The optical-frequency-comb-based (OFC-based) sampling method is of better efficiency than a heterodyne receiver when measuring non-cooperative signals over a large frequency range. However, ...under-sampling during the down-conversion process often results in missing frequency information, necessitating multiple OFCs for recovery. This article proposes a frequency-phase-mapping method with a single OFC is proposed to recover the missing frequency information. First, an asymmetric two-branch electro-optical-modulating structure is designed to acquire the phase difference caused by the time delay. Then, the acquired phase difference is mapped into the signal frequency by a complex unit circle without <inline-formula> <tex-math notation="LaTeX">2\pi </tex-math></inline-formula>-blur. A dimension-expanding procedure is proposed by introducing multimeasuring to enhance the robustness performance. The influence of frequency range, signal-to-noise ratio (SNR), and measuring times are analyzed in detail. The experiment indicates that the correct ratio of frequency recovery can reach 93.5% when the SNR is 20 dB, the frequency range is 1-12 GHz, and the measuring times are 2, demonstrating the proposed method's efficiency.
Spinel ferrite ceramics of nominal composition Ni0.5Zn0.3Co0.2Fe2O4 (NiZnCo) with various BaO doping were successfully synthesized for applications as novel high‐frequency magneto‐dielectric ...materials. The influences of BaO doping on the crystal phase, density, microstructure, and magnetic and dielectric performances in the frequency range of 0.1 to 5 GHz were systematically studied. It is revealed that the doped Ba2+ ions aggregate to the grain‐boundary regions and lead to the formation of BaFe2O4 phase that significantly restrains the growth of NiZnCo ferrite grains. Correspondingly, permeability and permittivity are effectively tailored through the varied grain size and density, which is demonstrated by the magnetic circuit model and the modified effective medium theory proposed herein. As BaO content x = 1.2‐1.8 mol%, the NiZnCo ferrites reveal the excellent performance with almost equal values of μ′ and ε′, yielding a characteristic impedance to be nearly identical as that of free space over a wide frequency range of the VHF and UHF bands. Furthermore, the magnetic loss is effectively reduced at high frequencies, where the typical tan δμ at 0.5 GHz is decreased to ~0.043 with a reduction of up to 37% and the loss factor (tan δμ/μ′) is as low as ~0.006.
Grid synchronization algorithms are of great importance in the control of grid-connected power converters, as fast and accurate detection of the grid voltage parameters is crucial in order to ...implement stable control strategies under generic grid conditions. This paper presents a new grid synchronization method for three-phase three-wire networks, namely dual second-order generalized integrator (SOGI) frequency-locked loop. The method is based on two adaptive filters, implemented by using a SOGI on the stationary αβ reference frame, and it is able to perform an excellent estimation of the instantaneous symmetrical components of the grid voltage under unbalanced and distorted grid conditions. This paper analyzes the performance of the proposed synchronization method including different design issues. Moreover, the behavior of the method for synchronizing with highly unbalanced grid is proven by means of simulation and experimental results, demonstrating its excellent performance.
A semiflexible E-shaped folded patch with a compact footprint of 30 mm <inline-formula> <tex-math notation="LaTeX">\times30 </tex-math></inline-formula> mm <inline-formula> <tex-math ...notation="LaTeX">\times3 </tex-math></inline-formula> mm (<inline-formula> <tex-math notation="LaTeX">0.091\lambda \times 0.091\lambda \times 0.0091\lambda </tex-math></inline-formula> at 912 MHz) is proposed for designing a miniature ultrahigh frequency tag for on-metal applications. The proposed tag antenna is simple in structure, and it has eight design parameters to achieve different levels of tuning. By changing the parameters, coarse and fine tunings can be easily performed to vary the tag's resonant frequency. In spite of its compactness, the proposed tag antenna is able to provide sufficient resistance and inductive reactance to enable conjugate match with the chip. Due to conjugate match, the proposed tag antenna has achieved a power transmission coefficient of ~1 and a maximum read distance of 14.5 m (with 4 W equivalent isotropic radiated power) on metal even it is electrically small. It has a radiation efficiency of 53%.
We introduce a method to diagnose and track the D region ionosphere (60–100 km). This region is important for long‐distance terrestrial communication and is impacted by a variety of geophysical ...phenomena, but it is traditionally very difficult to detect. Modern remote sensing methods used to study the D region are predominately near the very low frequency (VLF, 3–30 kHz) band, with some work also done in the high‐frequency and very high frequency bands (HF/VHF, 3–300 MHz). However, the frequency band between VLF and HF has been largely ignored as a diagnostic tool for the ionosphere. In this paper, we evaluate the use of 300 kHz radio reflections as a diagnostic tool for characterizing the D region of the ionosphere. We present radio receiver data, analyze diurnal trends in the signal from these transmitters, and identify ionospheric disturbances impacting LF/MF propagation. We find that 300 kHz remote sensing may allow a unique method for D region diagnostics compared to both the VLF and HF/VHF frequency bands, due to a more direct ionospheric reflection coefficient calculation method with high temporal resolution without the use of forward modeling.
Key Points
The frequency band around 300 kHz has been largely ignored for the purposes of ionospheric remote sensing
Utilizing these beacons may provide the temporal and spatial capabilities that both VLF and HF remote sensing cannot achieve
A new highly sensitive receiver can detect 300 kHz signals as far as 2500 km away, potentially opening up continental‐scale measurements
•Superharmonic synchronization in micromechanical resonator is utilized for the first time in the MEMS frequency multiplier.•121-order ultra-high frequency amplification is achieved with the ...improvement of frequency stability and SNR.•A novel frequency automatic tracking system is realized to expand the working range of the designed frequency multiplier.
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Frequency multipliers are widely present in electronic system, which always cooperates with low frequency local oscillator for delivering an output wave with a frequency that an exact integral multiple of the input frequency. Conventional frequency multiplier such as step recovery diode, field-effect transistors, low spurious harmonic, etc., usually has only two or three low multiplication factor. Multi-stage frequency doublers can accumulate the multiplication factor, however, has high power consumption and negative conversion gain. Here, we proposed a novel frequency multiplication mechanism utilizing superharmonic synchronization (SHS) effect in micromechanical resonator. We achieved up to 121th ultra-high frequency amplification with frequency stability of output signal 92 times improved and signal to noise ratio 20% increased. To solve the limitation of narrow synchronization range, a frequency automatic tracking system is designed to expand the working range from 0.62 Hz to 27.5 kHz. The proposed frequency amplification is a promising candidate for frequency multipliers and provides an alternative mechanism for micromechanical sensing and signal processing system.
In this letter, an investigation of the very high frequency-ultrahigh frequency (VHF-UHF) wireless broadband indoor channel is carried out. In particular, a wireless channel measurement campaign in ...an indoor environment has been made, in order to characterize the path loss in a broad set of frequencies. The wireless channel is sounded by using a set of discone wideband antennas and a vector network analyzer set to sweep the transmitted signal in the considered band. The measurement results lead to the derivation of a well specified indoor path loss exponent statistical model that takes into account the frequency dependence as well as the distance between the antennas. Three different statistical model refinements are presented, and each of them shows an enhanced ability to predict the path loss.
A novel dual-band ultrahigh-frequency (UHF) radio frequency identification (RFID) sensor tag, designed to operate on metallic surfaces, is proposed. This particular UHF RFID sensor tag is capable of ...operating in both the main RFID frequency bands of the European Telecommunications Standards Institute (ETSI) and the Federal Communication Commission (FCC). The dual-band operation of the UHF RFID sensor tag is based on a very simple concept; by flipping the UHF RFID sensor tag on a metallic surface, it can operate either in the ETSI or FCC RFID frequency bands. The impedance and radiation characteristics of the UHF RFID sensor tag are presented with an extensive analysis of the effects of the metallic surface on the UHF RFID sensor tag. In addition, an equivalent model of the UHF RFID sensor tag, which includes the effects of the metallic surface on the sensor tag, is proposed. The UHF RFID sensor tag has a small form factor and presents a satisfying read range of around 3 m for both the operating frequency bands in a metallic environment as well as a read range of 1.4 m when operating in free space.
In this work, we study the Sakaguchi-Kuramoto model with natural frequency following a bimodal distribution. By using Ott-Antonsen ansatz, we reduce the globally coupled phase oscillators to low ...dimensional coupled ordinary differential equations. For symmetrical bimodal frequency distribution, we analyze the stabilities of the incoherent state and different partial synchronous states. Different types of bifurcations are identified and the effect of the phase lag on the dynamics is investigated. For asymmetrical bimodal frequency distribution, we observe the revival of the incoherent state, and then the conditions for the revival are specified.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The thread-based ultra-high frequency radio frequency identification (UHF RFID) tag with a normal mode helix dipole antenna (NMHDA) shows great potential in anti-theft and implant wireless sensors; ...for the engineered and digitized design of the high-performance tag, it is necessary to know the physical relationship between the resonant frequency and structure parameters of the NMHDA. Previous work for the design of the NMHDA structure is based on the self-resonant principle, that is, zero port reactance, while the port impedance of the NMHDA in the UHF RFID tag thread at resonant frequency is ideally conjugate matching to the chip. Under the requirement of conjugate matching, this study built the physical relationship between the resonant frequency and structural parameters of the NMHDA (helical radius, helical pitch, and single arm length) by linking the chip impedance with the NMHDA impedance. Meanwhile, the reported equivalent impedance model of the NMHDA, consisted of a lumped inductor and a linear dipole antenna, was utilized and modified by considering the distributed capacitance deviation from the NMHDA geometry simplification as part of the lumped inductor. Finally, the physical relationship was put into practice for the design of an UHF RFID tag thread with expected resonant frequency, and the long reading range of the prototype (over 14 m) demonstrated the rationality of the modification. In addition, the discussion on the structure parameter of the NMHDA clarified the efficiency of our proposed method. Generally, the built physical relationship explicitly gives the physical effects of the structural parameters and provides a parametric method for the structure design of a NMHDA for the UHF RFID tag thread.
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