Daniel Oloumi

Miniaturized Reflectarray Unit Cell Using Fractal-Shaped Patch-Slot Configuration

This letter introduces a new class of miniaturized reflectarray unit cells with increased phase swing employing Minkowski fractal-shaped patch-slot elements. Square, 1st Minkowski, and 2nd Minkowski fractal patches are designed as a reflectarray unit cell. A slot with variable lengths of 0 <; Ls <; 6 mm is used in the ground plane to perform the phase variation function. The resonant frequency corresponding to the maximum phase swing is reduced from 10.6 GHz for the square patch down to 8.8 and 8.3 GHz for the first- and second-order Minkowski fractal patches, respectively, which is equivalent to 17% and 22% size reduction. Unit cells with different patch type and slot length are fabricated, and close agreement is observed between the measured and simulated results. As it has been proven for conventional phased array antennas, this size reduction can lead to a decrease in mutual coupling in reflectarray antennas. Alternatively, it allows for smaller distance between reflectarray antenna elements, which renders a wider beam-scanning range.

A Modified TEM Horn Antenna Customized for Oil Well Monitoring Applications

A TEM horn antenna with modified radiation pattern customized for oil well monitoring application is presented in this paper. The antenna is designed to operate in an oil saturated medium in the frequency range between 1.4 to 11 GHz. A complete design procedure for the proposed TEM horn antenna with a method to modify the radiation pattern is introduced here. The modification is conducted using nonuniform expansion of the antenna flares. Applying this technique eliminates ripples in the antennas main-lobe radiation pattern at higher frequencies, a problem which exists for conventional TEM horn antennas. The design coefficients which control the flare openings are optimized using CST Microwave Studio to achieve smooth main-beam radiation patterns while maintaining return loss more than 10 dB. Simulations are performed both in oil and free space. Free space simulations are done to provide a valid reference for antenna radiation pattern measurement as radiation pattern cannot be measured in oil. Simulation results are followed by the measurement results with a very good agreement. The fabricated dimensions of the antenna including balun section are limited to 89.2×49.2×78.2 mm. The designed antenna is utilized as a part of an ultrawideband radar system for oil well monitoring.

Imaging of Oil-Well Perforations Using UWB Synthetic Aperture Radar

Ultrawideband (UWB) synthetic aperture radar (SAR) as a tool for oil well perforation monitoring is experimentally investigated in this paper. Experiments are conducted on a lab prototype that emulates the small section of an oil well. Oil well perforations are scanned using the designed UWB radar system for different experimental conditions. High-resolution images in both down-range and cross-range are obtained by using UWB pulses and signal processing. High-quality images are constructed using SAR processing algorithm with the proposed modifications. Experiments are carried out for different perforation conditions such as open, partially clogged and fully clogged cases. It is shown by the experiments that the proposed radar technique and the data processing methods are capable of providing more revealing high-quality images. This approach can be applied effectively to monitor the oil well medium and detect well impairment locations.

Breast tumor detection using UWB circular-SAR tomographic microwave imaging

This paper describes the possibility of detecting tumors in human breast using ultra-wideband (UWB) circular synthetic aperture radar (CSAR). CSAR is a subset of SAR which is a radar imaging technique using a circular data acquisition pattern. Tomographic image reconstruction is done using a time domain global back projection technique adapted to CSAR. Experiments are conducted on a breast phantoms made of pork fat emulating normal and cancerous conditions. Preliminary experimental results show that microwave imaging of a breast phantom using UWB-CSAR is a simple and low-cost method, efficiently capable of detecting the presence of tumors.

Dual-band orthogonally-polarized slotted-Lozenge reflective unit cell tuned by MEMS varactor

A novel dual-band orthogonally-polarized MEMS reconfigurable slotted-Lozenge patch is introduced here. The dual-band performance of the lozenge patch (12 and 14 GHz) is due to different diagonal length. A cross slot is etched in the middle of patch to control the phase swing in each frequency and polarization. The effective slot length is controlled by MEMS capacitors with capacitance ratio of 1.5 resulting in phase swing of 345°. The reflect-array composed of this cell element would be able to radiate two independent beams at different frequencies and polarizations.

A TEM horn antenna with non-uniform expansion for oil well monitoring

A TEM horn antenna with non-uniform expansion to modify the radiation characteristics, operating from 1.4 to 11 GHz in oil medium is introduced. Main lobe radiation pattern ripple at higher frequencies which are the problem of conventional TEM horn antenna is suppressed. The expansions coefficient is tuned using CST Microwave Studio to achieve good return loss (less than 10dB) and radiation pattern. The horn is utilized as a part of an ultra-wideband radar system to monitor oil well with no metal casing.

SAGD Process Monitoring in Heavy Oil Reservoir Using UWB Radar Techniques

In this paper, practical considerations for steam assisted gravity drainage (SAGD) monitoring using ultra-wideband (UWB) radar are studied. The SAGD process and important factors to monitor its performance are discussed. Several experiments are conducted to evaluate the possibility of using UWB radar for SAGD process monitoring. All the experiments are carried out on a simplified laboratory prototype, which is a plateau of wet sand covered by dry sand to mimic the steamed area of the reservoir. The effect of the metal pipe on the pulse shape and propagation inside the reservoir is also experimentally studied. Additionally, a miniaturized Vivaldi antenna capable of radiating within oil-sand is designed, fabricated, and verified as a sensor for the radar monitoring system. Power budget and heterogeneity analysis of the heavy reservoir for different grades of Athabasca oil-sands are also studied. Results demonstrate the possibility of using UWB radar to detect and image the contour of the steamed area in the SAGD process. The information collected by the UWB radar can be used for optimizing steam injection to improve the usage of water and energy.

Studying the Superluminal Behavior of UWB Antennas and Its Effect on Near-Field Imaging

In this paper, the superluminal behavior of a radiated pulse in the near-field of an ideal dipole and an ultrawideband antenna is explained and demonstrated through simulations and measurements. The deformation of the radiated pulse in the near-field is illustrated using the ideal dipole antenna radiation as well as by a Vivaldi antenna through full-wave simulations and measurements. The apparent superluminal pulse velocity is due to the pulse reshaping of the radiated pulse in the near-field of the antenna. The pulse velocity is measured by tracking pulse peak, pulse envelope peak, and also calculating the pulse centrovelocity. The superluminal pulse peak velocity of the radiated pulse from a miniaturized Vivaldi antenna is confirmed through measurements in face-to-face and quasi-monostatic radar configurations. The effect of different values of pulse velocities on the quality of reconstructed images using synthetic aperture radar processing is demonstrated as well.

Tracking a biopsy needle inside a breast using UWB circular-SAR

This paper explores the possibility of guiding a biopsy needle inside a breast in real time using ultra-wideband (UWB) circular synthetic aperture radar (CSAR). Collecting a biopsy of a tumor growth inside a breast at the right location is essential for accurate diagnosis. In order to do so, real time navigation and imaging of the tumor location and the biopsy needle is critical. Using very short electromagnetic pulses (~100 Picosecond) with CSAR processing we demonstrate that one can perform near real time tracking of a biopsy needle to an accuracy of few millimeters. Signal processing techniques, such as envelop detection and generating positive image, are applied to enhance the image quality. The experimental results support the possibility of real time tracking of a biopsy needle.