Microwave Carrier Research Articles

Low cross-sensitivity and sensitivity enhanced FBG sensor based on OCMI with three cascaded FBGs

This paper presents a highly sensitive, temperature-insensitive optical carrier microwave interferometry (OCMI) system using a cascaded three fiber Bragg grating (FBG) structure to generate an enhanced Vernier effect for sensing applications. The enhanced Vernier effect is created by superimposing the interferograms of two separate interferometers formed by pairing the sensing FBG with each reference FBG. Experimental and theoretical results show that in strain sensing, the sensitivity based on enhanced Vernier effect is -4.642 MHz/µε, which is 66.3 and 61.4 times higher than that of strain sensor based on two single interferometers used to generate the enhanced Vernier effect in this system respectively. Compared with the strain sensor based on traditional Vernier effect, this sensor has higher sensitivity, and in addition the amplification factor for measuring sensitivity can be easily adjusted by changing the spatial distance between the three cascade FBGs. Moreover, the temperature sensitivity is decreased from -38.318 MHz/°C to -71.384 kHz/°C with temperature compensation. The sensor exhibits high resolution, high sensitivity, and low cross-sensitivity, making it great potential for measuring small physical changes in complex environments.

Vector magnetic field measurement based on fiber ring microwave photonic filter with the Vernier effect

A vector magnetic field sensor based on enhanced Vernier effect is experimentally demonstrated. The Vernier effect is generated from two microwave photonic filters (MPFs) with close free spectral range (FSR), which is constructed by the fiber ring (FR) and the optical carrier microwave interferometry (OCMI). Linear chirped fiber Bragg grating (LCFBG) is inserted in the FR to act as the dispersion element to provide time delay. By attaching the fiber Bragg grating (FBG) on the magnetostrictive material (MA), the magnetic field can be transferred into the wavelength shift, as well as the time delay of the FR and the frequency response of the FR-MPF. By choosing opposite dispersion of LCFBGs and closer FSRs, cascaded FR-MPFs based sensor can greatly improve the sensitivity. The sensitivities for the magnetic field intensity and direction are 127.71 kHz/Oe, the magnification factor of which is 432, and 418.16 kHz/deg. The proposed scheme has merits of high sensitivity and interference immunity, which is suitable for high precision measurement.

Effects of Microwave Power and Carrier Materials on Anthocyanins, Antioxidants, and Total Phenolic Content of Encapsulated Clitoria ternatea Flower Extract

Clitoria ternatea, also famously known as the blue pea flower (local name: bunga telang), has attracted interest among researchers due to its plethora of biological and pharmacological properties. It is rich in anthocyanin and widely used as a natural food colourant. However, the poor stability of active compounds may affect the therapeutic benefits and limit their application in the pharmaceutical and food industries. Hence, this work aims to study the effects of microwave encapsulation on the anthocyanins, antioxidants, and total phenolic content of Clitoria ternatea flower extract (CTFE). Microwave-assisted encapsulation (MAEC) was carried out at three different powers (300, 450, and 600 W) with different formulations of Gum Arabic (GA) and Maltodextrin Dextrose (MD) as carrier materials from 40% to 70% w/v. The total phenolic content (TPC), antioxidant activity, and anthocyanins in encapsulates were analysed for the formulations. The findings showed that increased microwave power increased TPC and antioxidant activity (P<0.05). However, adding carrier materials concentration above 60% reduced TPC and the antioxidant activity of microwave-encapsulated anthocyanin from CTFE. The best microwave-assisted encapsulation conditions of CTFE were found at 600 W microwave power with 50% w/v carrier materials GA/MD (ratio 1:1) concentration. The retention of anthocyanins, antioxidant activity, and TPC increased significantly (P<0.05) with increased microwave power and lower concentration of carrier materials. The MAEC approach to enhance the stability of anthocyanin in CTFE presents a high potential to expand its application as a high-value-added natural colourant.

Simple polarization-insensitive coherent RoF link with increased capacity.

A simple polarization-insensitive coherent radio-over-fiber (RoF) link with increased spectrum efficiency and transmission capacity is proposed and demonstrated. Instead of using two polarization splitters (PBSs), two 90° hybrids, and four pairs of balanced photodetectors (PDs) in a conventional polarization-diversity coherent receiver (PDCR), a simplified PDCR with only one PBS, one optical coupler (OC), and two PDs is employed in the coherent RoF link. At the simplified receiver, a novel, to the best of our knowledge, digital signal processing (DSP) algorithm is proposed to achieve polarization-insensitive detection and demultiplexing of two spectrally overlapping microwave vector signals as well as the elimination of the joint phase noise originating from the transmitter and the local oscillator (LO) laser sources. An experiment is performed. The transmission and detection of two independent 16QAM microwave vector signals at identical microwave carrier frequencies of 3 GHz with a symbol rate of 0.5 GSym/s over a 25-km single-mode fiber (SMF) is demonstrated. Thanks to the spectrum superposition of the two microwave vector signals, the spectral efficiency as well as the data transmission capacity is increased.

Interlayer Electrons Polarization of Asymmetric Metal Nanoclusters/g-C3 N4 for Enhanced Microwave Therapy of Pneumonia.

Interlayer interactions in two dimensional (2D) materials promote catalytic performance but often depend on the transport of inter rather than intralayer electrons. In this study, it is found that asymmetric metal-nanocluster-doped 2D g-C3 N4 greatly enhances catalytic performance by inducing microwave excitation of interlayer electron delocalization, resulting in a polarization of interlaminar charge transport for microwave disinfection and pneumonia therapy. Asymmetric Fe and Cu nanocluster doping (DCN-FeCu) enables g-C3 N4 to generate interlayer electrons under microwave irradiation, leading to interlayer polarization processes and electron delocalization effects, thus enhancing the interlayer migration efficiency of electrons. It also improves impurity energy levels and leads to a decrease in work function, allowing DCN-FeCu to produce microwave carriers across the photoelectric potential barrier under low-energy microwave radiation (2.45GHz). This asymmetric doping modulation produces layer number-dependent microwave electron excitations that are verified using multi-metal doping. Therefore, structurally modulated asymmetric doping of 2D materials with interfacial spatial effects can provide efficient microwave disinfection and pneumonia therapy.

Low cross-sensitivity and sensitivity-enhanced FBG sensor interrogated by an OCMI-based three-arm interferometer.

An FBG sensor interrogated by an optical carrier microwave interferometry (OCMI)-based three-arm Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. In our sensing scheme, the interferogram generated by interfering the three-arm-MZI middle arm with the sensing arm and the reference arm respectively is superimposed to produce a Vernier effect to increase the sensitivity of the system. The simultaneous interrogation of the sensing fiber Bragg grating (FBG) and the reference FBG by the OCMI-based three-arm-MZI provides an ideal solution to the cross-sensitivity problems (e.g. temperature vs. strain) associated with conventional sensors that produce the Vernier effect by cascading optical elements. Experimental results show that when applied to strain sensing, the OCMI-three-arm-MZI based FBG sensor is 17.5 times more sensitive compared to the two-arm interferometer based FBG sensor. And the temperature sensitivity is reduced from 371.858 KHz/°C to 1.455 KHz/°C. The prominent advantages of the sensor, including high resolution, high sensitivity, and low cross-sensitivity, make it a great potential for high-precision health monitoring in extreme environments.

Analysis of Tsunami Traveling Ionospheric Disturbances Due to Tsunami Using The GNSS-TEC Method

The Global Navigation Satellite System (GNSS) is a navigation satellite system that provides information on the position and speed of 3D objects on the earth’s surface. GNSS is increasingly being used in the field of survey and mapping work because of its high measurement accuracy, and its use can be done anywhere and anytime. The working principle of GNSS is to transmit digital data from satellites to receivers on the earth’s surface. The digital data is carried by a carrier microwave called the L-band. In the propagation path, the carrier microwave will pass through the ionosphere and troposphere. The collection of electrons contained in the ionosphere layer and the wet & dry components in the troposphere can disrupt the wave propagation path to be slower. This slow propagation will cause the accuracy of the results obtained during the measurement to be more inaccurate. The delayed wave data can obtain the Total Electron Content (TEC) value in the ionosphere layer. TEC is a value that represents the electron density in 1m2 in the ionosphere. The vertical movement of the land surface and seawater can suddenly cause acoustic waves that propagate towards the ionosphere layer, which causes the electron density to decompose. These disorders are known as Traveling Ionospheric Disturbances (TID). In this study, we studied the characteristics of the change in electron density in the ionosphere caused by the tsunami. The tsunami observed was a tsunami in the territory of Indonesia due to the eruption of Mount Tonga on January 15, 2022. The change in electron density was calculated from the significant difference in the TEC value during the tsunami propagation time. The calculation of the change in the TEC value is called the TEC reduction. TEC reduction is obtained by calculating the TEC value, calculated with the reference value of the polynomial curve. The result of the TEC reduction, which has a change in value at the same time as the tsunami is coming, is most likely the TID of the tsunami.

Sensitivity enhanced fiber optic temperature sensor based on optical carrier microwave photonic interferometry with harmonic Vernier effect

A sensitivity enhanced fiber optic temperature sensor based on optical carrier microwave interferometry (OCMI) with harmonic Vernier effect is proposed and experimentally demonstrated. The sensor is composed of two cascaded Mach–Zehnder interferometers (MZIs) with different optical length differences. Harmonic Vernier effect in microwave frequency domain is generated due to the free spectral range (FSR) difference in the microwave frequency response. Temperature sensing is realized by detecting the intersection of the inner envelopes of the measured frequency response curve. Experimental results demonstrate that sensitivity up to 580.45kHz/°C has been obtained by employing the harmonic Vernier effect, whose sensitivity amplification factor is up to 18.61. Through the application of harmonic Vernier effect in microwave domain, the amplification factor can be easily adjusted with much higher manufacturing tolerance and alleviate the measurement range restriction induced by the periodic frequency response.

Single-modulator Based Multi-Format Switchable Signal Generator Without Background Noise

A photonic multi-format background-free binarily modulated microwave signal generator using a single dual-polarization dual-parallel Mach–Zehnder modulator is proposed and demonstrated. The proposed generator features good reconfiguration and switchability. By simply adjusting the direct current biases of the modulator, amplitude shift keying (ASK), phase shift keying (PSK) and frequency-shift keying (FSK) microwave signals can be generated. Benefiting from the complementary intensity modulation, there is no residual baseband modulated signal in the generated binarily modulated signals. The system does not involve any optical or electrical filters, which ensures good tunability of the generator. By changing the frequency of the driven microwave carrier and bit rate of the electrical coded signal, the frequency and rate of the generated multi-format signals can be adjusted accordingly. The multi-format switchable signal generator has great potential in multi-functional communication and radar systems.

High-sensitivity optical fiber sensing based on a computational and distributed Vernier effect.

This article reports a novel concept of computational microwave photonics and distributed Vernier effect for sensitivity enhancement in a distributed optical fiber sensor based on an optical carrier microwave interferometry (OCMI) system. The sensor system includes a Fabry-Perot interferometer (FPI) array formed by cascaded fiber in-line reflectors. Using OCMI interrogation, information on each of the interferometers (i.e., sensing interferometers) can be obtained, from which an array of reference interferometers can be constructed accordingly. By superimposing the interferograms of each sensing interferometer and its corresponding reference interferometer, distributed Vernier effect can be generated, so that the measurement sensitivity of each of the sensing interferometers can be amplified individually. This technique is achieved entirely in software without any physical modification to the system and negates the need to carefully fabricate the reference interferometer to obtain the desired magnification factor, as is often the case for traditional Vernier effect-based optical fiber sensors. Importantly, the reference interferometers can be flexibly constructed such that the magnification factor for each sensing interferometer can be precisely and easily controlled. The operating principle is illustrated in detail, followed by a proof of concept. The experimental results match well with theoretical predictions.

Simulation of microwave electrodeless ultraviolet device and catalytic oxidation of toluene

AbstractIn order to improve the catalytic efficiency of toluene oxidation by heating catalyst and carrier in microwave single‐mode sintering furnace, the SJ‐1 microwave single‐mode sintering furnace is modified, and microwave electroless UV lamp is placed in the resonant cavity, and the catalytic efficiency of toluene is improved by using microwave electroless lamp in cooperation with microwave heating catalyst and carrier. In order to design the cavity, High‐Frequency Structure Simulator (HFSS) simulation is used to simulate it. The position of the waveguide, the position of the electroless UV lamp and its distance from the cavity center, and different input powers are simulated and analyzed, respectively. The electric field distribution diagram is obtained. According to the simulation analysis results, the waveguide on the left side, the cavity height of 300 mm, diameter of 160 mm aluminum alloy cavity is designed. The center of the lamp is 43 mm away from the center of the cylindrical cavity. The toluene catalytic efficiency is more than 94% at space speed of 6336.93 h−1, relative humidity of 50%, microwave input power of 455.6 W and initial toluene concentration of 60 ppm. It provides theoretical reference and guidance for the design of microwave electroless lamp thermal catalytic device.

Flux ramp modulation based hybrid microwave SQUID multiplexer

We present a hybrid microwave superconducting quantum interference device (SQUID) multiplexer that combines two frequency-division multiplexing techniques to allow multiplexing a given number of cryogenic detectors with only a fraction of frequency encoding resonators. Similar to conventional microwave SQUID multiplexing, our multiplexer relies on inductively coupling non-hysteretic, unshunted rf-SQUIDs to superconducting microwave resonators as well as applying flux ramp modulation for output signal linearization. However, instead of utilizing one resonator per SQUID, we couple multiple SQUIDs to a common readout resonator and encode the SQUID input signals in sidebands of the microwave carrier by varying the flux ramp modulation frequency for each SQUID. We prove the suitability of our approach using a prototype device and argue by means of fundamental information theory that our approach is particularly suited for reading out large cryogenic bolometer arrays.

Absorbing oxygen carrier induces phosphorus enrichment in sludge: Preparation and screening

Phosphorus recovery from sludge is considered a feasible approach. By combining the oxygen carrier gasification technology and microwave heating, an absorbing oxygen carrier (AOC) is used in this study to successfully induce phosphorus enrichment in sludge char. The AOC, which is based on iron and supported on SiC, has been prepared via ultrasonic impregnation. The effects of preparation conditions (particle size of SiC and loading of iron) on the phosphorus enrichment characteristics, thermal reaction performance of the AOC and sludge, and the wave absorption performance of the AOC were investigated. The results show that the AOC prepared using a SiC particle size of 36 mesh and iron loading of 10% can achieve a phosphorus enrichment of 91.30% in the sludge char when the temperature of the microwave reactor is 600 °C. In the thermal reaction test, AOC can effectively increase the rate and depth of sludge gasification reaction in the medium- and high-temperature reaction stages. Iron-based is loading on the SiC surface and has a good wave absorption performance (RL = -16.28 dB; effective absorption width is 3.54 GHz). Overall, this study provides a new and effective approach for utilizing sludge.

Photo-Generation of Tunable Microwave Carriers at 2 µm Wavelengths Using Double Sideband with Carrier Suppression Modulation

At 2 µm wavelengths (149.9 THz), hollow-core photonics band gap fibers have higher light power damage thresholds, stable polarization states, and lower losses of 0.1 dB/km. Additionally, a thulium-doped fiber amplifier can provide a gain of >35 dB. Specifically, an indium-rich InGaAs photodetector shows a naturally higher photoresponsivity at 2 µm wavelengths than the C-band. Therefore, using tunable photo-generated microwave technology at 2 µm wavelengths could achieve higher photo-to-electric power conversion efficiencies for higher RF output power applications using the same method at the same frequency. Here, a double sideband with the carrier suppression modulation method was experimentally applied on 2 µm wavelengths to generate tunable and stable microwave carriers. Comparison experiments were also applied on the 1.55 µm (193.4 THz)/1.31 µm wavelengths (228.8 THz) based on the same indium-rich InGaAs photodetector. Through normalization on the wavelength-corresponded squared external quantum efficiency to visualize the photo-to-electric power conversion efficiency at different wavelengths under the same input optical signal power, the ratio between the results at 2 µm wavelengths and C/O-band is abstracted as 1.31/1.98, approaching theoretical estimations. This corresponds to a power conversion efficiency increasement of ~1.16 dB/~2.98 dB. To our knowledge, this is the first study on 2 micron wavelengths that proves the corresponding high efficiency power conversion property.

Inhibited grain growth to strengthen the redox performance of CuFe2O4 via SiO2 as a support for the chemical looping gasification

The inert component is an important part of the oxygen carrier in the chemical looping gasification. In this study, a variety of characterization analyses were conducted to investigate a role of SiO2 in crystal structure, morphology, pore structure during multiple cycles of CuFe2O4/SiO2 oxygen carrier. It was shown that CuFe2O4 presented an excellent cycle stability. During cycles, the inert component SiO2 always keeps the same phase, and the active component CuFe2O4 is the continuous loss and gain of lattice oxygen. There are not change much in elemental composition of CuFe2O4 during multiple cycles. Inert component SiO2 inhibiting the loss of copper during multiple cycles that obtained from the SEM analyses. Combined with the Zener effect, it is found that the inert component SiO2 as second-phase particles in the boundary between the CuFe2O4 grains to be inhibited the growth of the CuFe2O4 grains, which would be maintain the integrity of the oxygen carrier microwave structure. This can be strengthen cycle stability in the chemical looping gasification. Therefore, SiO2 with zener pinning effect would be well the cycle stability of the oxygen carrier.

Microwave-Assisted Scalable Synthesis of Pt/C: Impact of the Microwave Irradiation and Carrier Solution Polarity on Nanoparticle Formation and Aging of the Support Carbon

Microwave-assisted (MW-assisted) synthesis of nanomaterials is a facile method for material development studies involving small-scale synthesis. The method is being explored further toward industrial scale production of nanoparticle catalyst. Here, optimization of the process parameters for a scalable synthesis of Pt/C through a MW-assisted polyol route using (NH4)2PtCl6 as the Pt precursor has been presented. Further, the impact of MW-irradiation on the carbon support surface structure and its effect on the electrochemical stability of the synthesized Pt/C have been explored. Pt/C electrocatalysts were synthesized using a MW synthesizer in an open system configuration. Effects of different process parameters, namely, solvent composition and hence solvent polarity, reaction time, and Pt precursor concentration on the structure and the electrochemical performance of the synthesized Pt/C catalysts were studied. A mixture of water and ethylene glycol with a water content of 30% v/v was found appropriate for achieving Pt nanoparticles with a particle size of ∼2 nm, suitable for a high electrochemically active surface area (ECSA) of ∼75 m2/gPt. Pt concentrations higher than 5 mM were found unsuitable due to incomplete reduction of the Pt precursor. The minimum reaction time for complete reduction of the Pt precursor was observed to be 400 s. However, increasing the MW treatment time beyond 400 s leads to growth of the Pt nanoparticles and hence reduction in ECSA. Porosity and surface area analysis suggests decreased pore size and surface area of the carbon support by the MW-irradiation during Pt/C synthesis. Hence, the initial electrochemical double layer capacitance (DLC) decreases with increasing MW-irradiation time, leading to the increased surface corrosion and the decreased bulk corrosion of the support carbon, monitored respectively through the relative change in DLC and the evolution of the quinone–hydroquinone redox peak during an accelerated stress test meant for durability assessment of the electrocatalysts.

Broadband Measurement of Error Vector Magnitude for Microwave Vector Signal Generators Using a Vector Network Analyzer

A frequency-domain method is proposed for the broadband measurement of Error Vector Magnitude (EVM) for Vector Signal Generators (VSGs). The technique is based on frequency-swept narrowband acquisitions performed with a Vector Network Analyzer (VNA) by exploiting a stable (yet unknown) reference signal to obtain phase-repeatable measurements, eventually allowing to refer the residual distortion contribution of the analog VSG output to its digital input. The method leverages on the formulation of a novel measurement-based model, which accounts for the IQ imbalance effect and allows to separate it from the actual distortion within the VSG, ultimately yielding accurate broadband EVM measurements at microwave carrier frequencies without any time-domain waveform reconstruction, completely avoiding the use of broadband receivers and corresponding calibration.

An opto‐electronic oscillator based on Fabry‐Perot stabilized dual‐wavelength fiber ring laser

AbstractThe authors experimentally demonstrate an opto‐electronic oscillator based on a dual‐wavelength fiber ring laser with an inline specially designed fiber‐Bragg‐grating‐based Fabry‐Perot filter. An erbium‐doped fiber amplifier initiates the process as a broadband light source while a second optical amplifier provides additional gain to increase the cavity power. By exploiting the two‐wavelength beating, a 10.3 GHz microwave carrier with 3‐dB linewidth of <200 Hz was generated with 77 dB signal‐to‐noise ratio. Phase noise of −100 dBc/Hz @10 kHz offset is achieved, which is very appropriate for microwave applications in X‐band that often require high extinction ratio and low phase noise.

Continuous microwave-to-optical transduction with atomic beam fluorescence

We present a method for performing microwave (MW)-to-optical transduction based on atomic beam magnetic resonance spectroscopy, where laser-induced beam fluorescence bridges two electromagnetic waves with significantly different frequencies. We experimentally demonstrate the real-time demodulation of an infrasonic wave signal encoded in a MW carrier by driving Cs beam Rabi (Ramsey) transition with a single (two separated) MW magnetic field(s), thus validating this method. A high signal-to-noise ratio (SNR) of above 90 dB was achieved for near-full modulation, and a MW field variation as small as 0.02% was detectable with a SNR > 10 dB by utilizing either of the transduction configurations. Our sensitive and continuous atomic beam MW transducers offer a promising platform for atomic communication and MW sensing.

Low jitter microwave pulse train generation based on an optoelectronic oscillator.

We demonstrate an approach to ultra-short pulse train generation with a low time jitter based on pulse compression of a frequency comb generated by a dual-loop optoelectronic oscillator (OEO). The proposed dual-loop OEO consists of two feedback loops, with one having a long loop length and the other a short loop length. In the long loop, a phase modulator (PM) cascaded with a Mach-Zehnder modulator (MZM) are employed, and in the short loop, only the MZM is included. Due to the Vernier effect, the use of the dual-loop structure can facilitate mode selection to generate a single-frequency microwave carrier with multiple optical sidebands corresponding to an optical comb. By adjusting the phase relationship between the optical sidebands using a dispersion compensating fiber (DCF), a stable optical pulse train is generated. Thanks to the low phase noise nature of an OEO, the generated pulse train has a low time jitter. The proposed approach is evaluated experimentally. A pulse train with a repetition frequency of 2.023 GHz and a pulse width of 40 ps is generated. The single-sideband (SSB) phase noise of the carrier frequency generated by the OEO is measured to be -118 dBc/Hz at a 10-kHz offset frequency, corresponding to a time jitter of the pulse train of 391.2 fs. The phase noise can be further reduced if an active cavity stabilization mechanism is adopted, enabling further reduction in the time jitter to the order of tens of femtoseconds.