Ahm Zahirul Alam

A proposed vertical path adjustment factor for dust storm attenuation prediction

In this paper an adjustment factor which reflects the vertical variation of dust storm (earth satellite links) has been derived based on the analysis of the vertical dust storm behavior. The paper has been divided to four parts. First an introduction to the dust storm phenomena and its effect on microwave signal attenuation. Secondly, observations of the behavior of the vertical dust storm intensity variation. Thirdly, the vertical path adjustment factor has been estimated. Lastly, a conclusion summarized the results and recommended further work. It has been found that the predicted attenuation without the vertical path adjustment factor is much higher than with the vertical path adjustment factor. Therefore, the vertical path adjustment factor will provide optimum utilization for the transmission resources.

Design of a pierce oscillator for CMOS SAW resonator

Development of microelectromechanical system (MEMS) based oscillators have drawn significant attention because it provides CMOS compatibility and multifrequency operations on a single chip. Recently, integrated MEMS resonators have shown great performance by attaining high quality factors and high frequency operations of up to the GHz range. Of interest, is fully integrated SAW resonator which can be connected to an oscillator circuit on the same chip. For oscillator circuit simulations, the CMOS SAW resonator was modeled using its RLC equivalent circuits. The insertion loss of CMOS SAW resonator used in this design is 35.8dB, with motional resistance Rx=8.95kΩ and the motional capacitance and inductance are Cx=199aF and Lx=350uH. For a MEMS resonator to be able to function as an oscillator it needs to be coupled with supporting circuits. There are various types of supporting oscillator circuit topologies namely the pierce oscillator, differential amplifier oscillator or the transimpedance amplifier circuit topology. The topology to be chosen depends on the design requirement, the loop gain of 1 and the zero phase shifts. For this work, the pierce circuit topology was chosen due to its simplicity and high frequency stability. This simple circuit comprising of 4 transistors, helps to achieve low power consumption and excellent phase noise characteristics. This paper will present the analysis, design and the simulation result of a high gain (>; 36dB) and low power pierce circuit topology for MEMS CMOS SAW resonator. The circuit was designed in 0.18um CMOS technology and yield open loop gain >; 36dB.

Modeling of optimum chiral carbon nanotube using DFT

The geometrical structure of carbon nanotubes has been calculated and analyzed in this paper. The analysis of carbon nanotube for Pz orbital, perpendicular to the graphene sheet and thus the nanotube surface forms a delocalized π network across the nanotube, which is responsible for its electronic properties. These electronic properties are obtained from tight binding (TB) model for graphene. Furthermore, optimized DFT calculation shows the optimum chiral of CNT, which is semiconducting zigzag for SWCNT and MWCNT.

A low-cost first-order sigma-delta converter design and analysis

This paper presents the design and analysis of an interface circuit for MEMS or biomedical sensor applications. This circuitry performs the function of an analog-to-digital converter. A first-order 1-bit sigma-delta (Σ-Δ) analog-to-digital converter is designed and simulated using Silterra 0.13μm CMOS process technology with power supply of 1.2V through Cadence. Then the circuit simulation results are transferred to MATLAB, in order to get the frequency domain power spectral density (PSD). The simulation results on noise and error analysis are compared with those from a traditional analog-to-digital converter to prove that sigma-delta is performing better in the case of weak signals acquisition.

Modeling of inductive coupling transducer for activation of low wattage electronic implants

A wireless power supply system based on inductive coupling approach has been developed for implantable biomedical devices that achieves excellent transducer performance by obviating the need for electrical connectors. In this paper, we report in detail the modeling and electrical analysis of an inductive power link for activation of microwatt electronic implants. As the biomedical application requires a safe and clean source of energy to power their operation, the implantable device sourced this power from an astable timer circuit in this system. The system is integrated with a 555 timer connected in astable mode, an inductive sensor, a receiver coil (represented by the secondary winding of transformer), a transmitter coil (represented by the primary winding of transformer) and a monitoring device.

Investigation of inductive coupling approach for non-contact bidirectional transfer of power and signal

Powering implantable low wattage biomedical devices and sensors through non-contact means is on the rise over the past recent years. In view of that, inductive coupling is currently the most favorable means of transferring energy for powering the low wattage implanted devices. The wireless inductive link works as an energy link to power up remote devices and also acts as a communication link to retrieve and write data to the same remote device by using the same set of inductive coils. This paper proposes an op-amp based inductive coupling circuit in order to analyze the magnetic coupling of two coils which can be applicable for the activation of microwatt electronic implants. The inductive powering system is incorporated with an op-amp circuit connected with an inductive sensor constructed by a receiver (embodied by the secondary winding of transformer), a transmitter coil (represented by the primary winding of transformer) and a monitoring device. Moreover this paper also discusses on some design considerations of the inductive power link and evaluates the work mathematically using MATLAB.

Design of a passive RFID tag antenna at 2.45 GHz for mounting on various platforms

This paper presents the design of a passive RFID tag antenna operating at 2.45 GHz. The electromagnetic simulation software called CST is used for design and simulation. A high gain (5.842dB), a good impedance matching with the microchip (−30.0 dB Return Loss) and a satisfactory read range performance (upto 5 m) was obtained. One approach of designing RFID tag is that the tag should be less sensitive to the various types of objects. The effects of obstacles on antennas characteristics have been investigated by placing the tag antenna against a metallic, rubber, glass and wood surfaces. Simulation results show slight variations which is within tolerance range.

EM radiation and evaluation of Specific Absorption Rate (SAR) in human body exposed to wireless-base station fields at IIUM campus

This paper presents the simulated specific absorption rate (SAR) in the human body using the measured incident electric field strength from wireless-base stations operating at the frequencies in the microwave range from 2 to 4 GHz. The software XFDTD 6.4 from Remcom Inc is used to determine the amount of energy (SAR) absorbed in the human body. XFDTD 6.4 is a three-dimensional full wave electromagnetic solver based on the finite difference time domain (FDTD) method [1]. A tri-axis isotropic probe with portable spectrum analyzer FSH3 and RFEX software is used to measure the incident electric field and incident power densities for all existing signals ranging from 800 MHZ to 2.5 GHz at student hostels and office premises near base stations in International Islamic University Malaysia, Gombak campus. The measured levels of exposure and energy absorption are compared to the values allowed by Malaysia Communication and Multimedia Commission (MCMC), and American National Standards Institute/Institute of Electrical and Electronic Engineers (ANSI/IEEE) recommendations for safety guidelines.

Automated person tracking using proximity capacitive sensors

A proliferating concern has been growing on the development of non-contact sensing and monitoring of human activities in health care sectors to avert accidents of elderly patients. Keeping in mind the limitations of the existing techniques, a novel sensing technique for human movement recognition has been proposed in this paper which uses capacitive proximity sensors. This paper works towards setting the stepping stone of implementing capacitive sensor for a living style profile through MATLAB simulation. The output response for various capacitance values is plotted here proving its utility for precise measurement of voltage which is proportional to the electrical properties of patients body at the sensing elements of the sensor. The output values measures the phase shift as a depiction of human movement. With the presence of a human body near sensor, signal waveform rises at a certain frequency peak and the movement of human body away from the sensor shows otherwise. The preliminary simulation result obtains accurate phase shift variations at a point frequency which is fruitful in further studies and reaching the ultimate goal of persons movement and activity tracking.

CNTFET inverter: A high voltage gain logic gate

Conventional CMOS technology provides a lot of opportunities in the field of electronics device. But presently, carbon nanotube field effect transistor (CNTFET) is a new technology for the application in the field of electronic device. Due to the limitation of the size of CMOS, CNTFETs are the promising substitute due to its nano scale size. CNTFET also shows the high stability, low power circuit design, high signal to noise margin (SNM) and high gain in the circuit design. A novel design of CNTFET based inverter with an optimum chiral vector is proposed in this paper. PSPICE platform is used to model and simulation this CNTFET inverter circuit. The proposed CNTFET inverter circuit is investigated based on noise margin characteristics. A maximum voltage gain of 45dB is observed from NCNTFET of the inverter and a high noise margin of 400mV and a low noise margin of 309mV are achieved from the proposed inverters. This approach is a useful technique for fabricating integrated logic devices and circuits based on CNTFETs.