A CMOS digitally programmable filter technique for VLSI applications

A novel technique for designing analog CMOS integrated filters is proposed. The technique uses digitally controlled current amplifiers (DCCAs) to provide precise frequency and/or gain characteristics that can be digitally tuned over a wide range. This paper provides an overview of the possibilities of using the DCCA as the core element in programmable filters. In mixed analog/digital systems, the digital tuning feature of the proposed approach allows direct interfacing with the digital signal processing (DSP) part. Basic building blocks such as digitally programmable amplifiers, integrators, and simulated active inductors are given. Systematic designs of second-order filters are presented. Fully differential architectures of the proposed circuits are developed. Experimental results obtained from 0.5 μm standard CMOS chips are provided.     

A New Adaptive Beamforming of Multiband Fractal Antenna Array in Strong-Jamming Environment

This paper proposes, for the first time, a new radiation pattern synthesis for fractal antenna array that combines the unique multi-band characteristics of fractal arrays with the adaptive beamforming requirements in wireless environment with high-jamming power. In this work, a new adaptive beamforming method based on discrete cbKalman filter is proposed for linear Cantor fractal array with high performance and low computational requirements. The proposed Kalman filter-based beamformer is compared with the Least Mean Squares (LMS) and the Recursive Least Squares (RLS) techniques under various parameter regimes, and the results reveal the superior performance of the proposed approach in terms of beamforming stability, Half-Power Beam Width (HPBW), maximum Side-Lobe Level (SLL), null depth at the direction of interference signals, and convergence rate for different Signal to Interference (SIR) values. Also, the results demonstrate that the suggested approach not only achieves perfect adaptation of the radiation pattern synthesis at high jamming power, but also keep the same SLL at different operating frequencies. This shows the usefulness of the proposed approach in multi-band smart antenna technology for mobile communications and other wireless systems.

     

Investigation of the fluid/structure interaction phenomenon in IC packaging

In the present study, experiment and simulation studies were conducted on the fluid/structure interaction (FSI) analysis of integrated circuit (IC) packaging. The visualisation of FSI phenomenon in the actual package is difficult due to limitations of package size, available equipment, and the high cost of the experimental setup. However, the experimental data are necessary to validate the simulation results in the FSI analysis of IC packaging. Scaled-up package size was fabricated to emulate the encapsulation of IC packaging and to study the effects of FSI phenomenon in the moulded package. The interaction between the fluid and the structure was observed. The deformation of the imitated chip was studied experimentally. The air-trap mechanism that occurred during the experiment is also presented in this paper. Simulation technique was utilised to validate the experimental result and to describe the physics of FSI. The predicted flow front was validated well by the experiment. Hence, the virtual modelling technique was proven to be excellent in handling this problem. The study also extends FSI modelling in actual-size packaging.     

The effect of heat treatments on the properties of Ti/Pt heating elements for gas sensor applications

Ti/Pt as heating element for gas sensor applications was fabricated on silicon (Si) wafer substrate. The fabricated device was subjected to heat treatment at different prescribed time periods for thermal stability. The energy dispersion spectroscopy (EDS) results of the device indicated that there were no Ti traces on the Pt surface after heat treatment at 450 °C for 3 and 4 h in an argon (Ar) atmosphere. A maximum temperature coefficient of resistance (TCR) with a value of 2.88×10^?3 K^?1 was obtained for the device with 3 h heat treatment.     

Performance Evaluation of Cost-Effective Multicast–Unicast Key Management Method

Group key management is one of the key security issues in multicast networks. The main challenge is to provide a secure group key management method which avoids high key update cost in terms of the number of transmitted keys. In order to achieve low key update cost for group key management, most of the existing methods increase their encryption/decryption cycles which requires a strong cryptographic function. In this paper, a cost-effective key management method is proposed to address the problem of high key update cost without increasing the encryption/decryption cycles. We evaluated our proposed method with existing tree-based methods by using Markov chain and Poisson Arrival Process. Results indicate the efficiency of our proposed method in reducing the key update cost significantly compared to the existing tree-based key management methods.     

Four-wave mixing reduction technique based on smart filter approach

This paper proposed a new technique to suppress the four-wave mixing (FWM) effect by using a smart filter technique. The behaviour of FWM and the performance of wavelength division multiplexing systems with 4 and 16 channels were simulated in the presence of the proposed technique. The simulation was also performed under different parameters such as input power, number of channels and channel spacing. The FWM power drastically decreases by 12 and 19 dB for the 4 and 16 channels, respectively, when the smart filter is used as compared with the conventional system. In terms of system performance, the suggested approach for 4 and 16 channels at the first channel offers low bit error rate (BER) values of 3.23 × 10^?23 and 1.7 × 10^?21, respectively. The smart filter with the channel spacing variation for the 4-channel system subsequently improved the BER value at the fourth channel. Results confirm that the smart filter approach is an active solution that can suppress the FWM effect in optical transmission systems.     

Fabrication of porous ZnO via electrochemical etching using 10 wt% potassium hydroxide solution

We described the fabrication of porous ZnO using the electrochemical etching method. ZnO thin films deposited by radiofrequency sputtering were etched electrochemically using 10 wt% KOH solution as an etching medium to obtain porous ZnO surface structure. A constant voltage of 15 V was applied to enhance the etching process. The etched samples were then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy to examine their structural and optical properties. XRD spectra showed that by performing the electrochemical etching process, porous ZnO could be obtained without severely deteriorating the crystallinity of the samples. Moreover, SEM characterization revealed that hillock-type porous ZnO was fabricated successfully. In addition, the cross-sectional SEM images revealed that there were only minimal changes in the layer thickness after the ZnO had been etched for various lengths of time. This finding shows the dominance of the vertical etching process. Notably, the intensity of PL spectra increased and the PL excitation peak exhibited a red shift trend as the etching time increased. These observations are due to the increase of the surface to volume ratio of the ZnO surface and the strain relaxation along the dislocation and grain boundary.     

BorderSense: Border patrol through advanced wireless sensor networks

The conventional border patrol systems suffer from intensive human involvement. Recently, unmanned border patrol systems employ high-tech devices, such as unmanned aerial vehicles, unattended ground sensors, and surveillance towers equipped with camera sensors. However, any single technique encounters inextricable problems, such as high false alarm rate and line-of-sight-constraints. There lacks a coherent system that coordinates various technologies to improve the system accuracy. In this paper, the concept of BorderSense, a hybrid wireless sensor network architecture for border patrol systems, is introduced. BorderSense utilizes the most advanced sensor network technologies, including the wireless multimedia sensor networks and the wireless underground sensor networks. The framework to deploy and operate BorderSense is developed. Based on the framework, research challenges and open research issues are discussed.     

Wireless LAN Access Point Placement Based on User Mobility

In a wide area campus, a university provides Wireless Local Area Network (WLAN) for users to connect to the Internet. Most users take advantage of this WLAN benefit by using their laptops. However, the number of smart phone users is growing fast. Since a smart phone is able to get an Internet connection using WLAN, users can use their smart phones without having to pay for a cellular operator. Users tend to use their smart phones more, due to their higher mobility compared to a laptop. This capability enables new services in the market, such as Fixed-Mobile Convergence (FMC), which integrates a fixed network (traditional telephony, WLAN) and a mobile network (cellular) to provide seamless voice communications anytime, anywhere. These new applications require a WLAN connection availability nearly everywhere. However, due to limited budgets, a university can only install APs in places with a high connection demand. We propose a novel WLAN AP placement technique that takes user mobility into consideration. This new approach is more complete than previous approaches, which mainly focus on coverage area and throughput data. Our technique has been implemented in our university. The results show the suitability of the WLAN access point locations in our university campus based on user mobility and activities.