Temperature-insensitive Strain Measurement Research Articles

Demodulation of CFBG With a Microwave Photonic Filter for Temperature-Insensitive Strain Measurement

Demodulation of CFBG With a Microwave Photonic Filter for Temperature-Insensitive Strain Measurement

Temperature characteristics of thick-film resistors and its application as a strain sensor with low temperature-sensitivity

Strain gauge made of thick-film resistors (TFRs) has great potential for civil engineering applications due to its relatively high strain sensitivity, good stability, low manufacturing cost, mass productability, and long life. Nevertheless, a persistent shortcoming of strain sensors is their thermal sensitivity. Temperature-insensitive strain measurement is important for applications. To address this issue, a thick-film resistor strain sensor with low temperature-sensitivity should be proposed and fabricated. In this paper, the effect of resistor paste components and firing temperatures on the temperature coefficient of resistance (TCR) of TFRs were studied systematically. TFRs made of various RuO2 concentrations (10 wt% to 30 wt%) fired on Al2O3 substrate at different firing temperatures (Tf) was investigated. The relationships between sheet resistivity, TCR and gauge factor (GF) were studied. The results show that hot TCR increases with increasing RuO2 concentration and firing temperature. In the vicinity of the minimum of the resistance–temperature curve (Tmin), the temperature has the least influence on the resistance value, and it can be considered that the TFR is temperature insensitive in a certain range. The effect of temperature on output strain can be evaluated by the ratio of TCR to GF. The results show that TCR, the ratio of TCR to GF and Tmin are all depended on sheet resistivity of thick-film resistors. By changing the concentration of the conductive phase and firing temperature, the sheet resistivity of TFRs can be controlled, and then strain sensors with low temperature-sensitivity for different ambient temperatures can be achieved.

Approach for temperature-insensitive strain measurement using a dual-core As2Se3-PMMA taper.

A temperature-insensitive strain sensor is proposed and demonstrated based on a dual-core As2Se3-polymethyl methacrylate(PMMA) taper. Longitudinal and transverse forces on the As2Se3 cores are induced by thermal expansion/contraction of the PMMA cladding due to an order of magnitude difference between the thermal expansion coefficients of As2Se3 and PMMA. At an optimal PMMA layer thickness, the wavelength shift caused by the thermally induced forces on the refractive index of the dual-core fiber cores counterbalances that caused by the thermally induced fiber length variation leading to temperature-insensitive transmission. Temperature-insensitive strain measurement over a temperature range from 30°C to 40°C is demonstrated in a dual-core As2Se3-PMMA fiber with an As2Se3 core diameter of 0.61μm and a PMMA cladding diameter of 34.4μm. Thermally induced forces in hybrid fibers open the path towards the realization of novel sensors and devices that are immune to temperature fluctuations.

Simultaneous measurement of strain and temperature using a polarization-maintaining photonic crystal fiber with stimulated Brillouin scattering

We demonstrate the simultaneous and distributed sensing of temperature and strain by combining the Brillouin dynamic grating (BDG) and Brillouin gain spectrum (BGS) using a polarization-maintaining photonic crystal fiber (PM-PCF). The characterization of the birefringence frequency shift of the PM-PCF shows that it remains almost unchanged within the temperature range of 5–80 °C, which allows a temperature-insensitive strain measurement using only the BDG. Combining the BDG and BGS, we demonstrate the simultaneous measurement of temperature and strain with a spatial resolution of 20 cm over a 5-m-long PM-PCF.

Temperature-insensitive strain measurement using in-fiber Bragg gratings inscribed in photonic crystal fiber

Two gratings with closely spaced center-wavelengths are written in either side of a splice between two cascaded photonic crystal fibers of same diameter. The relative wavelength-shifts in response to the temperature can be compensated by means of filling rational fluid material into the cladding air-holes. Separate measurement of strain with a high sensitivity can be achieved just by analyzing the wavelength-shifts of the reflection peaks. The presented discrimination method can well restrain the cross-sensitivity effect, and render a new category of inherently temperature-insensitive strain sensors.

Temperature-insensitive strain measurement using a birefringent interferometer based on a polarization-maintaining photonic crystal fiber

We propose a novel and simple scheme for a temperature-insensitive strain measurement by using a birefringent interferometer configured by a polarization-maintaining photonic crystal fiber (PM-PCF). The wavelength-dependent periodic transmission in a birefringent interferometer can be achieved by using a PM-PCF between two linear polarizers. Since the PM-PCF is composed of a single material, such as silica, the peak wavelength shift with temperature variation can be negligible because of the small amount of the birefringence change of the PM-PCF with temperature change. The measured temperature sensitivity is −0.3 pm/°C. However, the peak wavelength can be changed by strain because the peak wavelength shift is directly proportion to strain change. The strain sensitivity is measured to be 1.3 pm/μe in a strain range from 0 to 1600 μe. The measurement resolution of the strain is estimated to be 2.1 μe. The proposed scheme has advantages of simple structure and low loss without a Sagnac loop, temperature insensitivity, ease installation, and short length of a sensing probe compared with a conventional PMF-based Sagnac loop interferometer.

Simultaneous measurement of temperature and pressure by a single fiber Bragg grating with a broadened reflection spectrum

Simultaneous measurement of temperature and pressure with a single fiber Bragg grating (FBG) based on a broadened reflection spectrum is proposed and experimentally demonstrated. A novel double-hole structure of a cantilever beam is designed, and a FBG is affixed on the nonuniform strain area of the cantilever beam. The Bragg reflection bandwidth is sensitive to the spatially gradient strain but is free from the spatially uniform temperature. The wavelength peak shift and the bandwidth broadening of the FBG with a change of temperature and pressure allow for simultaneous discrimination between the temperature and the pressure effects. Standard deviation errors of 1.4 degrees C and 1.8 kPa were obtained with temperature and pressure ranges of 20 degrees C-100 degrees C and 0-80 kPa, respectively. This novel and low-cost sensor approach has considerable potential applications for temperature-insensitive strain measurement.

Temperature-insensitive strain measurement using differential double Bragg grating technique

A novel differential double Bragg grating sensor for temperature-insensitive strain measurement is presented. The sensor consists of two identical weak measuring and reference gratings separated by some distance. The reference grating is placed inside the silica capillary that made it almost strain insensitive. The basic idea in differential double Bragg grating sensor is to measure the energy of the oscillating term in the reflection spectrum of double Bragg grating structure. The normalized energy of the interference term depends on the pitch difference of the two gratings and does not change when pitch variations of both gratings are equal with temperature variation. Therefore, the normalized energy of the interference term can be used for the temperature-insensitive strain measurement.

Dynamic-strain measurement with dual-grating fiber sensor

A dual-grating sensor head, which was designed for temperature-insensitive strain measurement, was used to measure fast-varying strain perturbations. Using a Mach-Zehnder interferometer technique, we obtained ~0.1-muepsilon (microstrain) rms resolution with a 200-Hz strain input. The feasibility of measuring a dynamic-strain with a static-strain measuring configuration was also demonstrated.

Interferometric temperature-insensitive strain measurement with different-diameter fiber Bragg gratings

An interferometric strain-sensing system that combines an unbalanced Mach-Zehnder wavelength discriminator and spliced different-diameter fiber Bragg gratings is presented that has the capability to distinguish strain from temperature effects. Because the gratings are written in 135- and 165- microm -diameter fibers drawn from the same preform, when they are spliced they show similar temperature sensitivities but different responses to applied strain. Thus the relative Bragg wavelength difference of the two gratings is affected only by strain, and one can measure it accurately by monitoring the amplitude variation of the interference signal rather than the conventional phase variation.