Phase Shift Of Signal Research Articles

An Octagonal Acoustofluidic Device for Multimode Cell and Particle Patterning and Dynamical Manipulation

The combination of cell patterning and manipulation has become a popular field of research in the current clinical background and experimental environment, and the significance of patterning is helpful to study the relationship between cells. Acoustic-based manipulation methods have become the current mainstream method due to their excellent noncontact and biocompatibility, and high controllability. This work proposed an octagonal chamber enclosed by multiple piezoelectric (PZT) transducers to generate multiple modes of ultrasonic acoustic fields by configuring different excitation signals. Cells and particles can be manipulated at the fixed pressure nodes in the formed acoustic field, and diversified patterns, such as stripes, lattices, and hexagons, can be formed. Furthermore, based on the advantages of the multi-PZT configuration of the device, the pattern conversion and precise quantitative movement of cells and particles can be achieved by adjusting the phase parameters of the excitation signals. This work investigated the relationship between the combination of different PZT, the phase parameters of the excitation signal, and the pattern formation through numerical simulation and experiments. Also, the overall quantitative movements of the patterns were achieved by adjusting the phase shift of excitation signals of PZT transducers. The mathematical relationship between the relative movement offset and the wavelength was studied and verified. Finally, the device realized complex trajectory motion control of cells and particles by automatically and rapidly switching the working modes and phase parameters of the PZT transducers. As an open and low-cost device, this research can provide a new idea for cell patterning and position manipulation.

Application of phase-shifted full-bridge soft-switch technology in suspension chopper

Suspension chopper is a high-power electrical equipment which controls the suspension state of maglev train. Its performance directly determines the stability and safety of maglev train. However, the traditional suspension chopper has the problem of high voltage spikes of IGBT and load, which poses a threat to the safe operation of high-speed maglev train. In order to solve this problem, this paper designs a phase-shifted full-bridge suspension chopper, which only adds an auxiliary circuit and four parallel capacitors. The soft-switch is realized by using the phase-shifted control signals, so as to reduce the voltage spikes. Compared with other voltage spike suppression methods, the method has the advantages of good suppression of voltage spikes, simple circuit structure, less use of components, and insensitive to component parameters. The performance of the designed circuit is simulated by ANSYS Simplorer, and verified by experimental test platform. The simulation and experimental results show that the phase-shifted full-bridge suspension chopper can greatly reduce voltage spikes of the load and IGBT.

Intelligent Reflecting Surface Aided Secure Communication with Federated Learning

Applying federated learning into the covert communication can not only ensure the communication reliability, but also reduce the probability of enemy detection. The use of airspace resources is an effective way to achieve covert communication. However, most of the existing works on the airspace covert communication represented by MIMO need to adapt to the channel state and cannot improve the channel, resulting in the performance bottleneck of covert communication. The intelligent reflective surface (IRS) provides a new perspective for the covert communication by flexibly adjusting the reflection phase shift of the incident signal and intelligently configuring the wireless channel. However, the potential of IRS in the covert communication is far from being fully exploited. To solve this issue, this paper firstly performs a comprehensive literature review on the secure communication with the aid of federated learning, and then gives some challenges on the secure communication in poor channel state. In further, this paper provides some solutions to the challenges on the secure communication, where some results are provided to show the advantages. The research results have important theoretical and practical significance for forming a new research paradigm of airspace intelligent and controllable covert communication and promoting the application and popularization of covert communication in various fields of security.

Generation of a Fundamental/Doubled Frequency Phase-Coded Microwave Signal Based on Polarization Multiplexed Technology

Microwave photonic phase-shifting technology can be used to generate high-frequency, broadband, and tunable phase-coded microwave signals, which are helpful in solving the contradiction between the detection range and the range resolution in radar systems. A method for generating a reconfigurable carrier phase-coded signal of a fundamental or doubled carrier frequency, based on polarization multiplexed technology, is proposed and verified by the experiments in this paper. A dual-parallel dual-polarization Mach–Zehnder modulator (DP-DPMZM) and a polarization-dependent phase modulator (PD-PM) were used to load the carrier and the phase-shifting signal, respectively. By reasonably configuring the state of the RF switch and the bias voltages of the sub-DPMZM, the fundamental or doubled carrier frequency can be obtained through photoelectric conversion. The reconfigurable carrier frequency gives the system a wider work bandwidth range and can effectively reduce the frequency requirement for local oscillator (LO) signals. By adjusting the driving voltage, the broadband microwave signal can be phase-shifted within the range of 360°, and when the phase-shifted control signal is a multilevel amplitude signal, it can generate binary, quaternary, or other high-order phase-coded signals, which have high reconfigurable performance and potential application value in multifunctional radar systems. In addition, the scheme has wideband tunability, since no optical filter is involved. The proposed scheme was theoretically analyzed and experimentally verified. Binary, quaternary, and octal phase-coded signals, with fundamental and doubled frequencies centered at 8 GHz and 16 GHz, were successfully generated.

Passification-Based Robust Phase-Shift Control for Two-Rotor Vibration Machine

In this paper, the solution to the problem of robust control of the phase shift during rotation at a given speed of the unbalanced rotors for a two-rotor vibratory machine is presented. The solution to this problem is relevant for the development of vibration technologies (for example, a vibro-transportation of bulk materials). The proposed controller includes two proportional-integral (PI) rotor speed controllers with a cross-coupling, which receive signals with opposite signs from the phase shift controller. Unlike previous works, where a PI controller for phase shift control was also taken, including the adaptive controller with an implicit reference model (IRM), in the present paper, a relay-type signal controller with an integral component without a parametric adaptation is used. This approach allows, while maintaining robustness, to increase the operation speed and accuracy of the control process, avoiding at the same time the possible divergence of the tunable parameters due to the influence of noises and disturbances caused, among other things, by vibrations of the setup’s structural elements and measurement errors. For the control law design, the speed-gradient method was employed. For various types of reference phase-shift signals (constant, harmonic, chaotic), the results of extensive experimental studies performed on the mechatronic vibration setup and the simulations accomplished based on the results of identifying the parameters of the stand drive model are presented in the paper. The obtained results confirm the efficiency and robustness of the proposed algorithm and allow one to reveal the system performance properties.

A low profile, dual‐polarised, high gain patch antenna

AbstractA low‐profile patch antenna with dual‐polarisation and high gain is proposed in this study. It contains a primary radiator, a secondary radiator, and a planar feed network. The primary and secondary radiators are square patches placed 5 mm from each other. Two planar feed networks are electrically connected with the primary radiator through the stepped impedance transformer, providing equal amplitude and 180° phase shift signals. These two feed networks are settled in different layers to weaken the coupling effect. The resonance generated by the primary radiator is merged with the one by the secondary radiator, covering the 3.3–3.6 GHz band. Benefiting from the differential feed method, antenna specifications such as port isolation and cross‐polarisation discrimination (XPD) are ideal. Moreover, as the primary radiator is fed by planar microstrip, the overall height can be reduced, and the gain can be enhanced. Finally, a 2 × 2 subarray is investigated. Desirable results show that the proposed antenna is suitable for application in Massive Multiple Input and Multiple Output (MIMO) systems.

Investigation of Phase Shifts Using AUC Diagrams: Application to Differential Diagnosis of Parkinson's Disease and Essential Tremor.

This study was motivated by the well-known problem of the differential diagnosis of Parkinson's disease and essential tremor using the phase shift between the tremor signals in the antagonist muscles of patients. Different phase shifts are typical for different diseases; however, it remains unclear how this parameter can be used for clinical diagnosis. Neurophysiological papers have reported different estimations of the accuracy of this parameter, which varies from insufficient to 100%. To address this issue, we developed special types of area under the ROC curve (AUC) diagrams and used them to analyze the phase shift. Different phase estimations, including the Hilbert instantaneous phase and the cross-wavelet spectrum mean phase, were applied. The results of the investigation of the clinical data revealed several regularities with opposite directions in the phase shift of the electromyographic signals in patients with Parkinson's disease and essential tremor. The detected regularities provide insights into the contradictory results reported in the literature. Moreover, the developed AUC diagrams show the potential for the investigation of neurodegenerative diseases related to the hyperkinetic movements of the extremities and the creation of high-accuracy methods of clinical diagnosis.

Dispersed fringe cophasing method based on principal component analysis.

With the success of the Webb telescope, dispersed fringe sensing (DFS), with the significant merit of a large capture range, is proving to be a promising cophasing approach for a large-aperture segmented telescope. In this Letter, a novel, to the best of our knowledge, piston error extraction method based on principal component analysis (PCA) technology is proposed. In this method, all the one-dimension intensity distributions along the dispersion axis for different interference positions are regarded as a set of random phase-shifted interference signals. PCA technology is utilized to obtain its corresponding continuous principal phase and the piston error could be directly estimated proportionally from the slope of the phase-wavenumber line. This method avoids nonlinear operations, similar to Shi's traditional framework; no active move is needed for fine cophasing, and the method is also free of characteristic constant calibration in sidelobe peak displacement- and slope-based methods. Preliminary simulations of the method's coarse-then-fine cophasing ability with high accuracy are presented here to show its potential.

Adaptive lens for foveal vision, imaging, and projection over large clear apertures.

We report an electrically tunable liquid crystal device that enables the generation of lenses the diameters of which may be dynamically changed from sub-millimeter to multiple millimeter sizes. These lenses can be created in different regions of interest over very large (above 50 mm) optical clear apertures. The approach is based on the activation of periodically spaced contacts on a single serpentine-shaped electrode with phase-shifted electrical signals. It enables a highly reconfigurable operation of locally created lenses with variable position, diameter, optical power (OP) and aberrations. The preliminary demonstration of the capabilities of the proposed device is presented here by creating a local lens, moving its center over an area of 25 mm x 25 mm, gradually changing its diameter from 1.3 mm to 4.55 mm as well as by tuning its OP value from zero up to, respectively, ≈ 40 and ≈3.5 diopters. Typical driving signals are at the order of 3.5 V. We think that such lenses can be used for ophthalmic or augmented reality applications as well as in microscopy, adaptive panoramic cameras with large distorted field of view, dynamic projection, etc.

Vortex arrangement in an ultrathin superconducting bilayer disc

A direct current superconducting quantum interference device (SQUID) fixed on a recently developed superconducting bilayer disc is effective for studying fractional magnetic quantum and fractional vortices. However, such devices cannot magnetically image fractional vortices. To overcome this limitation, we compared the bilayer SQUID signal with and without a pinhole to experimentally investigate the vortex arrangement. We measured the amount of flux passing through the SQUID ring via the SQUID signal phase shift, which reflected the vortex locations. We measured the voltages of a series of 100 SQUIDs in which the bilayer discs were present under each SQUID. When we applied a constant bias current of 5.5 μA and swept the external magnetic field, a voltage appeared when the amount of magnetic flux passing through the SQUID ring became close to half of the flux quantum. A sharp voltage peak was obtained for the bilayers with a pinhole, whereas these peaks were broader for the bilayers without a pinhole. We evaluated the amount of the flux originating from the vortices trapped in the bilayer discs and estimated the vortex locations from the peak position. When the amount of flux originating from the trapped vortices increased, the bilayer discs without a pinhole exhibited reduced amounts of flux originating from the trapped vortices by approximately 15% compared to the bilayer discs with a pinhole. When no pinhole was present, the vortex locations varied inside the SQUID ring. The results indicated that the vortices were located at the same position for all 100 bilayer discs with a pinhole; therefore, we concluded that the pinholes must trap the vortices.

RoSense: Refining LOS Signal Phase for Robust RFID Sensing via Spinning Antenna

RFID sensing leveraging backscatter signal features (e.g., phase shift) from tags has gained increasing popularity in numerous applications but also suffers from negative impacts of environmental multipaths. Past works to address it rely on extra customized devices, labor-intensive offline training, or frequency channel hopping, all of which are non-ubiquitous or ineffective for real-life adoption. This article presents RoSense, a universal method to alleviate multipath reflections’ impacts by spinning the reader antenna, thus enabling more robust RFID sensing. Besides, RoSense requires no RF devices or offline training and operates in a nonintrusive manner. The key insight of RoSense is to exploit two properties of line-of-sight (LOS) signal when spinning the antenna, i.e., the linearity of phase changes and stability of received signal strength to attenuate the nonlinear and nonmonotonic effect of multipath signals and refine the phase shift of LOS signal. We have implemented a prototype of RoSense with COTS devices and studied two cases for evaluation: 1) material identification and 2) object localization. Experimental results show that RoSense can improve the material identification accuracy by up to 16.22% and reduce the mean localization error by up to 39.93%, greatly outperforming the state-of-the-art solutions.

An Advanced Switching Harmonic Cancellation Method for a Dual-Generator Power System in More-Electric Aircraft

Dual-generator power systems have attracted increased attention in recent years as it can significantly reduce the fuel assumption of aircraft engines allowing power transfer between different engine shafts. In such a system, two generators supply a common dc bus together. A dc-bus capacitor is required to filter switching harmonics to ensure that the dc-bus voltage satisfies the MIL-STD-704F standard. Due to the high current rating, this capacitor is normally bulky and heavy. This article aims to introduce a switching harmonic cancellation method, which can effectively reduce harmonics at the dc bus. This, in return, will extend the lifetime and reduce the weight of the dc-bus capacitor. With the assumption that power converters connected to the dc bus are modulated with the commonly used space vector pulsewidth modulation (SVPWM) technique, a simplified mathematical model to estimate both first and second switching harmonics is developed. Based on the proposed models, an advanced method of switching harmonic cancellation scheme is proposed through an adaptive phase shift of carrier signals for different power outputs of converters. Both simulation and experimental results are used to validate the proposed model and the suppression method.

Development of MEMS Airflow Volumetric Flow Sensing System with Single Piezoelectric Micromachined Ultrasonic Transducer (PMUT) Array

Compared to conventional ultrasonic flowmeters using multiple transducers, this paper reports, for the first time, an airflow volumetric flowmeter using a signal PMUT array to measure the flow rate in a rectangular pipe. The PMUT around 200 kHz is selected to fit the system requirements. All PMUT elements on this single array are then electrically grouped into transmitter and receiver. In order to minimize the crosstalk signal between transmitter and receiver, a phase shift signal is applied at the transmitter to reduce the amplitude of the crosstalk signal by 87.8%, hence, the resultant high sensing resolution. Based on the analog signal extracted from the single PMUT array, a complete flow sensing system is built by using the cross-correlation method and cosine interpolation, whereby the change in flow rate is reflected by the time of flight difference (dTof) recorded at the receiver. Meanwhile, the acoustic path self-calibration is realized by using multiple echoes. Compared with the previously reported MEMS flowmeters with dual or multiple PMUT devices, this paper proposes a single PMUT array flow sensing system, which is able to measure the flow rate changes up to 4 m3/h. With the implementation of a single device, the problem of ultrasound device/reflector misalignment during system setup is completely eradicated.

Corneal elastic property investigated by terahertz technology

Terahertz (THz) spectroscopy technique has been applied in ex vivo biomechanical properties analysis of human corneas. Upon the application of light pressure on the cornea, the photo elastic birefringent effect, anisotropic deformation, thickness changes and hydration levels will contribute to the sudden phase changes of terahertz time domain signal. The shelf lifetime study shows that the phase shift is reduced and cornea loose the biomechanical properties with the increase of hydration level. Mechanical behaviors have been further studied based on the “fresh” cut corneas with the similar hydration levels. THz signal was collected by focusing inside of the cornea to avoid the phase shift due to light stress caused movement of the corneal surface. By this way, the amount of THz signal refractive index variation is correlated to the elastic property of the corneas. The correlation between the THz signal phase shift and refractive index shift due to the corneal strain can be used to derive the elastic Young’s modulus. Our results demonstrated the THz spectroscopy, as a non-contact and non-invasive detection method, could be potential for understanding the mechanism of corneal deformation under the action of intraocular pressure in the physiological environment in future.

Thickness-Independent Measurement of Grain Moisture Content by Attenuation and Corrected Phase Shift of Microwave Signals at Multiple Optimized Frequencies

Inadequate drying and overdrying of grains due to the absence of timely and reliable information on moisture content (MC) aggravates grain postharvest loss. In this study, we investigate the real-time acquisition of MC using microwave free-space transmission measurements. A multifrequency swept signal is used to acquire the attenuation and phase-shift spectrum (2.00–10.00 GHz) of the paddy samples (9.553%–29.633% w.b.) for six thicknesses (1–6 cm). Based on the four rules that are followed in the phase-shift measurement, a phase-shift correction algorithm without any restrictions on the sample thickness is proposed to solve the phase-shift ambiguity that occurs when the sample thickness exceeds the wavelength. To choose the most effective frequencies, 17 candidate frequency subsets are generated by the recursive feature elimination algorithm, and the optimal frequency set, containing eight individual frequencies, is selected by using the Friedman and Nemenyi post hoc tests. The sample thickness and microwave characteristics are used as the input variables to establish the prediction models to achieve a thickness-independent measurement of the MC, and the support vector machine model yielded the best performance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R^2$</tex-math></inline-formula> = 0.992, RMSE = 0.555%, and MAE = 0.398%). The results of this study should encourage future research on the real-time acquisition of reliable MC information in food processing and agriculture-related industries.

Novel Microwave Frequency-Locked-Loop-Based Sensor for Complex Permittivity Measurement of Liquid Solutions

In this article, a new microwave frequency-locked-loop (FLL)-based sensor is proposed for complex permittivity measurement of liquid solutions. An interdigitated electrode split-ring resonator (IDESRR) is embedded in the FLL and used as a sensing device to distribute electric field in the near-field region and sense the permittivities of the liquid solutions with different concentrations. When the test liquid is placed on the IDESRR, a deviation will be introduced to the resonance frequency based on the perturbation theory. This frequency deviation accompanies a corresponding phase shift in the FLL operating frequency. The phase-shifted signal then leads the FLL to output a frequency-modulated (FM) signal, whose frequency deviation depends on the concentration level of the test liquid. The quadrature frequency discriminator is used to demodulate this FM signal and transfer it into dc voltages, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{I}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{Q}$ </tex-math></inline-formula> . Reference liquids with known permittivities are used to calibrate the proposed sensor and relate the measured voltages to the dielectric constant and loss tangent. In this article, the water–ethanol mixtures and water–glucose solutions are used as the test liquids to evaluate the measurement performance of the proposed FLL-based permittivity sensor. The measured results obtained using the proposed sensor agree very well with those obtained using the commercial dielectric probe. Moreover, since the proposed permittivity sensor has the benefits of a simple system architecture, high sensitivity, and not requiring a vector network analyzer (VNA), it has great potential to be developed as a new type of biomedical sample sensor.

Single-beam comagnetometer using elliptically polarized light for dual-axis rotation measurement.

We have developed a single-beam spin-exchange relaxation-free comagnetometer using elliptically polarized light for dual-axis rotation measurement. The light beam propagating through the glass cell is simultaneously used for optical pumping and signal extraction. Combined with transverse magnetic field modulation, the rotation information can be collected through a balanced polarimeter module and a lock-in amplifier. Also, we propose a decoupling method by adjusting the phase shift of the reference signal, allowing the device to realize biaxial signal decoupling while still maintaining its self-compensation state. Compared to those without decoupling, our method improves the performance of our device in its signal-to-noise ratio and rotation sensitivity. The single-beam comagnetometer scheme and the decoupling method have a positive impact on the development of miniaturized atomic sensors for high-precision inertial measurement.

Quadrature phase detection based on a laser self-mixing interferometer with a wedge for displacement measurement

We report a novel and simple method to generate a pair of self-mixing signals with quadrature phase difference in He-Ne laser by introducing a wedge into the external cavity. A wedge phase-shift laser self-mixing effect theory is developed to explain the phase-shift phenomenon, and the relationship between the phase difference and the distance from the center of the iris diaphragm to the center of the spot is given. Then a simple and effective wedge-quadrature laser self-mixing interferometer is established for displacement measurement by the quadrature phase detection method. Experimental results show that the max error is 182 nm for a target displacement of 20 μm. This structure provides a useful exploration for phase-shift signal generation and simplifies the self-mixing signal demodulation process with only a single four-quadrant inverse tangent operation, which has potential application in real-time displacement measurement.

Towards numerical simulation of high part load pulsations in Francis turbines

One of the most interesting operating points of Francis turbines is the high part load point, which is characterized by synchronous pressure pulsations of large amplitude. Physical mechanisms of these pulsations are not well understood. Experimental observations show that the frequency of the pulsations is 1.5 to 4 times higher than the runner rotation frequency and there exists a 180 degree phase shift of pressure signal measured in the spiral casing and in the draft tube. Numerical modeling this operating point is challenging as it has to account several complex phenomena: cavitation, rotating vortex rope and interaction of the turbine flow with the whole water system of the test rig. In the present paper we carried out a series of 1D-3D calculations of a model turbine in an attempt to simulate the high part load pulsations. 1D hydro-acoustic equations were used for the upstream waterways, while 3D Reynolds averaged Navier-Stokes model of two-phase mixture was used for the turbine. Although the main factors were taken into account, these computations were not able to capture the high part load pulsations. Namely, the frequency and amplitude of the pressure pulsations were significantly lower than those in the experiment, and there was no phase shift in turbine domain. In order to investigate the shortcomings of the present model, we considered a problem of propagation of disturbances in two-phase “liquid-gas” flows. Several 2D test cases were numerically investigated using both incompressible and compressible gaseous phase model. It was shown that in the absence of phase transfer the compressible model correctly represents the speed of sound in both homogeneous and stratified flow regimes. From the other hand, in case of phase transfer the model damps out propagation of pressure disturbances in upstream direction. This behavior explains the failure of the present 1D-3D model to correctly describe the acoustic properties of the two-phase flow in the draft tube, playing a crucial role in the development of high part load pulsations.

Dual-Circuit-Based Test Bench Design for HVDC Circuit Breaker Verification

High-voltage direct current (HVDC) circuit breaker development and deployment strongly depend on the testing process, which ensures that the HVDC circuit breakers will satisfy design requirements. This article presents an HVDC circuit breaker test bench circuit configuration that can provide controllable large output currents to simulate different fault conditions for the current breaking test and high output voltage for the dielectric withstand test. The current breaking test circuit is based on multiple cascaded power converters connected in parallel to provide the necessary output current capability. Each cascaded power converter is composed of multiple cells that are operated by a phase-shifted pulsewidth-modulated signal for greater controllability and higher quality of the output waveform. The dielectric withstand test circuit is a simple high-voltage source with a low power rating that can also be used to charge the test bench and the internal circuitry of the circuit breaker that is to be tested. The proposed test bench ensures that fault conditions can be replicated accurately and offers greater flexibility by being able to test mechanical, semiconductor-based, or hybrid HVDC circuit breakers with different current and voltage ratings on the same hardware without any changes. The idea and the operating principle of the proposed test bench are verified experimentally on a downscaled system that consists of three cascaded power converters connected in parallel with three cells per cascaded power converter and with a total equivalent switching frequency of 92.5 kHz.