Temperature Self-compensation Research Articles

Influence of Disturbing Factors in a System for Measuring Radial Clearances in Gas-Turbine Engines with Temperature Self-Compensation

This paper presents the results of analysis of the effect of disturbing factors on changes in the informative parameter of a single-coil eddy-current sensor, which are used as input data in studies of a radial clearance measurement system with self-compensation of temperature effects on the sensor. Conversion functions of the measuring circuit with the connected single-coil eddy-current sensor are obtained in analytical form. The conversion functions are dependences of the extreme code values at the measuring circuit output on radial clearances and temperature effects on the sensor taking into account disturbing factors (adjacent blades, blade temperature, axial displacements of the gas turbine engine compressor rotor). Quantitative estimates are obtained for influence functions of these disturbing factors on the calculated difference of the extreme code values in the system, which characterizes the measured parameter.

A D-Shaped Fiber Long-Range Surface Plasmon Resonance Sensor With High Q-Factor and Temperature Self-Compensation

A D-shaped fiber based long-range surface plasmon resonance (LRSPR) sensor with high quality factor ( $Q$ -factor) of 67.75 RIU−1 and temperature self-compensation was proposed and demonstrated. The multilayered architecture of the LRSPR sensor consisted of fiber/dielectric buffer layer (DBL)/Au film/analyte, and the deep penetration depth and long propagation distance of long-range surface plasmon polaritons made the LRSPR sensor possess high $Q$ -factor. The temperature-sensitive photoabsorption characteristic of the Terbium(III) complexes was utilized to provide temperature self-compensation for the refractive index (RI) measurement of the LRSPR sensor, and the LRSPR sensor realized simultaneous measurement of RI and temperature at the exact same location, which could eliminate the measurement error introduced by temperature to RI measurement. The simulation analysis, supported by finite element analysis (FEA) based on coupled-mode theory, was presented in detail. The simulation results showed that the electric field intensity on the surface of the LRSPR sensor was 2.52 times higher than that of the surface plasmon resonance (SPR) sensor and the sensitivity of the LRSPR sensor increased by 947.31 nm/RIU compared with the SPR sensor, implying the LRSPR sensor possessed more excellent sensing performance. An SPR sensor and a Terbium(III) complex-based LRSPR sensor were developed, and their RI sensing performance was systematically studied and tabulated. The experimental results showed that the $Q$ -factor of the LRSPR sensor was 2.56 times higher than that of the SPR sensor, which agreed well with the simulation results. The LRSPR sensor proposed in this paper possessed higher detection precision and presented greatly promising application prospects in the field of biochemistry.

An FBG-Sensing Two-Dimensional Vibration Sensor Based on Multi-Axis Flexure Hinge

Based on the unique advantages of fiber Bragg (FBG) in the field of vibration monitoring, a 2-D FBG accelerometer based on multi-axis flexure hinge is proposed. With the adoption of symmetrical multi-axis flexure hinges, the sensing probe has the same sensitivity in two measuring directions. The differential arrangement of the two couple FBGs can eliminate the influence of temperature, and in addition, its sensitivity is twice that of single FBG. The structure and principle of the sensor are explained, and its acceleration sensitivity and resonance frequency are analyzed theoretically in this paper. On this basis, the simulation analysis is carried out and two kinds of sensors for different occasions are made finally. Experimental studies show that the sensors can pick up the vibration signal accurately and have preferably temperature self-compensation effect under the condition form 20 °C to 90 °C. The stable frequency band of the max-sensor is 5 to 170 Hz, the acceleration sensitivity is up to 220 pm/g, the cross-interference in two measuring directions is not exceeding 4%, and the resonant frequency is 279.2 Hz. The min-sensor has a wide flat range from 20 to 600 Hz with an acceleration sensitivity of 40 pm/g. Its cross-interference is less than 3.5%, and the resonant frequency is 814.3 Hz.

Hypersonic Aerodynamic Force Balance Using Micromachined All-Fiber Fabry⁻Pérot Interferometric Strain Gauges.

This paper presents high-sensitivity, micromachined all-fiber Fabry–Pérot interferometric (FFPI) strain gauges and their integration in a force balance for hypersonic aerodynamic measurements. The FFPI strain gauge has a short Fabry–Pérot cavity fabricated using an excimer laser etching process, and the deformation of the cavity is detected by a white-light optical phase demodulator. A three-component force balance, using the proposed FFPI gauges as sensing elements, was fabricated, calibrated, and experimentally evaluated. To reduce thermal output of the balance, a simple and effective self-temperature compensation solution, without external temperature sensors, is proposed and examined through both oven heating and wind tunnel runs. As a result of this approach, researchers are able to use the balance continuously throughout a wide range of temperatures. During preliminary testing in a hypersonic wind tunnel with a free stream Mach number of 12, the measurement accuracies of the balance were clearly improved after applying the temperature self-compensation.

Quartz Crystal Microbalance for viscosity measurement with temperature self-compensation

This paper presents the design, fabrication, and experimental demonstration of a portable viscosity measurement system using an AT-cut quartz crystal resonator with a temperature compensation technique. The proposed sensor is designed to measure viscosity from room temperature to 65 °C with complete temperature compensation. A novel fixture to hold the crystal for the viscosity sensing is designed using CAD (Computer Aided Design) software and a 3D model prototype was fabricated using a 3D printer. Subsequently, the fabricated fixture was integrated with a crystal resonator and tested with various mixtures of glycerol and water solutions each with different viscosities. A beat frequency based temperature measurement and compensation technique was also proposed and has been implemented in the crystal resonator based force measurement system in the literature. The measurement system is portable, simple, and low cost making it convenient for laboratory-based viscosity measurements. The proposed fixture of the measurement system can be altered for real-time monitoring to quantify the viscosity of the continuous flowing aqueous liquids.

Sensitivity-Enhanced Strain Sensor Based on Thin-Core Fiber Modal Interferometer Interacted With Tilted Fiber Bragg Grating

A sensitivity-enhanced strain sensor constructed by a 7-mm-long thin-core fiber (TCF) splicing with a 10-mm-long tilted fiber Bragg grating (TFBG) was proposed. The modal interferometer formed by the TCF will interact with the spectrum of the TFBG to form an overlapped spectrum, which will extremely increase the axial strain sensitivity of the TFBG. Experimental results showed that the wavelength shifts of the resonant dip in the overlapped spectra for the applied axial strain have a high sensitivity of 0.67 pm/ $\mu \varepsilon $ . Meanwhile, the proposed sensor has the temperature self-compensation function for the variation of the external temperature simply by measuring the relative wavelength shifts of the Bragg mode of the TFBG.

Fiber-Optic Current Sensor Based on Ohmic Heating of Tin Sphere With Embedded Silicon Fabry–Perot Interferometer

A fiber-optic Fabry–Perot interferometer (FPI) is proposed and demonstrated as an electric current sensor based on ohmic heating with temperature self-compensation. The sensing head is fabricated by attaching a silicon pillar on the fiber tip as the FPI and inserted into a molten tin (Sn) sphere as the conducting medium. Two copper electrodes are also inserted into the Sn sphere and serve as the electrodes for current measurement. The electric current loaded on the Sn sphere will lead to a temperature rise that is measured with high resolution by the silicon FPI. A fiber Bragg grating is incorporated in the vicinity of the sensing head for temperature compensation. Both theoretical analysis and experimental results indicate that the peak or valley wavelengths of the silicon FPI have a linear response to the square of the measured current. The current responsivity of 1.83 nm/A2 has been experimentally obtained, with a resolution of 1.28 × 10–3 A at around 0.3 A.

Side-polished flexible SPR sensor modified by graphene with in situ temperature self-compensation.

Fiber-based techniques make it possible to implant a miniaturized and flexible surface plasmon resonance (SPR) sensor into the human body. However, for implantable applications, the miniaturization of fiber SPR sensors results in low sensitivity compared with traditional prism-type SPR sensors due to limited space and the effects of temperature fluctuations. Therefore, it is necessary to compensate for temperature drift in the measurements, such as the case of the quantification of the relationship between glucose concentration and SPR resonance wavelength. In this report, we proposed a highly sensitive fiber SPR sensor based on a side-polished structure modified by graphene for implantable continuous glucose monitoring with in situ temperature self-compensation using a long-period fiber grating (LPFG). The results demonstrate that the sensor with monolayer graphene achieved the best sensitivity of 3058.22 nm/RIU, and the LPFG achieves a maximum resolution of 0.042 nm/°C. The proposed SPR sensor enabled the detection of hypoglycemia, which is still a significant challenge for continuous glucose monitoring in a clinical setting.

Differential Fresnel-reflection-based fiber biochemical sensor with temperature self-compensation for high-resolution measurement of Cd2+ concentration in solution

A fiber biochemical sensor system was developed to measure cadmium (Cd2+) solution based on differential temperature self-compensation, which exhibits high sensitivity in detecting Cd2+. The device only consists of a light source, three couplers, two photodetectors, and two fiber sensing ends. Utilizing the efficient adsorption of cadmium ion by allylthiourea, the sensing head was prepared. The estimated concentration resolution of 4.9 × 10−7 mol/L and the standard deviation of concentration of 4.6 × 10−6 mol/L in large temperature range are achieved. The measured data is fitted to a second-order polynomial equation with good agreement. Moreover, the differential technique of the sensor can effectively eliminate concentration errors resulting from temperature fluctuations and environment effects, and thus real-time monitoring can be obtained.

Enhanced Sensitivity of a Love Wave-Based Methane Gas Sensor Incorporating a Cryptophane-A Thin Film.

A Love wave-based sensing chip incorporating a supramolecular cryptophane A (CrypA) thin film was proposed for methane gas sensing in this work. The waveguide effect in the structure of SiO2/36° YX LiTaO3 will confine the acoustic wave energy in SiO2 thin-film, which contributes well to improvement of the mass loading sensitivity. The CrypA synthesized from vanillyl alcohol by a double trimerisation method was dropped onto the wave propagation path of the sensing device, and the adsorption to methane gas molecules by supramolecular interactions in CrypA modulates the acoustic wave propagation, and the corresponding frequency shifts were connected as the sensing signal. A theoretical analysis was performed to extract the coupling of modes for sensing devices simulation. Also, the temperature self-compensation of the Love wave devices was also achieved by using reverse polarity of the temperature coefficient in each media in the waveguide structure. The developed CrypA coated Love wave sensing device was connected into the differential oscillation loop, and the corresponding gas sensitive characterization was investigated. High sensitivity, fast response, and excellent temperature stability were successfully achieved.

Liquid-State Environment Sensors Using Liquid Metal

Flexible devices have many potential applications in wearable electronics, robotics, health monitoring, and more. Mechanically deformable devices and sensors such as flexible devices enable conformal coverage of electronic systems on curved and soft surfaces. Sensors utilizing liquids confined in soft templates as the sensing component present the ideal platform for such applications, as liquids are inherently more deformable than solids. However, to date, current liquid-metal based strain sensors are incapable of resolving small pressure changes in the few kPa range, making them unsuitable for applications such as heart-rate monitoring which require much lower pressure detection resolution. In addition, liquid-based devices have been limited to metal lines based on a single liquid component given the difficulty in the fabrication of liquid-based junctions due to intermixing. Here we demonstrate state-of-art microfluidic environmental sensors using liquid metal, highly sensitive pressure sensor based on tactile diaphragm pressure sensor, and temperature/humidity/oxygen sensors with mechanically robust liquid-liquid “heterojunction”. This report will present an important advancement towards the realization of liquid-state electronic systems. Introduction Electronic devices and sensors which exhibit large amounts of mechanical deformability have many applications such as in smart wallpapers and human-machine interfaces for prosthetics. In this regard, tremendous advancements have been made in engineering solid-state electronic materials and devices on elastic substrates. Recently, sensors based on using liquid active components embedded within soft elastomeric substrates have shown much promise for such applications as liquids present the ultimate limit in deformability. In this paper, we report four microfluidic sensors using liquid metals, highly sensitive pressure sensor based on tactile diaphragm pressure sensor, and temperature/humidity/oxygen sensors with liquid-liquid “heterojunction”. The work presents an important step towards the potential realization of liquid-state electronic systems that offer new form factors and functionality. Current Result < Microfluidic diaphragm pressure sensor> In both sensors, the devices were fabricated by photolithography techniques using poly(dimethylsiloxane) (PDMS) as the substrate, and eutectic GaInSn (Galinstan) as electrodes. A microfluidic tactile diaphragm pressure sensor based on embedded Galinstan microchannels (70 µm width 70 µm height) capable of resolving sub-50 Pa changes in pressure with sub-100 Pa detection limits and a response time of 90 ms is demonstrated(Fig. 1). An embedded equivalent Wheatstone bridge circuit makes the most of tangential and radial strain fields, leading to high sensitivities of 0.0835 kPa-1 change in output voltage. The Wheatstone bridge also provides temperature self-compensation, allowing for operation in the range of 20-50 °C. As examples of potential applications, a polydimethylsiloxane (PDMS) wristband with an embedded microfluidic diaphragm pressure sensor capable of real time pulse monitoring(Fig. 2) and a PDMS glove with multiple embedded sensors to provide comprehensive tactile feedback of a human hand when touching or holding objects are demonstrated(Fig. 3). <Temperature/humidity/oxygen sensors with liquid-liquid “heterojunction”> In termes of temperature/humidity/oxygen sensors with liquid-liquid “heterojunction”, liquid metal was used as electrode, and ionic liquids as a sensing material(Fig. 4 and 5). As shown in Fig. 6, equivalent circuit of the sensors were established based on Nyquist plot The sensor showed stable sensitivity to temperature without hysteresis as shown in Fig. 7 with a 0.039/°C increase in conductivity, which is quite high compared to other reports. We also show proof of concept for humidity and oxygen gas sensing using three kinds of ionic liquids, 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][Otf]), 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMPYR][NTf2]). As shown in Fig. 7, the sensitivity of each ionic liquid to humidity and oxygen differed depending on the ionic liquid. For each type of stimuli, the sensing can be optimized by choosing the proper ionic liquid. In the future, multiple liquid heterojunction sensors, each with a different ionic liquid may be multiplexed into a fully integrated system to sense different stimuli with calibrated response. Figure 1

Design and Optimization of FBG Implantable Flexible Morphological Sensor to Realize the Intellisense for Displacement.

The measurement accuracy of the intelligent flexible morphological sensor based on fiber Bragg grating (FBG) structure was limited in the application of geotechnical engineering and other fields. In order to improve the precision of intellisense for displacement, an FBG implantable flexible morphological sensor was designed in this study, and the classification morphological correction method based on conjugate gradient method and extreme learning machine (ELM) algorithm was proposed. This study utilized finite element simulations and experiments, in order to analyze the feasibility of the proposed method. Then, following the corrections, the results indicated that the maximum relative error percentages of the displacements at measuring points in different bending shapes were determined to be 6.39% (Type 1), 7.04% (Type 2), and 7.02% (Type 3), respectively. Therefore, it was confirmed that the proposed correction method was feasible, and could effectively improve the abilities of sensors for displacement intellisense. In this paper, the designed intelligent sensor was characterized by temperature self-compensation, bending shape self-classification, and displacement error self-correction, which could be used for real-time monitoring of deformation field in rock, subgrade, bridge, and other geotechnical engineering, presenting the vital significance and application promotion value.

Optical spectral sweep comb liquid flow rate sensor.

In microfluidic chip applications, the flow rate plays an important role. Here we propose a simple liquid flow rate sensor by using a tilted fiber Bragg grating (TFBG) as the sensing element. As the water flows in the vicinity of the TFBG along the fiber axis direction, the TFBG's spectrum changes due to its contact with water. By comparing the time-swept spectra of the TFBG in water to that of the TFBG with water flowing over it, a spectral sweep comb was formed, and the flow rate can be detected by selecting a suitable sweeping frequency. The proposed sensor has a high Q-value of over 17,000 for the lower rate and a large detectable range from 0.0058mm/s to 3.2mm/s. And the calculated corresponding lower detectable flow rate of 0.03nL/s is 3 orders magnitude better than that of the current fiber flowmeter. Meanwhile, the proposed sensor has the temperature self-compensation function for the variation of the external temperature. We believe that this simple configuration will open a research direction of the TFBG-deriving theory and configuration for lower flow rate measurements for microfluidic chip applications.

夹持式温度自补偿光纤布拉格光栅应变传感测试技术

夹持式温度自补偿光纤布拉格光栅应变传感测试技术

Anisotropic electrical and abrasion-sensing properties of cement-based composites containing aligned nickel powder

The electrical properties of aligned nickel powder-filled cement-based composites and the abrasion-sensing properties of these composites, as evaluated based on the change in their resistance at varying abrasion depths, were investigated in this paper. Micrograph characterization of nickel powder distribution indicates that the electrical conduction path preferentially forms along the direction of the nickel powder alignment, which leads to increasingly anisotropic electrical properties under greater magnetic field strengths. The level of anisotropy was also determined to be strongly dependent on the nickel powder content. The maximum anisotropic electrical properties were achieved at the percolation threshold content of the nickel powder, which is the critical point for the formation of an effective conductive network. Based on the cement-based composites anisotropic electrical properties and a sectionalized electrode design, the composites filled with aligned nickel powder demonstrated good abrasion-sensing properties, with humidity and temperature self-compensation abilities.

One novel type of miniaturization FBG rotation angle sensor with high measurement precision and temperature self-compensation

In order to achieve rotation angle measurement, one novel type of miniaturization fiber Bragg grating (FBG) rotation angle sensor with high measurement precision and temperature self-compensation is proposed and studied in this paper. The FBG rotation angle sensor mainly contains two core sensitivity elements (FBG1 and FBG2), triangular cantilever beam, and rotation angle transfer element. In theory, the proposed sensor can achieve temperature self-compensation by complementation of the two core sensitivity elements (FBG1 and FBG2), and it has a boundless angel measurement range with 2π rad period duo to the function of the rotation angle transfer element. Based on introducing the joint working processes, the theory calculation model of the FBG rotation angel sensor is established, and the calibration experiment on one prototype is also carried out to obtain its measurement performance. After experimental data analyses, the measurement precision of the FBG rotation angle sensor prototype is 0.2 ° with excellent linearity, and the temperature sensitivities of FBG1 and FBG2 are 10 pm/℃ and 10.1 pm/℃, correspondingly. All these experimental results confirm that the FBG rotation angle sensor can achieve large-range angle measurement with high precision and temperature self-compensation.

Temperature Self-Compensation High-Resolution Refractive Index Sensor Based on Fiber Ring Laser

In this letter, a temperature self-compensation high-resolution refractive index (RI) sensor based on intracavity intensity-modulated sensing in a fiber ring laser is demonstrated. A fiber-optic multimode interferometer based on single-mode-no-core-single-mode fiber structure is cascaded with a fiber Bragg grating and used as a reflected sensing head to enhance intensity-modulated depth. It is inserted in a fiber ring laser as a wavelength selective filter and the intracavity intensity-modulated RI sensing is induced for the output intensity of the fiber laser. Furthermore, because the lasing wavelength of the sensor system is sensitive to temperature but insensitive to external RI, the temperature self-compensation measurement can be realized. The RI sensitivity is measured to be −4.98 mW/RIU from 1.3349 to 1.3665. Correspondingly, the relative intensity sensitivity achieves −196.1 dB/RIU from 1.3349 to 1.3544 and −744.6 dB/RIU from 1.3544 to 1.3665. The resolution of the fiber laser sensor is obtained as high as $2\times 10^{{{-10}}}$ RIU with the signal-to-noise ratio more than 55 dB.

Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring.

Flexible pressure sensors have many potential applications in wearable electronics, robotics, health monitoring, and more. In particular, liquid-metal-based sensors are especially promising as they can undergo strains of over 200% without failure. However, current liquid-metal-based strain sensors are incapable of resolving small pressure changes in the few kPa range, making them unsuitable for applications such as heart-rate monitoring, which require a much lower pressure detection resolution. In this paper, a microfluidic tactile diaphragm pressure sensor based on embedded Galinstan microchannels (70 µm width × 70 µm height) capable of resolving sub-50 Pa changes in pressure with sub-100 Pa detection limits and a response time of 90 ms is demonstrated. An embedded equivalent Wheatstone bridge circuit makes the most of tangential and radial strain fields, leading to high sensitivities of a 0.0835 kPa-1 change in output voltage. The Wheatstone bridge also provides temperature self-compensation, allowing for operation in the range of 20-50 °C. As examples of potential applications, a polydimethylsiloxane (PDMS) wristband with an embedded microfluidic diaphragm pressure sensor capable of real-time pulse monitoring and a PDMS glove with multiple embedded sensors to provide comprehensive tactile feedback of a human hand when touching or holding objects are demonstrated.

Probing Nanostrain via a Mechanically Designed Optical Fiber Interferometer

We propose an extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber sensor with a novel mechanical design for nano-scale strain measurement. In our proposed sensor, a designed mechanical structure consists of a cylinder and a square column attached to a stainless steel substrate. This simple and compact structure along with a fiber ceramic ferrule and a gold-coated reflective mirror as a packaged EFPI sensor can resolve nano-scale strain with temperature self-compensation. In comparison with the existing nanostrain sensing methods, no reference sensors and complicated configurations are needed. The strain measured by our proposed sensor ranges from 0 to 677 ne with a measurement accuracy of ±5 ne. This robust and easy-to-build geometry-based nano-scale strain sensor has great potential in nanotechnology, geophysical research, seismic monitoring, and other practical applications.

Design and FEM simulation for a novel resonant silicon MEMS gyroscope with temperature compensation function

A kind of resonant silicon micro-electro-mechanical systems (MEMS) gyroscope with self-temperature compensation function is designed to overcome the problem of conventional MEMS gyroscope, whose measuring precision is greatly affected by the temperature effect. Sensitive element of the system is composed of four symmetrically distributed double ended tuning fork (DETFs). They are of the same dimensions. Two of the DETFs which are closing to the proof mass are used to sense the force effect and temperature effect while the other two DETFs are just used to sense the temperature effect. By comparing these two different conditions, the self-temperature compensation model can be deduced. In order to verify the feasibility of the design, finite element method (FEM) is used to compute the performance of system. It is concluded that in the range of −20 to 80 °C, the maximum relative error of the resonant frequency variation is reduced from 16.3 to 3.1%. Simulating result indicates this scheme of design is effective to overcome the temperature effect of this kind of gyroscope.