Corner reflector tag with RCS frequency coding by dielectric resonators
Authors : Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija, Klaus Solbach, Thomas Kaiser
Abstract : For a novel indoor‐localization system, chipless tags with high retro‐directive radar cross section (RCS) under wide‐angle incidence are required as fixed landmarks. Tags based on
dielectric resonators (DRs) were proposed to provide identification by resonance frequency coding. To achieve a satisfactory read range for the localization system, the low RCS levels of these tags require a major boost. A solution was found by adopting the metallic corner reflector which is known for high RCS levels over a wide bandwidth and over a wide angle of incidence. The study presents a novel corner reflector design where notches in the RCS spectral signature are created by the attachment of arrays of dielectric resonators to the metallic surfaces of corner reflectors. It is shown that notches appear due to the increased scattering of the resonators at resonance and by the power loss due to grating lobes formed in addition to the specular reflection from the arrays and from the metallic surfaces. Results from electromagnetic simulations are verified by measurements of an example dihedral corner reflector of 100 × 100 mm2 plate size with two arrays of 3 × 3 DRs producing a notch signature at about 7 GHz.
Keywords :
Visit
Dielectric Resonator-Based Passive Chipless Tag With Angle-of-Arrival Sensing
Authors : Ali Alhaj Abbas; Mohammed El-Absi; Ashraf Abualhijaa; Klaus Solbach; Thomas Kaiser
Abstract : Passive chipless tags based on dielectric resonators (DRs) have been proposed for a novel millimeter-wave indoor self-localization system to mark fixed reference nodes. The tags employed in the system provide a unique spectral signature (resonance peaks) with much-increased radar cross section (RCS) by placing several identical DRs at the focal line of a spherical dielectric lens. Resonators of optimized geometry allow a modification of this original DR-lens tag by combining the lens with different size DRs which exhibit resonant frequencies separated by large frequency gaps. For easier manufacturing and testing, a demonstrator tag was designed for a “scaled” frequency range of 5–6 GHz with this configuration and is shown to produce spectral signatures of the monostatic RCS which are uniquely related to the angle of arrival (AoA) of the incident wave from a reader. Simulated signatures of a lens of 120-mm diameter with seven spherical DRs are presented and results are supported by experiment. Correlation processing of the signatures can give a resolution of few degrees in AoA while the bistatic RCS half power beamwidth is on the order of 20 and RCS levels of resonant peaks are produced between 0 and −6 dBm2
Keywords : Angle of arrival (AoA), backscatter radio frequency (RF) tag, dielectric resonator (DR), passive chipless RFID, radar cross sections (RCSS), spherical lens
Visit
Metallic reflectors with notched RCS spectral signature using dielectric resonators
Authors : Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija, Klaus Solbach and Thomas Kaiser
Abstract : Dielectric resonators are placed in front of metallic plane plate and corner reflectors. Excitation of the resonant mode produces strong scattering of an incident plane wave which shows up as narrow notch in the mono-static RCS spectral signature at the resonance frequency. Experimental proof at V-band is given with a corner reflector of cm-size with spherical dielectric
resonators of 0.8 mm diameter showing a notch at 64 GHz.
Keywords :
Visit
RCS Enhancement of Dielectric Resonator Tag Using Spherical Lens
Authors : Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija, Klaus Solbach and Thomas Kaiser
Abstract : The RCS of flat cylindrical Dielectric Resonators (DR) is investigated and found to be too low for an application of the resonators as tags in a novel indoor localization system at mm-wave frequencies. As a method to increase the RCS of a DR tag, we propose the combination with a constant-index spherical lens. The collimation and scattering properties of this lens type are found suitable for a combination with DRs. The optimum relative permittivity of the lens is found in the range of r = 1.6 to 2.8 and the optimum distance between lens surface and DR is found slightly larger than the radius of the DR. RCS enhancement is found to vary with the modes of the DR but increases approximately with the fourth power of the lens radius. However, RCS signatures become corrupted by scattering due to mismatch effects of large lenses such that the lens diameter has to be limited to 4 to 5 wavelengths with the RCS enhancement limited to about 30 to 35 dB. Simulation and experimental verification are performed at a down-scaled frequency
range from 4 GHz to 7 GHz using lenses of 60mm and 120mm diameter made of paraffin wax.
Keywords : dielectric resonator, spherical lens, radar cross sections, passive chipless RFID, back-scatter RF tag
Visit
Retrodirective Dielectric Resonator Tag With Polarization Twist Signature for Clutter Suppression in Self-Localization System
Authors : Ali Alhaj Abbas; Mohamed Haj Hassan; Ashraf Abuelhaija; Daniel Erni; Klaus Solbach and Thomas Kaiser
Abstract : In a recently proposed indoor self-localization system, we excite dielectric resonators (DRs) in linear polarization (LP) as retrodirective passive tags, either as single DR, small array of DRs, or in combination with a spherical dielectric lens. DR tags mounted close to a reflecting wall suffer from large clutter return, which can supercede the DR tag signatures. To separate both into orthogonal polarizations, we design a polarization twist tag with two DRs tilted by ±45° and spaced by λ /4. In the EM simulation and experiment, we show that this tag design allows efficient retrodirective scattering in cross polarization. The realized cross-polarization radar cross section (RCS) is equal to the scattering of a single DR in LP and 6 dB better than the RCS from a polarization splitting single DR with 45° tilt. This polarization signature is shown to allow separation of the DR signature from the high scattering level of a flat plate reflector placed behind the polarization twist DR tag. The potential of improving lens-DR combinations by using the polarization twist DR tag with circular polarization is also discussed.
Keywords : Clutter, Scattering, Resonant frequency, Polarization, Wires, Dielectrics, Radar cross-sections, Radio frequency
Visit
Wide-Angle RCS Enhanced Tag Based on Dielectric Resonator – Lens Combination
Authors : Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija, Klaus Solbach und Thomas Kaiser
Abstract : In a novel mm-wave localization system, dielectric resonators (DR) have been proposed as passive chipless RFID tags to mark fixed reference nodes. To counter clutter and improve the limited read range due to the low RCS level of a DR at millimeter-wave frequencies we propose a combination of several DRs with a dielectric spherical lens which allows improvement of up to 30 dB. The paper presents the design principle and shows simulation results and experimental verification of a scaled tag operating in the 10–12 GHz range and covering a range of incidence angle of the reader signal of ± 50°. A frequency sweeping RF reader can identify the tag (information) by the peak of the RCS level at its DR resonant frequency. For a multiple-tag scenario we can realize up to 12 different tags which can be discriminated unambiguously by their resonant frequencies in a 1: 1.2 frequency bandwidth.
Keywords : dielectric resonator; spherical lens; Radar Cross Sections; passive chipless RFID; back-scatter RF tag
Visit
A Pi-Shaped Compact Dual Tuned 1H/23Na Microstripline-Based Switch for 7-Tesla MRI
Authors : Ashraf Abuelhaija, Gameel Saleh
Abstract : In this article, a compact transmitting/receiving switch is designed with concentric microstriplines on the top and bottom faces of a coupler to handle RF signals to/from 1H and 23Na RF coils working specifically at 7-Tesla magnetic resonance imaging machines. A pi-shaped equivalent circuit, from the transmission line theory, has been used with outer and inner microstriplines to compact them in size. The switch has been designed using an electromagnetic wave simulator in order to transmit/receive RF signals to/from the RF coils at the specified resonance frequencies that match with the same speeds of precession of the 1H and 23Na atomic nuclei to support imaging as well as spectroscopic features that are used to monitor the metabolism changes as a measure to the existence of tumors. The proposed pi-shaped equivalent circuit has miniaturized the size of the designed dual tuned switch by around 70% compared to classical fabricated microstripline-based switch. This work adds promising benefits to multi-tuned switches in terms of capability to be integrated with multichannel RF coils. The proposed miniaturized dual tuned switch has revealed high isolation between inner and outer couplers and excellent insertion losses during transmit and receive modes for both 1H and 23Na MRI.
Keywords : 1H and 23Na Atomic Nuclei; Magnetic Resonance Imaging and Spectroscopy (MRI/MRS); Transmit/Receive (T/R) Switch; PIN Diodes; Hybrid Coupler
Visit
Decoupling network for Tx/Rx body coil for 7T MRI
Authors : Ashraf Abuelhaija, Sana Salamh, Osama Nashwan
Abstract : The parallel imaging technique is widely used in 7T MRI scanners. It employs multichannel RF coil arrays to apply a concurrent excitation and acquisition method. Concurrent excitation faces significant challenges in terms of electromagnetic coupling between the RF coil elements. In order to prevent interference between the RF coil elements' exciters, several decoupling methods have been developed to compensate for coupling and to permit independent work for the exciters. This paper studies the coupling between meander coils arranged in two different geometrical setups and investigates the isolation performance between the coils by applying two different decoupling networks depending on the geometrical setup of the coils. These two decoupling networks in addition to a T-shaped decoupling network have been integrated into a Tx/Rx body coil for 7 T to compensate for mutual coupling between array coil elements. The results have been obtained by using CST Microwave Studio (CST AG, Darmstadt, Germany)
Keywords : c resonance imaging, 7-Tesla, mutual coupling, decoupling network, radiofrequency coils, resonant circuit, transmit/receive coil
Visit
Dual tuned 1H/31P quadrature microstripline-based transmit/receive switch for 7 Tesla magnetic resonance imaging
Authors : Ashraf Abuelhaija, Gameel Saleh
Abstract : A dual tuned transmit/receive (T/R) Switch for 7 Tesla magnetic resonance imaging (MRI) that is based on concentric microstripline (MSL) coupler is introduced. The proposed switch is designed using two concentric MSL quadrature couplers on the top and bottom faces of the switch. The switch can be used to handle two frequency signals to/from two radio frequency (RF) coils. In this article, a 1H/31P atomic nuclei are excited. The two MSLs on the upper face of the switch are designed to transmit 298 and 120.6 MHz signals into RF coils, whereas each of the identical upper and lower MSLs are used to receive these signals from the RF coils. This switch can be used to transmit/receive signals from two RF coils at the same time, one work with 1H and the second with 31P atomic nuclei, and without any tuning. The proposed switch has been designed and simulated using the electromagnetic microwave studio computer simulation technology (CST). It demonstrates good matching (≈17 dB), low insertion loss (≈0.3) and high isolation (>70) for the 1H and 31P magnetic resonance signals at transmit mode. During receive mode, it demonstrates good matching (>20 dB), low insertion loss (≈0.2) and high isolation (>70) for the 1H and 31P magnetic resonance signals.
Keywords : 1H and 31P atomic nuclei; insertion loss; microstripline hybrid; PIN diodes; radio frequency coils;
Visit
Multi- and dual-tuned microstripline-based transmit/ receive switch for 7-Tesla magnetic resonance imaging
Authors : Ashraf Abuelhaija, Gameel Saleh, Osama Nashwan, Samer Issa, Sanaa Salama
Abstract : This article introduces two new designs of transmit/receive switches for 7-Tesla magnetic resonance imaging. Both designs based on a microstripline coupler technology. In the first design, a different single frequency signals can be handled to/from a radio frequency coil using smart tuning network. In the second design, a dual-tuned 1H/23Na transmit/receive switch is designed to handle a dual resonant signal to a dual resonant 1H/23Na coil, simultaneously and without tuning. In transmit and receive, the first design achieved good matching (-20 dB), and low insertion loss (0.78 dB) for the 1H, 19F, 31P, 13C, and 23Na magnetic resonance signals with high isolation (61 dB). Similarly, the dual-tuned 1H/23Na switch achieved good matching (<−11.5 dB) and low insertion loss (1.0 dB) with high isolation (67 dB), whereas for 1H/31P switch, good matching has been achieved (<−12 dB) and low insertion loss (0.96 dB) with high isolation (62 dB). The first proposed switch enables the use of the same switch with different coils resonating at Larmor frequencies of different atomic nuclei. The second switch can handle a dual resonant signal to a single dual resonant coil. The first design is promising in reducing the costs by using the same switch with different coils. The second design is promising in the integration with multichannel dual resonant coil.
Keywords : hybrid coupler, magnetic resonance imaging, PIN diodes, radio frequency
Visit
Multi-Tuned Radiofrequency Coil Using Microfluidically Tunable Capacitor for Magnetic Resonance Imaging/Spectroscopy at 7-Tesla
Authors : Ashraf Abuelhaija, Sanaa Salama, Mohammed El-Absi
Abstract : Multi-nuclear magnetic resonance imaging and spectroscopy are considered valuable tools due to their capability of diagnosis and monitoring of several diseases. They require multi-nuclear Radiofrequency coils in order to interrogate the proton (1H) and other nuclei (X-nuclei) in the human body. Such coils provide anatomical images by acquiring (1H) spectra and metabolites information by acquiring spectra of X-nuclei. In addition, the high signal received from proton (1H) is used for B0 shimming purposes. However, the signal strength for these X-nuclei is too low. Hence, the signal-to-noise-ratio is low. The main advantages of using multinuclear Radiofrequency coils are that they speed up the imaging process and reduce the spatial positioning error that might arise when replacing the Radiofrequency coil in order to perform imaging of different nuclei. In addition, comfortable environment will be provided for patients by avoiding any inconvenience of moving out and asking to replace the coils. In this paper, a multi-tunable microstrip transmission line Radiofrequency coil has been designed by using microfluidically tunable Radiofrequency capacitor. This capacitor offers a wide range of capacitance tuning which extends between Cmin=1.76 pF and Cmax=48.7 pF. Hence, a wide range of resonant frequencies (fmin=75 MHz - fmax=298 MHz) can be offered by this coil in order to excite several nuclei at a field strength of 7-Tesla.
Keywords : Magnetic Resonance Imaging (MRI); Magnetic Resonance Spectroscopy (MRS); Microstrip Transmission Line RF Coil; Double-Tuned (DT); Microfluidically Tuned Capacitor (µTC)
Visit
Port Decoupling Vs Array Elements Decoupling for Tx/Rx System at 7-Tesla Magnetic Resonance Imaging
Authors : Ashraf Abuelhaija, Sanaa Salama, and Tarik Baldawi
Abstract : Symmetrically excited meandered microstrip line RF coil elements are widely utilized in multichannel approaches which have been proposed to be integrated in ultra-high field MRI system (i.e., 7T and higher). These elements have demonstrated strong magnetic field in the deep areas in the object under imaging. Designing a radio frequency (RF) coil array that employs these elements without decoupling networks might cause non-optimized driving performance of coil array which in turn result in non-clear image. In this paper, two different methods of decoupling have been studied: port decoupling and array elements decoupling. For port decoupling, the coil elements have been designed at Larmor frequency (297.3 MHz) whereas for array elements decoupling, the coil elements have been designed at higher frequencies but matched at Larmor frequency. Port decoupling does not always mean element decoupling. Conventional decoupling methods, such as single capacitor or inductor, face challenges to realize the coil element decoupling for meandered microstrip arrays. An optimized reactive (T-shaped) network is needed in order to achieve element decoupling which in turn prevents distortion of the EM field. All simulation results have been obtained using the CST time domain solver (CST AG, Darmstadt, Germany).
Keywords :
Visit
Symmetrical and asymmetrical microstripline-based transmit/receive switches for 7-Tesla magnetic resonance imaging
Authors : Ashraf Abuelhaija, Gameel Saleh, Tarik Baldawi, Sanaa Salama
Abstract : The transmit/receive (T/R) switch is an important device in magnetic resonance imaging scanners whenever T/R radio frequency coils are intended to be used. It is placed between transmit amplifiers and T/R radio frequency coils. The T/R switch adds loss to the radio frequency (RF) transmit chain, reducing the delivered power to the coil and increasing the noise figure of the receive chain. Therefore, T/R switches should be designed for as low insertion loss as possible. In addition, they need to handle high power in transmit. In this article, three T/R switches for 7-Tesla magnetic resonance imaging scanners are designed using Eagle, and validated by simulation (HFSS & ANSYS) and measurement. Low reflection coefficients (< −20 dB), low insertion loss (≃0.3 dB), and high isolation (>40 dB) were demonstrated for the designed couplers. The fabricated microstripline-based switches were more robust than a design utilizing commercial couplers in terms of heat dissipation, high power capabilities, and lower insertion loss.
Keywords : insertion loss, isolation, magnetic resonance imaging (MRI), microstripline-based coupler, radiofrequency (RF) coil, transmit/receive (T/R) switch, ultra-high-field MRI
Visit
Chipless RFID Infrastructure Based Self-Localization: Testbed Evaluation
Authors : Mohammed El-Absi, Ali Al-haj Abbas, Ashraf Abuelhaija, Klaus Solbach, and Thomas Kaiser
Abstract : This paper presents a realistic feasibility of radio frequency identification (RFID) based self-localization of objects in real environments using simple infrastructure composed of chipless tags. These tags are designed as arrays of dielectric resonators (DR) in order to overcome the range limitations of the traditional chipless tags, where the DR array structure of the tags boosts the radar cross section (RCS) and, consequentially, extends the range coverage. Furthermore, an efficient algorithm for tag detection is proposed considering the environmental and hardware impairments that alter the backscattered signal from the tag. In this system, the reader interrogates the reference nodes, i.e. chipless tags, by a frequency-sweep RF signal, and the backscattered signals from the tags are captured and analyzed at the reader for detection, ranging and location estimation. A testbed is implemented with fabricated chipless RFID tags in order to evaluate the validity and accuracy of the proposed self-localization system. Experimental measurements based simulations are conducted in several scenarios in order to evaluate the proposed system. Moreover, an object (the reader) is moved to several locations in an interrogation area of 2.5×1.2 m, and, afterwards, its location is estimated. The averaged measured location error achieved based on the proposed system is approximately 5 cm with a variation of 0.9 cm as a minimum observed error and 7 cm as a maximum error.
Keywords : Radiofrequency identification, Resonant frequency, Resonators, Dielectrics, Signal processing algorithms, Hardware, Distance measurement
Visit
High-Accuracy Indoor Localization Based on Chipless RFID Systems at THz Band
Authors : Mohammed El-Absi, Ali Al-haj Abbas, Ashraf Abuelhaija, Feng Zheng, Klaus Solbach, and Thomas Kaiser
Abstract : Highly accurate indoor localization based on significantly low complex infrastructure has recently gained great interest for a variety of innovative location-based applications. In this regards, the chipless radio frequency identification (RFID) system is presented to be the low-cost solution, while time-based ranging using the ultrawide-band spectrum is promising to offer precise ranging capability. However, the current wide-band systems suffer from the spectrum and power limitations, which restrict the function of chipless RFID-based localization systems. Therefore, we propose terahertz (THz)-based chipless RFID localization system that enables a smart object localizing itself using the infrastructure composed from reference chipless tags. In more details, THz band offers huge bandwidth providing superior-resolution localization and large coding capacity. Moreover, we utilize the combination between dielectric resonator (DR) and lens to be designed as a frequency-coded chipless tag, where this combination increases the radar cross section of the chipless tags and, hence, extends their coverage zone. This cost-efficient design of the tag enables the dense deployment of low-cost infrastructure acting as reference anchors. Furthermore, we investigate the link budget of the proposed system in order to characterize the tag and distance-dependent spectral windows that are feasible for RFID-based localization. Afterward, the time-domain backscattered signal from a DR-Lens tag is analyzed in order to perform ranging and to calculate the relative distances between the DR-Lens tags and the reader leading to determining the reader position. Measurements are performed to prove the concept of the DR-Lens tag, while the numerical simulation is conducted to evaluate the proposed localization system. Simulation results show that the proposed system can reach superior accuracy of millimeter-levels.
Keywords : Localization, RFID, Large-scale MIMO, Chipless RFID, Dielectric Resonator (DR),
Lens, RToF, Estimation Accuracy
Visit
Indoor Large-Scale MIMO-Based RSSI Localization with Low-Complexity RFID Infrastructure
Authors : Mohammed El-Absi, Feng Zheng, Ashraf Abuelhaija, Ali Al-haj Abbas, Klaus Solbach, and Thomas Kaiser
Abstract : Indoor localization based on unsynchronized, low-complexity, passive radio frequency identification (RFID) using the received signal strength indicator (RSSI) has a wide potential for a variety of internet of things (IoTs) applications due to their energy-harvesting capabilities and low complexity. However, conventional RSSI-based algorithms present inaccurate ranging, especially in indoor environments, mainly because of the multipath randomness effect. In this work, we propose RSSI-based localization with low-complexity, passive RFID infrastructure utilizing the potential benefits of large-scale MIMO technology operated in the millimeter-wave band, which offers channel hardening, in order to alleviate the effect of small-scale fading. Particularly, by investigating an indoor environment equipped with extremely simple dielectric resonator (DR) tags, we propose an efficient localization algorithm that enables a smart object equipped with large-scale MIMO exploiting the RSSI measurements obtained from the reference DR tags in order to improve the localization accuracy. In this context, we also derive Cramer–Rao lower bound of the proposed technique. Numerical results evidence the effectiveness of the proposed algorithms considering various arbitrary network topologies, and results are compared with an existing algorithm, where the proposed algorithms not only produce higher localization accuracy but also achieve a greater robustness against inaccuracies in channel modeling
Keywords : localization; RFID; large-scale MIMO; passive RFID; RSSI; localization accuracy
Visit
A 32-channel parallel transmit system add-on for 7T MRI
Authors : Stephan Orzada, Klaus Solbach, Marcel Gratz, Sascha Brunheim, Thomas
M. Fiedler, Sören Johst, Andreas K. Bitz, Samaneh Shooshtary, Ashraf Abuelhaija,
Maximilian N. Voelker, Stefan H. G. Rietsch, Oliver Kraff, Stefan Maderwald,
Martina Flöser, Mark Oehmigen, Harald H. Quick, Mark E. Ladd
Abstract : A 32-channel parallel transmit (pTx) add-on for 7 Tesla whole-body imaging is presented. First results are shown for phantom and in-vivo imaging. The add-on system consists of a large number of hardware components, including modulators, amplifiers, SAR supervision, peripheral devices, a control computer, and an integrated 32-channel transmit/receive body array. B1+ maps in a phantom as well as B1+ maps and structural images in large volunteers are acquired to demonstrate the functionality of the system. EM simulations are used to ensure safe operation. Good agreement between simulation and experiment is shown. Phantom and in-vivo acquisitions show a field of view of up to 50 cm in z-direction. Selective excitation with 100 kHz sampling rate is possible. The add-on system does not affect the quality of the original single-channel system.
Keywords :
Visit
Analysis of an Integrated 8-Channel Tx/Rx Body Array for Use as a Body Coil in 7-Tesla MRI
Authors : Stephan Orzada, Andreas K. Bitz, Sören Johst, Marcel Gratz, Maximilian N. Völker, Oliver Kraff , Ashraf Abuelhaija, Thomas M. Fiedler , Klaus Solbach, Harald H. Quick and Mark E. Ladd
Abstract : In this work an 8-channel array integrated into the gap between the gradient coil and bore liner of a 7-Tesla whole-body magnet is presented that would allow a workflow closer to that of systems at lower magnetic fields that have a built-in body coil; this integrated coil is compared to a local 8-channel array built from identical elements placed directly on the patient. SAR efficiency and the homogeneity of the right-rotating B1 field component (B1+) are investigated numerically and compared to the local array. Power efficiency measurements are performed in the MRI System. First in vivo gradient echo images are acquired with the integrated array.
Keywords : 7 Tesla, integrated body array, whole body, MRI, body coil
Visit
Frequency-Coded mm-Wave Tags for Self-Localization System Using Dielectric Resonators
Authors : A. Jiménez-Sáez, A. Alhaj-Abbas, M. Schüßler, A. Abuelhaija, M. El-Absi, M. Sakaki, L. Samfaß, N. Benson, M. Hoffmann, R. Jakoby, T. Kaiser & K. Solbach
Abstract : The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays of DRs and combinations with dielectric lens and corner reflectors are investigated to boost the RCS while keeping the scattering retro-directive over wide-angle incidence. Satisfactory results are demonstrated experimentally in W-band with metal corner reflectors combined with planar arrays of DRs; the tags produce a high RCS level over a moderately broad angular range and a wide frequency range where they exhibit a notch at the resonance frequency of the dielectric resonators. These designs suffer from low coding range of 3 to 6 bit, degradations of RCS in angular range, and a difficult separation of the tag response from strong clutter. Both the suppression of large clutter interference by using time gating of the tag response and a larger coding range are promised by a chipless tag concept based on multiple high-Q resonators in photonic crystal (PhC) technology. Experimental samples are characterized as transmission resonators and as retro-directive tags at the 230 GHz band. As a concept to boost the retro-directive RCS with a truly wide-angle response, the integration of PhC resonators with a Luneburg lens is discussed.
Keywords : Radar cross-section . Photonic crystal . Dielectric resonator . Corner reflector. Luneburg Lens . Tag
Visit
Comprehensive Study on Decoupling Networks for 7 Tesla MRI based on Reactive Load Parasitic-Element
Authors : Sanaa Salama, Ashraf Abuelhaija, Tareq Baldawi, Samer Issa
Abstract : This work presents and evaluates the integrating of decoupling networks in MRI systems at 7 Tesla magnetic field strength. The parasitic element is reactive loaded. Four different cases of reactive loads are considered: capacitive load, inductive load, open circuited, and short-circuited loads are considered. The idea behind this technique is to reduce or even eliminate the effect of mutual coupling between the RF coil elements in magnetic resonance imaging (MRI)system. Two rectangular loops are used to compose a planar phased array. This structure is designed and optimized in CST at the Larmor frequency of 298.3 MHz corresponding to the 7 Tesla MRI system.
Keywords : Decoupling Network (DN), Matching Network (MN), Parasitic-Element, Capacitive & Inductive Load, Open and Short-Circuited Load
Visit
DESIGN OF A MICROSTRIP MAXIMALLY FLAT 7TH ORDER LOWPASS FILTER USING ADS SIMULATION
Authors : S. SALAMA, Y. BATTAH, A. ABUELHAIJA
Abstract : This work presents the design and analysis of a 7th order microstrip maximally flat low pass filter using insertion loss method in X-band range. The cutoff frequency at 10 GHz. An attenuation of more than 60 dB is obtained. The low pass filter was designed and simulated using Advanced Design System (ADS) software. The filter is implemented on Alumni substrate having a dielectric loss of 9.6 and substrate height of 1.6 mm. In addition, an optimization process for the stub lengths and widths is performed based on desired filter specifications. Due to coupling effect between adjacent stubs, the desired filter specifications become difficult to be achieved and the optimization process can solve for that by defining thresholds that match the desired filter specifications.
Keywords : Attenuation, Distributed elements, Insertion loss, Lumped elements, Maximally flat, Microstrip, Stubs
Visit
Inverted V Wire Yagi with Switchable Pattern Rotation for 14 MHz
Authors : Ashraf Abuelhaija and Klaus Solbach
Abstract : Yagi or quad, beam antennas are well established antenna types for improved directivity and gain com¬pared to a single dipole antenna. Using an electromechanical rotator, these antennas can be turned toward the desired direction in ±180° of azimuth. Due to the consider¬able inertia involved in most practical beam antennas, however, rotation is fairly slow. This makes it difficult under typical short wave propagation conditions, for example, to switch between two different directions while listening to an ongoing conversation, or to find the direction of a station that makes short transmissions. An alternative is offered by phased array antennas, in which the beam can be rotated by the switching of feed networks. With dif¬ferent phase excitations of the elements of the array, different beam patterns can be pro¬vided. The popular four square array of four vertical ground mounted monopole antennas with about quarter wave spacing and that pro-vide four beam directions with 90° separation in azimuth is an example of such a system. A comparable alternative with horizontal polarization has not been available, to the knowledge of the authors. A phased array of four horizontal dipoles arranged in a square is not a good idea because of the orienta¬tion and coupling of the dipoles arranged under an angle of 90°. Also, this array would require four poles to carry the dipoles high above the ground.
A simpler configuration was found that requires only one support pole and that uses inverted V wire dipoles to create a two ele¬ment Yagi antenna that can be remotely switched in its beam direction in steps of 60° in azimuth.
Keywords :
Visit
Dual Tuned Switch for Dual Resonance 1H/13C MRI Coil
Authors : Gameel Saleh and Ashraf Abuelhaija
Abstract : This paper introduces two transmit/receive switch designs for 7 Tesla magnetic resonance spectroscopic imaging. Both designs based on microstripline-based couplers. The first is a dual-tuned 1H/13C switch with two concentric microstriplines on each side of the switch. A branch line technique from transmission line theory is applied to compact the switch to half of its initial dimension. The second proposed design is a dual tuned 1H/13C microstripline-based switch with one microstripline in each side of the switch. The second design benefits from the harmonics of an initial resonance signal to shift the first and second harmonics to the same Larmor frequencies of the 1H and 13C nuclear spins when exposed to 7 Tesla static magnetic field. The first design serves 1H and 13C RF Coils, working independently. Whereas the second design works with a dual resonance 1H/13C RF coil. The first and second designs achieved good matching less than -15 dB and -10 dB, respectively. They achieved low insertion loss less than -0.6 dB and -1.2 dB, respectively. The isolation between couplers in the first design is higher than 60dB. Furthermore, the isolation between the amplifier port and the receiver for both switches designs are higher than 60dB as well. The proposed switches are promising in reducing the number of T/R switches and the area of the place they need in the transmit front-end when multichannel RF coils are used.
Keywords :
Visit
Analysis and Modelling of the Antenna Mode and Structural Mode Scattering of a Dielectric Resonator
Authors : Ali Alhaj Abbas, Maher Khaliel, Ashraf Abuelhaija, Mohammed El-Absi, Jahangir Alam, Klaus Solbach, Thomas Kaiser
Abstract : This paper presents an analysis of the backscattering of a dielectric resonator (DR) due to the antenna mode and the structural mode. More specifically, we focus on the structural mode scattering since the discussion of the RCS of DRs in the past has concentrated on analyzing the “Eigenmodes” only. Therefore, we present evidence for its existence and provide a qualitative and quantitative approximation. It is found that the structural scattering of a DR with high rel. permittivity can be approximated by the scattering of a metal body of the same dimensions as the DR. Furthermore, a mathematical model of the antenna mode scattering is provided using the multipole expansion and with the aid of filter theory. As a result of the superposition of both scattering modes, it is found that the structural mode scattering slightly alters the appearance of the “Eigenmodes” in frequency position, scattering level, quality factor, and shape.
Keywords : Dielectric resonator, Eigenmodes, radar cross section, EM scattering, structural mode, transient scattering, multipole expansion
Visit
Stepped Impedance 7th order Maximally Flat Low Pass Filter Using Microstrip Line for X-Band Applications
Authors : S Salama, Y Battah and A Abuelhaija
Abstract : In this paper stepped impedance 7th order maximally flat low pass filter is designed and analyzed for X-band range at 9 GHz cut-off frequency. The filter is printed on Alumni substrate of dielectric constant 9.6 and thickness of 1.6 mm. The obtained attenuation is more than 20 dB. The Advanced Design System (ADS) software is used to design and simulate the proposed low pass filter. In addition, a comparison between filter design using insertion loss method implemented in stubs and stepped impedance is presented and discussed.
Keywords :
Visit
Design of a Planar Inverted F-Antenna for Medical Implant Communications Services Band
Authors : Sanaa Salama, Duaa Zyoud, Razan Daghlas and Ashraf Abuelhaija
Abstract : A planar inverted F-implantable antenna is designed using the medical implant communications service (MICS) band (402–405MHz).The proposed antenna is designed using microstrip lines and short-circuited pin connecting between the ground plane and the patch. The total size of the proposed antenna is (24×32×2 mm3). The patch dimensions are (16×24 mm2). The calculated bandwidth at a return loss of -10 dB is 1MHz. The S-parameters, the near and far-fields, and the specific absorption rate (SAR) of the antenna is simulated and characterized. The design is carried out using CST Studio.
Keywords :
Visit
Design of a Dual-Band Planar Inverted F-L Implantable Antenna for Biomedical Applications
Authors : Sanaa Salama, Duaa Zyoud and Ashraf Abuelhaija
Abstract : In this paper, a dual-band planar inverted F-L implantable antenna, which operates at theMedical Implant Communications Services (MICS) and Industrial, Scientific, and Medical (ISM) bands, is introduced. The proposed antenna is printed on RO3010 substrate of thickness 2mm, relative permittivity 10.2, and loss tangent 0.0023. A short-circuit pin inserted between the ground plane and the patch is used to downsize the antenna. The dimension of the antenna is 27 × 19 × 2 mm3. The proposed implantable antenna covers a frequency band of 9.4 MHz [397-406.4 MHz] at MICS band with a return loss of -20.02dB at 403 MHz and a frequency band of 80 MHz [2.41-2.49 GHz] at ISM band with a return loss of -22.82 at 2.45 GHz. Design and analysis of the proposed antenna is carried out by Computer Simulation Technologies (CST) Microwave studio.
Keywords :
Visit
Experimental Demonstration of Double-Notch RCS Spectral Signature of Corner Reflector Tag for THz Self-Localization System
Authors : Klaus Solbach, Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija and Thomas Kaiser
Abstract : Dihedral corner reflectors with arrays of dielectric resonators fixed on the metal plates are shown to exhibit notched spectral signatures of the monostatic Radar Cross Section. Two distinct notches can be created using two arrays with different diameter of resonators. Due to about 45 unique notch combinations, the double-notch corner reflector allows a 5-bit frequency position coding while still producing a sharp pulse shape in time domain. Example designs at V-through G-band are experimentally demonstrated.
Keywords : Corner reflector, beacon, dielectric resonator, RCS
Visit
THz Passive RFID Tag Based on Dielectric Resonator Linear Array
Authors : Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija, Klaus Solbach and Thomas Kaiser
Abstract : In this paper, we propose a solution to mitigate the strong clutter signal for a use in a THz indoor self localization system using a chipless tag based on linear dielectric resonator arrays to enhance the Radar Cross Section (RCS) and therefore increase its detectability. Simulation results are presented for a five elements array separated by 0.8λ at 105 GHz where a 18 dB RCS enhancement is achieved. For a multiple tag scenario, seven frequency coded tags that take the binary values from 001 to 111 can be realized by coding bit 1 and 0 by the presence and the absence of three different resonance frequencies in the RCS spectrum, equivalently the presence and the absence of the dielectric resonator array with different dimensions. The tags can be discriminated with a free ambiguity over a wide range of incidence angle of the reader signal of -/+ 35°.
Keywords : Dielectric resonator, dielectric resonator array, radar cross section, passive chipless RFID.
Visit
Parasitic Element Based Decoupling Network for a Two-Element MRI Phased Array
Authors : Sanaa Salama and Ashraf Abuelhaija
Abstract : A parasitic-element based Decoupling Network (DN) for 7-Tesla Magnetic Resonance Imaging (MRI) phased arrays is presented to compensate for the effect of mutual coupling between array active elements. The DN network consists of an open circuited parasitic element in parallel between a two-element MRI array, each element in the array is a rectangular loop-shape microstrip transmission line Radio Frequency (RF) coil. L-shaped tunable matching network is integrated, the whole structure is optimized to operate at the resonant frequency of the 7-Tesla MRI system. Numerical modeling of the whole structure is carried out using CST to characterize and verify the performance of the open circuited parasitic element based decoupling network for a two-element MRI array.
Keywords : Decoupling network, MRI phased array, parasitic element, RF coil, and tunable matching network
Visit
High RCS Passive Tag based on Dielectric Resonator - 2D Lens Combination
Authors : Ali Alhaj Abbas, Mohammed El-Absi, Ashraf Abuelhaija, Klaus Solbach and Thomas Kaiser
Abstract : In this paper, a Lens-Dielectric Resonator combination is proposed to improve RCS of dielectric resonator tags to be used in a self-localization system where high RCS is essential to combat clutter signals. As a proof of concept, a cylindrical dielectric resonator is located in the focal area of a 200 mm diameter (3.5 λ at 5.2 GHz) 2D Luneburg Lens sandwiched between two tapered metal plates. Two approaches of realizing the continuous variation of the Luneburg lens dielectric permittivity are implemented, fabricated, and tested: by using stepped cylindrical layers of dielectric material (fabricated by machining process) and by using effective medium theory in which the lens is constructed from a group of cells made of various cuboids sizes connected to trapezoidal rods (fabricated by 3D printing technology using PP). A good compatibility between DR and lens is observed. The improvement in RCS is found to vary depending on DR resonance mode. For the HE 11 mode, a 20 dB improvement is achieved.
Keywords : Dielectric resonator, Luneburg lens, radar cross section, passive chipless RFID
Visit
Investigation of the transient EM scattering of a dielectric resonator
Authors : Ali Alhaj Abbas, Ashraf Abuelhaija, and Klaus Solbach
Abstract : Dielectric resonators have gained interest in RF identification and localization system concepts. This contribution reports observations from experiments and EM simulation with special focus on the transient behavior of the EM scattering of a ceramic resonator in free space. Explanation and analysis of the transient behavior is given using equivalent circuit modeling and EM simulation. The time constant of the particular resonant mode excited is shown to depend on the loaded quality factor of the resonant mode and governs the exponential charging up process and the exponential decay process of "ringing" of the resonator at its Eigen frequency. For an exciting RF pulse much shorter than the time constant, the resonator scattering amplitude increases linearly with increasing pulse length which allows to determine the structural response also. Forced excitation at a frequency offset from the resonant frequency will still produce free "ringing" at the resonator's Eigen frequency. The scattering amplitude is related to the Radar Cross Section of a dielectric resonator, but this only applies to the steady state of excitation.
Keywords : Dielectric resonator, transient, scattering, RCS
Visit
Distance and Tag Aware Localization in Indoor Terahertz Systems
Authors : Mohammed El-Absi, Ali Alhaj Abbas, Ashraf Abuelhaija, Klaus Solbach and Thomas Kaiser
Abstract : The accuracy of radio frequency identification (RFID) based time-of-flight ranging is considerably affected by the wireless channel within an indoor radio environment, where the bandwidth is considered the major limited factor for localization accuracy. Terahertz (THz) band offers bandwidth orders of magnitude greater than the lower-frequency communications; however, this band has different prorogation mechanisms influencing a wireless transmission compared to the lower frequency bands. The bandwidth of transmission at THz band is highly distance-dependent. Furthermore, since the wireless channel of RFID systems is a two-way pinhole channel, the design of the tag plays a key-role in capturing the usable bandwidth in THz bands. This paper studies RFID based localization at THz band in indoor environments. We analyze the impact of distance and tag design on the RFID link budget. We also characterize the tag and distance dependent spectral windows that are feasible for RFID based localization. The localization requirements for RFID based localization are also presented in order to achieve high accuracy localization.
Keywords : Localization, Terahertz, Time-of-Flight, Link Budget, Path Loss
Visit
Chipless tags infrastructure based localization in indoor environments
Authors : Mohammed El-Absi, Ashraf Abuelhaija, Ali Alhaj Abbas, Feng Zheng, Klaus Solbach and Thomas Kaiser
Abstract : In this work, we study dielectric resonator (DR) tag based localization using time difference of arrival (TDOA) method in indoor environments. DRs, which act as chipless tags, are used as reference nodes in order to localize an object equipped with a reader. The ringing behavior of the DR tags is utilized as the fingerprint of the tags, which is used to estimate TDOA using the cross-correlation algorithm. Simulations and measurements are performed to examine the performance of the proposed DR tags and the localization algorithm.
Keywords : Localization, Chipless Tag, Dielectric Resonator, TDOA
Visit
RParasitic element based decoupling of 7 tesla MRI coil array
Authors : Ashraf Abuelhaija; Stephan Orzada; Klaus Solbach
Abstract : For high and ultrahigh field MRI applications, parallel imaging that employs multi-channel RF coil arrays has been developed in order to reduce data acquisition time and to manipulate the Bi distribution by enabling RF shimming. However, implementing parallel imaging or parallel excitation still is considered a significant challenge in terms of high electromagnetic coupling among closely placed resonant elements in coil arrays. This contribution investigates the decoupling performance between coupled meandered microstrip line RF coil elements by applying the concept of parasitic decoupling elements. The design of the reactively loaded parasitic elements and evaluation of decoupling performance of a 2-element and an 8-element array of coils is based on EM simulation. Experimental verification of the method is presented in a 2-element array.
Keywords : Magnetic resonance imaging (MRI), mutual coupling, parallel transmit array, radio frequency (RF) coil
Visit
Comprehensive study on coupled meandered microstrip line RF coil elements for 7-Tesla magnetic resonance imaging
Authors : Ashraf Abuelhaija; Klaus Solbach; Stephan Orzada;
Abstract : This paper presents a study of a pair of coupled meandered microstrip line RF coil elements for use in 7T Magnetic Resonance Imaging. Both the distance to a load (absorbing medium/phantom) above the coils as well as to the RF shield below the coils are seen to have strong influence on the radiation resistance, Q-factor, resonance frequency, EM-field distributions and mutual coupling of the coil array. Numerical simulations were performed and experimental measurement for a specific case has been accomplished for verification.
Keywords : Magnetic resonance imaging, mutual coupling, RF coil, Q-factor, radiation resistance
Visit
Power amplifier for magnetic resonance imaging using unconventional Cartesian feedback loop
Authors : Ashraf Abuelhaija; Klaus Solbach; Adam Buck
Abstract : In MRI systems, RF fields are affected by the presence of the human body in the scanner causing mismatch between the RF coil and the feed cable. A power amplifier incorporating an unconventional Cartesian feedback loop is presented which works to maintain a fixed current in the RF coil against impedance variations. The performance of the system is investigated by model simulation, including stability analysis, linearity improvement and mismatch compensation. A prototype amplifier is measured to verify the model.
Keywords : Magnetic resonance imaging (MRI), Mismatch, Detuning, Cartesian feedback loop,
Power amplifier (PA)
Visit
7T Coil Decoupling in Near-Magnet Power Amplifier
Authors : Ashraf Abuelhaija and Klaus Solbach
Abstract : Mutual coupling between coil elements in parallel transmit array is considered a significant challenge in MRI applications. Induced current due to the interaction between elements disturbs the desirable independent control of current amplitude and phase in each coil element for RF-shimming purposes. In earlier studies on receive arrays, conventional decoupling techniques such as coil overlapping is used to minimize coupling between nearest-neighbor coils, and low input impedance preamplifiers are used to improve isolation between the non-nearest neighbors. For Tx arrays, the concept of mismatched termination of coils by power amplifiers for coil isolation was proposed and a comparison was presented. This contribution presents an investigation of decoupling (isolation) performance by using the output impedance of the 1 kW power amplifier designed for a 7 Tesla 32 channel near-magnet Tx array at the ELH Institute for Magnetic Resonance Imaging, Essen, Germany.
Keywords :
Visit
An Ultra-Low Output Impedance Power Amplifier for Tx Array in 7-Tesla Magnetic Resonance Imaging
Authors : Ashraf Abuelhaija; Klaus Solbach
Abstract : In Ultra high-field MRI scanners (3T and higher), parallel RF transmission techniques using multiple RF chains with multiple transmit elements are a promising approach to overcome the high-field MRI challenges in terms of inhomogeneity in the RF magnetic field and SAR. However, mutual coupling between the transmit array elements disturbs the desirable independent control of the RF waveforms for each element. This contribution demonstrates a 18 dB improvement of decoupling (isolation) performance due to the very low output impedance of our 1 kW power amplifier.
Keywords : EM coupling, Inter-element isolation, Magnetic resonance imaging (MRI), Parallel Transmit.
Visit
Near-Magnet Power Amplifier with built-in Coil Current Sensing
Authors : Klaus Solbach, Ashraf Abuelhaija, and Samaneh Shooshtary
Abstract : A new concept of a near-magnet PA is presented which operates without circulator/isolator but closely cooperates with the coil to allow control of the coil current. The concept features a voltage probe at the PA output and a tuned transmission line connecting the coil. The probe voltage is proportional to the coil current which allows control of the coil current under mismatch and mutual coupling from other coils in an pTx array without extra pick-up loop. The function is demonstrated by an experimental set-up creating a wide range of load impedance by varying the coil distance to a phantom.
Keywords :
Visit
Six-beam reconfigurable wire antenna
Authors : Ashraf Abuelhaija; Klaus Solbach
Abstract : A novel concept of a beam reconfigurable antenna is presented which rotates the beam of a 2-element Yagi antenna without mechanical rotation. The antenna is based on an arrangement of six wires extending radially from the apex of a support. A switch circuit is used to combine two wires into the driven dipole and two wires into the parasitic dipole. The paper presents the basic Yagi antenna using Inverted-V dipoles with verification of simulations by an experimental model at 1 GHz. A fully configurable array was built for operation at 14 MHz to serve in a short-wave direction finding system. Based on simulation, the antenna provides a gain of about 8 dBi and a front-to-back ratio of 10 to 15 dB. Improvements are expected from the use of horizontal dipoles or folded dipoles and additional radiator types can be configured, like single-dipole or vertical top-loaded radiator antennas. Realizations of the concept seem to be feasible up to the low microwave frequency range by suitable miniaturization of the switching circuit and such reconfigurable antennas may provide diversity gain in communication systems
Keywords : Wire antennas, array antennas, beam scanning, reconfigurable antennas
Visit