A Miniature, High Temperature, High Frequency Fiber Optic Pressure Sensor for Scramjet Flow Characterization

Urodynamic analysis is the predominant method for evaluating dysfunctions in the lower urinary tract. The exam measures the pressure during the filling and voiding process of the bladder and is mainly interested in the contraction of the bladder muscles. The data arising out of these pressure measurements enables the urologist to arrive at a precise diagnosis and prescribe an adequate treatment. A technique based on two optical fiber pressure and temperature sensors with a resolution of better than 0.1 cm H₂O (∼10 Pa), a stability better than 1 cm H₂O/hour, and a diameter of 0.2 mm in a miniature catheter with a diameter of only 5 Fr (1.67 mm), was used. This technique was tested in vivo on four patients with a real-time urodynamic measurement system. The optical system presented showed a very good correlation to two commercially available medical reference sensors. Furthermore, the optical urodynamic system demonstrated a higher dynamic and better sensitivity to detect small obstructions than both pre-existing medical systems currently in use in the urodynamic field.

This paper presents an optical fibre pressure and temperature sensor (OFPTS) system, which is adapted for use as a urodynamic pressure measurement system (UPS) for differential pressure measurement with temperature compensation. The OFTPS is based on a Fabry Perot interferometer (FPI), which acts as a pressure sensor and includes an embedded fibre Bragg grating (FBG) for temperature measurement. The sensor system is evaluated in a lower urinary tract (LUT) simulator, which simulates the bladder, rectum and detrusor muscle. The system was benchmarked against a commercially available urodynamic system, at the University Hospital Limerick (UHL) Urology Clinic. Both systems demonstrate a high correlation with a relative pressure variation of less than ±2.8cmH₂O for abdominal and ±4cmH₂O for vesical pressure. The repetitive measurement of the OFPTS system in the LUT simulator against the commercial system demonstrated the high repeatability. Furthermore, the low fabrication cost makes the OFPTS a potentially interesting instrument for urodynamic and other medical applications.

High sensitivity fiber optic pressure sensor is in great demand in in all aspects due to its advantages. However, the current high sensitivity optical fiber pressure sensor has the problems of large size and high cost. An optical fiber pressure sensor based on all-silica Fabry-Perot interference has been proposed in this paper. The sensor consists of single mode fiber, silica capillary and diaphragm made of coreless optical fiber. The diameter of the sensor is only 125 μm. With precise control of diaphragm thinning, the diaphragm thickness of F-P sensor is only 1.477 μm, the sensor manufactured in this way has sensitivity with 12.586 rad/MPa. The sensor is ease of manufacturing and low cost. Static calibration shown the advantages of the sensor are high sensitivity, good linearity, repeatability, reliability and low hysteresis.

Recent investigation of single crystal cubic zirconia fiber optic pressure sensor for high temperature environment application is reported in this paper. A fiber optic pressure sensor utilizing single crystal cubic zirconia as a structure material has been designed, developed and tested. The sensor head is a birefringence-based fiber optic sensor in which the will change with the pressure. The pressure response of the sensor has been measured from 0 to 1700Psi. Additional experimental results from room temperature to 1026 /spl deg/C show that cubic zirconia could be used for pressure sensor at high temperatures. Experiment results illustrate the feasibility to apply the designed single crystal cubic zirconia sensor for pressure measurement at high-temperature harsh industrial environments with further development.

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.

This paper presents an integrated microcavity optical fiber pressure sensor using exfoliated ultrathin graphene atomic layers as a reflective surface to form a Fabry–Perot (F-P) interferometric structure. The fabrication was based on the focused-ion-beam (FIB) micromachining and dry exfoliated graphene transfer method, where the sensor was fabricated directly on a facet of a standard SMF-28 single-mode fiber with the core diameter of $8~\mu \mathrm {m}$ and the cladding diameter of $125~\mu \text{m}$ . The air leakage from the cavity was negligibly small during the 30-min measurement time. The responsivity of pressure sensors, defined as the spectral shift of F-P fringes in response to the air pressure change, was achieved as large as 1.28 nm/mmHg at 1300-nm wavelength when using a diaphragm diameter of $20~\mu \text{m}$ . Demonstrated responsivity and compactness makes the sensor suitable for medical, environmental, and other applications. An analytical model was presented describing responsivity of an F-P pressure sensor with a thin diaphragm. It has predicted that reducing the diaphragm thickness below some critical value leads to the highest possible responsivity that no longer depends on the elastic properties or thickness of the diaphragm. This upper limit for the responsivity can be increased using the cavity shape other than a simple cylinder, while residual strength of the diaphragm results in reduced responsivity.

PDMS-based liquid-core optical fiber fluorescence pressure sensor

Optical fiber pressure sensors have been developed for use on a structurally-adaptive `smart wing'; further details of the design, fabrication and testing of the smart wing concept are presented in companion papers. This paper describes the design, construction, and performance of the pressure sensor and a combined optical and electronic signal processing system implemented to permit the measurement of a large number of sensors distributed over the control surfaces of a wing. Optical fiber pressure sensors were implemented due to anticipated large electromagnetic interference signals within the operational environment. The sensors utilized the principle of the extrinsic Fabry-Perot interferometer (EFPI) already developed for the measurement of strain and temperature. Here, the cavity is created inside a micromachined hollow-core tube with a silicon diaphragm at one end. The operation of the sensor is similar to that of the EFPI strain gage also discussed in several papers at this conference. The limitations placed upon the performance of the digital signal processing system were determined by the required pressure range of the sensors and the cycle time of the control system used to adaptively modify the shape of the wing. Sensor calibration and the results of testing performed are detailed.

This paper describes the modeling, fabrication, and characterization of a proof-ofconcept dynamic pressure sensor utilizing sapphire materials for the harsh environments of gas turbine engines. The harsh environment makes conventional instrumentation unsuitable for time-resolved, continuous, direct measurements. High temperature sensing is enabled by the use of sapphire materials due to a high melting point and corrosion resistance. The availability of commercial sapphire substrates and optical fibers provides a direct path for optical sapphire sensors with a matched coefficient of thermal expansion. The dynamic pressure sensor uses a fiber optic lever transduction mechanism with a remote photodiode optical readout allowing for isolation of the electronics from the harsh environment. A circular diaphragm is formed by joining two sapphire substrates using an alumina-based high temperature epoxy. The first substrate is 50 μm thick sapphire with a sputtered titanium/platinum reflective surface. The second substrate is a 1 mm thick sapphire substrate that has been machined to form a circular back cavity. Presented along with the sensor fabrication are a systems level dynamic model and a dc exploration of the performance of the fiber optic lever transduction. Finally, initial dynamic characterization of the frequency response function and linearity are presented with a resulting sensitivity of -113 dB re 1 V/Pa.

The miniature fiber optic Fabry-Perot pressure sensor with a silicon diaphragm was developed for medical applications. The configuration of this sensor was a 1-mm long fiber optic Fabry-Perot interferometer bonded to an 80 micrometers -thick diaphragm. The length of the sensor was about 1.5 mm and the area of the diaphragm was 1 mm x 1 mm. The phase shift of the interferometric sensor was proportional to the applied pressure. The relationship between the applied pressure and the phase change was nonlinear.

A novel all-silica fiber optic Fabry-Perot (FP) pressure sensor with pressure leading-in tube based on microbubble structure is developed and experimentally demonstrated. The FP cavity is formed by fixing the end face of the single-mode fiber (SMF) parallel to the outer surface of the microbubble, in which the microbubble with a diameter of about 318 μm is constructed at the end of silica hollow tube. When external pressure is transmitted on the inner surface of the microbubble by the pressure leading-in tube, the FP cavity length changes with the diameter of microbubble. Experimental results show that such a sensor has a linear sensitivity of approximately 4.84 nm/MPa at room temperature over the pressure range of 1.1 MPa; the sensor has a very low temperature coefficient of approximately 2 pm/°C from room temperature to 600°C. The sensor has advantages of extremely low temperature coefficient, compact structure, and small size, which has potential applications for measuring pressure in high-temperature environment.

Low cost, rugged and reliable fiberoptic sensors are being developed to meet the needs of geotechnical engineers. The primary emphasis has been on load and pressure sensors, including pore water pressure sensors. The microbend sensors developed have been tested in the laboratory up to water pressures of 100 psi and loads of 50 lb. Accuracy of sensor measurements are within 5% and is being improved upon. Sensors with larger range or more sensitivity can easily be built without changing the basic sensor design. A semi-automated calibration and testing system was developed to characterize the sensors. In this paper we describe some of the applications for the sensors, their construction, characterization system, and experimental performance.

A pressure and temperature sensor for downhole application is reported. Experiments show the sensor has sensitivity of 0.99μm/MPa and accuracy of 0.1%F.S. for pressure measurement. The sensor is successfully used for downhole 24-hours monitoring.

A fiberoptic system with a microstructure sensor element was used for measuring lumbar intervertebral disc pressure in a porcine model. The fiberoptic pressure sensor was inserted in the disc using a guiding needle. A reference sensor was also introduced into the same area of an adjacent disc. The fiberoptic sensor detected pressures from 0.7-8 bar in the disc. Dynamic measurements were carried out at frequencies between 2 and 10 Hz. No phase lag was observed between the applied force and the measured pressures. Sensitivity, dynamic response and available pressure range are all important design characteristics for which this fiberoptic sensor has a competitive edge.

Optical fibre pressure sensors have potential performance advantages over electrical sensors in measuring rapid transients such as shock waves from explosive blasts. We report the development of micromachined optical fibre Fabry–Pérot pressure sensors using a silicon dioxide or nitride diaphragm and detail the fabrication stages of the sensor body and diaphragm. The planar technology used is based on silicon deep etching and direct fusion bonding of silicon wafers. Test results for both types of diaphragm are presented. Sensors with rise times better than 3 µs, range 0.1 to 1 MPa and resolution ∼500 Pa have been demonstrated in explosives trials. Despite the difference in the sign of stress for the two diaphragm types, both demonstrated excellent high-speed response to explosively generated air shocks.