The photoacoustic sensor system based on Sagnac interference has extensive applications in perimeter security. Among them, the demand for synchronization recognition of multiple acoustic sources and integrated utilization becomes the key to expand its application field. By focusing on multi-source synchronization recognition, a lightweight optical-acoustic signal recognition algorithm that can be carried by an embedded system was studied. The collected optical-acoustic signals were extracted through preprocessing, Fast Fourier Transform (FFT), Mel filter bank (MFB), and other steps to obtain Mel spectrogram features, which were then used for optical-acoustic signal recognition using the MobilenetV3 network. The experimental results showed that this system achieved a synchronization recognition rate of 93% for six types of sounds, providing a possibility for implementing multi-sound recognition in embedded systems based on Sagnac interference photoacoustic sensor systems.
Fiber optic acoustic sensing system based on Sagnac interference is widely used in the field of perimeter security. However, the sensitivity of acoustic response varies drastically with frequency, which has become a bottleneck limiting the development of Sagnac photoacoustic sensing technology. An elastic structure is proposed to improve the sensitivity consistency of the photoacoustic sensing system based on Sagnac interference at different frequencies. The elastic structure of optical fiber pickup was optimized by finite element analysis, Solidworks and Comsol. Simulation results show that the designed titanium alloy-based elastomeric structure with a diameter of 110 mm, a height of 100 mm, and an elastomer wall thickness of 3 mm has significantly improved the consistency of the sensitivity of the acoustic response at different frequencies. This work provides a possibility for the application scenario expansion of photoacoustic sensing system based on Sagnac interference.
We propose an infrared biosensor for nanofluidic analysis based on graphene plasmonics, which consists of a nanochannel etching on a silicon substrate and a graphene sheet covered on the top of the channel. The change of refractive index due to the absorption of biomolecules in the nanochannel can be measured by detecting the wavelength shifts of resonant dips. To achieve the best optical performances of the biosensor, an optical model based on finite element method is built to optimize the structure parameters of the biosensor. Numerical simulation results show that a biosensor with a larger top width and a higher depth shows a better overall performance and a high sensitivity value of up to 1920nm/RIU can be achieved in an optimized structure. In addition, the biosensor can dynamically work at a wide range of infrared region by adjusting the Fermi level of graphene. Graphene is pre-coated with poly methyl methacrylate to overcome the effect that the portion of graphene over the nanochannel will be strained and the influence of the thickness of this coated layer on the performances of biosensor is very small. The designed graphene plasmonics devices will advance further applications of graphene in integrated nanofluidic analysis and infrared biosensors.
In this paper, we study the regular and flexible microstructured silicon theoretically using the Rigorous Coupled
Wave Analysis and Finite Difference Time Domain methods. We calculate the reflective spectra of the conical structures
of three different sizes by using the multi-step approximation. The calculated results show that the smallest 0.5μm
structures have the lowest reflectance. The angle dependence of the reflectance of microstructured silicon is also talked
about. Then the Finite Difference Time Domain method is used to simulate the absorptance of the regular and flexible
microstructured silicon of three different sizes. The simulated results show that the absorptance of flexible
microstructured silicon is a little lower than that of the regular microstructured silicon. At last, The absorption spectrum
of the flexible surface microstructured silicon is as high as 97% in the visible and insensitive to the change of the
incident angle of the light. The calculated results are verified by the measured spectra.
This paper proposes a novel Hadamard Transform near-infrared spectrometer based on MOEMS(Optical
micro-electro-mechanical system ) grating light modulator. A new method that grating light modulator combined with a
single near -infrared detector to detect spectrum is applied. The programmability of the grating light modulator linear
array is used to implement a Hadamard Transform encoding masks. Firstly, optics theory has been used to analyze the
essential principle of the spectrometer and the optical principle of grating light modulator. Then, It is theoretically
proved that the Hadamard Transform near-infrared spectrometer can reconstruct spectrum effectively and have a high
signal noise ratio. Finally, a new structure of the grating light modulator is given. Results of the software simulation
show that 5.5V maximum actuating voltage and 5 kHz response frequency are suitable for a miniature, portable,
cost-efficient spectrometer.
To compensate the measurement error induced by temperature and pressure variation in a tunable diode laser absorption
spectroscopy (TDLAS) system, an online self-calibration technique is introduced. More specifically, a reference gas cell
filled with known proportion target gas is placed on site, surrounded by working gas to be measured. Thereby, the
temperature and pressure inside the reference cell are equal to the gas outside. The TDLAS system acquires the
absorption spectrum of the reference gas cell and the working gas synchronously. And the concentration of the trace gas
in working gas can be easily obtained by calculating the absorption intensity proportion of both absorption spectrums
without considering the affection of temperature and pressure. The principle, design, and experiment of this technique
are presented in this paper.
In this paper, a novel all-fiber band pass filter based on a concatenated structure of multimode fiber, single-mode core
mode blocker and a single-mode long period fiber grating was reported. It can simultaneously serves as a band pass
filter and multimode-single-mode converter for interconnection between multimode fiber and single mode fiber
network. The theoretical analysis, designing, fabrication and experiments result were presented.
The Opto-electronic Technology Lab of Chongqing University (OTLCU) has been working on bridge structural health
monitoring using fiber optic sensors in the past decade. A remote sensing network based on the Extrinsic Fabry-Perot
Interferometer (EFPI) fiber sensor was developed and implemented on several large bridges in Chongqing, China. In this
paper, a brief review of the OTLCU's research progress in this field was presented. Contrastive experiments between the
EFPI strain sensor and the electrical strain patch (ESP) were introduced. Both internal embedding and surface mounting
of the EFPI were studied. The design of the sensing network and two implementation examples were discussed, and
some representative monitoring results were given.
KEYWORDS: Bridges, Probability theory, Information fusion, Data fusion, Artificial neural networks, Associative arrays, Silicon, Information technology, Data modeling, Optoelectronics
As the damage diagnosis of bridge structure is highly nonlinear in nature, it is difficult to develop a comprehensive model taking into account all of the independent variables, such as the structural and environmental properties, using conventional modeling techniques. In this study, a method was introduced for damage diagnosis of bridge structure by integration of BP artificial neural network (ANN) and information fusion based on D-S evidential theory. The basic probability assignment functions for data fusion were constructed according to the demand of the damage diagnosis and the real conditions of the bridge structure. And an application example of the proposed method was demonstrated. The results showed that the integration of the two strategy can remove the shortcoming of BP ANN with remaining of its advantages and promote the identified veracity of the whole diagnosis system.
With decades of research experience on optical sensors, Optoelectronic Technology Lab of Chongqing University (OTLCU) has studied on a variety of sensors system designed for practical use in health monitoring. In OTLCU, embedded and surface mounted fiber Fabry-Perot strain sensor has been developed for monitoring the local strain of both concrete and steel truss bridge. Optoelectronic deflect meter, with a group of optical level sensor in a series connected pipe, was developed for deflection monitoring and line shape monitoring of the bridges. Laser deflect meter, with a laser pointer and a sensors array, has been also developed for a dynamic deflection monitoring of the bridges. To monitoring the 2-Dimentional displacement of the bridge, a self-calibrating imaging system was developed. All these sensor systems have been applied in different bridges successfully. This paper briefly describes principle of these optical sensing systems, and also gives some representative results of the system in practical application of bridges.
In order to demodulate frequency division multiplexed optical fiber Fabry-Perot sensors with high accuracy and absolute cavity length, an improved cross-correlation method was presented. As the applying of a special correlating factor in it, the cross correlation function at every sensor's cavity length is a single peak and multiplexed sensors that cavity length is close to each other can be easily distinguished, and segment golden search method was employed to reduce computation and demodulating speed is fast. The multiplexing experiment of two sensors was accomplished with the help of general demodulating system constituted by broadband light source, spectrometer etc. The results showed that the system can demodulate the frequency division multiplexed signal of optical fiber Fabry-Perot sensors, and the least cavity length difference that can be distinguished among multiplexed sensors is less than 6μm and fluctuation of the cavity length is less than 0.073%.
In this paper, the grating light valve (GLV) is presented. A simple method based on multi-beam of light interference theory is put forward to analyze its optical performance. Computer simulation demonstrates that the dimension of its structure and light source have different influence on the diffractive efficiency. According to detecting system, the diffractive efficiency in the OFF state is about 3.8544x10-16 at the wavelength of 0.66um, about 2.8218x10-16at the wavelength of 0.5145um, 1.7846x10-16at the wavelength of 0.488um, which should ideally be zero. The result indicates that such method applied in the analysis of the GLV is agreeable and simpler. In order to gain higher diffractive efficiency, the air gap should be reduced.
In order to address application problem of fiber optic sensor in concrete, characteristics of concrete was analyzed deeply. Mechanical and metrological characteristics of both bare and packed fiber Fabry-Perot strain sensor were also analyzed in details. Modulus requirement and dimensional requirement of fiber strain sensor for concrete was deduced. A special measure of sleeve was proposed to get rid of drawback of packed fiber Fabry-Perot strain sensor in concrete. Corresponding procedures was also proposed to ensure survivability of the sensors when embedding fiber sensor into a concrete structure. An application example of fiber Fabry-Perot strain sensor network system in the Dafosi Bridge of Yangtze River at Chongqing has been presented to demonstrate the validity of this technique. With help of presented technique, 45 fiber Fabry-Perot strain sensors had been successfully embedded in 5 segments of gird during 9 months construction. The system was put into operation automatically from January 2003. Some typical results recorded by the system were presented. Constructing progress, tardo distortion trend, and temperature dependent fluctuation of gird was revealed in the result.
Dafosi Yangtze River Bridge, completed in August 2001, 1,176 meters long, with the longest main span of 450 meters in Asia in its design period, is one of the key projects of Yu-Qian Expressway and Out-Circle Ring and Round City Highway in Chongqing City. So it is significative to monitor the health of Dafosi Yangtze River Bridge after its completion. A remote health monitoring system is designed for Dafosi Yangtze River Bridge and implemented in the end of 2002. This system includes three subsystems, namely, sensing subsystem, local monitoring subsystem and remote monitoring subsystem. The sensing subsystem can gain the state information of the bridge via sensors, which installed in the key parts of the bridge, such as the fiber-optic strain sensors, the opto-electronic deflection sensors and the temperature sensors. Local sub-system can control all the sensors to collect health information periodically, store and transmit the health data to the remote subsystem via fiber cable. The remote subsystem can analyze and evaluate the health state of this bridge. In this paper, the whole system is introduced, and some monitoring results are presented.
This paper briefly describes a health monitoring system designed for use on the Dafosi Bridge, the largest cable-stayed bridge across the Yangtze River in western China. The system can be divided into two major components, one for measurement, and one for control and data processing. The measurement system itself includes four sensing subsystems relating to: 1) fiber optic strain sensing, 2) displacement sensing, 3) temperature sensing, and 4) dynamic measurements. The control and data processing system consists of three subsystems: 1) a local computer, 2) a communication subsystem, and 3) a host computer. Sensor outputs are pre-processed locally and sent to the host computer at the management center via the Internet. The system design and implementation are reviewed, and the results of data from two sensing subsystems are presented.
This paper presents a remote state monitoring system designed for and installed on the Hongcaofang Crossroad Bridge in Chongqing, China. In this system, three kinds of sensor, one of which is new, are installed in the bridge to periodically collect strain and deflection information. To control the operation of the sensors, a local computer is integrated in the pier of the bridge. The local computer processes the data from sensors, records processed results, and sends the state information to a host computer through the local Public Service Telephone Network (PSTN) using an ordinary modem. At the other terminus, the host computer receives and analyzes the data, stores the history information, queries the health state, and extracts abnormity information regarding the bridge. With the interconnect technology available through the PSTN, real time state information can be obtained on command in the monitoring room far from the bridge. This on-line monitoring system operated on the Hongcaofang Bridge for over two years. This paper reviews some of the more important results regarding both the strain and the two-dimensional deflection of the bridge, and discusses the experience gained thus far.
The development of fiber optic sensors for safety control of civil structures is over viewed in this paper. Main principle of fiber optic sensors such as Fiber Bragg Grating sensors, fiber F- P sensors and low coherent fiber Michelson interferometer is discussed. Some typical applications of fiber optic sensors in bridges, buildings and etc. are provided. The tendency of fiber optic sensors is forecasted.
An optical waveguide sensing method is proposed for monitoring the corrosion of steel in reinforced concrete structures. The method depends on the absorption of light in the waveguide by a metallic cladding which is applied at a particular location. When this cladding is exposed to a corrosive environment, it degrades, and the optical waveguide output increases. This sensing principle is analyzed, as is an electrochemical method proposed to lay the metal film onto the waveguide. In order to establish a reliable procedure for electroplating an Fe-C alloy film onto fused silica, we first investigated the use of a planar waveguide substrate, and electroless plating of silver onto SiO2 was introduced as the electroplating cathode. After analysis, an optical fiber version of the corrosion sensor was then fabricated using the electrochemical method. The sensor was intensively corroded with HNO3, NSS, and simulated concrete pore solutions. The experimental results are presented and to some degree coincide with theory.
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