Phase Shift Curve Research Articles

Ion-acoustic solitons oblique collisions in a magnetized ultra-relativistic degenerate plasma at critical compositions and nonzero temperatures

The mechanism of ion-acoustic (IA) soliton oblique collisions is examined at nonzero temperatures and critical compositions in a magnetized ultra-relativistic degenerate plasma using the extended Poincaré–Lighthill–Kuo (EPLK) method. Two conditions, referred to as the generic and critical cases, are obtained. Korteweg-de Vries (KdV) equations that govern the excitation of IA solitons and their phase shifts have been derived for the generic case. At a critical composition, modified KdV (mKdV) equations describe the nonlinear propagation of IA solitons, and thus the corresponding phase shifts are deduced. Furthermore, for an in-depth investigation, we examined the collision of two IA solitons of the same polarity and opposite polarities arising from oblique collisions at discrete times. In these two situations, the phase shifts of IA solitons due to the oblique collisions increase with an increase in the collision angle. The phase shift curve reaches its maximum value at the perpendicular collision. This work may aid in interpreting the features of IA solitons in a degenerate plasma, such as white dwarfs, that support soliton propagation.

Investigation on transient process of dense hydrogen microdischarge by dual-wavelength laser interferometry

In this paper, the transient process of single-pulse hydrogen microdischarge with peak discharge current of at constant pressure of is investigated by dual-wavelength laser interferometry. It is found that the phase shift signals related to electrons and excited H (n = 2) atom appear almost simultaneously after breakdown, with a delay of 700 ns compared with the current signal. The velocity of the ionization wave is thus estimated to be on the order of . Subsequently, the current and phase signals increase rapidly, indicating that the energy deposited is applied to heat electron and gas, and strong molecular ionization and atomic excitation process occur in microdischarge. The phase signal for excited H (n = 2) atoms shows the maximum value at and then decreases rapidly, while the current reaches the peak at . In the duration between these two peaks the electronic degrees of freedom (DOF) continue to gain energy from the external field, but the energy transferred to the atomic DOF decreases. After , the current drops first rapidly, and then slowly decreases until the end of the discharge. In discharge attenuation process, the energy flowing into all DOF decreases. The phase-shift dispersion curve is obtained by changing laser frequency. Through the global optimized fitting of the phase shift curve, the average line-of-sight density of excited H (n = 2) atoms is estimated to be in microdischarge, and the corresponding broadening information is given.

A Single-Layer Broadband Ka-Band Reflectarray Using Novel Windmill Elements

A single-layer novel windmill element is designed to broaden the bandwidth of reflectarray antenna (RA) in this communication. To obtain the enough phase range, a windmill ring patch and a circular ring patch are utilized to realize the multiresonant state. As a result, a linear phase shift curve which covers 473.6° phase range is achieved by optimizing the parameters. Based on that, a large proportion of phase shift curve keeps parallel from 27.5 to 42.5 GHz, it indicates the proposed element features broadband property. To this end, a single-layer offset-fed prototype with a square aperture of 80 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times80$ </tex-math></inline-formula> mm which is composed of 400 elements is designed, measured, and tested at Ka-band. Through detailed measurements, a peak gain of main beam is 27.86 dBi with an aperture efficiency of 51.7% has achieved at 37 GHz. The sidelobe level and cross-polarization are also lower than −17 and −25 dB, respectively. More importantly, the degradation of the peak gain from 27.5 to 40 GHz (35.71%) is less than 3 dB. The proposed antenna which features wide bandwidth with good radiation performance and simple structure will be suitable for 5G millimeter-wave communication.

Photonic-Assisted Microwave Frequency Measurement With Adjustable Channel Bandwidth Based on Spectrum-Controlled Brillouin Phase Shift

A photonics-based channel bandwidth tunable microwave frequency measurement (MFM) is analyzed and verified, which is implemented based on the principle of the frequency-to-phase-slope mapping (FTPSM) in stimulated Brillouin scattering (SBS). The spectrum-controlled Brillouin phase shift curve is created by using an optical frequency comb (OFC) pump instead of a single pump. As a result, the Brillouin phase shift response is superimposed to further realize a flexible and adjustable measurement bandwidth. Meanwhile, thanks to the relationship between the OFC pump and the unknown signal, the frequency measurement can be achieved by the property of monotonous frequency-to-phase-slope mapping. A proof-of-concept experiment is performed to verify the feasibility of the approach. By changing the number of OFC lines, the channel bandwidths of 500, 700, or 900 MHz are demonstrated, with a measurement error lower than 35 MHz. We believe that this FTPSM-based MFM system is a promising solution for radio frequency (RF) channelized receiver.

A single-layer low-cost reflectarray antenna using dual-resonant element approach

Abstract A single-layer wideband high efficiency reflectarray in Ku-band has been presented in this paper. A novel dual-resonant patch element approach has been analyzed and optimized to obtain good radiation performances within the operating frequency band. The phase shift range of 573° can be obtained with less steep linear phase shift curve. To compensate the differential spatial phase delays from the feed to the elements, the variable size technique has been utilized for obtaining required phase shifts. The reflectarray aperture has been designed, manufactured and measured. Measured results are in good agreement with the simulated ones. The measured gain of the reflectarray aperture at center frequency can reach 27.2 dBi, which is equivalent to aperture efficiency of 51.3%, and the 1-dB gain bandwidth of the aperture is 18.4%.

Double‐layer wideband reflectarray using polynomial optimization technology

In this article, a novel double-layer wideband reflectarray antenna using polynomial optimization technology is proposed. The reflectarray element has two main variable parameters. When each of the variables is adjusted, the reflectarray element cannot achieve 360° phase shift. However, as the two variables work together, 360° phase shift is easy to be achieved. The polynomial technology is used to connect the two variables, and the differential evolution algorithm is adopted to optimize the element to obtain the appropriate polynomial coefficients. The phase shift curves of different frequencies are parallel to each other and the slopes of the phase shift curves are consistent, which makes the proposed element achieve wideband characteristics. In order to verify the correctness of the proposed design method and reflectarray element, a 441-element reflectarray antenna was designed, processed, and measured. The proposed reflectarray antenna achieves 35% 1-dB gain bandwidth. At 12 GHz, the gain and efficiency of the proposed reflectarray antenna are 29 dBi and 62% respectively. In the whole bandwidth, the sidelobe was less than –16 dB and the cross-polarization was less than –38 dB. It is proved that polynomial automatic optimization technology can guide the design of the multi-variable wideband reflectarray antenna.

Linearized segmentation method for measuring the phase transfer function of a silicon Mach-Zehnder modulator by using the beat-frequency technique.

A linearity segmentation method for measuring the phase shift curve of silicon Mach-Zehnder modulators (SMZMs) as a function of applied electric field is presented. Applying a small sinusoidal signal to the traveling-wave electrode of the SMZM, the upper and lower arms of the SMZM produce differential phase modulation effect. Meanwhile, a local oscillator source with a wavelength-adjustable function is employed to heterodyne the intensity modulated optical signal of the SMZM; thus, the modulated intensity signal in the optical field domain is transformed into the low-frequency electric field domain. Meanwhile, a balanced detector with a low-speed transimpedance amplifier is exploited to realize photoelectric conversion, which can suppress the direct-current component and improve the anti-noise ability. Extracting the beat-frequency and first-order harmonic sideband signals in the case of phase bias is 0 and π, respectively, the phase shift slopes of the upper and lower arms can be calculated under different reverse PN voltages, and we can achieve the phase shift as a function of the modulation frequency and reverse PN voltage. The proposed method is supported by the simulation and measurement results and the key parameters of the SMZM, such as the radio frequency half-wave voltage, chirp characteristic, 3 dB bandwidth, etc., can be acquired from the phase shift curves of the upper and lower arms.

Fast and accurate tilt-shift-immune phase-shifting algorithm based on self-adaptive selection of interferogram subblocks and principal component analysis.

To eliminate the effect of tilt-shift error on the accuracy of phase-shifting interferometry (PSI), a fast and accurate tilt-shift-immune phase-shifting algorithm based on the self-adaptive selection of interferogram subblocks and principal component analysis (SSPCA) is proposed. First, each interferogram is divided into several subblocks, and principal component analysis and the least-squares method (LSM) are applied to obtain the phase-shift value of each subblock. Next, according to the correlation coefficients between each phase-shift curve, valid and invalid subblocks can be distinguished. Finally, all phase-shift values of the valid subblocks are used to fit the tilt phase-shift plane, and phase results can be obtained using the LSM. Simulations indicate that the accuracy of SSPCA can reach 0.03 rad both for small (1 rad) and large (${2}\pi $2π rad) tilt amplitudes, and it takes only one-tenth or less of the processing time of iterative algorithms. Experiments proved that SSPCA can be applied even without a precision phase shifter and thus provides a low-cost approach for PSI with both high precision and speed.

Hadron\u2013Hadron interactions from N_mathrm{{f}}=2+1+1 lattice QCD: the rho ,-resonance

We present a lattice QCD investigation of the rho -meson with N_mathrm{{f}}=2+1+1 dynamical quark flavours for the first time. The calculation is performed based on gauge configuration ensembles produced by the ETM Collaboration with three lattice spacing values and pion masses ranging from 230 to 500 MeV. Applying the Lüscher method phase-shift curves are determined for all ensembles separately. Assuming a Breit–Wigner form, the rho -meson mass and width are determined by a fit to these phase-shift curves. Mass and width combined are then extrapolated to the chiral limit, while lattice artefacts are not detectable within our statistical uncertainties. For the rho -meson mass extrapolated to the physical point we find good agreement with experiment. The corresponding decay width differs by about two standard deviations from the experimental value.

Tunable terahertz phase shifter based on dielectric artificial birefringence grating filled with polymer dispersed liquid crystal

An active terahertz (THz) anisotropic manipulation is based on a structure combined polymer dispersed liquid crystal (PDLC) with sub-wavelength dielectric gradient grating. In this structure, the PDLC works as an adjustable anisotropic material due to the change of the optical axis direction induced by applying a biased electric field, while the dielectric grating serves as an artificial high birefringence material. By using an appropriate design, the THz birefringence of this structure can be enhanced or offset under different biased voltages, and the phase shift curve of this structure becomes flatter than that of the pure PDLC cell due to the dispersion manipulation of the grating. Moreover, the experimental results fit with the simulative designing, demonstrating that the phase shift of the structure can vary from π to 0 near 0.8 THz when the electric field increases from 0 to 80V, and this device realizes the function of polarization conversion as a tunable THz half-wave plate. This work exhibits potential applications in THz functional devices, such as actively controlled phase shifters and polarization convertors combined LC with artificial microstructure.

Broadband phase shift engineering for terahertz waves based on dielectric metasurface

Broadband terahertz (THz) phase shift engineering and zero-dispersion waveplates based on dielectric metasurface have been investigated, of which structure is a periodical rectangular scattering units on silicon substrates. By designing proper geometric parameters of metasurface structure, the value, dispersion and bandwidth of the phase shift curves can be effectively manipulated. Based on this, the broadband half waveplate (HWP) and quarter waveplate (QWP) have been designed and fabricated. The experimental results show that the HWP can work in the broad range of 0.7–1.35 THz with the polarization conversion ratio (PCR) of close to 100% and the transmission of over 70%. And the QWP can operate in the range of 0.7∼0.85THz with the PCR of over 90% and the transmission of over 70%. The method of phase shift engineering based on dielectric metasurfaces and these broadband zero-dispersion waveplates have great potential in promoting the performance of THz application systems.

Development and characterization of an interferometer for calorimeter-based absorbed dose to water measurements in a medical linear accelerator.

The quantity of relevance for external beam radiotherapy is absorbed dose to water (ADW). An interferometer was built, characterized, and tested to measure ADW within the dose range of interest for external beam radiotherapy using the temperature dependence of the refractive index of water. The interferometer was used to measure radiation-induced phase shifts of a laser beam passing through a (10 × 10 × 10) cm3 water-filled glass phantom, irradiated with a 6 MV photon beam from a medical linear accelerator. The field size was (7 × 7) cm2 and the dose was measured at a depth of 5 cm in the water phantom. The intensity of the interference pattern was measured with a photodiode and was used to calculate the time-dependent phase shift curve. The system was thermally insulated to achieve temperature drifts of less than 1.5 mK/min. Data were acquired 60 s before and after the irradiation. The radiation-induced phase shifts were calculated by taking the difference in the pre- and post-irradiation drifts extrapolated to the midpoint of the irradiation. For 200, 300, and 400 monitor units, the measured doses were 1.6 ± 0.3, 2.6 ± 0.3, and 3.1 ± 0.3 Gy, respectively. Measurements agreed within the uncertainty with dose calculations performed with a treatment planning system. The estimated type-A, k = 1 uncertainty in the measured doses was 0.3 Gy which is an order of magnitude lower than previously published interferometer-based ADW measurements.

A dual polarization, broadband, millimeter‐wave reflectarray using modified cross loop element

ABSTRACTA Ka‐band reflectarray consisting of modified cross loop is investigated in this article for millimeter‐wave broadband dual‐polarization applications. It consists of 40 × 40 unit cells that covered an area of 200 × 200 mm2 and a multimode conical horn antenna which is connected to an orthomode transducer as the offset feed. Its unit cell is composed of a solid cross inside and a cross loop outside, which can lead to nearly 550° linear phase shift curve by varying its length. After this proposed structure has been analyzed and compared with the traditional wideband element (i.e., double cross loop), it is used in the reflectarray. An equivalent circuit model with an insightful field distribution is used to analyze their different behaviors when it resonated at the same operating frequency. For vertical and horizontal polarization modes, the peak gain are measured to be 34.3 and 33.5 dB, the aperture efficiency are 48.6% and 40.4% at the center frequency of 32 GHz, respectively. The 1.5 dB gain bandwidth are close to 18% and 15%, which is better than conventional millimeter‐wave single‐layer ones. This new reflectarray antenna is especially useful for millimeter‐wave broadband dual‐polarization applications. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:287–293, 2014

Interface effects on the quantum well states of Pb thin films

Using scanning tunneling spectroscopy, we have studied the interface effect on quantum well states of Pb thin films grown on various metal-terminated (Pb, Ag, and Au) n-type Si(111) surfaces and on two different p-type Si(111) surfaces. The dispersion relation E(k) of the electrons of the Pb film and the phase shift at the substrate interface were determined by applying the quantization rule to the measured energy positions of the quantum well states. Characteristic features in the phase shift versus energy curves were identified and were correlated to the directional conduction band of the silicon substrate and to the Schottky barrier formed between the metal film and the semiconductor. A model involving the band structure of the substrate, the Schottky barrier, and the effective thickness of the interface was introduced to qualitatively but comprehensively explain all the observed features of the phase shift at the substrate interface. Our physical understanding of the phase shift is critically important for using interface modification to control the quantum well states.

Measurement of phase and intensity by Dual-imaging Interferometry for performance evaluation of liquid crystal spatial light modulator

In order to evaluate the performance of liquid crystal spatial light modulator Dual-imaging Interferometry is proposed by introducing a dual-imaging system into Michelson interferometer to obtain phase and intensity for the measurement of multiple parameters. The feasibility of the proposed method is verified through theory analysis and experiments. Experimental results indicate that the range of phase shift is from 0 to 2.07 π, the nonlinearity of phase shift curve is 3.02% and the RMS of phase nonuniformity is 0.07 π. The rising and fall time are 13 ms and 16 ms, respectively. Dual-imaging Interferometry can be used to measure multiple parameters on one experimental setup in place of conventional methods and avoid the complicated operation and extra errors resulting from arranging different experimental setups.

Cerebral perfusion information obtained by dynamic contrast‐enhanced phase‐shift magnetic resonance imaging: comparison with model‐free arterial spin labelling

Phase-shift time curves following a bolus injection of gadolinium contrast agent were registered for grey-matter regions and large vessels in 14 subjects. Deconvolving a tissue phase-shift curve with a phase-based arterial input function resulted in a tissue residue function R(t). The peak value of R(t) provided a relative cerebral blood flow (CBF) index, while the area-to-height ratio of R(t) provided quantitative mean transit time (MTT). For comparison, quantitative CBF values in grey matter were acquired using model-free arterial spin labelling (ASL). The phase-based relative CBF estimates showed good linear correlation with ASL-based CBF (r = 0.82). Grey-matter MTT was 4.9 +/- 1.1 s (mean +/- SD).

SLOW LIGHT IN A TWO MICROSPHERE OPTICAL FIBER SYSTEM

The condition of being undercoupled and overcoupled for the lower microsphere is investigated respectively in two microspheres coupled with a fiber taper system. The effective phase shift curves which could occur in normal dispersion to generate slow light are different based on both situations. The influence of the loss coefficient and coupler parameter for each microsphere is interpreted in detail.

The practical inversion problem in molecular beam scattering

The present status of the inversion of molecular scattering data is reviewed with particular emphasis on the importance of the rapid quantal undulations. It is concluded that the semiclassical approximation may provide valuable guidelines for localized distortions in the phase–shift curve, but that the full quantum treatment is required for quantitative accuracy. The extension of the inversion techniques to the two–potential problem is also briefly discussed.

Elimination of instabilities in phase shift curves in phase-modulation atomic force microscopy in constant-amplitude mode

The authors propose phase-modulation atomic force microscopy (PM-AFM) in constant-amplitude mode using automatic gain control to prevent the instabilities of cantilever dynamics. Under the condition that the driving frequency is set to the resonant frequency of the cantilever, phase shift curve in constant-amplitude mode shows no discontinuity, which resembles a typical behavior of the frequency shift curve in frequency-modulation AFM. They demonstrate that PM-AFM in constant-amplitude mode can clearly resolve phase-separated structures on polymer blend film without instability. These results indicate that PM-AFM in constant-amplitude mode is more stable than that in constant-excitation mode.

Phase detection method with positive-feedback control using a quartz resonator based atomic force microscope in a liquid environment

An atomic force microscope (AFM) using a quartz resonator sensor has great potential as a highly sensitive force detection device. An AFM can detect the solvation force in a liquid environment. We used the phase detection method with positive feedback to improve AFM sensitivity. Phase shift curves as a function of distance show oscillations with periods that correspond to the diameter of a molecule placed between the AFM tip and the surface of a sample substrate. These oscillations are due to the solvation forces when the surface of the substrate is compressed with the AFM tip.