Absolute Measurement Technique Research Articles

Phase tracking using a Kalman filter based on probability density distribution in frequency-scanning interferometry

Frequency-scanning interferometry (FSI) utilizing external cavity diode lasers (ECDL) stands out as a potent technique for absolute distance measurement. Nevertheless, the inherent scanning nonlinearity of ECDL and phase noise pose a challenge, as it can compromise the accuracy of phase extraction from interference signals, thereby reducing the measurement accuracy of FSI. In this study, we propose a composite algorithm aimed at mitigating non-orthogonal errors by integrating the least-squares and Heydemann correction technique. Furthermore, we employ Kalman filtering for precise phase tracking. We introduce a parameter selection strategy based on the statistical distribution of instantaneous frequency to achieve the fusion estimation of phase observation values and theoretical models, which starts a new perspective for the application of multi-dimensional data fusion in FSI measurement. Through simulation and experimental validation, the efficacy of this approach is confirmed. The experimental results show promising outcomes: with an average phase error of 0.12%, a standard deviation of less than 1.7 µm in absolute distance measurement, and an average positioning accuracy error of 0.29 µm.

Techniques for Measurement of Serotonin: Implications in Neuropsychiatric Disorders and Advances in Absolute Value Recording Methods.

Serotonin (5-HT) is a monoamine neurotransmitter in the peripheral, enteric, and central nervous systems (CNS). Within the CNS, serotonin is principally involved in mood regulation and reward-seeking behaviors. It is a critical regulator in CNS pathologies such as major depressive disorder, addiction, and schizophrenia. Consequently, in vivo serotonin measurements within the CNS have emerged as one of many promising approaches to investigating the pathogenesis, progression, and treatment of these and other neuropsychiatric conditions. These techniques vary in methods, ranging from analyte sampling with microdialysis to voltammetry. Provided this diversity in approach, inherent differences between techniques are inevitable. These include biosensor size, temporal/spatial resolution, and absolute value measurement capabilities, all of which must be considered to fit the prospective researcher's needs. In this review, we summarize currently available methods for the measurement of serotonin, including novel voltammetric absolute value measurement techniques. We also detail serotonin's role in various neuropsychiatric conditions, highlighting the role of phasic and tonic serotonergic neuronal firing within each where relevant. Lastly, we briefly review the present clinical application of these techniques and discuss the potential of a closed-loop monitoring and neuromodulation system utilizing deep brain stimulation (DBS).

International Round Robin Test of Thermoelectric Generator Modules.

The status of metrology for the characterization of thermoelectric generator modules (TEM) is investigated in this work by an international round robin (RR) test including twelve laboratories from nine countries on three continents. Measurements have been performed with three samples of a Bi2Te3-based commercial TEM type, which has prevailed over three competing types during previous tests on the short- and long-term stability. A comparison of temperature-dependent results is provided up to 200 °C hot side temperature for the maximum power output Pmax, the incident heat flow (at maximum efficiency conditions), and the maximum efficiency ηmax. Data evaluation from all RR participants reveals maximum standard deviations for these measurands of 27.2% (Pmax), 59.2% (), and 25.9% (ηmax). A comparison between RR data sets and reference data from manufacturer specifications shows high deviations of up to 46%, too. These deviations reflect the absence of measurement guidelines and reference samples and confirm the need for improvements in the standardization of TEM metrology. Accordingly, the results of the RR are presented against the background of our own investigations on the uncertainty budgets for the determination of the abovementioned TEM properties using inhouse-developed characterization facilities, which comprise reference and absolute measurement techniques for the determination of heat flow.

National Standard and New Reference Material for Specific Heat Capacity Measurements.

Thermal analysis and calorimetry share a close relationship in the field of thermal research. With regards to the specific heat capacity, researchers have been able to realize absolute measurement techniques by utilizing drop, conduction, and adiabatic methods that are used in calorimetry. Furthermore, it is possible to optimize differential scanning calorimetry, which is a comparative measurement technique for the specific heat capacity used in thermal analysis, by improving the absolute measurement techniques. At the National Metrology Institute of Japan (NMIJ), we developed a new certified reference material (CRM) for comparatively measuring the specific heat capacity, the single-crystalline silicon-NMIJ CRM 5806a, using a new type of cryogenic adiabatic calorimeter equipped with a pulse-tube refrigerator working in the temperature range from 50 to 350 K. This CRM was produced in accordance with the quality specifications of NMIJ, and complies with the ISO/IEC 17025, ISO 17034, and ISO GUIDE 35 standards. This paper reports on the procedure for fabricating this CRM and using it to perform specific heat capacity measurements at low temperatures. The specific heat capacity was measured using a differential scanning calorimeter in the temperature range from 280 to 340 K. NMIJ CRM 5806a was used to calibrate the heat flow. It was found that the uncertainty evaluation became easier because one factor of the uncertainty evaluation could be removed using the CRM. We show that the development of the CRM using the adiabatic calorimeter has led to an improvement in the specific heat capacity measurement results obtained by the differential scanning calorimeter.

Multiwavelength Frequency Modulated CW Ladar: The Effect of Refractive Index

Frequency modulated continuous wave (FMCW) laser detection and ranging is a technique for absolute distance measurements with high performances in terms of resolution, non-ambiguity range, accuracy and fast detection. It is based on a simple experimental setup, thus resulting in cost restraint with potential wide spread, not only limited to research institutions. The technique has been widely studied and improved both in terms of experimental setup by absolute reference or active stabilization and in terms of data analysis. Very recently a multi-wavelength approach has been exploited, demonstrating high precision and non ambiguity range. The variability of refractive index along the path was not taken into account with consequent degradation of range accuracy. In this work we developed a simple model able to take into account refractive index effect in multi-wavelength FMCW measurement. We performed a numerical simulation in different atmospheric conditions of temperature, pressure, humidity and CO2 concentration showing a net improvement of range accuracy when refractive index modeling is used.

Precision improvement in frequency scanning interferometry based on suppression of the magnification effect

Frequency scanning interferometry (FSI) is a promising technique for absolute distance measurement and has been demonstrated in many industrial applications. However, in practice, the measurement precision is limited and sensitive to the variations of the measured distance while sweeping the optical frequency of the laser. The induced errors would be amplified by hundreds of times due to the magnification effect. In this paper, an incremental interferometer was established on the basic scheme of the FSI system for monitoring the variations of distance. The compensation could be achieved by multiplying the heterodyne signals from monitor and measurement interferometer without complex and time-costing data processing. The system performance has been verified by experiments for different kinds of vibrating targets. Finally, after compensation by suppression of the magnification effects, a measurement precision of 4.26 μm has been achieved in a range of 10 m.

High-precision frequency sweeping interferometry for absolute distance measurement using a tunable laser with sweeping range of 88 GHz

Distance measurement using frequency sweeping interferometry is an absolute distance measurement technique that allows for high accuracy over long distances. Notwithstanding, the measurement accuracy is affected by laser sweeping nonlinearity and limited sweeping range. In this work, an optimized post-processing linearization method is demonstrated to realize high-accuracy arbitrary distance measurement using a laser with small modulation range. The interference signal is sparsely resampled to eliminate the influence of the sweeping nonlinearity, and the absolute distance is obtained by analyzing the phase of the resampled signal. In the measurement system, a high-finesse Fabry–Pérot cavity placed in vacuum is used as the measurement reference, so the effect of dispersion mismatch is negligible. Moreover, the distance measurement result is determined by the linear fit of the phase of each resampled point. Therefore, the influence of target vibration and other external random noise can be partially eliminated, and the reliability of the result is high. In the experiment, the sweeping range of the laser source is only 88 GHz. Comparing with a fringe-counting interferometer, the standard deviation of the residual errors is 34 µm within a distance of 6.7 m.

Peak Detection Based on FPGA Using Quasi-Newton Optimization Method for Femtosecond Laser Ranging

Dual femtosecond laser ranging (DFLR) is an enabling absolute distance measurement technique which is advantageous of high measurement precision, fast update rate, and large unambiguous range. Peak detection, which requires repeated online solution of nonlinear curve fitting, is a key module of the DFLR system and its performance affects the accuracy and real-time of the ranging system. In addition, for long baseline measurements based on satellite-borne platforms, the DFLR system has requirements in high integration, low cost, and small size. This paper presents a peak detection implementation on a field-programmable gate array (FPGA) that employs a Broyden-Fletcher-Goldfarb-Shanno (BFGS) method to handle nonlinear curve fitting. FPGA is used to explore the possibilities of parallel architecture for the acceleration of peak detection, and realize the miniaturization of the system. The detailed architecture design of the peak detection module using BFGS method (PD-BFGS) and two hardware structures are proposed. Then, the PD-BFGS module is applied to a DFLR system and evaluated with experiments on the absolute distance measurement. The experimental results indicate that the PD-BFGS based on FPGA effectively reduces the peak detection error by 42.81%, compared with the peak detection module using Caruana's method. For the DFLR system, the ranging error is reduced by 63.63% and the real-time updating of the ranging results is guaranteed.

Using quantum entangled photons to measure the absolute photon detection efficiency of a multi-pixel SiPM array

Spontaneous parametric down-conversion (SPDC) of a visible pump photon is the generation of two less energetic, quantum entangled photons (QEPs), often in the near infrared (NIR), using a non-linear crystal e.g. beta barium borate. Since the detection of one QEP predicates the existence of its entangled twin, QEPs have previously been used to measure the absolute photon detection efficiency (PDE), η(λ), of a detector under test by measuring time-coincident events with an additional trigger detector, allowing evaluation of ηDUT(λ) without recourse to a calibrated reference detector. In this paper, the QEP absolute PDE measurement technique is outlined, and an extension of this technique is proposed to measure η(λ) for pixels on a multi-pixel array where each pixel provides an individual signal output. By treating all pixels in a multi-pixel array as indistinguishable, Monte Carlo simulations show that the symmetry of the measurement allows η(λ) to be determined for each pixel. A route towards experimental measurements using this technique with a 64-pixel SiPM array combined with a 64-channel waveform digitiser module is outlined.

Measurement of thermal conductivity of Li2TiO3 pebble bed by laser flash method

In order to verify the performance and safety of the solid-type breeding blanket concept, the thermal conductivity of the pebble bed is required as an essential parameter for design and analysis of the blanket. The hot wire, hot disk, guarded hot plate, and laser flash method are considered as measurement technique for the thermal conductivity of pebble bed. This study aims at the provision of the thermal conductivity of Li2TiO3 pebble bed, which is one of the candidates for tritium breeder material in the solid-type breeding blanket. The laser flash method was adopted due to its advantages compared with other methods, such as high accuracy and repeatability, easy sample preparation, absolute measurement technique, and so on. In this method, the thermal diffusivity is directly measured by the laser flash system, and then the thermal conductivity is obtained by multiplying density and specific heat to the measured thermal diffusivity. The thermal conductivity of the Li2TiO3 pebble bed with packing factor of 57% increased with increasing temperature up to 500 °C and was saturated to 1.3 W/m/K at more than 500 °C.

A New Precision Spectroscopy Based Method for Boltzmann Constant Determination and Primary Thermometry.

We propose a new independent thermometry method, line strength ratio thermometry (LRT), based on optical spectroscopy measurement of the line strength intensity ratio R between pairs of molecular transitions. Due to strong dependence of R on kT, a given measurement uncertainty δR for R reflects in a small uncertainty of kT determination. By assuming experimental uncertainties of R and T to be those reported in literature, we foresee a k determination at the 5 ppm level, which is better than the most precise k determination by using Doppler broadening thermometry (DBT). In the frame of a new definition of the SI Kelvin unit, based on k as fixed constant, once the k constant is exactly established, LRT is proposed as a high resolution noncontact thermometry technique for absolute temperature measurements of gas samples at the ppm level.

Exposing all the decay paths of 152Eu and their probabilities

Checking the 152Eu 13-year very complex decay scheme, the aim of this paper is the identification, followed by a graphical presentation of all its decay paths and their probabilities, based on the information about particles, emitted energies and probabilities. The decay path followed in the course of the decay process is defined by the cascade transitions from the parent ground state to the daughter ground state. They are 74 paths to the 152Gd ground state and 285 to 152Sm, totalizing 359 cascades. As the decay path is seen as a time-series, the probability to follow this path, calculated here by an excel spreadsheet, can simply be seen as a product of transition probabilities. All such data is necessary for the accurate primary standardization of 152Eu solution through methods as the CIEMAT/NIST for liquid scintillation counting or even the sum peak method, an absolute measurement technique used for activity standardization by gamma-ray spectrometry techniques. The idea is to expose and highlight the difficulties arising from the complexity of such decay, meeting the needs of a didactic presentation to the user community not specifically available in the literature.

Absolute standardization of the 133Ba by sum-peak method and comparison with other methods

This paper presents the absolute standardization of 133Ba by sum-peak method. 133Ba owns a complex decay and was used the sum coincidences between the average energy of characteristic X-rays (kα1 and kα2) and gamma-rays. The activity results presented uncertainty values below 0.3 % and were compared with those of other absolute activity measurement techniques. The results obtained are compared with other methods and confirm that this is an alternative, fast and efficient method for 133Ba standardization.

Measurement of the absolute neutron beam polarization from a supermirror polarizer and the absolute efficiency of a neutron spin rotator for the NPDGamma experiment using a polarized 3He neutron spin-filter

Accurately measuring the neutron beam polarization of a high flux, large area neutron beam is necessary for many neutron physics experiments. The Fundamental Neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS) is a pulsed neutron beam that was polarized with a supermirror polarizer for the NPDGamma experiment. The polarized neutron beam had a flux of ∼109 neutrons per second per cm2 and a cross sectional area of 10 × 12 cm2. The polarization of this neutron beam and the efficiency of a RF neutron spin rotator installed downstream on this beam were measured by neutron transmission through a polarized 3He neutron spin-filter. The pulsed nature of the SNS enabled us to employ an absolute measurement technique for both quantities which does not depend on accurate knowledge of the phase space of the neutron beam or the 3He polarization in the spin filter and is therefore of interest for any experiments on slow neutron beams from pulsed neutron sources which require knowledge of the absolute value of the neutron polarization. The polarization and spin-reversal efficiency measured in this work were done for the NPDGamma experiment, which measures the parity violating γ-ray angular distribution asymmetry with respect to the neutron spin direction in the capture of polarized neutrons on protons. The experimental technique, results, systematic effects, and applications to neutron capture targets are discussed.

Design and performance of spectroscopic filter of rotational Raman temperature lidar for absolute measurement

Rotational Raman temperature lidar for absolute measurement is an important method to directly detect the atmospheric temperature profile by using active remote sensing technology. Compared with the rotational Raman temperature relative measurement, the absolute measurement can avoid the systematic error caused by the calibration process, but its high-precision requirements of rotational Raman spectroscopic filter restrict the development of absolute measurement technique for atmosphere temperature. In order to achieve the absolute measurement technique of rotational Raman temperature lidar, the fine resolution of single rotational Raman line and the effective suppression 60-70 dB for the elastic scattering signal are the key factors for directly retrieving the atmospheric temperature by using the relationship between the single rotational Raman line and temperature. Based on the operational principle of grating, a two-stage parallel multi-channel Raman spectroscopic filter with one-order blazed grating and fiber Bragg grating is designed, and the parameters and optical path structure of the core cascade device (micron-level fiber array) are optimized. The optical path of the primary spectroscope is simulated, the wavelength difference between the rotational Raman lines of adjacent even rotational quantum numbers of nitrogen molecule (N2) gradually decreases from 0.4506 nm to 0.4475 nm. Compared with the average of approximately 0.4494 nm, its floating interval is -0.0012-+0.0019 nm, and the maximum centrifugal distortion of the rotational Raman spectra is approximately 0.0031 nm, which means that the centrifugal distortion ratio is 0.69%. Under the different values of incident angle , the diffraction position difference between adjacent rotational Raman lines varies from 124.43 m to 125.51 m, with a variation interval of -0.57-+0.51 m compared with a fixed value of 125 m. In order to test the matching consistency between rotational Raman spectra and the multi-channel fiber array, and to obtain the out-of-band suppression and channel coefficient of each fiber channel, an experimental system which consists of a first-order blazed grating, a convex lens and a fiber array is set up, and the atmospheric echo signal is simulated by using a broadband light-source and a semiconductor laser (LD). The experimental results show that the channel coefficient of the rotational Raman channels of the primary spectroscope is above 0.75, and the maximum deviation between the measured wavelength of extracted spectrum and the theoretical value is approximately 0.0398 nm, which means the the deviation degree is 8.86%. Each channel can provide more than 27 dB effective suppression to elastic scattering signal, and then by combining with the second spectroscope of fiber Bragg grating, the suppression at least is up to 62 dB. Therefore we can fine extract single rotational Raman line of even rotational quantum number.

A High-Isolation Two-Port Planar Antenna System for Communication and Radar Applications

This paper presents a novel approach to achieve a very high level of isolation between the two ports of a compact antenna system for communication and radar applications. Orthogonal polarization and a special symmetric arrangement of two-element arrays of transmitter and receiver antennas are used to achieve high isolation levels. Identical rectangular patch antennas are designed for operation at 6 GHz, and are arranged in a square grid configuration with 90° rotational symmetry in this design. A pair of transmitters and a pair of receivers are fed perfectly out of phase with 180° couplers. The entire system is simulated and fabricated. We measure the prototype antenna’s isolation, and use the absolute gain measurement technique and standard far field antenna pattern measurement technique to characterize it’s realized gain and radiation pattern. It is found that exploiting symmetry in this manner leads to isolation of 63.7 dB. This indicates that carefully designed and constructed systems could reasonably exhibit isolation on the order of 70 dB or more using this method.

Application of the sum-peak method to activity standardizations of 152Eu sources in LNMRI (BR)

The sum-peak method, an absolute measurement technique that uses coincidence counting and γ-ray spectrometry, was applied to activity standardization of 152Eu sources. The decay branch used was that of 152Sm, as it is almost entirely electron capture and exhibits X-rays with a high probability of coincidence with the 121.8keVgamma rays, as evidenced by the matrix technique used for complex decay schemes, a method for deriving counting rate equations describing coincidence summing of gamma and X-rays. The result was compared with the calibration performed by ionization chamber traceable to BIPM. The results presented uncertainty values of 0.50% (k = 1).

O problema de seleção de portfólio de projetos de pesquisa em instituições de ensino: um estudo de caso

Resumo: Este estudo propõe um modelo para apoiar o processo decisório na seleção de propostas de projetos de pesquisa científica em uma instituição de ensino e pesquisa. Na construção do modelo foi utilizado o método Analytic Hierarchy Process (AHP), combinando técnicas de mensuração relativa e absoluta. Tal combinação tornou possível tratar um grande número de projetos e mensurar, mais facilmente, todas as variáveis do problema de seleção. Como procedimento de pesquisa utilizou-se o estudo de caso, baseando-se em pesquisa exploratória, seguida de uma abordagem de modelagem quantitativa. Adicionalmente, empregaram-se pesquisa documental e entrevistas não estruturadas, a fim de compreender melhor o contexto da pesquisa e os objetivos institucionais e propor adaptações mais consistentes nos critérios de seleção de projetos de solicitação de bolsas e recursos para pesquisa na instituição. Este estudo contribui para a escolha de propostas de projetos de pesquisa mais aderentes aos objetivos institucionais, permitindo que gestores de instituições de ensino lidem com o problema de alocação de recursos limitados face o grande número de demandantes de projetos.

Multi-terahertz frequency sweeps for high-resolution, frequency-modulated continuous wave ladar using a distributed feedback laser array.

Swept-wavelength reflectometry is an absolute distance measurement technique with significant sensitivity and detector bandwidth advantages over normal pulsed, time-of-flight methods. Although several tunable laser sources exist, many exhibit short coherence lengths or require mechanical tuning components. Semiconductor distributed feedback laser diodes (DFBs) are advantageous as a swept source because they exhibit a narrow instantaneous linewidth and can be frequency-swept simply via a single injection current. Here, we present a novel bandwidth generation technique that uses a compact, monolithic, 12-element DFB array to create an effectively continuous, gap-free sweep. Each DFB is sequentially swept over 3.5 nm at 1,600 THz/s using a shaped current pulse, ensuring spectral overlap between each element. After combining the self-heterodyned return signatures, the transform-limited resolution of the 43.6 nm sweep is demonstrated to be ~27.4 μm in air with a precision of 0.18 μm at a distance of 1.4 m.

Pixel-by-pixel absolute phase retrieval using three phase-shifted fringe patterns without markers

This paper presents a method that can recover absolute phase pixel by pixel without embedding markers on three phase-shifted fringe patterns, acquiring additional images, or introducing additional hardware component(s). The proposed three-dimensional (3D) absolute shape measurement technique includes the following major steps: (1) segment the measured object into different regions using rough priori knowledge of surface geometry; (2) artificially create phase maps at different z planes using geometric constraints of structured light system; (3) unwrap the phase pixel by pixel for each region by properly referring to the artificially created phase map; and (4) merge unwrapped phases from all regions into a complete absolute phase map for 3D reconstruction. We demonstrate that conventional three-step phase-shifted fringe patterns can be used to create absolute phase map pixel by pixel even for large depth range objects. We have successfully implemented our proposed computational framework to achieve absolute 3D shape measurement at 40Hz.