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Vibration measurement is a crucial task in industrial systems, where vibration characteristics reflect health conditions and indicate anomalies of the devices. Previous approaches either work in an intrusive manner or fail to capture the micrometer-level vibrations. In this work, we propose mmVib, a practical approach to measure micrometer-level vibrations with mmWave radar. First, we derive a metric called Vibration Signal-to-Noise Ratio (VSNR) that highlights the directions of reducing measurement errors of tiny vibrations. Then, we introduce the design of mmVib based on the concept of Multi-Signal Consolidation (MSC) for the error reduction and multi-object measurement. We implement a prototype of mmVib, and the experiments show that it achieves 3.946% relative amplitude error and 0.02487% relative frequency error in median. Typically, the average amplitude error is only 3.174um when measuring the 100um-amplitude vibration at around 5 meters. Compared to two existing mmWave-based approaches, mmVib reduces the 80th-percentile amplitude error by 69.21% and 97.99% respectively.

The Constitution and the geometry aspects of any sensor is influenced by several factors involved in the assembling of sensor. It is basically influenced by parameter to be measured, method of measuring the measurand, nature of the parameter i.e. weather the parameter is chemical, biological, physical, optical, electrical, magnetic, mechanical or acoustic etc., environment around it, etc. In most of the cases, several sensors are developed, meant to measure a single parameter with maximum achievable sensitivity. In the present paper a fiber optic multipurpose sensor is described, which can be used to measure various physical quantities of liquids with well defined combination at room temperature (30 °C), employing a specific set of materials and methods in the design operation of the sensor. Exploiting all the advantages offered by the fiber optic technology, the sensor was calibrated to measure ultrasonic velocity, refractive index, density, dielectric constant, viscosity, molar volume, acoustic impedance, molar refraction, viscous relaxation time, adiabatic compressibility, free intermolecular length, Gibb’s free energy, absorption coefficient, internal pressure, free volume, mole fraction, concentration, effective mass at room temperature and examined to exhibit superiority in all respects compared to the conventional sensors.

The most important variables to consider in the design of antennas for RFED applications and effective communications are low cost, low profile, and reduced size. The dipole antenna, often known as a dipole aerial, is the most basic and widely used type of antenna. Among other antennas, this is one of the most straightforward antenna layouts. It may be achieved by applying a sinusoidal voltage differential between two thin metallic rods. The dipole antenna is a particularly important type of RF antenna that is frequently used for radio transmission and reception. For many types of antennas, this antenna can be employed as a radiating or driving element. This Dipole antenna may be used in the radio frequency spectrum sections HF, VHF and UHF. The major advantage of a dipole antenna is that it can serve as both a broadcast transmitter and receiver. So, to obtain the most crucial factors, we'll design an antenna in COMSOL Multi Physics and display the results as Radiation patterns.

This article presents a circuit model that is able to capture the full nonlinear behavior of an asymmetric electrostatic transducer whose dynamics are governed by a single degree of freedom. Effects such as stress-stiffening and pull-in are accounted for. The simulation of a displacement-dependent capacitor and a nonlinear spring is accomplished with arbitrary behavioral sources, which are a standard component of circuit simulators. As an application example, the parameters of the model were fitted to emulate the behavior of an electrostatic MEMS loudspeaker whose finite-element (FEM) simulations and acoustic characterisation where already reported in the literature. The obtained waveforms show good agreement with the amplitude and distortion that was reported both in the transient FEM simulations and in the experimental measurements. This model is also used to predict the performance of this device as a microphone, coupling it to a two-stage charge amplifier. Additional complex behaviors can be introduced to this network model if it is required.

In this paper, a novel optical rotary sensor based on laser self-mixing interferometry is developed for the full-circle rotation measurement. The proposed sensor is convenient to use for it does not need any contact with the target or a cooperative mirror. A prototype is fabricated and tested. The measured results demonstrate a good performance compared with other optical rotary sensors, in terms of the 0.1 μrad resolution, the 2.33×10-4 linearity and 2 μrad stability over one hour. Additionally, the repeatability error is below 14.66 mrad under 9-group full-circle tests, which exhibits the potential to be instrumentalized reliably. Error analysis and limitation discussion have been also carried out. Although the accuracy needs further improvement compared with the best rotary sensor, this method has its unique advantages of high resolution, non-cooperative target sensing and electromagnetic immunity. Hence, the proposed optical rotary sensor provides a promising alternative in precise rotation measurement, tremor tracing and nano-motion monitoring.In this paper, a novel optical rotary sensor based on laser self-mixing interferometry is developed for the full-circle rotation measurement. The proposed sensor is convenient to use for it does not need any contact with the target or a cooperative mirror. A prototype is fabricated and tested. The measured results demonstrate a good performance compared with other optical rotary sensors, in terms of the 0.1 μrad resolution, the 2.33×10-4 linearity and 2 μrad stability over one hour. Additionally, the repeatability error is below 14.66 mrad under 9-group full-circle tests, which exhibits the potential to be instrumentalized reliably. Error analysis and limitation discussion have been also carried out. Although the accuracy needs further improvement compared with the best rotary sensor, this method has its unique advantages of high resolution, non-cooperative target sensing and electromagnetic immunity. Hence, the proposed optical rotary sensor provides a promising alternative in precise rotation measurement, tremor tracing and nano-motion monitoring.

The hollow-cup Permanent Magnet (PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element (FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.

This paper presents a novel configuration of the eddy current speed sensor to measure the rotating speed of iron rods and shafts up to 3000 rpm. The proposed eddy current speed sensor has an axial airgap structure with one excitation coil and two antiserially connected pick up coils. The speed sensor is mounted in the end shaft part region. Different solid iron materials for rotating shaft are considered in the measurements and calculations to evaluate solid iron material effect on the eddy current speed sensor performance. 2D and 3D finite element method is utilized for the performance analysis of the speed sensor. Also, a 2D analytical method is developed for parametric analysis. A copper rod is also used to compare the speed sensor with the rotating iron shaft and copper shaft. Finally, two thin copper discs with different diameters are mounted on the solid iron shaft and their influences on the eddy current speed sensor were evaluated and measured to increase sensitivity and decrease sensor dependency on the permeability of the solid iron shaft. The achieved nonlinearity errors are about 0.2%.

Laser ultrasonic techniques (LUTs) are becoming widely used for damage detection based on full-field ultrasonic data. In general, LUTs provide threedimensional (3-D) ultrasonic signals from which significant informative features may be extracted about the health condition of a structure. In this paper, statistical convariance method is proposed to investigate 3-D ultrasonic features. A laser ultrasonic interrogation method based on a Q-switched laser scanning system was used to interrogate 3-D ultrasonic signals in to a 2 mm aluminum plate. The ultrasonic signals in three-dimensional (3-D) space were generated, indexed by spatial N (xdirection), spatial M (y-direction), and temporal K (t-direction) samples, respectively. Then, two sets of covariance matrices were obtained based on the vector variables in x-direction and y-direction respectively for all k time samples respectively. The covariance imaging and the corresponding variance map were obtained. The wavelength and group velocity of S0 and A0 modes were able estimated from the variance map. The wavelength of the S0 and A0 modes were estimated with the deviation error of 2.3% and 11% respectively. The group velocities of S0 and A0 modes were estimated with the deviation error of 1.8% and 0.9%. The analysis will be further performed to develop group velocity curves for a range of frequency in metal and composite plates.

The insulation impedance monitoring methods such as capacitance/dissipation factor (C/DF) monitoring methods have been proposed for the online stator insulation condition monitoring. By measuring the insulation leakage currents and the phase-to-ground voltages, the groundwall and phase-to-phase insulation impedances can be calculated in frequency domain. In the existing methods, the calculation is based on the assumption that the differential mode phase-to-ground voltage decreases linearly along the stator winding and no phase angle deviation is considered. However, the phase angles of the induced electromagnetic forces in stator winding in different slots depend on the slot positions. The assumption in the existing methods neglects this phase deviation and causes errors in the monitoring results. In order to eliminate this effect, the effect of the phase angle deviation on monitoring results is analyzed in this paper. Its dependency on the turn number, the winding configuration and the frequency of the selected monitoring signals is studied. A compensation method is proposed and the compensation coefficients are calculated for different winding cases for the demonstration purpose. The online experimental results prove that the accuracy of the online monitoring results is improved after the compensation.

In recent years, the development of electronic devices are trending to be smaller and lighter, the techniques for suppressing electromagnetic (EM) radiation need to comply with these trends. EM shields are widely used to suppress EM radiation from transmission lines. EM shield for interconnection cable such as flexible-printed-circuits (FPC) requires flexibility of shielding-material. Consequently, EM shield becomes much more thin metallic shield and may be implemented near the transmission lines in the future. However, frequency response of the transmission coefficients of the shielded-FPC has dispersion due to insufficient shielding performance for near magnetic field. Elucidating the relationship between dispersion of frequency response and time response of transmission characteristics of shielded-FPC turns to be an important indicator of shielding techniques. In this paper, experimental extraction has been proposed for detailed investigating the frequency dispersion of shielded-FPC by using the RLGC equivalent-circuit model. The experimental extraction method used S-parameters measured by using vector network analyzer. The unnecessary components such as connectors are compensated correctly by using proposed method. The frequency response of primary and secondary parameters extracted using the proposed method reproduces all the dispersion characteristics of shielded-FPC successfully. More importantly, quantitative evaluation using the RLGC equivalent-circuit model considering dispersion characteristics can be performed experimentally.

The fault feature of vibration signal is always submerged in heavy interference noise and strong pumping impulses in axial piston pump bearings. A fuzzy entropy assisted singular spectrum decomposition denoising method is introduced to extract bearing fault in axial piston pump. The raw measured data is adaptively decomposed to singular spectrum components. The fuzzy entropy of singular spectrum components is used to screen the component with critical information and remove the unrelated components. The remaining singular spectrum components are conducted for the secondary screening to decrease impulse interference based on the prior knowledge. Simulation results of signals with different noise intensity thoroughly validate performance. This method is applied to process practical engineering signals and the characteristic frequency intensity coefficient is taken as the evaluation index in the field. The experimental results show that the evaluation index of the presented technique are increased by 80%, 56% and 40%, respectively.

Summary Objective Past literature indicates that vibrato measurements of singers objectively changed (i.e., vibrato rate decreased and vibrato extent increased) from 1900 to the present day; however, historical audio recording technology may distort acoustic measurements of the voice output signal, including vibrato. As such, the listener's perception of historical singing may be influenced by the limitations of historical technology. This study attempts to show how the wax cylinder phonograph system—the oldest form of mass-produced audio recording technology—alters the recorded voice output signal of modern-day singers and, thus, provides an objective lens through which to study the effect(s) of historical audio recording technology on vibrato measurements. Methods Twenty professional Western opera singers sang a messa di voce on the vowel [a] and on the pitch C4 for male singers and C5 for female singers, three times into a flat-response omnidirectional microphone and onto an Edison Home Phonograph simultaneously. The middle 1–3 seconds (6–10 vibrato cycles) of each sample was analyzed for vibrato rate, vibrato extent, jitter (ddp), shimmer (dda), and fundamental frequency for each recording condition (wax cylinder phonograph or microphone). Steady-state and frequency-modulating sinewave test signals were also recorded under the multiple recording conditions. Results Results indicated no significant effect of recording condition on vibrato rate (mean [standard deviation], cylinder: 5.3 Hz [0.5], microphone: 5.3 Hz [0.5]) and no significant difference was found for mean fundamental frequency (cylinder: 389 Hz [137], microphone: 390 Hz [137]). A significant main effect of recording condition was found for vibrato extent (cylinder: ±103 cents [30], microphone: ±100 cents [31]). Additionally, mean jitter (ddp) (cylinder: 1.22% [1.09], microphone: 0.24% [0.12]) and mean shimmer (dda) (cylinder: 9.40% [4.90], microphone: 1.92% [0.94]) were significantly higher for the cylinder recording condition, indicating more cycle-to-cycle variability in the wax cylinder recorded signal. Analysis of test signals revealed similar patterns based on recording condition. Discussion This study validates past scholarly inquiry about vibrato measurements as extracted from digitized wax cylinder phonograph recordings by demonstrating that measured vibrato rate remains constant during both recording conditions. In other words, vibrato rate as measured from historical recordings can be viewed as an accurate representation of the historical singer being studied. Furthermore, it suggests that the value of prior vibrato extent measurements from these acoustic recordings may be slightly overestimated from the original voice output signals produced by singers near the beginning of the 20th century (i.e., a narrow vibrato extent might have been numerically smaller on average). Increased jitter and shimmer in the wax cylinder recording conditions may be indicative of nonlinearities in the phonograph recording or playback systems

As an increasingly recognized optical interferometric technique for nondestructive testing and evaluation, shearography has attracted extensive interest in various industrial applications. However, it suffers from the ignorance of the whole process of dynamic surface deformation and the difficulty in determining the depth-resolved information of inhomogeneities. In this regard, a novel speckle pattern interferometric modality named photothermal radar shearography is proposed. Unlike the differential mode of conventional shearography, the present work focuses on the dynamic surface displacement field channel technique with more comprehensive understanding of the subsurface structural information. With the utilization of frequency modulated photothermal excitation, the depth-distributed information of subsurface structures and inhomogeneities is encoded into the induced dynamic surface deformation. Using Hilbert transform and least-square method solved by discrete cosine transform, the time-domain interference signal of each pixel from the recorded speckle patterns sequence is demodulated and unwrapped to obtain the transient full-field shearographic phase distribution which indicates the dynamic surface deformation. In the meanwhile, incrementally delayed cross-correlation matched filtering allows for the localization of axial energy distribution to generate depth-selective structural display for tomography. This proposed transient-based interferometric methodology thus enables depth-tomographic profiles and three-dimensional visualization of subsurface anomalies for the first time, which significantly improves the superiority and attractiveness of shearography in providing insight into the status, performance and reliability of industry.

Confronting the challenge of replacing or recharging batteries for numerous low-power devices in IoT, the harvesting of ambient electromagnetic (EM) energy is considered a promising approach. Since EM energy is randomly distributed in the environment, omnidirectional antennas or multibeam antennas are better choices for their large coverages which enable them to collect as much energy as possible. However, omnidirectional antennas usually have low gains resulting in low receiving energy, and most multibeam antennas with high gains require complicated feeding networks. To address these issues, a six-beam antenna without a complex feeding network is proposed in this paper. It consists of a triangular patch array layer and a surface waveguide layer. A peak gain of 8.3 dBi, as well as a 3-dB beamwidth of 620 in H-plane and 560 in E-plane have been achieved, affording full azimuthal coverage within a certain elevation angle range. For demonstration, an EM energy harvester is constructed based on the proposed antenna. It can be observed that the implemented device can harvest almost the same amount of EM energy in different horizontal orientations, and acquire multi-fold DC power in the case of multiple EM transmitters.

The influence of rotor position error generated by resolver on electromagnetic noise of permanent magnet synchronous motors (PMSMs) is analyzed in this paper. The motor noise is mainly caused by the electromagnetic force acting on the surface of stator teeth or permanent magnets. Firstly, the influence of rotor position error on current harmonics is deduced theoretically. The spatial and temporal characteristics of the electromagnetic force are then analyzed. The results show that the rotor position error will introduce extra sideband frequency harmonics to the current and electromagnetic force. This will lead to more abundant noise harmonics. The field-oriented control (FOC) model and the electromagnetic finite element model (FEM) are then established to simulate the influence of rotor position error on current harmonics and electromagnetic force. Finally, a test is carried out to capture the phase current and noise spectrum. Both the simulation and test results are consistent with the theoretical analysis results. This study can give a reference to the source identification and optimization of acoustic performance for PMSMs in electric vehicles.

In this study, the simulation and experiment of a thermoacoustic Stirling heat engine (TASHE) with a phase-adjuster are demonstrated. The phase-adjuster is used as a tool to tune the acoustic field of the TASHE in order to maintain the high performance of the system. The core components of the TASHE comprising an ambient heat exchanger, regenerator, hot heat exchanger, and feedback pipe, are located in the torus section. Besides, there is a resonator pipe, connecting to the torus, which acts as compliance to maintain the system stability, and the phase-adjuster is installed at the end of the resonator. Firstly, the TASHE is modeled by DeltaEC to search for the optimal configurations of the prototype. Due to the variations of acoustic load or operating conditions from the design criteria, the engine absolutely cannot provide maximum output power. The proposed phase-adjuster could keep its high efficiency by re-matching the frequency. In the experiments, the self-excited and steady-state temperatures of the TASHE are around 755 K and 670 K, respectively. Here, this TASHE can provide an acoustic power of up to 40 W, and an energy conversion efficiency of 12.03%. In comparison, there is a reasonably good agreement between the measured and DeltaEC simulated results. This can reflect on the preciseness of the proposed model. In the case of the TASHE operated under the off-design condition, these scenarios certainly drop its efficiency. Consequently, the role of the phase-adjuster in improving its performance by tuning the acoustic field is presented here.

Nowadays, the piezoelectric transduction mechanism has a great concern to be used in the (micro-electromechanical systems) MEMS microphones. In piezoelectric microphones, the thickness, length, width of the piezoelectric and electrode materials are key parameters that need to be optimized in the design loop. The sensitivity is also another vital design factor for MEMS microphones. One common scenario in modeling the sensitivity is to build an electrical equivalent model from lumped components in any simulator. This approach generally requires specialist design expertise and substantial time to build a complete equivalent model. In this paper, a powerful simulation platform to design high-performance cantilever piezoelectric MEMS microphones with sensitivity estimation has been presented. This simulation platform, called MEMS microphone optimizer platform (MMOP), can predict a wide range of key issues related to the successful design of a MEMS Microphone such as the optimum values of piezoelectric material thickness, electrode material thickness, and the length of a cantilever. MMOP offers also the capability to simulate sensitivity directly from the input parameters of the designed model. To validate the proposed simulation platform, a real model of a cantilever MEMS microphone has been studied. In the performed simulations and analysis, sweeping dimensions in micrometer have been considered to predict the best performance. In the proposed model, Aluminum nitride (AlN) and molybdenum (Mo) were utilized as the piezoelectric material and electrode materials, respectively. A high agreement has been found between the theoretical results and the output of the MMOP platform. The platform opens the door for a fast optimized design with accurate results. Finally, MMOP enables a designer to simulate key issues that are specific to cantilever MEMS microphones, including optimized thickness values and predicted sensitivity.

A novel fiber Bragg grating (FBG) sensor with three-dimensional (3D) fused deposition modeling (FDM) approach is proposed for effective stress measurement in soil mass. The three-diaphragm structure design is developed to measure earth and water pressures simultaneously. The proposed transducer has advantages of small size, high sensitivity, low cost, immunity to electromagnetic interference and rapid prototyping. The working principle, design parameters, and manufacturing details are discussed. The proposed transducer was calibrated for earth and water pressures measurement by using weights and a specially designed pressure chamber, respectively. The calibration results showed that the wavelength of the transducer was proportional to the applied pressure. The sensitivity coefficients of the earth and water pressures were 12.633 nm/MPa and 6.282 nm/MPa, respectively. Repeated tests and error analysis demonstrated the excellent stability and accuracy of the earth and water pressure measurements. The performance of the proposed transducer was further verified by a model experimental test and numerical analysis, which indicated that the proposed transducer has great potential for practical applications. © 2021 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/ licenses/by-nc-nd/4.0/).

In this communication, a dual-polarized filtering magneto-electric dipole (FMED) antenna and arrays are proposed for 5G n258 (24.25-27.5 GHz) operations. The FMED antenna was devised to incorporate filtering mechanisms using a built-in substrate integrated waveguide (SIW) based filter plus slot-and-notch etching on the dipole element. As such, lower and upper radiation cutoffs and nulls were produced and tuned, independently. To overcome the problem of “high selectivity” of a filtering antenna that has not been correctly quantified and thus has no comparison, a new skirt measure metric named as radiation suppression index is initiated here. Design steps of the FMED element and novel feeding techniques are elaborated, where the SIW-based series-parallel slot-coupled feeders and the slot-coupled differential power divider were conceived for large-size array, to combat with the insertion losses. A prototype of the 4×4 FMED array was implemented and tested for experimental verification. A high gain of 16.8±1.4 dBi with a 3-dB gain bandwidth of 24-27.7 GHz and a radiation efficiency of 78% were accomplished.

Holographic acoustic field has shown great potential for non-contact robotic manipulations of millimeter or sub-millimeter size objects to effectively deliver acoustic power. The latest technology for generating dynamic holographic acoustic field is through phased transducer array, where relative phases of emitted acoustic waves from transducers are independently controlled to modulate the acoustic interference field. While the forward kinematics of a phased array based robotic manipulation system is simple and straightforward, the inverse kinematics (i.e., the mapping from a given holographic acoustic field to array phases for control purpose), however, is mathematically non-linear and unsolvable, presenting challenges in developing wider applications of holographic acoustic field for robotic manipulation. Considering, thus far, there are still no effective solutions reported, the authors put intensive efforts to solve this problem using a machine learning approach, which we refer to as AcousNet. Experimental results demonstrate the effectiveness of the proposed method for dynamic holographic acoustic field generation from phased transducer array.

Range-dependent clutter suppression is a challenging problem in non-sidelooking (NSL), bistatic, and conformal antenna array airborne radar, especially in the presence of range ambiguity. Superimposed stepped frequency (SSF) radar employs a small frequency increment across the stepped signals in each pulse, which induces a dimension related to slant range. In this paper, an airborne radar framework is established with SSF signal as the transmit waveform. Thus, a two-stage adaptive clutter suppression method is proposed which utilizes the degrees of freedom in range, space and time domains provided by airborne SSF radar. In the first stage, the secondary range dependence compensation (SRDC) approach is adopted to distinguish the clutter of each range region in the carrier frequency domain. Then, a target-free covariance matrix is estimated by the compensated data, and the covariance matrix is used for the range-ambiguous clutter separation in the carrier frequency domain. Thus, the space-time snapshot of each range region can be extracted. In the second stage, a clutter segmentation processing method is devised for residual clutter suppression.

The magnetic field inside a machine is responsible for the mechanical excitation of the stator structure, generating vibrations and thus, audible noise. In this paper, the Permanent Magnet Synchronous Motor (PMSM) is driven by using Sinusoidal Pulse Width Modulation (SPWM) technique, and then an investigation (cause and effect) of Acoustic Noise and Vibration (ANV) is presented. An equivalent lumped parametric modelling of end-to-end coaxially coupled shafts between PMSM and DC generator along with effective modal mass and modal participation factor accuracy enhancement technique, is presented to predict torsional vibration. The modal analysis approach is used to analyse the torsional vibration response, which is used to estimate the source of acoustic noise, and a mathematical approach is presented at the end to calculate ANV of electric drives. Theoretical and experimental investigations are carried out on a 1.07- kW, 4-poles, 36-slots, 3-phase PMSM drive. Analytical and numerical results are validated by experimental studies.

Permanent magnets vernier (PMV) machine is gaining more and more attention due to its high torque density contributed by multi-orders working harmonics, especially low-pole-pair numbers harmonics. Spoke array PM machine seems to be a good way to increase the machine working harmonics. But the flux barrier effect is revealed and it explains why the advantages of the spoke array PM vernier machine are not fully used. Thus, its low-pole-pair numbers harmonics could be further enhanced. In this paper, a novel structure—claw pole permanent-magnet vernier (CPPMV) machine is firstly proposed and its working principle is investigated. Then, the CPPMV machine is compared with the surface mounted PM vernier machine, the spoke array PM vernier machine and the spoke array PM vernier machine with alternate flux bridges in terms of their electromagnetic performances using equivalent circuit analysis and FEM. The result shows that claw pole structure can enhance the magnetic flux modulation effects, which increases the machine torque density. At last, a CPPMV machine prototype is manufactured and tested. Experimental results indicate that it reaches torque density of 30.5kNm/m3 and power factor of 0.84 under rated condition.

High field intensity electromagnetic radiation effect test is difficult to simulate in large-scale space, and the existing bulk current injection (BCI) technology has a limited application of the nonlinear system test. Starting from the coupling mechanism of shielded wire, an analysis model about the response of the equipment under test (EUT) is built-in radiation and injection conditions. In addition, the equivalent corresponding relationship originates between the injected excitation source voltage and the radiation field intensity. The basis for obtaining the source of the injection excitation and performing extrapolation tests is found, and the test method of BCI replacing high field intensity electromagnetic radiation is developed. Subsequently, the passing-through load and communication station tests are performed to verify the theoretical derivation and the test method. As indicated from the research results, the BCI is capable of accurately replacing the high field electromagnetic radiation effect test of the EUT, and the maximum test error reaches 2.7 dB, capable of satisfying the actual needs of the project.

This paper focuses on the electromagnetic vibration source and its reduction design in fractional-slot concentrated-windings (FSCW) permanent magnet (PM) machines. Firstly, the electromagnetic force and vibration characteristics of a 12-slot/10-pole FSCW PM machine are investigated. Then, four electromagnetic vibration sources are investigated and compared, in which the machine operates state is considered. The result shows that the electromagnetic force modulation and stator MMF harmonics are the two sources that contribute most to the vibration under rated and heavy load condition, respectively. Afterwards, two new designs to reduce the vibration caused by the electromagnetic force modulation and stator MMF harmonics are proposed, and the reduction principles are described in detail. Finally, the prototypes of the existing and proposed 12-slot/10-pole FSCW PM machines are manufactured. The tests are conducted to validate the theoretical analysis and proposed vibration reduction design.

A theoretical sea echo modeling of the floating-platform high-frequency hybrid sky-surface wave radar (HSSWR) is presented. The ionosphere is considered to be a no-tilt reflecting plane moving in the vertical direction. Subsequently, the first-order sea clutter cross section with consideration of the platform sway and yaw motion is derived. Simulations are conducted to explore the influences of the ionospheric movement and the platform oscillation motion on the sea clutter power spectrum. Simulation results indicate that the platform sway motion may induce additional peaks that distribute symmetrically concerning the Bragg peaks, while the platform yaw motion and the ionospheric movement may broaden even split the sea clutter. Experiments are conducted with the newly-developed HSSWR system, of which the receiving arrays are simultaneously deployed on a floating platform and the shoreside. Experimental measurements concerning the frequency shift, Doppler width, and the arrival angle of the E-layer/F-layer ionosphere reflected direct wave are compared and analyzed. The study demonstrates the feasibility of the proposed modeling and provides valuable guidelines for the sea clutter characteristics analysis and the data quality assessments of the floating-platform HSSWR.

In this paper, we describe a visible-light positioning system that uses the ambient-light sensor assembly in a smartphone as a receiver for illumination signals from LED-based room lighting. After correcting for missing or inconsistently sampled data captured by the receiver, we can identify the source LEDs contributing to the received signal via Fourier analysis of its frequency distribution. Localization of the smartphone is then achieved by trilateration of the distances to the various LEDs, which are calculated from the received signal strength for each LED. Experiments using multiple LEDs were conducted to evaluate the signal reception and positioning performance of the system. We found that multiple LEDs modulated at frequencies of over 70 Hz could be correctly identified from the received signal pattern. The 90th-percentile 2D positioning errors using low frequency signals (3.951-7.902 Hz) were less than 0.21 meter for a room illuminated by four LEDs arranged in a 1-m square on the ceiling at 2.22 meters height, where the smartphone was placed parallel on the floor from 1.4 meters height. Those using high frequency signals (111.619-114.582 Hz) in the same room setting showed 50th-percentile 2D position errors of less than 0.44 meter. The position calculation was offline and not implemented on real time. Potential applications and limitations of the proposed method are discussed.

Indoor localization based on the time-of-arrival (TOA) measurements of acoustic signals has advantages of low cost, high accuracy and no electromagnetic interference compared with other location technologies such as Bluetooth and Wi-Fi. However, conventional TOA estimation approaches based on peak extraction or fixed thresholds have difficultly maintaining high ranging accuracy and robustness in reverberant indoor enclosed environments. To address this situation, this paper presents an improved TOA estimation method for acoustic ranging in a reverberant environment that is composed of two processes. One is an acoustic reverberant cancellation technique based on the signal power spectra, and the other is a first-extremum-based match filter. To verify the performance of the improved TOA estimation method, indoor experiments were conducted in an enclosed noisy and reverberant underground parking garage. The experimental results demonstrate that the proposed algorithm is superior to a traditional quadratic cross-correlation and match filter in terms of estimation accuracy and robustness.

A double electrical excitation synchronous generator (DEESG) with an embedded brushless exciter is proposed to achieve brushless excitation for a brush excitation electrical excitation synchronous generator (EESG). A set of extra stator excitation windings is placed in the stator slots with armature coils to generate a static magnetic field. There are two sets of windings on the rotor: pulsating excitation winding (Wp) and main excitation winding (WF). The winding direction of the coils of Wp and WF on the same rotor-pole-body is the same. The AC voltage of Wp which is induced by static magnetic field provides dc excitation current for WF by diodes. Both currents in the coils of the Wp and WF generate the rotor excitation flux which induces voltage in the armature coils. In this study, the operating principle is analyzed theoretically. The no-load and load characteristics are studied using Maxwell. The influence of the novel winding structure on the output voltage when the load varies is also analyzed. The voltage regulation rate of DEESG is reduced because the rotor excitation currents can be increased with armature current. A 1.5 kVA prototype is fabricated for experiment. The measured results agree well with the theoretical and FE-predicted results.

Bearing‐only tracking of an underwater uncooperative target is essential to defend the sea territory. Considering the influences by uncertain underwater environment, the purpose of this work is to estimate 2‐D locations and velocities of an interested underwater target for non‐Gaussian environment. In this work, a fast particle filter (FPF) based on the traditional particle filter (PF) with novel jet transport (JT) technique is proposed to deal with this problem. Aiming to overcome the heavy computation burden of the traditional PF that limits most of its practical applications, the JT technique can dramatically reduce the computation time and complexity in the particle evolution process, which contributes huge computational complexities to the traditional PF. Then, the proposed FPF is tested through simulations in the 2‐D underwater uncooperative target tracking scenario. Finally, the Monte Carlo simulation results demonstrate that the proposed FPF can track the underwater uncooperative target with the similar accuracies as the traditional PF but only occupies less than 20% of the computational resources.

The influence of static eccentricity (SE) and dynamic eccentricity (DE) on the electromagnetic forces in internal- and external-rotor permanent magnet synchronous motors (PMSMs) is investigated in this paper. Firstly, the analytical model of the electromagnetic force is derived. By introducing the eccentricity coefficient, the influence of eccentricity on the electromagnetic force is then analyzed. The results show that SE change the spatial component of the electromagnetic force in internal-rotor motors while the frequency remains unchanged. While for the external-rotor motors, both the spatial order and frequency of electromagnetic force are affected by SE. Contrary to SE, DE introduces additional spatial components and sideband frequency harmonics to the electromagnetic force of internal-rotor motors. For external-rotor motors, only the spatial order is changed. In addition, axial-flux PMSMs suffer from extra unbalanced bending moment (UBM), which is a unique feature that differs from traditional radial-flux PMSMs. The expression of UBM caused by eccentricity is further derived. Finally, the theoretical analysis is validated by the simulation and test results respectively. This study will benefit the researchers and designers in terms of source identification and reduction of acoustic noise in PMSMs.

An elevation and azimuth direction-finding (DF) method is presented by introducing the pattern reconfigurable antenna (PRA) into a two-element array. An equivalent multi-dimensional array is built by the two-element PRA array with switchable beams of same or opposited directions. With the introduction of same-direction and opposite-direction modes of PRAs, the elevation and azimuth angles are estimated by the methods of time modulated array (TMA) and amplitude comparison, respectively. Meanwhile, a 2-D look-up table is built to correct the coning-error effect of the amplitude comparison. Compared with the conventional 2-D DF method with two orthogonal linear arrays, only a single linear array with not less than two elements is needed in the proposed method. Hence, it has the advantages of simple structure, compact size, and low cost. Simulated results are provided to verify the proposed 2-D DF method, and an S-band two-element PRA array is constructed to demonstrate its experimentally feasibility.

This paper presents a design of a compact wideband filtering dipole antenna with an omnidirectional radiation pattern. We analyze the radiation of three kinds of half-wavelength dipoles (strip, U-shaped strip and folded strip). It is found that these three diploes produce omnidirectional radiation patterns when they work on half-wavelength mode. In the proposed design, we make these three dipoles couple with each other to achieve wide bandwidth. In addition, both electric and magnetic coupling are observed at the lower band and the upper band, respectively. Therefore, two radiation nulls can be achieved without any extra circuit, which makes the proposed antenna filtering property and compact. A porotype is fabricated and measured to verified our idea. The results show that the proposed antenna has a 10-dB bandwidth of 42.51%, an in-band gain of ~2.4 dBi and an out-of-band radiation suppression more than 10 dB with a total size of 0.4λ0 × 0.06λ0. The above advantages of wide bandwidth, filtering property, small size and easy fabrication make the proposed antenna have potential applications on various wireless communication systems.

This paper introduces a design and analysis of a four directional radiation pattern antenna operating at 5.1 GHz. The proposed antenna consists of four center-fed copper arms placed over a substrate of relative permittivity er = 2.2. The substrate is backed with copper ground sheet. The design of this antenna is then modified to be frequency reconfigurable antenna by placing transformer oil (liquid which is operated at high frequency) within a container between the substrate and the ground. The modified antenna can be operated at different frequency ranges from 5.21 GHz to 6.56 GHz by varying the oil height in the container. Four PIN diodes are then added between the antenna’s four arms and the feeding point in order to add beam reconfigurability feature to the modified antenna. Finally, multiple reconfigurable antennas are obtained to radiate in different directions at different operating frequencies with different gain and HPBW values.

Different from the induced electromotive force (EMF) in armature winding, the induced EMF in excitation winding is detrimental to the performance of wound field synchronous machines by causing unstable excitation field and thus extra torque pulsation and losses. Moreover, it also imposes challenges to machine control, particularly for high-speed operation. This article investigates the induced EMF in the excitation winding of 3-phase non-overlapped stator wound field synchronous machines (SWFSMs). It has revealed that the amplitude of the excitation winding induced EMF is largely dependent on the slot-pole combination. Therefore, with suitable slot-pole combinations, the induced EMF issue will be significantly alleviated by eliminating low-order induced EMF harmonics. Although the excitation winding induced EMF can also be reduced by passive techniques, e.g., optimization and shaping of rotor pole arc, the average torque will be greatly degraded as well. Finally, the finite element predictions are validated by measurements on two prototyped non-overlapped SWFSMs.

The electromagnetic vibration and noise in motors is mainly induced by electromagnetic forces and magnetostrictive force. The low-frequency force waves have a great influence on the deformation of the motor stator core due to resonance. In this paper, a 2-D electromagnetic-mechanical coupling transient model was built based on the quadratic magnetic domain rotation model, considering the magnetostrictive characteristics of silicon steel sheet and the magnetoelastic coupling of materials. Through numerical simulation calculation and analysis, it was found that low-frequency force waves appeared in the motor stator, and the large amplitudes happened on the single and twice power frequency. The actual experimental measurements were designed in the rotating motor and the transformer to verify this phenomenon. It is concluded that the rotating field or the magnetic path distortion leads to the large amplitude at single-power frequency or rotating field frequency on the electrical equipment.

A combined computational and experimental study of flat radome materials for their use with high-power horn antennas operating over 18-45 GHz range is performed. The impact of a monolithic, thin-wall radome on antenna performance in the thermal, mechanical, and electromagnetic domains is considered. The structure must thermally handle high continuous wave power as well as mechanically withstand the impact of pressurization while preserving the electrical performance of a radome-less configuration. A simple test set for measuring radome deflection under high pressure is also discussed. Studies with available materials are conducted and it is found that the 76 μm thick Teflon coated fiberglass has the best performance balance in all domains. Other non-porous materials with comparable electrical and mechanical parameters will have similar behavior.

Numerical studies were performed to investigate the mechanism and potential of several active rotors for reducing low-frequency in-plane thickness noise generated by rotating blades. A numerical method coupling the blade element theory, prescribed wake model and Fowcs Williams-Hawkings (FW-H) equation was established for rotor noise prediction. It is indicated that the excitation force on the blade tip can generate anti-noise that to partly cancel the in-plane thickness noise with an appropriate actuation law. Results from the phase, frequency and amplitude sweeps show that the excitation force direction and actuation law are the crucial factors affecting the noise reduction, which determine the noise reduction area in the elevation and azimuth directions, respectively. The active trailing-flap rotor can generate the in-plane excitation force, but because of large lift-drag ratio the anti-noise is mainly from the vertical lift, which is caused by flap deflection similar to a variable camber airfoil. For the harmonic control rotor and active twist rotor, the excitation force is also attributed to the vertical blade lift. The vertical force can reduce the noise near the rotor plane, it will also cause the noise increase in most other areas. Finally, two new active rotors were proposed to generate the in-plane chordwise and spanwise excitation force. With the modified actuation law, the noise in most areas around the rotor was reduced, which improved the acoustic characteristics of rotor significantly.

In this letter, an ultra-wideband (UWB) antipodal tapered slot antenna with reflectionless notched band is proposed and investigated. The proposed antenna uses an integrated absorptive bandstop filter (ABSF), consisting of two quarter-wavelength open-circuit stubs and a 50 resistor, to form a reflectionless notched band. Consequently, the input energy at the notched frequency is absorbed by the resistor rather than reflected. An antenna prototype is designed and fabricated to validate the design. Both simulated and measured results present that the realized gain drops over 40 dB at 5.5 GHz, and the reflection coefficient is below -10 dB from 3.1 to 10.6 GHz. Besides, a low ringing level of -23.4 dB of the measured reception pulse shows a good time-domain performance. Therefore, the proposed antenna could be applied in UWB short-pulse system to inhibit the 5-GHz WLAN interference.

Transcranial ultrasound therapy has become a non-invasive method for treating neurological and psychiatric disorders, and studies have further demonstrated that multi-target transcranial ultrasound therapy is a better solution. At present, multi-target transcranial ultrasound therapy in small animals can only be achieved by the multi-transducer or phased array. However, multiple transducers may cause spatial interference, and the phased array system is complicated, expensive, and especially unsuitable for small animals. This study is the first to design and fabricate a miniature acoustic holography lens for multi-target transcranial ultrasound therapy in rats. The acoustic holographic lens, working at a frequency of 1.0 MHz, with a size of 10.08 mm × 10.08 mm and a pixel resolution of 0.72 mm, was designed, optimized, and fabricated. The dual-focus transcranial ultrasound generated based on the lens was measured; the full width at half maximum (FWHM) of the focal spots in y-direction were 2.15 and 2.27 mm, respectively, and in z-direction were 2.3 and 2.36 mm, respectively. The focal length was 5.4 mm, and the distance between the two focuses was 5.6 mm, close to the desired values of 5.4 mm and 6.0 mm, respectively. Finally, the multiple-target blood-brain barrier opening in rats' bilateral secondary visual cortex (mediolateral area, V2ML) was demonstrated using the transcranial ultrasound therapy system based on the lens. These results demonstrate the good performance of the multi-target transcranial ultrasound therapy system for small animals, including high spatial resolution, small size, and low cost.

We present a semianalytical method to obtain perfect transmission across abrupt H-plane bends in single-mode rectangular waveguides using a single passive polarizable element (scatterer). The underlying analysis and synthesis schemes are inspired by the rapidly-growing research on metagratings, typically used to manipulate wave trajectories in free-space. These sparse configurations of subwavelength polarizable particles (meta-atoms) are designed by careful tailoring of inter-element near-field and far-field interactions, relying on analytical models to resolve the required meta-atom distribution and geometry to facilitate a desired interference pattern when excited by the incident wave. Utilizing these metagrating design concepts, we develop a modal formalism for obtaining a collection of locations inside the bend junction, in which a passive scatterer may be placed to zero out the return loss. Subsequently, we propose two different shapes for the scatterer and discuss, for each of them, the ways in which their geometrical characteristics may be retrieved. This versatile and efficient methodology, verified via full-wave simulations, can be utilized to eliminate reflection loss in diverse bend configurations, often found in complex wave-guiding systems used for antenna feeding and power transmission. Moreover, these results demonstrate the usefulness and potential of metagrating design concepts for various applications, beyond free-space beam manipulation., Comment: 16 pages, 9 figures

A novel leaky-wave antenna (LWA) array capable of bilateral beamforming is investigated for applications in indoor and short-distance mobile communication. The antenna array is designed on a double-layer substrate-integrated waveguide (SIW) with a multiport feeding network. The upper layer is a four-port SIW with a tapered open stopband suppression structure and two tapered radiating slot arrays. By adjusting the periods and widths of slots, the two slot arrays radiate in different directions, and their radiation fields satisfy the cosecant-squared distribution. The lower layer is a single-port SIW power divider with an allocation ratio of 1:5 using a Z-shaped junction. There are transitions at both ends of the lower SIW for coupling energy up into the radiation layer. When feeding the upper layer from its two input ports individually, two dual broad-beams with beam directions of ± 25° and ± 45° can be generated, thus achieving amplitude-shaped dual-beam switching for smart beam switching antenna systems applied in short-distance mobile communication. When feeding the whole double-layer array through the input port of the power divider, the above two dual beams will be superposed together and form a cosecant-squared radiation pattern, which is suitable for uniform radio wave coverage along straight areas. The proposed array was fabricated and measured to validate its performance, and the results showed the efficiency of the design.

With the rapid development of vehicle information systems, liquid crystal displays (LCDs) have been widely used to enhance information experience. A linear vibration motor is usually placed behind the LCD to provide sufficient haptic feedback. A linear vibration motor with a large permanent magnet causes massive flux leakage around the display. As a result, it may cause unpredictable harm to people with implanted medical devices. Therefore, in this paper, a novel magnetic circuit design of a slim-width type linear vibration motor is introduced to reduce the static magnetic flux leakage. The haptic performance of the slim-width type linear vibration motor was analyzed using the electromagnetic-mechanical coupling method. Three types of experimental results were obtained to verify the analysis results. In conclusion, compared to the prototype motor, the slim-width type linear vibration motor proposed in this paper exhibits significant flux leakage reduction of 94.01% and 96.34% at the measuring positions. Furthermore, the slim-width type linear vibration motor exhibits an acceleration similar to that of the prototype motor.

In this letter, the cylindrical modal filtering is presented for digital holographic reconstruction (DHR) phase-less near-field (NF) measurement. The DHR phase-less NF facility can reconstruct the complex field of the antenna under test (AUT) by measuring only the intensity of the interference field on the AUT and reference antenna in one NF scanning plane. In addition to the retrieved AUT field, some unwanted items also exist in the reconstructed field. Hence, advanced filtering method is essential to extract the retrieved AUT field from the reconstructed field. In previous work, it is achieved by the back-projected (BP) filtering. In this work, the BP modal filtering is utilized to further improve the accuracy of the DHR phase-less NF measurement. To enhance the adequate modal separation between the desired and unwanted terms, the reconstructed field is firstly BP to the aperture plane, then represented with orthogonal cylindrical modes. Finally, the AUT field is extracted by twice modal filtering to remove the disturbances on two orthogonal directions. The simulation and experiment results indicate that compared with the results by the BP filtering, the accuracy of the DHR phase-less NF measurement has been improved 50% in valid angle by adopting the BP modal filtering.