Thermal Drift Research Articles

Limiting External Absorptivity of UAV-Based Uncooled Thermal Infrared Sensors Increases Water Temperature Measurement Accuracy

Thermal mapping of surface waters and the land surface via UAVs offers exciting opportunities in many scientific disciplines; however, unresolved issues persist related to accuracy and drift of uncooled microbolometric thermal infrared (TIR) sensors. Curiously, most commercially available UAV-based TIR sensors are black, which will theoretically facilitate heating of the uncooled TIR sensor via absorbed solar radiation. Accordingly, we tested the hypothesis that modifying the surface absorptivity of uncooled TIR sensors can reduce thermal drift by limiting absorptance and associated microbolometer heating. We used two identical uncooled TIR sensors (DJI Zenmuse XT2) but retrofitted one with polished aluminum foil to alter the surface absorptivity and compared the temperature measurements from each sensor to the accurate measurements from instream temperature loggers. In addition, because TIR sensors are passive and measure longwave infrared radiation emitted from the environment, we tested the hypotheses that overcast conditions would reduce solar irradiance, and therefore induce thermal drift, and that increases in air temperature would induce thermal drift. The former is in contrast with the conceptual model of others who have proposed that flying in overcast conditions would increase sensor accuracy. We found the foil-shielded sensor yielded temperatures that were on average 2.2 °C more accurate than those of the matte black sensor (p < 0.0001). Further, we found positive correlations between light intensity (a proxy for incoming irradiance) and increased sensor accuracy for both sensors. Interestingly, light intensity explained 73% of the accuracy variability for the black sensor, but only 40% of the variability in accuracy deviations for the foil-shielded sensor. Unsurprisingly, an increase in air temperature led to a decrease in accuracy for both sensors, where air temperature explained 14% of the variability in accuracy for the black sensor and 31% of the accuracy variability for the foil-shielded sensor. We propose that the discrepancy between the amount of variability explained by light intensity and air temperature is due to changes in the heat energy budget arising from changes in the surface absorptivity. Additionally, we suggest fine-scale changes in river-bed reflectance led to errors in UAV thermal measurements. We conclude with a suite of guidelines for increasing the accuracy of uncooled UAV-based thermal mapping.

Optical-resolution functional gastrointestinal photoacoustic endoscopy based on optical heterodyne detection of ultrasound

Photoacoustic endoscopy shows promise in the detection of gastrointestinal cancer, inflammation, and other lesions. High-resolution endoscopic imaging of the hemodynamic response necessitates a small-sized, high-sensitivity ultrasound sensor. Here, we utilize a laser ultrasound sensor to develop a miniaturized, optical-resolution photoacoustic endoscope. The sensor can boost the acoustic response by a gain factor of ωo/Ω (the frequency ratio of the signal light and measured ultrasound) by measuring the acoustically induced optical phase change. As a result, we achieve a noise-equivalent pressure density (NEPD) below 1.5 mPa·Hz-1/2 over the measured range of 5 to 25 MHz. The heterodyne phase detection using dual-frequency laser beams of the sensor can offer resistance to thermal drift and vibrational perturbations. The endoscope is used to in vivo image a rat rectum and visualize the oxygen saturation changes during acute inflammation, which can hardly be observed with other imaging modalities.

Innovative Delta Robot Sample Scanner

Synchrotron Endstations typically use a stack of coarse and fine motion stages to position and scan a sample in the beam. The serial nature of this design causes a low resonant frequency and hence limits the position stability. The combination of multiple stages also adds motion control and data analysis complexity. A large range parallel kinematic cartesian sample scanner has been designed, built, tested and installed to address these limitations. The stage combines a 3 mm travel range with < 3 nm RMS position jitter in the scan directions and < 1 nm/minute thermal drift during scanning. This paper describes and demonstrates the mechatronic design process of Dynamic Error Budgeting. The stage is installed and fully operational on beamline I14 at the Diamond Light Source being used for nanoscale XRF mapping, imaging and ptychography.

Thermomechanical analysis of the effects of homogeneous thermal field induced in the sensing coil of a fiber-optic gyroscope

A thermal field in the sensing coil of fiber-optic gyroscope gives rise to bias drift. The transient effect and the quasi-static effect are distinguished. The equations of this phenomenon developed in this article highlight the importance of knowing the strain field versus temperature along the optical fiber in the sensing coil. The influence of winding patterns on thermal bias is discussed using an analytical approach. To determine the strain field, a parameterized approach is proposed. An axisymmetric finite element model describing a double coated optical fiber is implemented. Thanks to this model, the thermo-mechanical behavior of the optical fiber coil is computed and explained in detail. Then, the computed strain field is validated with strain measurements by Rayleigh Optical Frequency Domain Reflectometry (Rayleigh-OFDR) for two different coils using two different optical fibers. The thermal bias drift for a spatial homogeneous thermal loading, referred to as Mohr effect in this paper, is computed. Finally, we point out that the contribution of radial and axial strains in the reference frame formed by the optical fiber coil is negligible compared to orthoradial strain on Mohr effect.

Evaluation of thermal-drift effect on strain measurement of energy pile

Fiber Bragg grating (FBG) strain sensors and electrical resistance strain (ERS) gauges are typically utilized to monitor the internal deformation of structures. However, a common problem inherent in these sensors is the unwanted thermal drift in the measurement results. This study first investigated factors influencing the thermal strain measurements of FBG strain sensors and ERS gauges through a series of calibration experiments. The results demonstrate that the relative error caused by the thermal output of the heated connection cables was as high as 90 %. Then a correction method for the thermal drift of the strain measurement was proposed. This correction method reduced the relative difference between the strain readings of bonded ERS gauges and FBG sensors from 82.6 % to around 10–20 %. Finally, FBG strain sensors and ERS gauges were employed to monitor the strain of the energy piles under cooling and heating cycles. The difference between the corrected readings from FBG strain sensors and ERS gauges was less than ± 10 %. The experimental results also reveal that the monitoring reliability of the FBG strain sensors was higher than the ERS gauges.

Nanoscale thermometry under ambient conditions via scanning thermal microscopy with 3D scanning differential method.

Local temperature measurement with high resolution and accuracy is a key challenge in nowadays science and technologies at nanoscale. Quantitative characterization on temperature with sub-100nm resolution is of significance for understanding the physical mechanisms of phonon transport and energy dissipation in nanoelectronics, optoelectronics, and thermoelectric devices. Scanning thermal microscopy (SThM) has been proved to be a versatile method for nanoscale thermometry. In particular, 2D profiling of the temperature field on the order of 10nm and 10 mK has already been achieved by SThM with modulation techniques in ultrahigh vacuum to exclude the parasitic heat flow between air and the cantilever. However, few attempts have been made to truly realize 2D profiling of temperature quantitatively under ambient conditions, which is more relevant to realistic applications. Here, a 3D scanning differential method is developed to map the 2D temperature field of an operating nanodevice under ambient environment. Our method suppresses the thermal drift and the parasitic heat flow between air and the cantilever by consecutively measuring the temperatures in thermal contact and nonthermal contact scenarios rather than in a double-scan manner. The local 2D temperature field of a self-heating metal line with current crowding by a narrowing channel is mapped quantitatively by a sectional calibration with a statistic null-point method and a pixel-by-pixel correction with iterative calculation. Furthermore, we propose a figure of merit to evaluate the performance of thermocouple probes on temperature field profiling. The development of nanoscale thermometry under ambient environment would facilitate thermal manipulation on nanomaterials and nanodevices under practical conditions.

Fiber-Optic Gyroscope Thermal Calibration through Two-Dimensional N-Order Polynomial for Landslide Displacement Monitoring

A fiber-optic gyroscope (FOG) with lower precision but higher cost advantage is typically selected according to working conditions and engineering budget. Thermal drift is the main factor affecting FOG precision. External thermal calibration methods by algorithms can effectively weaken the influence of thermal drift. This paper presents a thermal calibration method of a two-dimensional N-order polynomial (TDNP) and compares it with artificial neural network (ANN) methods to determine a software FOG thermal calibration method for landslide displacement monitoring. The TDNP thermal calibration coefficient matrix was established, and the thermal calibration capability of the TDNP method with different orders N was evaluated on the basis of error analysis. The ANN model with 1 to 18 hidden neural layers was established on the basis of LM, BR, and SCG algorithms to choose a suitable ANN. Finally, the mean absolute errors of FOG thermal calibration through the TDNP with different orders and the LM were compared. This method was applied in the Huangtupo landslide area, China. The results highlight that the TDNP method with order 5 had better performance and satisfied the requirements of landslide displacement monitoring. The research results can compensate for the lack of adaptability of the FOG thermal calibration method in landslide displacement monitoring.

Hybrid Integrated Dual-Microcomb Source

Dual-comb interferometry is based on self-heterodyning two optical frequency combs, with corresponding mapping of the optical spectrum into the radio-frequency domain. The dual comb enables diverse applications, including metrology, fast high-precision spectroscopy with high signal-to-noise ratio, distance ranging, and coherent optical communications. However, current dual-frequency-comb systems are designed for research applications and typically rely on scientific equipment and bulky mode-locked lasers. Here we demonstrate a fully integrated power-efficient dual-microcomb source that is electrically driven and allows turnkey operation. Our implementation uses commercially available components, including distributed-feedback and Fabry-Perot laser diodes, and silicon-nitride photonic circuits with microresonators fabricated in commercial multiproject wafer runs. Our devices are therefore unique in terms of size, weight, power consumption, and cost. Laser-diode self-injection locking relaxes the requirements on microresonator spectral purity and $Q$ factor, so that we can generate soliton microcombs resilient to thermal frequency drift and with pump-to-comb sideband efficiency of up to 40% at mW power levels. We demonstrate down-conversion of the optical spectrum from 1400 to 1700 nm into the radio-frequency domain, which is valuable for fast wide-band Fourier spectroscopy, which was previously not available with chip-scale devices. Our findings pave the way for further integration of miniature microcomb-based sensors and devices for high-volume applications, thus opening up the prospect of innovative products that redefine the market of industrial and consumer mobile and wearable devices and sensors.

Investigations of moiré artifacts induced by flux fluctuations in x-ray dark-field imaging

X-ray dark-field imaging using a grating interferometer has shown potential benefits for a variety of applications in recent years. X-ray dark-field image is commonly retrieved by using discrete Fourier transform from the acquired phase-stepping data. The retrieval process assumes a constant phase step size and a constant flux for each stepped grating position. However, stepping errors and flux fluctuations inevitably occur due to external vibrations and/or thermal drift during data acquisition. Previous studies have shown that those influences introduce errors in the acquired phase-stepping data, which cause obvious moiré artifacts in the retrieved refraction image. This work investigates moiré artifacts in x-ray dark-field imaging as a result of flux fluctuations. For the retrieved mean intensity, amplitude, visibility and dark-field images, the dependence of moiré artifacts on flux fluctuation factors is theoretically derived respectively by using a first-order Taylor series expansion. Results of synchrotron radiation experiments verify the validity of the derived analytical formulas. The spatial frequency characteristics of moiré artifacts are analyzed and compared to those induced by phase-stepping errors. It illustrates that moiré artifacts can be estimated by a weighted mean of flux fluctuation factors, with the weighting factors dependent on the moiré phase and different greatly for each retrieved image. Furthermore, moiré artifacts can even be affected by object’s features not displayed in the particular contrast. These results can be used to interpret images correctly, identify sources of moiré artifacts, and develop dedicated algorithms to remove moiré artifacts in the retrieved multi-contrast images.

A minimized and efficient low temperature loading device for indentation.

A minimized and efficient low temperature loading device cooling with Peltier coolers for indentation test is developed. Both specimen and indentation tip are immersed in 50% methanol-water solution, totally eliminating the contact thermal drift problem. Low temperature indentation tests down to 253.8K can be realized within 10min. The size of the device is miniaturized within 50 × 40 × 30mm3, and no vacuum environment is required. Monocrystalline copper is tested to perform the feasibility of the device. Based on the simple structure and stable experimental effect, the developed device can be integrated into various types of current indentation devices to attach low temperature testing ability.

Vertical gradient freeze growth of detector grade CdZnTeSe single crystals

We report the growth of detector grade Cd0.9Zn0.1Te0.97Se0.03 (CZTS) single crystals, a recently discovered quaternary semiconductor for room temperature radiation detection, by a vertical gradient freeze (VGF) method. VGF is a comparatively low-temperature growth method and avoids relative motion between the heater and the ampoule containing the precursor materials which minimizes any thermal drift or temperature fluctuations. As a result, CZTS single crystals with superior charge transport properties has been obtained. Growth of detector-grade CZTS single crystals using VGF method has not been reported yet. X-ray spectroscopy based elemental analysis showed that the grown crystals demonstrated the desired stoichiometry required for high resolution radiation detection. Planar detectors fabricated by deposition of gold contacts (∼0.07 cm2) demonstrated high bulk resistivity ∼1010 Ω-cm and a very low leakage current density of 2.8 × 10−8 A/cm2 at a bias of 100 V when measured at room temperature. The detectors showed excellent radiation response with 100 % charge collection efficiency when exposed to 5486 keV alpha particles. The electron mobility-lifetime (μτ) product was measured to be 3 × 10−3 cm2/V using a single polarity Hecht analysis which is at par with the recently reported values measured in CZTS grown using conventional Bridgman or travelling heater method. The electron mobility has been calculated to be 964 cm2V−1s−1 using a time-of-flight (TOF) method, a substantial improvement over that obtained from conventionally grown CZTS single crystals.

Raman lasing and other nonlinear effects based on ultrahigh-QCaF2 optical resonator

The calcium fluoride (CaF2) whispering gallery mode crystalline resonator is an excellent platform for nonlinear optical applications because of the decreasing in threshold caused by ultrahigh quality (Q) factor. In this paper, we achieved the observation of Raman lasing, first-order Raman comb, and second-order Raman lasing in a CaF2 disk resonator with a diameter of 4.96 mm and an ultrahigh-Q of 8.43×108 at 1550-nm wavelength. We also observed thermal effects in CaF2 disk resonator, and the threshold of thermo-optical oscillation is approximately coincident with Raman lasing, since the intracavity power increases rapidly when the power reaches the threshold, and higher input pump power results in longer thermal drift and higher Raman emission power. With a further increase in pump power, the optical frequency combs range is from 1520 nm to 1650 nm, with a wavelength interval of 4×FSR. It is a promising candidate for optical communication, biological environment monitoring, spectral analysis, and microwave signal sources.

Sub-millinewton thrust stand and wireless power coupler for microwave-powered small satellite thrusters.

The design and performance of a thrust stand for characterizing low-power electric propulsion thrusters are presented. The thrust stand is capable of sub-millinewton resolution for devices on the order of 1kg. The architecture is based on a counter-weighted hanging pendulum design, a variant of the standard hanging pendulum that employs a counterweight to increase force resolution. Thrust is measured in a displacement mode using the change in position of the pendulum arm as measured by an optical displacement sensor. Passive eddy-current damping is used to offset oscillations and decrease setting time. An in situ calibration rig using known masses is used to calculate thrust. The thrust stand features an adjustable counterweight for in-vacuum sensitivity adjustment. In addition, the design of a broadband (600-2490MHz) wireless microwave power coupler is presented. The device eliminates stiffness and thermal drift introduced by coaxial cables-typically the leading source of error in testing low-power microwave and radio frequency-powered thrusters. The thrust stand and coupler were tested using an electron cyclotron resonance magnetic nozzle thruster operating with xenon at flow rates from 1 to 10 sccm and powers ranging from zero (cold gas thrust) to 40W. The resulting measurements showed a force resolution of ∼10μN over a range of thrusts from ∼14 to 600µN.

Direct measurement of surface photovoltage by AC bias Kelvin probe force microscopy.

Surface photovoltage (SPV) measurements are a crucial way of investigating optoelectronic and photocatalytic semiconductors. The local SPV is generally measured consecutively by Kelvin probe force microscopy (KPFM) in darkness and under illumination, in which thermal drift degrades spatial and energy resolutions. In this study, we propose the method of AC bias Kelvin probe force microscopy (AC-KPFM), which controls the AC bias to nullify the modulated signal. We succeeded in directly measuring the local SPV by AC-KPFM with higher resolution, thanks to the exclusion of the thermal drift. We found that AC-KPFM can achieve a SPV response faster by about one to eight orders of magnitude than classical KPFM. Moreover, AC-KPFM is applicable in both amplitude modulation and frequency modulation mode. Thus, it contributes to advancing SPV measurements in various environments, such as vacuum, air, and liquids. This method can be utilized for direct measurements of changes in surface potential induced by modulated external disturbances.

Model of Thomson scattering from z-pinch plasma: Application in experimental design for Plasma Focus

The present work develops a model of Thomson scattering (TS) for z-pinch plasmas. Sustained on the phenomenology observed in dynamical-pinch discharges of interest in fusion studies, the plasma dynamics is modeled by axisymmetric bi-Maxwellian velocity distribution with axial and radial drift velocities. Expressions for TS form factor and screening integrals are deduced, and TS spectra are reconstructed. A characteristic temperature of the spectrum is identified, which is determined by a weighted-sum of the axial and radial temperatures, whose coefficients are given by the square of the respective axial and radial components of k→ over the square of the magnitude of k→. It is shown that it is not possible to determine the velocity distribution function of the plasma from just one direction of measurement. Additionally, an experimental setup, which requires two complementary observation directions for a complete determination of the proposed distribution function, is analyzed and its capacity to measure thermal anisotropy and drift velocities is studied for plasma conditions expected in the pinch phase of a plasma focus discharge.

Introducing Spontaneously Phase‐Separated Heterogeneous Interfaces Enables Low Power Consumption and High Reliability for Phase Change Memory

AbstractPhase‐change memory is one of the most promising candidates for the next generation nonvolatile memory, but their high power consumption and low reliability remain bottleneck problems that limit the data storage density and its storage‐class memory application. Here, an innovative phase change material with embedded self‐precipitated interfaces, where the nanoscale grains of phase change material are cut into interconnecting “crystal islands” by thermally stable self‐precipitated material with low thermal conductivity, is proposed. The precipitated material provides both thermal and atomic migration confinements in three dimensions. The thermal confinement enables low power consumption, and the atomic migration confinement enables high device reliability. The devices based on spontaneously phase‐separated O‐doped Sb2Te3 verify the material design, where Sb oxide acts as the precipitated heterogeneous phase and Sb–Te alloy as the phase change material. O‐doped Sb2Te3 device with 250 nm hole diameter shows an ultralow power consumption, down to a few hundreds of femtojoule, which is comparable with those of phase change nanowires. Besides, good thermal stability and low resistivity drift (drift coefficient 0.005) as well as excellent cycle endurance up to 108 times are also obtained at the same time. The doping fabrication process is quite compatible with current semiconductor industry.

Universal phase-shifting algorithm (UPSA) for nonuniform phase-step demodulation and null-testing criterion for phase accuracy gauging

We propose a non-iterative, universal phase-shifting algorithm (UPSA) for phase-demodulation regardless if the phase steps are linear, nonuniform, or even unknown. Nonlinear phase-step algorithms are important because those steps are not “floating-point” linear due to thermal drift, mechanical instabilities, or aging, even for commercial laser interferometers. Additionally, we propose a null-testing criterion to gauge the accuracy of the demodulated phase. Usually, novel PSAs are tested using simulations where we can compute the difference between the demodulated phase and the ideal one. This seems a vicious trap: usually, experimental phase gauging accuracy is unreachable having no prior access to the measuring phase. Here we offer a way to escape from this vicious circle by proposing a null-test that proves that the phase from experimental fringes is error-free. This null-test can be used for testing the phase quality of any PSA. In brief, we are proposing two interferometry tasks: 1) the UPSA for phase demodulation, and 2) a null-testing criterion which verify that the estimated phase is error-free.

Thermal drift reduction in photodiode dosimeters with switching bias

The effect of temperature on dosimetric measurements is a major limitation of solid-state dosimeters. This is especially true for PIN photodiode dosimeters, where the dark current depends exponentially on temperature. To minimize this effect, a compensation method is presented that relies on the diode structure itself without the need for an external sensor or device. During irradiation, the photodiode is periodically switched from reverse to forward polarization to determine the temperature of the device. This measurement is based on the linear dependence between the temperature and the forward voltage of the diode when it is operated at constant current. An electronic circuit implementing this procedure was developed and used for experimental characterization of the response to radiation of the BPW34S Si PIN photodiode. The proposed procedure reduced the uncertainty due to thermal drift by a factor of 7.5. In addition, an average dose rate sensitivity of 12 ± 2 nC/cGy was measured, with a sensitivity degradation below 2% for the irradiation cycle of 21.4 Gy performed under a 6 MV photon beam. We have shown that a p-n junction can be successfully used to compensate for the temperature effect on the dosimetric measurement.

Thermal drift correction method for laboratory nanocomputed tomography based on global mixed evaluation.

Nanocomputed tomography (nanoCT) is an effective tool for the nondestructive observation of 3D structures of nanomaterials; however, it requires additional correction phantom to reduce artifacts induced by the focal drift of the X-ray source and mechanical thermal expansion. Drift correction without a correction phantom typically uses rapidly acquired sparse projections to align the original projections. The noise and brightness difference in the projections limit the accuracy of existing feature-based methods such as locality preserving matching (LPM) and random sample consensus (RANSAC). Herein, a rough-to-refined correction framework based on global mixed evaluation (GME) is proposed for precise drift estimation. First, a new evaluation criterion for projection alignment, named GME, which comprises the structural similarity (SSIM) index and average phase difference (APD), is designed. Subsequently, an accurate projection alignment is achieved to estimate the drift by optimizing the GME within the proposed correction framework based on the rough-to-refined outlier elimination strategy. The simulated 2D projection alignment experiments show that the accuracy of the GME is improved by 14× and 12× than that of the mainstream feature-based methods LPM and RANSAC, respectively. The proposed method is validated through actual 3D imaging experiments.

Dual-axis thrust stand for the direct characterization of electrospray performance.

A dual-axis torsional thrust stand was successfully demonstrated at the Air Force Research Laboratory, enabling direct simultaneous thrust and mass loss measurement for the Air Force Electrospray Thruster Series 2 passively fed electrospray thruster. The dual-axis system is effectively two nulled torsional thrust stands sharing a single dual-axis gimbal with a thrust and mass resolution of ±0.2µN and ±0.04mg, respectively. The development of this system was inspired by a need for direct efficiency characterization of electrosprays via in situ mass measurements, and performance was compared to thruster masses measured pre- and post-testing using an analytical balance. Mass consumption data captured via the dual-axis stand, which is calibrated to a traceable uncertainty of 1.6%, varied between -5% and 18% as compared to analytical balance measurements throughout a multi-month testing effort highlighting the limitations in pre/post-weighing as a method for capturing propellant consumption due to absorption of atmospheric moisture when thrusters are removed from vacuum. Thrust stand tests were limited to short term operation with a daily available testing window of ∼5 h due to thrust stand drift following the 24 h cyclic temperature variations of the testing facility. A thorough investigation into the root cause of ambient thermal drift suggests that the thermal response of commercial flex-pivot bearings is directly producing spurious torques on the order of 10μNm/°C. Additionally, unresolved charging effects on thrust stand hardware currently limit thrust stand operation to tests operating with a positive thruster polarity. Further development and long duration test stability require both a targeted investigation into flex-pivot thermal response and minimization of facility effects.