Muhammad Yusof Ismail

Beam steering reflectarrays using liquid crystal substrate

Radar acquisition and tracking systems often require the generation of single or multiple dynamically reconfigurable beams, which must be steered rapidly within the scan volume. Microstrip phased arrays are often used for these applications because this type of antenna can normally be designed to satisfy the pattern shape and coverage requirements and the beam can be scanned simply by varying the phase of the individual elements in the periodic structure. In this paper we present the preliminary results of a study to exploit the electrical properties of anisotropic nematic liquid crystal (LC) substrate in order to create a phase shifter which is suitable for beam scanning reflectarray antennas. A finite element computer model is used to establish the relationship between the LC thickness and the obtainable reflection phase range for a patch element, where the change in material permittivity can be obtained by applying a DC voltage between the patch and the ground plane. Waveguide simulator measurements are used to demonstrate the validity of the predictions.

Development of Artificial Hand Gripper for Rehabilitation Process

This paper focuses on the development of a robotic hand that imitates the movement of a human hand. The basic movement of the surgeon hand was limited from a wrist, elbow and shoulder degree of freedom during an operation. The artificial hand gripper system requires sensors for a smooth and accurate movement. This allows large movement from the surgeon hand to be corrected on a small scale with a perfect incision and without any vibration. Although such a system available in the market, the utilization of robotic hand particularly in Malaysia for medical application are still very minimum due to its expensive cost. Therefore, in this research we plan to develop a reasonably cheaper home built robotic hand which can perform the task of a hand gripper as a beginning step. The initial objective of this research is to analyze and develop artificial arm with a strength limit proportional to the weight. Next, followed by the attachment of a wireless system on the prosthetic gripper via Radio Frequency (RF) transceiver. The system development involves a Programming Interfacing Circuit (PIC) 16F877 as a core processing for the instrumentation, communication and controlling applications. A series of flex force sensors are fitted in a leather glove to get reading from the movement of human fingers. Microcontroller will further use this information to control multiple servo that act as a mechanical hand inside the prosthetic gripper.

PERFORMANCE IMPROVEMENT OF REFLECTARRAYS BASED ON EMBEDDED SLOTS CONFIGURATIONS

An inflnite re∞ectarray antenna in the X-band frequency range has been designed, and various slot conflgurations have been proposed to optimize the design of reconflgurable re∞ectarray antennas in the X-band frequency range. It has been demonstrated that the introduction of slots in the patch element causes a decrease in the maximum surface current density (J) and electric fleld intensity (E) and hence causes a variation in the resonant frequency of the re∞ectarray. Waveguide simulator technique has been used to represent inflnite re∞ectarrays with a two patch unit cell element and scattering parameter measurements have been carried out using vector network analyzer. A change in resonant frequency from 10 GHz to 8.3GHz has been shown for a slot width of 0.5W (W is the width of patch element) as compared to patch element without slot. Furthermore, a maximum attainable dynamic phase range of 314 - has been achieved by using slots in the patch element constructed on a 0.508mm thick substrate with a maximum surface current density (J) of 113A/m and electric fleld intensity (E) of 14kV/m for 0.5W slot in the patch element.

Phase control of reflectarray patches using liquid crystal substrate

In this proof of concept study we employ numerical and measured results at X- band to demonstrate that the dielectric anisotropy of nematic state liquid crystal can be exploited to produce electronically controlled phase shifters for printed reflectarray antennas. Phase agility is realized by inserting a layer of liquid crystal in the region between the resonant patch array and the conductive ground plane. Applying a low frequency biasing voltage produces a small change in the permittivity of the substrate and this is shown to create a large shift in the phase of the reflected signal. Ansoft HFSS version 10.0 is employed to study the scattering behaviour of the array elements in the range 9¿11 GHz using the dielectric properties of commercially available liquid crystals. The simulated phase range, bandwidth and reflection loss are shown to be in close agreement with measurements that were obtained from a waveguide simulator. The most significant impact of this new active control strategy is in the mm and sub-mm wave band and therefore a technique is proposed for characterising the electrical performance of liquid crystals at these frequencies. This paper summarises the progress that has been made in the first stage of a collaborative academic/industrial project to investigate the feasibility of creating high frequency beam scanning reflectarray antennas for future space science instruments.

Resonant Elements for Tunable Reflectarray Antenna Design

This paper presents an accurate analysis of different configurations of reflectarray resonant elements that can be used for the design of passive and tunable reflectarrays. Reflection loss and bandwidth performances of these reflectarray elements have been analyzed in the X-band frequency range with the Finite Integral Method technique, and the results have been verified by the waveguide scattering parameter measurements. The results demonstrate a reduction in the phase errors offering an increased static linear phase range of 225° which allows to improve the bandwidth performance of single layer reflectarray antenna. Moreover a maximum dynamic phase range of 320° and a volume reduction of 22.15% have been demonstrated for a 10 GHz reflectarray element based on the use of rectangular patch with an embedded circular slot.

Application of liquid crystal technology for electronically scanned reflectarrays

Electronically steerable antenna systems are required for many applications including communication systems and radar. Normally these employ diode phase shifters to create the required aperture distribution. In this paper we show how the anisotropy property of liquid crystal (LC) material can be exploited to provide an integrated phase shifter for a printed patch antenna such as a reflectarray (N. Misran et al., 2003). This offers a simpler alternative to semiconductor devices and has the potential to overcome the limitations of existing phase shifter technology in the millimeter and submillimeter wave bands. In this paper we demonstrate the relationship between the LC thickness and the attainable phase range for a patch element in which the change in LC permittivity can be obtained by applying a dc voltage between the patch conductor and the ground plane. Simulations for different LC substrate thicknesses were carried out using the transmission line model (TLM) MICROSTRIPES and the finite element model (FEM) Ansoft HFSS. Measurements the scattering parameters of a 200 /spl mu/m and a 500 /spl mu/m thick patch reflectarray have been performed using waveguide simulator technique to demonstrate the validity of the predictions.

Integration of PIN diodes with slot embedded patch elements for active reflectarray antenna design

This work provides an investigation on the slot embedded patch configurations to be used as elements for the active reflectarray design. Rectangular slots have been introduced in the centre of the rectangular patch elements designed in the X-band frequency range. Waveguide scattering parameter measurements has been performed for the proposed slotted elements and a close agreement has been shown between the simulated and measured results in terms of resonant frequency, reflection loss and reflection phase. The use of PIN diodes integrated with the slotted patch elements has been successfully demonstrated for the design of active reflectarrays. It has been shown that frequency tunability from 9.64 GHz to 8.88 GHz can be achieved by using different states of PIN diode with 0.5W slotted patch element. Moreover the individual lumped component properties of PIN diodes have been investigated thoroughly for the optimum design of active reflectarrays.

Enhanced bandwidth reflectarray antenna using variable dual gap

The demand for low cost and less weight antenna with compact broadband features in communication system is rapidly increasing. In this work, the possibility of employing dual gap on square patch reflectarray antenna for bandwidth improvement is presented. The introduction of dual gap attached on square patch is shown to improve the bandwidth performance from 315 MHz to 397 MHz. Moreover 26% improvement of bandwidth performance offers an achievable static reflection loss of 0.28 dB. Several parameters of reflectarray antenna such as reflection loss, reflection phase, bandwidth and figure of merit (FoM) are also discussed in this work.

Performance of reflectarray cells printed on liquid crystal film

In this paper we demonstrate that the anisotropic property of liquid crystal can be exploited to control the phase of signals that are reflected from a reflectarray cell. Numerical and measured results at X-band are used to compare the plane wave scattering from two reflectarray cells which are constructed on liquid crystal film of thickness 200 mum and 500 mum. The phase agility, bandwidth and reflection loss are shown to be dependent on both the thickness and the voltage controlled permittivity of the tunable substrate. A tunable phase range greater than 250deg is achieved over a 6.1% bandwidth.

Transmission of Microwave Signal through Metal-Oxide Thin Film of Energy Saving Glass Using Different Shape of Frequency Selective Structure

Metal oxide thin films are widely used for energy saving glass coating. This coating has the ability of blocking the infrared signal while being transparent to other visible part of the spectrum. However, there is one critical disadvantage of this metal oxide coating which it attenuates useful radio frequency and microwave signal such as GSM mobile signal, personal communication, GPS signal through them. These important microwave signals are fall within the range of 800 MHz to 2200 MHz. Frequency selective structure has been applied to solve the attenuation of microwave signal. With the adding of frequency selective structure, it can bring huge improvement of the transmission loss through it. Computer simulation using CST software is used to investigate the transmission loss through the metal oxide coated glass. The frequency selective structure will be etched out from the metallic oxide coated on the glass. Results showed that different shape of the structure will have different peak transmission loss through the glass. When cross dipole and circle shape been simulated using CST software, it can clearly see that the transmission lost and peak frequency had changed drastically. Then, triangle and pentagon shape also have different transmission through it. In addition, conductivity and electrical properties of coated metal oxide thin film is also very important. The transmission through the different ohmic sheet resistance of metal oxide thin film was also investigated. The sheet resistance value was obtained from the reported experimental results. Simulated results showed that full width half maximum, maximum transmission loss and peak frequency loss was very much dependent on the metal oxide sheet resistance. Therefore, the control of the thickness and oxygen content in metal oxide thin film are very much important to optimize the transmission loss through it for energy saving glass applications.