Frequency Range Research Articles

Hybridization of Cockcroft-Walton and Dickson Voltage Multipliers for Maximum Output Through Effective Frequency Dedication in Harvesting Radio Frequency Energy

Objective: This study investigates solutions to the challenges of limited RF energy harvesting by designing a hybridized voltage multiplier system aimed at optimizing output across a wide frequency range. Theoretical Framework: The research centers on the principles and comparative efficiencies of the Cockcroft-Walton and Dickson voltage multipliers, known for their applications in RF energy harvesting. These multipliers’ performance was analyzed theoretically to guide a hybrid design that could adaptively respond to input frequency variations. Method: Voltage multipliers were designed and simulated in Multisim, with further analysis in MATLAB. Both the Cockcroft-Walton and Dickson voltage multipliers were subjected to a constant input of 1V across frequencies from 50 Hz to 5 GHz to assess their respective efficiencies. Subsequently, a hybrid voltage multiplier system was developed, combining an 8-stage Cockcroft-Walton and an 8-stage Dickson multiplier. A fast Fourier transform (FFT) frequency-selective algorithm, implemented in MATLAB, dynamically directed input voltages to the optimal multiplier based on frequency. Results and Discussion: Results showed that the Dickson multiplier excelled in the lower frequency range (50 Hz to 1 MHz), achieving a maximum output of 14.763V at 5 kHz and 10 kHz. In contrast, the Cockcroft-Walton multiplier was more effective in the higher frequency range (1 MHz to 5 GHz), reaching a peak output of 6.671V at 5 GHz. The hybrid system demonstrated efficient, frequency-dependent voltage multiplication and aligned well with anticipated performance metrics, suggesting an improvement in RF energy harvesting across the tested frequency range. Research Implications: This work contributes to the field of RF energy harvesting by introducing a frequency-adaptive system that enhances voltage output through targeted frequency routing. The results underscore the potential for hybrid designs to overcome limitations associated with individual voltage multipliers, presenting a versatile approach to harvesting RF energy effectively across broad frequency spectra. Originality/Value: By implementing a hybrid approach with a frequency-selective algorithm, this study offers an innovative solution for frequency-dependent RF energy harvesting. The findings provide a foundation for future research into adaptable energy harvesting systems that optimize voltage output across diverse frequencies, with practical implications for RF-powered devices and wireless energy transfer applications.

Low-noise soliton molecule generation with an in-phase controllable pulse number by third- and second-order dispersion compensation in an all-fiber erbium-doped oscillator

We report on the experimental results of high-order soliton molecule (SM) generation in an erbium-doped oscillator. The generation of 14 solitons with an average power of 48 mW, a pulse duration of 508 fs, a separation of 2.59 ps between pulses, and a repetition rate of 19 MHz at 1560 nm central wavelength was demonstrated. The stability of this generation was also evidenced by its low relative intensity noise (0.08% in the frequency range [10 kHz–1 MHz]), and a low Allan deviation of frequency repetition rate of 1.98⋅10−9 at an interval of 1 s (during 10 h of free-running measurements). Moreover, the accurate manipulation of SM order by changing the pump power was investigated; we showed the ability to generate with four, six, seven, nine, 10, 11, 13, and 14 pulses with high stable states between solitons. The change in the number of pulses occurred repeatably by increasing and decreasing the pump power, offering a stable source of a controllable number of pulses for potential applications in quantum computing.

Investigation of Charge Transfer Mechanism and Dielectric Relaxation in CsCdCl3 Perovskite

ABSTRACTThe exceptional optoelectronic capabilities of all‐inorganic metal halide perovskite semiconductor components open up a multitude of possible applications. Among all the metal halides, the chloride of cesium cadmium has not been investigated in great detail. Here, we describe a straightforward method for creating CsCdCl3 perovskite single crystals using the slow evaporation solution growth approach. These were investigated by utilizing X‐ray powder diffraction, and optical and impedance spectroscopies. The creation of a single‐phase with a hexagonal‐type structure was verified by the X‐ray powder diffraction (XRPD) data. The compound's semiconductor characteristics were verified by the optical measurement, indicating a direct band‐gap value of about 3.16 eV. The absorption and reflectance spectrum was also used to calculate and explain the optical extinction coefficient, Urbach energy, and skin depth as functions of the input photon's wavelength. Besides, the impedance spectroscopy technique was employed to investigate the characteristics of this component, across a frequency range of 10−1 Hz to 106 Hz and at temperatures ranging from 313 K to 453 K. The frequency behavior of the AC conductivity, σac, was analyzed using the universal Jonscher law. The outcomes of the charge transport investigation on CsCdCl3 imply that the perovskite material possessed a quantum mechanical tunneling (QMT) model for T < 363 K and a large polaron tunneling (OLPT) paradigm for T > 363 K. A correlation between the ionic conductivity and the crystal structure was established and discussed. Ultimately, the low dielectric loss and high dielectric constant of CsCdCl3 make it a promising material for energy harvesting devices.

Dependency of amplitude and phase characteristics of vasomotor oscillations on visual stimulation conditions and experiment duration

The intrinsic-signal optical imaging is widely used in experimental, theoretical and applied research of the mammal’s brain neocortex functional anatomy. However, a neural activity signal is hidden by the background activity, the amplitude of which is an order of magnitude larger than the mapping signal amplitude. Most of such background activity represents spontaneous oscillations in 0.01–0.15 Hz frequency range related to vasomotor oscillations. In this paper, we point out that such oscillations change their power and phase during the response time course. The most dramatic influence is intrinsic for 0.05–0.15 Hz oscillations. The power of vasomotor oscillations declines more quickly than the stability features of their phase characteristics. Departing from these data, we suggested approaches for minimization of role of vasomotor oscillations in functional maps resulting from intrinsic-signal optical imaging.

The Effects of Memantine on Cisplatin-induced Ototoxicity

Introduction: We aimed to investigate electrophysiologically and histopathologically, the protective effects of intratympanic memantine, an N-methyl-D-aspartate receptor antagonist, on ototoxicity caused by cisplatin, an anti-neoplastic agent used in many types of cancer. Methods: Thirty-seven guinea pigs with a normal auditory function were randomly allocated to group 1 (Cisplatin; n=8), group 2 (Memantine; n=8), group 3 (Cisplatin+Memantine; n=8), group 4 (Cisplatin+Physiological Serum [PS]; n=8), and group 5 (Control; n=5). Auditory assessments were conducted using distortion product otoacoustic emissions (DPOAE) within a frequency range of 1-32 kHz, and auditory brainstem responses (ABR) within 8-32 kHz. A single dose of cisplatin (12 mg/kg) was administered intraperitoneally, followed by intratympanic administration of 0.2 mL of either memantine or PS to both ears at least half an hour before cisplatin administration. Subsequent auditory evaluations were conducted 72 h after cisplatin administration. Histopathological analyses were performed using light microscopy of the right ear and scanning electron microscopy (SEM) of the left ear. Results: Auditory evaluations conducted before and after treatment revealed significant findings. Specifically, within groups 3 and 4, ABR thresholds were elevated at all frequencies (p=0.00), whereas the DPOAE signal-to-noise ratios were reduced at frequencies of 8, 12, 16, and 24 kHz (p=0.001, p=0.01, p=0.01, and p=0.00, respectively). Histopathologically, both light microscopy and SEM revealed that the cisplatin+memantine group exhibited fewer hair cells and nuclear degeneration in the spiral ganglion than the cisplatin and cisplatin+PS groups. Additionally, the stria vascularis thickness was greater in the cisplatin+memantine group than in cisplatin and cisplatin+PS groups. Conclusion: Despite the negative electrophysiological findings, the histopathological outcomes suggest that intratympanic memantine may have a potential protective effect against cisplatin-induced ototoxicity. However, further investigations are warranted to corroborate these findings and elucidate the underlying mechanisms of action of memantine.

Thermally Deposited Pt/InSe/Nb2O5/Ag Stacked Layers Designed as Negative Capacitance Sources and Antennas for 5 G/6 G Networks

Herein, Pt/InSe/Nb2O5/Ag (ISNO) stacked layers are designed as multichannel 5 G/6 G network antennas and negative capacitance (NC) sources. The devices are fabricated using thermal deposition technique to coat Pt/InSe thin films with transparent Nb2O5 dielectric windows. While Pt thin films induce the crystallinity of InSe, the Nb2O5 layer remains amorphous. The impedance spectroscopy studies show that the Pt/InSe/Ag (IS) and (ISNO) antenna channels exhibit resonance–antiresonance peaks at driving frequencies of ≈0.4 and ≈1.1 GHz, respectively. Both the IS and ISNO antenna channels exhibit the NC effect in a wide range of frequency domain. In addition, ISNO antennas show signal transmission above 1.70 GHz with a return loss value of 28 dB and voltage standing wave ratios of 1.20. The range of frequencies over which the antenna performs well (bandwidth) extends from 1.54 to 1.80 GHz. Practical tests of one‐port and two‐port reflection/transmission using a network analyzer operative in the frequency domain of 0.01–6.0 GHz highlight the system's differing isolation and coupling characteristics at 2.43 and 6.0 GHz, respectively. The high levels of isolation at 6.0 GHz assure the suitability of the system for applications requiring minimal reverse transmission and high signal integrity. The NC effect, wide bandwidth, and high signal isolation characteristics are preferable in electronics and 5 G/6 G networks.

Dual magnetoelectric antenna array with enhanced bandwidth and sensitivity for low-frequency communications

The magnetoelectric coupling effect demonstrated immense potential for miniaturizing antenna applications. However, due to the resonant nature of magnetoelectric (ME) antennas, their bandwidth tended to be relatively narrow. To address this limitation, our study introduced an array design based on coupled ME antennas. A tri-layer FeGa–PZT8–FeGa laminate structure was employed to construct the ME antennas, which utilized inter-array coupling to broaden the frequency range. Both the central frequency and sensitivity of the array structure were theoretically analyzed, and two methods for extending the frequency were proposed. By coupling two ME antennas of similar frequency in the series mode, the arrayed ME antennas exhibited enhanced sensitivity, increasing from 0.225 and 0.247 to 0.413 mV/nT, and an expanded bandwidth from 0.92–1.03 to 1.4 kHz, indicating improved performance through combined configuration. On the other hand, by coupling two ME antennas of different frequencies together in the series mode, a dual-frequency (97.8/98.97 kHz) ME antenna array was formed. The communication capabilities of the ME antenna array under weak magnetic fields were demonstrated using amplitude shift keying and frequency shift keying modulation methods. The designed array of ME antennas elevated low-frequency communication performance and possessed excellent magnetic field detection capabilities, thereby offering a cost-effective technological pathway for bioelectronic and marine communication design.

Transmission and Reflection Properties of Iron Pyrite-Epoxy Resin Composite for Electromagnetic Applications

This study examines the electromagnetic properties of a composite material composed of iron pyrite (FeS2) and epoxy resin, mixed in a 3:2 weight ratio to create a 10 cm3 cube. The research analyzes transmission and reflection coefficients and band gap parameters to determine its viability as an antenna substrate for electromagnetic wave applications. The composite displays a tunable band gap of 1.3 eV, enabling selective absorption and emission of electromagnetic radiation. The transmission coefficient achieved 90% throughout a frequency range of 1 GHz to 15 GHz, whilst the reflection coefficient was measured at 10%, significantly reducing reflecting losses. The epoxy resin binder was essential for preserving structural integrity and augmenting the dielectric characteristics of the composite, thereby raising transmission efficiency. UV-Vis spectroscopy showed an absorption value of 0.875% at the band gap, indicating efficient interaction with UV energy. The S21 transmission coefficient ranged from −10 dB to −80 dB, with a maximum of −40 dB at 6 GHz, indicating strong energy transfer capability for antenna applications. The S21 values exhibited negligible signal attenuation between 2 GHz and 7 GHz, indicating the material’s exceptional suitability for antenna substrates necessitating dependable transmission. The S11 reflection coefficient varied from −5 dB to −55 dB, with substantial decreases between 4 GHz and 14 GHz, when reflection decreased to −45 dB, signifying little signal reflection at essential frequencies. The results underscore the composite’s appropriateness for applications requiring high transmission efficiency, little reflection, and effective engagement with electromagnetic waves, especially as an antenna substrate. Measurements were performed using a vector network analyzer (VNA) to obtain the S11 and S21 characteristics, underscoring the material’s potential in sophisticated electromagnetic applications.

Establishment of a measuring unit based on Arduino board for recording vibrations on an agricultural tractor during tillage process

When it comes to agricultural tractor ergonomics, vibration is one of the most important factors to consider. However, little research has been done to evaluate this parameter and its impact on workers’ health. Therefore, the aim of this study was to fabricate a portable vibration measurement unit (PVMU) based on an Arduino microcontroller and a vibration sensor (accelerometer ADXL335). The PVMU performance was tested in combination with a commercially available three-axis USB vibration measurement device (VB10). Furthermore, the vibration measurements were used to calculate the tractor driver’s whole-body vibration load according to ISO 2631-1 along three perpendicular axes (X, Y, and Z) during soil tillage using a disk harrow under different tillage speeds of 4.0, 5.5, and 7.0 km/h at a tillage depth of 15 cm in a sandy loam soil. Performance tests of the PVMU and the commercially available three-axis USB vibration meter (VB10) revealed a highly significant level of agreement based on a correlation coefficient of 0.9822. It was found that the vibration level increases with increasing tillage speed. The highest vibration level, 0.80 m/sec2, was observed in the vertical direction (Z-axis) at a tillage speed of 7.0 km/h. The lowest vibration level, 0.12 m/sec2, was observed in the lateral direction (Y-axis) at a tillage speed of 4.0 km/h. The dominant frequency range of vibration transmitted to the tractor seat was found to be between 2.04 Hz and 20.14 Hz. The daily exposure values that is, A (8) determined during this study to assess the health hazards due to vibration for tractor drivers ranged from 0.01 m/sec2 to 0.06 m/sec2 lower than the recommended exposure action value (EAV) limit that is, 0.5 m/sec2. This means that there is no health risk for the driver during the soil tillage using a disk harrow plow. The PVMU proposed in this study is very reliable and can be used as a vibration assessment tool for other agricultural tractor-implement combinations.

Unobstructive and safe-to-wear watt-level wireless charger

A wearable microgrid that centralizes and distributes harvested energy across different body regions can optimize power utilization and reduce overall battery weight. This setup underscores the importance of developing cable-free wireless power transfer (WPT) systems for mobile and portable devices to eliminate the risks posed by wired connections, especially in dynamic and hazardous environments. We introduce a thin, stretchable, and safe hand band capable of watt-level wireless charging through the widely adopted Qi protocol operating at 130 kHz. The implementation of non-adhesive fabric encapsulation serves to protect the 50-μm-thin spiral copper antenna from mechanical strain, ensuring an overall hand band stretchability of 50%. We also create a stretchable “Ferrofabric”, characterized by a magnetic permeability of 11.3 and a tensile modulus of 75.3 kPa, that provides magnetic shielding for the antenna without compromising wearability. The “Ferrofabric” improves the coil inductance but induces core loss in AC application. By fully understanding and managing loss mechanisms such as the skin effect, proximity effect, core loss, and joule heating, we achieve a wireless charging efficiency of 71% and power delivery of 3.81 W in the kHz frequency range. Our WPT hand band is unobstructive to hand motion and can charge a handheld smartphone as fast as a desktop charger or power a battery-free chest-laminated e-tattoo sensor, with well-managed thermal and electromagnetic safety. Through a holistic electromagnetic, structural, and thermal design, our device culminates in a safe, rugged, and versatile solution for wearable WPT systems.

Effect of Coupling Impedance on Stability Assessment of Grid-Forming Converters Under Various Grid Conditions

The phenomenon of frequency coupling is widely observed in grid-forming (GFM) converters due to the presence of asymmetrical controls and nonlinear blocks. However, the factors influencing frequency coupling have not been thoroughly explored. This paper introduces a systematic small-signal impedance model of GFM converters that intuitively reflects the factors affecting frequency coupling and provides a detailed analysis of how coupling impedance affects stability. It is demonstrated that the influencing factors of coupling impedance are an active power loop and reactive power loop. Specifically, the active power loop influences coupling impedance characteristics near the fundamental frequency, while the reactive power loop impacts the entire frequency range. This paper first reveals that the reactive power loop has a more pronounced effect on frequency coupling than the active power loop. Additionally, the variation in the steady-state operating points also affects the degree of frequency coupling of the GFM converters, primarily affecting the coupling impedance characteristics beyond the fundamental frequency, and the low operating points tend to affect system stability adversely. Finally, simulation results validate the accuracy of the mathematical model and theoretical analysis.

Carbon based Composite Materials for Microwave Absorption in Low Frequency S and C Band: A Review

AbstractWith the rapid advancement of 5G technologies and electronic devices, there is a growing demand for microwave absorbing materials, especially those effective in low frequency microwave bands (2–8 GHz), making it an essential requirement. In recent years, many innovative microwave absorbers have been developed for low frequency absorption, with carbon/magnetic composite materials becoming particularly promising due to their various loss mechanisms and optimized impedance matching characteristics over a wide frequency range. However, there is currently a lack of a comprehensive review that summarizes the findings on low frequency absorbers. This review article thoroughly examines the current research on carbon/magnetic composite materials with efficient absorption performance in the low‐frequency S and C bands. It provides a detailed discussion of the microwave absorption performance of these composite materials. Furthermore, the composite design strategies, synthesis techniques, microstructure performance relationship, and microwave attenuation mechanisms are summarized. Lastly, the challenges and future outlook for low frequency microwave absorbing materials are addressed. This review article aspires to provide new insights into designing and synthesizing composite materials to accomplish effective low‐frequency microwave absorption, thereby promoting practical applications.

Resonant conversion of gravitational waves in neutron star magnetospheres

High-frequency gravitational waves are the subject of rapidly growing interest in the theoretical and experimental community. In this work we calculate the resonant conversion of gravitational waves into photons in the magnetospheres of neutron stars via the inverse Gertsenshtein mechanism. The resonance occurs in regions where the vacuum birefringence effects cancel the classical plasma contribution to the photon dispersion relation, leading to a massless photon in the medium which becomes kinematically matched to the graviton. We set limits on the amplitude of a possible stochastic background of gravitational waves using X-ray and IR flux measurements of neutron stars. Using Chandra (2–8 keV) and NuSTAR (3–79 keV) observations of RX J1856.6-3754, we set strain limits hclim≃10−26–10−24 in the frequency range 5×1017 Hz≲f≲2×1019 Hz. Our limits are many orders of magnitude stronger than existing constraints from individual neutron stars at the same frequencies. We also use recent JWST observations of the Magnetar 4U 0142+61 in the range 2.7×1013 Hz≲f≲5.9×1013 Hz, setting a limit hclim≃5×10−19. These constraints are in complementary frequency ranges to laboratory searches with CAST, OSQAR and ALPS II. We expect these limits to be improved both in reach and breadth with a more exhaustive use of telescope data across the full spectrum of frequencies and targets. Published by the American Physical Society 2024

Discriminating Landslide Waveforms in Continuous Seismic Data Using Power Spectral Density Analysis

AbstractDiscriminating landslides from other events in seismic records is challenging due to unclear phases and overlapped frequency content. We analyze the seismic waveform power spectral density (PSD) and its skewness to discriminate landslides from earthquakes and background noise. By comparing PSDs of landslides with small‐magnitude earthquakes and noise in the Alaskan region, we find distinct power decay trends in the 0.01–5 Hz frequency range. The method was successfully tested on the seismic waveforms of seven global landslides. Further, the statistical significance of the approach was tested on 835 landslide waveforms using probability density, skewness and crosscorrelation of waveform PSD. This novel integration of seismic waveform PSDs and their skewness analysis is found to be robust and statistically significant for automatic landslide detection in continuous seismic data, with vast potential for early warning through real‐time seismic networks.

Effect of skin thickness on electromagnetic dosimetry analysis of a human body model up to 100 GHz

Abstract The accuracy of electromagnetic (EM) exposure assessments depends mainly on the resolution of a voxel human body model. The resolution of the conventional human body model is limited to a few millimeters. In the millimeter wave (mmWave) frequency range, EM waves are absorbed by the superficial tissues in the human body. Therefore, resolution and skin thickness of the human body model are important for accuracy of the EM wave exposure metrics recommended by international human safety guidelines. Realistic thickness modeling of the skin tissue on the human body may provide greater accuracy in the EM exposure assessment, especially at mmWave frequency range. In this paper, effects of the skin thickness on the EM exposure metrics in one-dimensional multi-layered models obtained from different regions of the body model are investigated using the dispersive algorithm based on the finite-difference time-domain method over the frequency range from 1 to 100 GHz. Furthermore, effects of eyelid tissue in a human eye on the EM exposure metrics are studied over the frequency range. The EM exposure metrics such as absorbed power density, heating factor, and power transmission coefficient are calculated up to 100 GHz to evaluate the limits of EM wave exposure.

Comparison of the Sensitivity of Various Fibers in Distributed Acoustic Sensing

Standard single-mode telecommunication optical fiber is still one of the most popular in distributed acoustic sensing. Understanding the acoustic, mechanical and optical features of various fibers available currently can lead to a better optimization of distributed acoustic sensors, cost reduction and adaptation for specific needs. In this paper, a study of the performances of seven fibers with different coatings and production methods in a distributed acoustic sensor setup is presented. The main results include the amplitude–frequency characteristic for each of the investigated fibers in the range of acoustic frequencies from 100 to 7000 Hz. A single-mode fiber fabricated using the modified chemical vapor deposition technique together with a polyimide coating has shown the best sensitivity to acoustic events in the investigated range of frequencies. All of this allows us to both compare the studied specialty fibers with the standard single-mode fiber and choose the most suitable fiber for a specific application, providing an enhancement for the performance of distributed acoustic sensors and better adaptation for the newly aroused potential applications.

Shielding Effectiveness of Textile Woven Fabric with Carbon Nanotubes Yarn

ABSTRACT This study explores the electromagnetic properties of flat textile products enhanced with carbon nanotube (CNT) threads used as the weft. CNT threads, fabricated via dry-spinning, were integrated into fabrics by wrapping them around steel threads to form a solenoid-like structure. To further improve electromagnetic attenuation, the CNT yarn was coated with graphene oxide and silver nanoparticles. The research assessed the impact of these modifications on the fabric’s ability to attenuate alternating electromagnetic fields across a range of frequencies. Results showed enhanced attenuation at 30 MHz and 500 MHz. CNT yarn wrapped around steel threads achieved attenuation efficiencies of 18 dB at 30 MHz and 22 dB at 500 MHz, with a notable 10 dB improvement at 30 MHz over the reference. Fabrics with CNT yarn coated with graphene oxide demonstrated similar performance to the reference fabric at 500 MHz and an 8 dB increase at 30 MHz. Similarly, CNT yarn with silver nanoparticles showed comparable performance at higher frequencies but matched the reference at 30 MHz. These results indicate significant enhancement at lower frequencies, with benefits diminishing at higher. This study underscores the potential of integrating CNTs and metal nanoparticles into textiles to improve electromagnetic shielding, especially across specific frequencies.

Curing monitoring of adhesive layers between metal adherends by ultrasonic resonance technique

Abstract Layer resonance induced by ultrasonic wave incidence is applied to monitor the viscoelastic properties of a curing adhesive layer between metal plates. The theoretical analysis shows that when the adhesive layer is modeled as a linear viscoelastic material, the ultrasonic reflection spectrum takes local minima at the layer resonance frequencies depending on the wave velocity of the adhesive. On the other hand, the local minima of the reflection spectrum can be expressed as a function of the loss factor of the adhesive. Based on these results, a characterization technique for the wave velocity and the loss factor of a curing adhesive layer is proposed. This technique enables the evaluation of the viscoelastic properties even if the reflected waves from both faces of a bond layer cannot be separated. The proposed method is employed to investigate the curing behavior of bi-component epoxy adhesives. As a result, it is shown that the bonding condition affects the variation of the wave velocity and loss factor. The estimated wave velocity increases as the curing proceeds, while the loss factor sometimes takes a local maximum depending on the bonding condition and the frequency range. When the mixing ratio of the main and curing agents is imbalanced, the variation of the wave velocity becomes gradual. Furthermore, the increase in the curing temperature leads to fast changes in the wave velocity and loss factor. The proposed technique has the potential to provide insight into the curing behavior of the adhesive layer by incorporating it into other measurement methods and theories.

K/Ka‐Band–GaN–High‐Electron‐Mobility Transistors Technology with 700 mS mm−1 Extrinsic Transconductance

In this study, the impacts of fabrication technology and epitaxial layer design on the transconductance (gm) of radio frequency AlGaN/GaN high‐electron‐mobility transistors (HEMTs) are examined. Optimization of the SiNx passivation and AlGaN barrier design of 150 nm gate HEMTs enhances the extrinsic (at Vds = 10 V) and intrinsic (at Vds = 15 V) transconductance from ≈0.47/0.65 to ≈0.62/1.1 S mm−1. Notably, an extrinsic gm of 0.70 S mm−1 at Vds = 5 V is achieved, setting a new benchmark for the extrinsic transconductance of AlGaN/GaN HEMTs designed for the K/Ka frequency range with a breakdown voltage exceeding 100 V.

Calorimetric Measurements of a High-Power RF Signal

Development of a high-power RF signal meter based on the method of calorimetric measurements, which in some cases is the only possible one is presented. The device is as a system of elements exchanging either energy or information, the operation and interconnection of which ensures the stability of its functioning. The main elements of the device are: a coordinated load and a two-circuit water-air cooling system that convert RF energy first into thermal electrical energy, and then into internal energy of the coolant (working fluid). The measurement and control system provides information display on the monitor and generation of internal control signals. The work focuses on the process of converting electromagnetic energy into internal energy of the coolant, since the matched RF load is integrated into the cooling system and requires special design and technological solutions to ensure efficient operation. A cooling and measurement system has been designed to test the developed RF absorber with a power of up to 5 kW. The parameters of the cooling system were determined based on minimizing the time to achieve thermal equilibrium (time to establish readings) and the set parameters (input temperature no more than 35 °С, temperature difference no more than 40 °С). Based on calculations of the electrodynamic model constructed by the partial domain method, the geometric dimensions were determined at which the voltage standing wave ratio of the load in the operating frequency range (from DC to 1300 MHz) will be the smallest. The article presents the results of designing a high-frequency wattmeter cooled by a liquid (water), examines the thermophysical processes occurring in it and the influence of the presence of a coolant in the cooling circuit.