In this article, the impact of thermal radiation by the electron beam on the inner thermal state of a traveling wave tube (TWT) under operation is explored. A theoretical model for analyzing heat transfer by thermal radiation from the cylindrical electron beam is derived, in which the electron beam is treated as an equivalent dynamic circular disk with gray-body radiation from its side surface. By using the cathode temperature and the compression ratio of the electron beam in a TWT, the temperature of the equivalent disk is calculated. By considering the Bremsstrahlung radiation and the cyclotron radiation, the power radiated from the electron beam is derived, and the emissivities of the gray-body radiation from the equivalent disk are calculated. Using the parameters of a wideband TWT, we obtain the heat transfer via thermal radiation from the electron beam and conduct thermal analysis by simulation with and without considering thermal radiation from the electron beam, respectively. The result at 11 GHz shows that the temperature rise on the inner surface of the helix tape due to thermal radiation from the electron beam is 0.67 degrees C and 0.49 degrees C at the beginning/ending point of the helix, respectively. In the working frequency band, the temperature rise at the beginning point of the helix ranges from 0.65 degrees C to 0.72 degrees C, while that at the ending point ranges from 0.46 degrees C to 0.52 degrees C.

As a diffractive Micro-Opto-Electro-Mechanical system (MOEMS) device, the grating light valve (GLV) has high optical modulation efficiency and fast modulation rate, which can form many applications such as display and communication, and fast variable optical attenuator (FVOA) is one of the important ones. Benefiting from the low power consumption and polarization insensitivity characteristics of FVOA, an FVOA-based optical current transformer for high-voltage direct current (dc) measurement is proposed. A closed-loop optical feedback structure combining square-wave and step-wave is designed, which can track the phase shift introduced by the measured current in real time through the compensation phase shift generated by the step-wave, so as to solve the nonlinear problem of FVOA, and then improve the linearity, dynamic range, and sensitivity. The solution eliminates the need for a laser energy supply system, which increases the reliability. A prototype with a rated current of 800 A is developed, and the test results show that the ratio error (RE) fluctuation range is -0.35% to 0.38% at 80 A, -0.04% to 0.01% at 960 A, the RE and phase displacement of 1200 Hz harmonic current are -2.2% and 70 mu s, respectively, and the step response rising time in the range of 0.1-0.9 p.u. is about 135 mu s. These confirm that the prototype meets the error limit requirements of class 0.2% specified in GB/T 26216.1-2019.

For converging and switching huge amounts of multisource heterogeneous sensing data in the Internet of Things (IoT), we propose a hierarchical optical access switching networking (HOASN) architecture, the access domain of which is interconnected by passive optical distributing nodes (PODNs), distributed edge nodes (ENs) including sensing accessing interfaces. The structures of PODN, EN and SFM are proposed. And then, a cyclic signaling mechanism and a dynamic bandwidth allocation algorithm are proposed to realize pipelined transmission slot allocation and make full use of the uplink channel bandwidth resources. The simulation shows that the HOASN improves the throughput 6.9 % and 10.7%, and reduces the latency 16.4% and 35.3% for converging and switching sensing data in uplink channels, compared with two traditional Ethernet optical access schemes, respectively. Finally, we design and develop an EN prototype based on ARM Cortex-A72 series chip, set up a HOASN experimental system with two prototypes interconnected in the lab, and implement it in the Power IoT Demonstration Project in Tongli, Suzhou, China. All results show that the HOASN scheme can realize converging and switching with high throughput and low latency for sensing data.

This letter proposes a sandwich metamaterial window (SMW) for a W-band TE01 mode gyrotron travelling-wave tube (gyro-TWT), which is optimized using machine learning (ML) to achieve high transmissivity and low reflectivity in a wideband range. This SMW has three layers, BN-metal-BN, where the BN has a thickness of 1.05 mm. The metal layer is composed of hexagonal units allowing to improve the cold-test characterization of SMW. The ML optimization makes the SMW have a high simulation performance with S-11 less than -20 dB and S-21 higher than -0.14 dB within 12.15 GHz. Compared to conventional designs, the proposed SMW provides a thicker one to achieve comparable performance through a simplified fabrication process. Experimental validation confirms alignment with simulation results, demonstrating the feasibility of this approach. This work provides a scalable and cost-efficient methodology for high-frequency metasurface window design.

In order to improve the stability and reliability of the traveling wave tube (TWT), the optimization and design of the electron beam have become a key part in vacuum electronic devices. Laminar properties are a key parameter for evaluating the quality of the electron beam. The transverse displacement of the particles in the laminar electron beam is proportional to the transverse velocity. In the phase space distribution image of non-laminar properties electrons at a certain position, there is no linear relationship between the transverse displacement and the transverse velocity. The energies of particles in the electron beam are different, so the particles have different initial velocities. The particle source at the electron beam waist in the electron gun is used as a particle source for the beam wave interaction simulation. The output characteristics of the TWT more closely resemble the actual ones. A method of simplifying the particles at the electron gun beam waist into macroparticles using the K-means clustering algorithm is proposed. The macroparticle is used as a particle source in the TWT interaction zone for simulating the beam wave interaction, which reduces the simulation time from 5.53 to 0.65 h and improves the simulation efficiency. Compared with the original particle, both the simplified particle generated by the K-means clustering algorithm and the simplified particle generated by the mesh model greatly reduce the computational load of the interaction zone simulation. Compared with the results from the grid model, the simulation results of the beam-wave interaction of macroparticles, obtained by using the K-means clustering algorithm, are closer to those of the beam-wave interaction, obtained by using the original particles. By adjusting the cathode divergence angle and the distance between the anode and cathode of the electron gun of a certain type of TWT, the simulation results show that when the divergence angle is adjusted within a range of 0 degrees-1 degrees, the larger the divergence angle, the larger the radial root mean square emittance value, the worse the laminar properties of the electron beam, and the power of the output signal of the TWT decreases. When the distance between the anode and cathode is adjusted within a range of 0.8-1.6 mm, the radial root mean square emittance decreases from 2.51 to 2.22 mmmrad, the laminar properties of the electron beam are improved. The output power of the TWT increases from 328.34 to 414.10 W, and the operating frequency bandwidth with an output power greater than 300 W is expanded from 3 to 5 GHz. Therefore, the particle simplification model using the K-means clustering algorithm improves the simulation efficiency of the beam wave interaction. Based on the influence of the laminar properties of the electron beam on the performance of the TWT, the structural parameters of the electron gun can be optimized.

Optogenetic-based neuroprosthetic therapies are increasingly being considered for human trials. However, the optoelectronic design of clinical-grade optogenetic-based neuroprosthetic probes still requires some thought. Design constraints include light penetration into the brain, stimulation efficacy, and probe/tissue heating. Optimisation can be achieved through experimental iteration. However, this is costly, time-consuming and ethically problematic. Hence it is highly desirable to have an alternative to excessive animal trials. Thus, a simulation tool for optimising probe design can be an important benefit for the community. The challenge is to understand the interplay between the optical, neural and thermal aspects in the interaction of probe and living neural tissue. In this work, we propose a model which combines these aspects to allow clinically orientated neuroprosthetic teams to design neuroprosthetic probes for optogenetic therapies. Our model provides analyses for optical, thermal and optogenetic electrophysiological processes based on the energy equivalence and exchange among different physical fields. To validate and calibrate the model, optogenetic implantable neuroprosthetic arrayed probes based on miniature LEDs were developed. Then, optical, thermal measurement and neural photocurrent recording experiments were implemented on the probes. We can then provide analysis on exemplar arrayed neural probes.

To address the security problem of multi-branch tapping attacks in optical access networks, we propose a terminal thermal distribution (TTD)-based detecting and locating scheme. A TTD control module (TCM) including parts of attack detection, branch distinction, and location via effective thermal distribution product (ETDP) is set at the optical line terminal, can detect and locate the tapping attacks simultaneously occurring on multi-branch drop fiber links according to the feedback signals uploaded by each optical network units, and has the advantage of saving a lot of communication and computing resources for the physical layer. Meanwhile, what we believe to be a novel ETDP model is established to improve the efficiency of TTD image processing and judging. An experimental platform with two-branch drop fiber links and the corresponding measurements are set up in the laboratory, in which the single-wavelength OTDR analyzer is combined to verify and evaluate the experimental results of the scheme proposed in this paper. By comparing the experimental results of the TTD-based scheme with that of the OTDR, the detection success rate and location spatial resolution for multi-branch tapping attacks in the TTD-based detecting and locating scheme are around 98% and 0.006 km on average, respectively. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

This article presents a novel approach for achieving a compact high transmissivity mode converter (MC) using a metasurface-based mode converter (MMC). Specifically, the design of Ka-band MCs is proposed using this method, including TE10(R) -TE20(R) -TE01(C) (R denotes rectangular and C denotes circular, RC-MMC) and TE10(R) -TE30(R)(RR-MMC). The RC-MMC is designed in a transition metal waveguide with an alumina metasurface and a metallic resonant metasurface, while the RR-MMC is achieved using an alumina metasurface. The simulation results demonstrate that the S 21 exhibits a loss less than 0.5 dB in the 1.2-GHz bandwidth for RC-MMC and 2.3-GHz bandwidth for RR-MMC, respectively. In addition, S (21) can reach a maximum value of - 0.1 dB. Finally, a TE10(R) -TE20(R) MMC is fabricated and tested. The experimental results show that the - 3-dB bandwidth of this MMC is 2.39 GHz, and S 11 is less than - 16 dB. Using MMC instead of complex waveguide structures could pave the way for the miniaturization of MC for integration. This advancement could also extent to various applications, including the design of vacuum electronic devices and satellite-specific mode transmitters.

We propose an all-silicon TM-pass polarizer using a grating-assisted antisymmetric multimode waveguide (GAMW). The GAMW design facilitates the conversion of the undesired TE0 0 mode into the back-reflected TE1 1 mode, enabling efficient transmission of the desired TM0 0 mode with low insertion loss (IL) and high extinction ratio (ER). Furthermore, by cascading multiple GAMW structures, the device can filter TE0 0 mode over a broader spectral range effectively. The simulation results indicate that the single-GAMW-based polarizer achieves IL < 0.17 dB and ER > 40 dB in the wavelength range from 1480 nm to 1620 nm. When cascaded, the device expands the bandwidth to 275 nm (1435 nm-1710 nm), maintaining IL < 1 dB and ER > 40 dB simultaneously. The bandwidth can be further improved by cascading more GAMW structures working at different central Bragg wavelength. Limited by the measuring equipment, the measured wavelength range is between [1470 nm, 1630 nm]. The results of experiment demonstrate that the fabricated single-GAMW-based polarizer achieves IL < 0.65 dB and ER > 28.4 dB in 144 nm bandwidth ranging from 1470 nm to 1614 nm. For the cascaded-GAMW-based polarizer, IL < 0.83 dB and ER > 28.8 dB is achieved throughout the entire measuring wavelength range.

This article presents a gain-equalizing metamaterial pillbox window based on electromagnetically induced transparency effect (EITMPW). The electromagnetic (EM) characteristics and performance of a D-band folded waveguide slow wave structure (FWG SWS) traveling-wave tube (TWT) are analyzed to determine the input and corresponding loss characteristics for achieving equalized output power in band. The matching loss of the proposed EITMPW is designed to fit with the target loss, and the tested results of a W-band EITMPW basically agree with the simulated ones. In addition, the interaction model with EITMPW has lower gain fluctuation, below 0.31 dB, in the frequency range of 145-155 GHz, compared with the gain fluctuation of a TWT with the conventional pillbox window. Moreover, it improves the gain fluctuation of the FWG SWS TWT by integrating the gain equalizer into the pillbox window, which may have further applications in the compact microwave power module (MPM).

A pseudo-periodic helix slow wave structure (SWS) is proposed to provide high output power with wide bandwidth in Ka -band. The support rods with curved metal provide flat dispersion and high interaction impedance, while a pseudo-periodic SWS suppresses backward oscillation and improves output power. The simulation results show that the traveling wave tube (TWT) with this pseudo-periodic helix SWS produces an average output power of more than 600 W in the frequency range from 26 to 36 GHz with beam voltage and beam current of 11.287 kV and 0.3 A, respectively, with a maximum output power of 700 W at 31 GHz, corresponding to a maximum gain of 42.8 dB and an electronic efficiency of 20.5%. The multiphysics analysis reveals the influence of the high-frequency losses on the temperature distribution in the operating condition. The results indicate that the maximum temperature in the last 15 circles is concentrated at the end of the pseudo-period helix SWS with a peak temperature of 304 $^{\circ}$ C, resulting in better heat dissipation performance, easier structural fabrication, and less deformation.

The relationship between transverse velocity and transverse position of electron and the electron beam distribution in the helix TWT is analyzed. The gain of helix TWT is simulated by changing the angle spread of particle source under different laminar state of electron beam. The results show that the RMS-emittance can be used to quantify the laminar properties of electron beam in the helix TWT.

This paper reports a beam-wave interaction model with folded waveguide and frequency-selective attenuator. Four-cut split ring resonator and metal-substrate-metal structure are adopted to form the frequency-selective structure. The attenuator is designed to selectively attenuate the backward wave. Favorable transmission around the operating frequency can be achieved by the proposed attenuator. The wave in the input section can participate in the interaction in the output section. The PIC simulation shows that 66.7 W stable output power can be achieved by metamaterial-loaded interaction circuit. The output and reflection signals are stable for more than 20 ns without obvious oscillation, meaning for the effective suppression of the backward-wave oscillation.

In this paper, a low voltage standing wave ratio (VSWR) broad bandwidth microwave window based on metamaterial was presented for W-band gyro traveling wave tubes (Gyro-TWTs). The microwave window is designed on a dielectric surface, where the dielectric is boron nitride (BN). A sandwich-like structure is adopted, the top and the bottom layers are dielectrics, and the middle layer is metal. The thickness of each piece of dielectric is 0.4mm, and the thickness of metal is 0.0008mm. In the cold-test simulation, it achieves a bandwidth of 13.5GHz with VSWR below 1.2 at W-band, which is broader than that of pure BN dielectric.

The distribution parameters of electron beam have an important influence on the TWT interaction. To be more in line with the actual situation, the distribution of the electron beam generated by the electron gun is analyzed. According to the distribution of the energy and density of electron beam, the concentric rings of electron beams model is built, which simplifies calculation and contains information on electron beam. Based on the model, a nonuniform electron beam is obtained. The output power, gain and SNR are calculated. Through simulation analysis, the results show that nonuniformity leads to a decrease in the maximum output power, as well as a decrease in the gain and SNR.

The Smith-Purcell radiation produced by electrons moving closely to a grating can be enhanced by resonances. Here, we show a method to manipulate the directionality of the resonance-enhanced radiation. Using the rigorous coupled-wave analysis method, we compare the radiation from symmetric and asymmetric gratings, showing that the enhanced Smith-Purcell radiation can become unilateral with a perturbation that breaks the structural symmetry. Our work provides an effective method for frequency-domain calculation of Smith-Purcell radiation and also an approach to realize more efficient use of the radiation.

A rectangular split resonant ring (RSRR) metamaterial absorber (MMA) was proposed to suppress backward wave oscillation (BWO) in a ring-bar traveling wave tube (RB-TWT). The unit structure parameters of the RSRR were optimized to maximize the absorption of backward waves. The amplification performance of the proposed slow wave structure (SWS) was also carried out by using particle-in-cell (PIC) simulations. With an input power of 0.125 W, the operating bandwidth of the RB-TWT loaded with RSRR-MMA was 8–13 GHz, which was higher than that loaded with centralized attenuators (CAs; 8–11.5 GHz). The output power exceeded 5 kW with a gain of 46 dB in the range of 9.1–12.7 GHz. Furthermore, its saturated output power exceeded 5 kW, the saturated gain was over 41 dB, and the saturated electronic efficiency was more than 14.5% over the entire working frequency range of 8–13 GHz. Therefore, the RB-TWT with RSRR-MMA achieved a wider bandwidth compared with that of the RB-TWT with CA, where exhibits the potential application of RSRR-MMA in high-power vacuum electronic devices.

We propose a key generation scheme at the sensing layer of Internet of Things, which can protect huge amount of sensing data via utilizing the randomness of the data itself, as well as a few control parameters. The performance of this scheme, such as key generation rate and amount, is analyzed by simulation. Finally, the challenges in future research are pointed out.

A novel in- line closed-loop polarization maintaining fiber temperature sensor (CPMF-TS) is designed, which adopts a reciprocal configuration to reduce the susceptibility to optical path noises and environmental disturbances, and uses a closed-loop square-wave modulation and demodulation scheme to improve sensitivity, linearity, and dynamic range, while reducing the influence of system power fluctuations on accuracy. A CPMF-TS prototype was developed, whose performances were analyzed and compared with the open-loop scheme. The results show that the relative error (defined as the maximum error divided by the tested measured range) of CPMF-TS using 2.5 or 3.5 mm sensing fiber is 1.1%, which is less than 3% or 1.64% of the open-loop system after third- or fourth-order polynomial-fitting. The closed-loop scheme is shown to be effective in reducing the impact of sensor fiber cut length errors and optical power dependence on system performance, resulting in a more accurate and stable output over a wider temperature range. Combined with the inherent insulation and antielectromagnetic interference advantages of optical fiber sensors, CPMF-TS has obvious potential application prospects for accurate temperature measurement in high temperatures, high voltage or harsh electromagnetic field environments such as the transformer winding temperature measurement and the aeroengine temperature measurement.

A D-band folded waveguide (FWG) traveling-wave tube (TWT) with metamaterial absorber (MMA) is proposed, where the MMA is designed to suppress the backward oscillation in this FWG-TWT. The MMA consists of single splitter rings (SRs) with silica layer that adheres to the inner surface of a metallic waveguide. The absorption frequency of this MMA is well designed to cover the backward frequency of FWG slow wave structure (SWS). Therefore, this MMA achieves the transmission of forward wave and the attenuation of backward wave, which improves the performance of FWG-TWT. Simulation results show that 66.1 W saturated output power driven by 5 mW 150GHz input signal, with a corresponding gain of 41.2 dB, and a bandwidth of 18 GHz with output power greater than 40 W can be achieved with 90 periods SWS. The proposed FWG-TWT with MMA may provide a high gain for high frequency amplifier, where it is helpful to design an FWG-TWT with low input power.