Temperature Drift Research Articles

Temperature stability study of resonant angular scanning micromirrors with electrostatic comb-drive actuators

Resonant rotational scanning micromirrors with electrostatic comb-drive actuators are widely used in generating structured lights for 3D sensing, but their resonant scanning stability is affected considerably by the working temperature, which in turn compromises the sensing accuracy. The resonant scanning instability is mainly exhibited as the temperature drifts of the quality factor (Q) and the resonance frequency. In this paper, we focus on the Q variation due to the temperature dependence of air damping. The temperature dependence of the air damping in a comb-drive micromirror is investigated using both simplified analytical damping models and computational fluidic dynamic (CFD) models. The modeling results show that the temperature dependence of the viscous damping of the comb drive is opposite to that of the drag damping of the mirror plate, providing a means of minimizing the temperature dependence of Q by adjusting the structural parameters of the comb drive and the mirror plate. It has also been found from the modeling that the lengths of the comb-drive fingers and the mirror plate play the most significant role while the cavity height under the mirror plate has little effect if it is more than 10 % of the mirror plate length. Meanwhile, four micromirrors with different comb-finger or mirror-plate lengths are designed and fabricated. The testing results from these four fabricated mirrors have confirmed that the temperature coefficient of the Q value of an angular scanning comb-drive micromirror can be altered and ultimately compensated by changing the mirror-plate and/or comb-finger lengths.

Portable microwave radiometer for wearable devices

This paper presents a new circuit of the miniature microwave radiometer for wearable devices, which can be used to monitor the core body temperature (CBT) of internal human tissues continuously 24/7. The measurement results of the proposed device, as opposed to the known miniature wearable radiometers, remain unchanged when the impedance of the examined area varies. We have derived an analytical expression for radiometer measurement error based on parameters of device components. This formula allows accuracies to be estimated and optimal parameters of the circuit to be selected to minimise measurement error at a design stage. It is shown that measurement error is independent of the antenna reflection coefficient and the temperature of the radiometer front-end. A prototype of the single-channel miniature radiometer has 32 × 25 × 14 mm3 dimensions and USB interface communication with PC. A 28 -h run of the device has shown that it is highly stable, and a maximum drift in temperature is 0.15 °C. Operating frequency range was 3400−4100 MHz, supply voltage −5 V; power supply of the radiometer in measurement mode is 210 mA; time constant of the radiometer without being averaged is 0.6 s, at the same time, standard deviation δ = 0.17 °C, with further averaging during 4 s δ = 0.052 °C, with averaging during 30 s δ = 0.017 °C; when there were input reflections R2 = 0.25, an error in measuring brightness temperature shifted by 0.2 °C; with 10 °C variations in ambient temperature the shift was 0.15 °C.

–1 MV DC Filter and High-Voltage DC Measurement System for ITER Neutral Beam Injector System

This article proposes the one-package structure of –1 MV direct current (dc) filter circuit and dc measurement system composed of dc voltage dividers and dc current transducers (DCCTs). These apparatuses are becoming more important for the expansion of high-voltage dc (HVDC) power grids. However, at present, they are separately installed keeping a huge distance for air insulation, and an increase in equipment size and footprint has become a major issue. We succeeded in reducing the footprint to 1/100 by storing the aforementioned HVDC vital parts in one package of a pressure vessel. Our developed configuration uses sulfur hexafluoride (SF6) gas not only for insulation purpose but also as a refrigerant to forcibly ventilate vertically in order to allow the dc filter circuit, which is heat generation source, and the dc measuring instruments, which need to minimize the effect of temperature drift, to coexist. We also addressed another issue caused by the limited space in the one-package structure, where the stray capacitance of the dc voltage divider tends to become large and then lowers the measurement accuracy for transient voltage variation. As a countermeasure, the dc voltage divider is composed of much larger capacitance than the stray capacitance and additional damping resistance to avoid LC resonance with wiring inductance. The actual-product tests demonstrated the followings; the dc measurement system has satisfied high measurement accuracy of 0.5% and fast responsivity of 3.3 μ s retaining decay rate within −3 dB; the temperature rise of the dc voltage dividers and the DCCTs is reasonably suppressed; the dc measurement system and the dc filter circuit withstood DC −1.2 MV.

A Constant Current Digital Control Method for Primary-Side Regulation Active-Clamp Flyback Converter

Constant current controlled flyback converter is widely used in low power applications for its simple structure and low cost. In order to further improve the output power and the efficiency, active-clamp flyback converter with soft-switching technique is always used. To avoid the nonlinearity and temperature drift of opto-coupler in the feedback circuit, a constant current digital control method is proposed for a primary-side regulation active-clamp (PSRAC) flyback converter in this article. Soft-switching technique is realized in discontinuous conduction modulation mode with a modified active-clamp technique. To compensate the nonlinearity of the secondary diode current with primary-side regulation, a new output current estimation algorithm is put forward based on the charge balance principle. The output current is predicted from primary current and the auxiliary winding voltage, and constant output current control is realized with primary peak current control method. The cost is low as only one low speed digital-to-analog converter, three comparators and a digital controller are required. The proposed control scheme was verified by a field-programmable gate array controlled 5.4-10.8 V/1.80 A PSRAC flyback converter. The output current accuracy is within in 1.2% in different input and output condition and the peak efficiency is improved by 3.6% after active-clamp technique is used.

Nonuniformity Correction Design and Implementation for Infrared Image Based on FPGA and Artificial Neural Networks

Infrared imaging technology is widely used in military and civilian applications. However, due to the materials and manufacturing technology, the response of each unit in the infrared detector is not completely consistent, which leads to the nonuniformity of the infrared focal plane array. In this article, we propose a way to use artificial neural network by self-adaptively updating the correction coefficients based on FPGA. Compared with traditional calibration-based method, our method is more flexible and can avoid the effects of temperature drift efficiently.

Method and unit for dynamic control of conversion characteristics of spectrometric paths for multichannel charged particle registration systems

A method and unit for dynamic control of conversion characteristics of spectrometric paths of multichannel charged particle registration systems based on specialized microchip with a large degree of integration similar to IDE1140 in structure is proposed. The conversion characteristics are controlled during operation of the device by auto-adjusting the offset and gain of the scaling amplifier. The proposed method allows to use the entire dynamic range of the analog-to-digital converter and adjust the temperature drift for each channel at the hardware level during operation of the device.

Image reconstruction of TGZ3 grating by eliminating tip‐sample convolution effect in AFM

Accurate and meticulous measurement is an important prerequisite to obtain the real surface information of samples in atomic force microscopy (AFM). A severe problem is the frequent occurrence of measurement errors, which are mainly caused by the nonlinearity of the probe driver, the temperature drift of the system and the tip characteristics. The measurement errors caused by probe tip are the main source of errors in AFM nanoscale measurements. The shape and state of AFM tip will distort the AFM image from the actual sample morphology. If the information about the probe is known, the measurement error caused by the probe tip can be greatly reduced. In order to obtain accurate AFM images, a new method based on geometric measurement model and blind tip reconstruction is proposed to eliminate tip-sample convolution in the measurement of grating samples. The static and dynamic characteristics of the AFM tip are described by four parameters: cone angle, curvature radius, scanning inclination angle and mounting inclination angle. Finally, the feasibility and effectiveness of the new calibration method are verified by evaluating the image reconstruction quality. In conclusion, the proposed method can effectively reconstruct accurate AFM images of the grating.

Design and Fabrication of Temperature-Insensitive MEMS Pressure Sensor Utilizing Aluminum-Silicon Hybrid Structures

In order to meet the requirements for high sensitivity and low temperature drift of pressure sensors in the field of meteorological detection or tire pressure monitoring system (TPMS), this paper proposes a MEMS chip-level pressure sensor based on two pairs of aluminum-silicon hybrid structures, which are etched on the SOI wafer. The pressure sensor achieves the amplified piezoresistive effect by the micron thick ohmic contact between the boron-doped silicon and external aluminum shunt, as verified by finite element numerical simulation and experiment. Four symmetrical L-shaped raised structures are distributed around the square strained membrane, which enhance the stress of the pair of stress-sensitive aluminum-silicon hybrid structures. The other pair of hybrid structures placed outside the strained membrane of the sensor chip enables differential sensor output which is highly insensitive to temperature. The offset drift of differential output is reduced to −4.39%FS compared with that of single aluminum-silicon hybrid structure. Cooperated with temperature compensation structures, an additional thermodynamic control system by using PID algorithm to keep the working temperature stable can eliminate the temperature drift of sensor output. The feasibility of the thermodynamic control system is verified by steady-state thermal simulation. Experiment test results show that the sensitivity of a single aluminum-silicon hybrid structure can reach 0.283 mV/V/kPa at constant heating temperature of 50 °C, and whose thermal coefficient of offset (TCO) can be reduced from −6.92E-1 to −1.51E-3 %FS/°C in ambient temperature ranges of −20 to 50 °C.

The influence of a moderate temperature drift on thermal physiology and perception

Humans spend approximately 80–90% of their time indoors. In current practice, indoor temperatures in many buildings are controlled very tightly. However, allowing more variation in indoor temperature results in more energy-efficient buildings and could potentially improve human metabolic and cardiovascular health. Therefore, this study aimed to evaluate the effect of a drifting ambient temperature versus a fixed ambient temperature on thermal physiological parameters and subjective perception. A cross-over intervention design was conducted in 16 healthy men (age 26 ± 4 y; BMI 23.0 ± 1.7 kg/m2) between July 2018 and May 2019. All participants underwent two whole-day (8:30–17:00) experimental sessions, during which they were exposed to a drifting (17–25°C with a morning ramp of 2.58°C/h and afternoon ramp of -2.58°C/h) or constant ambient temperature (21°C) in randomized order. The experiments took place in respiratory chambers, which simulated a typical office environment and in which temperature conditions can be controlled accurately. Throughout the experimental sessions core and skin temperature, heart rate, blood pressure, energy expenditure as well as activity levels were measured. Subjective thermal perception, such as thermal comfort and sensation, was assessed by questionnaires every 30 min. Results reveal that energy expenditure was higher in the morning during the drifting session, which was accompanied by an increase in activity levels. Both drifting and fixed sessions were judged as comfortable although during the drift thermal comfort was lower in the morning and afternoon and higher during midday. The results indicate that a drifting ambient temperature can be applied in practice, and as such, can contribute to a healthier and more sustainable built environment. More research is needed to understand the role of a drifting temperature on the long term.

A temperature drift compensation method applied to fiber optic gyroscope north-seeking

The startup error of fiber optic gyroscope (FOG) in north-seeking is the error caused by the zero-bias drift of FOG caused by drastic change of the temperature in the starting process. The start-up error significantly increases north-seeking error during the cold startup phase compared to the stable phase, which prolongs the effective north-seeking time. Through the analysis of the factors affecting the temperature drift of FOG, the mul-ti-parameter linear model was established by empirical mode decomposition (EMD), autoregressive-moving average (ARMA) modeling and Kalman filtering to realize a temperature drift compensation method applied to FOG north-seeking. The experimental results show that the method can reduce the north-seeking startup error by nearly 80%, so that the startup north-seeking precision is equivalent to the stable phase and the effective north-seeking time is shortened.

Continuous Hue-Based Self-Calibration of a Smartphone Spectrometer Applied to Optical Fiber Fabry-Perot Sensor Interrogation.

Smartphone-based optical spectrometers allow the development of a new generation of portable and cost-effective optical sensing solutions that can be easily integrated into sensor networks. However, most commonly the spectral calibration relies on the external reference light sources which have known narrow spectral lines. Such calibration must be repeated each time the fiber and diffraction grating holders are removed from the smartphone and reattached. Moreover, the spectrometer wavelength scale can drift during the measurement because of the smartphone temperature fluctuations. The present work reports on a novel spectral self-calibration approach, based on the correspondence between the light wavelength and the hue features of the spectrum measured using a color RGB camera. These features are caused by the nonuniformity of camera RGB filters’ responses and their finite overlap, which is a typical situation for RGB cameras. Thus, the wavelength scale should be externally calibrated only once for each smartphone spectrometer and can further be continuously verified and corrected using the proposed self-calibration approach. An ability of the plug-and play operation and the temperature drift elimination of the smartphone spectrometer was experimentally demonstrated. Conducted experiments involved interrogation of optical fiber Fabry-Perot interferometric sensor and demonstrated a nanometer-level optical path difference resolution.

Analysis of Retrofit Solutions of a Ground Source Heat Pump System: An Italian Case Study

Ground coupled heat pumps are a notoriously efficient system for heating and cooling buildings. Sometimes the characteristics of the building and the user’s needs are such that the amount of heat extracted from the ground during the winter season can be considerably different from the amount injected in summer. This situation can cause a progressive cooling or heating of the ground with a negative effect on the energy efficiency and correct operation of the system. In these cases, an accurate sizing has to be done. In systems already built, it could be necessary to intervene a posteriori to remedy an excessive ground thermal drift due to the energy unbalance. In this work, such a situation relating to a real office building in Italy is investigated and several solutions are examined, one of which has been then implemented. In particular, a hybrid heat pump using as heat sink both the ground and external air is compared with common solutions through computer simulations using a dedicated numerical model, which has also been compared with monitoring data. As a result, the hybrid heat pump shows better performance and limits the thermal drift of the ground temperature.

Thermal Drifts of Capacitive Flow Meters: Analysis of Effects and Model-Based Compensation

Capacitive sensing has become a favorable measurement technology for flow metering in pneumatic conveying systems. Multielectrode sensing structures and tomographic signal evaluations enable spatially resolved flow parameter estimation, which is of particular interest for pneumatically conveyed solids due to inhomogeneous particle distributions within the pipeline. The noninvasive working principle of capacitive sensors is an important feature for the application in industrial processes with harsh environments. However, cross sensitivities of the capacitive probe cause effects, such as temperature drifts of the measurements. For a reliable operation of capacitive flow meters in harsh environments, induced drifts have to be compensated. In this article, we present the detailed analyses of thermal effects within capacitive sensors. Based on the findings, a model-based temperature compensation approach is developed within the Bayesian framework. The performance of the proposed compensation approach is analyzed by a measurement-based validation within a climate chamber and by a simulation-based uncertainty quantification. The capability to obtain temperature-independent estimates with calibration measurements acquired at room temperature is demonstrated.

Disturbance Elimination for the Modular Joint Torque Sensor of a Collaborative Robot

The ability to obtain accurate torque information and detect collision information is the key demand for collaborative robots. Given the highly integrated modular joint, the joint torque-sensing system is disturbed by other elements during online measurement, affecting the accuracy of measurement. For example, the torque ripple caused by the periodic deformation of the flexspline of the harmonic driver and the temperature drift due to the heating of motor are the two main factors affecting the measurement of the torque sensor. In this study, a torque sensor suitable for a modular joint is developed. Moreover, a strain gauge configuration based on a specified phase difference for torque ripple cancelation and a temperature compensation method based on the combination of the Wheatstone bridge and a nonlinear model are proposed. Finally, the performance of the developed sensor is experimentally evaluated.

Polariton relaxation and polariton nonlinearities in nonresonantly cw-pumped III-nitride slab waveguides

Polariton lasers are mostly based on planar cavities. Here we focus on an alternative configuration with slab waveguide modes strongly coupled to excitons confined in GaN/AlGaN quantum wells. We study experimentally and theoretically polariton relaxation at temperatures ranging from 4 to 200 K. We observe a good robustness of the lower polariton population peak energy position against temperature changes due to a balance between the shift of the exciton energy and the change in the normal mode splitting, a promising feature for future applications such as lasers and amplifiers where a small temperature drift in the emission wavelength is a desired asset. Finally, at $T=4\phantom{\rule{4pt}{0ex}}\mathrm{K}$ we observe the signature of polariton nonlinearities occurring in the continuous wave regime that are assigned to an optical parametric oscillation process.

Improving sensitivity and coverage of structural health monitoring using bulk ultrasonic waves

Practical ultrasonic structural health monitoring systems must be able to deal with temperature changes and some signal amplitude/phase drift over time; these issues have been investigated extensively with low-frequency-guided wave systems but much less work has been done on bulk wave systems operating in the megahertz frequency range. Temperature and signal drift compensation have been investigated on a thick copper block specimen instrumented with a lead zirconate titanate disc excited at a centre frequency of 2 MHz, both in the laboratory at ambient temperature and in an environmental chamber over multiple 20°C–70°C temperature cycles. It has been shown that the location-specific temperature compensation scheme originally developed for guided wave inspection significantly out-performs the conventional combined optimum baseline selection and baseline signal stretch method. The test setup was deliberately not optimised, and the signal amplitude and phase were shown to drift with time as the system was temperature cycled in the environmental chamber. It was shown that the ratio of successive back wall reflections at a given temperature was much more stable with time than the amplitude of a single reflection and that this ratio can be used to track changes in the reflection coefficient from the back wall with time. It was also shown that the location-specific temperature compensation method can be used to compensate for changes in the back wall reflection ratio with temperature. Clear changes in back wall reflection ratio were produced by the shadow effect of simulated damage in the form of 1-mm diameter flat-bottomed holes, and the signal-to-noise ratio was such that much smaller defects would be detectable.

A Mode-Localized Resonant Accelerometer With Self-Temperature Drift Suppression

This paper theoretically and experimentally demonstrates the temperature drift suppression capability of a mode-localized accelerometer based on three degree of freedom weakly coupled resonators. The theoretical model of the temperature characteristics of the amplitude ratio and frequency of the mode-localized accelerometer under the influence of Young's modulus were established. The effect of the temperature on the input conversion mechanism and weakly coupled resonators are both included in the model. The simulation results show that thermal stress is the main factor affecting the output metric of the mode-localized accelerometer with mechanical coupling beam and, consequently, a stress relief structure is proposed to suppress the effect of stress on the output metric. Compared with the mode-localized accelerometer without stress relief structure, the temperature coefficients of sensitivity and two output metrics of the accelerometer with the stress relief structure are both suppressed by one order of magnitude via the simulation and experiment verification from 30°C to 60°C. And the temperature suppression coefficient of amplitude ratio is improved by 43.9 times than that of the frequency which shows that the mode-localized accelerometer based on amplitude ratio has an excellent temperature drift suppression capability.

Effective linewidth shifts in single-molecule detection using optical whispering gallery modes

Here, we report shifts of the linewidth of a plasmon enhanced whispering gallery mode (WGM) of a glass microsphere cavity due to binding of single sub-kDa molecules. The observed linewidth of the WGM can either increase or decrease upon binding of single molecules depending on the location of their binding sites. The linewidth shifts arise due to the change in the unresolved frequency splitting of standing wave modes (SWMs). These SWMs are formed due to the scattering from the gold nanoparticles attached to the WGM. Monitoring the WGM linewidth provides a robust method for sensing single molecules over prolonged time periods as the linewidth is unaffected by changes in the host refractive index due to drifts in temperature, pressure, or change in the concentration of buffers.

An integrated packaged resonant accelerometer with temperature compensation.

This paper describes the design, fabrication, and testing of an integrated packaged sensor that is composed of a micro resonant accelerometer and a temperature sensor. The resonant accelerometer with differential configuration consists of double quartz resonators and a silicon substrate. When acceleration is applied along the sensing axis, the inertial force induced by the proof mass will transfer force to the resonators, which causes an opposite frequency shift of the dual quartz resonators. The loaded acceleration can be measured through detecting the differential frequency shift. The symmetric differential configuration response to spurious effects of thermal loading and inelastic effect causing prestress in the resonators is similar, which can be reduced by detecting the differential frequency, effectively. However, during the manufacture and packaging process, the otherness of residual stress in two quartz resonators results in that the response of resonators to temperature variation is not strictly the same. In other words, this temperature drift cannot be eliminated by the structure design. Thus, a temperature sensor and an accelerometer were packaged in a shell together. These novel integrated sensors can measure acceleration and temperature simultaneously. With the testing temperature data, a novel temperature compensation that is a combination of the variable coefficient regression and least squares support vector machine is used for improving the performance of the accelerometer. By means of this compensation and field programmable gate array, a real-time and online compensation is achieved. The tumble testing results indicate that the sensitivity of the accelerometer is ∼16.97 Hz/g. With the temperature compensation, the output drift of the scale factor is improved by 0.605 Hz/g in the full temperature range, which is from 0.072 Hz/g to 0.015 Hz/g. The drift of zero bias is improved from 345 mg to 1.9 mg.

A Characterization of the Performance of Gas Sensor Based on Heater in Different Gas Flow Rate Environments

The performance of gas sensors based on micro-heater is highly dependent on the environment temperature, heater temperature, and gas flow rate. The performance fluctuation of gas sensors induced by environment temperature drift can be reduced in different ways. In this article, different sizes and shapes of obstacles are placed around the sensitive component of the thermal conductivity gas sensor to study the effect of gas flow rate on the gas sensor performance. Both the simulation and experiment results indicate that the obstacle design can reduce the interference of gas flow rate on gas sensor performance. As the obstacle size increases, the influence of gas flow rate decreases and the dynamic detection accuracy of the gas sensor increases at the same gas flow rate, and the voltage variation of the sensor with quadrangular prism obstacle shape is minimal, and the gas velocity reduction effect is 1.77% better than cylinder obstacle shape. The effect of gas flow rate on the gas response is also investigated by detecting the voltage response of the MG811 gas sensor with and without thermostatical control. The result shows that the gas flow rate not only reduces the temperature of the sensor (direct influence), but also promotes the chemical reaction of the sensor, which releases a large amount of heat (indirect influence). The corresponding relationship between voltage response and gas flow rate is obtained through controlling the temperature of sensitive components thermostatically. This article provides a new angle for improving the accuracy of the gas sensor in different gas flow rate environments, which can improve the detection rate of the wireless monitoring system.