arXiv subjects

C Liu

Publications and source records attributed to C Liu.

8 recordsLinked to original sources

arXiv2026

Coherent power combining of four-way injection-locked 5.8-GHz magnetrons based on a five-port hybrid waveguide combiner

A high-efficiency power-combining method for four-way 5.8-GHz magnetrons based on the external injection-locking technique is presented in this article. The method uses a nonisolated, lossless five-port hybrid waveguide combiner for power combining. Meanwhile, the injection-locking technology has been applied to magnetrons for achieving coherent power combining. The phase fluctuation of the injection-locked magnetron, without the presence of a phase-locked loop, measured nearly 2.5 degree. In contrast, when a phase-locked loop was introduced, the phase fluctuation reduced significantly to approximately 0.5 degree. This phase accuracy can fully meet the requirements of combining experiments. Four magnetrons worked in injection-locked states without phase-locked loop. The proposed power-combining system is designed, measured, and analyzed. Measurement results show that a high-power-combining efficiency of over 95% is achieved by injection-locked magnetron without PLL, with the best efficiency reaching up to 97.7% with phase control of the injected signals. Experimental results reveal that the magnetron phase-pushing effects and the ripple in high-power dc voltage and current have a minor impact of approximately 4% on the combining efficiency.

physics.app-ph↗

arXiv2026

A Novel Stability Improvement Method of S-Band Magnetron Systems Based on Its Anode Current Feature

Magnetrons are widely used as a high-efficiency, large-power, and low-cost microwave source. This article proposes a method to improve the magnetron output characteristics based on regulating its anode current by a novel active distortion eliminator. It takes advantage of the constant current state of MOSFETs to suppress the anode current ripple and eliminate the magnetron output ripples. An improved switch-mode power supply is applied to a 1-kW commercial S -band magnetron in the experiment. The peak-to-peak anode current ripple is reduced from 31 to 7 mA. The spectral width of the free-running magnetron is decreased from 246 to 87 kHz. In the injection locking state, the spur noise is significantly reduced with a maximum suppression strength of 23 dB at a 100-Hz offset. The peak-to-peak value of the magnetron magnitude and phase jitter are suppressed to 15% and 16% of their original values at a power injection ratio of 0.13. This method provides a novel approach for stabilizing the output phase of an injection-locked magnetron, making it promising for applications in phased arrays, wireless power transfer, particle accelerators, large-power communication, and other scenarios that require high phase stability.

physics.app-ph↗

arXiv2026

Novel miniaturized low-pass filters from artificial transmission line structures

A novel design on miniaturized low-pass filters from artificial transmission line structures is proposed. Reactance components, i.e. capacitors and inductors, are directly constructed from microstrip structures based on electromagnetic simulation and parameter extraction. The constructed reactance components are integrated to build low-pass filters. The results of two 5th-order Butterworth and 0.5 dB ripple Chebyshev low-pass filters, which are realized by the proposed method, are presented. The proposed low-pass filter is compact and its size is only 23% of a conventional filter. The simulation agrees well to the measurements, which shows the validation of the proposed design method. The miniaturized low-pass filters have good applications in microwave systems.

physics.app-ph↗

arXiv2025

A Novel Injection-Locked S-Band Oven Magnetron System Without Waveguide Isolators

A novel injection-locked S-band microwave oven magnetron system is proposed, analyzed, and experimented. The magnetron is considered as a two-port oscillator, and the filament structures of it are used as a port for injection locking. To our knowledge, it is the first time that microwaves have been injected through magnetron filaments. The microwave is injected into the magnetron filter box using a self-designed injection structure, entering the resonant cavity through filament leads. The intrinsic isolation between the magnetrons output and filament is utilized as an isolator. No waveguide circulators or couplers between the injection source and the magnetron were used in the system, resulting in low cost and compact injection locking. Two types of injection structures were performed. The maximum locking bandwidth of 0.7 MHz was achieved at an injection ratio of 0.2. The weight and volume of the proposed injection-locked magnetron system were reduced to 28% and 16%, respectively. The magnetron output is successfully locked by an external signal. The experiment results reveal that the proposed low-cost injection-locked oven magnetron system works reliably. It has significant potential applications for future microwave ovens with frequency-selective heating to improve both efficiency and uniformity.

physics.app-ph↗

arXiv2025

A C-band microwave rectenna using aperture-coupled antenna array and novel Class-F rectifier with cavity

A rectenna (rectifying antenna) is usually applied to a microwave power transmission (MPT) system as a terminal, which receives microwave (MW) power and converts them into DC power. A 5.8 GHz aperture-coupled patch antenna array is developed with a gain of 19.5 dBi, which is a part of the rectenna. A novel Class-F rectifier with a series diode is proposed to achieve a high rectifying efficiency based on harmonic termination techniques. The input circuit of the proposed rectifier is taken into consideration to reach the Class-F condition, while mostly only the output circuit is involved in conventional Class-F designs. A low-pass filter based on defected ground structure is implemented, which not only blocks the harmonics produced in rectifying but also presents desired impedance at harmonics. The current and voltage waveforms on the diode are well enforced. The radiation feature of the rectifier is presented as well. It shows that an optimized cavity, which shields the parasite radiation, may achieve a 5% enhancement on the MW-to-DC conversion efficiency. A C-band rectifier based on HSMS-286 Schottky diode is fabricated and measured. A MPT simple demo system is constructed with the proposed rectifier and antenna. A measured maximum MW-to-DC conversion efficiency of 72% is achieved on the rectifier. The design method is extremely valuable in a high conversion efficiency rectenna design based on harmonic termination techniques.

physics.app-ph↗

arXiv2021

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$

We report the studies of detailed magnetic relaxation and isothermal magnetization measurements in the vortex state of the 112-type iron-pnictide Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$ superconductor with $T_c$ $\sim$ 22 K. In the isothermal $M(H)$, a well defined second magnetization peak (SMP) feature is observed in the entire temperature range below $T_c$ for measurements with $H$ $\parallel$ $c$-axis. However, for $H$ $\parallel$ $ab$-planes, the SMP feature is suppressed at low temperatures, which might be due to 2D Josephson vortices forming at low temperatures and high magnetic fields in such an anisotropic system. A rigorous analysis considering the magnetic relaxation data for $H$ $\parallel$ $c$-axis suggests an elastic to plastic pinning crossover across $H_p$, which also seems accompanied with a possible phase transition in vortex lattice near $H_p$. Moreover, point disorder and surface defects are likely to be the dominant sources of pinning, which contribute to the $\delta l$-type of pinning in the sample. A high $J_c$, in access of 10$^5$ A/cm$^2$ observed could potentially make this material technologically important.

cond-mat.supr-con↗

arXiv2020

Intrinsically patterned two-dimensional materials for selective adsorption of molecules and nanoclusters

Two-dimensional (2D) materials have been studied extensively as monolayers 1-5, vertical or lateral heterostructures 6-8. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules 9,10. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.

cond-mat.mtrl-sci↗

arXiv2018

Quantum Critical Phenomena in a Compressible Displacive Ferroelectric

The dielectric and magnetic polarizations of quantum paraelectrics and paramagnetic materials have in many cases been found to initially increase with increasing thermal disorder and hence exhibit peaks as a function of temperature. A quantitative description of these examples of 'order-by-disorder' phenomenona has remained elusive in nearly ferromagnetic metals and in dielectrics on the border of displacive ferroelectric transitions. Here we present an experimental study of the evolution of the dielectric susceptibility peak as a function of pressure in the nearly ferroelectric material, strontium titanate, which reveals that the peak position collapses towards absolute zero as the ferroelectric quantum critical point is approached. We show that this behaviour can be described in detail without the use of adjustable parameters in terms of the Larkin-Khmelnitskii-Shneerson-Rechester (LKSR) theory, first introduced nearly 50 years ago, of the hybridization of polar and acoustic modes in quantum paraelectrics, in contrast to alternative models that have been proposed. Our study allows us to construct for the first time a detailed temperature-pressure phase diagram of a material on the border of a ferroelectric quantum critical point comprising ferroelectric, quantum critical paraelectric and hybridized polar-acoustic regimes. Furthermore, at the lowest temperatures, below the susceptibility maximum, we observe a new regime characterized by a linear temperature dependence of the inverse susceptibility that differs sharply from the quartic temperature dependence predicted by the LKSR theory. We find that this non-LKSR low temperature regime cannot be accounted for in terms of any detailed model reported in the literature, and its interpretation poses a new empirical and conceptual challenge.

cond-mat.mtrl-sci↗