We describe an improved two-dimensional optical scanning technique combined with an ultrafast Sagnac interferometer for delayed-probe imaging of surface wave propagation. We demonstrate the operation of this system, which involves the use of a single focusing objective, by monitoring surface acoustic wave propagation on opaque substrates with picosecond temporal and micron lateral resolutions. An improvement in the lateral resolution by a factor of 3 is achieved in comparison with previous setups for similar samples.

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Scanning ultrafast Sagnac interferometry for imaging two-dimensional surface wave propagation

Fiber Optic Smart Structures

The automation and intellectualization of the manufacturing processes in the iron and steel industry needs the strong support of inspection technologies, which play an important role in the field of quality control. At present, visual inspection technology based on image processing has an absolute advantage because of its intuitive nature, convenience, and efficiency. A major breakthrough in this field can be achieved if sufficient research regarding visual inspection technologies is undertaken. Therefore, the purpose of this article is to study the latest developments in steel inspection relating to the detected object, system hardware, and system software, existing problems of current inspection technologies, and future research directions. The paper mainly focuses on the research status and trends of inspection technology. The network framework based on deep learning provides space for the development of end-to-end mode inspection technology, which would greatly promote the implementation of intelligent manufacturing.

https://www.mdpi.com/2076-3417/8/11/2195/pdf

Research Progress of Visual Inspection Technology of Steel Products—A Review

trains, ~~i~t~~n~~t~ilcs , and aircraft. I-IOWcvcr, ceceiit advances wciulcl allow tlic building in an carthqunkc to respond ta tlic forces appiicd to riiitigatc the cffcct of the earthquake on tlic striictiirc. Thc author hegins by dcfiiiiiig “siii;irt” structures and iiiaterials tlien clescribcs instruinciitcil riiarerinls and various sciising tccliiioiogies. The insjority of the book covers how film optic sciisors are uscrl for meiisuriiig pliysicd, thcrinnl, chcrnical, nnd 1hcIieiiiic;il quantities. A clxipier (>I) actiiator ucclin iqiies iuci udcs piuoelcc t r ic mite I: i als, clcctrartieological fluids, clcctrascrictivc tnntci:ials, magnctostrictivc materials, elcctroinagiietic actuation, hydraulics, atid shape inerrlory alloys. Two chapters COVCI’ signal processing, concrol, and applications for “smiirt” structures. Thc filial two chapters deal with the fiitwc of ‘‘uimrt” iiiaterials xud a descriptioii of “si~iart” mnterials. Althougli v;iguc, the authors clescription til truly L‘sitinrt” tua

Smart Structures and Materials

https://orbit.dtu.dk/files/126890142/Tilted_Sensor.pdf

Method for independent strain and temperature measurement in polymeric tensile test specimen using embedded FBG sensors

This paper describes a fiber optic sensor suitable for noncontact detection of ultrasonic waves. This sensor is based on the fiber optic Sagnac interferometer, which has a path-matched configuration and does not require active stabilization. Quadrature phase bias between two interfering laser beams in the Sagnac loop is applied by controlling the birefringence using a fiber polarization controller. A stable quadrature phase bias can be confirmed by observing the interferometer output according to the change of phase bias. Additional signal processing is not needed for the detection of ultrasonic waves using the Sagnac interferometer. Ultrasonic oscillations produced by conventional ultrasonic piezoelectric transducers were successfully detected, and the performance of this interferometer was investigated by a power spectrum analysis of the output signal. Based on the validation of the fiber optic Sagnac interferometer, noncontact detection of laser-generated surface waves was performed. The configured Sagnac interferometer is very effective for the detection of small displacement with high frequency, such as ultrasonic waves used in conventional nondestructive testing (NDT).

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer

The present invention is effective in that automatically corrected temperature can be measured using one light source and one optical detector.

Optic fiber distributed temperature sensor system with self-correction function and temperature measuring method using thereof

A temperature-compensating fiber Bragg grating(FBG) sensor having two different FBGs in one fiber line was applied to the real time measurement of mechanical normal strain in structures. Measurement of mechanical strains of the aluminum beam surface by the double FBG sensor was performed under various thermal conditions, which was compared with results of electrical resistance strain gage. The FBG sensor fabricated in this study could detect accurately values of mechanical strains without containing any thermal strain component.

Application of a Temperature-Compensating FBG Sensor to Strain Measurement

Smart structures needs lots of sensor installation to sense their status and also the external environmental change. Wireless technique can give a good solution to install sensors without heavy cables. So, in this work, a wireless device was developed to transmit static strain and elastic wave propagation of structures. The specification of this device was as follows: 2.4 GHz of transmitted frequency, 8 channels, 57,600 bps of the transmitted speed, and 10 mW of the transmitted power. In order to confirm the wireless device’s feasibility, a beam test was performed with five optical fiber strain sensors and two piezo-ceramic sensors with the wireless instrumentation.

Wireless Instrumentation for Monitoring of Smart Structures

Smart structures are to be possessed many functions to sense the external effects, such as seismic loads, temperature, and impact by some explosion, influenced on the safety of structures. This work was focused on the development of a sensing function of smart structures to get the temperature distribution on structures to detect fire occurrences. A fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor system was developed to detect the fire occurrence by measuring the temperature distribution of a building’s exterior surfaces. This fiber optic sensor system was constructed with a laser diode and two electro-optic modulators, which made this system faster than systems using only one electro-optic modulator. The temperature distributed on an optical fiber can be measured by this fiber optic BOTDA sensor. An optical fiber, 1400 m in length, was installed on the surface of a building. Using real-time processing of the sensor system, we were able to monitor temperature distribution on the building’s surfaces, and changes in temperature distribution were also measured accurately with this fiber optic sensor.

Il Bum Kwon

Papers

Noncontact detection of ultrasonic waves using fiber optic Sagnac interferometer

Optic fiber distributed temperature sensor system with self-correction function and temperature measuring method using thereof

Application of a Temperature-Compensating FBG Sensor to Strain Measurement

Wireless Instrumentation for Monitoring of Smart Structures

Application of Fiber Optic BOTDA Sensor for Fire Detection in a Building