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This paper presents an Inductive Power Transfer (IPT) system for Electric Vehicle (EV) charging with Power Class Interoperability (PCI) between the SAE WPT3 (10 kW) and WPT5 (50 kW) power classes using a multi-coil Bi-Polar Pad (BPP) Vehicle Assembly (VA) magnetic topology. The objective is to provide wireless PCI for electric taxis and fleet vehicles which may require WPT5 charging while on shift and WPT3 off shift charging. The design process of the WPT3/5 BPP VA magnetics is presented. Alternative methods of ferrite core layout and coil overlap to reduce form factor and cross-coupling are investigated. A dual active bridge topology using LCC-LCC tuning demonstrates effective dual-sided control, combining conduction angle, active bridge phase shift, and Selective Coil Energization (SCE) to provide system functionality essential to PCI. Active bridge phase shift is utilized to adjust the relative secondary to primary phase past 90° to enable Zero-Volt Switching (ZVS) in the active bridges when operating at either power class. Experiments demonstrate the proposed WPT3/5 BPP VA charging from an above ground WPT3 UGA, and flush ground mounted WPT5 GA, and show an efficiency increase of 3.6% and 0.7% respectively when the proposed control method is used. The performance of the proposed system is shown to be comparable to other IPT systems at either power class.

A wideband wide-scan array based on dual-polarized elements is presented in this paper. The proposed element consists of two flared metallic wings and two shorting posts over a ground plane which is excited by a RF connector vertically. Without complex feeding network, the antenna element features wideband, low-profile, and high power handling capability. Besides, elements do not require electrical connection and can be arranged with gaps between neighbors, allowing for modular construction. The dual-polarized array in a square lattice can achieve wideband wide-scan performance. To verify the design, an $11\times 11$ prototype has been fabricated and measured. The measurements of this prototype are presented and are in good agreement with the simulations. The results reveal that the array element can achieve a relative bandwidth of 100% for VSWR $\le 3$ at scans out to $\theta \,\, = \,\, 45^{\circ }$ and an enhanced gain of 1 dB in lower frequency band. The array can obtain better than 20 dB polarization purity at 4 GHz and scan loss of lower than 3 dB over the band, respectively.

A bridgeless rotor of a synchronous reluctance machine is proposed to enhance the performance of high-power and -speed synchronous reluctance machines (SynRMs). Unlike traditional transversally laminated designs that rely on radial and tangential ribs or bridges to provide mechanical integrity for the rotor, the suggested rotor incorporates separate flux guides attached to non-magnetic back plates to form SynRM rotor modules that are stacked on the shaft of the machine. This innovative structure eliminates the need for radial and tangential bridges which form a performance-deteriorating bottleneck in the design of high-power SynRMs. The paper presents a detailed analysis of the electromagnetic and mechanical aspects of the proposed bridgeless rotor synchronous reluctance machine (BLRSynRM). Furthermore, a comprehensive optimization method is implemented to demonstrate the capabilities of the proposed BLRSynRM along with comparison with conventional transversally laminated SynRM. The results show a significant increase in torque and power factor compared with conventional structure rotor. However, the proposed bridgeless structure introduces new electromagnetic and mechanical challenges to machine design and they are explained and overcome in this research.

The research on high power 190 GHz doubler based on the GaAs Schottky diodes is proposed in this paper. The frequency doubler comprises a improved diode configuration that increases the number of anodes by changing the diode arrangement to improve power handling capacity. Electromagnetic and thermal simulation is utilized to demonstrate that the doubler can carry more power. The input power is gradually pumping from 200 mW to 500 mW with an applied DC bias of −15 V. And the peak efficiency of the doubler is measured to be 17%, while the maximum output power is 85 mW at 190 GHz.

This article presents a novel frequency-tapered Ring Bar Slow Wave Structure (RBSWS) for high-gain and wide-bandwidth Traveling Wave Tubes (TWTs) operating in the K-band for space applications. Starting from an analytical circuit model of the RBSWS, a conical-cut geometry is introduced to reduce the phase velocity. Our proposed novel RBSWS operates over a frequency range of 18.8 to 20.1 GHz, under a cathodic voltage and current of 19.8 kV and 0.3 A, respectively. Particle-In-Cell (PIC) results, carried out by CST Studio 2023, show a very high output peak power of 840.5 W at a gain of 20.2 dB, for an input power of 8 W, and an electron efficiency of 15.3%. The tapered RBSWS-TWT achieves a wider bandwidth, higher output power, and higher electron efficiency with respect to the untapered RBSWS-TWT, demonstrating the effectiveness of the proposed structure.

High-Power electric grid networks require extreme security in their associated telecommunication network to ensure protection and control throughout power transmission. Accordingly, supervisory control and data acquisition systems form a vital part of any critical infrastructure, and the safety of the associated telecommunication network from intrusion is crucial. Whereas events related to operation and maintenance are often available and carefully documented, only some tools have been proposed to discriminate the information dealing with the heterogeneous data from intrusion detection systems and to support the network engineers. In this work, we present the use of deep learning techniques, such as Autoencoders or conventional Multiple Correspondence Analysis, to analyze and prune the events on power communication networks in terms of categorical data types often used in anomaly and intrusion detection (such as addresses or anomaly description). This analysis allows us to quantify and statistically describe high-severity events. Overall, portions of alerts around 5-10% have been prioritized in the analysis as first to handle by managers. Moreover, probability clouds of alerts have been shown to configure explicit manifolds in latent spaces. These results offer a homogeneous framework for implementing anomaly detection prioritization in power communication networks.

This paper presents a small-size, low-profile antenna for anti-attacking systems that work against unmanned GNSS-guided attacking vehicles to protect a vital area. The proposed antenna has the ability to handle, theoretically, a peak power up to 157.7 kW. It has a cylindrical shape with a diameter of 75.4 mm and a height of 12.8 mm on a low-cost FR-4 substrate. This small size allows the integration of the proposed antenna with any portable system that prevents the attacks of GNSS-guided vehicles. The proposed antenna covers the whole GNSS frequency band with a fractional impedance bandwidth of 32.5% (1.16–1.61) GHz and a fractional axial ratio bandwidth of 37.6% (1.1–1.61) GHz utilizing a sandwiched structure. This broadband performance is realized using capacitive feeding. The proposed design maintains circularly polarized radiation over a wide elevation angle of 132° and a 360° azimuth angle which makes the proposed design suitable for GNSS anti-attacking systems.

As the traditional power drive circuit is difficult to meet the requests of high-power high-frequency proportional solenoid fast drive, this paper proposes a push-pull energy storage pulse width modulation (PWM) power drive circuit. The circuit is equipped with an energy storage module, which releases energy when the proportional solenoid coil is charged, supplements the output of the power supply current, and shortens the arrival time of the steady-state current. When the coil is discharged, it recovers energy and shortens the time for the coil current to return to zero. In this paper, a theoretical model of push-pull energy storage power drive circuit is established, and simulation analysis and experimental verification are carried out for a proportional solenoid coil with rated current of 3.3A and power of 79W. The results show that the push-pull storage PWM power drive has excellent input-output linearity, minimal ripple, and good steady-state current output performance. Compared with the traditional single switch and reverse discharging power drives, the coil charging speed under the push-pull energy storage type power drive is increased by 25%, and the discharge speed is increased by 95% and 45% respectively.

Tapered Yb-doped fiber (T-YDF) can balance the suppression of transverse mode instability (TMI) and stimulated Raman scattering (SRS) in high power fiber lasers. In this work, we have constructed an all-fiberized master oscillator power amplifier emitting at the central wavelength of 1050 nm based on a T-YDF and investigated the laser performance in respective co-pumped and counter-pumped configurations. The results show that the T-YDF can effectively mitigate SRS effect in short-wavelength fiber lasers. A nearly single mode beam quality (M2∼1.20) is obtained at output power of 3 kW-level. In particular, the SRS suppression ratio in the co-pump and counter-pump scheme is about ∼33.2 dB at ∼3039 W and ∼46.6 dB at ∼2818 W, respectively. By further optimizing the structure of the tapered active fiber, it is promising to further improve the output power and beam quality in short-wavelength fiber lasers.

This paper reviews the latest developments in microwave acoustic wave devices. After an introduction and brief history of bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices, a review is given for guided SAWs and XBARs - two new technologies, which are promising for future 5G applications. Following this, we discuss recent simulation techniques, such as 3D finite element method (3D FEM) and simulation of nonlinearities, as well as filter synthesis. Next, a review on tunable and reconfigurable acoustics is given. Finally, we present the latest developments in microwave acoustics for millimeter-wave (mm-wave) operation as well as BAW oscillators.

For wireless communication systems with a long distance or severe interference, the insufficient transmit power limits the system performance. In this case, the maximum transmit power depends on the nonlinearity and the saturation region of the power amplifier (PA), which is referred to as a nonlinearity-constrained problem in this paper. To increase the transmit power as high as possible in a nonlinearity-constrained system, this paper proposes an autoencoder-based system to jointly optimize the modulation scheme and transmit power. The optimal solution can achieve a tradeoff between increasing the transmit power and reducing the nonlinear distortion. Meanwhile, the optimized signal constellation and the neural network-based receiver can effectively improve the capacity against nonlinear distortion. The simulation results indicate that the proposed method outperforms conventional methods in terms of symbol error rate (SER) and transmit power, and the SER of the proposed method is close to the SER lower bound of the nonlinear PA.

A high-power dual-wavelength laser based on coaxial end-pumping scheme with composite Nd:YAG and Nd:YAP crystals was demonstrated. A theoretical model was built to analyze the thermal lens and accurately calculate the thermal focal length of laser gain medium pumped by a divergent beam. The experiment was carried out with a plane-convex cavity and a V-shape cavity for high-power output. The Q-switched laser produced 9.1 W pulsed dual-wavelength output (4.7 W at 1064 nm and 4.4 W at 1079 nm) at 25-kHz pulse repetition rate with synchronized pulse duration of 35 ns, corresponding to the optical-to-optical efficiency of 30.3%. The continuous-wave (CW) output power reached 15.5 W at laser diode (LD) pump power of 40 W, corresponding to a slope efficiency of 40.9% and an optical-to-optical conversion efficiency of 38.9%. The powers at two wavelengths were almost equivalent and the fluctuations were both less than 2.3%. To our best knowledge, it was the highest output power for stable CW dual-wavelength lasers based on diode-end-pumped configuration.

This letter reports the successful development of an S-band short-length, high-efficiency, coaxial cavity multi-beam relativistic klystron amplifier (CCMB-RKA). The simulation in one-dimensional genetic algorithm, capable of giving high-efficiency parameters, predicted 67% efficiency of CCMB-RKA, taking the interaction length as 600 mm, beam voltage as 420 kV, and beam current as 230 A. However, for accurate results, the CCMB-RKA was simulated again using three-dimensional code CHIPIC, taking RF input power, beam voltage, and beam current as 4.4 kW, 420 kV, and 3.22 kA ($= {14} \times {230}$ A, 14 being the beam number), respectively, predicting the output power, gain, and efficiency of the device as 810 MW, 53 dB, and 60%, respectively. Finally, the designed CCMB-RKA was built and experimented with. Through 20 groups of the comparative experiments, the GW-level RF output power of the device, typically, 1.027 GW (peak), 60 ns pulse was demonstrated with 55% efficiency, 370 phase jitter, and 53 dB gain, taking the RF input power, beam voltage, and beam current as 4.8 kW, 453 kV, and 4.1 kA, respectively. The results establish the potential of the CCMB-RKA developed for high-power microwave applications. [ABSTRACT FROM AUTHOR]

A homemade double-tapered Yb-doped fiber is employed in a high-power narrow-linewidth fiber amplifier to improve the thresholds of nonlinear effects and transverse mode instability (TMI) effect. A bidirectional pumping configuration is employed, and a phase-modulated single-frequency fiber laser serves as the seed laser. As a result, an output power of 3630 W with 0.21 nm linewidth (stimulate Brillouin scattering limited) and an output power of 4180 W with 0.59 nm linewidth (TMI limited) are realized, corresponding to the slope efficiency of ∼77%. The beam quality at the maximum output power is ${\rm M}_{\rm x}^{2}= 1.57, {\rm M}_{\rm y}^{\rm 2} = 1.39$. The results could provide a well reference for the power scaling of narrow-linewidth Yb-doped fiber amplifier. [ABSTRACT FROM AUTHOR]

A ${G}$ -band multigap extended interaction klystron (EIK) adopting mode overlap method with ladder-type structure is proposed to achieve high power, high efficiency, and broad bandwidth. The gap number is set larger than the conventional EIK to achieve its potential. The high-frequency characteristics of the modes in output cavity are studied. The length ratio of long and short slots is optimized to obtain appropriate mode frequency interval and effective characteristic impedance. In our scheme, the gap number of output cavity is determined as 17 with the mode overlap of $\pi $ mode and $15/ 16\pi $ mode. The circuit structure and working conditions are carefully designed and optimized to solve the problem of instability under large gap number. With a beam current of 0.3 A, a voltage of 15.8 kV, and a magnetic field of 0.75 T, the particle-in-cell simulation shows that with the increase of frequency, the output cavity can work with two modes overlap and expand the 3-dB bandwidth to 1.32 GHz, which is more than two times of our previous work. Also, a maximum output power of 870 W, an efficiency of 18.4%, and a gain of 46.4 dB are finally obtained. The numerical simulation results definitely demonstrate the feasibility of mode overlap and its ability to the expansion of EIK bandwidth in the terahertz band. [ABSTRACT FROM AUTHOR]

In order to obtain a high-power radiation source in the W-band, a 95-GHz extended interaction oscillator (EIO) with high voltage was designed and tested in this article. The overall structure of the designed EIO is introduced, and the simulation results of the slow wave structure are shown. Experimental test results show that, at a high duty cycle of 50%, the 95.1-GHz radiation peak power of 3.5 kW is achieved when an electron beam with 2 A and 42.8 kV is injected. The experimental test of the designed EIO has guiding significance for miniaturized vacuum devices to obtain high-power radiation source. [ABSTRACT FROM AUTHOR]

This article develops a high-power piezoelectric transformer based on the sandwiched piezoelectric transducer with multioutput characteristics. An advanced high-power voltage transformation technology is realized via using the superior mechanical robustness of the sandwiched piezoelectric transducers. High-power sandwiched piezoelectric transformers (s-PTs) with the unique crisscrossed structure are constructed by four sandwiched piezoelectric transducers with two modes, i.e., antiphase mode and in-phase mode, due to the coupled vibration of the central metal cuboid. Moreover, the related electromechanical equivalent circuit model (EECM) of the s-PTs is established in which two loss factors are introduced into this model, and its impedance characteristics, voltage gains, and power gains are studied as well. The accuracy of EECM is verified by the finite element method and experiments. Results reveal that s-PT has three outputs, and its voltage gains and power ratios are affected by load resistance and loss. The output power of the s-PTs can reach at least 45 W, and the s-PTs can keep the efficiency of ∼35% under high-input electric power, which provides a new idea for high-power piezoelectric transformers. [ABSTRACT FROM AUTHOR]

This article proposes methods of predicting and preventing thermal failure within high-power ferrite structures of electric vehicle (EV) wireless charging inductive power transfer (IPT) by improving their ferrite layouts. A high-power IPT magnetic design suitable for wirelessly charging an EV at 50 kW using a heuristic approach is presented, where the chosen design achieves reduced heating within the magnetic structure. Recommendations are made that both avoid ferrite fracturing due to magnetic hotspots and cause temperature differentials across ferrite tiles, and regarding airgap distribution between ferrite tiles to reduce loss-inducing circulating flux within the ferrite structure without reducing coupling. Power transfer was simulated in ANSYS and PLECS under misaligned conditions, and validated experimentally with 93.7% system efficiency. Thermal tests performed under rated volt-amps found the magnetics temperatures (after 30 min) could be reduced from 168 to 67 °C using an improved magnetic layout that reduced the thermal gradients within the ferrite tiles by 70%. Leakage fluxes were targeted and validated to be below 15 μT, 950 mm from the center of the vehicle under rated power and worst-case misaligned conditions. [ABSTRACT FROM AUTHOR]

Compared with conventional systems, high power puts forward more requirements on the balun: the materials and structures should be more reliable, able to withstand high power, and have extremely high transmission efficiency. Based on the electromagnetic field theory and the visual optimization method by CST MW Studio, a parallel-connected coaxial cavity balun is proposed in this article that can realize the balance–unbalance conversion in almost the entire shortwave frequency band (4.4–27 MHz). For further improvement of the transmission efficiency and the reduction of voltage standing wave ratio (VSWR), an antenna tuning unit (ATU) was added to the unbalanced port of the cavity, which lowered the VSWR from 1.5 to 1.1. The theoretical value of the breakdown power of the balun is also calculated, and it is much larger than the transmit power. The results of the scaled mode measurement are consistent with the simulation results: the amplitude imbalance of the balanced port is within ±0.5 dB, the phase difference is 180° ± 5°, and the withstand power is at least three times the transmit power, which fully demonstrates that the proposed balun is suitable for high-power shortwave transmitting systems. [ABSTRACT FROM AUTHOR]

High-power terahertz frequency quantum cascade lasers operating in both pulsed and continuous wave (CW) modes are demonstrated. High Al composition four quantum wells active region based on diagonal structure are employed to suppress the escape of electrons into continuum and thermally activated LO-phonon scattering, as evidenced by the activation energy value of ~14.4 meV extracted from the experimental data. The devices operate in a frequency range of 3.8 - 4.05 THz and have a pulsed maximum operating temperature of ~119 K. The total optical output power from an uncoated laser is 1.57 W and the maximum single-facet emission power from an HR coated one is 1.03 W in pulsed mode at 7 K. The maximum output power of ~256 mW is obtained by a 2.5-mm-long device operating in CW mode with a low threshold current density of 188.6 A/cm2 at 15 K. [ABSTRACT FROM AUTHOR]

A metallic ring-based, diode-integrated, low-profile, power-dependent metasurface working from 3 to 3.6 GHz is proposed in this letter. Unlike the previous study which shifts a band up and down to change the impedance of the surface, the triggering of the diodes directly transforms the structure from a surface wave supportive state to a self-induced bandgap topology if exposed to high-power radio-frequency (RF) illumination. We demonstrate the concept by conducting the electromagnetic (EM)-circuit co-simulation and measurements for a 6-by-8 unit 2-D prototype. Near-field scan experiments verify that the proposed topology works in two distinct states, the on and off states, and high-power measurements prove that the reflection varies with the incident signal power. The highest 10 dB decrement in transmission occurs at 3.3 GHz with 52 dBm illumination. This structure can be used to protect sensitive devices from large signals while otherwise supporting a communication channel for small signals. [ABSTRACT FROM AUTHOR]

This paper presents an improved white light-emitting-diode (LED) wireless transmitter for the Joint Illumination and Communication (JIC) System, which consists of two parts: the driver circuit and the pre-emphasis circuit. The main purpose of the driver circuit part is to solve the problem of dissipated power when sweeping the remaining carriers during the signal modulation of the high-efficiency, high-power and high-speed white LED driver. A push-pull structure driver with a current conduction angle less than 180 degrees is proposed, which is analogous to a Class C power amplification driver, thus avoiding the simultaneous existence of voltage and current on the driver circuit when the remaining carriers are swept out, and improves the efficiency of the LED driver. On this basis, the pre-emphasis circuit part adopts the phase shift technology to improve the data transmission rate, and the system efficiency has also been improved. Then, an improved class C push-pull structure white LED driver with phase shift pre-emphasis technology is formed. This novel driver and pre-emphasis technology achieve a system efficiency of 95.73% with a 10 W LED. The test results show that the system communication -3 dB bandwidth expanded from the original 8.3 MHz to 13.67 MHz, and the best-obtained transceiver baud rate is 25 Mbps at a distance of 1.3 m with BER of 1.63 × 10-4. The test result verifies that the LED driver proposed in this paper is currently the highest figure of merit (FoM) for high power JIC systems.

Semiconductor optical amplifiers (SOAs) offer direct electrical injection, power consumption, integration, and anti-radiation advantages over optical fiber amplifiers. However, saturation output power and gain bandwidth have been limited in traditional structure SOAs. We demonstrate a monolithic integrated SOA with broad spectrum, high power, high gain, and small spectral linewidth expansion. The device adopts a two-stage amplified large optical cavity structure, and a lower optical field confinement factor is obtained by adjusting the thickness of the waveguide layer. The lower optical field confinement factor is conducive to improving the coupling efficiency and the maximum output power. Our device, fabricated only by standard i-line lithography with micron-scale precision, obtains excellent and stable performance. When the input power is set to 1 mW, the output power is 419 mW with a gain of 26.23 dB. When the input power is set to 25 mW at 25 °C, the output power increases to 600 mW with a gain of 13.8 dB. The corresponding gain bandwidth of 3 dB measures at least 70 nm. The spectral linewidth after the SOA is 1.15 times wider than that of the seed laser.

We report on the development of a 940-nm diode laser bar based on epitaxially stacked active regions by employing a tunnel junction structure. The tunnel junction and the device parameters were systematically optimized to achieve high output and power conversion efficiency. A record quasi-continuous wave (QCW) peak power of 1.91 kW at 25 °C was demonstrated from a 1-cm wide bar with a 2-mm cavity length at 1 kA drive current (200 μs pulse width and 10 Hz repetition rate). Below the onset of the thermal rollover, the slope efficiency was as high as 2.23 W/A. The maximum power conversion efficiency of 61.1% at 25 °C was measured at 300 A. Reducing the heatsink temperature to 15 °C led to a marginal increase in the peak power to 1.95 kW.

We present an numerical and experimental analysis of a Yb:YAG thin disk regenerative amplifier. Group velocity dispersion, third order dispersion, and self-phase modulation (SPM) effects are considered in the simulations of the amplification process. By virtue of the simulations, a compact femtosecond Yb:YAG thin-disk chirped-pulse regenerative amplifier delivering an average power of 50 W at a central wavelength of 1030 nm with a propagation factor of M2 < 1.4 at a repetition rate of 200 kHz and a pulse duration of 500 fs was constructed. Numerical simulation based on this Yb:YAG thin-disk was carried out to investigate the pulse parameters evolution in each round trip. The measured experimental results in pulse width, spectrum, and pulse energy together fitted quite well with the numerical simulation. This plays an important role in the design of high-peak-power regenerative amplifier and will facilitate further power scaling and suppression of gain narrowing of the whole system.

An interleaved parallel LLC converter is proposed as a DC/DC converter for a digital off-board charger in accordance with the high output power requirements of modern electric vehicle chargers. The proposed converter utilizes a hybrid control strategy of pulse frequency modulation (PFM) and pulse width modulation (PWM) that can greatly increase the adjustable output voltage range. As a result of these designs, a silky target voltage can be achieved. The proposed LLC converter has been rigorously analyzed and parametrically designed. To verify the design parameters of the proposed LLC converter, a laboratory prototype with an output voltage range of 40–110 V and a maximum output power of 20 kW was fabricated. The rated output voltage and rated output current are 80 V and 200 A, respectively, while its switching frequency range is 100–250 kHz and its resonant frequency is 153 kHz. This prototype exhibits incredible robustness and stability and achieves flexibility, stability, and sensitivity to automatically adapt to the target output voltage value.

Microwave-induced thermoacoustic (TA) imaging, combining high microwave contrast with high ultrasonic resolution has the potential to revolutionize applications such as continuous healthcare monitoring, point-of-care imaging, and biometric authentication. However, the size, cost, and integration of a high-power microwave transmitter is a key bottleneck in making TA imaging truly portable, affordable, and ubiquitous. Toward that end, this work presents a compact 4.9-GHz pulsed power amplifier (PA) with a 4.87-mm2 active area implemented in a 55-nm BiCMOS technology, operating in a duty-cycled mode and achieving 37.3-dBm peak output power—the highest demonstrated peak power in PAs fabricated on a silicon substrate with deep submicron CMOS integration. We also reconstruct the first known high-fidelity TA images of tissue phantoms using an integrated silicon PA. [ABSTRACT FROM AUTHOR]

Highly oversized mode converters are the critical devices for high power millimeter-wave transmission systems, characterizing high power capacity and low loss. In order to improve the conversion efficiency from TE01 to TE11 mode, the mode coupling mechanism of oversized elliptical waveguides is explored, and an optimal ellipticity interval to obtain the high conversion efficiency is deduced by analyzing the mode coupling capacity. Considering that ellipticity can affect the power capacity, breakdown thresholds of different operating modes in elliptical waveguides are studied. Based on the analyses, a synthesis method to design the elliptical mode converter integrating the mode conversion efficiency and the power capacity is proposed. A highly oversized mode converter working in $W$ -band is designed, and the simulation results demonstrate that the mode converter achieves the high conversion efficiency over 95% in a relative bandwidth of 19.6%. In order to validate the design, a prototype of the mode converter is fabricated, and the high purity of outputted TE11 mode is verified by the measurement. The oversized mode converter designed by the proposed synthesis method features high efficiency, broad bandwidth, and high power capacity, enabling its full utilization of the potential of gyrotron traveling-wave tubes (gyro-TWTs). [ABSTRACT FROM AUTHOR]

Several designs of magnetrons are discussed in the literature, which are mainly for industrial heating applications. Exotic applications such as current drive systems for plasmas, seeker systems, and accelerator systems may have power and frequency requirements, which are usually not met in the ISM band. This article presents the design of a 3.7-GHz 8-kW continuous wave (CW) magnetron, which can be used as a potential source for the lower hybrid current drive (LHCD) system of a tokamak. The simulation results predict a CW output power of about 8 kW with a 62% efficiency. Furthermore, a novel design of a 16-kW CW stacked magnetron is also presented with a simulated efficiency of 63%. [ABSTRACT FROM AUTHOR]

We introduced a phase-locking mechanism of millimeter-wave magnetrons coupled through a carefully designed coupling bridge. For such a structure, two Ka-band 22-vane rising-sun magnetron circuits operated in the $\pi $ -mode were phase-locked tightly as a whole through a double-ridged coupler. Moreover, the double-ridged coupler was optimized to suppress mode competition between zero-phase and $\pi $ -phase difference mode, which achieved high-efficiency phase-locking. Total output power of the two identical magnetrons nearly doubled the output power of a free-running magnetron and efficiencies of them were nearly the same. Extension of this phase-locking mechanism to high-power applications appears feasible with more elements in an array of the millimeter-wave magnetrons. [ABSTRACT FROM AUTHOR]

A high-power 300 GHz solid-state source chain based on GaN doublers is proposed. The two doublers working at 150 GHz and 300 GHz are designed and fabricated. The pulsed output power exceeds 1000 mW at 148 GHz to 152.5 GHz with an efficiency of 21 % to 29 %. At 151 GHz, a peak pulsed output power of 1322 mW with 27 % efficiency is derived, while a peak efficiency of 33.1 % is determined at 150 GHz with an input power of 2.3 W. The fabricated 300 GHz doubler delivers pulsed output power that is greater than 110 mW from 292 GHz to 305 GHz with an efficiency of 11.3 % to 14.7 %. A peak output power of 183.4 mW with 13.9 % efficiency is obtained at 302 GHz. [ABSTRACT FROM AUTHOR]

In this article, a four-phase current-fed push–pull dual active bridge converter is proposed for applications requiring high power and a wide-voltage range. In addition to the conventional advantages of a small filter inductor, a small clamp capacitor, and low current stress in the primary switches due to the effect of four-phase interleaving, the proposed converter has a low total rms current of switches when operating at a wide-voltage range compared with the existing two- and three-phase converters. Also, the proposed converter was shown to be capable of the complete ZVS turn-on of all switches under a wide duty cycle range of 0.25–0.75 in both power-flow directions when small auxiliary inductors were added. A balanced four-phase transformer structure is proposed not only to cancel the dc-flux offset caused by the dc component of the primary winding current but also to reduce the core volume, footprint, and height of the transformer compared with the separated-core transformer. The experimental results from a 15-kW prototype are provided to validate the proposed concepts. The converter achieved a peak efficiency of 98% and maintained high efficiency when operated at a wide-voltage range. [ABSTRACT FROM AUTHOR]

A high power Ho:YAP laser in-band pumped by a home-constructed Tm doped all fiber master oscillator power amplifier (MOPA) is reported. The optically polished and uncoated Ho:YAP laser yielded over 107 W of output power at ~2117.1 nm with 215.4 W of absorbed pump power, corresponding to a slope efficiency of 50.6% with respect to the absorbed pump power. The beam quality M2 parameter was measured at 80 W of output power to be ~3.2 and ~2.6 in x- and y-directions, respectively.

In this paper, the development of two high power 220 GHz frequency triplers is proposed. The GaAs Schottky diodes with six nodes are applied to realize high efficiency 220 GHz tripler, while the application of GaN Schottky diodes with eight nodes is another attempt to improve power handling of the 220 GHz tripler. To reduce thermal effect of high power multipliers, the AlN substrates with high thermal conductivity are applied to provide better heat dissipation at the diode areas. A combination of electrical and thermal model of the Schottky diodes is established while the optimization of 220 GHz triplers are realized with 3D electromagnetic (EM) simulation and harmonic balanced simulation. Good agreement is achieved between the simulated results based on electro-thermal model and measured performances of the triplers. At room temperature, peak efficiency of the tripler based on GaAs Schottky diodes is 17.8%, while the maximum output of the tripler is 38.2 mW with 300 mW input power. As for the 220 GHz GaN Schottky diode tripler, measured results show that the maximum power handling is beyond 400 mW. The peak efficiency and maximum output are 4.7% and 18.4 mW, respectively. The proposed methods of developing high power multipliers can be applied in higher frequency band in the future.

This article presents W- and G-band voltage-controlled oscillators (VCOs) fabricated in a 60 nm GaN high electron-mobility transistor (HEMT) process with ƒT/ƒMAX of 190/250 GHz. Two W-band fundamental VCOs (VCO1 and VCO2) are designed without and with a varactor, respectively. In addition, a G-band push–push VCO (VCO3) is designed to demonstrate feasibility of a GaN power source in the sub-terahertz band. The measurement shows that VCO1 and VCO2 exhibit output power of 22.5 and 22.6 dBm and dc-to-RF efficiency of 14.7% and 16.8% at 87.5 and 86.5 GHz, respectively. The power and efficiency are the highest values among the previously reported GaN VCOs operating beyond 50 GHz. Furthermore, VCO2 achieves a wide tuning range of 9.0 GHz (77.5–86.5 GHz). The VCO3 exhibits high output power of 9.3 dBm at 180.6 GHz. To the best of the authors’ knowledge, this is the first demonstration of a G-band VCO in a GaN technology. The W- and G-band VCOs occupy compact chip areas of 0.48 and 0.32 mm2, respectively. [ABSTRACT FROM AUTHOR]

In this work, QDs/hBNs/silicone annular fins (QDs-AF) are proposed as a new type of packaging structure to establish rapid heat dissipation pathways between QDs and heat sink. The QDs-AF structure was firstly designed based on commercial LEDs modules. Then, the annular fin materials including QDs, thermally conductive hBN platelets (hBNs), and silicone were determined by balancing the tradeoff of optical and thermal performances. Finally, the optimal structure of QDs-AF was obtained through thermal simulation by changing the values of fin thicknesses of different initial QDs-AF structures. According to the optimal QDs-AF structure with 4 fins and fin thickness of 0.28 mm, we fabricated the QDs-AF and its WLEDs. Compared with QDs-WLEDs, the maximum surface working temperature of QDs-AF-WLEDs was reduced by 20 °C at 1000 mA. In addition, the QDs-AF-WLEDs showed an excellent optical performance with a high color rendering index of 90.3 and a high luminous efficiency of 124.1 lm $\text{W}^{-1}$. The application of QDs-AF in WLEDs is a new and significant method to achieve a lower working temperature and protect QDs from thermal quenching in WLEDs. [ABSTRACT FROM AUTHOR]

We demonstrate the laser performance of a LD end-pumped Er:YSGG crystals with different doping concentrations comparatively. The experimental results show that 30 at. % Er:YSGG crystal with dimensions of 2 mm × 2 mm × 8 mm has the best laser output. In continuous-wave (CW) mode and pulse mode, the maximum output powers of 1.37 and 1.20 W are achieved, corresponding to slope efficiencies of 23.62% and 22.91%, respectively. To the best of our knowledge, compared with other Er3+-doped garnet laser crystals, we obtained a larger power and higher efficiency CW laser simultaneously for LD end-pumped Er:YSGG crystal. The beam quality factor M2 in x and y directions are determined to be 1.64/1.65, suggesting the Er:YSGG laser possesses a higher beam quality. All these results indicate that Er:YSGG is a promising mid-infrared gain medium for high efficiency and high power laser operation. [ABSTRACT FROM AUTHOR]

We present an numerical and experimental analysis of a Yb:YAG thin disk regenerative amplifier. Group velocity dispersion, third order dispersion, and self-phase modulation (SPM) effects are considered in the simulations of the amplification process. By virtue of the simulations, a compact femtosecond Yb:YAG thin-disk chirped-pulse regenerative amplifier delivering an average power of 50 W at a central wavelength of 1030 nm with a propagation factor of M2 < 1.4 at a repetition rate of 200 kHz and a pulse duration of 500 fs was constructed. Numerical simulation based on this Yb:YAG thin-disk was carried out to investigate the pulse parameters evolution in each round trip. The measured experimental results in pulse width, spectrum, and pulse energy together fitted quite well with the numerical simulation. This plays an important role in the design of high-peak-power regenerative amplifier and will facilitate further power scaling and suppression of gain narrowing of the whole system. [ABSTRACT FROM AUTHOR]

We report on the development of a 940-nm diode laser bar based on epitaxially stacked active regions by employing a tunnel junction structure. The tunnel junction and the device parameters were systematically optimized to achieve high output and power conversion efficiency. A record quasi-continuous wave (QCW) peak power of 1.91 kW at 25 °C was demonstrated from a 1-cm wide bar with a 2-mm cavity length at 1 kA drive current (200 μs pulse width and 10 Hz repetition rate). Below the onset of the thermal rollover, the slope efficiency was as high as 2.23 W/A. The maximum power conversion efficiency of 61.1% at 25 °C was measured at 300 A. Reducing the heatsink temperature to 15 °C led to a marginal increase in the peak power to 1.95 kW. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) cold-cathodes hold much promise in a variety of millimeter-wave and terahertz vacuum electronic radiation devices due to their inherent near instantaneous temporal turn-on and near-ideal ideal field electron emission performance. Here we report on the development of a CNT cold-cathode Ka-band backward-wave oscillator (BWO). Using a novel beam compression stage, theoretical studies, simulation results, and empirical findings collectively demonstrate that this device affords an unprecedentedly high output power of 230 W at a technologically important operating frequency of 33.65 GHz. The developed magnetic injection electron gun achieves a high emission current of 265.5 mA (emission current density of 188.3 mA/cm2) and a high focused beam current density of 18.5 A/cm2, which our studies suggest, is essential to the BWOs high output power. [ABSTRACT FROM AUTHOR]

High power and narrow vertical divergence lasers for the 980 nm wavelength range based on the photonic crystal (PC) structure are investigated. The structure of the PC layers and the position of the quantum well (QW) are optimized through mode analysis, which to maximize the output power of the PC laser. A broad area (BA) laser with 300 μm width and 4 mm cavity length yields 41.8 W output with far-field divergence angles of 16.5° in lateral and 16.8° in vertical at full width at half maximum (FWHM) under continuous-wave (CW) 48 A operating current at 5 °C. [ABSTRACT FROM AUTHOR]

We demonstrated a mode-controllable fiber laser system with output power of 1.4 kW level. The system consists of a kilowatt-scale master oscillator power amplifier and an active feedback control system based on the stochastic parallel-gradient descent algorithm. We can convert the LP01 and LP11 modes by performing an extremum search for power in the bucket of the output beam. Under the same pump power, we obtain the mode conversion of LP11 to LP01, and the efficiency is as high as 99.5%. The maximum output power of LP11 and LP01 mode are 1396 W and 1389 W, respectively, with corresponding slope efficiencies of 85.8% and 84.1%. [ABSTRACT FROM AUTHOR]

State-of-the-art wireless power transfer (WPT) systems, based on conventional copper coils, are known to exhibit efficiencies well above 90% when operated in the resonantly coupled mid-range regime. Besides full system efficiency, the area- and weight-related power densities of the transmission coils are key figures of merit for high power applications. This article reports on a fully functional WPT system, consisting of single pancake high-temperature superconducting (HTS) coils on the transmitter and the receiver side, which exceeds the power density of most conventional systems. Despite a compact coil size, a dc-to-dc efficiency above 97% is achieved at 6 kW output power. Next to the fundamental coil design, analytical and numerical simulations of the ac loss in the HTS coils are shown, taking into account both hysteresis and eddy current contributions. The results are validated by experimental ac loss measurements of single coils, obtained by a standard lock-in technique up to frequencies of 4 kHz. Finally, experimental results of the full system performance at different frequencies and load conditions are presented. [ABSTRACT FROM AUTHOR]

This article presents the frequency-locked high-power RF oscillator using a gallium nitride (GaN) high electron mobility transistor (HEMT) amplifier and phase-locked loop (PLL) for 2.4-GHz industrial, scientific, and medical (ISM) band applications. The proposed architecture exploits the GaN power amplifier in the positive-feedback loop, whereas the desired phase shift for the target oscillating frequency is regulated from the PLL. To the best of our knowledge, this work is the first to employ the frequency locking scheme for a high-power solid-state RF oscillator. A detailed analysis of the oscillation conditions and the efficiency is provided. The prototype circuit is implemented with hybrid phase shifters and a fractional-N frequency synthesizer. The implemented RF oscillator circuit operates from 2.3 to 2.575 GHz and achieves a low phase noise of −131.8 dBc/Hz at a 1-MHz offset frequency. The power efficiency of the proposed oscillator reaches 58%, and the PLL incurs only 0.2% efficiency degradation. [ABSTRACT FROM AUTHOR]

This letter proposes a new emitter-base-collector-base-emitter (EBCBE) SiGe HBT suited for high power RF switches. Two collector-base-emitter (CBE) SiGe HBTs are merged into a single EBCBE SiGe HBT, not only to double its maximum voltage swing, but also to decrease its active area and parasitics. To further boost its power handling, a capacitive voltage distribution and a collector floating are incorporated into the new EBCBE SiGe HBT. A X-band λ/4 shunt single-pole-double-throw (SPDT) switch using the EBCBE SiGe HBT achieves measured insertion losses and isolations of 1.2/1.3 and 29.2/23.0 dB at 10 GHz in TX/RX modes, respectively. In TX mode, measured input 1-dB power compression (P1dB) is 25.4 dBm, and it can be extended to 28.5 dBm at −0.6 V base bias of the EBCBE SiGe HBT. [ABSTRACT FROM AUTHOR]

Energy consumption is one of the major concerns when planning large-scale high energy accelerator projects such as the future circular collider (FCC) and similar accelerators. To address this problem, we will describe the concept and simulations of a 1.4 MW, 800 MHz two-stage multibeam klystron (TS MBK) having a high efficiency (~80%) and compact design. [ABSTRACT FROM AUTHOR]

In this paper, we present an optical structure for two-stage beam combination to realize a high-power fiber-coupled diode laser source. In the first stage, dense spectral combination based on reflecting volume Bragg gratings is implemented for combining five diode laser blocks with a spectral separation of 1.5 nm, to a high output power submodule. In the second stage, submodules are further coaxially multiplexed by polarization beam combination and coarse spectral combination to obtain a higher output power. In the process of the beam combination, thermal effects of combining elements are also investigated. By using a temperature control, the diode laser source can steadily produce 3120-W power from an optical fiber with 105-μm core diameter and 0.2 numerical aperture. This paper demonstrates the benefits of this combination structure and the effectiveness of the temperature control.

A 500-kW continuous-wave (CW) high-power 3-dB divider is designed for the 4.6-GHz lower hybrid current drive system in the Experimental and Advanced Superconducting Tokamak (EAST). A multistepped structure is used to increase the power capacity, and a water cooling structure is introduced to reduce the thermal deformation and gas breakdown, which keeps the maximum steady-state temperature of the divider below 60 °C under full-power (500 kW) operation. The result of the simulations of the electric field shows that the power capacity of the multi-stepped structure is more than twice compared with the traditional design. Moreover, the divider shows excellent performance in the low-power test, with low return loss (-35 dB) and similar division ratio (S21 = -3.004 dB and S31 = -3.035 dB) at 4.6 GHz. Both the division ratio test and the full reflection test were carried out successfully under 250-kW CW, which suggests that the development of the 3-dB divider satisfies the design requirements.

High power semiconductor disk lasers (SDLs) were demonstrated based on the thermal management using pre-metalized diamond heat-spreader. The processing of pre-metallization using Cu-Sn alloy was developed. The resultant and influence of pre-metallization on the thermal performance of SDLs were investigated. It was found that the pre-metalized diamond heat-spreader was able to improve effectively not only the thermal resistance but also the bonding quality. 38% decrease on the thermal resistance of SDL was realized. The CW power exceeding 27 W, limited by the available pump power, was demonstrated.

In this paper, heterogeneously integrated III-V on silicon (III-V/Si) Mach-Zehnder interferometer (MZI) modulators providing record results for both linearity and high-power operation are described. Devices include hybrid III-V/Si phase modulation sections in a Si MZI, and with a single-drive push-pull operation provide a spurious-free dynamic range (SFDR) as high as 112 dB·Hz2/3 at 10 GHz, comparable to commercial lithium niobate modulators. Optical power levels up to 100 mW into the modulator provide no degradation in device linearity, with modulators demonstrating typical SFDRs of 110 dB·Hz2/3. These III-V/Si MZI modulators, using a 500-nm ``thick'' Si layer for III-V integration, demonstrate applicability for high-SFDR analog fiber-optic links without need for an erbium-doped fiber amplifier.