Flexible Frequency Research Articles

High-Order Balanced Dual-Band HTS BPF With Flexible Frequency Ratio and Sharp Rejection Skirts

In this article, a new class of high-order balanced dual-band high-temperature superconducting (HTS) bandpass filter (BPF) based on modified multimode stub-loaded resonators (SLRs) is presented. First, a detailed theoretical analysis of the multimode SLRs is provided to obtain insight into their frequency response characteristics under the differential-mode (DM) and common-mode (CM) operations. Specifically, the SLRs under the DM operation are designed to generate their second and third resonant modes in the two specified passbands, and they are sequentially cascaded by alternate <inline-formula> <tex-math notation="LaTeX">$J$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> inverters for sharp rejection skirts. Following that, the working mechanism of the CM rejection of the resonator is investigated for achieving good CM suppression performance for this filter. Finally, for experimental validation, an eighth-order prototype filter is designed and fabricated on the MgO substrate with double-sided YBa2Cu3Oy (YBCO) thin films. Good agreement between measured and simulated results is obtained, and the filter is at the same time with low insertion loss, flexible frequency ratio, sharp rejection skirts, and good CM suppression level.

Polarization-insensitive ultrathin fractal shaped frequency selective surface for ultra wide band shielding

An ultrathin and flexible Frequency Selective Surface (FSS) for ultra-wideband electromagnetic interference (EMI) shielding has been proposed in this article. The novelty of the suggested design lies in its capacitive coupled Greek cross-shaped fractal structure that is printed on a single and flexible layer dielectric substrate having an extremely thin thickness of 0.0013λ 0 , where λ 0 refers to the free space wavelength of the lower cutoff frequency. The introduction of capacitive coupling approach between the modified Greek cross fractal metallic structure and four symmetrical triangularly slotted conventional right-angled triangular metallic geometry results in an excellent ultra-wide stopband (UWSB) of more than 154% (2.07–15.76 GHz) and 105% (4.38–14.05) for < −10 dB and < −20 dB fractional bandwidth, respectively. The conformal configuration of the proposed geometry also exhibits a significantly better bandwidth more than 148.89% (−10 dB) and 109.5% (−20 dB) for UWSB. To accomplish the physical interpretation of the proposed FSS, the equivalent circuit model optimization has been illustrated also. Furthermore, the proposed structure demonstrates strong polarization independence and angular stability under both TE and TM polarization. Finally, the ultra-wideband shielding characteristics of both the planer and conformal designs have been confirmed experimentally in a free space measuring system.

Design of a novel compact and flexible chipless RFID tag based on an improved U-shaped resonator

Miniaturization, flexibility and high coding capacity design are very important while considering the development of chipless tags. In this paper, a flexible high-encoding capacity chipless radio frequency identification (RFID) tag with a compact structure is designed using Polyimide, a flexible material with high-temperature resistance as the substrate. The tag works in the band of 1.5∼10.5 GHz, the coding density of 4.348 bits/cm2 is obtained with four alternating nested improved U-shaped resonance structures. Frequency shift coding is realized by changing the structural parameters of the resonator. The production process is simple because only one conductive layer is needed. Because of its flexible and low-cost characteristics, it provides more possibilities for the promotion of RFID technology. A good agreement between simulation and measurement validates the feasibility of the design concept.

Flexible and Wearable Hybrid RF and Solar Energy Harvesting System

In this article, we demonstrate a flexible and wearable hybrid radio frequency (RF) and solar energy harvesting system for powering wearable electronic devices. The system consists of a flexible transparent antenna, a flexible transparent rectifying circuit, and an amorphous silicon solar cell. By utilizing transparent stacked structure, the rectenna and the solar cell can provide more hybrid output power to accommodate more application scenarios. The flexible transparent antenna shows two impedance matching bandwidths of 3.5–3.578 and 4.79–5.09 GHz, covering n78/n79 fifth-generation (5G) communication frequency band and 5-GHz WiFi frequency band. At the frequency of 3.5 GHz, the flexible transparent rectifying circuit achieves a high RF-to-dc conversion efficiency of 54.67% at 13 dBm RF input power. In the room with a light intensity of 210 lux, compared with a single solar cell, the hybrid energy harvesting system can obtain an additional 35.6%–769.5% output power when the RF source power is varied from 4 to 10 dBm. These results demonstrate that the proposed flexible and wearable RF-solar energy harvester can provide reliable electric power supply, which can be a potential candidate for powering wearable electronic devices, distributed sensors and IOT devices.

Flexible force sensitive frequency reconfigurable antenna base on stretchable conductive fabric

With the development of wireless technology and flexible electronics, flexible frequency reconfigurable antennas have been directly used as sensors to detect mechanical signals. As an important frequency reconfigurable antenna, microstrip antenna has been widely studied in the field of flexible and flexible electronics in recent years. However, the stretchability of microstrip antennas usually comes at the cost of reducing the conductivity of the radiated conductor. Here, we report a flexible force sensitive frequency reconfigurable microstrip antenna, which fabricated by silver fiber conductive fabric with a double-wire braided structure. In order to increase the detection of pressure, an elastic dielectric layer with a microhemispheric array was introduced into the microstrip antenna to extend the frequency band width of the reconfigurable antenna. The relative frequency of the antenna varied from 0% to −12.9%, and the sensing sensitivity was −1.9 kPa−1. As potential applications, we demonstrate the use of a flexible frequency reconfigurable antenna base on stretchable conductive fabric as a strain sensor capable of measuring bending angle and movements of a human finger. The change in the resonance frequency with the externally applied tensile strain in this antenna design has a sensitivity of 3.448, manifesting a 4.19- and a 13.79-fold increase of sensitivity when compared to those in previous reports that used arched or both-planes serpentine rectangular microstrip antenna. This is of great significance for the application of wearable antenna in wireless mechanical sensing technology.

A Flexible Control Strategy of Air-Conditioning Cluster Participating in Primary Frequency Modulation

As renewable energy resources are gradually connected to the grid, demand response gradually develops and expands. As a response resource with a huge proportion of the load, the role of air-conditioning load is gradually being valued. The paper first describes the equivalent thermal parameter model of the air-conditioning load. Then, an air-conditioning cluster aggregation model is established based on Monte Carlo with uncertainties considered. Finally, the paper proposes a flexible trigger frequency setting method to provide a relatively consistent amount of adjustment in different situations. And the simulation proves the effectiveness of the method.

Design and implementation of an S-band transmitter for nanosatellites with new configuration

In this paper, the author presents the design and implementation of an Sband transmitter for nanosatellites. By combining heterostructure field effect transistors (HFET) and laterally diffused metal–oxide–semiconductor (LDMOS) technology and using flexible structure and flexible control method, this research obtained 60 dB gain power when input is -14 dBm, output power is 46 dBm (more than 25 W) in 2,1 GHz -2,3 Ghz frequency; phase noise is -80 dBc/Hz at 100 KHz offset frequency. Unlike other traditional transmitters, this transmitter was designed with multi-stages which have multi-peaks resonance to expand bandwidth to respond to the requirement of generation of the complex signal in wide band. Moreover, the phase locked loop (PLL) in frequency synthesizer makes the frequency conversion more flexible and output frequency more stable; thermal problem in module also was solved by using thermistor and operation mode. Measurement results prove that the design does not only satisfy the requirements of nanosatellites but also can be applied to other satellites together with their ground station because it has open configure with flexible structure and flexible control method.

Clinical Outcomes of Different Warfarin Self-Care Strategies: A Systematic Review and Network Meta-Analysis.

To compare the effects of different strategies for warfarin self-care. PubMed, EMBASE, CENTRAL, CINAHL, ProQuest Dissertations & Theses, and OpenGrey were searched from inception to August 2021. Randomized controlled trials (RCTs) of warfarin self-care, either patient self-testing (PST) or patient self-management (PSM), were included. Self-care approaches were classified based on the TIP framework (theme, intensity, provider): (1) PST ≥1/week via e-Health (PST/High/e-Health); (2) PST ≥1/week by health care practitioner (PST/High/HCP); (3) PST <1/week via e-Health (PST/Low/e-Health); (4) PSM ≥1/week by e-Health (PSM/High/e-Health); (5) PSM ≥1/week by patient (PSM/High/Pt); (6) PSM <1/week by patient (PSM/Low/Pt); and (7) PSM with flexible frequency by patient (PSM/Flex/Pt). Mean differences (MDs) and risk ratios (RRs) with 95% confidence interval (CI) were estimated using frequentist network meta-analyses with a random-effects model. The certainty of evidence was evaluated using CINeMA (Confidence in Network Meta-Analysis). Sixteen RCTs involving 5,895 participants were included. When compared with usual care, time in therapeutic range was higher in PSM/High/Pt and PST/High/e-Health with MD [95% CI] of 7.67% [0.26-15.08] and 5.65% [0.04-11.26], respectively. The certainty of evidence was rated as moderate for these findings. The risk of thromboembolic events was lower in the PSM/Flex/Pt group when compared with PST/High/e-Health (RR: 0.39 [0.20-0.77]) and usual care (RR: 0.38 [0.17-0.88]) with low and very low level of evidence, respectively. There was no significant difference in the proportion of international normalized ratio (INR) values in range, major bleeding, and all-cause mortality among different self-care features. Patient self-care (either PST or PSM) by measuring INR values at least once weekly is more effective in controlling the INR level.

3D Flexible Frequency Selective Surface with Stable Electromagnetic Transmission Properties

AbstractFrequency selective surfaces (FSS) that can be tightly laminated to complex nondevelopable surfaces have a wide range of applications in many engineering areas. This paper presents a 3D flexible FSS prepared by mechanically guided 3D assembly, capable of being conformally adhered to complex surfaces, while maintaining stable frequency selective properties as well as transmission performance. The stretching strain applied to the prestrained ecoflex substrate can precisely tune and control the buckled 3D metal structures, which leads to the stretchability of the flexible FSS, introduces the increase of the inductance inside the metal cells, and expands the metal gap resulting in a reduction of the capacitance between the unit cells. The mutual correlation of capacitance and inductance ensures in the mechanism that the FSS transmission characteristics will not be significantly affected by the applied strain, as verified by calculations using the equivalent circuit method. Both the results obtained by the experiments and simulations indicate that the resonant frequency of the 3D flexible FSS is 5.7 GHz and the bandwidth at −10 dB is 0.94 GHz, while the resonant frequency shift will not exceed 0.45 Hz, and −10 dB bandwidth change will not exceed 0.32 GHz with applied strain of 17.8% in the ecoflex substrate. At the same time, the 3D flexible FSS maintains stable transmission performance for oblique incidence, with only 0.5 GHz frequency shift at 45° incidence. This stretchable flexible FSS with stable electromagnetic (EM) properties may find potential applications in EM shielding and spatial filtering due to its high flexibility, ready applicability, and cost‐effectiveness.

Comparative Feasibility Studies of High Voltage Circuit Breaker Operating in the LFAC System With Different Frequencies

With the development of the flexible low frequency transmission technology following the improvement of offshore wind power transmission, it is of great significance to investigate the operation adaptability of the main equipment especially under the low frequency conditions. A comparative study was performed in the present work to discuss the dynamic operation performance of a 252 kV/50 kA puffer-type circuit breaker influenced by the system operational frequency. Since the decreased operational frequency would result in a longer arc duration, a pre-designed driving mechanism with characteristics of high speed control was proposed and compared with a conventional unit. Moreover, as one of the reasonable indicators to evaluate the interruption performance of the circuit breaker, the critical rate of rise of recovery voltage (RRRV) that the circuit breaker can withstand after the arc extinguishment under different low frequencies were computationally obtained by an established arc model. The effects of the frequency change on the arc dynamic characteristics during the interruption of circuit breaker were comprehensively discussed as well and it could reasonably provide technical optimisation for the development of low-frequency-based circuit breaker for further engineering applications by analysing its interruption feasibility.

A Low-profile Dual-band Hybrid Coupler with Flexible Frequency Band Ratio

A Low-profile Dual-band Hybrid Coupler with Flexible Frequency Band Ratio

A Simple Structure Dual-Band Dual-Circularly Polarized Antenna With Controlled Frequency Ratio

This paper proposes a dual-band dual-circularly polarized (CP) aperture-coupled patch antenna with flexible frequency ratio. By simply etching a modified S-shaped slot at the central of a circular patch, dual-band dual-CP operation is realized. In addition, the frequency ratio of the two CP bands can be flexibly controlled by optimizing the length parameters of the S-shaped slot arms. As a result, the frequency ratio can be tuned from 1.12 to 1.46 according to different requirements. For demonstration, the circularly polarized patch antenna operating at 3.42 and 3.85 GHz is manufactured and tested. The measured 3-dB axial-ratio (AR) bandwidth is 1.1% and 2.3% for the right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP), respectively. The measured gains at the lower and upper bands are 9.4 and 9.8 dBic, respectively.

Compact, flexible and highly selective wideband complementary FSS with high angular stability

AbstractThis article presents a novel miniaturized (0.105λ0 × 0.105λ0) flexible complementary frequency selective surfaces (CFSS) structure with sharp band edge selectivity and very high angular stability. To explore two diverse applications as a passband and stopband filter, a novel complementary convoluted square loop (CCSL) type structure has been designed and investigated on ultrathin dielectric material of thickness 0.0023λ0. The second-order wide controllable passband with fractional bandwidth of 19.23% (−3 dB) and remarkably wide stopband of 64.7% (−10 dB) and 54.8% (−20 dB) respectively have been achieved by using a cascaded resonating structure which is composed of asymmetrical meandered CCSL array, arranged on two ultrathin dielectric layers with air foam separation. This particular format would lead to sharp band edge selectivity with steep roll-off (72.43 dB/GHz) and an excellent passband selectivity factor (0.731). An equivalent lumped LC circuit in conjunction with the transmission line model has also been adopted to comprehend the physical mechanism of the proposed single layer and double layer structures. Further, better passband and stopband angular stability at an oblique incident angle of 45° and the bending characteristics have also been investigated thoroughly for the proposed flexible CFSS to check their employability in different conformal structures with WiMAX passband and WLAN stopband application.

Wideband Tunable Frequency Converter Based on an OEO Using a DP-QPSK Modulator

Flexibility and tunability are critical for frequency conversion in antenna, radar and modern communication systems. In this study we propose and experimentally demonstrate a wideband tunable frequency converter by using an optoelectronic oscillator (OEO) to generate high-purity local oscillator (LO) signal for flexible frequency conversion. In the proposed frequency converter, a dual-polarization quadrature phase shift-keying (DP-QPSK) modulator is utilized to receive the signal to be converted and also to form a tunable OEO based on a dispersion-induced microwave photonic filter. By adjusting the bias voltage of the DP-QPSK modulator, an LO signal with accurate adjustable frequency is generated by the OEO. The measured phase noise of generated LO signal can reach -110 dBc/Hz at 10 kHz offset. An experiment is performed to verify the feasibility of this proposed frequency converter. The 7.6-GHz radio frequency (RF) signal is freely converted to different intermediate frequency (IF) signals, respectively. Moreover, the proposed microwave photonic converter is applied into wireless transmission systems. A 1-Gb/s NRZ wireless signal centered at 6.5 GHz is down-converted to baseband successfully.

Functional flexible photonics-assisted frequency measurement based on combination of stimulated Brillouin scattering and a Mach – Zehnder interferometer

A functional flexible photonics-assisted frequency measurement (PFM) is proposed. Owing to polarisation multiplexing, the electro-optic (O/E) conversion can be performed in a single optical path, which endows the system high stability and concise configuration. Moreover, using a specially designed functional coarse/accurate frequency measurement (C/AFM) module, a large covering range, moderate accuracy, and fast response frequency measurement results can be ensured in a radar warning receiver (RWR), whereas high accurate results can be used in an electronic countermeasures receiver (ECMR). The simulation results show that a strict monotonous amplitude comparison function (ACF) can be constructed based on the structure of a Mach – Zehnder interferometer (MZI) to map the signal frequency, with a measurement error of less than 0.2 GHz in the range of 1 – 31 GHz. This coarse measurement results can be used to perform radar warning. Based on this result, a highly accurate frequency measurement result is achieved through stimulated Brillouin scattering (SBS). The results reveal that the accuracy is improved to better than 20 MHz. Noteworthy, the C/AFM module consists of purely passive devices, which makes this system meet the potential of integration.

A Multifunctional and Miniaturized Flexible Active Frequency Selective Surface

In this letter, a flexible multifunctional active frequency selective surface (AFSS) with miniaturized units is proposed, and it is simulated, fabricated, and measured. In the proposed scheme, the flexible AFSS structure adopts p-i-n diodes for function control, realizing the arbitrary selection of electromagnetic-wave transmission and reflection functions and polarization selection function in the range of 8–12 GHz. The flexible multifunctional AFSS structure consists of two frequency selective surface (FSS) layers with p-i-n diodes on the top and bottom, a thin, flexible dielectric layer in the middle, and vias for connecting the FSS layers. The deigned structure does not need additional bias feeders, which can reduce the interference to the transmission performance of AFSS. Finally, it is found that the experimental results of the AFSS structure are in good agreement with the simulation results.

Parameter Identification of Optimized Fractional Maximum Power Point Tracking for Thermoelectric Generation Systems Using Manta Ray Foraging Optimization

Thermoelectric generation systems (TEGSs) are used to convert temperature difference and heat flow into DC power based on the Seebeck theorem. The basic unit of TEGS is the thermoelectric module (TEM). TEGSs have gained increasing interest in the research fields of sustainable energy. The output power from TEM is mostly reliant on differential temperature between the hot and cold sides of the TEM added to the value of the load. As such, a robust MPPT strategy (MPPTS) is required to ensure that the TEGS is operating near to the MPP while varying the operating conditions. Two main drawbacks may occur in the conventional MPPTSs: low dynamic response, such as in the incremental resistance (INR) method, and oscillations around MPP at steady state, such as in the hill climbing (HC) method. In the current research work, an optimized fractional MPPTS is developed to improve the tracking performance of the TEGS, and remove the two drawbacks of the conventional MPPTSs. The proposed strategy is based on fractional order control (FOC). The main advantage of FOC is that it offers extra flexible time and frequency responses of the control system consent for better and robust performance. The optimal parameters of the optimized fractional MPPTS are identified by a manta ray foraging optimization (MRFO). To verify the robustness of the MRFO, the obtained results are compared with ten other algorithms: particle swarm optimization; whale optimization algorithm; Harris hawks optimization; heap-based optimizer; gradient-based optimizer; grey wolf optimizer; slime mould algorithm; genetic algorithm; seagull optimization algorithm (SOA); and tunicate swarm algorithm. The maximum average cost function of 4.92934 kWh has been achieved by MRFO, followed by SOA (4.5721 kWh). The lowest STD of 0.04867 was also accomplished by MRFO. The maximum efficiency of 99.46% has been obtained by MRFO, whereas the lowest efficiency of 74.01% was obtained by GA. Finally, the main findings proved the superiority of optimized fractional MPPTS compared with conventional methods for both steady-state and dynamic responses.

Flexible Ultra-Wide Electro-Optic Frequency Combs for a High-Capacity Tunable 5G+ Millimeter-Wave Frequency Synthesizer

This paper presents a new scheme of a cost-effective tunable millimeter-wave (MMW) frequency synthesizer based on an ultra-wideband electro-optic frequency comb. The architecture for the quasi-tunable millimeter-wave frequency synthesizer mainly consists of a compact ultra-wide flat electro-optic frequency comb and a multi-tone frequency generator, which only includes a quantum dot mode-locked laser, a LiNbO3 dual-driving Mach–Zehnder modulator (DD-MZM) and Uni-traveling-carrier photodiode (UTC-PD). MMW signals generated with a quasi-tunable frequency are experimentally demonstrated. The difference in power is obtained for the different frequencies. The linewidth of the quasi-tunable frequency signals is less than 273 Hz. In addition, the single side band (SSB) phase noise of the 25, 37.5, 50 and 75 GHz is measured as −115, −106, −102 and −95 dBc/Hz at an offset of 1 kHz, respectively. The proposed frequency synthesizer has ultra-low phase noise, quasi-tunable frequency and simple structure. The research results of the frequency synthesizer are applied for 5G+ transmission with radio wave working at K-band and V-band. The flexible, compact and robust MMW frequency synthesizer is suitable for the future of ultra-high capacity 5G+ communication.

Flexible Multi-band Dual-chirped Microwave Waveforms Generation with Double Bandwidth

ABSTRACT 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.

Long-distance Φ-OTDR with a flexible frequency response based on time division multiplexing.

In this study, a long-distance phase-sensitive optical time domain reflectometry (Φ-OTDR) with a flexible frequency response based on time division multiplexing is proposed and experimentally demonstrated. Distributed flexible frequency vibration sensing over long distance can be realized by reconfiguring the system layout in a time-division-multiplexed manner by re-routing the Rayleigh backscattered signals for segmented processing with extra erbium-doped fiber amplifiers added only instead of any other complex signal amplification or pulse modulation mechanisms. Through time-division-multiplexed reconfiguration, the tradeoff between sensing distance and vibration frequency response in Φ-OTDR system is largely relieved. Compared with the traditional system layout, the proposed system allows a flexible frequency response in each sensing fiber segment without any crosstalk among them. In experiments, distributed vibration sensing with a frequency response up to 4.5 kHz is achieved over a sensing distance of 60km by the proposed system, which is not possible in a conventional Φ-OTDR system. Furthermore, the frequency response flexibility of the proposed system is further verified by successfully identifying a vibration event with a frequency of up to 20 kHz at the end of a 52-km-long fiber.