scholarly journals External Modulation Optical Coherent Domain Reflectometry with Long Measurement Range

Sensors ◽  
2021 ◽  
Vol 21 (16) ◽  
pp. 5510
Author(s):  
Yinghong Xue ◽  
Yueping Niu ◽  
Shangqing Gong
Keyword(s):  
Spatial Resolution ◽  
Frequency Modulation ◽  
Probe Pulse ◽  
High Spatial Resolution ◽  
Single Point ◽  
Measurement Range ◽  
Measuring Time ◽  
Linear Frequency ◽  
External Modulation ◽  
Coherent Domain

Optical coherent domain reflectometry (OCDR) can achieve a high spatial resolution that is independent of the bandwidth of the receiver, but the measurement range is usually very limited. Here we propose an external modulation OCDR system, in which a pair of linear frequency-modulated pulses generated by one modulator are employed as the probe pulse and the reference, respectively. The spatial resolution is determined by the frequency modulation range of the pulse, and the measurement speed is boosted by orders because the proposed technology can simultaneously diagnose a section of fiber with each pair of pulses, while only a single point can be accessed at a time in typical OCDR. In the demonstrational experiment, a measurement range of up to 50 km is achieved with a spatial resolution of 1.4 m and a measuring time of less than 30 s.

scholarly journals TLS and GB-RAR Measurements of Vibration Frequencies and Oscillation Amplitudes of Tall Structures: An Application to Wind Towers

2020 ◽  
Vol 10 (7) ◽  
pp. 2237 ◽  
Author(s):  
Serena Artese ◽  
Giovanni Nico
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Single Point ◽  
Sampling Rate ◽  
Oscillation Amplitude ◽  
Oscillation Mode ◽  
Longitudinal Section ◽  
Vibration Frequencies ◽  
Tall Structures ◽  
Oscillation Modes

This article presents a methodology for the monitoring of tall structures based on the joint use of a terrestrial laser scanner (TLS), configured in line scanner mode, and a ground-based real aperture radar (GB-RAR) interferometer. The methodology provides both natural frequencies and oscillation amplitudes of tall structures. Acquisitions of the surface of the tall structure are performed by the TLS with a high sampling rate: each line scan provides an instantaneous longitudinal section. By interpolating the points of each line, oscillation profiles are estimated with a much better precision than each single point. The amplitude and frequency of the main oscillation mode of the whole structure are derived from the TLS profiles. GB-RAR measurements are used to measure the vibration frequencies of higher oscillation modes which are not caught by the TLS due its lower precision in the measurement of displacements. In contrast, the high spatial resolution of TLS measurements provides an accurate description of oscillation amplitude along the tower, which cannot be caught by the GB-RAR, due to its poorer spatial resolution. TLS and GB-RAR acquisitions are simultaneous. The comparison with the analytical solution for oscillation modes demonstrates that the proposed methodology can provide useful information for structural health monitoring (SHM). The methodology does not require the use of targets on the structure and it can be applied during its normal use, even in presence of dynamic loads (wind, traffic vibrations, etc.). A test was carried out on a wind tower where the synergistic use of TLS and GB-RAR made it possible to fully describe the spectral properties of the tower and at the same time measure the amplitude of the first oscillation mode along the tower with a high spatial resolution.

scholarly journals Echo-based Single Point Imaging (ESPI): A novel pulsed EPR imaging modality for high spatial resolution and quantitative oximetry

2012 ◽  
Vol 218 ◽  
pp. 105-114 ◽  
Author(s):  
Sankaran Subramanian ◽  
Nallathamby Devasahayam ◽  
Shingo Matsumoto ◽  
Keita Saito ◽  
James B. Mitchell ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Imaging Modality ◽  
Single Point ◽  
Pulsed Epr

scholarly journals Ka Band Holographic Imaging System Based on Linear Frequency Modulation Radar

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6527
Author(s):  
Yang Meng ◽  
Chuan Lin ◽  
Jiefeng Zang ◽  
Anyong Qing ◽  
Natalia K. Nikolova
Keyword(s):  
Spatial Resolution ◽  
Frequency Modulation ◽  
Imaging System ◽  
Low Cost ◽  
Three Dimensional ◽  
Reconstruction Algorithm ◽  
Linear Frequency Modulation ◽  
Planar System ◽  
Ka Band ◽  
Linear Frequency

Millimeter wave (MMW) technology is expanding rapidly into security screening for dangerous items concealed under clothing. It uses safe non-ionizing radiation and penetrates clothing well. We present a new planar system at Ka band for the three-dimensional simultaneous imaging of both sides of an inspected person where the images are produced in real time by a recently proposed generalized holographic reconstruction algorithm. Low-cost linear frequency modulation (LFM) radar technology is used along with a simple but efficient method for system calibration. Experimental characterization of the spatial resolution and the sensitivity of the system prototype has been carried out. It is established that the achieved spatial resolution is 6 mm or better if the item is not obscured by clothing and it may deteriorate to 7 mm depending on the clothing hiding the item. The spatial sensitivity is confirmed to be at least 2 mm.

High spatial resolution AEM observations of yttrium segregation in chromia scales grown on Co-45%Cr

1986 ◽  
Vol 44 ◽  
pp. 518-519
Author(s):  
K. Przybylski ◽  
A. J. Garratt-Reed ◽  
G. J. Yurek
Keyword(s):  
Spatial Resolution ◽  
Outer Surface ◽  
Maximum Concentration ◽  
High Spatial Resolution ◽  
Reactive Elements ◽  
Chromia Scales

The addition of so-called “reactive” elements such as yttrium to alloys is known to enhance the protective nature of Cr2O3 or Al2O3 scales. However, the mechanism by which this enhancement is achieved remains unclear. An A.E.M. study has been performed of scales grown at 1000°C for 25 hr. in pure O2 on Co-45%Cr implanted at 70 keV with 2x1016 atoms/cm2 of yttrium. In the unoxidized alloys it was calculated that the maximum concentration of Y was 13.9 wt% at a depth of about 17 nm. SIMS results showed that in the scale the yttrium remained near the outer surface.

Integration of Core-Edge Spectroscopy Methods for the Study of Polymers

1996 ◽  
Vol 54 ◽  
pp. 154-155
Author(s):  
E. G. Rightor
Keyword(s):  
Excited State ◽  
Polymer Blends ◽  
Gas Phase ◽  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Electronic States ◽  
Core Electron ◽  
Bulk Solids ◽  
Development Application

Core edge spectroscopy methods are versatile tools for investigating a wide variety of materials. They can be used to probe the electronic states of materials in bulk solids, on surfaces, or in the gas phase. This family of methods involves promoting an inner shell (core) electron to an excited state and recording either the primary excitation or secondary decay of the excited state. The techniques are complimentary and have different strengths and limitations for studying challenging aspects of materials. The need to identify components in polymers or polymer blends at high spatial resolution has driven development, application, and integration of results from several of these methods.

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