Rodica Ramer - Academia.edu (original) (raw)
Papers by Rodica Ramer
Wireless Sensor Network (WSN) comprises of micro sensor nodes with limited energy and processing ... more Wireless Sensor Network (WSN) comprises of micro sensor nodes with limited energy and processing ability. It is used in military as well as civil applications. In order to enhance the network life time by the period of a particular mission, many routing protocols have been devised. One of these are network clustering, in which network is partitioned into small clusters and each cluster is monitored and controlled by a node, called Cluster Head (CH). The CH should be powerful, closer to the cluster-centroid, less vulnerable and has low mobility, so that it can aggregate the data from its own cluster nodes and then send it directly to the Base Station (BS). In this paper, we are using the method of evolutionary computing for the selection of the CHs. The BS periodically runs the proposed algorithm to select new CHs after a certain period of time. Results show that network life time is drastically increases by the help of evolutionary computing.
A number of c-axis oriented MgB2 thin films were grown in-situ by pulsed laser deposition (PLD) o... more A number of c-axis oriented MgB2 thin films were grown in-situ by pulsed laser deposition (PLD) on Al2O3-R cut, and the pinning properties were investigated using transport, DC magnetisation and magneto-optical imaging (MOI) techniques. It was found that at temperatures below 10K and large applied DC magnetic fields, the irreversibili ty line of insitu MgB2 thin films is higher that a bulk material. The critical current density Jc of in-situ thin fi lms is less dependent on the applied magnetic field B than the current density Jc of an ex-situ MgB2 film or bulk. The penetration of magnetic field inside the film is uniform, and it follows the theoretical prediction for a homogenous thin film.
2018 International Semiconductor Conference (CAS), 2018
This paper presents the study and simulation results of a millimetre-wave based device for cancer... more This paper presents the study and simulation results of a millimetre-wave based device for cancerous skin tissue detection. A probe that could be implemented using inexpensive silicon planar fabrication is proposed. It permits easy system-on-chip integration with other silicon devices to achieve an entire measuring tool for easy deployment. We used the available open literature basal cell carcinoma (BCC) data considerations, for initial development and simulation validation. This study showed that the reflection coefficients vs frequency could capture useful information indicating the possible BCC presence at millimetre-wave frequencies by using both magnitude and phase of the reflection coefficients. It was found that a dual-band approach, 100 to 150 GHz and 200 to 250 GHz, has the ability to highlight deviations from the normal skin.
High-quality single crystals are well suited to the investigation of some intrinsic material prop... more High-quality single crystals are well suited to the investigation of some intrinsic material properties. A modified Bridgman method using a sharp temperature gradient (approximately 300 C cm) was used to grow Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8+x] single crystals. Although the samples was contained in alumina ampoules, no aluminium contamination of the samples was detected. Blade-shaped crystals up to [approximately]
IEEE Microwave and Wireless Components Letters, 2017
2021 IEEE Asia-Pacific Microwave Conference (APMC), Nov 28, 2021
A 3D printed differential waveguide coupler utilizing TE20 mode is reported in this paper. It exh... more A 3D printed differential waveguide coupler utilizing TE20 mode is reported in this paper. It exhibits a 43% bandwidth operating from 13 to 20.3 GHz with a coupling magnitude of 3dB and variations of 0.6 dB. The device expands on existing coupling techniques and utilizes a novel 70% bandwidth ultra-wideband waveguide balun designed to produce the higher-order mode and facilitate measurement. The overall device possesses differential waveguide ports while offering comparable performance to typical fundamental mode waveguide directional couplers.
This paper presents the study and analyses on substrate integrated waveguide (SIW) Y-type power d... more This paper presents the study and analyses on substrate integrated waveguide (SIW) Y-type power dividers. In traditional configurations, a potential stop peak exists and separates the dominant frequency band. To overcome this drawback, a Y-type power divider with an enhanced bandwidth is proposed, where the reflection at the stop peak is reduced. The broadband characteristic relies on the adjustment of the TE10 and TE30 modes in the coupling region. The symmetric topology could ensure balanced phase and amplitude properties at two output ports. For the demonstration, the prototype is fabricated by the printed circuit board (PCB) process. Measurements agree well with simulations, and a fractional bandwidth of 50.26% around the centre frequency of 15 GHz is measured with 10 dB return loss.
Microwave and Optical Technology Letters, Apr 8, 2018
A novel concept of reconfiguring high Q-factor iris filters, to operate in different frequency ba... more A novel concept of reconfiguring high Q-factor iris filters, to operate in different frequency bands, is presented. Compared to traditional iris filters, the air-filled irises are here replaced with dielectric substrate, similarly as the concept of substrate integrated waveguide. By controlling RF MEMS switches placed on the dielectric substrate, the equivalent iris width and thickness, and the resonant cavity length can be reconfigured simultaneously. As a demonstration of the concept, this article has proposed a thirdorder bandpass filter consisting of 3 waveguide sections made of brass and 4 inverters fabricated on Rogers RT/ duroid 5880 substrate. Constant absolute bandwidths between different states and theoretical unloaded Q-factor of 1800 are achievable in our approach.
A low cost high-efficient microstrip line fed antenna for 60 GHz communications is presented. An ... more A low cost high-efficient microstrip line fed antenna for 60 GHz communications is presented. An investigation for microstrip antenna presently being working at lower microwave frequency has been done for 60 GHz communication. A new geometry has been presented in form of H shaped design with feeding from microstrip line. The results have been simulated using high frequency structural simulator (HFSS).There is a comparison between two antennas one with superstrate and one without superstrate is also presented. The use of superstrate has resulted in improved bandwidth and increased gain. The presented antennas are for broadband communications offering 6.3 GHz and 7.1 GHz bandwidth for one without and one with superstrate respectively.
A novel substrate integrated waveguide (SIW) H-plane horn antenna with additional split-ring and ... more A novel substrate integrated waveguide (SIW) H-plane horn antenna with additional split-ring and dielectric structures has been proposed in this paper. This antenna operates at 27 GHz with a simulated gain of 10.2 dBi. It presents reduced side-lobes compared to the traditional SIW horn antenna. Fed by a coaxial connector and realized on AR450 PTFE based laminate, it is affordable, easy to fabricate and presents reasonably high gain.
Waveguide switchable bandstop and bandpass filter designs are demonstrated in this paper. The des... more Waveguide switchable bandstop and bandpass filter designs are demonstrated in this paper. The designs are based on the design of rectangular waveguide that has switching planar bandstop resonators inserted on the sidewall. These switchable bandstop resonators consist of two identical metal patches separated by switching elements. The switching elements can be of RF MEMS or semiconductor transistor type. These resonators allow electrically switching of the waveguide while providing close to ideal on-state insertion loss and narrow stop band during off-state. These switches permit the switchable bandstop and bandpass filters design. The concept is demonstrated for a switchable five-pole bandstop filter and a switchable three-pole bandpass filter, both at the centre frequency of 14.25 GHz and for 500 MHz bandwidth.
Ferroelectrics, 2002
The electromechanical and piezoelectric properties of PT-type ceramics can be modified both by A ... more The electromechanical and piezoelectric properties of PT-type ceramics can be modified both by A or B site substitution in the perovskite, and by varying the porosity of the material. In this work rare earth modified lead titanate material with the general formula (Pb 0.88 Nd 0.036 Dy 0.044 ) (Ti 0.98 Mn 0.02 )O 3 , was prepared by the
IEEE Transactions on Antennas and Propagation, Mar 1, 2022
This article presents a novel leaky-wave antenna (LWA) based on a dielectric-filled rectangular w... more This article presents a novel leaky-wave antenna (LWA) based on a dielectric-filled rectangular waveguide (RWG) and fed by a higher order mode. The proposed quasi-uniform LWA has a compact configuration that is suitable for microwave applications, featuring the omnidirectional radiation patterns and low cross-polarization. In the frequency band of interest, the higher order mode, i.e., the TM11 mode, performs as a fast wave in the proposed quasi-uniform LWA, radiating via the transverse slots etched on the walls. The advantage of the TM11 mode for LWA applications is analyzed and demonstrated. This higher order mode is excited via a mode convertor from an inline coaxial line to the dielectric-filled RWG. For the reduction in sidelobe levels at high frequencies, −25 dB Taylor amplitude distribution is applied to the etched slots. The dielectric-filled LWA with the inline coaxial feeding is fabricated and measured. The measurement is consistent with the simulation, showing frequency-driven beam-scanning capability with low cross-polarization in the elevation plane. The simulated and measured radiation patterns in the azimuth plane illustrate the omnidirectional radiation patterns and thus confirm the radiating performance of the TM11 mode in the proposed LWA. The advantages of the scanned beams and omnidirectional radiations are promising for radar systems.
IEEE Transactions on Microwave Theory and Techniques, Feb 1, 2020
By switching high <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-... more By switching high <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-factor 3-D waveguide bandpass filters with planar radio frequency micro-electromechanical system (RF MEMS)-based elements, a channel aggregation technique is developed in this article. These planar elements play the role of generating an effective phase shift when activated, detuning the resonant cavities of the bandpass filter, and contributing minimal insertion loss when deactivated. The proposed detuning system also has the advantage of not affecting the other operating filter channels connected to manifolds in a switchable waveguide filter bank. A two-channel prototype, based on the Australian satellite <italic>Ku</italic>-band, with 500-MHz bandwidth, at 14.25-GHz (CH1) and 16.25-GHz (CH2) frequencies, is designed, fabricated, and measured demonstrating the channel aggregation operation. When using only two waveguide bandpass filters with no external switches, four different passband states are implemented, e.g., both channels disable (00), channel 2 enables only (01), channel 1 enables only (10), and both channels enable (11). The system provides excellent channel isolation of better than 35 dB over the disabled channels. For the enabled channels, the filters maintain a measured <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-factor of over 800, and better than 15 dB return loss. The measurements confirm that the detuning elements have a minimal impact on the manifolds and other channel filters, regardless of the operating states.
IEEE Transactions on Microwave Theory and Techniques, Sep 1, 2018
This paper presents a simple, low-cost, hours-long fabrication method for microwave waveguide com... more This paper presents a simple, low-cost, hours-long fabrication method for microwave waveguide components of high RF performance. The technique combines 3-D-printed configurations with liquid metal waveguide structures. As a demonstration, a fused deposition modeling multimaterial 3-D consumer-grade printer and liquid gallium were used. A conductive polylactic acid (PLA) waveguide flange was 3-D printed along, in-one-go, with standard PLA for the rectangular waveguide liquid metal enclosures. Microwave WR62 waveguides, resonators, and filters operating in Ku-band were designed, fabricated, and tested. The RF performance of the fabricated waveguide devices is in agreement with the simulations demonstrating better than 1.29 dB/m attenuation in the waveguide and better than 1000 Q-factor for the resonator and the filter at 13 GHz. The fabricated devices demonstrate a new option of an economical fabrication technology for high RF performance microwave waveguide-based devices that can be delivered in hours-time, anywhere, anytime with minimal equipment deployment and investment.
The paper proposed a new fabrication technique for microwave devices using liquid metal conductor... more The paper proposed a new fabrication technique for microwave devices using liquid metal conductor and 3D printed dielectric containers. 3D printed conductive dielectric materials provide electrical connections to the liquid metal at the input and output ports. These input/ output ports and the dielectric container were analyzed to determine their impact on the RF performance. Simulation results of a WR62 rectangular waveguide transmission line, waveguide resonator, a three-pole iris filter and a horn antenna were presented. The RF performance achieved satisfactory RF performance validating the proposed fabrication concept.
Electronics, Nov 10, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
2022 International Symposium on Antennas and Propagation (ISAP), Oct 31, 2022
Wireless Sensor Network (WSN) comprises of micro sensor nodes with limited energy and processing ... more Wireless Sensor Network (WSN) comprises of micro sensor nodes with limited energy and processing ability. It is used in military as well as civil applications. In order to enhance the network life time by the period of a particular mission, many routing protocols have been devised. One of these are network clustering, in which network is partitioned into small clusters and each cluster is monitored and controlled by a node, called Cluster Head (CH). The CH should be powerful, closer to the cluster-centroid, less vulnerable and has low mobility, so that it can aggregate the data from its own cluster nodes and then send it directly to the Base Station (BS). In this paper, we are using the method of evolutionary computing for the selection of the CHs. The BS periodically runs the proposed algorithm to select new CHs after a certain period of time. Results show that network life time is drastically increases by the help of evolutionary computing.
A number of c-axis oriented MgB2 thin films were grown in-situ by pulsed laser deposition (PLD) o... more A number of c-axis oriented MgB2 thin films were grown in-situ by pulsed laser deposition (PLD) on Al2O3-R cut, and the pinning properties were investigated using transport, DC magnetisation and magneto-optical imaging (MOI) techniques. It was found that at temperatures below 10K and large applied DC magnetic fields, the irreversibili ty line of insitu MgB2 thin films is higher that a bulk material. The critical current density Jc of in-situ thin fi lms is less dependent on the applied magnetic field B than the current density Jc of an ex-situ MgB2 film or bulk. The penetration of magnetic field inside the film is uniform, and it follows the theoretical prediction for a homogenous thin film.
2018 International Semiconductor Conference (CAS), 2018
This paper presents the study and simulation results of a millimetre-wave based device for cancer... more This paper presents the study and simulation results of a millimetre-wave based device for cancerous skin tissue detection. A probe that could be implemented using inexpensive silicon planar fabrication is proposed. It permits easy system-on-chip integration with other silicon devices to achieve an entire measuring tool for easy deployment. We used the available open literature basal cell carcinoma (BCC) data considerations, for initial development and simulation validation. This study showed that the reflection coefficients vs frequency could capture useful information indicating the possible BCC presence at millimetre-wave frequencies by using both magnitude and phase of the reflection coefficients. It was found that a dual-band approach, 100 to 150 GHz and 200 to 250 GHz, has the ability to highlight deviations from the normal skin.
High-quality single crystals are well suited to the investigation of some intrinsic material prop... more High-quality single crystals are well suited to the investigation of some intrinsic material properties. A modified Bridgman method using a sharp temperature gradient (approximately 300 C cm) was used to grow Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8+x] single crystals. Although the samples was contained in alumina ampoules, no aluminium contamination of the samples was detected. Blade-shaped crystals up to [approximately]
IEEE Microwave and Wireless Components Letters, 2017
2021 IEEE Asia-Pacific Microwave Conference (APMC), Nov 28, 2021
A 3D printed differential waveguide coupler utilizing TE20 mode is reported in this paper. It exh... more A 3D printed differential waveguide coupler utilizing TE20 mode is reported in this paper. It exhibits a 43% bandwidth operating from 13 to 20.3 GHz with a coupling magnitude of 3dB and variations of 0.6 dB. The device expands on existing coupling techniques and utilizes a novel 70% bandwidth ultra-wideband waveguide balun designed to produce the higher-order mode and facilitate measurement. The overall device possesses differential waveguide ports while offering comparable performance to typical fundamental mode waveguide directional couplers.
This paper presents the study and analyses on substrate integrated waveguide (SIW) Y-type power d... more This paper presents the study and analyses on substrate integrated waveguide (SIW) Y-type power dividers. In traditional configurations, a potential stop peak exists and separates the dominant frequency band. To overcome this drawback, a Y-type power divider with an enhanced bandwidth is proposed, where the reflection at the stop peak is reduced. The broadband characteristic relies on the adjustment of the TE10 and TE30 modes in the coupling region. The symmetric topology could ensure balanced phase and amplitude properties at two output ports. For the demonstration, the prototype is fabricated by the printed circuit board (PCB) process. Measurements agree well with simulations, and a fractional bandwidth of 50.26% around the centre frequency of 15 GHz is measured with 10 dB return loss.
Microwave and Optical Technology Letters, Apr 8, 2018
A novel concept of reconfiguring high Q-factor iris filters, to operate in different frequency ba... more A novel concept of reconfiguring high Q-factor iris filters, to operate in different frequency bands, is presented. Compared to traditional iris filters, the air-filled irises are here replaced with dielectric substrate, similarly as the concept of substrate integrated waveguide. By controlling RF MEMS switches placed on the dielectric substrate, the equivalent iris width and thickness, and the resonant cavity length can be reconfigured simultaneously. As a demonstration of the concept, this article has proposed a thirdorder bandpass filter consisting of 3 waveguide sections made of brass and 4 inverters fabricated on Rogers RT/ duroid 5880 substrate. Constant absolute bandwidths between different states and theoretical unloaded Q-factor of 1800 are achievable in our approach.
A low cost high-efficient microstrip line fed antenna for 60 GHz communications is presented. An ... more A low cost high-efficient microstrip line fed antenna for 60 GHz communications is presented. An investigation for microstrip antenna presently being working at lower microwave frequency has been done for 60 GHz communication. A new geometry has been presented in form of H shaped design with feeding from microstrip line. The results have been simulated using high frequency structural simulator (HFSS).There is a comparison between two antennas one with superstrate and one without superstrate is also presented. The use of superstrate has resulted in improved bandwidth and increased gain. The presented antennas are for broadband communications offering 6.3 GHz and 7.1 GHz bandwidth for one without and one with superstrate respectively.
A novel substrate integrated waveguide (SIW) H-plane horn antenna with additional split-ring and ... more A novel substrate integrated waveguide (SIW) H-plane horn antenna with additional split-ring and dielectric structures has been proposed in this paper. This antenna operates at 27 GHz with a simulated gain of 10.2 dBi. It presents reduced side-lobes compared to the traditional SIW horn antenna. Fed by a coaxial connector and realized on AR450 PTFE based laminate, it is affordable, easy to fabricate and presents reasonably high gain.
Waveguide switchable bandstop and bandpass filter designs are demonstrated in this paper. The des... more Waveguide switchable bandstop and bandpass filter designs are demonstrated in this paper. The designs are based on the design of rectangular waveguide that has switching planar bandstop resonators inserted on the sidewall. These switchable bandstop resonators consist of two identical metal patches separated by switching elements. The switching elements can be of RF MEMS or semiconductor transistor type. These resonators allow electrically switching of the waveguide while providing close to ideal on-state insertion loss and narrow stop band during off-state. These switches permit the switchable bandstop and bandpass filters design. The concept is demonstrated for a switchable five-pole bandstop filter and a switchable three-pole bandpass filter, both at the centre frequency of 14.25 GHz and for 500 MHz bandwidth.
Ferroelectrics, 2002
The electromechanical and piezoelectric properties of PT-type ceramics can be modified both by A ... more The electromechanical and piezoelectric properties of PT-type ceramics can be modified both by A or B site substitution in the perovskite, and by varying the porosity of the material. In this work rare earth modified lead titanate material with the general formula (Pb 0.88 Nd 0.036 Dy 0.044 ) (Ti 0.98 Mn 0.02 )O 3 , was prepared by the
IEEE Transactions on Antennas and Propagation, Mar 1, 2022
This article presents a novel leaky-wave antenna (LWA) based on a dielectric-filled rectangular w... more This article presents a novel leaky-wave antenna (LWA) based on a dielectric-filled rectangular waveguide (RWG) and fed by a higher order mode. The proposed quasi-uniform LWA has a compact configuration that is suitable for microwave applications, featuring the omnidirectional radiation patterns and low cross-polarization. In the frequency band of interest, the higher order mode, i.e., the TM11 mode, performs as a fast wave in the proposed quasi-uniform LWA, radiating via the transverse slots etched on the walls. The advantage of the TM11 mode for LWA applications is analyzed and demonstrated. This higher order mode is excited via a mode convertor from an inline coaxial line to the dielectric-filled RWG. For the reduction in sidelobe levels at high frequencies, −25 dB Taylor amplitude distribution is applied to the etched slots. The dielectric-filled LWA with the inline coaxial feeding is fabricated and measured. The measurement is consistent with the simulation, showing frequency-driven beam-scanning capability with low cross-polarization in the elevation plane. The simulated and measured radiation patterns in the azimuth plane illustrate the omnidirectional radiation patterns and thus confirm the radiating performance of the TM11 mode in the proposed LWA. The advantages of the scanned beams and omnidirectional radiations are promising for radar systems.
IEEE Transactions on Microwave Theory and Techniques, Feb 1, 2020
By switching high <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-... more By switching high <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-factor 3-D waveguide bandpass filters with planar radio frequency micro-electromechanical system (RF MEMS)-based elements, a channel aggregation technique is developed in this article. These planar elements play the role of generating an effective phase shift when activated, detuning the resonant cavities of the bandpass filter, and contributing minimal insertion loss when deactivated. The proposed detuning system also has the advantage of not affecting the other operating filter channels connected to manifolds in a switchable waveguide filter bank. A two-channel prototype, based on the Australian satellite <italic>Ku</italic>-band, with 500-MHz bandwidth, at 14.25-GHz (CH1) and 16.25-GHz (CH2) frequencies, is designed, fabricated, and measured demonstrating the channel aggregation operation. When using only two waveguide bandpass filters with no external switches, four different passband states are implemented, e.g., both channels disable (00), channel 2 enables only (01), channel 1 enables only (10), and both channels enable (11). The system provides excellent channel isolation of better than 35 dB over the disabled channels. For the enabled channels, the filters maintain a measured <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula>-factor of over 800, and better than 15 dB return loss. The measurements confirm that the detuning elements have a minimal impact on the manifolds and other channel filters, regardless of the operating states.
IEEE Transactions on Microwave Theory and Techniques, Sep 1, 2018
This paper presents a simple, low-cost, hours-long fabrication method for microwave waveguide com... more This paper presents a simple, low-cost, hours-long fabrication method for microwave waveguide components of high RF performance. The technique combines 3-D-printed configurations with liquid metal waveguide structures. As a demonstration, a fused deposition modeling multimaterial 3-D consumer-grade printer and liquid gallium were used. A conductive polylactic acid (PLA) waveguide flange was 3-D printed along, in-one-go, with standard PLA for the rectangular waveguide liquid metal enclosures. Microwave WR62 waveguides, resonators, and filters operating in Ku-band were designed, fabricated, and tested. The RF performance of the fabricated waveguide devices is in agreement with the simulations demonstrating better than 1.29 dB/m attenuation in the waveguide and better than 1000 Q-factor for the resonator and the filter at 13 GHz. The fabricated devices demonstrate a new option of an economical fabrication technology for high RF performance microwave waveguide-based devices that can be delivered in hours-time, anywhere, anytime with minimal equipment deployment and investment.
The paper proposed a new fabrication technique for microwave devices using liquid metal conductor... more The paper proposed a new fabrication technique for microwave devices using liquid metal conductor and 3D printed dielectric containers. 3D printed conductive dielectric materials provide electrical connections to the liquid metal at the input and output ports. These input/ output ports and the dielectric container were analyzed to determine their impact on the RF performance. Simulation results of a WR62 rectangular waveguide transmission line, waveguide resonator, a three-pole iris filter and a horn antenna were presented. The RF performance achieved satisfactory RF performance validating the proposed fabrication concept.
Electronics, Nov 10, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
2022 International Symposium on Antennas and Propagation (ISAP), Oct 31, 2022