Fiber Bragg grating pressure sensor based on multi-hinges three-levers structure

A fiber Bragg grating (FBG) pressure sensor packaged by using a hard core in the membrane is presented. By utilizing the unique membrane‐based FBG packaging method, its pressure sensitivity has been effectively enhanced. The pressure sensitivity of the FBG reaches 5.75 × 10−3/MPa within the pressure range of 0–0.16 Mpa. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1279–1281, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24335

With its unique capabilities, the optical fiber Bragg grating has been used as a key component in the development of many sensors. Incorporating the theory of thin plates, the authors have developed an FBG-based pressure sensor by strategically attaching FBGs on the surface of a thin circular plate. The flexural strain in the circular plate induced by pressure applied to the circular plate is sensed by either a single FBG placed radially crossing a neutral point, or two FBGs placed respectively in zones where the strains are of opposite signs. When one FBG is used (i.e., the chirped FBG design), the applied pressure relates to the change in the chirped bandwidth of the FBG reflected waveform. When two FBGs are used (i.e., the differential FBG design), the pressure experienced by the circular plate is correlated to the difference in central wavelength from the two FBGs. In either case the sensing mechanism is immune to temperature fluctuation. The same configuration can potentially be applied for other purposes such as a load cell or displacement transducer. This paper describes the design principles of the FBG pressure sensor and demonstrates its capabilities through laboratory calibrations over a wide range of temperatures.

Compared to conventional piezoelectric sensors, fiber Bragg grating (FBG) sensors have many advantages. This paper reviews the development of FBG pressure sensor. The features and application scopes of several types of pressure sensors are discussed. We designed a FBG pressure sensor based on a thin-walled cylinder. The relationship between the central wavelength of FBG and the pressure is derived. The experimental pressure sensitivity is 0.079nm/MPa, and the linearity of sensor is 0.999. Through the discussion of fiber properties, compression sensitizing techniques of FBG is proposed.

In this paper, we present fiber Bragg grating pressure sensors written in twin-hole microstructured fibers for high temperature operation above 800 °C. A Ti: Sapphire ultrafast laser is used to inscribe type II grating in two-hole optical fibers. The fiber Bragg grating resonance wavelength shift and peak splits are studied as a function of external hydrostatic pressure from 15 psi to 2000 psi. The ultrafast laser inscribed grating pressure sensor shows stable and reproducible operation above 800 °C. This paper demonstrates highly multiplexible pressure sensor technology for high temperature environment.

A film-type multipoint pressure sensor was developed by using an optical fiber with the Fiber Bragg Grating (FBG), which enable to measure the pressure only by sticking the sensor on a body surface. In this paper, the developed pressure sensor and the pressure measurement system are described. In order to clarify the performance of the FBG pressure sensor, pressure distributions on NACA4412 airfoil model were measured in wind tunnel test. The measured pressure was compared with CFD simulation results and other experiment data. It was found that the pressure variation on the wing surface was well measured by the developed FBG pressure sensor both in positive and negative pressure sides for various attack angles.

We report a novel fiber Bragg grating pressure sensor embedded in carbon fiber reinforced material that is capable of monitoring the foot pressure of diabetic patients.

In order to meet the demand for high-sensitivity pressure detection, this paper proposes a design method for a fiber Bragg grating (FBG) pressure sensor based on a diaphragm-lever composite structure. By constructing a diaphragm deformation-lever displacement amplification mechanism, the pressure sensitivity of the sensor is effectively improved. Firstly, a theoretical model for the transmission of pressure signal-diaphragm deformation displacement-lever displacement amplification-FBG strain wavelength shift is established. The sensor sensitivity is theoretically analyzed through a geometric model, and it is concluded that the theoretical amplification ratio of the diaphragm-lever composite structure is 3.464, with a sensitivity of 84.101 nm/MPa. Then, SolidWorks is used for sensor design and modeling, and the Ansys simulation platform is employed for iterative optimization to determine structural parameters such as grating diameter and length. Finite element analysis is used to simulate and calculate the amplification ratio and sensitivity, yielding a simulated amplification ratio of 3.229 and a sensitivity of 78.091 nm/MPa. These results are highly consistent with the theoretical analysis, verifying the reliability of the theoretical model. Finally, a physical sensor is fabricated according to the optimized structure, and packaging and testing systems are built to complete the characteristic testing of the sensor. Experimental results show that within the range of 0-0.1 MPa, the amplification ratio of the diaphragm-lever composite structure is 2.841, and the pressure sensitivity is 69.042 nm/MPa, which are basically consistent with the theoretical and simulation results. The linearity is 99.9%, and the repeatability error and hysteresis error are 1.160% and 0.623%, respectively.

Real-time monitoring of dynamic liquid-level is very important in oilfield. A novel method combining pressure measurement and temperature profile measurement is proposed in this paper to measure dynamic liquid-level of oil-well in real-time. A fiber Bragg grating pressure sensor based on an eccentric-pushrod structure is used to measure downhole pressure, and the multimode fiber is used to measure temperature profile. The initial position of the dynamic liquid-level can be determined by the inflection point of the temperature profile. The density of the liquid in the well is calculated from the initial pressure and the dynamic liquid-level. Base on this data, the real-time position of the dynamic liquid-level can be obtained only by using the pressure data. Experimental results show that the method that combining pressure measurement and temperature profile measurement can provides real-time and accurate monitoring of oil-well dynamic liquid-level data.

Ultra-long and large-diameter underwater bored piles are widely used in deep-water bridge foundations; however, key construction parameters such as concrete surface elevation and tremie conduit embedment depth are still largely measured manually, resulting in low levels of automation and limited data traceability. Accurate monitoring of these parameters is essential to ensure construction quality and prevent defects such as pile breakage or mud inclusion. This study aims to develop an intelligent monitoring system to achieve real-time and automated measurement of concrete pouring height and conduit embedment depth during underwater pile construction. An integrated intelligent sensing system was developed combining fiber Bragg grating (FBG) pressure sensors, distributed fiber optic temperature sensing (DTS), RFID-based conduit counting, and a PLC-controlled automated monitoring device. Laboratory experiments and field tests were conducted to evaluate the feasibility of fiber optic pressure and temperature sensing for detecting the concrete interface. Laboratory tests demonstrated that fiber optic pressure and temperature sensors can effectively identify the interface between mud, laitance, and concrete during pouring. Field experiments showed that concrete level monitoring based on intelligent sensing achieved an error ranging from 0.25 m to 0.5 m, while dynamic tracking of the concrete surface achieved accuracy within approximately 0.3 m. The system was successfully applied in the Hangzhou Bay Cross-Sea Bridge project, confirming its reliability in engineering practice. The proposed monitoring system significantly improves the automation and informatization of underwater bored pile construction. Compared with traditional manual sounding methods, it provides higher monitoring frequency, improved accuracy, and real-time data transmission through a cloud platform, enabling traceable management of concealed works. The system offers a practical and cost-effective solution for intelligent construction of deep foundations and supports the digital transformation of pile foundation engineering.

Based on super-molecule self-assembly and entropy-driven self-assembly mechanisms, the coupling agent was evolved into colloid spheres with average diameter of 2-2. 3 μm on the fiber Bragg grating (FBG) with silicon substrate, and the coupling mechanism among polymer, coupling agent and FBG was analyzed. The polymer coated FBG pressure sensors was capsulated by uniform coupling mode and self-assembly coupling mode of the coupling agent respectively, and their performance parameters were tested. It was shown, adopting the self-assembly coating of coupling agent and with the same other capsulated technologies, that the measuring range of the sensor expanded from 0.6 MPa to 1.6 MPa, the repeated times for coupling failure increased from 54 to 125 times and the pressure sensitivity coefficient enhanced from 1.09 to 2.98. By controlling the diameter of the spheres and the line density, the measuring range and the sensitivity of the FBG pressure sensors can be obviously improved.

The safety of SCUBA divers remains at high risk in deep-sea owing to multiple factors such as dangerous surrounding, rely upon technical equipment necessary for life support, decreased underwater navigation, and communication infrastructure. Gradual decrease and increase in water temperature and pressure corresponding to depth are among the most common problems that cause most of the fatalities in deep-sea diving. Therefore, different gadgets for accurate measurement of vital parameters, reliable navigation, and seamless communication are of prime importance. In this paper, we propose an all-optical technique for local and remote monitoring of underwater temperature and pressure for deep-sea SCUBA divers based on fiber Bragg grating (FBG) sensors and underwater optical communication-single mode fiber (UWOC-SMF) integrated transmission system. The proposed technique is implemented using two FBG temperature and pressure sensors fixed over diver’s suit and UWOC-SMF integrated transmission system for simultaneous local and remote monitoring of underwater temperature and pressure. Remote monitoring of underwater temperature and pressure is achieved at ship station through a remotely operated underwater vehicle (ROV) and UWOC-SMF integrated transmission system by means of shifts in the original Bragg wavelengths of sensors due to temperature and pressure variations. The performance of the sensors is analyzed for pressure and temperature in the range of 0 to 6.4 MPa (≈0 to 655 mH2O) and 40 to −2°C, respectively corresponding to different depths. The results show that the proposed technique can work well in the deep ocean over a range of pressures and temperatures of 0–7 MPa and 40 to −2°C while achieving a temperature sensitivity of 4.3 p.m./°C and a pressure sensitivity of 30.5 p.m./MPa. Clear spectra of reflected signals from FBG sensors at ship station are achieved after signal transmission over UWOC-SMF hybrid link.

A high sensitive pressure sensor based on Fiber Bragg grating (FBG) integrated with a thin metal diaphragm was designed and demonstrated. To enhance the pressure sensitivity FBG is firmly glued across the diameter of the diaphragm. Under pressure, the diaphragm deforms and produces an induced strain along the length of the fiber causes shift in Bragg wavelength of the FBG. Pressure measurement is made by measuring the Bragg wavelength shift against change in pressure. The sensor was tested up to the maximum pressure of 140 psi and the corresponding pressure sensitivity was found to be 0.0204 nm/psi, which is approximately 970 times higher than that can be achieved with a bare FBG. The experimental results show good agreement with the theoretical results and possess good linearity and repeatability. This sensor can be used for the measurement of medium pressure, liquid level and depth of underwater.

A model of MEMS based Bragg Grating Pressure Sensor is analytically proposed in this paper. In MEMS pressure sensor, the shift of wavelength of only one Bragg grating incorporated into a waveguide gives an erroneous outcome because of the cross sensitivity rendered by different parameters including temperature. In this design, the sensor consisting of dual identical Waveguide Bragg Gratings (WBGs) integrated in a curved waveguide in silicon micro-machined circular diaphragm is presented. The pitch of the Bragg gratings changes upon the application of pressure on the diaphragm, and hence, the corresponding wavelength is shifted. As the wavelength shifts because of the temperature, in the two identical waveguide gratings in equal amount, the error occurs due to the change of temperature can be eliminated. So, the Pressure Sensitivity (PS) can be measured correctly. A parametric analysis of this proposed sensor is performed utilizing MATLAB 2015a programming. Pressure sensitivities are found to be 2.0 and 1.8 picometre per Pascal for the two Bragg gratings.

In-fiber Bragg grating pressure sensor with an offset temperature compensation is designed. The accuracy of 0.05 MPa and the dynamic band of 0 - 20 MPa are achieved at ambient temperatures up to 120 °C.