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Lithium silicon vanadium oxide (Li3.6Si0.6V0.4O4) was synthesized by microwave-assisted solid-state reaction with grinding times of 1, 2, 4, and 6 h and applied as electrode material using silica from rice husk ash and crushed V2O3 and LiNO3 at 600 watts. This research found that the influence of microwave heating affects the generation Li3.6Si0.6V0.4O4 and the microwave wattage can remove excess nitrate in the system. As a result of different wattages, different products are produced, with 600 watts providing good crystallinity. Fourier transform infrared (FTIR) and Raman spectroscopy were used to measure bond vibrations within the molecules to confirm the presence of (Si − O), (Li − O), (Si − O−Si), and (V–O), while X-ray diffraction was conducted to confirm the phase of Li3.6Si0.6V0.4O4 as an orthorhombic lattice. X-ray absorption near edge structure (XANES) identified oxidation states of vanadium in the product as V4+ and V5+ while scanning electron microscopy (SEM) images showed the morphology to be highly porous with compact crystallinity. The product has high specific capacitance with a grinding time of 6 h and heated at 600 W at 289–461 F.g−1 using a scanning rate of 5 mV.s−1. [ABSTRACT FROM AUTHOR]

The dielectric properties of lignite were studied by using the resonant cavity perturbation method. The effect of temperature, particle size, moisture content, and microwave frequency were investigated. Results showed that the variation of dielectric parameters could be divided into four stages: Stage I (25–200°C), Stage II (200–550°C), Stage III (550–800°C), and Stage IV (800–1000°C). The dielectric properties increased with particle size due to its high void ratio. The higher moisture content leads to the higher dielectric properties. The frequency of 915 MHz was more appropriate to dispose the tonnage material in high power industrial than that of 2450 MHz. Additionally, the micro-structure of lignite was analyzed by the scanning electron microscope (SEM) and the fourier transform infrared spectroscopy (FT-IR). The characterization analyses demonstrated that a large quantity of pores and cracks were generated in lignite surface because of the microwave pumping effect. The polar substances in sample selectively absorbed and transferred microwave into heat and then evaporated water to steam, causing an instantaneous increase in internal pressure. There was a uni-directional mass and heat transfer process from the interior to the surface under the steam driving force, which caused a great number of pores and cracks emergence to substantially facilitate the removal of moisture content and accelerate heat dissipation. And the apparent aromaticity of lignite dried by microwave could be increased and the capability of potential re-absorption could be decreased. Meanwhile, the mechanisms of microwave heating and generation of cracks and pores were analyzed in detail. These results could provide a theoretical basis for microwave processing of lignite. [ABSTRACT FROM AUTHOR]

A multi-band dual-chirp linearly frequency modulated (LFM) signal-generation scheme with doubled chirp bandwidth and flexible center frequency and band numbers is proposed. In the scheme, the polarization multiplexed multi-tone optical signals with chirped phases are generated via a dual-polarization dual-parallel Mach–Zehnder modulator (DPMZM) cascaded with a polarization modulator. The two polarization multiplexed lightwaves are recombined as two linearly polarized beams by a polarization beam splitter and are detected by a balanced photodiode with a photocurrent that includes the multi-band dual-chirp LFM signal with doubled bandwidth and multiplied central frequencies but does not have a dc component. Since the orders and numbers of the generated optical sidebands are changed by adjusting the bias voltages of a DPMZM, we can obtain the multi-band dual-chirp LFM signal flexibly. Based on simulation, four-band, six-band and two seven-band dual-chirp LFM signals are generated with four groups of bias voltage configurations. For each case, every dual-chirp LFM signal of the generated multi-band dual-chirp LFM signal has a 5-GHz bandwidth and a time-bandwidth product of 512. The auto-correlations and ambiguity function of the generated LFM signal show good performance of pulse compression and range-Doppler resolution. [ABSTRACT FROM AUTHOR]

A photonics method is proposed to generate a microwave linearly chirped signal with improved central frequency, doubling bandwidth, amplitude and phase modulation capability. In the scheme, a dual-polarization integrated modulator combined with an optical filter are utilized to generate an orthogonally polarized optical signal. Then, the optical signal is injected into a polarization modulator (PolM) to perform data modulation. By controlling the polarization state of the orthogonally polarized optical signal, amplitude or phase of the generated microwave linearly chirped signal will be changed according to the driving data sequence. The proposed scheme is verified by simulation. Linearly chirped signals with central frequency tuned from 14 to 29 GHz, bandwidth tuned from 4 to 10 GHz are generated. ASK linearly chirped signals with bit-rate tuned from 156.25 to 1250 Mbps are demonstrated. Generation of a PSK linearly chirped signal and its coherent demodulation are verified. Besides, 4ASK, 4PSK and QPSK linearly chirped waveforms are achieved, and time-bandwidth product improvement is confirmed. The proposed method features parameter tunability and modulation format agility, which can be potentially employed in radar and wireless covert communication systems. [ABSTRACT FROM AUTHOR]

Influence of the density of mode spectrum in the gyrotron cavity on the possibility of stable single-mode operation has been investigated for high-order modes. Interaction of the operating mode with its two neighboring satellites, symmetrically spaced in frequency, is analyzed. Some threshold value of mode spectrum density dependent on the beam current is found. [ABSTRACT FROM AUTHOR]

A configuration for triangular-shaped microwave signal generator is proposed and analysed. In the proposed model, a single-drive Mach–Zehnder modulator operated under the push–pull mode is firstly driven by a sinusoid signal. The lightwave is then split into two branches and converted by a balanced photodetector. According to the analysis, the output photocurrent contains infinite sinusoidal harmonics of the driven frequency. By adjusting three variables (modulation index, bias state and optical time delay), the power of the first three harmonics can be arbitrarily controlled. Such a property can be used in triangular-shaped microwave generation with adjustable symmetrical coefficient δ. The theory and discussion are proposed in this work. A fitting error η is defined to evaluate the waveform quality. With a defined η < 6%, the symmetrical coefficient can be adjusted within a range of 20% ≤ δ ≤ 80%. [ABSTRACT FROM AUTHOR]

A microwave photonic generation scheme of triangular waveform using cascaded dual-drive Mach-Zehnder modulators (DDMZMs) and FBG is proposed. We show that a frequency-doubled and power-variable triangular waveform can be obtained. The double frequency can reduce the high-frequency requirement of the local oscillation signal (LO) source. The introduction of the second modulator can improve the stability of the scheme. The simulation results show that the power of the triangular is variable; the stability is optimized when the first modulation index is in 0 1; the similarity coefficient is greater than 0.998, which is 0.006 higher than one-stage-modulation scheme. Meanwhile, the similarity coefficient remains over 0.992 when the DC drifting difference value of and is in −90 60 mV, and it remains over 0.99 when the phase difference of the two LO sources varies from −10° to 10°. It verifies the tolerance of DC drifting and phase desynchrony of the system. [ABSTRACT FROM AUTHOR]

The drying kinetics, microstructural alteration, and rehydration properties of raspberry samples were studied experimentally in this work. Five different drying programs with the application of microwaves (MW) and ultrasound (US) were used, including convective drying (CV) as a reference test. The drying experiments were performed using a hybrid chamber dryer equipped with airborne ultrasound and microwave generators. The modified Page model was successfully used to describe the drying kinetics of raspberry fruits. Next, microstructural properties (porosity and total pore volume) of the dried samples were determined from the postprocessing of the images which were acquired using a lab-scale X-ray microtomograph. The results show a significantly shorter drying time by 54–64% for CVUS, 69% for CVMW, and 79% for CVMWUS; and a lower energy consumption resulting in energy saving of 14–23% for CVUS, 54% for CVMW, and 59% for CVMWUS as compared to CV. It is also shown that the average drying rate of raspberry samples increases by maximum fourfold with the application of both ultrasound and microwave radiations in CV. In addition, a higher porosity, total pore volume, and a better rehydration property were found for the raspberry samples dried with US than with MW assistance. [ABSTRACT FROM AUTHOR]

A simplified filterless frequency octupling scheme by connecting an intensity modulator (IM) with a dual-parallel Mach–Zehnder (DPMZM) in series is proposed in this paper. The LO signal is distributed into two parts, and one part is used to drive the IM and the other part is applied to drive the DPMZM’s upper sub-modulator, both at the peak point. The lower sub-modulator is only driven by dc bias, and the parent modulator works at null point. By properly adjusting dc bias of the lower sub-modulator, only ±4th-order optical sidebands dominate at the output of the DPMZM. The approach is verified by experiments, and 32-GHz and 40-GHz millimetre waves (mm-waves) are generated using 4-GHz and 5-GHz LO signals, respectively. We acquire a 15-dB electrical spurious suppression ratio (ESSR) and a relatively good phase noise of the signal. Compared with other schemes, the scheme is simple in configuration because only an IM and a DPMZM are needed. What’s more, the scheme is tunable in frequency as no filter is used. [ABSTRACT FROM AUTHOR]

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a?/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability. [ABSTRACT FROM AUTHOR]

The main objective of these experiments is to identify the possibilities for proving a microwave technology for thermal reticulation of electric insulations deposited on metallic supports. To avoid the occurrence of phenomena that could affect the integrity of the microwave generator, the system has been equipped with a load for absorbing the residual power in microwaves. The charge placed in the applicator is made of a microwave - transparent plastic coil through which water circulates. The insulating material used during the experiments was P772 special tape impregnated in epoxy resin deposited on a metallic support through rolling. The quality of the electric insulation obtained by means of the microwave technology is better compared with the conventional methods. [ABSTRACT FROM AUTHOR]