CPW‐fed compact thin‐film UWB antenna with dual band‐notched characteristics

This paper presents a new compact thin‐film ultrawideband (UWB) antenna with dual band‐notched characteristics. The antenna contains a rectangular slot with a fork‐like tuning stub. To achieve the dual band‐notched characteristics, narrow and U‐shaped slots are inserted on the radiator. This antenna is printed on a Mylar film substrate of 0.3 mm thickness with a dielectric constant of 3.2. The antenna has compact dimensions of 34.5 × 27.3 mm². It operates in the frequency range 2.9–11.3 GHz with impedance matching covering the entire bandwidth and reasonable radiation properties. It also exhibits dual band‐notched characteristics. One of the notched frequencies is in the range 3.3–3.7 GHz (WiMAX band) and the other in the range 5.1–5.8 GHz (WLAN band). The antenna is designed and simulated by using the commercial IE3D software, which is based on the method of moments. The antenna was fabricated and measured using Agilent E363B PNA network analyzers. The characteristics of the fabricated antenna show high correlation with those obtained from the simulation. The results confirm that the proposed antenna can achieve notch performance for WLAN and WiMAX communication systems and is also suitable for various portable UWB applications. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Simulation study of an optimized current matching for In0.39Ga0.61N/In0.57Ga0.43N/In0.74Ga0.26N triple-junction solar cells

This paper deals with the design and optimization of a triple-junction (TJ) solar cell using indium gallium nitride (InGaN) material. Two tunnel diodes are used to ensure connection between the different subcells. A comprehensive study is performed by means of 2D numerical simulations to locate the best bandgap combination that leads to an optimized current matching. During the simulations, the doping concentration and the base thickness are considered as fitting parameters for the top and the middle subcells. The In_0.39Ga_0.61N/In_0.57Ga_0.43N/In_0.74Ga_0.26N bandgap combination is supposed to be 2.02 eV/1.52 eV/1.13 eV. A high short-circuit current density (13.313 mA/cm²) is achieved by assuming a base thickness of 1 µm for each subcell and a p/n doping ratio of 5?×?10¹⁸ cm^?3/5?×?10¹⁵ cm^?3 in the top cell, 1.5?×?10¹⁹ cm^?3/1.5?×?10¹⁶ cm^?3 in the middle cell, and 7.5?×?10¹⁸ cm^?3/7.5?×?10¹⁵ cm^?3 in the bottom cell. The optimized structure has an improved open-circuit voltage (2.877 V), fill factor (83%), and conversion efficiency (33.11%).

     

Dimmable integrated CMOS LED driver based on a resonant DC/DC hybrid‐switched capacitor converter

This paper presents a 7.7 ‐ mm² on‐chip LED driver based on a DC/DC resonant hybrid‐switched capacitor converter operating in the MHz range with and without output capacitor. The converter operation allows continuously dimming the LED while keeping control on both peak and average current. Also, it features no flickering even in the absence of output capacitor and for light dimmed down to 10% of the nominal value. The capacitors and switches of the LED driver are integrated on a single IC die fabricated in a low‐cost 5 V 0.18‐μm bulk CMOS technology. This LED driver uses a small (0.7 mm²) inductor of 100 nH, which is 10 times smaller value than prior art integrated inductive LED drivers, still showing a competitive peak efficiency of 93% and achieving a power density of 0.26 W/mm² (0.34 W/mm³).     

Optimization of different structural parameters of GeSn/SiGeSn Quantum Well Infrared Photodetectors (QWIPs) for low dark current and high responsivity

Dark current and responsivity are two important parameters of quantum well infrared photodetectors (QWIPs). An optimization approach is applied herein to achieve low dark current along with high responsivity for a GeSn/SiGeSn QWIP. The dark current is reduced by varying different physical parameters of well and barrier, operating temperature and bias voltage of the QWIP. To optimize the QWIP, the detectivity is calculated. The results show that the optimally designed GeSn/SiGeSn QWIP can achieve a low dark current of 2.35 pA at 2 V with a peak responsivity of 1.24 A/W at 4.3 µm and a high detectivity of 3.47?×?10¹² cm · Hz^1/2 W^?1 at 2 V and 77 K. Finally, the frequency response of the optimally designed GeSn/SiGeSn QWIP device is estimated. The theoretically predicted higher detectivity with respect to previously reported SiGe/Si QWIPs and GeSn/SiGeSn interband QWIPs indicates a promising future for GeSn/SiGeSn intersubband QWIPs.

     

Gradient nonlinearity correction in liver DWI using motion-compensated diffusion encoding waveforms

Objective 

To experimentally characterize the effectiveness of a gradient nonlinearity correction method in removing ADC bias for different motion-compensated diffusion encoding waveforms.

Methods

The diffusion encoding waveforms used were the standard monopolar Stejskal–Tanner pulsed gradient spin echo (pgse) waveform, the symmetric bipolar velocity-compensated waveform (sym-vc), the asymmetric bipolar velocity-compensated waveform (asym-vc) and the asymmetric bipolar partial velocity-compensated waveform (asym-pvc). The effectiveness of the gradient nonlinearity correction method using the spherical harmonic expansion of the gradient coil field was tested with the aforementioned waveforms in a phantom and in four healthy subjects.

Results

The gradient nonlinearity correction method reduced the ADC bias in the phantom experiments for all used waveforms. The range of the ADC values over a distance of ± 67.2 mm from isocenter reduced from 1.29 × 10^–4 to 0.32 × 10^–4 mm²/s for pgse, 1.04 × 10^–4 to 0.22 × 10^–4 mm²/s for sym-vc, 1.22 × 10^–4 to 0.24 × 10^–4 mm²/s for asym-vc and 1.07 × 10^–4 to 0.11 × 10^–4 mm²/s for asym-pvc. The in vivo results showed that ADC overestimation due to motion or bright vessels can be increased even further by the gradient nonlinearity correction.

Conclusion

The investigated gradient nonlinearity correction method can be used effectively with various motion-compensated diffusion encoding waveforms. In coronal liver DWI, ADC errors caused by motion and residual vessel signal can be increased even further by the gradient nonlinearity correction.

     

Electrically stable low voltage operating ZnO thin film transistors with low leakage current Ni-doped Ba0.6Sr0.4TiO3 gate insulator

We report on the fabrication of low-voltage ZnO thin-film transistors using 1% Ni-doped Ba_0.6Sr_0.4TiO₃ as the gate insulator. The Ni-doped BST, deposited by RF magnetron sputtering at room temperature, significantly reduced leakage current density to less than 6 × 10⁻⁹ A/cm, as compared to a current density of 5 × 10⁻⁴ A/cm for undoped BST films at 0.5 MV/cm. The ZnO thin-film transistor with the Ni-doped BST gate insulator exhibited a very low operating voltage of 4 V. The field-effect mobility, the current on/off ratio and subthreshold swing were 2.2 cm² V/s, 1.2 × 10⁶, and 0.21 V/dec respectively.     

A very low complexity IR‐UWB transmitter with BPSK modulation for balanced antenna

A very low complexity impulse radio‐ultrawideband (IR‐UWB) transmitter suitable for balanced antenna is presented. This all‐digital transmitter employs the binary phase‐shift keying (BPSK) modulation scheme and eliminates the need for a balun. Also, a new Gaussian monocycle pulse generator is proposed which is used as impulse transmitted signal. The transmitter circuit was designed in 0.18‐μm complementary metal–oxide–semiconductor technology. The post‐simulation results show that the core chip size was only 0.02 mm². The output amplitude pulse yielded 150 mV peak‐to‐peak under a supply voltage of 1.8 V. Simulation results show that the transmitter consumes 8.5 pJ/pulse for 200‐MHz pulse repeating frequency. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Diffusion-weighted imaging of the spine using radialk-space trajectories

Introduction Diffusion-weighted MR imaging (DWI) of the spine requires robust imaging methods, that are insensitive to susceptibility effects caused by the transition from bone to soft tissue and motion artifacts due to breathing, swallowing, and cardiac motion. The purpose of this study was to develop a robust imaging method suitable for DWI of the spine. Methods and subjects A radialk-space spin echo sequence has been implemented, which is sell-navigating because each acquisition line passes through the origin ofk-space. Influence of cardiac motion and associated flow of cerebrospinal fluid is minimized by cardiac gating with a finger photoplethysmograph. The sequence has been tested on a 1.5T system. Diffusion-weighted images of six normal volunteers were acquired in the sagittal plane with 4b values between 50 and 500 s mm⁻². Because of the symmetries of the cord, diffusion measurements in the head-foot (HF) or left-right (LR) directions were sufficient to measure the dominant effects of anisotropy. Results The apparent diffusion coefficients (ADCs) measured, respectively, in the LR and HF directions were (0.699 ± 0.050) × 10⁻³ and (1.805 ± 0.086) × 10⁻³ mm² s⁻¹ in the spinal cord. (1.588 ± 0.082) × 10⁻³ and (1.528 ± 0.052) × 10⁻³ mm² s⁻¹ in the intervertebral disks, and (0.346 ± 0.047) × 10⁻³ and (0.306 ± 0.035) × 10⁻³ mm² s⁻¹ in the vertebrae of the cervicothoraeic spine. Conclusion Diffusion-weighted spin echo sequences with radial trajectories ink-space provide a means of achieving robust, high quality diffusion-weighted imaging and measuring ADCs in the spine. The application of the diffusion-weighting gradients in different directions allows diffusion anisotropy to be measured.     

七频段金属外壳手机天线的设计

提出了一种应用在金属外壳手机终端上,实现了-6dB以下的带宽为800~960 MHz,1 710~3 000 MHz频段的天线设计。为了保证辐射性能和所需带宽,在金属的手机外壳的短边上开宽为2mm的U型槽,在馈电处采用电容匹配和一个可切换的电路接地枝节实现GSM850/900 (824~960 MHz),DCS/PCS/UMTS2100(1 710~2 170 MHz),LTE2300/2500 (2 300~2700 MHz)七个频段的覆盖。手机尺寸为152 mm×72 mm×6.8 mm,天线的净空区域为7 mm×70 mm。通过实物测试,手机天线的辐射效率,在低频824~960 MHz频段中为38%~46%,在1 710~2 700 MHz中,辐射效率为可达38%~64%。该天线具有很好的辐射性能,适合应用于金属外壳的移动终端中。     

Building high transduction coefficient BiScO3–PbTiO3 piezoceramic and its power generation characteristics

Improving the power generation characteristics of piezoelectric energy harvesters requires the construction of piezoelectric ceramics with high transduction coefficient (d₃₃ × g₃₃), which remains a big challenge. In this paper, guided by piezoelectric energy harvester applications, the relationship between the composition, microstructure and transduction coefficient of (1?? x)BiScO₃–xPbTiO₃ material is systematically studied. The results demonstrated that the sample with a composition of x =?0.64 not only has a high Curie temperature (426 °C) which is beneficial to improve the working stability of the device, but also has a very high d₃₃ × g₃₃ value (15,110?×?10^?15 m²/N), which is significantly superior to the commercial PZT system. Excellent electrical performance can be attributed to the fact that the composition of x =?0.64 located near MPB has a very high piezoelectric charge constant (505 pC/N) at the same time with moderate dielectric constant (1907). The cantilever-type energy harvester made of optimized composition generated a high output power density of 2.93 μW/mm³ at room temperature, which charged a commercial 47 μF electrolytic capacitor to 22 V in just 220 s and lighted up 72 LEDs for 0.1~0.2 s. Further, x =?0.64 harvester exhibited a large output voltage of 2.76 V even at 350 °C, suggesting its potential use for powering high temperature wireless sensors.

     

An area-efficient,large time-constant log-domain filter for low-frequency applications

This paper proposes a simple technique to increase the time constant of a log-domain filter. By using the proposed technique, the capacitor value can be reduced considerably; hence, overall area of the circuit can be reduced. A second-order log-domain low-pass filter (LPF) is implemented in UMC 65-nm complementary metal-oxide semiconductor (CMOS) technology to validate the proposed technique. It occupies an area as low as 0.005 mm² and operates with a 0.5-V supply. For a cutoff frequency of 100 Hz, the filter consumes a power of 4 nW. By adjusting the bias current, the cutoff frequency can be linearly tuned from 10 to 500 Hz. The filter has the figure of merit (FoM) of 0.68×10⁻¹³ J, which is on par with many designs listed in the literature. The filter uses the lowest capacitance/pole (0.92 pF) among the similar designs given in the literature, which shows that the present design is area efficient.     

Apparent diffusion coefficients of 31P metabolites in the human calf muscle at 7 T

Purpose

In this study, we aimed to measure the apparent diffusion coefficients (ADCs) of major phosphorous metabolites in the human calf muscle at 7 T with a diffusion-weighted (DW)-STEAM sequence.

Methods

A DW-STEAM sequence with bipolar gradients was implemented at 7 T, and DW MR spectra were acquired in three orthogonal directions in the human calf muscle of six healthy volunteers (TE/TM/TR = 15 ms/750 ms/5 s) at three b-values (0, 800, and 1200 s/mm²). Frequency and phase alignments were applied prior to spectral averaging. Averaged DW MR spectra were analyzed with LCModel, and ADCs of ³¹P metabolites were estimated.

Results

Four metabolites (phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi) and glycerol phosphorylcholine (GPC)) were quantified at all b-values with mean CRLBs below 10%. The ADC values of PCr, ATP, Pi, and GPC were (0.24 ± 0.02, 0.15 ± 0.04, 0.43 ± 0.14, 0.40 ± 0.09) × 10^–3 mm²/s, respectively.

Conclusion

The ADCs of four ³¹P metabolites were successfully measured in the human calf muscle at 7 T, among which those of ATP, Pi and GPC were reported for the first time in humans. This study paves the way to investigate ³¹P metabolite diffusion properties in health and disease on the clinical MR scanner.

     

Wide‐band dual‐resonance capacitive cross‐coupled divide‐by‐5 injection‐locked frequency divider

A wide locking range divide‐by‐5 injection‐locked frequency divider (ILFD) is proposed and was implemented in the TSMC 0.18‐μm 1P6M CMOS process. Conventional divide‐by‐5 ILFD has limited locking range. The proposed divide‐by‐5 ILFD is based on a capacitive cross‐coupled voltage‐controlled oscillator (VCO) with a dual‐resonance resonator, which is implemented in the divide‐by‐5 ILFD to obtain a wide overlapped locking range. At the drain‐source bias V_DD of 0.9 V and at the incident power of 0 dBm, the measured locking range of the divide‐by‐5 ILFD is 3.2 GHz, from the incident frequency 9.4 to 12.6 GHz, the percentage is 29.09%. The core power consumption is 2.98 mW. The die area is 0.987 × 1.096 mm².     

Duo triangle-shaped rectangular microstrip-fed patch antennas input and output parameters investigation

Conventional rectangular microstrip-fed patch antennas are initially investigated numerically within the frequency band 2.0 to 2.8 GHz for Wi-Fi applications. In order to enhance the input parameters of the underlying antennas, three prototypes are designed. A split is diagonally loaded on a conventional radiating patch to achieve a duo triangle-shaped microstrip-fed patch antenna in the first step. The conducting ground plane of the conventional and the duo triangle-shaped patches is modified to design the microstrip-fed monopole and duo triangle-shaped monopole antennas in the second and third steps, respectively, within the frequency band of 2.0 to 7.0 GHz. Concepts of voltage and current waves as well as classical electrostatics approach solutions are used to, respectively, investigate the return loss bandwidth and the electric field radiation pattern of the proposed antennas. Numerical simulations show some relevant antenna performances such as a triple-band, a −10-dB return loss bandwidth of 29% , a gain of 7.5 dB, and a calculated half power beam width of 120^° in E-plane.     

A compact quadruple crossed-dipole microstrip antenna designed for dual frequency and beam scanning operation

A synthesis of a compact crossed-dipole microstrip antenna is introduced. An attempt is made to include most of the operating characteristics required in modern communication systems. The antenna is composed of four crossed dipoles, forming a 2×2 element planar array that radiates an elliptically polarized field, operates in the ranges from 1.8 GHz to 1.9 GHz (DCS) and from 2.5 GHz to 2.8 GHz (UMTS) and has a satisfactory power gain. The feeding of interconnected dipoles is obtained using folded microstrip lines that minimize the size of the structure and also the parasitic radiation. The overall array has eight probe-fed ports. Their suitable phase excitation can drive the antenna to produce patterns with a maximum value in the desired directions.     

3D magnetic resonance fingerprinting on a low-field 50 mT point-of-care system prototype: evaluation of muscle and lipid relaxation time mapping and comparison with standard techniques

Objective

To implement magnetic resonance fingerprinting (MRF) on a permanent magnet 50 mT low-field system deployable as a future point-of-care (POC) unit and explore the quality of the parameter maps.

Materials and methods

3D MRF was implemented on a custom-built Halbach array using a slab-selective spoiled steady-state free precession sequence with 3D Cartesian readout. Undersampled scans were acquired with different MRF flip angle patterns and reconstructed using matrix completion and matched to the simulated dictionary, taking excitation profile and coil ringing into account. MRF relaxation times were compared to that of inversion recovery (IR) and multi-echo spin echo (MESE) experiments in phantom and in vivo. Furthermore, B₀ inhomogeneities were encoded in the MRF sequence using an alternating TE pattern, and the estimated map was used to correct for image distortions in the MRF images using a model-based reconstruction.

Results

Phantom relaxation times measured with an optimized MRF sequence for low field were in better agreement with reference techniques than for a standard MRF sequence. In vivo muscle relaxation times measured with MRF were longer than those obtained with an IR sequence (T₁: 182 ± 21.5 vs 168 ± 9.89 ms) and with an MESE sequence (T₂: 69.8 ± 19.7 vs 46.1 ± 9.65 ms). In vivo lipid MRF relaxation times were also longer compared with IR (T₁: 165 ± 15.1 ms vs 127 ± 8.28 ms) and with MESE (T₂: 160 ± 15.0 ms vs 124 ± 4.27 ms). Integrated ΔB₀ estimation and correction resulted in parameter maps with reduced distortions.

Discussion

It is possible to measure volumetric relaxation times with MRF at 2.5 × 2.5 × 3.0 mm³ resolution in a 13 min scan time on a 50 mT permanent magnet system. The measured MRF relaxation times are longer compared to those measured with reference techniques, especially for T₂. This discrepancy can potentially be addressed by hardware, reconstruction and sequence design, but long-term reproducibility needs to be further improved.

     

High-resolution imaging of the excised porcine heart at a whole-body 7 T MRI system using an 8Tx/16Rx pTx coil

Introduction

MRI of excised hearts at ultra-high field strengths (\({\mathrm{B}}_{0}\)≥7 T) can provide high-resolution, high-fidelity ground truth data for biomedical studies, imaging science, and artificial intelligence. In this study, we demonstrate the capabilities of a custom-built, multiple-element transceiver array customized for high-resolution imaging of excised hearts.

Method

A dedicated 16-element transceiver loop array was implemented for operation in parallel transmit (pTx) mode (8Tx/16Rx) of a clinical whole-body 7 T MRI system. The initial adjustment of the array was performed using full-wave 3D-electromagnetic simulation with subsequent final fine-tuning on the bench.

Results

We report the results of testing the implemented array in tissue-mimicking liquid phantoms and excised porcine hearts. The array demonstrated high efficiency of parallel transmits characteristics enabling efficient pTX-based B₁⁺-shimming.

Conclusion

The receive sensitivity and parallel imaging capability of the dedicated coil were superior to that of a commercial 1Tx/32Rx head coil in both SNR and T₂*-mapping. The array was successfully tested to acquire ultra-high-resolution (0.1 × 0.1 × 0.8 mm voxel) images of post-infarction scar tissue. High-resolution (isotropic 1.6 mm³ voxel) diffusion tensor imaging-based tractography provided high-resolution information about normal myocardial fiber orientation.

     

A 2- to 12-GHz 65-nm transmit/receive CMOS DP8T switching matrix for ultra-wideband antenna arrays

An ultra-wideband 2- to 12-GHz transmit/receive (T/R) double-pole–eight-throw (DP8T) switching matrix is developed with a 65-nm complementary metal oxide semiconductor (CMOS) process for a radar-based breast cancer detection system. The measured average insertion losses are 5.2, 7, and 10.6 dB at 2, 6, and 12 GHz, respectively, with input and output matching bandwidths of 2 to 12 GHz and a third-order input intercept point (IIP3) of 31 dBm at 8 GHz. The power consumption is less than 1 mW for a 1.2-V power supply. To the best of the authors' knowledge, this is the first reported DP8T CMOS switching matrix to replace the conventional mechanical switch to control a portable radar antenna.     

Fundamental experiment and numerical simulation of pre-ionized inert gas plasma MHD electrical power generation

The experiments of pre-ionized inert gas plasma MHD electrical power generation are conducted, and the performance and plasma behavior in the experimental generator are examined through time-dependent r-_ two-dimensional numerical simulation. In the experiment, an enthalpy extraction ratio of 4.01% has been obtained with a disk-shaped MHD generator with radio-frequency pre-ionization. In the numerical simulation, at an assumed inlet electron temperature around 5600 K (inlet ionization degree 0:10 × 10⁻⁴)_6600 K (1:36 × 10⁻⁴), the plasma structure is similar to the non-uniform structure observed in the experiment. An enthalpy extraction ratio around 2_5% matches well with that in the experiment. At a suitable inlet electron temperature of 7000 K (3:15 × 10⁻⁴)_8000 K (1:79 × 10⁻³), although non-uniform plasma structure still occurs, a high enthalpy extraction ratio over 10% is expected.     

Dynamic DTI (dDTI) shows differing temporal activation patterns in post-exercise skeletal muscles

Object

To assess post-exercise recovery of human calf muscles using dynamic diffusion tensor imaging (dDTI).

Materials and methods

DTI data (6 directions, b = 0 and 400 s/mm²) were acquired every 35 s from seven healthy men using a 3T MRI, prior to (4 volumes) and immediately following exercise (13 volumes, ~7.5 min). Exercise consisted of 5-min in-bore repetitive dorsiflexion-eversion foot motion with 0.78 kg resistance. Diffusion tensors calculated at each time point produced maps of mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (RD), and signal at b = 0 s/mm² (S₀). Region-of-interest (ROI) analysis was performed on five calf muscles: tibialis anterior (ATIB), extensor digitorum longus (EDL) peroneus longus (PER), soleus (SOL), and lateral gastrocnemius (LG).

Results

Active muscles (ATIB, EDL, PER) showed significantly elevated initial MD post-exercise, while predicted inactive muscles (SOL, LG) did not (p < 0.0001). The EDL showed a greater initial increase in MD (1.90 × 10^?4mm²/s) than ATIB (1.03 × 10^?4mm²/s) or PER (8.79 × 10^?5 mm²/s) (p = 7.40 × 10^?4), and remained significantly elevated across more time points than ATIB or PER. Significant increases were observed in post-exercise EDL S₀ relative to other muscles across the majority of time points (p < 0.01 to p < 0.001).

Conclusions

dDTI can be used to differentiate exercise-induced changes between muscles. These differences are suggested to be related to differences in fiber composition.