RF Response Research Articles

Monitoring and Control of MEMS Tunable Filters Using Inductive Proximity Sensing

This paper presents a monitoring and control system for MEMS tunable evanescent-mode cavity filters. Inductive proximity sensing is utilized to detect the deflection of the tuning MEMS membrane. The sensed deflection is used as a feedback for a closed-loop control of the MEMS bias voltage to deliver the desired deflection and, hence, desired RF response based on an input from the user. The sensing spiral inductor also functions as an electrode for the electrostatic actuation of the membrane. The presented system is analyzed, optimized, and experimentally implemented on a bandstop filter tunable in the 30–42-GHz range. The measured results show that the system is capable of tuning the filter to the desired response with good repeatability of notch frequency (less than 1% error) and with stable long-term response (better than 1.6% drift), which falls within the 20-dB bandwidth of the filter.

A novel bioavailable hydrogenated curcuminoids formulation (CuroWhite™) improves symptoms and diagnostic indicators in rheumatoid arthritis patients - A randomized, double blind and placebo controlled study

Rheumatoid arthritis (RA) is an inflammatory disease that cause chronic pain, disability and joint destruction. The present placebo controlled randomized study aimed to evaluate the efficacy of a novel hydrogenated curcuminoid formulation-CuroWhite™, in rheumatoid arthritis (RA) patients. Twenty four RA patients were randomized in 1:1:1 ratio to receive 250 mg, 500 mg CuroWhite or placebo as one capsule a day, over a period of three months. Improvement in the ACR response, changes in disease activity assessed using the DAS 28 score, change in physical function assessed on change in ESR, CRP, RF values were evaluated before and after the study. Results suggested that patients who received CuroWhite both low and high doses reported statistically significant changes in their clinical symptoms towards end of the study when compared with placebo. There were significant changes in DAS28 (50–64%) VAS (63–72%) ESR (88–89%), CRP (31–45%) RF (80–84%) values and ACR response for CuroWhite groups in comparison with placebo. Thus, CuroWhite acts as the analgesic and anti-inflammatory product for management of RA by the reduction of the inflammatory action which was confirmed by improvement in ESR, CRP, VAS, RF, DAS-28 and ACR responses. CuroWhite was significantly effective against RA with highly safe without serious side effects and well tolerated.

Design, fabrication and characterization of SAW devices on LiNbO3 bulk and ZnO thin film substrates

In this paper, surface acoustic wave (SAW) devices with various designs were fabricated on two types of piezoelectric substrates of LiNbO3 bulk material and thin piezoelectric ZnO film on silicon. Different sizes, orientation and types of SAW devices were laid out on the same mask to compare their RF performance with a same fabrication. Devices were fabricated using lift-off technology with a double photoresist technique to achieve a steeper and narrower SAW pattern with a depth-to-width ratio of 1.27 and a steep resist angle of 85°. The devices were then characterized using RF probe station together with vector network analyzer. RF performance was also verified by 2D computer simulation implementing both electrical and piezoelectric physics models using the same device dimensions in the mask layout. RF response of 128°Y LiNbO3 from experiments agrees with simulation fairly well while the devices on ZnO/Si have larger frequency distribution due to process variation of the ZnO thin film on silicon wafer. Quality factor of 34,000 was obtained from the SAW device fabricated in LiNO3 substrate and this Q value has a strong dependency on the numbers electrodes of IDT fingers and reflectors. Temperature dependency was also measured for future wireless sensor application. The temperature coefficient of frequency of 16 μm wavelength devices of LiNbO3 substrate was −87.5 ppm/°C and was −72.41 ppm/°C for 12 μm wavelength devices.

Improved broadband (75–110 GHz) radio frequency characteristics of MEMS shunt switches on quartz substrate

This paper presents improved W-band (75–110 GHz) radio frequency characteristics of micro-electromechanical switches in T and π-matched configurations. The switch structures consist of Au metallic bridge (s) suspended over the coplanar waveguide (CPW) signal line drawn on quartz substrate. Here, a high impedance transmission line is introduced on both the sides of the bridge structure to reduce the return loss. To further tune up the broadband RF response the bridge width (40–80 µm) as well the dielectric thickness (0.15–0.18 µm) are varied. At optimum condition (bridge width: 60 µm; dielectric thickness: 0.18 µm), the T-matched RFMEMS switch structure exhibits return loss better than − 20 dB; insertion loss ~ − 0.2 dB and isolation better than − 30 dB in full W-band frequency range. In π-match configuration, a short section of high impedance transmission line is being introduced between two switch structures for impedance matching. RF parameters of the π-matched shunt switch structure are studied as a function of width (10–40 µm) and length (30–180 µm) of the high impedance transmission line. At optimum condition (line width: 30 µm; length: 130 µm), the π-matched switch structure exhibits return loss: better than − 15 dB; insertion loss: better than − 0.5 dB; and isolation: better than − 45 dB over the entire W-band. From the equivalent circuit modeling, the equivalent inductance, capacitance and resistance values for the optimized switch structures are also reported.

On characterization of symmetric type capacitive RF MEMS switches

This paper presents the design, fabrication and characterization of capacitive type MEMS switch for space and terrestrial communication applications. The deviation in measured actuation voltage and RF response of the switches are discussed in terms of the process variation which occurred unintentionally during the fabrication of devices. For example the measured actuation voltage is 15 V, about 20% higher than the designed voltage of 12.25 V. The deviation corresponds to the increase in thickness of the membrane while electroplating. The impact of process parameters on mechanical resonance frequency of the switches, and on/off time is also discussed. Measured S-parameters shows isolation of > − 20 dB for 7–16 GHz and an insertion loss better than − 0.6 dB up to 20 GHz. The capacitance ratio of the fabricated switch is 77, which is 15% lower than the designed capacitance ratio. The switch has been tested for 1 million 65 thousand cycles without switching failure. The deviation of simulated and measured results is discussed in the following sections.

On the origin of rheumatoid factors: Insights from analyses of variable region sequences

ObjectivesRheumatoid factors (RFs) are thought to play an important role in rheumatoid arthritis (RA), but are also found in healthy donors (HDs). Previous studies examined variable region sequences of these autoantibodies at a time when knowledge of the human germline repertoire was incomplete. Here we collected and analyzed RF sequence data from the literature to elucidate how RFs develop and whether their characteristics differ between RA patients and HDs. MethodsA database was built containing nucleotide sequences of RF heavy and light chain variable domains and characteristics including affinity, isotype and specificity, all collected from published papers. Gene usage and mutation frequencies were analyzed using IMGT/HiV-QUEST. Selection strength was assessed with the BASELINe tool. ResultsSequences were retrieved for 183 RF clones (87 RA; 67 HDs; 29 other). No biased gene usage was observed for RA and HDs. However, there does appear to be skewed gene usage in RFs from patients with mixed cryoglobulinemia. Mutation frequency varies considerably between RFs, and isotype-switched clones have significantly more mutations. Monospecific RFs carry more mutations than polyspecific RFs; no difference was found for RA- versus HD-derived RFs. Overall, reported affinity is low (median 1 µM), with a non-significant trend toward higher affinity of RA-derived RFs. Mutation frequency and affinity did not appear to be correlated. BASELINe analysis suggests an overall lack of positive selection and less negative selection strength in RA-derived RFs. ConclusionsRFs derived from RA patients have similar properties as those derived from HDs. The RF response can be characterized as a moderately matured autoantibody response, with variable levels of somatic hypermutation, but low affinity.

MRI-based, wireless determination of the transfer function of a linear implant: Introduction of the transfer matrix.

PurposeWe introduce the transfer matrix (TM) that makes MR‐based wireless determination of transfer functions (TFs) possible. TFs are implant specific measures for RF‐safety assessment of linear implants. The TF relates an incident tangential electric field on an implant to a scattered electric field at its tip that generally governs local heating. The TM extends this concept and relates an incident tangential electric field to a current distribution in the implant therewith characterizing the RF response along the entire implant. The TM is exploited to measure TFs with MRI without hardware alterations.Theory and MethodsA model of rightward and leftward propagating attenuated waves undergoing multiple reflections is used to derive an analytical expression for the TM. This allows parameterization of the TM of generic implants, e.g., (partially) insulated single wires, in a homogeneous medium in a few unknowns that simultaneously describe the TF. These unknowns can be determined with MRI making it possible to measure the TM and, therefore, also the TF.ResultsThe TM is able to predict an induced current due to an incident electric field and can be accurately parameterized with a limited number of unknowns. Using this description the TF is determined accurately (with a Pearson correlation coefficient R ≥ 0.9 between measurements and simulations) from MRI acquisitions.ConclusionThe TM enables measuring of TFs with MRI of the tested generic implant models. The MR‐based method does not need hardware alterations and is wireless hence making TF determination in more realistic scenarios conceivable.

Investigation and statistical modeling of InAs-based double gate tunnel FETs for RF performance enhancement * * Project supported by the Department of Science and Technology, Government of India under SERB Scheme (No. SERB/F/2660).

In this paper, RF performance analysis of InAs-based double gate (DG) tunnel field effect transistors (TFETs) is investigated in both qualitative and quantitative fashion. This investigation is carried out by varying the geometrical and doping parameters of TFETs to extract various RF parameters, unity gain cut-off frequency (ft), maximum oscillation frequency (fmax), intrinsic gain and admittance (Y) parameters. An asymmetric gate oxide is introduced in the gate-drain overlap and compared with that of DG TFETs. Higher ON-current (ION) of about 0.2 mA and less leakage current (IOFF) of 29 fA is achieved for DG TFET with gate-drain overlap. Due to increase in transconductance (gm), higher ft and intrinsic gain is attained for DG TFET with gate-drain overlap. Higher fmax of 985 GHz is obtained for drain doping of 5 × 1017 cm−3 because of the reduced gate-drain capacitance (Cgd) with DG TFET with gate-drain overlap. In terms of Y-parameters, gate oxide thickness variation offers better performance due to the reduced values of Cgd. A second order numerical polynomial model is generated for all the RF responses as a function of geometrical and doping parameters. The simulation results are compared with this numerical model where the predicted values match with the simulated values.

Pulsed Sagnac Loop Phase-Modulated Microwave Photonic Link

We present a novel Sagnac loop phase-modulated microwave photonic link with a pulsed optical source. Unlike a conventional Sagnac loop, the optical phase offset of the loop can be adjusted to quadrature by applying a synchronized modulation signal to an in-loop phase shifting phase modulator. Thereby, it exemplifies the fundamental RF response. With balanced detection, a proof-of-concept link demonstrated an output noise floor of −164 dBm/Hz, which is ~4 dB above the shot noise floor, and a spurious free dynamic range of 104.8 dB Hz2/3.

RF and microwave dielectric response investigation of high-k yttrium copper titanate ceramic for electronic applications

The dielectric properties of YCTO bulk capacitors were investigated as a function of temperature from 25°C to 150°C and at microwave frequencies in comparison to a SiO2 bulk sample. The results confirm the high-k character of the YCTO ceramic, in addition to the low AC conductivity, namely ε′ = 40.1 and σ = 6×10−8Scm−1 at 1MHz, and show a weak frequency and temperature (25°C–150°C) dependence. A temperature coefficient value of −601ppm°C−1 for the dielectric constant (TCε′) was estimated at 100kHz. In the GHz regime, a comparison with bulk SiO2 confirms the higher YCTO dielectric permittivity. These results demonstrate high-k YCTO ceramic as a very promising material with high potentiality for electronic applications.

Imaging the paramagnetic nonlinear Meissner effect in nodal gap superconductors

Boundary surfaces of nodal gap superconductors can host Andreev bound states (ABS) which develop a paramagnetic response under external RF field in contrast to the bulk diamagnetic response of the bulk superconductor. At low temperature this surface paramagnetic response dominates and enhances the nonlinear RF response of the sample. With a recently developed photoresponse imaging technique, the anisotropy of this "paramagnetic" nonlinear Meissner response, and its current direction (angular) and RF power dependence has been systematically studied. A theoretical model describing the current flow in the surface paramagnetic Andreev bound state, the bulk diamagnetic Meissner state, and their response to optical illumination is proposed and it shows good agreement with the experimental results.

The conceptual design of high temporal resolution HCN interferometry for atmospheric pressure air plasmas

A heterodyne interferometer operating at the frequency f = 890 GHz has been designed for measuring the electron density of atmospheric pressure air plasmas, it's density range is from 1015 to 3×1019 m−3 and the pressure range is from 1 Pa to 20 kPa. The system is configured as a Mach\ obreakdash-Zehnder type interferometer. The light source is hydrogen cyanide (HCN) laser with a wavelength of 337 μm, which is suitable for the high density area, 1018 to 3×1019 m−3, of atmospheric pressure air plasmas. The HCN laser power is up to 100 mW. The intermediate frequency, shifted by 500 kHz, is generated by the Doppler shift with a high speed rotating grating (HSRG), which is installed in a vacuum vessel with gas pressure less than 1 Pa. With the HSRG, the temporal resolution of the HCN interferometry can reach to 2 μs. Beam path analysis based on Gaussian optics is used in the design of the optical system. The VDI planar-diode Integrated Conical Horn Fundamental Mixers optimized for high sensitivity—typical RF responsivity is around 900 V/W —will be used in the HCN interferometry. The detailed optical design and opto-mechanical design for the HCN interferometry are presented.

High-performance and high-reliability SOT-6 packaged diplexer based on advanced IPD fabrication techniques

A diplexer offering the advantages of compact size, high performance, and high reliability is proposed on the basis of advanced integrated passive device (IPD) fabrication techniques. The proposed diplexer is developed by combining a third-order low-pass filter (LPF) and a third-order high-pass filter (HPF), which are designed on the basis of the elliptic function prototype low-pass filter. Primary components, such as inductors and capacitors, are designed and fabricated with high Q-factor and appropriate values, and they are subsequently used to construct a compact diplexer having a chip area of 900μm×1100μm (0.009 λ0×0.011 λ0, where λ0 is the guided wavelength). In addition, a small-outline transistor (SOT-6) packaging method is adopted, and reliability tests (including temperature, humidity, vibration, and pressure) are conducted to guarantee long-term stability and commercial success. The packaged measurement results indicate excellent RF performance with insertion losses of 1.39dB and 0.75dB at operation bands of 0.9GHz and 1.8GHz, respectively. The return loss is lower than 10dB from 0.5GHz to 4.0GHz, while the isolation is higher than 15dB from 0.5GHz to 3.0GHz. Thus, it can be concluded that the proposed SOT-6 packaged diplexer is a promising candidate for GSM/CDMA applications. Synthetic solution of diplexer design, RF performance optimization, fabrication process, packaging, RF response measurement, and reliability test is particularly explained and analyzed in this work.

Impactful study of dual work function, underlap and hetero gate dielectric on TFET with different drain doping profile for high frequency performance estimation and optimization

This manuscript presents a comparative study of different combination for the dual workfunction gate material, underlap and hetero gate dielectric tunnel field-effect transistors (TFET’s). Their performances have been analyzed in terms of ON-state current, ambipolar behaviour and RF response along with different drain doping profile. For this, the Dual work function of gate provides enhancement in ON-state current by reducing the tunnel barrier width at source/channel interface. Whereas, the underlap of gate is done near to the drain region, helps in reduction of ambipolar conduction by creating deficiency of hole for the conduction, which is major hurdle for TFET. Further, the combinations of the dual workfunction and underlap give combine advantages of both such as improve ON-state current and suppressed ambipolar current. Apart from this, the combination of hetero gate dielectric dual workfunction under lapping leads to superior device performance in terms of ON-state current and ambipolar behaviour. The use of hetero gate dielectric and Gaussian doping profile with gate underlap reduces the gate to drain capacitance that also improves the RF parameters of the device.

2D SQIF arrays using 20 000 YBCO high Rn Josephson junctions

Superconducting quantum interference filters (SQIFs) have been created using two dimensional arrays of YBCO step-edge Josephson junctions connected together in series and parallel configurations via superconducting loops with a range of loop areas and loop inductances. A SQIF response, as evidenced by a single large anti-peak at zero applied flux, is reported at 77 K for step-edge junction arrays with the junction number N = 1 000 up to 20 000. The SQIF sensitivity (slope of peak) increased linearly with N up to a maximum of 1530 V T−1. Array parameters related to geometry and average junction characteristics are investigated in order to understand and improve the SQIF performance in high temperature superconducting arrays. Initial investigations also focus on the effect of the SQUID inductance factor on the SQIF sensitivity by varying both the mean critical current and the mean inductance of the loops in the array. The RF response to a 30 MHz signal is demonstrated.

Remote magnetic resonance sounding for exploration of pore space microstructure and aquifer macrostructure

Proton nuclear magnetic resonance is a type of nuclear magnetic resonance (NMR), which is widely used to detect hydrogen containing liquids, like water or hydrocarbons. The use of the Earth’s magnetic field allows remote detection of fluids sub surface without generating an independent magnetic field that is expensive and complex enough to apply. An important feature of NMR in the Earth’s field is that the signals produced by snow and ice are generally unobservable under experimental conditions created for liquid water prospecting. The characteristics of the RF response are associated with the molecular environment of the nuclei. This allows detecting NMR signals of water in pores of various size.

Design Aspects of a New Reliable Torsional Switch with Excellent RF Response

This paper proposes a metal contact RF MEMS switch which utilizes a see-saw mechanism to acquire a switching action. The switch was built on a quartz substrate and involves vertical deflection of the beam under an applied actuation voltage of 5.46 volts over a signal line. The see-saw mechanism relieves much of the operation voltage required to actuate the switch. The switch has a stiff beam eliminating any stray mechanical forces. The switch has an excellent isolation of −90.9 dB (compared to − 58 dB in conventional designs ), the insertion of −0.2 dB, and a wide bandwidth of 88 GHz (compared to 40 GHz in conventional design ) making the switch suitable for wide band applications.

InP-Based Waveguide Triple Transit Region Photodiodes for Hybrid Integration with Passive Optical Silica Waveguides

We report on a novel InP-based 1.55 μm waveguide triple transit region photodiode (TTR-PD) structure for hybrid integration with passive optical silica waveguides. Using the beam propagation method, numerical analyses reveal that, for evanescent optical coupling between a passive silica waveguide and the InP-based waveguide TTR-PD, a coupling efficiency of about 90% can be obtained. In addition to that, an absorption of about 50% is simulated within a TTR-PD length of 30 µm. For fabricated TTR-PD chips, a polarization dependent loss (PDL) of less than 0.9 dB is achieved within the complete optical C-band. At the operational wavelength of 1.55 µm, a reasonable PDL of 0.73 dB is measured. The DC responsivity and the RF responsivity are achieved on the order of 0.52 A/W and 0.24 A/W, respectively. Further, a 3 dB bandwidth of 132 GHz is experimentally demonstrated and high output-power levels exceeding 0 dBm are obtained. Even at the 3 dB cut-off frequency, no saturation effects occur at a photocurrent of 15.5 mA and an RF output power of −4.6 dBm is achieved. In addition to the numerical and experimental achievements, we propose a scheme for a hybrid-integrated InP/silicon-based photonic millimeter wave transmitter.

IgG Subclass Specificity Discriminates Restricted IgM Rheumatoid Factor Responses From More Mature Anti-Citrullinated Protein Antibody-Associated or Isotype-Switched IgA Responses.

To investigate the presence and patterns of specific IgG subclass recognition by IgM rheumatoid factor (IgM-RF) and IgA-RF with a newly developed enzyme-linked immunosorbent assay (ELISA), which can discriminate between polyspecific and restricted RF responses. Polyspecific and restricted RF responses were determined with our ELISA, which uses individually coated recombinant IgG subclasses instead of polyclonal IgG as target antibodies. Fine specificity was determined using target antibodies with single amino acid mutations in the Fc region. In a screening panel of 93 sera that were previously found to be IgM-RF positive in a conventional RF assay, we were able to discriminate between sera with polyspecific IgM-RF responses (i.e., RF responses directed against all 4 IgG subclasses) and those with restricted IgM-RF responses, with low or absent relative reactivity against IgG2, IgG3, or IgG4. We found the largest variation for anti-IgG3 reactivity. Samples without detectable anti-IgG4 reactivity formed an independent group from the other restricted RF responses and the polyspecific RF responses. The specificity of these anti-IgG4-negative sera could be pinpointed to single amino acid differences between IgG1 and IgG4. Polyspecific RF responses more often showed signs of RF response maturation, with more isotype switching to IgA-RF, as compared to restricted RF responses. In a cohort of IgM-RF+ and/or anti-citrullinated protein antibody (ACPA)-positive arthralgia patients, we found restricted RF responses in 35% (49 of 140) of RF+/ACPA- patients, while RF+/ACPA+ patients, who have a much higher risk of developing rheumatoid arthritis, virtually always (123 of 128 [96%]) showed a polyspecific RF response. IgG subclass-specific RF distinguishes between immature restricted RF responses and potentially more pathogenic, ACPA-associated polyspecific responses.

Enhanced two dimensional electron gas transport characteristics in Al2O3/AlInN/GaN metal-oxide-semiconductor high-electron-mobility transistors on Si substrate

The authors report on Al2O3/Al0.85In0.15N/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor (MOS-HEMT) on Si fabricated by using atomic layer deposited Al2O3 as gate insulator and passivation layer. The MOS-HEMT with the gate length of 2 μm exhibits excellent direct-current (dc) characteristics with a drain current maximum of 1270 mA/mm at a gate bias of 3 V and an off-state breakdown voltage of 180 V for a gate-drain spacing of 4 μm. Also, the 1 μm-gate MOS-HEMT shows good radio-frequency (rf) response such as current gain and maximum oscillation cut-off frequencies of 10 and 34 GHz, respectively. The capacitance-voltage characteristics at 1 MHz revealed significant increase in two-dimensional electron gas (2DEG) density for the MOS-HEMT compared to conventional Schottky barrier HEMTs. Analyses using drain-source conductivity measurements showed improvements in 2DEG transport characteristics for the MOS-HEMT. The enhancements in dc and rf performances of the Al2O3/Al0.85In0.15N/GaN MOS-HEMT are attributed to the improvements in 2DEG characteristics.