodologies under study. Potential linkage with joint investigation of anisotropic composite panels carried out by NUS and L2S with support of a French-Singaporean MERLION program, will be pointed out in addition. Notice that most of the material presented in the seminar has been resulting from a close partnership of L2S with the DISC Department of CEA LIST in Saclay and the MEANDER group of the University of West-Macedonia in Kozani, in particular marked by the on-going PhD thesis of R. Miorelli. The said research is also developed inside the so-called CIVAMONT project associating 15+ academic laboratories in Europe within the challenging field of elastic and electromagnetic non-destructive testing.

Prof. Wolfgang-Martin Boerner, Professor Emeritus and Director of UIC-ECE Communications, Sensing & Navigation Laboratory Dept of ECE, University of Illinois

23 March 2012 1500-1700 hrs @ Executive Seminar Room (S2.2-B2-53), Nanyang Technological University

With the un-abating global population increase our natural resources are stressed as never before, and the global day/night monitoring of the terrestrial covers from the mesosphere to the litho-sphere becomes all the more urgent. Microwave radar sensors are ideally suited for space imaging because those are almost weather independent, and microwaves propagate through the atmosphere with little deteriorating effects due to clouds, storms, rain, fog aerosol and haze. Globally humidity, haze and aerosols next to cloudiness are increasing at a rather rapid pace, whereas only 20 years ago all of those covered 48% of the globe, today those have increased to about 62% and within another 20 years may exceed 80% for irreversible reasons. Thus, optical remote sensing from space especially in the tropical and sub-tropical vegetated belts is already and will become ever more ineffective, and microwave remote sensing technology must now be advanced strongly and most rapidly hand in hand with digital communications technology because operationally it is more rapidly available especially for disaster mitigation assistance. The basic radar technologies to do the job at day and night are the multimodal Synthetic Aperture Radar (SAR) sensors, first developed for air-borne sensing implemented as for example in 1978 with the first space-borne digital Sea-Sat L-Band SAR which had severe limitations in that it was of fixed wide swath-width at a single arbitrary polarization (HH) and of rather poor 25m resolution. In the meantime, fully polarimetric multi-modal high resolution SAR systems at multiple frequencies and incidence angles were introduced first with the multi-band AIRSAR of NASA-JPL culminating in the once-only pair of SIR-C/X-SAR shuttle missions of 1994 April and October, which laid the ground work for true day/night space remote sensing of the terrestrial barren and vegetated land and ocean covers using multi-band polarimetric SAR. Thereafter, the Canadian CCRS, the German DLR and the Japanese NASDA & CRL {now JAXA & NICT} took over introducing and steadily advancing the Convair-580, the E-SAR (now F-SAR) and Pi-SAR airborne highly advanced fully polarimetric sensors platforms, respectively. These separate international multi-modal fully polarimetric and also interferometric airborne SAR developmental efforts culminated in a well coordinated group effort of three independent teams eventually launching and operating Fully Polarimetric Satellite SAR Sensors at L-Band (ALOS-PALSAR launched by JAXA/Japan in 2006 January - and to be followed by ALOS-PALSAR-2 &3); at C-Band (RADARSAT-2 launched by CSA-MDA in 2007 December - to be followed by independent RADARSAT-3&4) and at X-Band (TerraSAR-X launched by DLR-Astrium in 2007 July with the follow-on tandem mission TanDEM-X launched in June 2010) . Thus, international collaboration on advancing day & night global monitoring of the terrestrial covers was demonstrated with the launch of the three fully polarimetric multi-modal SAR Satellites at L-, C-, X-Band and its first tandem satellite-pair update of the DLR TanDEM-X. Recently NASA-JPL is joining these global efforts again, and all of these efforts will be topped by the near-future joint DLR-JPL DESDynI/Tandem-L wide-swath, high-resolution fully polarimetric sensor implementation.

Dr. Shah Nawaz Burokur, Institut d’Electronique Fondamentale, Univ.

21 March 2012 1000-1100 hrs @ Seminar Room (E5-03-20), National University of Singapore

The use of judiciously engineered metamaterials in novel class antennas and microwave devices is presented. In this seminar, I will review the research activities of the IEF/PSud in the field, discussing the motivations of this research as well as the applications for aeronautical and telecommunication domains. 

Dr. Sebastian Hantscher, Fraunhofer Institute for High Frequency Physics and Radar Techniques, Department Millimeter Wave Radar and High Frequency Sensors

21 March 2012 1430-1600 hrs @ Potential Seminar Room (Connexis North Level 13), Institute for Infocomm Research

The seminar talk will cover the following topics:
• Overview about security scanners on airports • Active radar systems • System design and RF components • Principle of the synthetic aperture and image formation • Results (1D and 2D apertures)
• Passive radar systems • Radiometer basics and system design • Stand-off detection

Prof. Michael A. Jensen, Department of Electrical and Computer Engineering, Brigham Young University

The development of multiple-input multiple-output (MIMO) technology for wireless communication more than a decade ago pushed the research community to explore not only the temporal but also the spatial characteristics of multipath propagation, and as a result we now have a relatively complete understanding of the point-to-point MIMO channel. However, as highlighted in this talk, new applications of MIMO technology require that we obtain an even deeper appreciation of the nature of the propagation channels and the features of the parallel radio chains required for MIMO implementation. For example, we present coherent propagation measurements from multiple cellular base stations to demonstrate the potential benefits of cooperative MIMO signaling for multi-user communications. This analysis shows that cooperative MIMO signaling can provide multi-user throughput gains that are significantly higher than what can be achieved using more traditional multiple-access strategies under favorable channel conditions. We also present an analysis of how antennas and electromagnetic propagation can be used to establish secret encryption keys for enhancing communication security.

The 60GHz 4-element phased-array transmit/receive (TX/RX) system-in-package (SiP) antenna modules in 65nm CMOS technology are presented. The design is based on the all-RF architecture with 4-bits RF switching type phase shifters, variable gain amplifiers, 4:1 Wilkinson power combiner/divider, low noise amplifier, power amplifier, 6-Bits Unary digital-to-analog converter, etc. The 2x2 TR phased array have been packaged with 4 antennas in a low temperature co-fired ceramic (LTCC) module. The Tx/Rx ICs are flip-chip bonded onto LTCC substrates and then assembled onto printed circuit boards with bond wires. Electrical characteristics of the RF signal traces from IC to antenna array are investigated, including wideband transition design by coax-via and flip-chip compensation. The antenna array is designed on the other side opposite to the flipped chip, using the backed cavity to achieve more than 20% bandwidth and isolation design for better array performance. The radiation efficiency of antenna element may exceed 90%. The phased-array beam steering has been demonstrated with good agreement between simulation and measurement. Besides, the LTCC SiP module with 4×4 antenna arrays of low mutual coupling for 60-GHz phased-array transceiver applications are also proposed, demonstrating beam patterns with a wide range of scanned angle 60° in the E-plane and 30° in the H-plane, and a peak gain greater than 15 dBi over the entire band.

27 January 2012 1600-1700 hrs @ School of EEE, Nanyang Technological University

Antenna design is often an art, practiced by engineers who frequently rely on years of experience they have to modify the existing designs in order to develop new ones that can better meet the desired performance specifications. Recently, new concepts for antenna design have been introduced via the use of “Transformation Electromagnetics,”or T-EM, where we transform Maxwell’s Equations from one coordinate system to another in order to design material parameters of the medium in which an antenna is embedded, with a view to realizing a desirable antenna performance that may be difficult to achieve by using conventional approaches and/or with conventional media. The original papers on Transformation EM, more specifically on Transformation Optics (TO), described how one could bend or distort the propagation of light around an object to conceal it electromagnetically, i.e., to cloak it. This was accomplished by mapping the initial configuration of the electromagnetic fields on to a Cartesian mesh. The twisting of the Cartesian mesh, in essence, transforms the coordinates of the electromagnetic fields, which, in turn, helps conceal a given object or to cloak it. Transformation optics relies on the basic concept that, in principle, it is possible to manipulate the propagation of electromagnetic waves in any fashion, for the desired application, by capitalizing on the fact that Maxwell’s equation are invariant to coordinate transformation. It is worthwhile to recognize, however, that this is only true provided we concurrently transform the material parameters as well, as we go from one coordinate system to another, in a manner dictated by the Transformation Optics paradigm. It should be realized that these materials often fall in the category of Metamaterials (MTMs), because they are not available in nature and, hence, must be artificially synthesized. Recently, the application of Transformation Optics has gone well beyond cloaking, and has been found useful for designing antennas as well. This aspect will be the focus of this presentation in which we will discuss the design of both antennas and scatterers by using the principles of coordinate transformation. Next, we will introduce an alternative viewpoint—also useful for designing antennas and related systems—that is based upon the transformation of EM fields from the input to the output planes of a material slab, whose parameters are adjusted to achieve the desired transformation of the aperture fields of the above two planes, as the fields impinging upon the slab propagate through it. The main advantage of the proposed approach, which we will refer to herein as the TF method, is that it does not rely upon the transformation of the geometry from one co-ordinate system to another. As a consequence, the material parameters needed to achieve the desired goal, namely the transformation of the incident field into the desired one in the output aperture, are not only likely to be realistic and physically realizable, but are also less dispersive than those needed in the TO approach mentioned above. In addition, they have low loss and can be designed to handle both the polarizations.

Prof. Jian-Ming Jin, Electromagnetics Laboratory and Center for Computational Electromagnetics, University of Illinois at Urbana-Champaign

13 January 2012 1530-1700 hrs @ Seminar room, 15th floor, Connexis, Fusionopolis

Antennas play a critical role in wireless communication, remote sensing, space exploration, defense,electronic warfare, and many other electronic systems. Quantitative antenna analysis is important to the design and optimization of antennas, especially complex antennas that are not easily designed by intuitive approaches, such as ultra-wideband antennas and phased arrays designed with novel materials. In this talk, we will provide an overview on the development and application of the time domain finite element method for the broadband analysis of antennas and phased arrays. After a brief introduction of the time-domain finite element method for solving Maxwell’s equations, we will discuss the major challenges for the time-domain finite element analysis of antenna and phased-array problems, which include (1) truncation of open free space, (2) modeling of antenna feeds and network, (3) modeling of novel dispersive materials, (4) modeling of large antennas and finite phased arrays, and (5) modeling of infinite periodic phased arrays. For each challenge, we will describe the state-of-the-art solutions and demonstrate their practical applications. The techniques presented are also applicable to a variety of electromagnetic modeling problems such as modeling of electronic packaging and electromagnetic compatibility problems.

Prof. Viswanathan N Bringi, Professor, School of Electrical and Computer Engineering, College of Engineering, Colorado State University

The promise of more accurate measurement of rainfall by radar has been the driving force for the introduction of dual-polarized technology in weather radars. The U.S. National Weather Service has undertaken a major upgrade to add dual-polarization technology to their ~150 Doppler weather radars within the next few years. MeteoFrance has also decided to go ahead and implement this technology for operational uses whilst the U.K. Met Office is developing the technology in-house with the intent of modernizing their radar network in the future. One important impact of this technology is towards improved rainfall input to hydrological models for flood predictions, especially the extreme rainfall events. Radars can often, but not always, provide the needed high spatial (few 100s of meters) and temporal resolutions (~ few minutes or better) needed for urban or small basin hydrology. Dual-polarized radar technology has long been studied at the S-band (~ 3 GHz) and C-band (~5.5 GHz) frequencies, and more recently a revival at X-band (~10 GHz) has taken hold. Indeed, there has been a rapid proliferation of compact dual-polarized X-band radar networks dedicated for hydrology. This talk will describe the recent advances, as well as pros and cons, in measurements of rainfall using radars at these three important frequencies.

Prof. Koichi Ito, Department of Medical System Engineering, Director, Research Center for Frontier Medical Engineering, Chiba University, Japan

11 January 2012 1530-1730 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

Recently, a study on body-centric wireless communications has become an active and attractive area of research because of their various applications such as e-healthcare, support systems for specialized occupations, monitoring systems for elderly and handicapped people, entertainment, and so on. Whereas UHF bands are subjects of interest especially in Europe and USA, HF bands are of great interest especially in Japan. Hence, all of the prospective frequencies are in an extremely wide range, and an objective idea on how to select a right frequency band for individual applications is required. As for the antennas, many types of wearable (on-body) and implantable (in-body) antennas have been reported. Currently in our laboratory, we have been studying on frequency dependence of basic characteristics of simple wearable antennas as well as body-centric wireless communication channels in the range of HF to UHF (3 MHz – 3 GHz). Also, we have been investigating numerically and experimentally thin implantable antennas in UHF band. In this presentation, firstly, electric field distributions around the human body wearing a small top-loaded monopole antenna are numerically calculated and compared in a wide range of HF to UHF bands. Then, received open voltages at receiving antennas which are equipped at several different points on the human body are numerically investigated. The received open voltages are also numerically calculated and compared with several different postures of the human body. Next, several conventional as well as practical wearable antennas are briefly introduced. Finally, some basic performances of miniaturized thin implantable antennas are numerically calculated in UHF band. Typical experimental validations are also demonstrated.

Prof. Koichi Ito, Department of Medical System Engineering, Director, Research Center for Frontier Medical Engineering, Chiba University, Japan

10 January 2012 1530-1730 hrs @ Franklin Seminar Room (Fusionopolis, 11th floor, Connexis South Tower), Institute for Infocomm Research

In recent years, various types of medical applications of microwave antennas have widely been investigated and reported. Such applications fall into three main categories; Information transmission, diagnosis and treatment. In this presentation, three different types of antennas which have been studied in our laboratory are introduced. Firstly, a pretty small antenna for an implantable monitoring system is presented. A cavity slot antenna is a good candidate for such a system. Some numerical and experimental characteristics of the antenna are demonstrated. Secondly, some different antennas or “RF coils” for MRI systems are introduced. In addition, SAR (specific absorption rate) distributions in the abdomen of a pregnant woman generated in a bird cage coil are illustrated. Finally, after a brief overview of thermal therapy and microwave heating, coaxial-slot antennas and array applicators composed of several coaxial-slot antennas for minimally invasive microwave thermal therapies are introduced. Then a few results of actual clinical trials by use of coaxial-slot antennas are demonstrated from a technical point of view. Other therapeutic applications of the coaxial-slot antennas such as hyperthermic treatment for brain tumor and intracavitary hyperthermia for bile duct carcinoma are introduced.