RF Measurements Research Articles

The Impact of Gate Annealing on Leakage Current and Radio Frequency Efficiency in AlGaN/GaN High-Electron-Mobility Transistors

Gallium Nitride (GaN) high-electron mobility transistors (HEMTs) are highly promising for high-frequency and high-power applications due to their superior properties, such as a wide energy bandgap and high carrier density. The performance of GaN HEMTs is significantly influenced by the interfacial states of the AlGaN barrier, and gate annealing has emerged as a key process for reducing leakage currents and enhancing DC/RF characteristics. This research investigates the impact of gate annealing on AlGaN/GaN HEMTs, focusing on two main aspects: leakage current reduction and improvements in DC and RF efficiency. Through comprehensive electrical analysis, including DC and RF measurements, the effects of gate annealing were experimentally evaluated. The results show a significant reduction in gate leakage current and noticeable improvements in DC/RF performance for the devices that underwent gate annealing. The study confirms that the annealing process can effectively enhance device performance by modifying the material properties at the gate interface.

S-band high-gradient low β single-periodic magnetically coupled standing-wave accelerating structure for a proton therapy linac

S-band high-gradient accelerating structures were proposed to accelerate protons from 30 to 230 MeV for a compact proton therapy linac in Institute of Modern Physics. A backward traveling wave structure and a single-periodic magnetically coupled standing wave structure were designed, and differences between these two structures were analyzed to select a more suitable one for the proton therapy linac. In this paper, a novel single-periodic magnetically coupled standing-wave accelerating structure was studied, with an optimized nose cone that related to a smaller peak surface electric field and higher shunt impedance, with the reduced number of coupling holes and mechanical von Mises stress thus making it possible for higher duty factor and longer rf pulse operation, also with larger coupling holes and improved cell-to-cell coupling thus making this structure suitable for operating in π mode. An 11-cell high-power prototype for β=0.26 particles was developed with an active length of 143 mm. This prototype cavity is supposed to operate at an accelerating gradient of 30 MV/m with 0.1% duty factor, corresponding to a maximum surface electric field of 105 MV/m and a peak rf power of 3.43 MW. Cavity design, optimization, manufacture, rf measurement, and high-power test will be discussed in this paper. Published by the American Physical Society 2024

Design, Molecular Docking, Synthesis, and ADME Studies of Novel Amide Derivatives of Diflunisal and Aspirin Compounds as Preferential Selective Cox-2 Inhibitor

The synthesize of novel NSAI compounds (Aspirin and diflunisal derivatives) as a preferential selective COX-2 inhibitors, and evaluate their anti-inflammatory, safety and G.I.T. side effects. Aspirin and diflunisal conjugated with selected moiety of heterocyclic rings to enhance anti-inflammatory activity with preferential COX-2 selectivity, decrease GIT side effects, this aim achieved by 4-(4-Fluorophenyl) isoxazol-5-amine conjugation. The produced derivatives underwent IR and 1H-NMR spectra analysis, and a melting point and Rf measurement were used to verify their purity. The preliminary pharmacological activity showed that compounds 2and 6 have significantly more anti-inflammatory outcome than all synthesized compounds, in which Compound (2) showed a highest anti-inflammatory action with low gastric effects, and compound (6) showed a good anti-inflammatory activity with lowest ulcer index. ADME study showed all ligands was pargeted to passive absorbed orally except compound (7) was failed, so they showed good bioavailability except compound (7) fail might due to its high molecular > 500. According to a docking research, the docked compounds' PLP fitness on COX-2 ranged from (66.55 to 88.43). while (51.44 to 78.88) on COX-1, consequently they might show preferentially selective COX-2 inhibitors. Compound (6) showed highest COX -2 affinity (88.43) even celecoxib (83.35), but compound (6) showed higher affinity fox COX-1than celecoxib. While compounds (3 and 7) produced lowest COX-2 affinity (66.55 and 66.75) respectively. The all of studies, anti-inflammatory, ulcer index, ADME and molecular docking results showed good correlation in respect to compounds (6 and 2).

Thin channel Ga2O3 MOSFET with 55 GHz fMAX and >100 V breakdown

This Letter reports a highly scaled 90 nm gate length β-Ga2O3 (Ga2O3) T-gate MOSFET with a power gain cutoff frequency (fMAX) of 55 GHz. The 60 nm thin epitaxial Ga2O3 channel layer was grown by molecular beam epitaxy, while the highly doped (n++) source/drain regions were regrown using metal organic chemical vapor deposition. Maximum on current (IDS,MAX) of 160 mA/mm and trans-conductance (gm) around 36 mS/mm were measured at VDS = 10 V for LSD = 1.5 μm device. Transconductance and on current are limited by high channel sheet resistance (Rsheet). Gate/drain breakdown voltage of 125 V was measured for LGD = 1.2 μm. We extracted 27 GHz current gain cutoff frequency (fT) and 55 GHz fMAX for 20 V drain bias for unpassivated devices. While no current collapse was seen initially for both drain and gate lag measurements for 500 ns pulse, moderate current collapse was observed after DC, RF measurements caused by electrical stressing. We calculated a high fT. VBR product of 3.375 THz V, which is comparable to the state-of-the-art GaN HEMTs. This figure of merit suggests that Ga2O3 could be a potential candidate for X-band application.

Multimodal surface coils for low field MR imaging

Low field MRI is safer and more cost effective than the high field MRI. One of the inherent problems of low field MRI is its low signal-to-noise ratio or sensitivity. In this work, we introduce a multimodal surface coil technique for signal excitation and reception to improve the RF magnetic field (B1) efficiency and potentially improve MR sensitivity. The proposed multimodal surface coil consists of multiple identical resonators that are electromagnetically coupled to form a multimodal resonator. The field distribution of its lowest frequency mode is suitable for MR imaging applications. The prototype multimodal surface coils are built, and the performance is investigated and validated through numerical simulation, standard RF measurements and tests, and comparison with the conventional surface coil at low fields. Our results show that the B1 efficiency of the multimodal surface coil outperforms that of the conventional surface coil which is known to offer the highest B1 efficiency among all coil categories, i.e., volume coil, half-volume coil and surface coil. In addition, in low-field MRI, the required low-frequency coils often use large value capacitance to achieve the low resonant frequency which makes frequency tuning difficult. The proposed multimodal surface coil can be conveniently tuned to the required low frequency for low-field MRI with significantly reduced capacitance value, demonstrating excellent low-frequency operation capability over the conventional surface coil.

Comprehensive characterization of a high‐performance double heterojunction InGaAs pHEMT for linear power‐efficient amplifiers applications

AbstractThis article centers its attention on the phenomenon of electrostatics, linearity, analogue, and RF performance of a 0.5 μm × (2 × 100) μm double heterojunction AlGaAs/InGaAs/GaAs pHEMT using on‐wafer DC and RF measurements up to 50 GHz. With a high ION/IOFF ratio (1.21 × 107) and low subthreshold slope (72.7 mV/dec), a flat and high transconductance over a wide range of Vgs has been achieved for the tested device. Furthermore, the input intercept and higher‐order voltage intercept point both attained large values with low intermodulation and harmonic distortion. Regarding RF parameters, the intrinsic gain has been achieved up to 28 dB. The GBW up to 750 GHz was attained, with the highest fT and fmax values being 24.5 GHz and 99.3 GHz, respectively. Since the device has very low intrinsic capacitance, parameters like TFP, GFP, and GTFP also showed excellent results. The high intrinsic gain and TGF indicate ample potential of the device for use as an amplifier. Investigating the parameters reveals the device to have very good linearity and amplifying capability.

Low insertion loss interposer approach for RF applications based on commercial LTCC tape, alkaline-free glass and printed metallization

Materials with high RF performance are in increasing demand due to the needs of modern telecommunications. Glass and low-temperature co-fired ceramics (LTCCs) are both interesting candidates for the design of complex signal transmission systems. Glass can be processed in large panels, and has suitable structure dimensions for silicon processing, but its multilayer capability is limited. LTCC is a mature technology for complex multilayer assemblies, but the structure dimensions and conductor line resolution are restricted by the need to use screen printing technology. The approach presented here combines the advantages of both technological domains: a thin glass sheet is bonded with no additional material to a LTCC multilayer ceramic and sintered to form a tight joint. Metallization of the glass is created using printable pastes and electroplating. Two fabrication routes are compared: etching of printed thick film metal layers, and semi-additive structuring. The results of RF measurements show a low attenuation per unit length for both types of metallization, indicating that our approach is a promising one for the integration of heterogeneous systems of RF transmission modules.

Compact HOM-damping structure of a beam-accelerating TM020 mode rf cavity

A compact HOM-damping beam-accelerating rf cavity was developed to mitigate coupled-bunch instabilities in electron storage rings. This cavity operates in the TM020 mode, characterized by a high Q-value and a high shunt impedance. The new HOM-damping mechanism leverages the unique field distributions of the TM020 mode, allowing direct embedding of rf absorbing materials into the cavity body. This novel structure underwent validation through rf simulations and measurements using a model cavity resonating at 508.58 MHz in the TM020 mode with a shunt impedance of 6.8 MΩ and designed to have HOM impedances of less than 0.1 MΩ longitudinally and 0.5 MΩ/m transversely. We also fabricated and tested a prototype cavity, showcasing its HOM-damping efficacy and high-power functionality at 120 kW, generating an accelerating voltage of 900 kV. This prototype operated successfully at full power, confirming the viability of both the damping structure and its high-power application.

RF Packaging and Design for Development of High Performance 5G mmWave Modules

5G sub-6GHz networks have already been deployed in many regions around the world. However, the deployment of 5G mmWave networks is yet to meet expectations. This is partly because of the challenges associated with hardware development of 5G mmWave systems. One example of such a challenge is to overcome the severe degradation of signal-to-noise (SNR) ratio due to intra- and inter-system signal losses at mmWave frequencies. This deteriorates the signal quality, limits transmission distances and may lead to unreliable mobile communication. In this work, we present RF packaging platforms and technologies as well as an approach for scalability of 5G RF frontend integrated circuits (ICs) and antennas which overcome intra- and inter-system losses. This leads to the development of high-performance and scalable 5G MIMO (multiple input multiple output) modules for reliable mobile communication at mmWave frequencies. The platforms provide very short and low-loss signal paths with few geometrical discontinuities between the frontend ICs and antennas. This leads to significant reduction in signal reflections and attenuation, thus improving the matching efficiency of the antennas and the equivalent isotropic radiated power (EIRP) of the entire system. The platforms also enable antennas to be integrated on layers directly above the ICs, and thereby ensures scalability of the ICs and antennas in both lateral dimensions for 5G mmWave massive MIMO. To demonstrate the functionality of our proposed packaging platforms, technologies and antennas, we performed in-depth RF designs, measurements and characterization of packaging materials, technologies and platforms as well as antennas for 5G mmWave applications.

Navigating The Complexity Overcoming Mobility Obstacles in Massive MIMO Systems with MIMO Antennas.

This research investigates the synergy between Massive Multiple Input, Multiple Output (MIMO) systems and mobility challenges, with a focus on the pivotal role played by Multiple Antenna Systems (MIMO antennas). Employing a sophisticated experimental setup featuring a 3.5 GHz Massive MIMO base station equipped with 64 MIMO antennas, mobile terminals on motorized platforms, and advanced RF measurement tools, the study explores adaptive beamforming, spatial multiplexing, and diversity techniques. Results from 100 experiments, each lasting 10 minutes, reveal that adaptive beamforming dynamically improves user tracking in response to mobility-induced channel variations. Spatial multiplexing and diversity techniques enhance throughput and reliability, especially in high user mobility scenarios. The quantitative findings align with existing literature, providing practical insights for the deployment of MIMO antennas. The study addresses limitations and proposes avenues for future research, enhancing our understanding of MIMO antenna applications and contributing to the evolution of wireless communication technologies in dynamic environments.

Design, Optimization and Performance Assessment of Single Port Film Bulk Acoustic Resonator through Finite Element Simulation.

In this paper, the study is supported by design, FEA simulation, and practical RF measurements on fabricated single-port-cavity-based acoustic resonator for gas sensing applications. In the FEA simulation, frequency domain analysis was performed to enhance the performance of the acoustic resonator. The structural and surface morphologies of the deposited ZnO as a piezoelectric layer have been studied using XRD and AFM. The XRD pattern of deposited bulk ZnO film indicates the perfect single crystalline nature of the film with dominant phase (002) at 2θ = 34.58°. The AFM micrograph indicates that deposited piezoelectric film has a very smooth surface and small grain size. In the fabrication process, use of bulk micro machined oxide (SiO2) for the production of a thin membrane as a support layer is adopted. A vector network analyzer (Model MS2028C, Anritsu) was used to measure the radio frequency response of the resonators from 1 GHz to 2.5 GHz. As a result, we have successfully fabricated an acoustic resonator operating at 1.84 GHz with a quality factor Q of 214 and an effective electromechanical coupling coefficient of 10.57%.

Construction and measurement of the prototype side-coupled standing-wave tube for electron Linac

Due to Iran's growing need for accelerators in various applications, NSTRI (Nuclear Science and Technology Research Institute) has defined a 6 MeV e-Linac (electron linear accelerator) project for medical and inspection applications. This electron accelerator has a side-coupled standing wave tube that operates in π/2 mode at the frequency of 2998.5 MHz. This paper presents a summary of the construction and cold test stage of the prototype tube for this accelerator. The prototype tube was constructed from aluminum and clamped with bolts.In the cold test stage, low-power RF measurements werecarried out using a side-coupled cavity tuning method and a bead-pull measurement technique. Using a network analyzer, magnetic and electric probes, and a mechanical structure constructed for this tube made the RF tuning possible. After tuning, the resonant frequency, unloaded quality factor, and effective shunt impedance of the aluminum tube were achieved at 2998.57 MHz, 7970, and 83.25 MΩ/m respectively.

A-118 Evaluation of Mindray Cystatin C Assay

Abstract Background Cystatin C is a low molecular weight non-glycosylated alkaline protein, with a molecular weight of 13kDa. It is formed by all nucleated cells in human at a constant rate. The only pathway of Cystatin C in vivo is excretion through glomerular filtration and absorbed by proximal renal tubular epithelial cells, which was decomposed finally. Therefore, the concentration of Cystatin C in serum is almost not affected by external factors, such as weight, age, gender, etc. Compared with creatinine and urea, it is an ideal endogenous marker for monitoring glomerular filtration function. Currently, the most methods on the market for testing Cystatin C are either latex enhanced immunoturbidimetric method, or immunoturbidimetric method. These methods usually use polyclonal antibodies from different animal species, which are sometime susceptible to the interference from rheumatoid factors reported in the literature, resulting in false positive results. The anti-RF interference ability of this reagent was enhanced by selecting the optimal antibody and optimizing reagent formulation. This study evaluated performances of the Cystatin C assay on Mindray BS-2000M system. Method Mindray Cystatin C assay is based on latex immunno-agglutination. Latex nanoparticles were coated with anti-Cystatin C antibody. Reagent of this assay contains R1 buffer and R2 with latex particles coupled with anti-Cystatin C antibodies. The assay starts with R1 and sample incubation for 5 min and then R2 is added. After another 5 min of incubation, agglutination occurs, leading to turbidity increasing. The turbidity is measured at 570 nm. Multi-level (5-point) calibration is used. Cystatin C concentrations are obtained from the calibration curve with signals from the assay with patient samples. Following basic assay performances were evaluated: precision, limit of detection, linearity, method comparison, interference and high dose hook. Results The precision study followed EP05-03 protocol. The repeatability and within-lab CVs on the BS-2000M system with 2 QC and 3 patient samples were ranged from 0.9% to 5.3%, respectively. Limit of detection was 0.1 mg/L and linearity was given up to 8.63 mg/L. The assay (y) shows good accuracy when compared with Roche Cystatin C (x) assay on the cobas 701: y = 1.0055x - 0.0268 (r2 = 0.9994, n = 109). The assay showed no significant with bilirubin up to 40 mg/dL, with hemoglobin up to 500 mg/dL, with lipids up to 500 mg/dL, and with rheumatoid factors up to 1200 IU/mL that is about 0.3% out of a total of 55 184 samples collected from our customers in China with RF measurements. No prozone was observed with the assay up to the high cystatin C concentration of 800 mg/L tested. Conclusion From this evaluation, we confirmed that Mindray Cystatin C assay can measure serum Cystatin C precisely and accurately, and with good performance against rheumatoid factors interference. It is suitable for use in routine clinical laboratories.

Additive Manufacturing of an IH-Type Linac Structure from Stainless Steel and Pure Copper

Additive manufacturing (AM) of metals has the potential to provide significant benefits for the construction of future particle accelerators. The combination of low cost manufacturing of complex geometries in combination with efficiency gains from improved linac design enabled by AM may be one way towards future cost-effective green accelerator facilities. As a proof of concept, we present a high-efficiency Zeff=280 MΩ/m, 433.632 MHz IH-DTL cavity based on an AM design. In this case, the complex internal drift tube structures with internal cooling channels have been produced from 1.4404 stainless steel and from pure copper using AM. The prototype cavity, as well as stainless steel AM parts have been electroplated with copper. We present results from successful vacuum tests, low level RF measurements of the cavity, as well as the status of preparations for high-power RF tests with a 30 kW pulsed power amplifier.

RF measurement and tuning for an Alvarez-type drift tube linear accelerator without post couplers

Alvarez-type Drift Tube Linacs (DTLs) are commonly adopted to accelerate the proton or heavy ion beam with the speed range about 0.04∼0.4 times of the light speed in vacuum. Acquisition of appropriate frequency and distribution of the electromagnetic field, and the field stability inside the Alvarez-type DTL cavity are essential to achieve good beam characteristics. The field requirement can be achieved through tuning by tuners and post couplers when the cavity is off-line. The field stability of cavity is usually measured by the tilt sensitivity and the minimum frequency interval between the operation mode and the nearest neighbor mode. The frequency interval will increase with the reduction of the number of the acceleration units (cells) inside the cavity, which is beneficial to fulfill the tilt sensitivity requirement. If the field stability condition is naturally satisfied, the post couplers inside the DTL cavity are not needed, and the cavity frequency and field distribution can be tuned merely by tuners. In this paper, the tuning method based on the pseudo-inverse matrix is applied to the Alvarez-type DTL cavity without post couplers in Xi’an 200 MeV proton application facility (XiPAF). The method is improved by an expanded matrix algorithm and the tuning process is optimized to expedite the iteration during the tuning. The XiPAF DTL cavity has 23 cells and 5 tuners. By adjusting the insertion depths of the tuners, the tuning was achieved in merely one round of iteration. After tuning, the relative error of the peak field distribution and resonant frequency of the cavity reached to within ±3% and 325 ± 0.007 MHz (25°C, vacuum), respectively. It was verified that the field stability meets the requirement from the physical design both before and after tuning.

Physics design, fabrication, RF measurement and beam commissioning of a dual beam drift tube linac

A novel type dual-beam drift tube linac (DB-DTL) prototype was firstly designed to prove the feasibility of the multi-beam type DTL at the institute of modern physics. The physics design, cavity fabrication, low-power RF measurement, RF conditioning and beam commissioning of the DB-DTL cavity were completed and presented in this paper. Operating at 81.25 MHz, the DB-DTL was designed to accelerate 10 mA proton from 0.56 MeV to 2.5 MeV. The field distribution of the DB-DTL cavity were measured at low RF power level and particle tracing using measured field were done, which both agree well with the physics design. The measured Q 0 value and the shunt impedance are 11606 and 172 MΩ/m, respectively. The RF conditioning and the first beam commissioning of the DB-DTL cavity were completed. The beam experiment platform was built at the Lanzhou university due to the academy research cooperation between the institute of modern physics, Sun Yat-sen university and Lanzhou university. Based on the existing experiment condition, 2.5 MeV proton acceleration and measurement were successfully achieved at 42 kW (0.85*Q 0)) RF power of the DB-DTL cavity, which match the physics design very well.

Measurement based study of microwave double channel pHEMT device

ABSTRACT The paper presents the measurement study of a double channel pHEMT device. Its focus is on examining impacts of several parameters including probe pitch size, position and the applied pressure on the measurements. The impact of probe pitch size, position and applying suitable amount of pressure and more pressure than required on the measuring perspective of a double channel pHEMT was investigated. As noted from the collected data, these impacts are most likely related to the stability factor, current gain and maximum available gain of the studied microwave device. The measurement was done using two probes with pitch sizes of 200 µm and 150 µm, and the probes were placed in the middle of the device’s contact pads while exerting appropriate pressure. For double channel pHEMT on wafer, the outcome can be deemed similar for both pitch sizes. On the other hand, the probe with pitch size of 200 µm is utilised for applying more pressure than required where the probe occupied the entire pads of the device and the findings are skewed. Finally, it was found that the RF measurement is frequently affected by these conditions while the DC measurements are unaffected or have a minor effect.

Automated computation of radiographic parameters of distal radial metaphyseal fractures in forearm X-rays.

Radiographic parameters (RPs) provide objective support for effective decision making in determining clinical treatment of distal radius fractures (DRFs). This paper presents a novel automatic RP computation pipeline for computing the six anatomical RPs associated with DRFs in anteroposterior (AP) and lateral (LAT) forearm radiographs. The pipeline consists of: (1) segmentation of the distal radius and ulna bones with six 2D Dynamic U-Net deep learning models; (2) landmark points detection and distal radius axis computation from the segmentations with geometric methods; (3) RP computation and generation of a quantitative DRF report and composite AP and LAT radiograph images. This hybrid approach combines the advantages of deep learning and model-based methods. The pipeline was evaluated on 90 AP and 93 LAT radiographs for which ground truth distal radius and ulna segmentations and RP landmarks were manually obtained by expert clinicians. It achieves an accuracy of 94 and 86% on the AP and LAT RPs, within the observer variability, and an RP measurement difference of 1.4 ± 1.2° for the radial angle, 0.5 ± 0.6mm for the radial length, 0.9 ± 0.7mm for the radial shift, 0.7 ± 0.5mm for the ulnar variance, 2.9 ± 3.3° for the palmar tilt and 1.2 ± 1.0mm for the dorsal shift. Our pipeline is the first fully automatic method that accurately and robustly computes the RPs for a wide variety of clinical forearm radiographs from different sources, hand orientations, with and without cast. The computed accurate and reliable RF measurements may support fracture severity assessment and clinical management.

3D-printed dual-band energy harvester for WSNs in green IoT applications

This paper describes the 3D-printed open Double Square Loop (DSL) Frequency Selective Surfaces (FSSs) based Radio Frequency energy harvester specifically designed for the purpose of capturing Wi-Fi ambient RF energy. The proposed dual-band energy harvesting circuit is a suitable applicant for low-power green IoT Wireless Sensor Networks. The inclusion of FSS in the receiver improved the antenna’s gain by 42% and 74% at 2.4 GHz and 5.2 GHz, respectively, and consequently, enhanced the conversion efficiency. Due to FSS-backed dual-band antenna, the proposed configuration gathers a significant amount of RF ambient energy from the surroundings. The collected RF energy is then converted into DC voltage using a three-stage Villard RF rectifier cum multiplier. The Fused Deposition Modeling (FDM) of 3D printing is employed to create the designed prototype on a biodegradable Polylactic Acid substrate. RF measurements are taken with horn antenna and signal generator to evaluate the proposed design. At 2.4 GHz, the constructed prototype has a conversion efficiency of 67.90% and a corresponding output voltage of 2.36 V, whereas, at 5.2 GHz, it achieves an efficiency of 34.01% with output voltage of 1.67 V, at 0 dBm input power. The proposed configuration has a good correlation between simulated and measured outcomes.

A new design for the RF electron gun of the Iranian Light Source Facility (ILSF)

A new π mode RF electron gun is proposed for the Iranian Light Source Facility. This RF gun will be fabricated using a newly developed method based on clamping the parts together instead of vacuum brazing. In this method, RF contact and vacuum seal are mutually provided by a special copper gasket. The first section of this article describes the new π mode RF gun and its expected performance in detail. The report of our recent R&D tests on the new fabrication method is discussed in the next section. We performed the RF and vacuum measurements on a single-cell structure, and the copper gasket provided suitable RF contact, and a vacuum pressure of 2.5×10−7 mbar was also reached after 1 h of pumping with a turbo-molecular pump without baking. In the last section, we investigated using a high-current and low-emittance DC triode electron gun to be mounted on the RF gun as an alternative cathode assembly. The simulation results of this proposed scheme were compatible with our previous studies. The research and development of the new π mode RF electron gun and the proposed cathode assembly will begin soon.