Long-range, high-precision absolute distance measurement technology based on alternately oscillating optoelectronic oscillator

Angular displacement sensor plays an indispensable role in high-precision angular measurement and position feedback. With the development of sensing technology, some traditional incremental measurement methods have been unable to meet the requirements such as anti-interference ability, lossless of power-off data information and other factors that are susceptible to environment and mechanical system changes. Therefore, this paper has proposed a method based on combined measurement for absolute measurement of time-grating angular displacement sensor, which is mainly assembling two time-grating sensors that use different pole pair in a co-prime relationship on the axis. By this method, it can build high-precision and high-resolution sensor that meets vernier-subdivision principle in the form of a combination of sensor and fine sensor. The sensor model and simulation experiment results are introduced by Inventor 2016 and ANSYS Maxwell 16.0, respectively. Then, the absolute position measurement method is validated by analyzing the initial phase of the induced electromotive force of the simulation experiment results with the mathematical method. Experiment results show the absolute measurement method is feasible.

We propose and experimentally validate a simplified optoelectronic oscillator (OEO)-based angular velocity sensing scheme with time-division optical carrier switching. This scheme utilizes only a single OEO oscillation loop structure, where the wavelengths of two input lasers are matched to the two output ports of a delay-line interferometer, respectively. Consequently, when the magneto-optic switch toggles between the two wavelength carriers, the phase difference induced by the Sagnac effect generates opposite frequency shifts in the microwave signal generated by the OEO. Meanwhile, the identical OEO loop ensures common-mode suppression of environmental disturbances. Experimental results demonstrate that by performing beat-frequency detection on these oscillation signals, the zero-bias stability is improved by 74.2dB, reaching 1.36×10-2 °/s. The measurement sensitivity reaches 99.11 kHz/(rad/s). This system configuration is significantly simplified, enhancing its practicality and zero-bias stability.

We propose a dual-comb ranging system based on synthetic-wavelength interferometry. It can realize absolute distance measurement with ∼2.7m ambiguity range, ∼3nm precision within ∼10ms averaging time.

A new approach for high-speed physical random bit generation (RBG) based on broadband random optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. In this scheme, a broadband random OEO based on Rayleigh scattering (RS) is employed as the entropy source of RBG. Compared with other broadband random OEOs which require an additional pump source, the optical signal output from the laser in the proposed scheme can realize excited Brillouin scattering as well as acting as an optical carrier. Benefiting from the introduction of randomly distributed feedback by RS, which breaks the limitation of the fixed loop length of the conventional chaotic OEO, the signals generated by the proposed broadband random OEO have random characteristics. Meanwhile, the generated signals exhibit wide and flat frequency spectrum characteristics due to the avoidance of semiconductor chaotic laser relaxation oscillations. The experimental results show the proposed RBG technique can generate physical random bits with a rate of up to 500 Gb/s which can fully pass the NIST test.

On the basis of analyzing the main error sources of ultrasonic distance measurement, a millimeter-range high-precision ultrasonic distance measurement system was developed. The STM32 processor was used as control core of the system. We chose 200 KHz transmitting-receipting ultrasonic transducer and increased the environmental temperature compensation and back wave gain compensation. Meanwhile, the study proposed a method without additional hardware circuit which using STM32 processor to measure the pulse width of the echo wave, correct the lag time of the echo and further improve the accuracy of measurement. The experimental results demonstrated that ranging accuracy was less than 1mm in the range of 1000 mm with the conditions of using air as medium and existing the good reflective object. The system has simple and reasonable structure, with good stability, convenient measurement, high precision and could be suitably applied to the field of high precision measurement.

The causes which prevent an increase in the accuracy of the refractive indices for high-precision electronic distance measurements are described. It is shown that there is a large number of molecular resonances in the visible and IR spectrum which are due to practically all atmospheric components and not just the trace gases. It is also shown that in such conditions the Rayleigh, Lorentz-Lorenz and Sellmeier formulae need to be corrected. Methods for the correction and experimental testing are proposed.

This article gives an overview of available methods and techniques for geodynamic monitoring, such as the high-precision geometric re-leveling, high-precision linear-angular constructions, high-precision distance measurements, laser scanning, global navigation satellite systems, laser interferometers and strainmeters, radar satellite interferometry. The experience of applying these technologies in different physiographic regions is also described. The tools used in measurements, which provide the maximum achievable accuracy of methods in modern conditions, are demonstrated. A table is made with the summary characteristic of instrumental methods to measure the parameters of current movements of the Earth crust. On the basis of the performed comparative analysis of modern methods, techniques and technical means for execution of geodynamic monitoring, the most effective ones have been chosen from the methods listed above. Such methods include methods of high-precision geometric levelling of I and II classes, as well as the global navigation satellite systems. Complex use of these methods will allow to obtain reliable data about the geodynamic situation of the investigated area.

Membrane proteins play a central role in biology as the gatekeepers of all cellular compartments. And transmembrane signaling through membrane bound kinases is a particularly important process for cellular adaptation to a changing environment. In prokaryotes, the membrane bound HK, which is part of the ubiquitous two-component system, is the most common type of signal transduction employing a protein phosphorylation mechanism. Due to their lipid-bound native environment, structural studies of membrane bound HKs have remained challenging for a spectrum of techniques. The first five chapters of this thesis will be dedicated to the functional and structural studies of a membrane HK CitA, which is activated for cross-phosphorylation upon citrate binding by hydrolysis of ATP molecules, employing NMR spectroscopy. The new regime of ultra-fast MAS NMR has allowed the application of 1H-detected experiments to more challenging system. We employed this method for the residue specific assignment of the PASpc construct of CitA and gained chemical shift information of the previously unavailable TM helices, along with their linker regions (Chapter 2). This new piece of information confirms the formation of a P-helix at the end of the PASp domain to further residues downstream, as well as reveals the loosening of a conserved KK linker upon citrate binding between the TM2 helix and the PASc domain. The role of cytosolic PAS domain in HK activation has remain unsolved since the discovery of HKs over 30 years ago. Based on the functional mutants in the PASc domain of CitA, sPRE profile and NMR visibility, an anti-parallel to parallel dimer rearrangement model for CitA activation in its PASc domain was proposed. However, direct structural evidence and functional data confirming the validity of this structural model is still lacking. We investigated the functional impact of this model on the CitA phosphorylation rate by tracking the ATP hydrolysis using 31P NMR (Chapter 3). An attenuation of CitA’s kinase activity when the anti-parallel N288D mutant PASc domain, instead of the parallel WT PASc domain, was attached to the DHp domain is observed by us. This confirms the functional relevance of this dimer transition in the activity of CitA. The same 31P NMR method provides a convenient way to test the functionality of CitA with different chemical tags, which is a pre-requisite for site-specific inter-dimer distance measurement. We found that tagging CitA with a small CF3 group of a cysteine mutation site, N308C, at the end of the PASc domain retains its functionality and responsiveness to citrate binding, while tagging of the same site with MTSL does not. This paves the way for gaining site specific evidence to prove the anti-parallel to parallel transition upon citrate binding using DNP enhanced 19F NMR (Chapter 4). From this, we found a large change in inter-N308C distance between the citrate free (more than 20 Å apart) and the citrate bound state (11 Å).This supports the drastic anti-parallel to parallel dimer transition directly. Although our data are collected using a fragment of CitA lacking the DHp domain, they provide key information regarding the structural rearrangement of PASc that lead to HK activation in the context of the TM helices. Combined with the 1H-detected MAS NMR assignment, the works presented here suggest that the P-helix formation at the end of PASp, the piston-like upward motion of the TM2 helix, the KK domain loosening at the linker between the TM2 helix and the PASc domain, and the anti-parallel to parallel dimer transition are key events in the activation of CitA with citrate binding. Internuclear distance determination is the foundation for NMR-based structure calculation. However, high-precision distance measurement is a laborious process requiring lengthy data acquisitions due to the large set of multidimensional spectra needed at different mixing times. This prevents application to large or challenging molecular systems. The last chapter of this thesis will present a new approach, transferred-rotational-echo double resonance (TREDOR), a heteronuclear transfer method in which we simultaneously detect both starting and transferred signals in a single spectrum. This co-acquisition is used to compensate for coherence decay, resulting in accurate and precise distance determination by a single parameter fit using a single spectrum recorded at an ideal mixing time. We showcase TREDOR with the microcrystalline SH3 protein using 3D spectra to resolve resonances. By combining the measured N–C and H–C distances, we calculate the structure of SH3, which converges to the correct fold, with a root-mean-square deviation of 2.1 Å compared to a reference X-ray structure. This demonstrates TREDOR as a fast and straightforward method for determining structures via magic-angle spinning NMR.

We propose a technique to achieve high-speed and high-precision distance measurement via phase demodulation of broadband optical carrier-based microwave interferometry (OCMI). An in-phase and quadrature (I/Q) processing scheme is designed and incorporated to measure the phase shift induced by target distance. The results could be efficiently derived from a minimum of one pair of detected outputs with immunity to power fluctuations. To extend the non-ambiguous measurement range while maintaining high resolution, a multifrequency-based phase unwrapping procedure is implemented. In the meantime, a driving module is utilized to effectively amplify and stabilize the signal. Experiments were carried out to evaluate the feasibility and performance of the proposed OCMI distance measurement method, which exhibits good accuracy, stability, and reliability. The maximum residual error is found to be 0.084 mm and the relative error is less than 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . Moreover, the method is capable to perform thousands of measurements within a few seconds, thus the OCMI-based dynamic target tracking has been achieved.

Pulsar timing arrays (PTAs) are anticipated to detect continuous gravitational waves (GWs) from individual supermassive black hole binaries (SMBHBs) in the near future. To identify the host galaxy of a GW source, PTAs require significantly improved angular resolution beyond the typical range of 100–1000 square degrees achieved by recent continuous GW searches. In this study, we investigate how precise pulsar distance measurements can enhance the localization of a single GW source. Accurate distance information, comparable to or better than the GW wavelength (typically 1 pc) can refine GW source localization. In the near future, with the advent of Square Kilometre Array (SKA), such high-precision distance measurements will be feasible for a few nearby pulsars. We focus on the relatively nearby pulsars J0437-4715 (156 pc) and J 0030 + 0451 (331 pc), incorporating their actual distance uncertainties based on current very long baseline interferometry measurements and the anticipated precision of the SKA-era. By simulating 87 pulsars with the GW signal and Gaussian white noise in the timing residuals, we assess the impact of the pulsar distance information on GW source localization. Our results show that without precise distance information, localization remains insufficient to identify host galaxies under 10 ns noise. However, incorporating SKA-era distance precision for nearby pulsars J0437-4715 and J 0030 + 0451 can reduce localization uncertainties to the required level of 10 − 3 deg 2 under 10 ns noise. Localization accuracy strongly depends on the geometric configuration of pulsars with well-measured distances and improves notably near and between such pulsars. The improvement of the localization will greatly aid in identifying the host galaxy of a GW source and constructing an SMBHB catalog. It will further enable follow-up electromagnetic observations to investigate the SMBHB in greater detail.

We demonstrate a 200-MHz all polarization-maintaining, repetition-rate-locked femtosecond fiber laser system with a total electrical power consumption of 11 W. The center wavelength, spectral width, pulse width, and average output power of the laser are 1558.8 nm, 34 nm, 139 fs, and 77.6 mW, respectively. The proposed laser system that integrates all optical components and locking electronics has a volume less than 1.5 L, a mass of 1.3 kg, and a fast locking time of 3 s (from the free running state to the repetition-rate-locked state). Using a hydrogen maser as the frequency reference, after locking, the Allan deviation is 2.8 mHz at a gate time of 1 s. Further, we place the repetition-rate-locked fiber laser system on a homemade shaker table with peak and rms accelerations of 1.97 and 0.7 g, respectively; the experimental results show that the locking state can be maintained robustly with Allan deviation of 2.0 mHz. The highly integrated, robust fiber laser system has potential applications in the areas of ultralow-noise microwave generation and high-precision distance measurement in outdoor environments.

Objectives:To compare the diagnostic reliability of optic nerve sheath diameter (ONSD) ultrasonography with a transcranial Doppler (TCD)-based absolute intracranial pressure (ICP) value measurement method for detection of elevated ICP in neurological patients. The ONSD method has been only tested previously on neurosurgical patients.Methods:A prospective clinical study of a non-invasive ICP estimation method based on ONSD correlation with ICP and an absolute ICP value measurement method based on a two-depth TCD technology has recruited 108 neurological patients. Ninety-two of these patients have been enrolled in the final analysis of the diagnostic reliability of ONSD ultrasonography and 85 patients using the absolute ICP value measurement method. All non-invasive ICP measurements were compared with ‘Gold Standard’ invasive cerebrospinal fluid (CSF) pressure measurements obtained by lumbar puncture. Receiver-operating characteristic (ROC) analysis has been used to investigate the diagnostic value of these two methods.Results:The diagnostic sensitivity, specificity, and the area under the ROC curve (AUC) of the ONSD method for detecting elevated intracranial pressure (ICP >14·7 mmHg) were calculated using a cutoff point of ONSD at 5·0 mm and found to be 37·0%, 58·5%, and 0·57, respectively. The diagnostic sensitivity, specificity, and AUC for the non-invasive absolute ICP measurement method were calculated at the same ICP cutoff point of 14·7 mmHg and were determined to be 68·0%, 84·3%, and 0·87, respectively.Conclusions:The non-invasive ICP measurement method based on two-depth TCD technology has a better diagnostic reliability on neurological patients than the ONSD method when expressed by the sensitivity and specificity for detecting elevated ICP >14·7 mmHg.

The paper proposes a comparison between a three-dimensional (3D) exact solution and several two-dimensional (2D) numerical solutions. Numerical methods include classical 2D finite elements (FEs), and classical and refined 2D generalized differential quadrature (GDQ) solutions. The free vibration analysis of two different configurations of functionally graded material (FGM) plates and cylinders is proposed. The first configuration considers a one-layered FGM structure. The second one is a sandwich configuration with external classical skins and an internal FGM core. Low and high order frequencies are analyzed for thick and thin simply supported structures. Vibration modes are investigated to make a comparison between results obtained via the 2D numerical methods and those obtained by means of the 3D exact solution. The 3D exact solution is based on the differential equations of equilibrium written in general orthogonal curvilinear coordinates. This exact method is based on a layer-wise approach where the continuity of displacements and transverse shear/normal stresses is imposed at the interfaces between the layers of the structure. The 2D finite element results are obtained by means of a well-known commercial FE code. Classical and refined 2D GDQ models are based on a generalized unified approach which considers both equivalent single layer and layer-wise theories. The differences between 2D numerical solutions and 3D exact solutions depend on the considered mode, the order of frequency, the thickness ratio of the structure, the geometry, the embedded material and the lamination sequence.

In the solar reflective band, the on-board calibration method based on a solar diffuser (SD) is the mainstream calibration method. However, the calibration accuracy is limited by the measurement accuracy of the SD bidirectional reflectance distribution function (BRDF) in the laboratory. The limitations of the light sources and detectors hinder accurate BRDF measurements in the short-wave infrared band, particularly beyond 1700 nm. In this study, the angle integration-band crossing transfer (AIBCT) method is proposed for SD BRDF measurement to avoid the influence of the Fourier spectrometer's signal processing and detector nonlinearity in the absolute measurement. The method utilized the relationship between the BRDF and directional-hemispherical reflectance, and calculated the spectral distribution of the SD BRDF at the standard in-plane geometry with an 0° incidence zenith angle and a 45° reflection zenith angle (0:45) by integration. The absolute measurement result of the 0:45 SD BRDF at 1150 nm was used as the standard for transfer to the short-wave infrared band. The SD BRDF at 0:45 was generalized to other geometries through relative measurements based on the reciprocity theorem. The mean relative error of the results of the AIBCT and absolute measurement methods was less than 0.3 % in the range of 1100 nm to 1600 nm. Analysis of the results showed that the AIBCT method’s measurement uncertainty (coverage factor k = 2) of the 0:45 SD BRDF is better than 0.84 % at 1100 nm to 2300 nm and 1.05 % at 2300 nm to 2500 nm. Furthermore, the AIBCT method was found suitable for the ultraviolet band.

Cost-efficient multi-objective synchronous ranging solutions are highly desired in many fields such as manufacturing and infrastructure. However, traditional laser ranging methods have limitations in absolute ranging and multi-channel expansion. In this paper, a multi-channel absolute distance measurement method based on optical carrier-based microwave scanning interferometry (OCMSI) is proposed. After microwave scanning and synchronous demodulation, the amplitude spectrums and phase spectrums of interference signals are established. The transmission signals of each channel can be separated and reconstructed by using the discrete Fourier inverse transform. Additionally, it is demonstrated that the designed global optimization algorithm for extracting free spectral range can effectively reduce the impact of detection errors and channel interference. Existing interferometers can achieve multi-channel parallel absolute distance measurement without the need for additional modulation, demodulation, and optoelectronic detection devices. Experimental results have shown that the system structure is simple, and the ranging accuracy of for 3 channels is higher than ± 60 μm within at least 35 m optical path.