This report describes an application of relaxation technique to the alternating direction implicit finite-difference time-domain (ADI-FDTD) method. The ADI-FDTD method is quite stable even when the CFL condition is not satisfied. However, the ADI-FDTD method is computationally more complicate than the conventional FDTD method and this method requires to solving the tri-diagonal matrix equation. Thus, this method may require more computational cost than the standard FDTD method due to the large scale tri-diagonal matrix solution corresponding to a large number of meshes. In this report, relaxation-based solution technique is discussed for the matrix solution and a simple numerical example is shown. As a result, it is confirmed that ADI-FDTD method with the relaxation technique is useful for the acceleration of the electromagnetic field simulation.

In this review paper we showcase recent activities on silicon photonics science and technology research in Hong Kong regarding two important topical areas--microresonator devices and optical nonlinearities. Our work on silicon microresonator filters, switches and modulators have shown promise for the nascent development of on-chip optoelectronic signal processing systems, while our studies on optical nonlinearities have contributed to basic understanding of silicon-based optically-pumped light sources and helium-implanted detectors. Here, we review our various passive and electro-optic active microresonator devices including (i) cascaded microring resonator cross-connect filters, (ii) NRZ-to-PRZ data format converters using a microring resonator notch filter, (iii) GHz-speed carrier-injection-based microring resonator modulators and 0.5-GHz-speed carrier-injection-based microdisk resonator modulators, and (iv) electrically reconfigurable microring resonator add-drop filters and electro-optic logic switches using interferometric resonance control. On the nonlinear waveguide front, we review the main nonlinear optical effects in silicon, and show that even at fairly modest average powers two-photon absorption and the accompanied free-carrier linear absorption could lead to optical limiting and a dramatic reduction in the effective lengths of nonlinear devices.

Advances in smart card technology encourages smart card use in more sensitive applications, such as storing important information and securing application. Smart cards are however vulnerable to side channel attacks. Power consumption and electromagnetic radiation of the smart card can leak information about the secret data protected by the smart card. Our paper describes two possible hardware countermeasures that protect against side channel information leakage. We show that power analysis can be prevented by adopting photo-coupling techniques. This method involves the use of LED with photovoltaic cells and photo-couplers on the power, reset, I/O and clock lines of the smart card. This method reduces the risk of internal data bus leakage on the external data lines. Moreover, we also discuss the effectiveness of reducing electromagnetic radiation by using embedded metal plates.

A new structure learning approach for Bayesian networks (BNs) based on dual genetic algorithm (DGA) is proposed in this paper. An individual of the population is represented as a dual chromosome composed of two chromosomes. The first chromosome represents the ordering among the BN nodes and the second represents the conditional dependencies among the ordered BN nodes. It is rigorously shown that there is no BN structure that cannot be encoded by the proposed dual genetic encoding and the proposed encoding explores the entire solution space of the BN structures. In contrast with existing GA-based structure learning methods, the proposed method learns not only the topology of the BN nodes, but also the ordering among the BN nodes, thereby, exploring the wider solution space of a given problem than the existing method. The dual genetic operators are closed in the set of the admissible individuals. The proposed method is applied to real-world and benchmark applications, while its effectiveness is demonstrated through computer simulation.

In one-cell-frequency-reuse Orthogonal Frequency Division Multiple Access based Time Division Multiple Access (OF/TDMA) systems, communication is blocked by interference from adjacent cells. The most promising solution would be an adaptive modulation and coding scheme that is controlled by estimating the signal-to-interference ratio (SIR). However, there has so far been no way to accurately estimate the SIR using the spreading codes for OF/TDMA systems, because of the asynchronous fast Fourier transform (FFT). In this paper, we propose a novel SIR estimation method that uses a spread pulse-wave symbol and carrier interferometry. Moreover, to introduce multi- input multi-output systems, we modify the proposed method by allocating a different spreading code to each cell. Computer simulation confirmed that the SIR is estimated accurately even if the FFT is asynchronous. On cell boundaries, the average estimation errors that are a ratio between accurate and estimated propagation characteristics are less than 2 dB.

An ultra-deep polymer cavity structure exposed using deep X-ray lithography is used as a template for metal electroforming to produce a 24-GHz cavity resonator. The metal cavity is 1.8 mm deep and has impressive structure, including extremely vertical and smooth sidewalls, resulting in low conductor loss. The measured resonator has an unloaded quality factor of above 1800 at a resonant frequency of 23.89 GHz.

Sensor networks are often deployed in unattended environments, thus leaving these networks vulnerable to false data injection attacks in which an adversary injects forged reports into the network through compromised nodes, with the goal of deceiving the base station or depleting the resources of forwarding nodes. Several research solutions have been recently proposed to detect and drop such forged reports during the forwarding process. Each design can provide the equivalent resilience in terms of node compromising. However, their energy consumption characteristics differ from each other. Thus, employing only a single filtering scheme for a network is not a recommendable strategy in terms of energy saving. In this paper, we propose a fuzzy-based adaptive filtering scheme selection method for energy saving. A fuzzy rule-based system is exploited to choose one of three filtering schemes by considering the false traffic ratio, the security threshold value, distance, and the detection power of the filtering scheme. The adaptive selection of the filtering schemes can conserve energy, and guarantee sufficient resilience.

In this paper, we propose a multipath en-route filtering method to deal with the problems caused by black hole attacks and selective forwarding attacks. Our result shows that the method is more resilient to these problems up to a certain number of compromised nodes than the statistical en-route filtering scheme.

A periodically loaded ultra wideband (UWB) bandpass filter based on the electromagnetic band-gap (EBG) concept is presented. Compact wideband filters with steep transition bands can be designed easily using this novel methodology. Unit cells in the EBG circuit model are realized by capacitive and inductive parallel loading of a transmission line. These unit cells are cascaded to realize bandpass filters whose bandwidth depends on the reactive loading of unit cells. The number of unit cells determines the steepness of the band edges of the filter. The main advantage lies in the fact that the size of unit cells can be small because electrical length of transmission line segments in unit cells can be chosen arbitrarily, hence the final filter structure becomes small in size. A microstrip filter with 60% bandwidth is designed and the physical size is compared with a conventional wideband bandpass filter designed with quarter wavelength admittance inverters.

In OFDM systems, the pilot signal averaging channel estimation is generally used to identify the channel state information (CSI). In this case, large pilot symbols are required for obtaining an accurate CSI. As a result, the total transmission rate is degraded due to large number of pilot symbols transmission. To reduce this problem, in this paper, we propose time-frequency interferometry (TFI) for OFDM to achieve an accurate CSI.

Yamada, Harashima, and Miyakawa proposed to use a trellis constructed based on a syndrome former for the purpose of Viterbi decoding of rate-(n-1)/n convolutional codes. In this paper, we extend their code-trellis construction to general rate-k/n convolutional codes. We show that the extended construction is equivalent to the one proposed by Sidorenko and Zyablov. Moreover, we show that the proposed method can also be applied to an error-trellis construction with minor modification.

To evaluate whether electromagnetic disturbances that leak from PC displays contain information or not, we need to reconstruct the information from the measured disturbance. This requires a special receiver, and not all test houses have a special receiver. In this paper, we propose performing the evaluation with the spectrum analyzers commonly used for EMI measurement. First, we select a spectrum that containing the frequency component of the vertical sync signal using a spectrum analyzer (SA1). Then, we measure the video output of SA1 using another spectrum analyzer (SA2) and evaluate the disturbance from the frequency component of the horizontal sync signal.

This paper describes near-zero ultra-flattened chromatic dispersion and low confinement loss that can be achieved from a decagonal photonic crystal fiber (D-PCF). The finite difference method with anisotropic perfectly matched boundary layer (PML) is used for the numerical analysis. It is demonstrated that it is possible to design a four-ring D-PCF with ultra-flattened dispersion of 0 0.69 ps/(nm-km) in a 1.30 to 1.75 µm wavelength range and 0 0.22 ps/(nm-km) in a 1.35 to 1.65 µm wavelength range with very low confinement losses of order 0.0011 dB/km. The proposed D-PCF shows promising dispersion tolerance.

We designed subthreshold analog MOS circuits implementing an inhibitory network model that performs noise-shaping pulse-density modulation (PDM) with noisy neural elements, with the aim of developing a possible ultralow-power one-bit analog-to-digital converter. The static and dynamic noises given to the proposed circuits were obtained from device mismatches of current sources (transistors) and externally applied random spike currents, respectively. Through circuit simulations we confirmed that the circuit exhibited noise-shaping properties, and signal-to-noise ratio (SNR) of the network was improved by 7.9 dB compared with that of the uncoupled network as a result of noise shaping.

Basic microwave properties of magnetic photonic (MPC) and degenerate band edge (DBE) crystals are investigated mathematically and experimentally. Two dimensional and three dimensional models are considered demonstrating the very high sensitivity and field growth associated with these crystals. A major part of the paper deals with the development of realistic anisotropic periodic structures using a combination of layers constructed from thin film frequency selective surfaces, alumina, titanate and calcium vanadium garnet (CVG) materials. Measurements for antenna applications demonstrate and validate the theoretical performance of the MPC and DBE crystals. The latter part of the paper will present an exciting and promising development relating to microwave circuit applications. Specifically, a novel dual-line printed circuit is presented to emulate propagation in anisotropic media. As such, the MPC and DBE phenomena can be realized using very simple printed circuits (coupled lines). Lastly, physically small printed antennas and arrays based on the coupled transmission lines are presented.

The electric fields inside and outside a car must be carefully determined when designing a wireless communication system to be employed in the car. This paper introduces an effective simulation method and a precise measurement method of electric field distributions in a cabin of a simplified scale car model. A 1/3 car model is employed for ease of measurement. The scaled frequency of 2859 MHz, 3 times 953 MHz, is employed. The use of a moment method simulator utilizing the multilevel fast multipole method allows calculations to be performed on a personal computer. In order to judge the accuracy of simulation results, convergence of simulation output in accordance with segment size (triangle edge length) changes is ensured. Simulation loads in the case of metallic body only and a metallic body with window glass are also shown. In the measurements, an optical electric field probe is employed so as to minimize the disturbances that would otherwise be caused by metallic feed cable; precise measurement results are obtained. Comparisons of measured and simulated results demonstrate very good agreement which confirms the accuracy of the calculated results. 3-dimensional electric field distributions in the car model are shown and 3-dimensional standing wave shapes are clarified. Moreover, calculated and measured radiation patterns of the car model are shown so the total electric field distributions around a car are clarified.

In order to support driving safety, TPMS (Tire Pressure Monitoring System) has been introduced in U.S.A. and Europe. In Japan, the AIRwatch system has been developed and commercialized. Some studies were made to clarify the electric field environment of this system. However, no detailed calculation of the electric field between the transmitter in the tire and the receiving antenna has been published. This paper clarifies the electric field environment of the Japanese system through electromagnetic simulations by a high performance MoM simulator that utilizes the MLFMM scheme. First of all, electric wave emissions from an antenna mounted in a tire are shown to be larger than that of the same antenna in free space. The tire rubber effects are also investigated. Next, electric field distributions on the windshield holding the receiving antenna are calculated. By comparing calculated electric field levels with those in the free space condition, car body interruptions are clarified. Because car body interruptions are not so severe, it is shown that the free space electric field levels can be used as rough design parameters. Moreover, electric field changes due to tire rotation are also clarified. Calculation accuracy is confirmed by the good agreement with measured data collected from a 1/5 scale car model. To permit estimations to be made in actual situations, the effects of the ground are also investigated. This simulation study introduces a lot of important data useful in TPMS system design.

This paper presents the switched-beam slot antenna over the electromagnetic band-gap (EBG) reflector. This antenna is composed of two slot elements fed with a phase difference and the EBG reflector, which is used in order to realize a low profile structure. The radiation characteristics of this antenna are calculated using the FDTD method. Calculations show that the height of the antenna using the EBG reflector is 60 % lower than that of the antenna using a perfect electric conductor (PEC) reflector. The radiation characteristics at the center of the operating frequency band in the EBG reflector are equivalent to that in the PEC reflector. It is shown that the tilt angle of the main beam in the elevation plane varies with the operating frequency, and the variation in the case of the EBG reflector is caused by its frequency-dependent reflection phase. Moreover, the radiation pattern of the fabricated antenna is measured. The results demonstrate that the low profile design can be achieved by using the EBG reflector, and reveal the influence of the EBG reflector on the antenna efficiency.

We present a parallel multilevel fast multipole algorithm aimed at low cost parallel computers such as GRID computer environments and clusters of workstations. The algorithm is a scheduling algorithm where work packets are handled in a certain order to ensure minimal idle time of the processors and to avoid simultaneous bursts of communication between the processors. The algorithm is implemented on a method of moment discretization of a two-dimensional TM electromagnetic scattering problem. Examples of several optical devices with a size up to 28 500 wavelengths are presented.

A 3D micromagnetic model is established to analyze the dynamics of single-pole-type (SPT) heads, in which a main pole and a soft underlayer (SUL) are included. It is found that, in an SPT head whose write pole thickness Lm and pole width W are 40 nm each, the throat height should be no greater than the pole tip width to avoid high remnant field at the static state. The influences of the head's parameters and the damping constant on switching time of SPT head are analyzed respectively. The crystalline anisotropy field of SUL is also proved to have great effect on the switching characteristics: a high anisotropy field along the cross-track direction could stabilize the magnetic moments in SUL and greatly shorten the switching time.