Large Average Power Research Articles

Pulsed fiber laser with MoyV1-ySe2-based saturable absorber

Exploring a new nonlinear material is important for ultrafast optics. Ternary transition metal chalcogenides are coming into view as a prospective kind of optoelectronic materials because of the unique physical and chemical properties. Herein, the MoyV1-ySe2 nanosheets were made by using the liquid phase exfoliation method, and their application in Q-switched Er-doped fiber (EDF) laser was studied. It was found that MoyV1-ySe2 materials has the remarkable nonlinear saturable absorption properties. By incorporating the MoyV1-ySe2-microfiber SA into an EDF cavity, the Q-switched operation was obtained. The narrowest pulse duration and largest pulse energy were 1.8 μs and 121.9 nJ. A large average output power of 26.84 mW was reached at pump power of 900 mW. The large signal-to-noise ratio of 75 dB verifies the superb stable property of Q-switched state. These results confirm that as a Q-switcher, MoyV1-ySe2-microfiber possesses a fine performance on good stability and high power pulsed fiber lasers.

Aeroacoustics-driven jet-stream wind energy harvester induced by jet-edge-resonator

Wind energy harvesting has attracted attention for the past few decades as a potential solution to supply sustainable power for wireless sensors network (WSN). In this paper, we reported an aeroacoustics-driven piezoelectric energy generator (APEG) without moving parts to scavenge wind energy. Aeroacoustics principle, a complex Multiphysics process including the coupling among physics fields of fluid, solid, acoustics and electricity, was used for converting wind energy to mechanical energy applied on the APEG. At 79.6 m/s jet velocity, the APEG delivers high closed-circuit current (4.7 mA) at 1.5 kΩ, open-circuit voltage (12.9 V), and large average output power (15.5 mW). This result was further validated by powering up different commercial electronic devices. Moreover, the complex aeroacoustics principle was studied both experimentally and theoretically. The velocity distribution of flow field and stress distribution of piezoelectric unit were simulated and analyzed. The proposed APEG with simple structure, small volume and high performance is promising for supplying sustainable power for WSN at harsh environment such as high-speed aircrafts.

A new method for spatial mode shifting of stabilized optical cavities for the generation of dual-color X-rays

We propose an innovative method to shift the transversal position of the focal point of an optical cavity keeping it actively frequency stabilized. Our cavity is a 4 mirrors bow-tie cavity and the spatial shift of the resonant mode is obtained by properly rotating the two curved mirrors by piezo actuators. This method allows us to move the transversal position of the cavity focal point of 135µm in a time of 50ms, keeping the resonance condition of the cavity by means of the Pound–Drever–Hall technique. We propose to use this technique for the generation of 2-color X-rays via Inverse Compton Scattering (ICS). This technique exploits the large average power stored in the high finesse cavity by shifting the laser beam with respect to the electron beam trajectory, hence controlling the spatial superposition of the electron and photon beams in the interaction region. Arranging two cavities assembled one on top of the other, with different collision angle with the electron beam, allows the generation of X-ray bursts of different energies just by swiftly moving the two cavities, switching the two focal points onto the electron beam trajectory, thus activating in sequence two different ICS spectral lines.

High Entropy Semiconductor AgMnGeSbTe4 with Desirable Thermoelectric Performance

AbstractA new p‐type high entropy semiconductor AgMnGeSbTe4 with a band gap of ≈0.28 eV is reported as a promising thermoelectric material. AgMnGeSbTe4 crystallizes in the rock‐salt NaCl structure with cations Ag, Mn, Ge, and Sb randomly disordered over the Na site. Thus, a strong lattice distortion forms from the large difference in the atomic radii of Ag, Mn, Ge, and Sb, resulting in a low lattice thermal conductivity of 0.54 W m−1 K−1 at 600 K. In addition, the AgMnGeSbTe4 exhibits a degenerate semiconductor behavior and a large average power factor of 10.36 µW cm−1 K−2 in the temperature range of 400–773 K. As a consequence, the AgMnGeSbTe4 has a peak figure of merit (ZT) of 1.05 at 773 K and a desirable average ZT value of 0.84 in the temperature range of 400–773 K. Moreover, the thermoelectric performance of AgMnGeSbTe4 can be further enhanced by precipitating of Ag8GeTe6, which acts as extra scatting centers for holes with low energy and phonons with medium wavelength. The simultaneous optimization in power factor and lattice thermal conductivity yields a peak ZT of 1.27 at 773 K and an average ZT of 0.92 (400–773 K) in AgMnGeSbTe4‐1 mol% Ag8GeTe6.

Ultra Reliable Communication via Optimum Power Allocation for HARQ Retransmission Schemes

In this work, we develop low complexity, optimal power allocation algorithms that would allow ultra reliable operation at any outage probability target with minimum power consumption in the finite blocklength regime by utilizing Karush-Kuhn-Tucker (KKT) conditions. In our setup, we assume that the transmitter does not know the channel state information (CSI). First, we show that achieving a very low packet outage probability by using an open loop setup requires extremely high power consumption. Thus, we resort to retransmission schemes as a solution, namely Automatic Repeat Request (ARQ), Chase Combining Hybrid ARQ (CC-HARQ) and Incremental redundancy (IR) HARQ. Countrary to classical approaches, where it is optimal to allocate equal power with each transmission, we show that for operation in the ultra reliable regime (URR), the optimal strategy suggests transmission with incremental power in each round. Numerically, we evaluate the power gains of the proposed protocol. We show that the best power saving is given by IR-HARQ protocol. Further, we show that when compared to the one shot transmission, these protocols enable large average and maximum power gains. Finally, we show that the larger the number of transmissions is, the larger power gains will be attained.

Operation Efficiency Analysis Study of Photovoltaic System Fixed Type and Variable Type

This study introduces the comparison of efficiency levels of photovoltaics systems by analyzing various installation systems of photovoltaics systems and optimization techniques and proposes a system using techniques In this study, the generation time and power generation of two types of photovoltaic power generation system were measured and compared. Comparing the monthly power generation time with the power generation amount, it is found that there are many fixed variable photovoltaic power generation systems with a large average daily power generation time of 0.8h and an average power generation capacity of 2,871kw from November to December. Total Fixed Variable Total Daily Power Generation Time 2.4h The power generation amount is 23,184kw, showing a large amount of electric power generation.

Lead-Free Piezoelectric MEMS Energy Harvesters of (K,Na)NbO3 Thin Films on Stainless Steel Cantilevers

We fabricated piezoelectric MEMS energy harvesters (EHs) of lead-free (K,Na)NbO3 (KNN) thin films on microfabricated stainless steel cantilevers. The use of metal substrates makes it possible to fabricate thin cantilevers owing to a large fracture toughness compared with Si substrates. KNN films were directly deposited onto Pt-coated stainless steel cantilevers by rf-magnetron sputtering, thereby simplifying the fabrication process of the EHs. From XRD measurement, we confirmed that the KNN films on Pt-coated stainless steel cantilevers had a perovskite structure with a preferential (001) orientation. The transverse piezoelectric coefficient e31f and relative dielectric constant εr were measured to be -3.8 C/m2 and 409, respectively. From the evaluation of the power generation performance of a KNN thin-film EH (length: 7.5 mm, width: 5.0 mm, weight of tip mass: 25 mg), we obtained a large average output power of 1.6 µW under vibration at 393 Hz and 10 m/s2.

Optimizing of mathematical modeling of induced current for electronic anti-fouling system and estimate of system performance under different excitation signal

A new optimizing method of mathematical analytical modeling of induced current for electronic anti-fouling technology is used in the present study to solve the problem of large calculated amount and complex deducing process caused by traditional segmented function method under different excitation signal, and an exact 2D finite element method is used to calculate induced current in a real electronic anti-fouling system, and the finite element calculation results can fit well with the results calculated by the optimizing analytical model of induced current under the excitation signal with different waveform. Furthermore, the average power density of induced current and the efficiency of energy transformation for EAF system are calculated to estimate the system performance under different excitation signal. The calculation result shows that: 1 the positive – negative square wave excitation signal can make the largest average power density of induced current and the sine wave excitation signal makes the smallest; 2 the sawtooth wave excitation signal can make the highest efficiency of energy transformation and the positive – negative square wave excitation signal makes the lowest.

Microcutting and Hollow 3D Microstructures in Glasses by In-volume Selective Laser-induced Etching (ISLE)

3D microfluidic devices and assembled micro mechanics inside fused silica glass are produced directly from digital CAD data e.g. for markets like medical diagnostics. To exploit the potential productivity of new high average power fs-lasers (150 W – 1 kW) a modular high speed scanning system has been developed. Acousto-optical beam deflection, galvo-scanners and translation stages are controlled by CAM software. Using a lens with 10 mm focal length a focus radius of 1 μm is scanned with a velocity of 12 m/s on 400 μm track radius enabling the up-scaling of the ISLEprocess using large repetition rate and large average power.

Coding for Inductively Coupled Channels

Inductive coupling is a technique wherein one device (the reader) induces an electrical current in another device (the tag), thereby providing not only power for the tag, but also a communication channel. In this paper, we focus exclusively on the reader-to-tag channel. The first part of this paper presents modulation codes that possess a high minimum and a high average power. This is important, since the tag gets its entire power from the received signal, and the information should be modulated in a way that maximizes the power transferred to the tag. The presented modulation codes compare favorably to codes used in radio frequency identification applications today. The second part of the paper describes modulation codes with some error-correcting capabilities. In fact, most errors in the reader-to-tag channel are due to incorrect timing. Here, we propose to model the timing errors in the reader-to-tag communication channel by a simple bit-shift channel, and we will present optimal (in the sense of maximizing the code rate for a given block length) single bit-shift error-correcting codes for this simple bit-shift channel that also have large average power.

Influencing Parameters Analysis of Solar Energy Regenerator Performance

The paper studied the effect of running and structural parameters on solar energy regenerator performance, in which pebble was storage material. Comparing simulated values to tested values of outlet air temperature, good agreement was achieved, which proved the model was correct. Taking average regenerative power as target function, the simulated results showed that the larger inlet air temperature, the larger average regenerative power. The smaller void fraction, the larger average regenerative power. The larger cross section velocity, the larger average regenerative power.

New Insights into Optimal Discrete Rate Adaptation for Average Power Constrained Single and Multi-Node Systems

The throughput-optimal discrete-rate adaptation policy, when nodes are subject to constraints on the average power and bit error rate, is governed by a power control parameter, for which a closed-form characterization has remained an open problem. The parameter is essential in determining the rate adaptation thresholds and the transmit rate and power at any time, and ensuring adherence to the power constraint. We derive novel insightful bounds and approximations that characterize the power control parameter and the throughput in closed-form. The results are comprehensive as they apply to the general class of Nakagami-m (m ≥1) fading channels, which includes Rayleigh fading, uncoded and coded modulation, and single and multi-node systems with selection. The results are appealing as they are provably tight in the asymptotic large average power regime, and are designed and verified to be accurate even for smaller average powers.

Efficient, polarised, gain-switched operation of a Tm-doped fibre laser

We present a monolithic, robustly polarised thulium fibre laser which produces pulses with 25 ns duration and energy of up to 35 µJ. A pulsed 1.55 μm source was used to gain switch the laser at repetition rates of up to 300 kHz, producing average powers of up to 8 W at 2.044 µm. To the best of our knowledge this is the highest power gain-switched thulium fibre laser and it is also the first with a linearly polarised output. The large repetition rate, pulse energy and average power will enable efficient energy extraction from a large mode-area, polarisation maintaining thulium fibre amplifier.

Efficient microwave processing of oil–water emulsion cylinders with lateral and radial irradiations

Abstract A detailed theoretical analysis has been carried out to assess the role of lateral and radial irradiations on the microwave heating of 2D cylinders for both o/w and w/o emulsion samples. Lateral irradiation represents the sample incident at one direction with the source at infinity whereas radial irradiation represents the situation where the sample is incident with microwave radiations from the coaxial cylindrical cavity at infinity. For both of lateral and radial irradiations, the effective microwave incidence from the source is assumed to be identical. A preliminary analysis on the microwave heating of samples has been carried out via average power within a sample vs. sample diameter for emulsions with various ϕ values (volume fraction of the disperse phase). The samples with smaller diameter are found to have larger average power with radial irradiation for both o/w and w/o emulsion samples. The hot spot formation within a sample is found to be a strong function of lateral/radial irradiation for various emulsion compositions. The radial irradiation or conventional microwave heating with turntable rotation in ovens is not favorable especially for large w/o samples as the hot spot occurs at the center resulting in larger thermal gradient. The present work provides guideline on the heating policy based on either lateral or radial irradiation depending on the sample size and emulsion dielectric properties.

Generation of 287 W, 55 ps pulses at 78 MHz repetition rate from a cryogenically cooled Yb:YAG amplifier seeded by a fiber chirped-pulse amplification system

We generate linearly polarized, 287 W average-power, 5.5 ps pulses using a cryogenically cooled Yb:YAG amplifier at a repetition rate of 78 MHz. An optical-to-optical efficiency of 41% is obtained at 700 W pump power. A 6 W, 0.4 nm bandwidth picosecond seed source at 1029 nm wavelength is constructed using a chirped-pulse fiber amplification chain based on chirped volume Bragg gratings. The combination of a fiber amplifier system and a cryogenically cooled Yb:YAG amplifier results in good spatial beam quality at large average power. Low nonlinear phase accumulation as small as 5.1 x 10(-3) rad in the bulk Yb:YAG amplifier supports power scalability to a > 10 kW level without being affected by self-phase modulation. This amplification system is well suited for pumping high-power high-repetition-rate optical parametric chirped-pulse amplifiers.

Role of lateral and radial irradiations on efficient microwave processing of food cylinders

A detailed theoretical analysis has been carried out to assess the role of lateral and radial irradiations on microwave heating of 2D cylinders for beef and oil samples. The lateral irradiation may represent the sample incident at one direction and the radial irradiation refers to sample exposed to uniform microwave intensities at all directions. For both lateral and radial irradiations, the effective microwave incidence from the source is assumed to be identical. A preliminary analysis on microwave heating of samples has been shown via average power within a sample vs sample radius for beef and oil samples. The samples with smaller radius are found to have larger average power with radial irradiation for both beef and oil samples. The hot spot formation within a sample is found to be a strong function of lateral/radial irradiation for various food dielectrics. The radial irradiation is found to be not favorable especially for large oil samples where the hot spot occurs at the center resulting in larger thermal gradient that contrasts earlier works which established that the radial irradiation minimizes the thermal gradient irrespective of sample size. The present work provides guideline on heating policy based on either lateral or radial irradiation depending on sample size and food dielectric properties.

An Industrial Streamer Corona Plasma System for Gas Cleaning

For pulsed corona plasma applications, it becomes important to develop pilot systems with large average power and high-energy conversion efficiency. Since the beginning of 2000, we have been working on an industrial corona plasma system with tasks of 10-30 kW in average power and higher than 90% of total energy conversion efficiency. The pulsed-power source should have the following specifications: rise time of 10-25 ns, pulsewidth of 50-150 ns, pulse repetition rate of up to 1000 pulses per second, peak voltage pulse of 70 kV, peak current of 3.5 kA, dc bias voltage of 10-35 kV, and energy per pulse of up to 30 J. Sixteen parallel wire cylinder reactors are used to match the source. Gas and reactor temperatures can be controlled individually with water flow around the outside of those cylinders. The system is designed for gaseous oxidation and electrostatic dust precipitation. The system has been used for up to 17 kW in average power. This paper reports the system in detail, discusses issues related to the matching between the source and the reactor, and presents an example of industrial demonstrations on odor abatement at 1000 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /h. Finally, this paper also gives a general guideline for design of corona plasma systems

Long lifetime, triggered, spark-gap switch for repetitive pulsed power applications

In this article a critical component for pulsed power applications is described: the heavy-duty switch. The design of a coaxial, high repetition rate, large average power, and long lifetime spark-gap switch is discussed. The switch is used with a fail-free LCR trigger circuit. Critical issues for switch design are presented together with experimental results. It is observed that the switch has a good stability, and its lifetime is estimated to be in the order of 1010 shots (∼106C) at 10J∕pulse, 60kV and 100ns pulses. Measurements were performed with 20 and 34kV average switching voltage (100ns pulses, energy per pulse 0.4 and 0.75J, respectively). For up to 450pulses∕s (pps), pre-firing can be prevented by increasing the gap pressure (up to 2.5 and 7bars, respectively), no gas flush is required. Above 450pps, up to 820pps, a forced gas flow of maximal 35Nm3∕h, is required for stable operation. Measurements on the time delay and jitter of the switch demonstrate that these values are influenced by pressure, flow, and pulse repetition rate. For 34kV average switching voltage the time delay and time jitter vary between 35 and 250 and 10 and 80μs, respectively. For 20kV average switching voltage these values are: 30–160 and 4–50μs. During a test run of 2.5h (at 100Hz, 0.75J∕pulse) the feasibility of the switch was proved, and the switching voltage jitter was less than 0.7%.

Pre-scrambling method for PAPR reduction in OFDM communication systems

An orthogonal frequency division multiplexing (OFDM) system has a number of orthogonally modulated subcarriers, which can give a large peak-to average power (PAPR). The PAPR reduces the efficiency of RF power amplifier in OFDM systems. In this paper, we propose a new PAPR reduction method, which pre-scrambles data sequence for high speed data processing in OFDM. The proposed method uses a correlator for the reduction of PAPR value and calculations. We have compared the new method with a partial transmit sequences (PTS) method. As a result, the new method has shown that it permits a considerable improvement in the computational complexity with achieving a reasonable PAPR reduction.

A compact free electron laser device operating in the UV-soft X-ray region

We discuss the design elements of a compact free electron laser device, operating, in an oscillator–amplifier configuration, up to the soft X-ray region. We show that, the source can provide radiation from extreme UV to soft X-ray region, with significantly large output peak and average laser power with undulator lengths not exceeding 7 m.