Kamran Ghorbani

Dual polarized wide-band aperture stacked patch antennas

A wide-band, dual polarized printed antenna is designed and developed in this paper. The antenna is based upon an aperture stacked patch layout and incorporates a simple dual-layered feeding technique to achieve dual-polarized radiation. The printed antenna has a measured 10 dB return loss bandwidth of 52% and an isolation between the excitation ports of greater than 39 dB over this frequency range. The gain of the antenna is 7.4 dBi /spl plusmn/ 0.4 dB and the typical issues associated with incorporating an aperture excited solution are resolved by using a cross-shaped reflector patch to ensure the front-to-back ratio is greater than 20 dB.

Developing a Wireless Implantable Body Sensor Network in MICS Band

Through an integration of wireless communication and sensing technologies, the concept of a body sensor network (BSN) was initially proposed in the early decade with the aim to provide an essential technology for wearable, ambulatory, and pervasive health monitoring for elderly people and chronic patients. It has become a hot research area due to big opportunities as well as great challenges it presents. Though the idea of an implantable BSN was proposed in parallel with the on-body sensor network, the development in this area is relatively slow due to the complexity of human body, safety concerns, and some technological bottlenecks such as the design of ultralow-power implantable RF transceiver. This paper describes a new wireless implantable BSN that operates in medical implant communication service (MICS) frequency band. This system innovatively incorporates both sensing and actuation nodes to form a closed-control loop for physiological monitoring and drug delivery for critically ill patients. The sensing node, which is designed using system-on-chip technologies, takes advantage of the newly available ultralow-power Zarlink MICS transceiver for wireless data transmission. Finally, the specific absorption rate distribution of the proposed system was simulated to determine the in vivo electromagnetic field absorption and the power safety limits.

Enhanced tunability of magnetron sputtered Ba0.5Sr0.5TiO3 thin films on c-plane sapphire substrates

Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1to20GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200kV∕cm and total device Q of more than 15 (up to 20GHz) were achieved following postdeposition annealing at 900°C.

A novel wide-band tunable RF phase shifter using a variable optical directional coupler

We present a novel RF phase-shifter design with a usable bandwidth of 80:1. The design is verified through demonstration of a proof of concept device, consisting of a readily available voltage variable optical coupler fabricated from LiNbO/sub 3/, combined with an fiber-optic delay line. The design is analyzed theoretically and measurement of the device confirms the predicted range of operation. Methods of extension of this range of operation are discussed.

Strain Sensors with Adjustable Sensitivity by Tailoring the Microstructure of Graphene Aerogel/PDMS Nanocomposites

Strain sensors with high elastic limit and high sensitivity are required to meet the rising demand for wearable electronics. Here, we present the fabrication of highly sensitive strain sensors based on nanocomposites consisting of graphene aerogel (GA) and polydimethylsiloxane (PDMS), with the primary focus being to tune the sensitivity of the sensors by tailoring the cellular microstructure through controlling the manufacturing processes. The resultant nanocomposite sensors exhibit a high sensitivity with a gauge factor of up to approximately 61.3. Of significant importance is that the sensitivity of the strain sensors can be readily altered by changing the concentration of the precursor (i.e., an aqueous dispersion of graphene oxide) and the freezing temperature used to process the GA. The results reveal that these two parameters control the cell size and cell-wall thickness of the resultant GA, which may be correlated to the observed variations in the sensitivities of the strain sensors. The higher is the concentration of graphene oxide, then the lower is the sensitivity of the resultant nanocomposite strain sensor. Upon increasing the freezing temperature from -196 to -20 °C, the sensitivity increases and reaches a maximum value of 61.3 at -50 °C and then decreases with a further increase in freezing temperature to -20 °C. Furthermore, the strain sensors offer excellent durability and stability, with their piezoresistivities remaining virtually unchanged even after 10 000 cycles of high-strain loading-unloading. These novel findings pave the way to custom design strain sensors with a desirable piezoresistive behavior.

The Effect of Ply Orientation on the Performance of Antennas in or on Carbon Fiber Composites

In this paper, the anisotropic conductivity efiect of quasi- isotropic carbon flber laminates on conformal load-bearing antenna structures (CLAS) is presented. The conductivity of a quasi-isotropic IM7/977-3 CFRP laminate is measured using waveguide techniques. The results show that orientation of the surface ply relative to the polarization of the incident E-fleld has a major in∞uence on the re∞ectivity. This difierence is attributed to the fact that carbon flbres oriented parallel to the E-fleld plies behave as good conductors, while ofi-axis plies present as lossy dielectric layers with a flnite conductivity. This anisotropic behavior of the ply layers is shown to have a distinctive in∞uence on the operation of both microstrip patch and slot antennas.

Angularly Stable Frequency Selective Surface With Miniaturized Unit Cell

A new type of Frequency Selective Surface (FSS) with miniaturized resonator element is proposed. The FSS structure is shown to have a FSS unit cell dimension that is miniaturized to 0.067 λ0. Miniaturization of the FSS unit cell is achieved by coupling two meandered wire resonators separated by single thin substrate layer. The capacitance due to the small separation between the meandered wire elements results in a lowering of the resonant frequency. To demonstrate the validity of the design, the meandered wire resonator FSS was fabricated and tested using a free space measurement facility. The FSS produces a stable angular response up to 80 degrees for TE and TM incident angles.

A varactor tuned branch-line hybrid coupler

This paper introduces a novel branch-line 90/spl deg/ hybrid coupler incorporating varactor diodes which allow tuning of the frequency response. A design covering the DCS, PCS and IMT2000 cellular frequency bands (1710-2170 MHz) is presented. Given a varactor tunability of 2.5:1, simulations suggest 20 dB return loss and 3/spl plusmn/1 dB coupling is achievable across each transmit and receive sub-band by tuning the varactors. These results offer an improvement over a conventional single-section branch-line hybrid centred at 1950 MHz, and some miniaturisation is also achieved due to the capacitive loading. A prototype is constructed using commercially available varactor diodes, and reasonable agreement between the measured and simulated results is achieved.

3D frequency selective surfaces

A novel 3D Frequency Selective Surface (FSS) architecture based on a circular ring unit element is presented. The circular ring was made 3D by creating a cylindrical element of a certain length, adding an extra degree of freedom into the structure. The length of the cylinder is shown through electromagnetic simulation to have a signiflcant efiect on the frequency characteristics of the FSS. Increasing the length of the cylinder can change the FSS from a band-stop to a band-pass fllter response. The center frequency of both band pass and band stop responses can also be tuned with adjustment to the length. Dielectric materials are introduced in the center of the cylindrical unit cell elements to simultaneously obtain a stop and pass band with a sharp transition. For high dielectric fllling materials, the 3D periodic structure exhibits negative refractive index metamaterial properties. A parametric analysis was conducted on these new cylindrical unit elements, and a prototype 3D FSS structure has been constructed and experimentally validated.

Complex Dielectric Measurements of Forest Fire Ash at X-Band Frequencies

Dielectric measurements of powdered forest fire ash have been investigated and presented using the Nicholson-Ross-Weir method within a WR-90 waveguide (X-band 8-12 GHz). The dielectric measurements of five samples have been outlined and taken at a room temperature of 22.8 °C. Permittivity ε for five different species has been presented within this letter. These include Eucalypt, Bracken Fern, She Oak, Wattle, and Cypress. The Eucalypt sample was tested dry and with a 30% moisture content by weight. The dry Eucalypt sample was found to have a permittivity value of approximately 2.32 ± 0.025 with a loss tangent of 0.005 ± 0.0025.