A fast LED calibration method under near field lighting based on photometric stereo

Two compact resonant near-field sensors are introduced for the characterization of aqueous solutions at 5 GHz. They are based on folded substrate-integrate circular half-mode resonators with a planar sensing tip. Owing to the planar design, the sensor is simple and cheap to manufacture, and a sample can be easily coupled to the resonator from the top. The operating principle of the sensor is explained and verified by both simulation and measurement. The radiation of the sensors is quantified by means of a quality factor analysis. Finally, a previously introduced calibration method based on the perturbation theory is applied to the sensors and its accuracy is improved by choosing more suitable reference materials.

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A Geometric Calibration Method of Hydrophone Array Based on Maximum Likelihood Estimation with Sources in Near Field

Journal of Marine Science and Engineering ◽

10.3390/jmse8090678 ◽

2020 ◽

Vol 8 (9) ◽

pp. 678

Author(s):

Nan Zou ◽

Zhenqi Jia ◽

Jin Fu ◽

Jia Feng ◽

Mengqi Liu

Keyword(s):

Maximum Likelihood ◽

Maximum Likelihood Estimation ◽

Signal To Noise Ratio ◽

Near Field ◽

Likelihood Estimation ◽

Calibration Method ◽

Optimization Method ◽

High Signal ◽

Geometric Calibration ◽

Environment Experiment

Considering the requirement of the near-field calibration under strong underwater multipath condition, a high-precision geometric calibration method based on maximum likelihood estimation is proposed. It can be used as both auxiliary-calibration and self-calibration. According to the near-field geometry error model, the objective function of nonlinear optimization problem is constructed by using the unconditional maximum likelihood estimator. The influence of multipath on geometric calibration is studied. The strong reflections are considered as the coherent sources, and the compensation strategy for auxiliary-calibration is realized. The optimization method (differential evolution, DE) is used to solve the geometry errors and sources’ position. The method in this paper is compared with the eigenvector method. The simulation results show that the method in this paper is more accurate than the eigenvector method especially under high signal-to-noise ratio (SNR) and multipath environment. Experiment results further verify the effectiveness.

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Measurements of Interferometer Parameters at Reception of GLONASS and GPS Signals

Latvian Journal of Physics and Technical Sciences ◽

10.1515/lpts-2016-0033 ◽

2016 ◽

Vol 53 (5) ◽

pp. 24-30

Author(s):

M. Nechaeva ◽

D. Adamchik ◽

Vl. Bezrukovs ◽

N. Dugin ◽

I. Shmeld ◽

...

Keyword(s):

Measurement Errors ◽

Near Field ◽

Calibration Method ◽

Effective Area ◽

Radio Telescopes ◽

Gps Navigation ◽

Correlation Interferometer ◽

Accuracy Of Results

Abstract The present paper deals with the calibration method of interferometers with antennas having a small effective area, on the quasinoise signals of GLONASS and GPS navigation satellites. Algorithms for calculation of antenna coordinates and instrumental delay from the analysis of correlation interferometer response to signals of satellites in the near field of the instrument were reviewed. The method was tested in VLBI experiments on interferometers with medium and large baselines that included radio telescopes of NIRFI and VIRAC. The values of the antenna coordinates and instrumental delay with an error within the limits of one discrete were obtained. The sources of measurement errors and ways to improve the accuracy of results were analysed.

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