Miniature all-fiber Fabry-Perot sensor for simultaneous measurement of pressure and temperature

This article presents a miniature, high-sensitivity, all-silica Fabry-Perot fiber-optic sensor suitable for simultaneous measurements of pressure and temperature. The proposed sensor diameter does not exceed 125 μm and consists of two low-finesse Fabry-Perot resonators created at the tip of an optical fiber. The first resonator is embodied in the form of a short air cavity positioned at the tip of the fiber. This resonator utilizes a thin silica diaphragm to achieve the sensor's pressure response. The second resonator exploits the refractive index dependence of silica fiber in order to provide the proposed sensor's temperature measurement function. Both resonators have substantially different lengths that permit straightforward spectrally resolved signal processing and unambiguous determination of the applied pressure and temperature.     

Integrated optical micromachined pressure sensor with spectrally encoded output and temperature compensation

A promising type of optical pressure sensor combines an integrated optical interferometer with a micromachined diaphragm on a shared silicon substrate. We have demonstrated a sensor of this type that uses an unbalanced Mach-Zehnder waveguide interferometer together with a broadband source to produce a spectrally encoded measurement. This spectral encoding mechanism is advantageous as it is not readily degraded by transmission through optical fibers. We have also demonstrated a means to obtain a temperature-compensated pressure measurement by interrogating both polarization eigenmodes of the interferometer.     

Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC

An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.     

Embedded micromachined fiber-optic Fabry-Perot pressure sensors in aerodynamics applications

Small size, high bandwidth pressure sensors are required for instrumentation of probes and test models in aerodynamic studies of complex unsteady flows. Optical-fiber pressure sensors promise potential advantages of small size and low cost in comparison with their electrical counterparts. We describe miniature Fabry-Perot cavity pressure sensors constructed by micromachining techniques in a turbine test application. The sensor bodies are 500 /spl mu/m squared, 300 /spl mu/m deep with a /spl sim/2 /spl mu/m-thick copper diaphragm electroplated on one face. The sensor cavity is formed between the diaphragm and the cleaved end of a single mode fiber sealed to the sensor by epoxy. Each sensor is addressed interferometrically in reflection by three wavelengths simultaneously, giving an unambiguous phase determination; a pressure sensitivity of 1.6 radbar/sup -1/ was measured, with a typical range of vacuum to 600 kPa. Five sensors were embedded in the trailing edge of a nozzle guide vane installed upstream of a rotor in a full-scale turbine stage transient test facility. Pressure signals in the trailing edge flow show marked structure at the 8 kHz blade passing frequency. To our knowledge, this is the first report of sensors located at the trailing edge of a normal-sized turbine blade.     

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.     

Optical-fiber sensor for simultaneous measurement of pressure and temperature: analysis of cross sensitivity

The use of a highly elliptical core two-mode fiber for simultaneous measurement of pressure (radial pressure or hydrostatic pressure) and temperature is presented. The sources of errors are discussed. Expressions are developed to calculate the cross sensitivities. From the numerical examples, some useful conclusions are given.     

Design and analysis of a PZT-based micromachined acoustic sensor with increased sensitivity

The ever-growing applications of lead zirconate titanate (PZT) thin films to sensing devices have given birth to a variety of microsensors. This paper presents the design and theoretical analysis of a PZT-based micro acoustic sensor that uses interdigital electrodes (IDE) and in-plane polarization (IPP) instead of commonly used parallel plate-electrodes (PPE) and through-thickness polarization (TTP). The sensitivity of IDE-based sensors is increased due to the small capacitance of the interdigital capacitor and the large and adjustable electrode spacing. In addition, the sensitivity takes advantage of a large piezoelectric coefficient d33 rather than d31, which is used in PPE-based sensors, resulting in a further improvement in the sensitivity. Laminated beam theory is used to analyze the laminated piezoelectric sensors, and the capacitance of the IDE is deduced by using conformal mapping and partial capacitance techniques. Analytical formulations for predicting the sensitivity of both PPE- and IDE-based microsensors are presented, and factors that influence sensitivity are discussed in detail. Results show that the IDE and IPP can improve the sensitivity significantly.     

Oxygen pressure and measurement temperature dependence of defects related bands in zinc oxide films

The ZnO films were fabricated by pulsed laser deposition at various oxygen pressure on single crystal silicon substrate. The structural and optical properties were investigated at various measurement temperature. The results showed that all the films have good c-axis preferred orientation. The different defects in films were fabricated which can be caused by various oxygen pressure. The films deposited at 1 Pa oxygen pressure have the most intense and narrow UV emission, and did not exhibit the deep band emission at the various measurement temperature. With the decrease of measurement temperature, the V_O-, O_i- and O_Zn-related band energy decreases, which is opposed to the V_Zn-related defects, meanwhile, the intensity of O_i-related emission peak has a sharp increase.     

Accurate measurement of the radius of curvature of a concave mirror and the power dependence in a high-finesse Fabry-Perot interferometer

We describe the accurate measurement of the radius of curvature of a concave mirror in a Fabry-Perot interferometer with a finesse of 78,100. The radius of curvature of the concave mirror is determined by measuring the free spectral range and the transverse-mode range with the frequency response functions. The radii of curvature at two orthogonal (x and y) axes on the mirror surface resulting from the polishing nonisotropy were accurately measured to be r(x) = 1008.46 mm and r(y) = 1006.94 mm, respectively, with an accuracy of 8 × 10(-5). This accuracy is the best to our knowledge. The power dependence of the radii of curvature to the cavity internal intensity at a steady state was measured to be dr(x)/dI(c) = +60 μm/(MW/cm(2)) at the x axis and dr(y)/dI(c) = +47 μm/(MW/cm/(2)) at the y axis to an intensity of 2.1 MW/cm(2).     

Extrinsic fiber-optic Fabry-Perot interferometer sensor for refractive index measurement of optical glass

A simple fiber-optic sensor based on Fabry-Perot interference for refractive index measurement of optical glass is investigated both theoretically and experimentally. A broadband light source is coupled into an extrinsic fiber Fabry-Perot cavity formed by the surfaces of a sensing fiber end and the measured sample. The interference signals from the cavity are reflected back into the same fiber. The refractive index of the sample can be obtained by measuring the contrast of the interference fringes. The experimental data meet with the theoretical values very well. The proposed technique is a new method for glass refractive index measurement with a simple, solid, and compact structure.     

Simultaneous measurement of temperature and pressure

It is shown theoretically and experimentally that nuclear quadrupole resonance can be used to measure temperature and pressure simultaneously. Pis’ma Zh. Tekh. Fiz. 24, 54–57 (January 26, 1998)     

Vibration: history and measurement with an extrinsic Fabry-Perot sensor with solid-state laser interferometry

We have studied the history of vibration and demonstrate a laser-based noncontact interferometric vibration sensor. The sensor promises the measurement of microdisplacement by using a Fabry-Perot cavity formed between a partially coated gradient-index lens and a movable reflector. Displacement is determined by the detection of interference fringes caused by phase modulation within the cavity. The sensor was tested in conjunction with both multimode and single-mode fiber transmission. Calibration with multimode fiber produced a fringe-contrast function that decreased monotonically with displacement. This calibration allowed at least 30 fringes to be discriminated, giving a displacement resolution of 0.034 mum across a range of 10.2 mum. Dynamic tests demonstrated a working range of at least 3.74 mum at frequencies as high as 2 kHz. Similar tests in which single-mode fiber was used indicated a dynamic working range of at least 4.29 mum.     

Uniaxial pressure dependence of the Debye temperature in metals

The electrical resistance and its temperature coefficient have been measured for a platinum foil as a function of uniaxial pressure over the pressure range 0 to 60 MPa. The measurements were performed at room temperature using the transient hot-strip method. The data are analyzed using the electrical resistivity formula within the Block-Grüneisen approximation. The pressure dependence of the Debye temperature was directly obtained from an expansion of this formula and using the basic definition of the temperature resistivity coefficient. The reliability of the experimental data was then verified using the basic definition of Grüneisen constant. Within the investigated pressure range, the analysis supports the interpretation that the change in resistance of platinum under pressure is mainly due to the change in the amplitude of the atomic vibrations that are directly related to the change in Debye temperature. The pressure dependence of resistance and the Debye temperature of the platinum were reasonably good in spite of the approximations involved.     

硅压阻式微压力传感器的研制及性能测试

硅微压力传感器由于体积小、重量轻、精度高、成本低等特点应用很广泛,在某些领域已取代传统的传感器。进一步研制小体积高精度的传感器,扩大其应用范围已势在必行。本工作主要从提高传感器的性能角度来分析掩膜版设计中的重要问题,并对设计制作的传感器进行静态测试,取得了满意的实验结果。     

A multifunctional atmospheric pressure and air temperature sensor

The operating principle of a sensor for simultaneously measuring atmospheric pressure and air temperature using a semiconductor material with a transverse piezoelectric emf is considered. A method of investigating the metrological characteristics of the sensor and test results are presented. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 31–32, January, 2000.     

基于数值分析的压力传感器温度补偿方法研究

现有的压力传感器存在温度漂移和非线性等问题。在-40～80℃工作温度下进行压力传感器标定试验,建立一种基于数值分析的结合三次样条插值、最小二乘法、牛顿插值法的压力传感器温度补偿模型,并基于试验标定数据进行仿真,结果表明:采用该压力传感器温度补偿方法后,最大零点偏移和最大灵敏度误差分别为5.597 Pa和0.2%,最大相对误差为0.19%,极大地修正了压力传感器的温度漂移,该温度补偿模型的可行性和实用性得到验证。     

Dynamic strain measurement using an extrinsic Fabry-Perot interferometric sensor and an arrayed waveguide grating device

In this paper, we demonstrate an interrogation system, based on an arrayed waveguide grating, capable of monitoring dynamic strain in a cantilever beam at frequencies up to 5 kHz (limited by the actuator) with a similar precision to resistive strain gauges.     

Fabrication and testing of bulk micromachined silicon carbide piezoresistive pressure sensors for high temperature applications

This paper explores the development of high-temperature pressure sensors based on polycrystalline and single-crystalline 3C-SiC piezoresistors and fabricated by bulk micromachining the underlying 100-mm diameter (100) silicon substrate. In one embodiment, phosphorus-doped APCVD polycrystalline 3C-SiC (poly-SiC) was used for the piezoresistors and sensor diaphragm, with LPCVD silicon nitride employed to electrically isolate the piezoresistor from the diaphragm. These piezoresistors fabricated from poly-SiC films deposited at different temperatures and doping levels were characterized, showing -2.1 as the best gauge factor and exhibited a sensitivities up to 20.9-mV/V*psi at room temperature. In a second embodiment, epitaxially-grown unintentionally nitrogen-doped single-crystalline 3C-SiC piezoresistors were fabricated on silicon diaphragms, with thermally grown silicon dioxide employed for the piezoresistor electrical isolation from the diaphragm. The associated 3C-SiC/SiO/sub 2//Si substrate was fabricated by bonding a (100) silicon wafer carrying the 3C-SiC onto a silicon wafer with thermal oxide covering its surface. The 3C-SiC handle wafer was then etched away in KOH. The diaphragm was fabricated by time etching the silicon substrate. The sensors were tested at temperatures up to 400/spl deg/C and exhibited a sensitivity of 177.6-mV/V*psi at room temperature and 63.1-mV/V*psi at 400/spl deg/C. The estimated longitudinal gauge factor of 3C-SiC piezoresistors along the [100] direction was estimated at about -18 at room temperature and -7 at 400/spl deg/C.     

Broadband D2 coherent anti-stokes Raman spectroscopy for single-shot pressure and temperature determination with a Fabry-Perot etalon

A method is demonstrated that employs a Fabry-Perot etalon to modulate a broadband coherent anti-Stokes Raman spectroscopy signal beam spatially to obtain enhanced resolution and spectral information for single-shot measurements of pressure and temperature. Resulting images are analyzed by; first, fits to Fabry-Perot patterns for single rovibrational lines; second, a line-shape analysis for a single rovibrational line; and third, a mapping of the Fabry-Perot channel spectra to a linear spectrum. Measurements of the D(2) Raman Q-branch lines were made for a D(2) in Ar mixture to take advantage of the large pressure shift and rovibrational line spacing. Peaks are located to better than 0.5% of the free spectral range of the etalon (approximately 0.01 cm(-1)) and a quantitative analysis of the pressure shifting and broadening is determined for the 1-10-MPa range. Finally, temperature and pressure determination using a band-fitting analysis is demonstrated.