We study the long wavelength electromagnetic resonances of interacting cylinder arrays. By using ... more We study the long wavelength electromagnetic resonances of interacting cylinder arrays. By using a normal modes expansion where the effects of geometry and material are separated, it is shown that two parallel cylinders with different radii have electromagnetic modes distributed symmetrically about depolarization factor 1 2. Both sets couple to longitudinal and transverse components of the external field, but amplitudes of symmetric depolarization factors become exchanged when considering longitudinal or transverse polarization. We also find that amplitudes satisfy sum rules that depend on the
A h k a d -I n this paper, a new configuration for aneutral point clamped PWM inverter and its co... more A h k a d -I n this paper, a new configuration for aneutral point clamped PWM inverter and its control strategy is proposed. The proposed configuration consists of an auxiliary circuit with four switching devices, and a single full-bridge inverter. The control method is based on closedloop regulation of the instantaneous line-to-line output voltages. The proposed scheme is simple. has fast rcsponse. and is effective for reducing the size of the DC-link capacitors. The performance of the systcm is verified by computer simulation and by experiment.
inverters is proposed. The closed-loop system uses the two-axis components of the transformed lin... more inverters is proposed. The closed-loop system uses the two-axis components of the transformed line-to-line voltage vectors as the control variables. In its linear control range, the PWM method includes two operating modes, namely, low and high references. At high references' mode, the output voltage is generated by switching among four vectors instead of three to improve the waveform generation. The proposed system has a linear control range 15.5% wider than conventional phase control methods. Furthermore, the control range can be easily expanded beyond the higher linear controllable range up to the square waveforms without suddenly increasing the waveform distortion. Therefore, the fundamental component of the output voltage can be smoothly and continuously controlled from zero up to square waveforms. The control circuit includes a hysteresis controller that is capable of stabilizing the neutral point potential variations within fixed limits during steady and transient states. The control method also offers high performance and fast response. Computer simulations and experimental results on a laboratory-tested motor drive are given to validate the proposed control scheme.
inverters is proposed. The closed-loop system uses the two-axis components of the transformed lin... more inverters is proposed. The closed-loop system uses the two-axis components of the transformed line-to-line voltage vectors as the control variables. In its linear control range, the PWM method includes two operating modes, namely, low and high references. At high references' mode, the output voltage is generated by switching among four vectors instead of three to improve the waveform generation. The proposed system has a linear control range 15.5% wider than conventional phase control methods. Furthermore, the control range can be easily expanded beyond the higher linear controllable range up to the square waveforms without suddenly increasing the waveform distortion. Therefore, the fundamental component of the output voltage can be smoothly and continuously controlled from zero up to square waveforms. The control circuit includes a hysteresis controller that is capable of stabilizing the neutral point potential variations within fixed limits during steady and transient states. The control method also offers high performance and fast response. Computer simulations and experimental results on a laboratory-tested motor drive are given to validate the proposed control scheme.
IEEE Transactions on Antennas and Propagation, 2000
ABSTRACT A method is proposed by which a large number of characteristic modes of an arbitrary str... more ABSTRACT A method is proposed by which a large number of characteristic modes of an arbitrary structure are tracked over a very wide frequency range; it is necessary for any serious wideband modal analysis of complex structures. The method can track a large number of modes using the modal eigenvectors from a generalized eigenvalue problem parameterized by frequency and has been successfully applied to over one hundred antenna geometries. The method is detailed and applied to two distinct geometries and the results discussed.
SIMPLE STRUCTURE MULTILEVEL INVERTER USEFUL FOR AC MOTOR DRIVES
Electric Machines & Power Systems, 1997
In this paper, a new simplified configuration for a multilevel PWM inverter and its control strat... more In this paper, a new simplified configuration for a multilevel PWM inverter and its control strategy is proposed. The proposed configuration consists of an auxiliary circuit with four switching devices, and a single full-bridge inverter. For medium power applications, the new circuit ...
An improved voltage vector control method for neutral-point-clamped inverters
IEEE Transactions on Power Electronics, 1995
Abstract-A new PWM method for Neutral-Point-Clamped (NPC) inverters is introduced. The method is ... more Abstract-A new PWM method for Neutral-Point-Clamped (NPC) inverters is introduced. The method is based on closed-loop control of the line-to-line voltage vectors. It uses inde-pendent hysteresis comparator controllers to regulate the direct and quadrature axis components of the three ...
Electromagnetic field excited by a line source placed at the edge of an impedance wedge
IEEE Transactions on Antennas and Propagation, 1991
Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 39, NO. I, JULY 1991 1043 7 0 0 mo an... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 39, NO. I, JULY 1991 1043 7 0 0 mo an 600 800 ~OOD ROO WO moo is00 THETA (DEGREES) Fig. 2. Monostatic RCS for an anisotropic ellipsoid of revolution. ...
Antenna design and analysis using characteristic modes
Antennas and Propagation Society International Symposium, 2007
Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raine... more Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raines and Roberto G. Rojas ElectroScience Laboratory, Department of Electrical and Computer Engineering, The Ohio State ...
1] An asymptotic Green s function technique is presented for the calculation of the surface field... more 1] An asymptotic Green s function technique is presented for the calculation of the surface fields on a perfect electric conductor circular cylinder covered with a dielectric layer. The sources are apertures located on the perfect electric conductor surface. This method is very efficient and valid for large cylinders in terms of wavelengths. The new representation is obtained via Watson s transformation and integral contour deformations. The efficiency of the method results from the circumferentially propagating representation of the Green s function as well as the efficient numerical evaluation of various integrals. Numerical results are presented showing good agreement when compared to other solutions as well as measurements.
Antenna design and analysis using characteristic modes
2007 IEEE Antennas and Propagation International Symposium, 2007
Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raine... more Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raines and Roberto G. Rojas ElectroScience Laboratory, Department of Electrical and Computer Engineering, The Ohio State ...
2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014
ABSTRACT In this paper presents a compact MIMO array platform to operate at 2.6GHz Long Term Evol... more ABSTRACT In this paper presents a compact MIMO array platform to operate at 2.6GHz Long Term Evolution (LTE) band for wireless communication systems. The array consists of four compact patch antennas on a dielectric substrate with total dimensions of 125×62.5×1.27mm3. Modifications of the ground plane along with systematic placement and orientation of each antenna on top of the substrate plays a key role to reduce the mutual coupling which normally degrades the MIMO arrays performance. The modifications of the ground plane, placement, and orientation of each antenna on the array was done based on the insights provided by the theory of CM. The CM-based approach considers the chassis as a fundamental structure, and by examining the set of characteristic currents in the PCB/dielectric substrate, allows the designer to define the position of each antenna of the MIMO array.
Two-dimensional Green's function for a wedge with impedance faces
IEEE Transactions on Antennas and Propagation, 1997
Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 45, NO. 12, DECEMBER 1997 1799 Two-Di... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 45, NO. 12, DECEMBER 1997 1799 Two-Dimensional Green's Function for a Wedge with Impedance Faces Michael F. Otero and Roberto G. Rojas, Senior Member, IEEE ...
A fast and accurate algorithm is explored for solving two-dimensional electromagnetic scattering ... more A fast and accurate algorithm is explored for solving two-dimensional electromagnetic scattering from electrically large finite strip arrays on grounded dielectric slabs. The induced current is computed efficiently using the novel spectral algorithm, a recently proposed fast single-level matrix-vector product algorithm that reduces the operation count to O(N), where N is the number of unknowns. This algorithm was originally cast into a forward-backward method, but it can equally be used to accelerate the matrix-vector products on conjugate gradient techniques. Both, transverse magnetic and transverse electric polarizations have been considered.
Theory of surface enhanced Raman scattering in colloids
The Journal of Chemical Physics, 1993
We present a theory of surface enhanced Raman scattering (SERS) that gives a response enhancement... more We present a theory of surface enhanced Raman scattering (SERS) that gives a response enhancement of up to ten orders of magnitude for pyridine on silver. The signal obtained depends on the laser frequency and is consistent with available experimental data. Our theory emphasizes the ...
Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency
Journal of Applied Physics, 2009
Page 1. Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency ... more Page 1. Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency Shadi S. Alshannaqa and Roberto G. Rojas Department of Electrical and Computer Engineering, ElectroScience Laboratory ...
Efficient computation of surface fields excited on a dielectric-coated circular cylinder
IEEE Transactions on Antennas and Propagation, 2000
Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 48, NO. 10, OCTOBER 2000 1507 Efficie... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 48, NO. 10, OCTOBER 2000 1507 Efficient Computation of Surface Fields Excited on a Dielectric-Coated Circular Cylinder Vakur B. Ertürk and Roberto G. Rojas, Senior Member, IEEE ...
We study the long wavelength electromagnetic resonances of interacting cylinder arrays. By using ... more We study the long wavelength electromagnetic resonances of interacting cylinder arrays. By using a normal modes expansion where the effects of geometry and material are separated, it is shown that two parallel cylinders with different radii have electromagnetic modes distributed symmetrically about depolarization factor 1 2. Both sets couple to longitudinal and transverse components of the external field, but amplitudes of symmetric depolarization factors become exchanged when considering longitudinal or transverse polarization. We also find that amplitudes satisfy sum rules that depend on the
A h k a d -I n this paper, a new configuration for aneutral point clamped PWM inverter and its co... more A h k a d -I n this paper, a new configuration for aneutral point clamped PWM inverter and its control strategy is proposed. The proposed configuration consists of an auxiliary circuit with four switching devices, and a single full-bridge inverter. The control method is based on closedloop regulation of the instantaneous line-to-line output voltages. The proposed scheme is simple. has fast rcsponse. and is effective for reducing the size of the DC-link capacitors. The performance of the systcm is verified by computer simulation and by experiment.
inverters is proposed. The closed-loop system uses the two-axis components of the transformed lin... more inverters is proposed. The closed-loop system uses the two-axis components of the transformed line-to-line voltage vectors as the control variables. In its linear control range, the PWM method includes two operating modes, namely, low and high references. At high references' mode, the output voltage is generated by switching among four vectors instead of three to improve the waveform generation. The proposed system has a linear control range 15.5% wider than conventional phase control methods. Furthermore, the control range can be easily expanded beyond the higher linear controllable range up to the square waveforms without suddenly increasing the waveform distortion. Therefore, the fundamental component of the output voltage can be smoothly and continuously controlled from zero up to square waveforms. The control circuit includes a hysteresis controller that is capable of stabilizing the neutral point potential variations within fixed limits during steady and transient states. The control method also offers high performance and fast response. Computer simulations and experimental results on a laboratory-tested motor drive are given to validate the proposed control scheme.
inverters is proposed. The closed-loop system uses the two-axis components of the transformed lin... more inverters is proposed. The closed-loop system uses the two-axis components of the transformed line-to-line voltage vectors as the control variables. In its linear control range, the PWM method includes two operating modes, namely, low and high references. At high references' mode, the output voltage is generated by switching among four vectors instead of three to improve the waveform generation. The proposed system has a linear control range 15.5% wider than conventional phase control methods. Furthermore, the control range can be easily expanded beyond the higher linear controllable range up to the square waveforms without suddenly increasing the waveform distortion. Therefore, the fundamental component of the output voltage can be smoothly and continuously controlled from zero up to square waveforms. The control circuit includes a hysteresis controller that is capable of stabilizing the neutral point potential variations within fixed limits during steady and transient states. The control method also offers high performance and fast response. Computer simulations and experimental results on a laboratory-tested motor drive are given to validate the proposed control scheme.
IEEE Transactions on Antennas and Propagation, 2000
ABSTRACT A method is proposed by which a large number of characteristic modes of an arbitrary str... more ABSTRACT A method is proposed by which a large number of characteristic modes of an arbitrary structure are tracked over a very wide frequency range; it is necessary for any serious wideband modal analysis of complex structures. The method can track a large number of modes using the modal eigenvectors from a generalized eigenvalue problem parameterized by frequency and has been successfully applied to over one hundred antenna geometries. The method is detailed and applied to two distinct geometries and the results discussed.
SIMPLE STRUCTURE MULTILEVEL INVERTER USEFUL FOR AC MOTOR DRIVES
Electric Machines & Power Systems, 1997
In this paper, a new simplified configuration for a multilevel PWM inverter and its control strat... more In this paper, a new simplified configuration for a multilevel PWM inverter and its control strategy is proposed. The proposed configuration consists of an auxiliary circuit with four switching devices, and a single full-bridge inverter. For medium power applications, the new circuit ...
An improved voltage vector control method for neutral-point-clamped inverters
IEEE Transactions on Power Electronics, 1995
Abstract-A new PWM method for Neutral-Point-Clamped (NPC) inverters is introduced. The method is ... more Abstract-A new PWM method for Neutral-Point-Clamped (NPC) inverters is introduced. The method is based on closed-loop control of the line-to-line voltage vectors. It uses inde-pendent hysteresis comparator controllers to regulate the direct and quadrature axis components of the three ...
Electromagnetic field excited by a line source placed at the edge of an impedance wedge
IEEE Transactions on Antennas and Propagation, 1991
Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 39, NO. I, JULY 1991 1043 7 0 0 mo an... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 39, NO. I, JULY 1991 1043 7 0 0 mo an 600 800 ~OOD ROO WO moo is00 THETA (DEGREES) Fig. 2. Monostatic RCS for an anisotropic ellipsoid of revolution. ...
Antenna design and analysis using characteristic modes
Antennas and Propagation Society International Symposium, 2007
Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raine... more Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raines and Roberto G. Rojas ElectroScience Laboratory, Department of Electrical and Computer Engineering, The Ohio State ...
1] An asymptotic Green s function technique is presented for the calculation of the surface field... more 1] An asymptotic Green s function technique is presented for the calculation of the surface fields on a perfect electric conductor circular cylinder covered with a dielectric layer. The sources are apertures located on the perfect electric conductor surface. This method is very efficient and valid for large cylinders in terms of wavelengths. The new representation is obtained via Watson s transformation and integral contour deformations. The efficiency of the method results from the circumferentially propagating representation of the Green s function as well as the efficient numerical evaluation of various integrals. Numerical results are presented showing good agreement when compared to other solutions as well as measurements.
Antenna design and analysis using characteristic modes
2007 IEEE Antennas and Propagation International Symposium, 2007
Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raine... more Page 1. Antenna Design and Analysis Using Characteristic Modes Khaled A. Obeidat*, Bryan D. Raines and Roberto G. Rojas ElectroScience Laboratory, Department of Electrical and Computer Engineering, The Ohio State ...
2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014
ABSTRACT In this paper presents a compact MIMO array platform to operate at 2.6GHz Long Term Evol... more ABSTRACT In this paper presents a compact MIMO array platform to operate at 2.6GHz Long Term Evolution (LTE) band for wireless communication systems. The array consists of four compact patch antennas on a dielectric substrate with total dimensions of 125×62.5×1.27mm3. Modifications of the ground plane along with systematic placement and orientation of each antenna on top of the substrate plays a key role to reduce the mutual coupling which normally degrades the MIMO arrays performance. The modifications of the ground plane, placement, and orientation of each antenna on the array was done based on the insights provided by the theory of CM. The CM-based approach considers the chassis as a fundamental structure, and by examining the set of characteristic currents in the PCB/dielectric substrate, allows the designer to define the position of each antenna of the MIMO array.
Two-dimensional Green's function for a wedge with impedance faces
IEEE Transactions on Antennas and Propagation, 1997
Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 45, NO. 12, DECEMBER 1997 1799 Two-Di... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 45, NO. 12, DECEMBER 1997 1799 Two-Dimensional Green's Function for a Wedge with Impedance Faces Michael F. Otero and Roberto G. Rojas, Senior Member, IEEE ...
A fast and accurate algorithm is explored for solving two-dimensional electromagnetic scattering ... more A fast and accurate algorithm is explored for solving two-dimensional electromagnetic scattering from electrically large finite strip arrays on grounded dielectric slabs. The induced current is computed efficiently using the novel spectral algorithm, a recently proposed fast single-level matrix-vector product algorithm that reduces the operation count to O(N), where N is the number of unknowns. This algorithm was originally cast into a forward-backward method, but it can equally be used to accelerate the matrix-vector products on conjugate gradient techniques. Both, transverse magnetic and transverse electric polarizations have been considered.
Theory of surface enhanced Raman scattering in colloids
The Journal of Chemical Physics, 1993
We present a theory of surface enhanced Raman scattering (SERS) that gives a response enhancement... more We present a theory of surface enhanced Raman scattering (SERS) that gives a response enhancement of up to ten orders of magnitude for pyridine on silver. The signal obtained depends on the laser frequency and is consistent with available experimental data. Our theory emphasizes the ...
Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency
Journal of Applied Physics, 2009
Page 1. Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency ... more Page 1. Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency Shadi S. Alshannaqa and Roberto G. Rojas Department of Electrical and Computer Engineering, ElectroScience Laboratory ...
Efficient computation of surface fields excited on a dielectric-coated circular cylinder
IEEE Transactions on Antennas and Propagation, 2000
Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 48, NO. 10, OCTOBER 2000 1507 Efficie... more Page 1. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 48, NO. 10, OCTOBER 2000 1507 Efficient Computation of Surface Fields Excited on a Dielectric-Coated Circular Cylinder Vakur B. Ertürk and Roberto G. Rojas, Senior Member, IEEE ...
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