GaAs-based fiber-optic pressure sensor

A new sensor developed for measurement of hydrostatic pressure up to at least 100 MPa at a standard range of ambient temperatures is described. The sensor exploits the displacement of the optical absorption edge occurring in semiconductors under the influence of hydrostatic stress as a result of pressure-induced energy shifting of conduction band extrema. The sensing element is composed of an intrinsically pure GaAs single crystal configured in the form of a microprism located at the sensor tip, and attached to two multimode (50/125 μm) optical fibers designed to deliver input light to the sensor and to output a pressure-modulated light signal to the outside of a pressure region. Characterization of the sensor has been performed for pressures up to 100 MPa and for temperatures ranging from 5 to 50°C. A procedure has been proposed involving the use of two sensors (active and compensating) to minimize temperature drift through appropriate signal processing     

White-light interferometric fiber-optic pressure sensor

A novel configuration for a fiber-optic white-light interferometric sensor is presented which allows for absolute measurements of hydrostatic pressure with an improved operation range. The performance of two fibers (York bow-tie 800 and especially designed elliptical-core side-hole fiber) used as sensing elements was experimentally studied. The sensor itself was composed of two equal lengths of the fiber spliced at 90°. This structure assures temperature compensation and enables application of a Wollaston prism as a receiving interferometer. A step delay line made of crystalline quartz was used to increase the operation range of the sensor     

Smart interpolator for a fiber-optic pressure sensor

A smart interpolator is proposed to improve the long-term stability of a fiber-optic pressure sensor. This method relies on decomposing the compensation model into signal and reference channel parameters. Analysis shows that this interpolator can be used for self-calibration and cancellation of the long-term drift. Experiments prove its effectiveness.     

A fiber-optic pressure-gradient sensor

Translated from Izmeritel'naya Tekhnika, No. 11, p. 36, November, 1991.     

Miniature fiber-optic pressure sensor with a polymer diaphragm

The fabrication and experimental investigation of a miniature optical fiber pressure sensor for biomedical and industrial applications are described. The sensor measures only 125 microm in diameter. The essential element is a thin polymer diaphragm that is positioned inside the hollow end of an optical fiber. The cavity at the fiber end is made by a simple and effective micromachining process based on wet etching in diluted HF acid. Thus a Fabry-Perot interferometer is formed between the inner fiber-cavity interface and the diaphragm. The fabrication technique is described in detail. Different sensor prototypes were fabricated upon 125 microm-diameter optical fiber that demonstrated pressure ranges from 0 to 40 and from 0 to 1200 kPa. A resolution of less than 10 Pa was demonstrated in practice. The fabrication technique presented facilitates production of simple and low-cost disposable pressure sensors by use of materials with that ensure the required biocompatibility.     

Coherence-multiplexed fiber-optic sensor systems for measurements of pressure and temperature changes

A digital demodulation method for read-out of phase changes induced in coherence-multiplexed sensors based on highly birefringent fibers is described. The method employs the fringe counting principle and enables registration of the phase shifts simultaneously induced in two multiplexed sensors with a maximum frequency of 10 kHz and resolution of 1/4 of the interference fringe. The performance of three multiplexed systems interrogated using the proposed detection method is investigated. The first system is composed of two serial multiplexed sensors serving for measurements of pressure and temperature changes in the same location, while the two other systems are composed of two parallel or serial multiplexed temperature-compensated sensors serving for pressure measurements at different locations.     

Temperature desensitization of a fiber-optic pressure sensor by simultaneous measurement of pressure and temperature

A fiber-optic hydrostatic pressure sensor initially temperature compensated by optical means is further desensitized below the limits associated with second-order effects by the method proposed in this paper. We achieved this goal by using an integrated system of two coherence-multiplexed separate sensor components for simultaneous measurement of hydrostatic pressure and temperature and by on-line numerical processing of measurement data delivered simultaneously from both sensor parts. The system is based on highly birefringent fibers, employs electronic scanning, and can be used for quasi-static measurements.     

A novel MOEMS pressure sensor: Modelling and experimental evaluation

This paper presents a novel MOEMS (Micro Opto Electromechanical Systems) pressure sensor suitable for localized precision measurements in high temperature environments. The sensor is based on a micromachined Fabry-Perot device (MFPD) that uses a thin film microcantilever beam as the top mirror and a silicon substrate as the bottom mirror of the optical microcavity. The major effect that the viscosity and density of the air surrounding the MFPD have on the viscous damping provides the mechanism for the detection of the pressure. A major advantage of this configuration is that there is no need for a sealed microcavity since the air is trapped by the viscous damping effects. The sensor has been tested up to 90 psi and pressure sensitivities of about 0·04%/psi with a MFPD sensor with a resonant frequency of about 46·7 kHz have been measured.     

Holographic Bragg grating input-output couplers for polymer waveguides at an 850-nm wavelength

Bragg gratings used as input-output couplers in polymeric waveguides have been demonstrated at infrared wavelengths. These Bragg grating couplers were holographically formed volume phase gratings with a near-45 degrees fringe slant angle embedded directly into a waveguide layer. A photopolymer was used for both producing a planar waveguide and constructing the embedded Bragg grating coupler. A coupling efficiency of 23% for input and 5% for output has been achieved at 850 nm. The output-coupling beam profiles are also discussed.     

A fiber-optic fluorescence sensor for lithium ion in acetonitrile

A novel fiber-optic fluorescence sensor based on a controlled-release reagent for the determination of lithium ion in organic solvents is proposed. The fluorogenic indicator 2-(2-hydroxyphenyl)benzoxazole is contained in a mini-polyethylene tube as the reagent reservoir and is brought into contact with the analyte solution by diffusion across a poly(vinyl chloride) (PVC) membrane to form a strongly fluorescent complex at the membrane/solution interface. The fluorescence signals produced are measured via two joined optical fibers positioned closely to the backside of the PVC membrane for light illumination and collection. The sensor is useful for measuring Li+ at concentrations in acetonitrile ranging from 1.0 x 10(-6) to 1.0 x 10(-2) M with a detection limit of 3.0 x 10(-7) M. The steady-state response can be reached within seconds, and the signal changes are fully reversible. The sensor shows minimal interference effects from other alkali metal and alkaline earth metal cations and has good stability and durability when stored in acetonitrile solutions.     

A renewable-reagent fiber-optic sensor for measurement of high acidities

A renewable-reagent fiber-optic HNO(3) sensor was developed for HNO(3) measurement in the 0.1-10.0 M range. The HNO(3) sensor employs a tubular Nafion cation-exchange membrane to extract acid species from an external HNO(3) sample into an internal flowing reagent solution. In high-concentration HNO(3) samples, incomplete HNO(3) dissociation results in a significant concentration of neutral HNO(3) species in addition to protons. As both neutrals and protons are potentially membrane-permeable species, various reagent compositions were tested to examine the contributions of both acid transfer mechanisms. Continuous reagent flow limited internal acid accumulation and transferred reagent to the sensor optical detection cell. All reagent compositions included cresol red as a colorimetric indicator, which was measured within the sensor detection cell. Careful fiber-optic alignment provided sufficient light throughput in a backscatter illumination mode to allow use of a photodiode array detector for visible spectral acquisition. The use of Ca(2+) as a reagent countercation produced notable reductions in HNO(3) sensor response to interferent cations and temperature changes. Sensor measurement of HNO(3) samples in the tested concentration range produced average relative standard deviations of less than 0.4%. Control over reagent flow rate should allow for extension of the HNO(3) sensor measurement range to 16.0 M HNO(3).     

A fiber-optic current sensor based on a differentiating Sagnacinterferometer

A fiber-optic current sensor (FOGS) based on a differentiating Sagnac interferometer (DSI) is demonstrated to measure high-voltage ac current in electric power systems from 5 A to 3200 A. A transducer consisting of Rogowski coil and piezoelectric cylinder (PZT) is used as the phase modulator, which is placed in the high-voltage side. The DSI is placed in the ground side. A simple analytical expression for the sensor has been derived, and the input-output performance and the temperature dependence of FOGS have been experimentally investigated. The simple sensor geometry gives high accuracy and sensitivity, wide dynamic range, and immunity from slow-variance temperature and other environmental fluctuations     

A novel optical pressure sensor based on surface plasmon polariton resonator

We propose a Metal–Insulator–Metal structure consists of two surface plasmon polaritons (SPPs) and an H-shaped resonator. The reflectance spectrum is numerically simulated by the two-dimensional finite-difference time-domain method. The results show that this structure can act as a pressure sensor. To our knowledge, this is the first proposal to utilize the SPP resonator to form a pressure sensor. The size of the SPP resonator can be as small as a few hundred nanometers. The nano-scale pressure sensor opens a wide field for potential applications in biological and biomedical engineering.     

Atmospheric pressure plasma jet operated at narrow gap spacings

The atmospheric pressure plasma jet (APPJ) makes use of a dielectric-barrier-free radio-frequency (RF) glow discharge for the production of a non-equilibrium plasma. Usually the APPJ is operated in the alpha mode at gap spacings in the mm range, where the alpha sheath thickness is in the order of 200-300 μm. Narrow gap spacings are experimentally not yet investigated, but it is expected that the bulk region of the alpha discharge should disappear and the discharge should exhibit a sheath-only structure.In order to provide experimental evidence for such situations, APPJs with gap spacings down to 0.1 mm are investigated. The electric properties of the APPJ are studied by measuring the current and voltage characteristics. Time-averaged images of the front view of the discharge are taken with a digital camera. By using an image-intensified gateable video camera the time development of the discharge is studied with nanosecond resolution.It was possible to sustain alpha discharges at gap spacings down to 100 μm, whereby the voltage needed decreases down to an rms voltage of 70 V. A weak indication for a laterally oscillating sheath in the 100 μm gap was found.     

Interferometric fiber-optic sensor embedded in a spark plug for in-cylinder pressure measurement in engines

Pressure sensing in an internal combustion engine with an intrinsic fiber Fabry-Perot interferometer (FFPI) integrated with a spark plug is demonstrated for the first time. The spark plug was used for the ignition of the cylinder in which it was mounted. The FFPI element, protected with a copper/gold coating, was embedded in a groove in the spark-plug housing. Gas pressure inthe engine induced longitudinal strain in this housing, which was also experienced by the fiber-optic sensing element. The sensor was monitored with a signal conditioning unit containing a chirped distributed-feedback laser. Pressure sensitivities as high as 0.00339 radians round-trip phase shift per pounds per square inch of pressure were observed. Measured pressure versus time traces showed good agreement with those from a piezoelectric reference sensor mounted in the same engine cylinder.     

A novel fibre-optic vibration sensor

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

A novel pressure sensor based on series-coupled double microring resonators with a simple beam

We propose and analyse a novel optical pressure sensor based on series-coupled double microring resonators (SDMRRs) on a simple beam. The pressure applied on the sensor is measured through the change of the optical transmission spectrum at the output port. The optical transmission performances of the SDMRRs have been analysed and compared with the single and paralleled-coupled structures by the method of finite element analysis and numerical simulation. The simulation results showed that the stress sensitivity is 0.0225?kPa^–1 and linear measurement range of the sensor is 30?kPa. Furthermore, the influence of the amplitude transmission coefficient, half round phase shift and microring radius on the sensitivity have been investigated to optimize the sensor performance. This proposed sensor can be used for the smaller pressure detection in automotive, aerospace, oil/logging equipment and other harsh environmental application.     

A dual-mode thickness-shear quartz pressure sensor

The development of a dual-mode thickness-shear quartz pressure sensor to meet the demanding performance requirements of oil-field applications is discussed. The objective was to develop a sensor with an operating pressure range of 0-103.42 MPa (0.15 000 lb/in(2)), a temperature range of -10 to +175 degrees C, a pressure calibration accuracy of 6894.8 Pa (1 lb/in(2)), and resolution of 68.95 Pa (0.01 lb/in(2)) with 1-s counter gate time. Doubly rotated cuts with piezoelectric coupling to both the C-modes of vibration were investigated. A theoretical study and general design considerations in the development of such sensors are described. Experimental results were obtained for two sensor designs: one uses a cylindrical design with the SBTC-cut, and the other, called SPA, is a special resonator design vibrating around 5 MHz without any activity dips. Pressure sensitivity of approximately 145 Hz/MPa (1 Hz/lb/in(2)) at 175 degrees C is obtained. Laboratory evaluation of the static and dynamic performances is discussed for the prototypes based on the SPA design.     

A ZnO nanowire vacuum pressure sensor

In this study, we report the growth and characterization of lateral ZnO nanowires (NWs) on ZnO:Ga/glass templates. Using x-ray diffraction and micro-Raman spectroscopy, it was found that crystal quality of the as-grown ZnO NWs is good. It was also found that the average length and average diameter of the laterally grown ZnO NWs were 5?μm and 30?nm, respectively. A vacuum pressure sensor was then fabricated using a single NW bridging across two electrodes. By measuring the current-voltage characteristics of the samples at low pressure, we found that the currents were of 17, 34.28, 57.37 and 96.06?nA for the ZnO NW measured at 1 × 10(-3)?Torr, 1 × 10(-4)?Torr, 3 × 10(-5)?Torr and 5 × 10(-6)?Torr, respectively. These values suggest that the laterally grown ZnO NWs prepared in this study are potentially useful for vacuum pressure sensing.