Constant Phase Shift Research Articles

Integrated microwave photonic phase shifter with full tunable phase shifting range (> 360°) and RF power equalization.

We report a novel microwave photonic phase and amplitude control structure based on a single microring resonator with a tunable Mach Zehnder interferometer reflective loop, which enables the realization of a continuously tunable microwave photonic phase shifter with enhanced phase tuning range while simultaneously compensating for the RF power variations. The complimentary tuning of the phase and amplitude presents a simplistic approach to resolve the inherent trade-off between maintaining a full RF phase shift while eliminating large RF power variations. Detailed simulations have been carried out to analyze the performance of the new structure as a microwave photonic phase shifter, where the reflective nature of the proposed configuration shows an effective doubling of the phase range while the amplitude compensation module provides a parallel control to potentially reduce the RF amplitude variations to virtually zero. The phase range enhancement, which is first verified experimentally with a passive only chip, demonstrates the capability to achieve a continuously tunable RF phase shift of 0-510° with an RF amplitude variation of 9 dB. Meanwhile, the amplitude compensation scheme is incorporated onto an active chip with a continuously tunable RF phase shift of 0-150°, where the RF power variations is shown to be reduced by 5 dB while maintaining a constant RF phase shift.

Sub-3 Å apoferritin structure determined with full range of phase shifts using a single position of volta phase plate

Volta Phase Plate (VPP) has become an invaluable tool for cryo-EM structural determination of small protein complexes by increasing image contrast. Currently, the standard protocol of VPP usage periodically changes the VPP position to a fresh spot during data collection. Such a protocol was to target the phase shifts to a relatively narrow range (around 90°) based on the observations of increased phase shifts and image blur associated with more images taken with a single VPP position. Here, we report a 2.87 Å resolution structure of apoferritin reconstructed from a dataset collected using only a single position of VPP. The reconstruction resolution and map density features are nearly identical to the reconstruction from the control dataset collected with periodic change of VPP positions. Further experiments have verified that similar results, including a 2.5 Å resolution structure, could be obtained with a full range of phase shifts, different spots of variable phase shift increasing rates, and at different ages of the VPP post-installation. Furthermore, we have found that the phase shifts at low resolutions, probably related to the finite size of the Volta spots, could not be correctly modeled by current CTF model using a constant phase shift at all frequencies. In dataset III, severe beam tilt issue was identified but could be computationally corrected with iterative refinements. The observations in this study may provide new insights into further improvement of both the efficiency and robustness of VPP, and to help turn VPP into a plug-and-play device for high-resolution cryo-EM.

Fast Robust Dejitter and Interslice Discontinuity Removal in MRI Phase Acquisitions: Application to Magnetic Resonance Elastography.

MRI phase contrast imaging methods that assemble slice-wise acquisitions into volumes can contain interslice phase discontinuities (IPDs) over the course of the scan from sources, including unavoidable physiological activity. In magnetic resonance elastography (MRE), this can alter wavelength and tissue stiffness estimates, invalidating the analysis. We first model this behavior as jitter along the z-axis of the phase of 3D complex-valued wave volumes. A two-step image processing pipeline is then proposed that removes IPDs. First, constant slicewise phase shift is removed with a novel, non-convex dejittering algorithm. Then, regional physiological noise artifacts are removed with novel filtering of 3D wavelet coefficients. Calibration of two pipeline coefficients, the dejitter parameter α and the wavelet band high-pass coefficient ωc , was first performed on a finite-element method brain phantom. A comparative investigation was then performed, on a cohort of 48 brain acquisitions, of four approaches to IPDs: 1) the proposed method; 2) a "control" condition of neglect of IPDs; 3) an anisotropic wavelet-based method; and 4) a method of in-plane (2D) processing. The present method showed medians of [Formula: see text] Pa for a multifrequency wave inversion centered at 40 Hz which was within 6% of methods 3) and 4), while neglect produced [Formula: see text] estimates a mean of 17% lower. The proposed method reduced the value range of the cohort against methods 3) and 4) by 29% and 31%, respectively. Such reduction in variance enhances the ability of brain MRE to predict subtler physiological changes. Our theoretical approach further enables more powerful applications of fundamental findings in noise and denoising to MRE.

Dual-Band Differential Phase Shifter Using Phase- Slope Alignment on Coupled Resonators

In this letter, we propose a new class of phase shifter which can provide different constant phase shifts at two bands for the first time. The prescribed phase shifts $\Delta \Phi _{\mathbf {1}}({f}_{\mathbf {1}})$ and $\Delta \Phi _{\mathbf {2}}({f}_{\mathbf {2}})$ and frequency ratio ( ${n} ={f}_{\mathbf {2}}/{f}_{\mathbf {1}}$ ) of the two bands can be obtained by the developed dual-band phase-shifting line on C-section. Meanwhile, the dual-band phase-slope alignment is first realized by virtue of the two groups of coupled resonators, resulting to independently control the phase slopes at two separated bands as required. The closed-form equations and design charts are further given. For verification, a prototype dual-band phase shifter operating at 3.0 and 5.4 GHz ( $n = 1.8$ ) is designed, fabricated, and tested. The measured results show the proposed phase shifter exactly achieves prescribed constant phase shifts of 90° ± 2.3° over 2.76–3.31 GHz (18%) and 180° ± 2.7° over 4.97–5.80 GHz (15%). Both the simulation and measured results are recorded with good agreement.

Dielectric Steering of a 3-D Printed Microwave Slot Array

A steerable, three-dimensional printed, traveling-wave microwave slot array is presented. Inserted dielectric bars change the guide wavelength in the array, adding a constant phase shift between radiating slots. This in turn achieves a tilt angle of the main lobe away from boresight. The ability to adjust the direction of a beam radiated or received by a high-gain slot array with fixed physical mounting has a practical advantage compared to physically rotating the array: It minimizes the volume required for the mounted array. Mounting volume scales as W tan θ , where W is the array width and θ is the steering angle. The work presented here has W = 186.2 mm and θ = 8.5°, so the change in mounting volume thickness is 27.9 mm. This array is 11.6 mm thick, so the mounting volume is reduced by a factor of 3.4. Opening the center line of the back side of the array waveguides allowed the insertion of dielectric bars along the center of each waveguide. The described device was both simulated and built, and the experimental device achieved 8.5° of continuously adjustable beam steering with a reduction in realized gain of 2.1 dB.

High-color-purity transmissive colors with high angular tolerance based on metal/dielectric stacks

Abstract In this work, high-color-purity transmissive colors with high angular tolerance are proposed. The metal/dielectric film stacks, by means of induced transmission effect, are able to achieve ∼ 60% peak transmission and ∼ 60 nm transmission band, so as to cover a large color gamut. The filter presents good incident angle insensitivity up to 60 degrees, ascribed to the combined contribution of the constant total phase shift within the intermediate dielectric layer and the relatively high refractive index of the dielectric layers. And the matching of the optical admittances for metal/dielectric layers is responsible to the high transmission of the metal-based film stack. Moreover, the optical constants of silver film, affected by deposition technology have a great impact on the optical property of the color device including the bandwidth and peak transmission. And the thickness of the top dielectric layer as well as the metal/dielectric stack number can also alter the performance of the color filter.

Dynamic cerebral autoregulation estimates derived from near infrared spectroscopy and transcranial Doppler are similar after correction for transit time and blood flow and blood volume oscillations

We analysed mean arterial blood pressure, cerebral blood flow velocity, oxygenated haemoglobin and deoxygenated haemoglobin signals to estimate dynamic cerebral autoregulation. We compared macrovascular (mean arterial blood pressure-cerebral blood flow velocity) and microvascular (oxygenated haemoglobin-deoxygenated haemoglobin) dynamic cerebral autoregulation estimates during three different conditions: rest, mild hypocapnia and hypercapnia. Microvascular dynamic cerebral autoregulation estimates were created by introducing the constant time lag plus constant phase shift model, which enables correction for transit time, blood flow and blood volume oscillations (TT-BF/BV correction). After TT-BF/BV correction, a significant agreement between mean arterial blood pressure-cerebral blood flow velocity and oxygenated haemoglobin-deoxygenated haemoglobin phase differences in the low frequency band was found during rest (left: intraclass correlation=0.6, median phase difference 29.5° vs. 30.7°, right: intraclass correlation=0.56, median phase difference 32.6° vs. 39.8°) and mild hypocapnia (left: intraclass correlation=0.73, median phase difference 48.6° vs. 43.3°, right: intraclass correlation=0.70, median phase difference 52.1° vs. 61.8°). During hypercapnia, the mean transit time decreased and blood volume oscillations became much more prominent, except for very low frequencies. The transit time related to blood flow oscillations was remarkably stable during all conditions. We conclude that non-invasive microvascular dynamic cerebral autoregulation estimates are similar to macrovascular dynamic cerebral autoregulation estimates, after TT-BF/BV correction is applied. These findings may increase the feasibility of non-invasive continuous autoregulation monitoring and guided therapy in clinical situations.

Investigation of rotating mode behavior in BWR out-of-phase limit cycle oscillations – Part 1: Reduced order model

Previous neutronic/thermal-hydraulic (TH) coupled numerical simulations using full-core TRACE/PARCS and SIMULATE-3K BWR models have shown evidence of a specific “rotating mode” behavior (steady rotation of the symmetry line, i.e. constant phase shift of approximately 90° between the first two azimuthal modes) in out-of-phase limit cycle oscillations, regardless of initial conditions and even if the first two azimuthal modes have different natural frequencies. This suggests a nonlinear coupling between these modes; otherwise, the phase shift between these modes would change at a constant rate during the limit cycle. The goal of the present work is to gain further insights on the rotating mode behavior using a simplified mathematical model which contains all of the important physics for this application while providing sufficient flexibility and simplicity to allow for in-depth understanding of the underlying phenomena. This was accomplished using a multi-channel, multi-modal reduced-order model, using a modification of the fixed pressure drop boundary condition to simulate channel coupling via the inlet and outlet plena, in order to destabilize the out-of-phase mode over the in-phase mode. Examination of the time-dependent solution of the nonlinear system showed a clear preference for rotating mode behavior in the four-channel model under stand-alone TH conditions and for conditions with weak neutronic feedback. When neutronic feedback was strengthened (i.e., larger reactivity feedback coefficients), the side-to-side mode (stationary symmetry line) was favored instead. Additional analyses using higher-fidelity numerical modeling, as well as a physical explanation for the rotating behavior seen in both sets of analyses, will be provided in a companion paper (“Part 2”).

Investigation of rotating mode behavior in BWR out-of-phase limit cycle oscillations – Part 2: TRACE/PARCS model and physical explanation

Previous neutronic/thermal-hydraulic (TH) coupled numerical simulations using full-core TRACE/PARCS and SIMULATE-3K boiling water reactor (BWR) models have shown evidence of a specific “rotating mode” behavior (steady rotation of the symmetry line, i.e. constant phase shift of approximately 90° between the first two azimuthal modes) in BWR out-of-phase limit cycle oscillations, regardless of initial conditions and even if the first two azimuthal modes have different natural frequencies. This suggests a nonlinear coupling between these modes; otherwise, the phase shift between these modes would change at a constant rate during the limit cycle. The previous paper (“Part 1”) presented a series of results to examine this rotating behavior with a reduced-order model. The goal of the present study is to provide additional analyses of the predicted rotating mode behavior using higher-fidelity numerical modeling, as well as a physical explanation for why this mode is favored over side-to-side or other oscillatory behaviors from a TH perspective. Results are presented using TRACE and TRACE/PARCS for a small number of parallel channels, which confirmed that the conclusions developed from the reduced-order model remain applicable when applying a full two-fluid, six-equation, finite-volume modeling approach. From these results, a physical explanation has been put forth to explain why the rotating symmetry line behavior is preferred from a TH standpoint, demonstrating that predominantly out-of-phase unstable systems are most unstable when the variation in the total inlet flow rate is minimized (which minimizes the effective single-phase to two-phase pressure drop ratio) and that the rotating mode is the most successful in minimizing this total flow rate variation as compared with the side-to-side case or any other oscillation pattern. The conclusion is that the rotating mode will be favored for any out-of-phase unstable system of parallel channels with no neutronic feedback or relatively weak neutronic feedback. Previous analyses have indicated that systems with sufficiently strong neutronic coupling may favor the side-to-side oscillation mode over the rotating mode; this topic is left as a subject of future investigation.

Design and Analysis of CCII-Based Oscillator with Amplitude Stabilization Employing Optocouplers for Linear Voltage Control of the Output Frequency

This paper shows the topology design of a simple second-order oscillator based on two three-port current conveyors, two resistors, and two grounded capacitors, as well as its modification to a voltage-controlled oscillator (VCO). In comparison with many previous works, the following useful conceptual novelties and improvements were made in this study. Both resistors presented in the topology can be employed to tune of the oscillation frequency by the simultaneous driving of two optocouplers with resistive output stage. The current gain of the current conveyor ensures the control of the oscillation condition. The proposed solution offers advantages (in comparison with many standard so-called single-resistance-controllable types) of improved dependence of the frequency of oscillation (FO) on a driving force (extended tuning of the FO), constant ratio of amplitudes of generated waveforms when the FO is tuned, low complexity (taking into account auxiliary circuitry for optocouplers), and comfortable tuning of the FO by a single control voltage. The oscillator produces waveforms with tunable frequency having a constant 45-degree phase shift between them. The relative sensitivities of the proposed solution achieve typical values for these second-order systems (−0.5). Experimental verification confirmed the expected behavior in the operational band between 1 and 10 MHz tuned by a DC voltage from 1.7 to 5 V. This indicates a significant reduction of the driving force ratio (3:1 in our case) in comparison with standard tuning approaches required for a ratio of 10:1 for FO adjustment. Output amplitudes reached 100 and 150 mV in the observed tunability range with distortion ranging between 0.7 and 3.3%.

Proposal and Synthesis Design of Wideband Filtering Differential Phase Shifters With a Pair of Out-of-Band Transmission Zeroes

In this paper, a new class of wideband filtering phase shifters with a pair of controllable out-of-band transmission zeroes is presented for the first time. The proposed wideband filtering differential phase shifter consists of two stub-loaded multimode resonators (SLMMR) in the main and reference branches, which can provide a constant phase shift and self-realized generalized Chebyshev filtering function with controllable transmission zeroes by properly setting the impedance ratio $R_{\mathrm {z}}$ of the loaded stub. On the one hand, the prescribed phase shift value, phase deviation, and phase shift bandwidth are deduced that basically dominated by resonant modes of SLMMR together with electrical lengths of the phase-shifting lines. On the other hand, the phase properties of transmission zeroes are systematically investigated to demonstrate that they arouse little effect on the phase shift performance, but highly improve the frequency selectivity in theoretical analysis. Based on the presented synthesis method which simultaneously considers wideband phase shift and bandpass filtering function, the circuit parameters of the entire proposed phase shifter can be synthesized with prescribed phase shift value, phase deviation, bandwidth, return loss, and transmission zero positions. Besides, the phase shift and return loss bandwidth can be determined in the design process. As design examples, two 90° wideband filtering phase shifters with different specifications are synthesized, designed, and fabricated to validate our proposed approach.

Digital Speckle Photography of Subpixel Displacements of Speckle Structures Based on Analysis of Their Spatial Spectra

We have investigated the capabilities of the method of digital speckle interferometry for determining subpixel displacements of a speckle structure formed by a displaceable or deformable object with a scattering surface. An analysis of spatial spectra of speckle structures makes it possible to perform measurements with a subpixel accuracy and to extend the lower boundary of the range of measurements of displacements of speckle structures to the range of subpixel values. The method is realized on the basis of digital recording of the images of undisplaced and displaced speckle structures, their spatial frequency analysis using numerically specified constant phase shifts, and correlation analysis of spatial spectra of speckle structures. Transformation into the frequency range makes it possible to obtain quantities to be measured with a subpixel accuracy from the shift of the interference-pattern minimum in the diffraction halo by introducing an additional phase shift into the complex spatial spectrum of the speckle structure or from the slope of the linear plot of the function of accumulated phase difference in the field of the complex spatial spectrum of the displaced speckle structure. The capabilities of the method have been investigated in natural experiment.

Dynamics of a 1D array of inhibitory coupled chemical oscillators in microdroplets with global negative feedback.

We have investigated the effect of global negative feedback (GNF) on the dynamics of a 1D array of water microdroplets (MDs) filled with the reagents of the photosensitive oscillatory Belousov-Zhabotinsky (BZ) reaction. GNF is established by homogeneous illumination of the 1D array with the light intensity proportional to the number of BZ droplets in the oxidized state with the coefficient of proportionality ge. MDs are immersed in the continuous oil phase and diffusively coupled with the neighboring droplets via inhibitor Br2 which is soluble in the oil phase. At chosen concentrations of the BZ reactants, illumination suppresses the BZ oscillators. Without GNF, or at a very small ge < 0.29, local inhibitory coupling leads to out-of-phase oscillations of the neighboring BZ droplets with an almost constant phase shift Δφ between them, which makes a space-time plot of the BZ MDs look like a staircase. At 0.3 < ge < 0.6, regular oscillatory clusters consisting of distant BZ MDs (mostly 5-6 phase clusters) emerge. At 0.6 ≤ ge ≤ 1.0, chaotic clusters are observed. At 1.2 < ge < 1.8, regular (mostly 3-4-phase) clusters emerge again. At 1.8 < ge < (3-4), complex clusters with different (but multiple) periods of oscillation are observed. At the same time, some droplets stop oscillating. At large enough ge (>4), in the region of two-phase clusters (with several suppressed BZ MDs), final patterns seem to resemble the initial patterns. Intensive computer simulations with the ordinary differential equations support experimental results.

Microwave beam steering of planar antennas by hybrid phase gradient metasurface structure under spherical wave illumination

To facilitate the microwave beam steering of planar antennas in both elevation and azimuth planes, a radially gradient quasi-transparent hybrid metasurface (RGHMS) structure is proposed. The circular aperture of RGHMS is comprised of two different phase profiles in the single structure. Half of the circular aperture introduces a gradient phase shift, whereas the other half provides a constant phase shift to the incident spherical wave. Since the obtained wavefront modulation for the beam tilting is realized using the combination of aforementioned phase profiles in a single metasurface (MS), it is considered as a hybrid structure. The proposed circular RGHMS with a radius of 1.2λ0 is placed at a height of 0.43λ0 from the feed antenna by considering the geometrical centers of RGHMS and antenna aperture coinciding with each other. The in-plane translation of the RGHMS modulates the wavefront of the incident wave, which results in 0° to 18° beam steering of planar antenna in the elevation plane. Moreover, in-plane rotation of RGHMS around the antenna axis facilitates the beam steering in the azimuth plane with a full 360° azimuthal coverage. The proposed structure is designed at the center frequency of 10 GHz and introduces uniform beam shapes with the gain of 12.3–14.3 dBi during the beam steering. The strategy of combining two different types of phase profile in a single MS eludes the requirement of the phase correcting lens, and thus can directly be illuminated through the spherical wavefront of antenna in the near field. Moreover, the microwave beam steering in both planes with fairly high gain and compact configuration is revealed.

Compact Wideband Phase Shifter Using Microstrip Self-Coupled Line and Broadside-Coupled Microstrip/CPW for Multiphase Feed-Network

In this letter, a compact wideband phase shifter using a microstrip self-coupled line and a broadside-coupled microstrip/CPW (BCMC) structure is proposed for multiphase feed-network. With a uniform phase reference, such a phase shifter can achieve multiphase responses by adjusting instinct self- and broadside couplings for constant phase shifts within a wideband. Then, with the combination of proposed phase shifters and a microstrip Wilkinson power divider, a multiphase feed-network can be implemented. To verify the mechanisms mentioned earlier, a wideband feed-network is fabricated with measured multiphase responses (i.e., 0°, 5.625°, 11.25°, 22.5°, 45°, 90°, and 180°) and maximum insertion loss of 1.57 dB from 1.7 to 2.3 GHz.

Proposal and Synthesis Design of Differential Phase Shifters With Filtering Function

In this paper, a new class of filtering differential phase shifters is proposed and developed, which can provide constant phase shift and self-embedded filtering function at the same time. In contrast to its traditional counterparts, the proposed phase shifter consists of two bandpass filter (BPF) branches and the phase properties of generalized ${n}$ th-order BPF network are systematically studied at first time. With derived closed-form formula of phase slope, the synthesis method is presented to design the proposed filtering differential phase shifters with prescribed arbitrary phase shift value, passband ripple, and bandwidth. The filter order, which dominates frequency selectivity, is considered in the synthesis design of proposed phase shifter as well. The tradeoff between the frequency selectivity and phase shift is discussed. In addition to the advanced features of multifunction and simple geometry, the proposed filtering differential phase shifters can achieve compact size, low amplitude imbalance, and multiway polyphase capability. To validate the proposed concept and synthesis method, two filtering differential phase shifters with single-phase (90°) and five-way polyphase (45°, 90°, 135°, and 180°) are designed, fabricated, and measured. The simulated and measured results coincide well with the prescribed performances in phase shift and magnitude.

Phase shift between respiratory oscillations in cerebral blood flow velocity and arterial blood pressure

We aim to investigate whether phase shift between respiratory oscillations in cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP) is associated with changes in cerebral autoregulation (CA) or reflects the mechano-elastic properties of the cerebrovascular bed. The relationships between respiratory phase shift and slow wave phase shift versus cerebrovascular time constant (the product of cerebrovascular resistance and compliance) and the index of CA (Mx) were analyzed during breathing at 6, 10, and 15 breaths min−1 in 39 volunteers. With increasing respiratory rate the time constant, Mx, and respiratory phase shift decreased, whereas slow wave phase shift increased. The time constant correlated moderately strongly with the respiratory phase shift (R = 0.49, p 0.001) and did not correlate with the slow wave phase shift. The slow wave phase shift was significantly associated with Mx (R = −0.46, p 0.001). The respiratory phase shift more accurately reflects the mechano-elastic properties of the cerebrovascular bed, whereas CA is better described by the slow wave phase shift.

A Universal Reference Line-Based Differential Phase Shifter Structure With Simple Design Formulas

The conventional differential phase shifter configurations usually require different reference lines to provide constant phase shifts over a certain bandwidth. This results in high design complexity, especially for the multiway and poly-phase applications. To solve this problem effectively, a new differential phase shifter configuration based on the parallel stubs loaded transmission line is proposed. The phase of different main lines in the proposed structure can be easily aligned with that of the same reference line by simply changing the position of the loading stubs, which has a linear relationship with the desired phase shift. The new phase aligning approach and the universal reference line bring about simplicity in design and implementation. For demonstration purposes, a group of differential phase shifters is designed, fabricated, and measured. The corresponding constant phase shifts (from 45° to 135° with a step of 15°) are obtained between the main lines and the reference line, over a bandwidth of 55.6% with small insertion loss and phase deviation.

Viterbi Detection Method of π/4-QPSK Signal in VDE

Aiming at the complexity of communication environment, the bad signal quality and influence of different parameters in the study of VHF data exchange (VDE) satellite, a detection method of viterbi is proposed in this paper. According to the characteristic of π/4-QPSK signal, this method constructs signal phase states, and gives a cost function of decoding based on the maximum likelihood criterion, and then by using the thoughts of viterbi to decode. The complexity of this method is relatively low, and it is easy to implement for baseband signal detection. The simulation results show that this method has good detection performance, which is about 9dB better than traditional methods under the same Eb/No. It can be applied to the conditions with interference, time delay, frequency offset and phase shift which has good robustness and anti-interference performance, and the detection performance is not affected by constant frequency offset and phase shift.

Tunable, omnidirectional structural color on reflection based on metal-SiOx-metal structure

An omnidirectional structural color based on the metal-SiOx-metal stack structure is proposed, which can present the same perceived color for a broad range of incidence angles. The tunable structural color can be obtained with adjustable intermediate dielectric layer by simply adjusting the deposition condition, especially the oxygen flow rate during the deposition processes. The resonance condition can be satisfied across the whole visible light region with this special dielectric. The strong absorption caused by the resonance within the metal-SiOx-metal structure accounts for the efficient spectral filtering feature, and the constant phase shift within the dielectric layer leads to angle insensitivity of this color filter. This simple color tuning method for omnidirectional structural colors can have a great potential in various applications such as displaying, imaging, colorful decoration, anti-counterfeiting and so forth.