Transceiver Array Research Articles

Helmholtz transceiver array for improving the |B 1|-field homogeneity at 7-T magnetic resonance imaging

A 16-channel transceiver radiofrequency (RF) array using Helmholtz coils was designed to improve the RF transmission |B 1 + |-field homogeneity for human brain magnetic resonance imaging (MRI) at 7 T. A numerical simulation of the proposed Helmholtz transceiver array was performed using the finite-difference time-domain method—the subset of the finite-element method simulation. The simulation results of proposed 16-channel Helmholtz transceiver array were compared with the generally used rectangular transceiver array in term of their |B 1 + |-field and specific absorption rate (SAR). The simulation of each single element in 16-channel Helmholtz and rectangular transceiver arrays was compared using water phantom in term of their magnetic flux |B 1| homogeneity for the full width at half maximum. From the simulation results, the proposed 16-channel Helmholtz transceiver array configuration offers superior |B 1 + |-field homogeneity and low SAR at 7 T. These modifications to the coil geometries of the transceiver array coil could be applied to a 7-T MRI, and also extended to increase the homogenous coverage on |B 1 + |field with low SAR.

A 71–86-GHz Phased Array Transceiver Using Wideband Injection-Locked Oscillator Phase Shifters

This paper presents the first phased array transceiver operating from 71 to 86 GHz using injection-locked oscillators (ILOs) for phase shifting. A folded-cascode ILO is proposed to extend the locking range of an array of oscillators. Frequency multiplication covers a 10-GHz tuning range with 23-dB power gain. Each ILO path covers more than ±300° and exhibits low amplitude variation with respect to phase shift range ( $3.4\times2.1$ mm2 area implementing in the 90-nm BiCMOS technology and consuming 386.4 mW in the TX mode and 286 mW in the RX mode per element.

In vivo imaging of electrical properties of an animal tumor model with an 8-channel transceiver array at 7 T using electrical properties tomography.

To develop and evaluate a technique for imaging electrical properties ((EPs), conductivity and permittivity) of an animal tumor model in vivo using MRI. Electrical properties were reconstructed from the calculated EP gradient, which was derived using two sets of measured transmit B1 magnitude and relative phase maps with the sample and radiofrequency (RF) coil oriented in the positive and negative z-directions, respectively. An eight-channel transceiver microstrip array RF coil fitting the size of the animal was developed for generating and mapping B1 fields to reconstruct EPs. The technique was evaluated at 7 tesla using a physical phantom and in vivo on two Copenhagen rats with subcutaneously implanted AT-1 rat prostate cancer on a hind limb. The reconstructed EPs in the phantom experiment was in good agreement with the target EP map determined by a dielectric probe. Reconstructed conductivity map of the animals revealed the boundary between tumor and healthy tissue consistent with the boundary indicated by T1 -weighted MRI. A technique for imaging EP of an animal tumor model using MRI has been developed with high sensitivity, accuracy, and resolution, as demonstrated in the phantom experiment. Further animal experiments are needed to demonstrate its translational value for tumor diagnosis. Magn Reson Med 78:2157-2169, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Evaluation of transmit efficiency and SAR for a tight fit transceiver human head phased array at 9.4T.

Ultra-high field (UHF, ≥7T) tight fit transceiver phased arrays improve transmit (Tx) efficiency (B1+ /√P) in comparison with Tx-only arrays, which are usually larger to fit receive (Rx)-only arrays inside. One of the major problems limiting applications of tight fit arrays at UHFs is the anticipated increase of local tissue heating, which is commonly evaluated by the local specific absorption rate (SAR). To investigate the tradeoff between Tx efficiency and SAR when a tight fit UHF human head transceiver phased array is used instead of a Tx-only/Rx-only RF system, a single-row eight-element prototype of a 400MHz transceiver head phased array was constructed. The Tx efficiency and SAR of the array were evaluated and compared with that of a larger Tx-only array, which could also be used in combination with an 18-channel Rx-only array. Data were acquired on the Siemens Magnetom whole body 9.4T human MRI system. Depending on the head size, positioning and the RF shim strategy, the smaller array provides from 11 to 23% higher Tx efficiency. In general, the Tx performance, evaluated as B1+ /√SAR, i.e. the safety excitation efficiency (SEE), is also not compromised. The two arrays provide very similar SEEs evaluated over 1000 random RF shim sets. We demonstrated that, in general, the tight fit transceiver array improves Tx performance without compromising SEE. However, in specific cases, the SEE value may vary, favoring one of the arrays, and therefore must be carefully evaluated.

Compact transmit receive hybrid electromagnetic isolation in antenna array transceiver system for full duplex applications

This study presents a hybrid electromagnetic isolation mechanism in a transceiver array antenna operating at 5.8 GHz. Maximum isolation between transmitting and receiving array antennas, at a very close spacing (3 mm = 0.058 λ 0 ), and minimum mutual coupling between each array elements is achieved without antenna radiation pattern degradation. The achieved separation is equivalent to 44% size reduction compared with conventional half wavelength spacing criterion. Each of the transmitting and receiving array antennas is a four-element linear microstrip patch array antenna. The employed hybrid isolation technique is composed of defected ground structure, to minimise coupling between array elements, and uniplanar electromagnetic bandgap, to minimise the coupling between the transmitting and receiving antennas. The resulting transceiver array antenna system fulfils -35 dB mutual coupling between array elements, and 60 dB isolation between opponent transmitting and receiving array antennas. The proposed design procedures are discussed and analysed using electromagnetic full wave simulations. Results were verified through experimental measurements for reflection coefficient, mutual coupling and radiation characteristics in which a good agreement with simulated results is granted.

Recent progress in Taiwan on integrating moving vehicles for acoustic tomography applications

Coastal seas around Taiwan exhibit a wide variety of oceanographic processes associated with the complex bottom topography, tides, winds (monsoons and typhoons), the Kuroshio, and the others. Conventional oceanographic measurements (e.g., acoustic Doppler current profiler) do not provide a synoptic image of the dynamic processes unless a large number of instruments are deployed. Ocean Acoustic Tomography (OAT) is an effective method for mapping the time-evolving spatial distribution of ocean current and temperature. As illustrated by Cornuell et al. (1989), the small spatial scale of ocean features is resolved by incorporating a ship-towed transceiver to the moored transceiver array, referred to as moving ship tomography (MST). The MST technique is applied to the ocean current reconstruction in coastal seas around Taiwan and is extended by using an autonomous underwater vehicle (AUV) as an alternative carrier for the transceiver. This talk presents a brief summary of the recent experiments and our upcoming project. Included are 1) a series of current-mapping experiments integrating moving vehicles in shallow-water environments and 2) simulation study of MST for experiment design on mapping the Kuroshio-induced current wakes of Green Island southeast of Taiwan.

Element decoupling of 7 T dipole body arrays by EBG metasurface structures: Experimental verification

Metasurfaces are artificial electromagnetic boundaries or interfaces usually implemented as two-dimensional periodic structures with subwavelength periodicity and engineered properties of constituent unit cells. The electromagnetic bandgap (EBG) effect in metasurfaces prevents all surface modes from propagating in a certain frequency band. While metasurfaces provide a number of important applications in microwave antennas and antenna arrays, their features are also highly suitable for MRI applications. In this work we perform a proof-of-principle experiment to study finite structures based on mushroom-type EBG metasurfaces and employ them for suppression of inter-element coupling in dipole transceive array coils for body imaging at 7T. We firstly show experimentally that employment of mushroom structures leads to reduction of coupling between adjacent closely-spaced dipole antenna elements of a 7T transceive body array, which reduces scattering losses in neighboring channels. The studied setup consists of two active fractionated dipole antennas previously designed by the authors for body imaging at 7T. These are placed on top of a body-mimicking phantom and equipped with the manufactured finite-size periodic structure tuned to have EBG properties at the Larmor frequency of 298MHz. To improve the detection range of the B1+ field distribution of the top elements, four additional elements were positioned along the bottom side of the phantom. Bench measurements of a scattering matrix showed that coupling between the two top elements can be considerably reduced depending on the distance to the EBG structure. On the other hand, the measurements performed on a 7T MRI machine indicated redistribution of the B1+ field due to interaction between the dipoles with the structure. When the structure is located just over two closely spaced dipoles, one can reach a very high isolation improvement of −14dB accompanied by a strong field redistribution. In contrast, when put at a certain height over the antennas the structure provides a moderate isolation improvement together with a slight increase of B1+ level. This study provides a tool for the decoupling of dipole antennas in ultrahigh field transceive arrays, possibly resulting in denser element placement and/or larger subject-element spacing.

Concurrent Dual -Band T/R/Calibration Switch Module With Quasi-Elliptic Dual-Bandpass Frequency Response Implementing Metamaterial Transmission Line and Negative Resistance

A novel dual-band transmit/receive (T/R) switch module with an integrated calibration path, hereafter a T/R/Calibration switch module, is developed for dual $K/Ka$ -band array systems, especially digital beam-forming antenna array system, using 0.18- $\mu{\hbox{m}}$ BiCMOS technology. A unique quasi-elliptic dual-bandpass frequency response is achieved in its reception and calibration paths with the use of a composite right/left-handed metamaterial transmission line structure coupled with the Colpitts-style negative-resistance generation circuit. The proposed T/R/Calibration switch module architecture provides a self-calibration for both transmission and reception from the farthest end of an array transceiver excluding antennas, thereby offering an accurate calibration function for the synthetic aperture radar consequently. The newly proposed T/R/Calibration switch topology enhances the opportunity of standalone operation of multi-band array transceivers by the integrated self-calibration capability, while still fulfilling the low-noise and high-power needed for the transceivers for reception and transmission via bidirectional low-noise amplifier/power amplifier, respectively.

Three‐layered radio frequency coil arrangement for sodium MRI of the human brain at 9.4 Tesla

PurposeA multinuclei imaging setup with the capability to acquire both sodium (23Na) and proton (1H) signals at 9.4 Tesla is presented. The main objective was to optimize coil performance at the 23Na frequency while still having the ability to acquire satisfactory 1H images.MethodsThe setup consisted of a combination of three radio frequency (RF) coils arranged in three layers: the innermost layer was a 27‐channel 23Na receive helmet which was surrounded by a four‐channel 23Na transceiver array. The outer layer consisted of a four‐channel 1H dipole array for B0 shimming and anatomical localization. Transmit and receive performance of the 23Na arrays was compared to a single‐tuned 23Na birdcage resonator.ResultsWhile the transmit efficiency of the 23Na transceiver array was comparable to the birdcage, the 23Na receive array provided substantial signal‐to‐noise ratio (SNR) gain near the surface and comparable SNR in the center. The utility of this customized setup was demonstrated by 23Na images of excellent quality.ConclusionHigh SNR, efficient transmit excitation and B0 shimming capability can be achieved for 23Na MRI at 9.4T using novel coil combination. This RF configuration is easily adaptable to other multinuclei applications at ultra high field (≥ 7T). Magn Reson Med 75:906–916, 2016. © 2015 Wiley Periodicals, Inc.

Novel splittable N-Tx/2N-Rx transceiver phased array to optimize both signal-to-noise ratio and transmit efficiency at 9.4T.

The goal of this study was to optimize signal-to-noise ratio (SNR) and parallel receive (Rx) performance of ultrahigh field (UHF) (≥7T) transceiver arrays without compromising their transmit (Tx) efficiency. UHF transceiver head phased arrays with a tight fit improve Tx efficiency in comparison with Tx-only arrays, which are usually larger so that Rx-only arrays can fit inside. However, having ≥16 elements inside a head transceiver array presents decoupling problems. Furthermore, the available number of Tx channels is limited. A prototype of a splittable transceiver phased array was constructed. The array consisted of four flat surface Tx loops positioned in two rows. Each loop could be split into two smaller overlapped Rx loops during reception. Experimental data demonstrated that both SNR and parallel reception performance improved substantially by doubling the number of Rx elements from four to eight. As a proof of concept, we developed and constructed a novel splittable transceiver phased array that allows doubling of the number of Rx elements while keeping both Tx and Rx elements at the same distance from the subject. Both Tx and Rx performance can be optimized at the same time using this method. Magn Reson Med 76:1621-1628, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Spectrum Efficiency Analysis and Adaptive Transceiver Design for Single-Carrier Multiuser Transmission

In this paper, the spectrum efficiency of multiuser single carrier (SC) transmission is considered. In SC multiuser transmission, multiuser access can be realized by using interference suppression, e.g., SC frequency-domain adaptive antenna array (SC-FDAAA) transceiver, or by orthogonal frequency allocation among users, e.g., SC frequency-division multiple access (SC-FDMA) transceiver. To evaluate the system spectrum efficiency, the signal-to-interference-plus-noise ratio (SINR) at the output of the SC-FDAAA receiver and the SC-FDMA receiver is derived, respectively. The system spectrum efficiency is then evaluated and compared for both transceivers. It is shown that under the assumption of slow transmit power control, the system spectrum efficiency of the SC-FDMA transceiver does not change with the number of users, whereas the spectrum efficiency of the SC-FDAAA transceiver reaches its maximal value by an optimal number of users, which is determined by both the number of receive antennas and the target receive signal-to-noise ratio (SNR). With this observation, an SC-adaptive transceiver is proposed based on unorthogonal frequency allocation and frequency-domain interference suppression to improve the system spectrum efficiency, and the proposed scheme has been shown to be effective by numerical results.

16-channel bow tie antenna transceiver array for cardiac MR at 7.0 tesla.

To design, evaluate, and apply a bow tie antenna transceiver radiofrequency (RF) coil array tailored for cardiac MRI at 7.0 Tesla (T). The radiofrequency (RF) coil array comprises 16 building blocks each containing a bow tie shaped λ/2-dipole antenna. Numerical simulations were used for transmission field homogenization and RF safety validation. RF characteristics were examined in a phantom study. The array's suitability for high spatial resolution two-dimensional (2D) CINE imaging and for real time imaging of the heart was examined in a volunteer study. The arrays transmission fields and RF characteristics are suitable for cardiac MRI at 7.0T. The coil performance afforded a spatial resolution as good as (0.8 × 0.8 × 2.5) mm(3) for segmented 2D CINE MRI at 7.0T which is by a factor of 12 superior versus standardized protocols used in clinical practice at 1.5T. The proposed transceiver array supports 1D acceleration factors of up to R = 6 without impairing image quality significantly. The 16-channel bow tie antenna transceiver array supports accelerated and high spatial resolution cardiac MRI. The array is compatible with multichannel transmission and provides a technological basis for future clinical assessment of parallel transmission techniques at 7.0 Tesla. Magn Reson Med 75:2553-2565, 2016. © 2015 Wiley Periodicals, Inc.

Sodium MRI of the human heart at 7.0 T: preliminary results.

The objective of this work was to examine the feasibility of three-dimensional (3D) and whole heart coverage (23)Na cardiac MRI at 7.0 T including single-cardiac-phase and cinematic (cine) regimes. A four-channel transceiver RF coil array tailored for (23)Na MRI of the heart at 7.0 T (f = 78.5 MHz) is proposed. An integrated bow-tie antenna building block is used for (1)H MR to support shimming, localization and planning in a clinical workflow. Signal absorption rate simulations and assessment of RF power deposition were performed to meet the RF safety requirements. (23) Na cardiac MR was conducted in an in vivo feasibility study. 3D gradient echo (GRE) imaging in conjunction with Cartesian phase encoding (total acquisition time T(AQ) = 6 min 16 s) and whole heart coverage imaging employing a density-adapted 3D radial acquisition technique (T(AQ) = 18 min 20 s) were used. For 3D GRE-based (23)Na MRI, acquisition of standard views of the heart using a nominal in-plane resolution of (5.0 × 5.0) mm(2) and a slice thickness of 15 mm were feasible. For whole heart coverage 3D density-adapted radial (23)Na acquisitions a nominal isotropic spatial resolution of 6 mm was accomplished. This improvement versus 3D conventional GRE acquisitions reduced partial volume effects along the slice direction and enabled retrospective image reconstruction of standard or arbitrary views of the heart. Sodium cine imaging capabilities were achieved with the proposed RF coil configuration in conjunction with 3D radial acquisitions and cardiac gating. Cardiac-gated reconstruction provided an enhancement in blood-myocardium contrast of 20% versus the same data reconstructed without cardiac gating. The proposed transceiver array enables (23)Na MR of the human heart at 7.0 T within clinical acceptable scan times. This capability is in positive alignment with the needs of explorations that are designed to examine the potential of (23)Na MRI for the assessment of cardiovascular and metabolic diseases.

Capacitive Proximity Communication With Distributed Alignment Sensing for Origami Biomedical Implants

Origami implant design is a 3D integration technique which addresses size and cost constraints in biomedical implants. This paper presents a capacitive proximity interconnect scheme that enables chip-to-chip communication across folds in the Origami implant, allowing increased flexibility of chip placement and orientation. The capacitive plate array senses link quality and chip-to-chip alignment, and adapts the data rate at each plate accordingly, shutting down poorly-coupled links to save power. Instead of using separate plate arrays for alignment sensing and communication, this interconnect embeds the alignment sensor and transceiver arrays within the same set of plates, so that link quality can be measured at the communications plates directly, thus simplifying their adaptation to alignment. In order to save power and area, the sensor circuitry is distributed across the array and shares functional blocks with the transceiver. Data rates from 10–60 Mbps are achieved over 4–12 µm of parylene-C, with efficiencies up to 0.180 pJ/bit.

Three-layered radio frequency coil arrangement for sodium MRI of the human brain at 9.4 Tesla.

A multinuclei imaging setup with the capability to acquire both sodium ((23) Na) and proton ((1) H) signals at 9.4 Tesla is presented. The main objective was to optimize coil performance at the (23) Na frequency while still having the ability to acquire satisfactory (1) H images. The setup consisted of a combination of three radio frequency (RF) coils arranged in three layers: the innermost layer was a 27-channel (23) Na receive helmet which was surrounded by a four-channel (23) Na transceiver array. The outer layer consisted of a four-channel (1) H dipole array for B0 shimming and anatomical localization. Transmit and receive performance of the (23) Na arrays was compared to a single-tuned (23) Na birdcage resonator. While the transmit efficiency of the (23) Na transceiver array was comparable to the birdcage, the (23) Na receive array provided substantial signal-to-noise ratio (SNR) gain near the surface and comparable SNR in the center. The utility of this customized setup was demonstrated by (23) Na images of excellent quality. High SNR, efficient transmit excitation and B0 shimming capability can be achieved for (23) Na MRI at 9.4T using novel coil combination. This RF configuration is easily adaptable to other multinuclei applications at ultra high field (≥ 7T).

Monolithic optical phased-array transceiver in a standard SOI CMOS process.

Monolithic microwave phased arrays are turning mainstream in automotive radars and high-speed wireless communications fulfilling Gordon Moores 1965 prophecy to this effect. Optical phased arrays enable imaging, lidar, display, sensing, and holography. Advancements in fabrication technology has led to monolithic nanophotonic phased arrays, albeit without independent phase and amplitude control ability, integration with electronic circuitry, or including receive and transmit functions. We report the first monolithic optical phased array transceiver with independent control of amplitude and phase for each element using electronic circuitry that is tightly integrated with the nanophotonic components on one substrate using a commercial foundry CMOS SOI process. The 8 × 8 phased array chip includes thermo-optical tunable phase shifters and attenuators, nano-photonic antennas, and dedicated control electronics realized using CMOS transistors. The complex chip includes over 300 distinct optical components and over 74,000 distinct electrical components achieving the highest level of integration for any electronic-photonic system.

A 94 GHz 3D Image Radar Engine With 4TX/4RX Beamforming Scan Technique in 65 nm CMOS Technology

This paper presents a fully-integrated 3D image radar engine utilizing beamforming for electrical scanning and precise ranging technique for distance measurement. Four transmitters and four receivers form a sensor frontend with phase shifters and power combiners adjusting the beam direction. A built-in 31.3 GHz clock source and a frequency tripler provide both RF carrier and counting clocks for the distance measurement. Flip-chip technique with low-temperature co-fired ceramic (LTCC) antenna design creates a miniature module as small as 6.5 × 4.4 × 0.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Designed and fabricated in 65 nm CMOS technology, the transceiver array chip dissipates 960 mW from a 1.2-V supply and occupies chip area of 3.6 × 2.1 mm 2. This prototype achieves ±28° scanning range, 2-m maximum distance, and 1 mm depth resolution.

A Silicon Micromachined Eight-Pixel Transceiver Array for Submillimeter-Wave Radar

An eight-pixel transceiver array for operation in a 340 GHz imaging radar is presented. Silicon micromachining is applied to fabricate the submillimeter-wave front-end components to increase the density and uniformity of the array while lowering the cost compared to metal machining. Performance comparable with discrete metal machined housings was achieved with the 340 GHz transmitter nominally producing 0.5 mW and the mixers having a DSB noise temperature of 2000 K with a conversion loss of 8 dB. Radar performance is primarily limited by the isolation of the hybrid coupler, which is typically 28 dB, but excellent imaging performance is still achieved and improvements in penetration compared to higher frequency imaging radars is demonstrated.

Multichannel Double-Row Transmission Line Array for Human MR Imaging at Ultrahigh Fields.

In microstrip transmission line (MTL) transmit/receive (transceive) arrays used for ultrahigh field MRI, the array length is often constrained by the required resonant frequency, limiting the image coverage. The purpose of this study is to increase the imaging coverage and also improve its parallel imaging capability by utilizing a double-row design. A 16-channel double-row MTL transceive array was designed, constructed, and tested for human head imaging at 7 T. Array elements between two rows were decoupled by using the induced current elimination or magnetic wall decoupling technique. In vivo human head images were acquired, and g-factor results were calculated to evaluate the performance of this double-row array. Testing results showed that all coil elements were well decoupled with a better than -18 dB transmission coefficient between any two elements. The double-row array improves the imaging quality of the lower portion of the human head, and has low g-factors even at high acceleration rates. Compared with a regular single-row MTL array, the double-row array demonstrated a larger imaging coverage along the z-direction with improved parallel imaging capability. The proposed technique is particularly suitable for the design of large-sized transceive arrays with large channel counts, which ultimately benefits the imaging performance in human MRI.

Tilted microstrip phased arrays with improved electromagnetic decoupling for ultrahigh-field magnetic resonance imaging.

One of the technical challenges in designing a dedicated transceiver radio frequency (RF) array for MR imaging in humans at ultrahigh magnetic fields is how to effectively decouple the resonant elements of the array. In this work, we propose a new approach using tilted microstrip array elements for improving the decoupling performance and potentially parallel imaging capability.To investigate and validate the proposed design technique, an 8-channel volume array with tilted straight-type microstrip elements was designed, capable for human imaging at the ultrahigh field of 7 Tesla. In this volume transceiver array, its electromagnetic decoupling behavior among resonant elements, RF field penetration to biological samples, and parallel imaging performance were studied through bench tests and in vivo MR imaging experiments.In this specific tilted element array design, decoupling among array elements changes with the tilted angle of the elements and the best decoupling can be achieved at certain tilted angle. In vivo human knee MR images were acquired using the tilted volume array at 7 Tesla for method validation.Results of this study demonstrated that the electromagnetic decoupling between array elements and the B1 field strength can be improved by using the tilted element method in microstrip RF coil array designs at the ultrahigh field of 7T.