Slot Frequency Research Articles

Improved slot synchronization method for high-speed photon-counting communication based on SNSPD arrays

In optical communication systems based on photon-counting protocols, using highly efficient superconducting nanowire single-photon detectors (SNSPDs) is currently considered an effective solution for achieving high communication rates. However, in the process of increasing the communication channel throughput by reducing the slot width, as the slot frequency increases to the GHz level, the sub-nanosecond-level jitter caused by detection systems becomes non-negligible relative to the entire signal slot and greatly affects the accuracy of slot synchronization. To accurately characterize the photon arrival distribution of SNSPDs and further reduce communication error rates, we constructed a system. Through data analysis, we discovered that the photon arrival intensity distribution under the influence of jitter conforms to a non-homogeneous Poisson process (NHPP) and proposed a correction model for the photon arrival distribution and provided the corrected expression for the maximum likelihood estimation (MLE) algorithm. In subsequent experiments, combined with a blind search strategy, we enhanced the robustness of the model under different slot offset states and reduced the hardware complexity of existing synchronization schemes. The results show that at signal photons Ks=1.624 and background noise photons Kb=0.016 per symbol, the ideal Poisson model's hard decision error rate is 10.56 %, while the corrected model achieves an error rate close to the ideal synchronization performance at 8.9 %.

Maximum likelihood synchronization algorithm correction for photon-counting communications with blocking loss.

To realize deep space optical communications with high capacity and sensitivity, synchronization of pulse-position modulation (PPM) signals is crucial. In this study, the maximum likelihood synchronization algorithm based on inter-symbol guard times was generalized to the scenario with strong blockage of single-photon detectors, where higher PPM slot frequency and signal-noise ratio could be adopted. Furthermore, a slot frequency offset compensation method was proposed, and simulations and experiments were performed to verify the performance improvement of the proposed corrected synchronization algorithm under blockage. The results indicated that the deadtime-corrected synchronization scheme could effectively overcome the performance degradation of the original model under high photon flux, provide estimation (0.02749 slots @ root-mean-square error) close to the Cramér-Rao Bound, and error rates close to ideal synchronization in the experiment.

Vibration Calculation and Analysis for Permanent Magnet Assisted Reluctance Motor with Rotor Slots Based on Air Gap Relative Permeance

A calculation model of radial electromagnetic force wave for permanent magnet assisted reluctance motor (PMaSynRM) with rotor slots is proposed in this paper. By introducing complex air gap relative permeance, the improved magnetic potential permeability method is applied to the calculation of electromagnetic force wave of the PMaSynRM. Considering the influence of both stator and rotor slots, the characteristics of electromagnetic force wave are analyzed theoretically. A multi‐physical coupling model of PMaSynRM is established. The natural frequency of the stator core is obtained by modal finite element analysis and modal hammer experiment. The harmonic response is analyzed by loading electromagnetic force wave into the structure field and the vibration on the housing surface is calculated. The results show that although the amplitude of electromagnetic force is small at zero‐order slot frequency, the vibration caused by electromagnetic force at frequency of stator slots and rotor slots, especially at the rotor slot frequency, is the biggest vibration source. The effectiveness and regularity of the calculation model are verified by the prototype vibration experiments. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Design of compact dual‐band shared‐aperture antenna system based on frequency selective surface

AbstractA miniaturized dual‐band dual‐polarization base station antenna array operating at 2.4–2.8 and 4.6–5.0 GHz is proposed in this paper. The upper‐band unit is embedded in the lower‐band unit to miniature the array size. The size of the proposed shared‐aperture antenna element is 0.28 × 0.28 . To ensure the normal radiation of dual‐band under the small frequency ratio, a meander slot frequency selective surface structure is introduced, which is electromagnetically transparent to the lower‐band unit and function as metal ground for the upper‐band unit to ensure the normal radiation of the upper and lower‐band units, respectively. Simulation and measured results show that the antenna array meets the following design specifications: dual‐band operating (voltage standing wave ratio [VSWR] < 2), mutual coupling less than −20 dB basically, satisfactory gain and radiation characteristics.

A Low-RCS Folded Reflectarray Combining Dual-Metasurface and Rasorber

A strategy for folded reflectarray with low detectability and enhanced gain is presented. For this purpose, the folded reflectarray is engineered by combining a polarization-conversion focusing metasur face, a frequency selective rasorber (FSR), and a diffusion metasurface. The FSR is composed of a lossy layer and a single-polarized I-shaped slotted frequency selective surface (FSS) between which the diffusive metasurface is inserted for in-band and out-of-band cross-polarized low radar cross-sectional (RCS) reduction. Therein, the antenna exhibits a transmission window and two out-of-band absorptions due to the FSR for copolarized radiation. In contrast to detection, the system operated for both wave incidence. For cross-polarized wave incidence, a wideband RCS reduction is enabled due to the wave-diffusive function of the inserted metasurface. The half profile is guaranteed since the wave bounces two times between the FSS and focusing metasurface. The numerical and experimental results coincide well, both indicating that the low-RCS folded reflectarray achieves a peak gain of 23.5 dB at 10.2 GHz, corresponding to an aperture efficiency of 37.8%. Besides, the antenna achieves 10 dB monostatic RCS reduction within 4.6–8.8 GHz and 9.6–13.8 GHz under copolarization detection and a 10 dB monostatic RCS reduction from 8.4 to 19 GHz under cross-polarization detection. Moreover, good invisibility is also achieved for bistatic RCS reduction.

Analysis and design of a single layer double square slot frequency selective surface with single stopband between double passbands

AbstractSquare loop and square slot are the simplest and commonly used elements of frequency selective surfaces (FSSs) providing bandstop and bandpass responses, respectively. Despite it is already known that employment of a double square slot structure presents a tunable stopband between two passbands, it is not clear which parameters of the structure are crucial for tuning the inbetween stopband. We propose an analysis of a double square slot FSS considering its element as a parallel connection of square slot and square loop predicting two geometrical parameters of the constituent square loop are crucial for tuning the inbetween stopband. The stopband is tunable by changing geometrical parameters of the constituent square loop and does not depend on geometries of the constituent square slot. The validity of this analytical prediction is verified by full wave EM simulation results.

Analysis and Reduction of Slot Frequency Vibration of PMSMs With the Force-Harmonic Coupling Model Considering Phase Angle Characteristic

This paper establishes the force-harmonic coupling model considering phase angle characteristic for the analysis and reduction of the slot frequency force harmonic of PMSMs. Compared with the traditional analytical model, the significant influence of the force phase angle on the coupling relationship among force components is considered in the model. Firstly, the force-harmonic coupling model considering phase angle characteristic is deduced based on the Maxwell stress tensor, and considering the influence of the force phase angle on the coupling relationship among force components contributing to the slot frequency force harmonic, these force components are divided in to a series of combinations of positive and negative components. Combined the finite element model, the coupling model is verified. Based on the coupling relationship, the principle of the rotor-step skewing is further explained as the mutual compensation effect of the positive and negative force components, and the slot frequency vibration is effectively offset through choosing the appropriate segment number and skewed angle. Finally, the optimized prototype is tested, and the measured results are in good agreement with the FEM results.

Real-Time and High-Speed Underwater Photon-Counting Communication Based on SPAD and PPM Symbol Synchronization

Photon-counting detectors can increase the range of underwater optical wireless communication (UWOC) by enhancing the detection sensitivity and have thus become an active research area in recent years. However, system performance still needs to be improved in the reported underwater photon-counting communication (UPCC) experiments. In this study, a real-time, high-speed UPCC system was designed and experimentally validated based on a single-photon avalanche diode (SPAD). A reliable symbol synchronization method based on pulse-position modulation (PPM) was developed. This method achieved slot synchronization by using a narrow-pulse-width laser and a simple matched filter and realizes frame synchronization through an improved synchronization sequence. In addition, channel errors were corrected by serially concatenated convolutionally coded PPM (SCPPM), and digital signals were processed in real time based on field-programmable gate arrays (FPGAs). Finally, desktop communication experiments were completed at a slot frequency of 25 MHz and a communication rate of 6.21 Mbps. The system exhibited a bit error rate (BER) of less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–7</sup> , a received optical power of only −84.3 dBm, and an efficiency of 1.35 photons per bit.

Approximate analytical method for hexagonal slot frequency selective surface analysis

In this article, an efficient approximate analytical method for hexagonal slot frequency selective surface (FSS) analysis is proposed. The main contribution of this article is to derive the tangential incident electric field along each oblique strip complementary to the hexagonal slot, so that Kirchhoff type circuit can be established according to the transmission line parameters and distributed sources. The current distribution is solved using Kirchhoff current law and continuity condition for potential. The transmission characteristic can then be calculated following Munk's scheme. Meanwhile, the physical nature of Munk's scheme is studied. The periodic circuit equations are derived from the corresponding electromagnetic field boundary conditions. The approximate closed-form expressions for aperture field and patch surface current distribution of common FSS elements can be calculated by the method of moments. From the analysis, it is known that the receiving current and transmitting current corresponds to the basis function and test function, respectively. Measured and simulated results of a symmetric hybrid radome composed of hexagonal slot are carried out to verify the accuracy and efficiency of the presented method. The CPU time is about 600 and 0.4 second for CST and the proposed method, respectively.

Wideband transverse electromagnetic cell design and its application in frequency selective surface measurement

An open transverse electromagnetic cell (TEM cell) that covers L-band, S-band, and C-band is proposed in this paper. According to impedance matching theory analysis, the characteristic impedance of coaxial connector and microstrip with air as substrate are considered, which are combined with a taper gradient section to realize the function of TEM cell. The proposed TEM cell was modeled and simulated in CST Microwave Studio. Through full-wave simulation, the proposed TEM cell demonstrates a wideband transmission characteristic, S11 less than −10 dB from 1 to 8 GHz, which is relatively rare among the designs that have been reported. The test flow and data post-processing method are given. To verify the effectiveness of the test method, an example of measuring a classical square slot frequency selective surface that their resonance frequency is 3.7 GHz is designed and simulated in the TEM cell. To verify the simulated results, a prototype is fabricated and measured with the proposed TEM cell. The experimental result demonstrates a good agreement with the simulated result, which indicates that the designed TEM cell has good test performance.

Vibration Reduction Characteristics of Permanent Magnet DC Motors With Sawtooth Edge Poles

It is known that the slot frequency vibration is the one of the main components in electromagnetic vibration spectrum of permanent magnet DC motors (PMDCM). After finding that the vibration reduction scheme of the piecewise varying pole width (PVPW) is only effective for the odd order harmonic of slot frequency vibrations by analytical method, the PM pole with sawtooth edge is put forward to reduce all harmonic components of slot frequency vibrations of PMDCM. In this article, after the air gap flux density and radial force density are analyzed, the two vibration sources, radial force and bending moment, are derived for the motor with sawtooth edge poles (SEP). Then the optimized pole shape is obtained to reduce all harmonic components of both the radial force and bending moment at the same time. Three dimensional finite element method of electromagnetic field and structure are used to calculate the magnetic flux density, radial force and vibration for the motors of PVPW and SEP. Three permanent magnet motors with fixed pole width (FPW), PVPW and SEP are manufactured and tested. The comparison and verification show that SEP is better than the other two schemes in general.

Vibration Reduction by Magnetic Slot Wedge for Rotating Armature Permanent Magnet Motors

There is only slot frequency electromagnetic vibration and no pole frequency vibration in rotating armature permanent magnet motor (RAPMM), which is the advantage of this motor. The open of slot makes the air-gap magnetic field distorted and causes the harmonic of electromagnetic excitation force. In order to reduce the slot frequency vibration of the RAPMM, the method of placing magnetic slot wedge (MSW) at the slot opening is put forward accordingly. Through the finite-element simulation, it is finally shown that the MSW is capable of weakening the harmonic of the air-gap flux density, as well as decreasing the high-frequency component of the electromagnetic excitation force. Therefore, it is acknowledged that MSW can suppress the cogging torque and the vibration of corresponding frequency on the stator significantly. Finally, it is confirmed by the experiments that the built-in MSW is an effective measure for reducing the vibration of the RAPMM.

A novel low‐radar cross section microstrip antenna based on slotted frequency selective surface

AbstractA novel low‐radar cross section (RCS) microstrip antenna with radiation performance and antenna volume maintained is proposed in this paper. Different from other antenna RCS reduction methods, the proposed antenna applies shaping method on frequency selective surface (FSS) ground plate to achieve further RCS reduction. In order to obtain the effect of subtracting square slots, an antenna with normal FSS ground is designed as reference antenna. The modified antenna with slotted FSS ground shows more significant RCS reduction compared with reference antenna in the frequency range 4 to 7.5 GHz, the maximum RCS reduction is 14.62 dBsm at 4.22 GHz. And the gain of the modified antenna is increased about 0.2 dB in contrast with the reference antenna. Besides, the modified and reference antenna are fabricated and measured. It is shown that the simulation and measured results are in good agreement.

Analysis of Zeroth-Mode Slot Frequency Vibration of Integer Slot Permanent-Magnet Synchronous Motors

For the integer slot permanent-magnet (PM) driving synchronous motor, the zeroth-mode slot frequency vibration and noise play a significant vibroacoustic role in the low-frequency domain. For conventional analysis in literature, it is usually assumed that the zeroth-mode vibration is caused by the zeroth-order radial force harmonic. But in this paper, the genuine reason for zeroth-mode vibration is proposed and discussed in detail, which is different from the conventional analysis. The teeth chopping effect is proposed and demonstrates that the slot number order radial force is the root of the zeroth-mode vibration of the motor. After the analysis of the zeroth-mode vibration in existing research work is presented, the teeth chopping effect is introduced and described. The amplitudes of the zeroth-order and slot number order forces are compared with an analytical method, while their amplitudes and caused deformations of these forces are calculated with the finite-element method (FEM). Finally, to validate the analytical and FEM results, a 6-pole 36-slot PM driving motor is manufactured and tested, and the results are in good agreement with those of the FEM results.

Single LED-based 46-m underwater wireless optical communication enabled by a multi-pixel photon counter with digital output

Presently, most of the long-reach underwater wireless optical communication (UWOC) systems employ laser diodes rather than light-emitting diodes (LEDs) as the transmitters. Due to lasers’ smaller divergence angles, those UWOC systems could realize longer communication links. Although LED-based long-reach UWOC has distinguished advantages, it suffers from very low received optical power. Fortunately, highly sensitive multi-pixel photon counter (MPPC) and energy efficient pulse position modulation (PPM) pave a way towards LED-based long-reach UWOC. In this paper, we investigated the underlying working principle of an MPPC and proposed a UWOC system based on single LED as well as a lens-free MPPC with digital output. The relationship between the MPPC p.e. threshold and its received optical power was theoretically studied and further proved by experimental results. Single 2.3-MHz, 3-W blue LED was used as the transmitter to generate 8-PPM to 64-PPM signals with a 5-MHz slot frequency. After a 46-m underwater transmission, the measured BERs were all below the forward error correction (FEC) limit, which were achieved with less than 100 incident photons during each pulse slot.

Exciting Force and Vibration Analysis of Stator Permanent Magnet Synchronous Motors

Exciting Force and Vibration Analysis of Stator Permanent Magnet Synchronous Motors

Analysis and Discussion of the Indirect Testing Method for the Losses of Permanent Magnet Synchronous Machines

The losses of permanent magnet synchronous machine (PMSM) are always cared in the machine system, since the losses mainly determine the temperature-rise and efficiency of the machine. An indirect-testing method for the losses of PMSM has been proposed in order to measure the losses without any mechanical load in the test. The aims of this paper are to analyze the influence factors on this method and discuss the application of this method. The influences of the pole–slot combination, saturation, harmonic content, and frequency on the test error are analyzed. To validate the analysis, the indirect-testing losses and the direct-testing losses are compared with the test of a PMSM prototype.

Decreasing base units-unequally spaced channel allocation algorithm for dense wavelength division multiplexed transmission systems

We propose an unequally spaced channel allocation algorithm, i.e., decreasing base units-unequally spaced (DBU-US) algorithm tested for high-capacity dense wavelength division multiplexed (DWDM) transmission systems. The new scheme decides upon the number of base units (BUs) covering the entire bandwidth and the allocation of different number of channels in the BUs. Starting from BUi = 0, the number of channels in each subsequent BU(BUi = 1 , 2 , 3 ) reduces by a factor of 2, “i” being the index of the BUs. The BUi , BUi + 1 , … have even and odd slot frequency allocations, which creates a substantial degree of unequal channel spacing, which virtually proves to reduce the four wave mixing (FWM) products effectively for any number of transmitted channels. When compared with existing unequal channel allocation schemes of unequally spaced repeated unequally spaced (URUS), alternately paired URUS (APRUS), a reduction of 6.25% and 13.7% in bandwidth is observed, respectively. Similarly, a reduction of FWM products by 45.5%, 41.3%, and 31.7% is observed, when compared with URUS, paired URUS, and APRUS, respectively. The FWM intensities generated by DBU-US are reported to be 5 dBm lesser when compared to widely accepted URUS scheme. Therefore, it is concluded that DBU-US is superior and is considered suitable for DWDM transmission systems.

Analysis of slot-based radiators using TCM and its application in MIMO antennas

In this article, with the help of the theory of characteristic modes (TCM), it is found that the introduction of circular slots in a chassis modifies the chassis modes. Based on the location of the slot, different chassis modes will be affected. For a fixed location, the slot to chassis size ratio plays an important role in its effect on the radiating bandwidth (BW). For a small size ratio, a modified chassis mode will be created without affecting the radiating BW. The current concentration across the slot depends on the shape of the slot (circular, rectangular, triangular, or square) and its location on the chassis. Moreover, the effect of multiple circular slots on the chassis modes is investigated. For slots introduced in a symmetrical fashion, that is, four elements, the modes are not affected and are similar to the original chassis ones. We also investigate the principle behind frequency reconfigurability using TCM analysis. The varactors used for frequency reconfigurability do not alter the radiating BW (Modal Significance plots) but only help in the input impedance matching at different frequency bands of the same mode. If a mode is excited purely using a proper feeding arrangement, the same frequency reconfigurable antenna will behave as a wide band one. Based on the detailed analysis presented in this work, a compact multiple-input-multiple-output annular slot frequency reconfigurable antenna operating between 1.8 and 2.45 GHz is presented. Frequency tuning is achieved using varactor diodes.

Induction Motor Stator Fault Diagnosis by Rotor Slots Harmonics Tracking Using Prony Improved Approach

The short-circuit fault diagnosis is essential in order to avoid irreversible damages that could affect the stator circuit of the induction motor. For this purpose, this paper addresses a new approach based on Prony's high resolution spectral analysis method to avoid the drawbacks of the well-known method based on the power spectral density estimation by Periodogram technique. This new approach, called Root-Prony, allows a better frequency resolution even on a very short acquisition time as well as a better detection even on very small magnitudes. Moreover, and in order to reduce the computation time of this approach, this paper proposes to analyze only the band around the first rotor slot frequencies. The choice of this band allows avoiding any confusion with the frequency signatures of external phenomena which appear most often in very low frequencies. The experimental results obtained show the efficiency and the reliability of this new approach in tracking the induction motor stator winding degradation.