Omar Ramahi - Academia.edu (original) (raw)
Papers by Omar Ramahi
Scientific Reports
In this paper, we present an entirely simulation-based method to predict the performance of a com... more In this paper, we present an entirely simulation-based method to predict the performance of a complete rectenna system that includes all its components: the receiving antenna, the matching circuits between the antenna and the rectification circuit, and the load circuit. Whereas previous efforts to predict the performance of a rectenna system subdivided the system into the antenna part (radiation to AC power conversion) and the circuit part (AC power to DC power conversion), and made assumptions about the performance of the non-linear part of the rectenna based on a specified power level and frequency, in this method, the radiation part of the system is incorporated into the simulation by using Thevenin theorem. The method proposed in this work enables the rectenna designer to predict the performance of the complete rectenna system, at the design stage, for variation in the incident field’s power density, angle of incidence, and operating frequency. Such performance prediction was no...
In this paper, challenges of combining machine learning techniques with near-field microwave prob... more In this paper, challenges of combining machine learning techniques with near-field microwave probes for breast tumor detectionis presented. The concept of using microwaves imaging (MI) modality for breast tumors detection is based on the electrical propertiescontrast between normal and tumors breast tissues. MI utilizedmicrowave signals to illuminate the breast tissues using near fieldprobes placed at different locations surrounding the breast. Thebackscattered microwaves signals are then received by the sameprobes. Diagnosis breast tumor is done by estimating the variations in the response of the reflection coefficient of the probe. Machine learning techniques are applied to accentuate the variancein the sensor’s responses for both healthy and tumorous cases.The main challenge of using the machine learning technique withnear-field microwave probes for breast tumor detection is to find asuitable combination of features and classifiers which discriminatesbetween the normal and abnorm...
2006 IEEE MTT-S International Microwave Symposium Digest, 2006
1986 Antennas and Propagation Society International Symposium
ABSTRACT
2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011
Abstract It is shown that, under some resonance conditions, a microstrip patch antenna can be des... more Abstract It is shown that, under some resonance conditions, a microstrip patch antenna can be designed to achieve the highest possible gain when covered with a superstrate at the proper distance in free space. The transmission line analogy and the cavity model are ...
2002 IEEE MTT-S International Microwave Symposium Digest (Cat. No.02CH37278)
Electrical performances of 4-port n:n dual-spiral transformers fabricated in a thick plated coppe... more Electrical performances of 4-port n:n dual-spiral transformers fabricated in a thick plated copper on silicon process are analyzed. Multiport data analysis techniques and compact modeling are used to study the relationships between the physical and the electrical attributes of the devices. Analytical models, based on measurements from 50 MHz to 20 GHz, are used to explore achievable device performance under
It is found that by repeating two insulator layers with different electron affinities and keeping... more It is found that by repeating two insulator layers with different electron affinities and keeping the total insulator thickness constant, the asymmetry and nonlinearity values can have significant impact on the behavior of Metal-Insulator-Metal diodes. The asymmetry value of a diode with a double insulator layer was recorded as 3, however, for a quadra insulator layer diode; the asymmetry value was recorded as high as 90. The new MIM diode design promises a strong impact on emerging applications such as energy harvesting from fast switching electromagnetic waves.
IEEE Antennas and Propagation Society Symposium, 2004., 2004
ABSTRACT In recent studies, high-impedance surfaces (HIS) also known as electromagnetic bandgap s... more ABSTRACT In recent studies, high-impedance surfaces (HIS) also known as electromagnetic bandgap structures (EBG) have been successfully employed to suppress simultaneous switching noise (SSN) generated between power buses of printed circuit boards (PCB). HIS structures, when embedded in a PCB, can suppress electromagnetic wave propagation within a predictable range of frequencies. In this paper, a highly-accurate model for HIS structures embedded in PCBs is presented. This circuit is then added to a physics-based model for power buses of PCBs, creating a compact 3D model to represent the power bus together with Embedded HIS (EHIS) structures. The circuit models presented allow for accurate prediction of the center frequency and bandgap of the EHIS without a priori full-wave modeling of single or multiple cells.
2008 Second International Conference on Communications and Electronics, 2008
The helical antenna can be made significantly smaller with little sacrifice in its most desirable... more The helical antenna can be made significantly smaller with little sacrifice in its most desirable properties. We propose here a method for reducing the size of helical antennas, and demonstrate its efficacy on a fairly typical antenna with a low number of turns (N = 6). After investigating several methods, we demonstrate that by introducing a periodic sinusoidal pattern along
IEEE Antennas and Propagation Society Symposium, 2004., 2004
ABSTRACT
2006 European Microwave Conference, 2006
ABSTRACT The paper proposed a novel photonic crystal delay line which can generate two different ... more ABSTRACT The paper proposed a novel photonic crystal delay line which can generate two different time-delays. This two port device can be implemented with silicon-on-insulator (SOI) technology. The authors show that two different time delays, 1.68ps and 3.3ps, are achievable with a device size less than 25mum, which corresponds to slowing light by a factor of 40. Guidelines for maintaining high isolation between the two ports and for achieving low reflection from corners were discussed. Finally, applications for this delay lines were presented
2004 International Symposium on Electromagnetic Compatibility (IEEE Cat. No.04CH37559)
Page 1. Understanding and Validating Practical EMUEMC Antennas using Numerical Codes Shahrooz Sha... more Page 1. Understanding and Validating Practical EMUEMC Antennas using Numerical Codes Shahrooz Shahpamia'.', Mohammad H. Kermani'.' and Omar M. Ra~nahil.~.' 'Electrical and Computer Engineering Department, 'Mechanical ...
2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), 2013
ABSTRACT Tunneling of electromagnetic energy can take place in narrow (sub-wavelength) channels f... more ABSTRACT Tunneling of electromagnetic energy can take place in narrow (sub-wavelength) channels filled with either the epsilon-near-zero materials or resonant wires. Since the tunneling is accompanied by very intense electric fields, the resulting frequency response is highly selective. In this paper, a microstrip bend is studied that supports energy tunneling. It has been shown, through full-wave simulations, that the tunneling mode is highly frequency selective and depends on the wire length and substrate permittivity. Hence very high-Q resonant cavities can be designed that may have potential applications in filtering and sensing applications. The microstrip technology, compared to the rectangular waveguides, is low cost, robust, easily fabricated and suitable for planar integration.
Microwave and Optical Technology Letters, 2013
We present an analytical formula to calculate the resultant effective permittivity of a metamater... more We present an analytical formula to calculate the resultant effective permittivity of a metamaterial medium composed of unit cells with complementary structures. Complementary metamaterial
![Research paper thumbnail of Comments on "A super absorbing boundary condition for the analysis of waveguide discontinuities with the finite-difference method" [and reply]](https://attachments.academia-assets.com/118128664/thumbnails/1.jpg)
](IEEE Microwave and Guided Wave Letters, 1998
In the above letter, 1 the authors may have overlooked our paper, which introduced a numerically ... more In the above letter, 1 the authors may have overlooked our paper, which introduced a numerically derived Absorbing Boundary Condition for the solution of open region scattering problems [1]. In [1], the idea was to present the unknown field or its derivative at a terminal node in terms of a weighted summation of neighboring nodes that lie in the interior. The weighting coefficients are solved for by representing the field at the terminal node in terms of a finite number of its spatial harmonics (three or five dominant harmonics). In [1], we demonstrated the concept by applying it to cylindrical harmonics in the context of the finite-element method, whereas the authors of the above letter 1 considered planar waveguide harmonics in the context of the finite-difference method.
IEEE Antennas and Propagation Magazine, 2002
IEEE Transactions on Antennas and Propagation, 2009
Range-Doppler images are widely used to classify different types of UAVs because each UAV has a u... more Range-Doppler images are widely used to classify different types of UAVs because each UAV has a unique range-doppler signature. However, a drone's range-doppler signature depends on its movement mechanism. This is why the classifier accuracy would be degraded if the effect of the mechanical control system wasn't taken into consideration, which may lead to a non-unique signature of a drone while in-flight. In this paper, a full-wave electromagnetic CAD tool is used to investigate the effect of the control systems of a quadcopter and a hexacopter UAVs on their range-doppler signatures. A Mechanical Control-Based Machine Learning (MCML) algorithm is introduced to classify the two UAVs and its accuracy is found to exceed 90%.
Progress In Electromagnetics Research M
A novel quad-band bandpass filter (BPF) consisting of two deformed W-shaped microstrip Stepped-Im... more A novel quad-band bandpass filter (BPF) consisting of two deformed W-shaped microstrip Stepped-Impedance Resonators (SIRs) with different dimensions is proposed. The W-shaped SIRs are miniaturized from E-shaped SIRs, and each one of the SIRs generates two passbands and thus four passbands centered at 3.18 GHz, 4.51 GHz, 5.46 GHz, and 8.43 GHz with fractional bandwidth of 6.7%, 9.1%, 8.4%, and 8.2% were obtained. Compared with the basic SIR structures and E-shaped structures, the effective area of the miniaturized SIR is reduced by more than 60% and 20%, respectively. The operating frequency bands can be determined by switching the diodes that are connected to the cross coupling lines of the two SIRs. The improved design can be used for 5G and other applications.
Using micro-doppler signatures is an effective way to classify different types of UAVs, as well a... more Using micro-doppler signatures is an effective way to classify different types of UAVs, as well as other airborne objects such as birds. To generate signatures for drones, radar measurements are needed; however, these measurements are limited to the types of available drones, the radar parameters, the targets’ range, and the environments in which these measurements are conducted. In this paper, a new method for generating signature datasets is introduced. The method uses full-wave electromagnetic simulation software. Using this method, radar drones’ datasets can be generated using different types, sizes, drone materials, radar parameters, detected range, targets speed, and rotor RPM for rotary drones. A 77 GHz modeled FMCW radar is used to create dataset for classification purposes. Finally, a Convolutional Neural Network (CNN) algorithm is used to classify five types of drones. Based on the results, the classification of the drones is found to exceed 97% accuracy.
Scientific Reports
In this paper, we present an entirely simulation-based method to predict the performance of a com... more In this paper, we present an entirely simulation-based method to predict the performance of a complete rectenna system that includes all its components: the receiving antenna, the matching circuits between the antenna and the rectification circuit, and the load circuit. Whereas previous efforts to predict the performance of a rectenna system subdivided the system into the antenna part (radiation to AC power conversion) and the circuit part (AC power to DC power conversion), and made assumptions about the performance of the non-linear part of the rectenna based on a specified power level and frequency, in this method, the radiation part of the system is incorporated into the simulation by using Thevenin theorem. The method proposed in this work enables the rectenna designer to predict the performance of the complete rectenna system, at the design stage, for variation in the incident field’s power density, angle of incidence, and operating frequency. Such performance prediction was no...
In this paper, challenges of combining machine learning techniques with near-field microwave prob... more In this paper, challenges of combining machine learning techniques with near-field microwave probes for breast tumor detectionis presented. The concept of using microwaves imaging (MI) modality for breast tumors detection is based on the electrical propertiescontrast between normal and tumors breast tissues. MI utilizedmicrowave signals to illuminate the breast tissues using near fieldprobes placed at different locations surrounding the breast. Thebackscattered microwaves signals are then received by the sameprobes. Diagnosis breast tumor is done by estimating the variations in the response of the reflection coefficient of the probe. Machine learning techniques are applied to accentuate the variancein the sensor’s responses for both healthy and tumorous cases.The main challenge of using the machine learning technique withnear-field microwave probes for breast tumor detection is to find asuitable combination of features and classifiers which discriminatesbetween the normal and abnorm...
2006 IEEE MTT-S International Microwave Symposium Digest, 2006
1986 Antennas and Propagation Society International Symposium
ABSTRACT
2011 IEEE International Symposium on Antennas and Propagation (APSURSI), 2011
Abstract It is shown that, under some resonance conditions, a microstrip patch antenna can be des... more Abstract It is shown that, under some resonance conditions, a microstrip patch antenna can be designed to achieve the highest possible gain when covered with a superstrate at the proper distance in free space. The transmission line analogy and the cavity model are ...
2002 IEEE MTT-S International Microwave Symposium Digest (Cat. No.02CH37278)
Electrical performances of 4-port n:n dual-spiral transformers fabricated in a thick plated coppe... more Electrical performances of 4-port n:n dual-spiral transformers fabricated in a thick plated copper on silicon process are analyzed. Multiport data analysis techniques and compact modeling are used to study the relationships between the physical and the electrical attributes of the devices. Analytical models, based on measurements from 50 MHz to 20 GHz, are used to explore achievable device performance under
It is found that by repeating two insulator layers with different electron affinities and keeping... more It is found that by repeating two insulator layers with different electron affinities and keeping the total insulator thickness constant, the asymmetry and nonlinearity values can have significant impact on the behavior of Metal-Insulator-Metal diodes. The asymmetry value of a diode with a double insulator layer was recorded as 3, however, for a quadra insulator layer diode; the asymmetry value was recorded as high as 90. The new MIM diode design promises a strong impact on emerging applications such as energy harvesting from fast switching electromagnetic waves.
IEEE Antennas and Propagation Society Symposium, 2004., 2004
ABSTRACT In recent studies, high-impedance surfaces (HIS) also known as electromagnetic bandgap s... more ABSTRACT In recent studies, high-impedance surfaces (HIS) also known as electromagnetic bandgap structures (EBG) have been successfully employed to suppress simultaneous switching noise (SSN) generated between power buses of printed circuit boards (PCB). HIS structures, when embedded in a PCB, can suppress electromagnetic wave propagation within a predictable range of frequencies. In this paper, a highly-accurate model for HIS structures embedded in PCBs is presented. This circuit is then added to a physics-based model for power buses of PCBs, creating a compact 3D model to represent the power bus together with Embedded HIS (EHIS) structures. The circuit models presented allow for accurate prediction of the center frequency and bandgap of the EHIS without a priori full-wave modeling of single or multiple cells.
2008 Second International Conference on Communications and Electronics, 2008
The helical antenna can be made significantly smaller with little sacrifice in its most desirable... more The helical antenna can be made significantly smaller with little sacrifice in its most desirable properties. We propose here a method for reducing the size of helical antennas, and demonstrate its efficacy on a fairly typical antenna with a low number of turns (N = 6). After investigating several methods, we demonstrate that by introducing a periodic sinusoidal pattern along
IEEE Antennas and Propagation Society Symposium, 2004., 2004
ABSTRACT
2006 European Microwave Conference, 2006
ABSTRACT The paper proposed a novel photonic crystal delay line which can generate two different ... more ABSTRACT The paper proposed a novel photonic crystal delay line which can generate two different time-delays. This two port device can be implemented with silicon-on-insulator (SOI) technology. The authors show that two different time delays, 1.68ps and 3.3ps, are achievable with a device size less than 25mum, which corresponds to slowing light by a factor of 40. Guidelines for maintaining high isolation between the two ports and for achieving low reflection from corners were discussed. Finally, applications for this delay lines were presented
2004 International Symposium on Electromagnetic Compatibility (IEEE Cat. No.04CH37559)
Page 1. Understanding and Validating Practical EMUEMC Antennas using Numerical Codes Shahrooz Sha... more Page 1. Understanding and Validating Practical EMUEMC Antennas using Numerical Codes Shahrooz Shahpamia'.', Mohammad H. Kermani'.' and Omar M. Ra~nahil.~.' 'Electrical and Computer Engineering Department, 'Mechanical ...
2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), 2013
ABSTRACT Tunneling of electromagnetic energy can take place in narrow (sub-wavelength) channels f... more ABSTRACT Tunneling of electromagnetic energy can take place in narrow (sub-wavelength) channels filled with either the epsilon-near-zero materials or resonant wires. Since the tunneling is accompanied by very intense electric fields, the resulting frequency response is highly selective. In this paper, a microstrip bend is studied that supports energy tunneling. It has been shown, through full-wave simulations, that the tunneling mode is highly frequency selective and depends on the wire length and substrate permittivity. Hence very high-Q resonant cavities can be designed that may have potential applications in filtering and sensing applications. The microstrip technology, compared to the rectangular waveguides, is low cost, robust, easily fabricated and suitable for planar integration.
Microwave and Optical Technology Letters, 2013
We present an analytical formula to calculate the resultant effective permittivity of a metamater... more We present an analytical formula to calculate the resultant effective permittivity of a metamaterial medium composed of unit cells with complementary structures. Complementary metamaterial
IEEE Microwave and Guided Wave Letters, 1998
In the above letter, 1 the authors may have overlooked our paper, which introduced a numerically ... more In the above letter, 1 the authors may have overlooked our paper, which introduced a numerically derived Absorbing Boundary Condition for the solution of open region scattering problems [1]. In [1], the idea was to present the unknown field or its derivative at a terminal node in terms of a weighted summation of neighboring nodes that lie in the interior. The weighting coefficients are solved for by representing the field at the terminal node in terms of a finite number of its spatial harmonics (three or five dominant harmonics). In [1], we demonstrated the concept by applying it to cylindrical harmonics in the context of the finite-element method, whereas the authors of the above letter 1 considered planar waveguide harmonics in the context of the finite-difference method.
IEEE Antennas and Propagation Magazine, 2002
IEEE Transactions on Antennas and Propagation, 2009
Range-Doppler images are widely used to classify different types of UAVs because each UAV has a u... more Range-Doppler images are widely used to classify different types of UAVs because each UAV has a unique range-doppler signature. However, a drone's range-doppler signature depends on its movement mechanism. This is why the classifier accuracy would be degraded if the effect of the mechanical control system wasn't taken into consideration, which may lead to a non-unique signature of a drone while in-flight. In this paper, a full-wave electromagnetic CAD tool is used to investigate the effect of the control systems of a quadcopter and a hexacopter UAVs on their range-doppler signatures. A Mechanical Control-Based Machine Learning (MCML) algorithm is introduced to classify the two UAVs and its accuracy is found to exceed 90%.
Progress In Electromagnetics Research M
A novel quad-band bandpass filter (BPF) consisting of two deformed W-shaped microstrip Stepped-Im... more A novel quad-band bandpass filter (BPF) consisting of two deformed W-shaped microstrip Stepped-Impedance Resonators (SIRs) with different dimensions is proposed. The W-shaped SIRs are miniaturized from E-shaped SIRs, and each one of the SIRs generates two passbands and thus four passbands centered at 3.18 GHz, 4.51 GHz, 5.46 GHz, and 8.43 GHz with fractional bandwidth of 6.7%, 9.1%, 8.4%, and 8.2% were obtained. Compared with the basic SIR structures and E-shaped structures, the effective area of the miniaturized SIR is reduced by more than 60% and 20%, respectively. The operating frequency bands can be determined by switching the diodes that are connected to the cross coupling lines of the two SIRs. The improved design can be used for 5G and other applications.
Using micro-doppler signatures is an effective way to classify different types of UAVs, as well a... more Using micro-doppler signatures is an effective way to classify different types of UAVs, as well as other airborne objects such as birds. To generate signatures for drones, radar measurements are needed; however, these measurements are limited to the types of available drones, the radar parameters, the targets’ range, and the environments in which these measurements are conducted. In this paper, a new method for generating signature datasets is introduced. The method uses full-wave electromagnetic simulation software. Using this method, radar drones’ datasets can be generated using different types, sizes, drone materials, radar parameters, detected range, targets speed, and rotor RPM for rotary drones. A 77 GHz modeled FMCW radar is used to create dataset for classification purposes. Finally, a Convolutional Neural Network (CNN) algorithm is used to classify five types of drones. Based on the results, the classification of the drones is found to exceed 97% accuracy.