Fiber Optic Pressure Sensor Research Articles

High sensitivity fiber optic esophageal pressure sensor based on OFDR

In this paper, a distributed esophageal pressure measurement sensor is proposed. Optical frequency domain reflection (OFDR) technology is adopted to measure the axial strain change of the optical fiber. By designing a sensitizing structure, the sensing performance can be well improved. The analysis based on finite element simulation of the sensor is carried out and its feasibility is verified. Compared with the solid high-resolution esophageal manometry system widely used at this stage, the proposed sensor is low cost and simple in structure. The sensitivity of the sensor can reach 65.920μɛ/kPa.

3D printing of a fiber optic pressure sensor

Soil pressure is an important parameter for soil tillage. This study provides an alternative method for the fabrication of novel fiber optic pressure sensors which can be used for the measurement of soil pressure in the field. Optical Frequency Domain Reflectometry (OFDR) based distributed fiber optic sensor was adopted as a sensing element and embedded inside 3D printed prototypes to fabricate pressure sensors. During the fabrication process, both internal temperature and strain distributions of the printed Polylactic Acid filament (PLA) were systematically monitored and analyzed. Monitoring data show that the inner temperature rise of all prototypes is limited (less than 45 ℃) in comparison with the printing temperature of the printer nozzle (220 ℃). Both the peak temperature and the obtained temperature at the end of printing are linearly proportional to the change in infill densities. Both the measured peak strain and final strain at the end of printing are less than 580 με, which resulted from the thermal expansion of melted PLA extruded out of the printer’s nozzle. All measured strains were found to increase linearly as the increase of infill densities. Calibration tests of pressure sensors, including static and cyclic loading tests, and soil compaction tests, indicate that the measured strain of the fiber optic sensor embedded inside the pressure sensor can be used to calculate vertical pressure applied on the top surface.

Parallel Cross-Correlation Algorithm for the Fast Interrogation of High-Finesse Fiber-Optic Fabry-Perot Sensors

It is still a challenge to realize the absolute optical path difference (OPD) demodulation of the high-finesse fiber-optic Fabry-Perot (FP) sensors with a high resolution and high speed. This paper proposes an improved parallel cross-correlation (PCC) algorithm for the absolute OPD interrogation of the high-finesse FP sensors. The proposed demodulation algorithm is simulated and analyzed to verify the feasibility of the algorithm for sensors with different reflectivity or OPDs with large dynamic range. A high-finesse fiber-optic FP pressure sensor with a cavity length of about 1500 µm and reflectivity of 62.5% has been used to carry out the experiment. Results show that the measurement resolution of the PCC algorithm can reach the sub-nanometer level, the sensor' sensitivity is about 3.93 nm/KPa, which is similar to the theoretical value. By exploring the effect of reflectivity on the demodulation results, it is found out that accurate results are still obtainable even though the exact reflectivity is unknown. In addition, thanks to the multi-threading of computers and the parallel computing method proposed in this paper, the demodulation speed would be further improved.

Approaches to Determining the Residual Life of the Main Components of the Helicopter, Taking Into Account the Flight Profiles Performed

The purpose of research is development of an alternative approach to determining the residual life of the product, based on the conversion of the energy of deformed power elements of the airframe structure into the consumption of an equivalent product resource through a monitoring system based on fiber-optic strain sensors.Methods. The analysis of existing methods for assessing the technical condition of the main components of aircraft products and determining their residual life based on information about the technical condition, on the basis of which the synthesis of the algorithm for determining the residual life of the main components of the helicopter, taking into account the technical condition, was carried out.Results. In the course of the study, the existing methods of assessing the technical condition of the product were classified. The shortcomings in the existing concept of determining the residual resource are indicated, the main of which is the lack of the possibility of predicting the residual resource based on the technical condition of the object (operational history). An alternative approach to determining the residual life of the main components of the helicopter is proposed, with an explanation of the approximate methodology for assessing the technical condition of the main components and the product as a whole, the composition and description of the main stages of the implementation of this approach. The composition and the sensitive element in the control system of the current technical condition of the main components of the product are determined. A fiber-optic sensor with a Bragg grid (fiber-optic pressure sensor ВОДД-1.XXX ПИКВ.401143.003 ТУ) was selected as a sensitive element for the implementation of the monitoring system.Conclusion. The proposed approach to determining the residual life of the main components of the helicopter combines high reliability indicators, which is due to the fixation of the operation history of a particular helicopter, the simplicity of determining the residual life of the product and the absence of the need for special measuring instruments in operating companies.

All-Silica diaphragm-based optical fiber fabry-perot pressure sensor fabricated by CO2 laser melting capillary end face

An all-silica Diaphragm-based miniature optical fiber pressure sensor based on the Fabry-Perot (FP) interferometric principle is proposed. The FP structure is composed of a single-mode fiber and a fiber capillary end face diaphragm by a CO2 laser welding. The fabrication process and parameter control of all-silicon diaphragm are introduced in detail, and the pressure performance test system of FP is set up. The experimental results show that the fiber optic FP sensor has good sensitivity and linearity to air pressure, the sensitivity can reach 9.48 pm/kPa when the pressure ranges from 0 to 200 kPa, and the linearity is 0.998. All-silica diaphragm-based fiber FP pressure sensor fabricated by CO2 laser melting capillary end face is more compact, easy to produce, and has great potential in the extreme harsh environment.

Estimating vibration artifacts in preclinical experimental assessment of actuator efficiency in bone-conduction hearing devices

ObjectivesTest feasibility of a means to distinguish artifact from relevant signal in an experimental method for pre-clinical assessment of bone conduction (BC) stimulation efficiency based on measurement of intracochlear pressure (ICP). MethodsExperiments were performed on fresh-frozen human temporal bones and cadaver heads. In a first step, fiber optic pressure sensors inserted into the cochlea through cochleostomies were intentionally vibrated to generate relative motion versus the stationary specimen, and the resulting ICP artifact recorded, before and after attaching the sensor fiber to the bone with glue. In a second step, BC stimulation was applied in the conventional location for a commercial bone anchored implant, as well as two alternative locations closer to the otic capsule. Again, ICP was recorded and compared with an estimated artifact, calculated from the previous measurements with intentional vibration of the fiber. ResultsIntentional vibration of the sensor fiber creates relative motion between fiber and bone, as intended, and causes an ICP signal. The stimulus does not create substantial promontory vibration, indicating that the measured ICP is all artifact, i.e. would not occur if the sensor were not in place. Fixating the sensor fiber to the bone with glue reduces the ICP artifact by at least 20 dB. BC stimulation also creates relative motion between sensor fiber and bone, as expected, from which an estimated ICP artifact level can be calculated. The ICP signal measured during BC stimulation is well above the estimated artifact, at least in some specimens and at some frequencies, indicating “real” cochlear stimulation, which would result in an auditory percept in a live subject. Stimulation at the alternative locations closer to the otic capsule appear to result in higher ICP (no statistical analysis performed), indicating a trend towards more efficient stimulation than at the conventional location. ConclusionsIntentional vibration of the fiber optic sensor for measurement of ICP can be used to derive an estimate of the artifact to be expected when measuring ICP during BC stimulation, and to characterize the effectiveness of glues or other means of reducing the artifact caused by relative motion of fiber and bone.

Glass Additive and Subtractive Manufacturing of a Fiber Optic Rotary Encoder for Downhole Pressure Sensing

This article presents a fiber optic rotary encoder-based pressure sensor for downhole applications. The rotary encoder, which is composed of an encoding pad and an all-glass optical fiber sensing head, converts the rotation angles of a pressure transducer to digital codes. The optical fiber only serves as the telemetry channel to directly transmit the data in digital format such that the environmental temperature influence and the long-time drift are minimized. The glass additive and subtractive manufacturing (ASM) techniques are used to embed the multichannel optical fibers into a bulk-fused silica glass substrate. Because the fused silica glass shares a similar material property to the optical fiber (e.g., thermal expansion coefficient), the optical fiber sensing head is well sealed and fixed even at an elevated temperature. The picosecond laser blackening technique is used to fabricate the high reflectivity contrast encoding pad with high accuracy. The proposed pressure sensor was manufactured and experimentally verified to have a signal-to-noise ratio (SNR) of 23 dB and a linear pressure response with a root-mean-square error (RMSE) of 0.37. During the 400-h 250 °C long-term stability test, there was no digital code variation. In addition, a mathematical model to study the relationships between the sensor’s performances and design parameters was established. According to the model, a 12-bit encoder (0.02% pressure sensitivity) can be achieved with a radius of 20 mm.

Inactivation of Vibrio vulnificus and Vibrio parahaemolyticus in cryogenically frozen oyster meat using steam venting technology

A combination of steam-venting packaging and microwave cooking may be used to inactivate Vibrio vulnificus and Vibrio parahaemolyticus in oyster meat. This study investigated temperature and pressure profiles in the headspace of a steam venting package with the steam-generated inside of the package resulting from microwave heating. To determine steam venting time to inactivate pathogens, fresh oyster meat ( Crassostrea virginica ) was inoculated with either Vibrio vulnificus or Vibrio parahaemolyticus , cryogenically frozen (−20 °C), and packaged in microwavable trays in 50 and 100 g portions. Trays were film sealed with nitrogen in the headspace and stored in a freezer for 12 h. The film acted as a barrier against rapid moisture loss and promoted even temperature distribution in the oyster meat. Steam venting occurred due to steam pressure generated inside the package. Venting was used to prevent overheating. Data collection of temperature and pressure inside the package during microwaving was performed in a Microwave Workstation using fiber optic temperature and fiber optic pressure sensors. Temperature and pressure profiles showed that after 10 s of heating, the temperature of the oyster meat was the same both internally and upon the surface. The venting time in the 100 g package took 1.53 times longer than in the 50 g package, while the venting pressure was 52% lower than in the 50 g package. After 50 s and 60 s of microwave cooking at 100% power on 50 g and 100 g of oyster meat, respectively, total inactivation of both pathogens was achieved. The study demonstrated the steam venting package, and microwave heating could provide even heating, prevent overheating, and inactivate pathogens. • Steam venting package and microwave heating provided even heating in oyster meat. • Optical fiber sensing is an excellent tool for temperature measurement during microwave heating. • Steam venting package and microwave heating inactivate pathogens less than 1 min. • Steam venting package film prevented moisture loss in oyster meat during microwaving.

A Fiber-Optic Non-Invasive Swallowing Assessment Device Based on a Wearable Pressure Sensor.

We developed a wearable swallowing assessment device using a hetero-core fiber-optic pressure sensor for the detection of laryngeal movement during swallowing. The proposed pressure sensor (comfortably attached to the skin of the neck) demonstrated a high sensitivity of 0.592 dB/kPa and a linearity of R2 = 0.995 within a 14 kPa pressure band, which is a suitable pressure for the detection of laryngeal movement. In addition, since the fabricated hetero-core fiber-optic pressure sensor maintains appreciable sensitivity over the surface of the sensor, the proposed wearable swallowing assessment device can accurately track the subtle pressure changes induced by laryngeal movements during the swallowing process. Sixteen male subjects and one female subject were evaluated in a variety of age groups ranging from 30 to 60 years old. For all subjects, characteristic swallowing waveforms (with two valleys based on laryngeal movements consisting of upward, forward, backward, and downward displacements) were acquired using the proposed wearable swallowing assessment device. Since the denoted time of the first valley in the acquired waveform determines the "aging effect", significant differences in swallowing functions among the different age groups were ultimately determined based on the time of the first valley. Additionally, by analyzing each age group using the proposed device, due to p-values being consistently less than 0.05, swallowing times were found to exhibit statistically significant differences within the same groups.

Temperature-insensitive Quasi-distributed Fiber-optic Fabry-Perot High-pressure sensing based on microwave interference system

A temperature-insensitive quasi-distributed fiber-optic high-pressure sensing technique based on cascaded extrinsic Fabry-Perot (EFP) sensing units and an optical carrier based microwave interference system (OCMI) is proposed and demonstrated. The EFP unit formed by hollow-core photonic bandgap fiber has advantages of low-insertion loss and low temperature–pressure cross sensitivity, and the OCMI system based on a tunable single-wavelength light can simultaneously reconstruct optical interferograms of multiple EFP units. Experimental results show the optical interferograms reconstructions of three cascaded EFP units are well agreement with those using an optical spectrum analyzer. Moreover, the EFP unit has a wide measurement range of 0 ∼ 100 MPa and a low temperature–pressure cross-sensitivity of –0.02 MPa/℃, which can be comparable to that of a point fiber-optic pressure sensor. This technique provides a new idea of high-performance distributed pressure sensing.

Optical Fiber Pressure Sensor Based on Sapphire Wafers Processed by Femtosecond Laser

Optical Fiber Pressure Sensor Based on Sapphire Wafers Processed by Femtosecond Laser

Fabricating Air Pressure Sensors in Hollow-Core Fiber Using Femtosecond Laser Pulse.

In this paper, a hollow core fiber was spliced with standard single-mode fibers to form a fiber optic gas pressure sensor, and its sensing characteristics with single hole or multi-holes punched on the hollow core fiber with femtosecond laser pulses were investigated. The experiments demonstrate that the air pressure sensitivity of the single hole sensor was -3.548 nm/MPa, with a linearity of 99.45%, while its response times for air pressure's rise and fall were 4.25 s and 2.52 s, respectively. The air pressure sensitivity of the ten-hole sensor was up to -3.786 nm/MPa, with a linearity of 99.47%, while its response times for air pressure's rise and fall were 2.17 s and 1.30 s, respectively. Theoretical analysis and experimental results indicate that the pressure sensitivity of the sensor with an anti-resonant reflecting guidance mechanism mainly comes from the refractive index change of the air inside the hollow core fiber. The proposed device with multi-holes drilled by a femtosecond laser has the advantages of fabrication simplicity, low cost, fast response time, good structural robustness, high repeatability, high sensitivity to air pressure, and insensitivity to temperature (only 10.3 pm/°C), which makes it attractive for high pressure sensing applications in harsh environments.

Occluded insertion loss from intracochlear pressure measurements during acoustic shock wave exposure

IntroductionInjuries to the peripheral auditory system are among the most common results of high intensity impulsive noise exposure. Hearing protection can mitigate this injury, but careful assessment of the insertion loss they provide is necessary. Insertion loss is typically measured using microphone-based acoustic manikins to measure the decrease in sound pressure level transmitted into the ear canal, which precisely measure the change in air conducted sound, but neglect alternate pathways to the inner ear such as bone conduction. In a previous study we reported intracochlear pressures in cadaveric human specimens to acoustic shock waves, which revealed a substantial bone conducted component (Greene, et al., 2018). Here we evaluate insertion loss to several hearing protection devices (HPDs) in those same specimens using intracochlear pressure measurements. MethodsHuman cadaver heads were exposed to impulsive acoustic pressure waves with peak overpressures of 7 and 28 kPa (171 & 183 dB SPL). Ear canal (EAC), middle ear, and intracochlear sound pressure levels were measured bilaterally with fiber-optic pressure sensors. Surface-mounted sensors measured SPL and skull strain near the opening of each EAC and at the forehead. Responses were measured with specimen ears unoccluded, as reported previously, as well as fitted with four types of HPDs. Impulse peak insertion loss (IPIL) and impulse spectrum insertion loss (ISIL) were calculated for each HPD. ResultsFor all HPDs, IPIL generally increases with exposure level, though ISIL tended to be more consistent, and the spectral characteristics across frequency appear to be highly dependent on exposure level. ISIL measured in the ear canal tended to overestimate insertion loss measured in the cochlea, particularly at frequencies > 1 kHz; however, low signal-to-noise in intracochlear pressures limited comparisons. As a proof of concept, 36 low-level unoccluded exposures, were averaged together, and the resulting signal-to-noise ratio was improved by up to 15 dB. ConclusionsInsertion loss measured in the cochlea was lower than in the ear canal, suggesting substantial contributions from transmission pathways in parallel with air conduction (e.g., bone conduction) were present, which will require novel strategies to mitigate. However, high variance was observed, and noise reduction strategies should be utilized in future studies to facilitate more precise insertion loss estimates.

Compact-Packaged and Diaphragm-Lever Structured Fiber-Optic Temperature and Pressure Sensors for Oil and Gas Well Applications

A small-sized sensor combined with a diaphragm structure and a lever structure is proposed for application in high-temperature and high-pressure environments. The feasibility of the structure is verified from both theory and simulation, and the relationship between the change of the Bragg wavelength and the pressure is established. Differential measurements of temperature and pressure are achieved using two fiber Bragg gratings (FBGs). The experimental data show that the pressure sensitivity of the sensor is 28.86 pm/MPa in the range of 0–30 MPa, and the correlation coefficient is 0.9969. The pressure sensitivity of the improved structure is 29.76 pm/MPa and the correlation coefficient is 0.9999. The sensor’s temperature sensitivity is 32.66 pm/°C in the range of 50 °C–200 °C. The structure can be applied to the measurement of temperature and pressure in oil and gas wells.

Multipoint pressure sensing at up to 900 °C using a fiber optic multimode interferometer

We demonstrate a multipoint optical fiber pressure sensor for high temperature operation using multimode interference. Each sensing element consists of a four-hole asymmetric multimode fiber acting as the pressure sensing fiber, spliced between two standard polarization-maintaining single mode fibers. Multiple sensing elements are serially connected for multipoint pressure sensing and demultiplexing is achieved using Fourier analysis. The spatial frequency associated with each sensing element is separated by having distinct optical path lengths. The pure silica material of the sensing fiber enables high-temperature operation. As a proof of concept, we demonstrate two-point pressure sensing at a temperature up to 900 °C with negligible crosstalk between the sensing elements and good stability. Our demonstrated sensor has potential applications in heavy industry where spatially resolved measurements of pressure at high temperature may lead to improvements in efficiency and safety.

Liquid Pressure Sensor Based on Fiber Bragg Grating with an Adjustable Structure.

In this paper, a fiber-optic liquid pressure sensor is designed and developed by encapsulating the fiber Bragg grating (FBG) inside the adjustable double-flange cylinder rigid structure with flexible polymer polydimethylsiloxane (PDMS). Within the elastic deformation range of the PDMS, the proposed adjustable FBG-based liquid pressure sensor is proven to change its measuring range while maintaining high measurement sensitivity by simply adjusting the structure, that is, the sensor can achieve high measurement sensitivity in various liquid levels. In addition, the simulation and experimental results show that the sensor sensitivity can be enhanced by the proper changes of the structural parameters, such as the inner diameter, etc. The proposed sensor has shown that it has good linearity and stability, which provides a new opportunity for the monitoring of liquid pressure in oceans, dams and other environments.

Micro-Bubble F-P Cavity and FBG Cascade Structure-Based Pressure Sensor With Temperature Self-Compensation for Minimally Invasive Surgery.

This paper presents a high-sensitivity optical fiber pressure sensor with temperature self-compensation for pressure measurement in minimally invasive surgery through a cascade structure of Fabry-Perot (F-P) interferometer and fiber Bragg grating (FBG). A micro-bubble is configured at the tip of the fiber to form an F-P cavity that is sensitive to pressure. A loose optical fiber inscribed with an FBG element is cascaded with the F-P cavity leading to temperature compensation for the designed sensor. The sensing theoretical model has been derived and combined with the finite element method (FEM) simulation the sensor structure has been determined as well. Fabrication processing of the designed sensor has been optimized and explored by experiments. Calibration experiment results indicate that the pressure sensitivity of the designed sensor is 8.93 pm/kPa, which is consistent with the simulated value. The temperature coupled error is less than 3.89% leading to a capability for temperature self-compensation. Several heart-vascular simulation experiments have been carried out to investigate the dynamic performance of the designed sensor, which shows the measured pressure errors within this confidence interval of [-2.56%, 2.54%] correspond to high confidence of 0.95. An in-vivo intracranial pressure (ICP) measurement experiment on the rat brain has been conducted to further validate the feasibility and effectiveness of the designed sensor.

Fiber Lateral Pressure Sensor Based on Vernier- Effect Improved Fabry-Perot Interferometer.

A fiber optic pressure sensor that can survive 2200 psi and 140 °C was developed. The sensor’s pressure sensitivity was measured to be 14 times higher than bare FBG when tested inside stacks of ultra-high-molecular-weight polyethylene (UHMWPE) composite fabric. The sensitivity can be further improved 6-fold through the Vernier effect. Its tiny sensing length (hundreds of microns) and uniform outer diameter (125 µm) make it a suitable candidate for real-time point pressure monitoring under harsh environments with limited space, such as in composite-forming procedures.

New Experimental Results Show the Application of Fiber Optic to Detect and to Track Gas Position in Marine Risers and Shed Light on the Gas Migration Phenomenon Inside a Closed Well

SummaryThe main objective of this paper is to present and discuss the results and significant observations gathered during 13 experimental runs conducted in a full-scale test well at Louisiana State University (LSU). The other two objectives of this manuscript are to show the use of distributed fiber-optic sensing and downhole pressure sensors data to detect and track the gas position inside the test well during the experiments, and to discuss experimental and simulated data of the gas migration phenomenon in a closed well.An existing test well at LSU research facilities was recompleted and instrumented with fiber-optic sensors to continuously collect downhole data and with four pressure and temperature downhole gauges at four discrete depths within an annulus formed by 9 5/8 in. casing and 2 7/8 in. to a depth of 5,025 ft. A chemical line was attached to the tubing allowing the nitrogen injection at the bottom of the hole. The research facilities were also equipped with a surface data acquisition system. The experiments consisted in injecting nitrogen into the test well filled with water by two means: either injecting it down through the chemical line or down through the tubing to be subsequently bullheaded to the annulus. Afterward, either the nitrogen was circulated out of the well with a backpressure being applied at surface to mimic a managed pressure drilling (MPD) operation or left to migrate to the surface with the test well closed.During the runs, the three acquisition systems (fiber optic, downhole gauges, and surface data acquisition) recorded all relevant well control parameters for a variety of gas injected volumes (2.0–15.1 bbl), circulation rates (100–300 gal/min), and applied backpressures (100–300 psi). The experimental results gathered by the acquisition systems were very consistent in measuring gas velocities inside the well. The numerical model predictions matched very close to the pressure behavior observed in the experimental trials. In the gas migration experiments, it was observed that the stabilized casing pressure at the end of gas migration is less than the initial bottomhole pressure, and it is a function of the volume of gas injected in the well. These facts are supported by the numerical simulation results.In this paper, we show the possibility of the use of fiber-optic and downhole pressure sensors information to detect and track the gas position inside a well or the marine riser during normal or MPD operations. Additionally, the vast amount of experimental data gathered during the experiments in which the nitrogen was left in the closed well to migrate to surface helped shed light on the controversial issue concerning the surface pressure buildup while the gas migrates to surface in a closed well. Numerical simulations were all instrumental for supporting the findings.

Study on phase demodulation algorithm of fiber optic pressure sensor based on nonlinear differential equation

Fiber optic Fabry–Pérot sensors have been widely developed with unique advantages, such as ease of reuse, resistance to electromagnetic interference, light weight, and their ability to work in extreme environments. There are many demodulation methods that can be applied to fiber optic Fabry–Pérot sensors, including the intensity demodulation method, spectral demodulation, and the phase carrier method, but these demodulation methods cannot meet the requirements that take into account range, speed, and dynamic and static demodulation capabilities. In view of these problems, this paper uses nonlinear differential equations to solve the problem of simultaneous measurement of a large number of ranges and dynamic and static parameters. The measuring interferometer in the demodulation module was built using a polarizing interferometer, which avoids the difficulty in optical wedge processing when using a Fizeau interferometer. Regarding the problems of high and low signal-to-noise ratios of the generated signal, for the problem that the introduction of dispersion in the crystal causes the demodulation result of the traditional demodulation method to be wrong, a nonlinear differential equation is proposed to achieve the correct demodulation of the fiber optic sensor: the slow demodulation speed problem. This paper designs the acquisition, transmission, and processing system based on digital signal processing and a field-programmable gate array, which provide a hardware platform for real-time demodulation. Finally, experiments to test the resolution, linearity, stability, and repeatability of the interferometer were carried out on the designed demodulation system.