Radio Frequency Input Power Research Articles

Ultrafast (≈10 GHz) mid-IR modulator based on ultrafast electrical switching of the light–matter coupling

We demonstrate a free-space amplitude modulator for mid-infrared radiation (λ ≈ 9.6 μm) that operates at room temperature up to at least 20 GHz (above the −3 dB cutoff frequency measured at 8.2 GHz). The device relies on the ultrafast transition between weak- and strong-coupling regimes induced by the variation of the applied bias voltage. Such transition induces a modulation of the device reflectivity. It is made of a semiconductor heterostructure enclosed in a judiciously designed array of metal–metal optical resonators, that—all-together—behave as an electrically tunable surface. At negative bias, it operates in the weak light–matter coupling regime. Upon application of an appropriate positive bias, the quantum wells populate with electrons, and the device transitions to the strong-coupling regime. The modulator transmission remains linear with input radio frequency power in the 0–9 dBm range. The increase in optical powers up to 25 mW exhibit a weak beginning of saturation a little bit below.

Dielectric‐Doped 2D Tellurium Diodes for Zero‐Bias Radio Frequency Power Detection

AbstractThis work presents a 2D tellurium (Te)‐based diode that exploits the doping achieved by atomic layer deposited (ALD) Al2O3 to enhance its rectifying performance. The proposed device comprises a Schottky junction that is dielectric‐doped to significantly reduce the reverse bias current. A boosted current responsivity four times higher compared to that of undoped devices is achieved, maximizing the performance for radio frequency (RF) power detectors. The application measurement results demonstrate sensitivities as low as −45 dBm, and at −30 dBm RF input power outstanding tangential responsivities up to 6.5 kV W–1, 4.3 kV W–1, and 650 V W–1 at 0.5, 1, and 2.5 GHz, respectively, while reaching linear dynamic range (DR) of over 30 dB. These are the highest reported values for 2D‐based material devices by almost two orders of magnitude. Furthermore, the DR is ≈10 dB larger compared to state‐of‐the‐art power detectors based on bulk semiconductors.

Absolute measurement of vacuum ultraviolet fluxes from inductively coupled plasmas via metal surface photoemission currents

Quantifying vacuum-ultraviolet (VUV) fluxes typically requires vacuum-compatible spectrometers and is often associated with significant cost and effort. A simple technique for the absolute measurement of local VUV fluxes from plasmas using the photoemission from a set of coated metal plates, is described. The radiant power from a 13.56 MHz hydrogen plasma operating at 40–87 mTorr and with an radio frequency (RF) input power from 100 to 120 W was investigated by irradiating a set of 2 cm diameter Au, Ag and Cu plates. The variation in photoemission currents was compared with the photoelectric yield curves to estimate the absolute flux incident on the surfaces in the 113–190 nm range. The measured fluxes were found to have an uncertainty of 5%–30% when compared with the VUV spectrometer measurements. The VUV output power was found to have a maximum at a pressure of 70–80 mTorr and to increase with RF power. In all cases, the VUV output power was measured to be approximately 12%–16% of the RF input power to the matching network, in good agreement with spectroscopy results.

Model-Optimizing Radiofrequency Parameters of 3D Finite Element Analysis for Ablation of Benign Thyroid Nodules.

Radiofrequency (RF) ablation represents an efficient strategy to reduce the volume of thyroid nodules. In this study, a finite element model was developed with the aim of optimizing RF parameters, e.g., input power and treatment duration, in order to achieve the target volume reduction rate (VRR) for a thyroid nodule. RF ablation is modelled as a coupled electro-thermal problem wherein the electric field is applied to induce tissue heating. The electric problem is solved with the Laplace equation, the temperature distribution is estimated with the Pennes bioheat equation, and the thermal damage is evaluated using the Arrhenius equation. The optimization model is applied to RF electrode with different active tip lengths in the interval from 5 mm to 40 mm at the 5 mm step. For each case, we also explored the influence of tumour blood perfusion rate on RF ablation outcomes. The model highlights that longer active tips are more efficient as they require lesser power and shorter treatment time to reach the target VRR. Moreover, this condition is characterized by a reduced transversal ablation zone. In addition, a higher blood perfusion increases the heat dispersion, requiring a different combination of RF power and time treatment to achieve the target VRR. The model may contribute to an improvement in patient-specific RF ablation treatment.

Wearable and long-range MXene 5G antenna energy harvester

Wireless and long-range energy transmission is an essential technology in the era of the Internet of Things, and currently it still relies on rigid and bulky metal antennas, which is incompatible with future wearable electronics. Here, we report a wearable and long-range MXene (Ti3C2Tx) 5G antenna energy harvester system that functions reliably as a wireless and battery-free power source for uninterrupted sensing and wireless data transmission. The MXene 5G antenna can efficiently harvest radio frequency (RF) electromagnetic energy at a 5G frequency range 1 band of 915 MHz, under a minimum input RF power density of 0.005 mW·cm−2, about 16 times lower than the threshold value for a control copper antenna. The device shows good mechanical bendability as it keeps over 99% power transfer efficiency at a bending angle of 90°. Our results open a new route for developing next-generation wireless powering for wearable electronics.

Highly sensitive spin-torque diodes based on in-plane magnetized magnetic tunnel junctions

We investigate the highly sensitive spin torque diode (STD) effect in a magnetic tunnel junction (MTJ) with an in-plane polarizer and an in-plane free layer. Under injection locking mechanisms, a high rectification voltage of 12 mV is obtained with an input radio frequency power of 1 μW under direct current bias current and a weak magnetic field, corresponding to a high sensitivity of 12 000 mV/mW. In addition, we use the nonlinear rectification characteristics of STD to mimic a neuron with a ReLU-like activation function to perform the recognition of handwritten digits in the Mixed National Institute of Standards and Technology database, where a produced accuracy of up to 93.53% is obtained. These findings suggest that the MTJ with in-plane magnetized electrodes holds promising potential in developing high sensitivity STDs for Internet of Things applications and neuromorphic computing.

A High-Power Capacity Transistor-Based Rectifier With Wide Input Power Range

This letter proposes a methodology for realizing the rectifier with a wide radio frequency (RF) input power range for large power capacity applications. The comprehensive analysis is given in this letter under the condition of class-F operation mode. The optimum conduction angle of the transistor corresponding to the maximum input power dynamic range is determined. Theoretical rectification efficiency of over 60% can be obtained in a 30 dB in-depth input power level. For validation, an RF-dc rectifier operating at 2.45 GHz is designed based on the GaN transistor. Measurements demonstrate that the rectification efficiency of between 60.4% and 82.1% is realized with a fixed dc load of 115 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $</tex-math> </inline-formula> when the RF input power is from 18 to 43 dBm. To the best of the authors’ knowledge, it is the first realization of a transistor-based RF-dc rectifier with a large input dynamic range of over 25 dB. The proposed rectifier shows great potential to be used in future high-power wireless power transfer (WPT) applications.

High-efficiency 2.45 and 5.8 GHz dual-band rectifier design with modulated input signals and a wide input power range

&lt;span lang="EN-US"&gt;This paper presents a new rectifier design for radio frequency (RF) energy harvesting by adopting a particular circuit topology to achieve two objectives at the same time. First, work with modulated input signal sources instead of only continuous waveform (CW) signals. Second, operate with a wide input power range using the Wilkinson power divider (WPD) and two different rectifier diodes (HSMS2852 and SMS7630) instead of using active components. According to the comparison with dual-band rectifiers presented in the literature, the designed rectifier is a high-efficiency rectifier for wide RF power input ranges. A peak of 67.041% and 49.089% was reached for 2.45 and 5.8 GHz, respectively, for CW as the input signal. An efficiency of 72.325% and 45.935% is obtained with a 16 QAM modulated input signal for the operating frequencies, respectively, 69.979% and 54.579% for 8PSK. The results obtained demonstrate that energy recovery systems can use modulated signals. Therefore, the use of a modulated signal over a CW signal may have additional benefits.&lt;/span&gt;

Magnetic and electric properties of spinel oxide CoV2O4 (001) films

The epitaxial film growth of CoV2O4 (CVO) on a MgO (001) substrate was successfully achieved using a reactive co-sputtering technique. To explore the conductive CVO films at RT, we grew the films under various conditions, including oxygen-gas flow rates and input radio-frequency power for each target. The Néel temperature of the film was approximately 160 K, which is consistent with previously reported values for bulk CVO. The film was found to be conductive over a wide temperature range and exhibited a negative resistivity temperature coefficient. The mechanism governing the temperature-dependent resistivity of the film can be explained using the one-dimensional variable range-hopping model, at least for temperatures higher than the Néel temperature. The CVO films exhibited a lattice constant close to that of spinel ferrites; therefore, they can be used as conductive buffer layers for electrodes in spintronic applications.

Electrical Characteristics of Gated Anode Diodes Based on Normally Off Recessed‐Gate GaN High‐Electron‐Mobility Transistors for Rectenna Applications

AlGaN/GaN high‐electron‐mobility transistor (HEMT)‐based gated‐anode diodes (GADs) for a 5.8 GHz rectenna application are proposed. An anode of the GAD is formed by connecting a gate and a drain of a normally off GaN HEMT. Herein, a wide recessed HEMT structure reported in the previous article is modified to a buried‐type recessed gate HEMT structure. The gate‐to‐cathode distance is optimized to maximize device performance. Typical direct current (DC) characteristics of the HEMTs are a threshold voltage (Vth) of +0.4 V and a maximum drain current (Imax) of 450 mA mm−1. GADs using the HEMTs show the characteristics of maximum forward current (If) of 600 mA mm−1and reverse breakdown voltage (BVr) of more than 100 V. The GAD using the recessed gate structure HEMT is shown to significantly improveIfandBVrsimultaneously compared to the previous work using the wide recessed gate structure. The rectifying performance of a bridge‐type rectifier simulated with SPICE model of the GAD shows radio frequency (RF)–DC conversion efficiency of 84% and RF input power of 13 W at 5.8 GHz using four GADs with each gate width (Wg) of 400 μm.

Prediction and optimization of thrust performance from plasma diagnostics in the inductively coupled plasma of an RF ion thruster

Ion thrusters have acquired extensive applications in the space industry with their advantages of high efficiency, high specific impulse, and long lifetime. To operate a radio-frequency (RF) ion thruster successfully, a high-frequency current must be generated to facilitate the discharge of inductively coupled plasma. In this study, with support of trial and error, it is discovered that the thrust performance of an RF ion thruster depends on not only the RF power but also on other critical parameters, such as the propellant flow rate, ion grids voltages, and RF input power. A surrogate model, namely – the Kriging model, is employed to simplify the estimation and optimization of thrust performance. The thrust and specific impulse are selected to be the crucial metrics for used Kriging models for categorizing all types of propulsions. On the basis of Kriging model simulations, the designed RF ion thruster can achieve a thrust of 1.9 mN, a specific impulse of 1649.5 s, and a thrust efficiency of 48% under a propellant flow rate of 4 sccm, grids’ voltage difference of 2500 V, and an RF input power of 40 W.

Wideband Power-Dependent Power Limiter Based on Distributed Low-Temperature Superconductor rf-SQUIDs for Cryogenic RF Receivers

A novel design of a radio-frequency (RF) power limiter for protecting sensitive superconductor receiver components from high-power microwave signals is presented. In this approach, two low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T} _{c}$ </tex-math></inline-formula> superconductor microstrip lines, one of which is coupled with an array of RF superconducting quantum interference devices (rf-SQUIDs), are combined with a pair of hybrid couplers to provide the power limiting operation at very low RF power levels. The key concept is built on the fact that a microstrip line coupled to an array of rf-SQUIDs behaves as a power-dependent phase shifter and its phase can be controlled by the input RF power. This phenomenon is exploited to achieve the desired RF power-limiting operation. The device is fabricated using an eight-layer niobium-based superconducting process node SFQ5ee by MIT Lincoln Laboratory (MIT-LL). A monolithically integrated wideband hybrid coupler is used in this design as it dictates the bandwidth of the overall device. The operating frequency of the power limiter is 10 GHz with a 2-GHz bandwidth. The performance of the device is measured for input RF power levels ranging from −30 to +10 dBm, as well as arising intermodulation products are experimentally investigated. The output power increases linearly with the input power up to −15 dBm, and for higher power levels, the device offers an increasing attenuation to limit the output RF power starting above −15 dBm.

Closed-Loop Composite Welding and Bonding System Using Radio-Frequency Heating and Pressure

Polymer parts often replace traditional metallic parts in load-bearing applications due to their high strength-to-weight ratio, with thermoplastics at the forefront. Conventional manufacturing processes rely on using fasteners or adhesives to hold composite assemblies together, but thermoplastics can be welded together. Ultrasonic welding is widely used but becomes challenging for complex geometries, and new parameters need to be developed for different polymers and specimen geometries. In this work, we developed a closed-loop welding machine that employs the recent discovery of radio-frequency (RF) heating of carbonaceous materials. The machine is successfully able to weld polylactic acid (PLA) coupons with graphitic RF susceptors at the bondline in less than 2 min and using less than 50 W of input RF power. We found that a higher areal density of the graphitic paint lowers the mechanical properties of the weld because the carbonaceous materials hinder polymer chain diffusion. A significant change was not observed in weld properties for welding pressure ranges between 0 and 0.3 MPa. However, increasing out-of-plane welding displacement increased the modulus and strength of the weld. This work provides an interesting new automated system for welding polymer composites using RF fields, with potential applications in various manufacturing industries.

Photonic-assisted multi-frequency measurement based on frequency-to-power mapping and serial channelization

A novel photonic approach to multi-frequency measurement based on frequency-to-power mapping and serial channelization is proposed and demonstrated. In this proposal, a light wave from a laser diode (LD) is split into two branches. In the upper branch, a dual-port Mach–Zehnder interferometer (MZI) is used to perform frequency-to-power mapping. While in the lower branch, an optical wavelength scanner based recirculating frequency shifting (RFS) loop is used to generate multiple serial optical local oscillators (LOs) to down-convert the outputs of the dual-port MZI at the corresponding time window. Therefore, the unknown radio-frequency (RF) frequencies can be unambiguously estimated by the multiple monotonous amplitude comparison functions (ACFs) obtained from the power ratios between two down-converted electrical signals. Only two low-frequency photodetectors (PDs) with narrow bandwidth are employed, which guarantees a simple structure and low cost. In addition, the proposal has robustness to the bias drift of the MZM and input RF power. Simulation results indicate that the multi-frequency identification within 5 μs is achieved over the measurement range up to 19 GHz with an accuracy better than ± 20 MHz. Furthermore, the system is easily extended to higher frequency and larger bandwidth (e.g., 100 GHz).

Far-Field Wireless Power Transfer for the Internet of Things

A complete end-to-end far-field wireless power transfer (WPT) is proposed and studied in this paper for the application of the Internet of Things (IoT) at the industrial, scientific, and medical (ISM) band of 2.4 GHz. The radiative WPT has achieved a remarkable attraction for the capability to transfer power in the long range. We propose two approaches. In the first approach, a 2×4 microstrip patch transmitter antenna array with a high gain and a narrow beamwidth is proposed that is rotated toward the IoT device using a small stepper motor. The performance of the rectifier in the receiving circuit was separately analyzed, and 17.54% efficiency was achieved with a load of 0.6 kΩ for the circuit, while the input power was 10 dBm. The overall system test was performed and the targeted result was investigated considering the distance between the transmitter and the receiver, and an input radio frequency (RF) power of 5 dBm to 15 dBm at 2.4 GHz. The second approach uses a 1×4 transmitter antenna array fed through a Butler matrix to provide four individual beams with a 22.5∘ angular separation, and 90∘ total angular coverage. The goal was to focus the power into four angular locations and to reduce the power waste in other directions. A mobile app was developed to control the direction of the beam. A system efficiency of as much as 19% was measured for an input RF power of 0 dBm and a resistive load of 62 kΩ.

High kinetic inductance NbTiN superconducting transmission line resonators in the very thin film limit

We examine the DC and radio frequency (RF) response of superconducting transmission line resonators comprised of very thin NbTiN films, &amp;lt;12 nm in thickness, in the high-temperature limit, where the photon energy is less than the thermal energy. The resonant frequencies of these superconducting resonators show a significant nonlinear response as a function of RF input power, which can approach a frequency shift of Δf=−0.15% in a −20 dB span in the thinnest film. The strong nonlinear response allows these very thin film resonators to serve as high kinetic inductance parametric amplifiers.

Planar cw N2O laser with RF excitation

The article presents the results of studying and optimizing the output power and spectral characteristics of radiation of a sealed-off continuous wave (cw) planar N2O laser depending on the input radio frequency power and the size of the interelectrode gap in the discharge, on the composition and pressure of the working gas mixture N2O:N2:He:Xe, on the time of continuous operation of the laser. The effect of adding carbon monoxide CO to the working gas mixture is discussed. The maximum values of the output power—17.5 W and the efficiency—7.3% were obtained in a sealed-off cw N2O laser, which significantly exceed the known values. When N2 was replaced by air in the gas mixture: N2O:Air:He:Xe = 2.3:2.3:5:0.4, the laser output power was 10.6 W. The radiation powers of N2O and CO2 lasers are 13.1 W and 18.6 W, respectively, when the working mixture in the emitter is replaced and the same operating conditions are applied—the input power is 180 W and the pressure of the working gas mixture is 30 Torr.

Dual-Mode RF Mixer for Low-Power Direct-Conversion Receiver

In this work, a dual-mode (DM) radio frequency (RF) mixer is studied and validated over the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -band to meet the ultralow-power requirement of direct-conversion receiver architectures. The proposed RF mixer combines two operation modes, namely, RF energy harvesting mode and RF mixing mode, which are implemented within a single passive multiport interferometric circuit. This approach aims at harvesting part of the RF energy for powering specific low-power active devices toward the energy autonomy of RF receiver systems. For this proof-of-concept study, a circuit is prototyped and tested. The experimental results show promising performance. Inter-port isolation better than 20 dB is achieved over a frequency range of 22–26 GHz, together with good RF-to-dc conversion efficiency (up to 45% with RF input power of 40 mW), and appreciable RF mixer conversion loss over a wideband (average 12.8 dB).

Power-Efficient Passive Beamforming and Resource Allocation for IRS-Aided WPCNs

This paper studies an intelligent reflecting surface (IRS)-assisted wireless-powered communication network (WPCN), where a hybrid access point (HAP) broadcasts energy signals to multiple devices for their energy harvesting in the downlink (DL) and then the devices use the harvested energy to transmit information signals to the HAP in the uplink (UL) with the help of an IRS. In particular, we propose three types of IRS beamforming configurations, namely <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fully dynamic IRS beamforming (FDBF)</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">partially dynamic IRS beamforming (PDBF)</i> , and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">static IRS beamforming (SBF)</i> , to strike a balance between the system performance and signaling overhead as well as implementation complexity. Moreover, we adopt a practical non-linear energy harvesting (EH) model, and leverage a power-splitting (PS) EH receiver architecture with multiple rectifiers to avoid the input radio frequency power to get stuck into the saturation regime. We aim to minimize the transmit energy consumption at the HAP by jointly optimizing the DL/UL time allocation, the HAP/devices transmit power, the PS factor, and IRS phase shifts, subject to a set of minimum throughput requirements for individual devices. To address the resulting non-convex optimization problems, a successive convex approximation (SCA) based alternating optimization algorithm is proposed. Moreover, we study the case with the ideal linear EH model and two algorithms, namely SCA-based algorithm and semidefinite relaxation (SDR) algorithm, are proposed. Simulation results demonstrate the effectiveness of our proposed designs over various benchmark schemes and also unveil the importance of the joint design of IRS beamforming and PS rectifiers for achieving energy efficient WPCNs in practice.

Soundness evaluation of J-PARC RF ion source after 5-month continuous operation

In the J-PARC user operation from Nov. 2020 – Apr. 2021, continuous operation of J-PARC Radio Frequency (RF) negative hydrogen ion (H-) source up to 3,651 hours (5 months) has been achieved. The ion source was operated with the output H- current of 60 mA, the duty factor (for plasma generation) 2% and the input RF power up to 30 kW. After the operation, phase space diagrams at the Radio Frequency Quadrupole linac (RFQ) entrance were measured by the emittance monitor at the ion source test stand (IS-TS) under the same operation condition as in the J-PARC Linac. Comparison of the phase spaces and the beam emittances between the ion sources in the present and the previous operations shows slight difference. From the direct observation of the antenna coil, no exhaustion or the decrease in the thickness of the enamel coating of the coil have been confirmed. The results indicate the possibility of the next goal of the long-run up to 7 months, which is the same as the full duration of the J-PARC user operation in 1 year.