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The developing terahertz wireless communication demands higher performance modulators. In this Letter, a mechanism of resonance mode transformation for a high-speed terahertz direct amplitude modulator with rather low insertion loss and high modulation depth is presented. By embedding an H-shaped resonance structure, which consists of a fin-line and two flip-flopped GaAs Schottky diodes, into the E-wall of a waveguide, the fed terahertz waves are modulated by the inductive-capacitive (LC) resonance transformation of the structure. Based on this mechanism, a modulator working in the frequency band around 140 GHz is fabricated and packaged. Thanks to the LC resonance transformation, the presented modulator exhibits a low insertion loss of 1.8 dB at 138 GHz, a large modulation depth higher than 99% at 148 GHz, and high modulation speeds up to 30 Gbps at 146 GHz. Accordingly, the presented mechanism paves a promising route to develop high performance terahertz direct modulators, which is of great significance for terahertz high-speed wireless communication. [ABSTRACT FROM AUTHOR]

A microwave power transmission (MPT) demonstration system was assembled to comprehensively emulate the operating mode of MPT in space solar power station (SSPS). Based on solid power amplifier and phased antenna array, this system comprised three main parts, that is, microwave power transmitting subsystem, microwave power rectenna subsystem, and power beam steering subsystem. It was employed to validate the constraint relationship between beam collection efficiency and the sizes of transmitting antenna and rectenna, transmission distance, operation frequency. High efficiency rectifying and accurate beam steering were also demonstrated. The power transmitting antenna was composed of 64 sub‐arrays of patch antennas, with the dimension of 1.2 × 1.2 m2. In addition, the rectenna array was constructed as a corner truncated square with the side length of 2 m. Its design was based on the concept of perfectly matched layer and integrated rectifying surface. The power beam steering subsystem, implemented with software retrodirective idea, pointed the microwave beam to the rectenna according to the direction of arrival of the pilot signal. The experimental MPT system, operating at 5.8 GHz, transmitted 910 W microwave power across 30 m distance. At the power receiving end, the optimum rectenna conversion efficiency of 49.3% was obtained. With aid of the beam steering subsystem, beam granularity, and beam steering accuracy of 0.23 and 0.18° were achieved, respectively. The compositive experiment verified all function as power transmitting, receiving, rectifying, and steering of MPT system. MPT technology is thus driven toward engineering application, and will ultimately space solar power exploration. [ABSTRACT FROM AUTHOR]

The prevalence of varicoceles in male infertility is increasing; however, the exact mechanism is unknown, and no direct studies of varicose spermatic veins have been conducted. Three patients with varicocele infertility were included to explore the possible factors that cause varicocele infertility, and varicose and nearby normal veins were harvested by varicocelectomy. RNA sequencing was performed on six vascular samples, followed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses of the screened differential expressed genes which were validated by quantitative reverse transcription‐polymerase chain reaction. The genomes of the patients were analysed using next‐generation sequencing to screen for genetic factors behind varicocele infertility. 1171 genes were upregulated and 2772 were downregulated in varicose spermatic veins compared with those in normal veins. These genes were significantly enriched in the alcohol consumption pathway. HIST1H4C, HIST1H4F, HIST1H4K, TM9SF1, and TMEFF1 were significantly differentially expressed. The genomic results identified patients with mutations in CFTR, NANOS1, SRCAP, GATA4, GCM2, TUBB1, ALDH7A1, ANTXR1, and MAP3K1. In conclusion, our results indicated that Alcohol consumption may be a cause of varicoceles. Mutations in certain genes, such as CFTR, may be a cause of male infertility due to varicoceles. [ABSTRACT FROM AUTHOR]

As the operating frequency increases, the output power of traditional frequency doublers becomes too low to drive the next stage devices. To address this problem, a double-layer meta-chip circuit consisting of a symmetrical split ring (SSR) structure with a doubler circuit is presented. It combines the transmission mode in the rectangular waveguide with the resonance mode in the meta structure. The meta structure improves the coupling efficiency between the diode and electromagnetic energy, strengthens the electric field at the diode, and ultimately enhances the efficiency of the frequency doubler at low input power. From 160–180 GHz, the experiments show that the frequency doubler with SSR achieved a peak efficiency of 22.4% with an output power of 10.6 mW. Its performance of maximum output power is 45.2% better than the traditional structure, which provides an important technical approach to achieve higher efficiency at low input power. [ABSTRACT FROM AUTHOR]

Text similarity, as an important basis for scoring subjective items in the examination, directly determines the examination results of candidates and the work efficiency of teachers. Therefore, this paper first introduces the theoretical basis of text similarity computing and compares different calculation methods. Then, the text-similarity algorithm is designed, where by conceptualizing text terms, the computing methods based on corpus and knowledge base are combined. Then, according to the similarity computing model of text terms, an automatic grading system for exercises is designed, including the design of technical architecture, the design of functional modules, and the realization process of comprehensive grading. Among them, the grading module is the core module of the system and the key to automatic grading. The systematic test results show that the problem scoring system designed in this paper has little difference from manual marking and can achieve good scoring results. [ABSTRACT FROM AUTHOR]

The efficiency of a rectenna varies under the influences of receiving polarization tilt angle, operating frequency, input power, and load value in different applications. Yet, no reported rectenna can realize stable efficiency when all these factors vary within a wide range. To solve this problem, an all-polarized rectenna is proposed in this article, composed of a dual-input rectifier and a dual-polarized (DP) antenna. By introducing a novel six-port coupler, the rectifier maintains stable efficiency at wideband, wide input power, and dc load ranges. Moreover, the efficiency of the rectifier keeps stable when the antenna receives power at different polarization tilt angles. Accordingly, a DP antenna with extended bandwidth and 3-dB beamwidth is implemented. Finally, the rectenna is formed. The prototype can maintain beyond 70% of the peak efficiency from 1.7 to 2.5 GHz. At a power density as low as 1 μW/cm2, efficiency can reach 24.4%. Furtherly, the rectenna is demonstrated by forming a battery-less digital clock. The clock can be powered wirelessly by a WiFi router or cellular base station with maximum distances of 1 or 70 m respectively. Besides, the clock can successfully function under significant transmitting-direction deviation or polarization misalignment between the power source and the rectenna. [ABSTRACT FROM AUTHOR]

This paper presents a perfectly matched inhomogeneous receiving metasurface for line source incidence, based on the effective medium equivalency. Each building block of the inhomogeneous metasurface has effective constitutive parameters that satisfy a specific relationship dependent on the location of the line source. By doing so, the reflection from the receiving metasurface for the cylindrical wave incidence can be significantly suppressed, improving the total reception efficiency greatly. Theoretical analysis, numerical calculation, full‐wave simulations and experimental results are consistent with each other, showing promising applications in some short‐range wireless power transmission systems, where the incident wave is non‐planar. [ABSTRACT FROM AUTHOR]

Noncontact measurements of material parameters have important applications in various fields. In this paper, we propose a noncontact measurement of complex permittivity for electrically small samples at microwave frequencies. Based on Rayleigh approximation, we propose a noncontact measurement approach that can linearly retrieve complex permittivity from the measured impedance change. Using a subwavelength resonance, far-field radiation can be effectively suppressed, and thus the measurement is not notably influenced by unwanted environmental reflection. With the features of simple calibration and noncontact measurement, our method can be widely used in repeated on-site measurements of complex permittivity for small-sized samples at microwave frequencies. [ABSTRACT FROM AUTHOR]

Alibakhshikenari, B. S. Virdee, C. H. See, P. Shukla, S. Salekzamankhani, R. A. Abd-Alhameed, F. Falcone, and E. Limiti, Sci. Publisher's Note: "High-performance direct terahertz modulator based on resonance mode transformation for high-speed wireless communication" [Appl. Phys. Alibakhshikenari, B. S. Virdee, C. H. See, R. A. Abd-Alhameed, F. Falcone, and E. Limiti, Sci. [Extracted from the article]

The state-of-the-art phased array-based digital beamforming systems suffer from disadvantages of high power consumption, high cost, and system complexity due to the massive use of transmitter/receiver (T/R) modules and high-speed digital and digital–analog mixed devices. In this paper, we point out that by proposing a new concept “complex domain” radio frequency (RF) frontend, the relatively slowly changed waveform delay information required to accomplish adaptive beamforming can be separated from wideband RF signals, based on which a self-contained beamforming system can be implemented with a low-speed baseband. By introducing vector RF multipliers in the proposed frontend, the amplitude and phase of RF signals can be simultaneously controlled by the real and imaginary parts of complex numbers, such that beamforming algorithms derived in complex domain can be directly applied without any form of transformation. By doing so, the massive use of conventional T/R modules and high-speed baseband devices can be avoided. Theoretical analysis and experimental demonstration based on commercial components have validated the proposed approach. Our method is able to significantly simplify the realization and decrease the cost of wideband digital beamforming systems, and can be widely used in low cost, power efficient beamforming applications. [ABSTRACT FROM AUTHOR]

An RF–DC rectifier is an important part in a wireless power transfer system. Diode-based rectifiers are widely used in low-power harvesting scenarios, and for high power, a transistor based on the time-reversal duality was proposed. This paper presents a high-efficiency self-synchronous RF–DC rectifier based on a waveform-guided design method and an improved rectification model of a commercial GaN device. The main contributions of this paper are that (1) an improved transistor model with correct reverse bias is built for accurate rectifier simulation, and (2) a new design method of self-synchronous RF–DC rectifier is proposed: as soon as the operating mode of the rectifier, input power, and DC load are set, matching and coupling network can be calculated directly based on waveform-guided method, thus design and adjustment process of a conventional power amplifier (PA) due to the duality between a PA and a rectifier would no longer be required. A 5.8 GHz self-synchronous RF–DC rectifier is designed for validation, and the optimum RF–DC conversion efficiency is 68% with 12 W input power as well as 19.9 V output DC potential with 50 Ω load resistance. The proposed rectifier is suitable for high input power rectification applications of wireless power transfer. [ABSTRACT FROM AUTHOR]

This article presents a novel interdigital capacitor resonator (ICR), which has a high spurious frequency and compact size. A six-pole high-temperature superconducting (HTS) bandpass filter (BPF) has been designed and fabricated with this ICR on a double-sided MgO-based YBCO thin film. Measurement at cryogenic temperature shows a fractional bandwidth of 0.4%, and an ultra high spurious passband at about 4.1 f0. Moreover, the measurement shows a good agreement with simulation in wideband response. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:443-447, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27324 [ABSTRACT FROM AUTHOR]

Wearable systems are important for future smart home care for the disabled and ageing population. One of the key challenges is the power supply. One solution is to develop an energy harvesting system suitable for providing power wirelessly. The matching network and filter in traditional energy harvesting system occupy lots of space, introduce additional losses, and reduce the total efficiency. This paper presents a novel filtering antenna suitable for wearable energy harvesting systems. The developed antenna has a broadband operation, harmonics suppression, compact size, and low cost. Firstly, a novel technique for broadband filtering antenna modeling and design in order to realize complex input impedance is presented. By adjusting the external quality factors and coupling coefficients of the resonators, complex impedance matching can be realized. Then, the theory of characteristic mode is used for the modal analysis of the filtering antenna. To verify the design concept, a C‐band circularly polarized filtering antenna with complex impedance is designed and fabricated. The results show that the impedance bandwidth is more than 14.5% with a peak gain higher than 8.5 dBi. The proposed antenna is conjugate matched to the rectifying circuit at 5.8 GHz and mismatched at the second harmonic frequency to suppress the harmonic reradiation, leading to a compact rectenna structure. [ABSTRACT FROM AUTHOR]