High-resolution Temperature Sensor Research Articles

Intrusions and turbulent mixing above a small Eastern Mediterranean seafloor-slope

Abstract Growing evidence is found in observations and numerical modelling of the importance of steep seafloor topography for turbulent diapycnal mixing leading to redistribution of suspended matter and nutrients, especially in waters with abundant internal tides. One of the remaining questions is the extent of turbulent mixing away from and above nearly flat topography, which is addressed in this paper. Evaluated are observations from an opportunistic, week-long mooring of high-resolution temperature sensors above a small seafloor slope in about 1200 m water depth of the Eastern Mediterranean. The environment has weak tides, so that near-inertial motions and -shear dominate internal waves. Vertical displacement shapes suggest instabilities to represent locally generated turbulent overturns, rather than partial salinity-compensated intrusions dispersed isopycnally from turbulence near the slope. This conclusion is supported by the duration of instabilities, as all individual overturns last shorter than the mean buoyancy period and sequences of overturns last shorter than the local inertial period. The displacement shapes are more erratic than observed in stronger stratified waters in which shear drives turbulence, and better correspond with predominantly buoyancy-driven convection-turbulence. This convection-turbulence is confirmed from spectral information, generally occurring dominant close to the seafloor and only in weakly stratified layers well above it. Mean turbulence values are 10-100 times smaller than found above steep ocean topography, but 10 times larger than found in the open-ocean interior.

Canopy cover and microtopography control precipitation-enhanced thaw of ecosystem-protected permafrost

Northern high-latitudes are projected to get warmer and wetter, which will affect rates of permafrost thaw and mechanisms by which thaw occurs. To better understand the impact of rain, as well as other factors such as snow depth, canopy cover, and microtopography, we instrumented a degrading permafrost plateau in south-central Alaska with high-resolution soil temperature sensors. The site contains ecosystem-protected permafrost, which persists in unfavorable climates due to favorable ecologic conditions. Our study (2020–2022) captured three of the snowiest years and three of the four wettest years since the site was first studied in 2015. Average thaw rates along an across-site transect increased nine-fold from 6 ± 5 cm yr−1 (2015–2020) to 56 ± 12 cm yr−1 (2020–2022). This thaw was not uniform. Hummock locations, residing on topographic high points with relatively dense canopy, experienced only 8 ± 9 cm yr−1 of thaw, on average. Hollows, topographic low points with low canopy cover, and transition locations, which had canopy cover and elevation between hummocks and hollows, thawed 44 ± 6 cm yr−1 and 39 ± 13 cm yr−1, respectively. Mechanisms of thaw differed between these locations. Hollows had high warm-season soil moisture, which increased thermal conductivity, and deep cold-season snow coverage, which insulated soil. Transition locations thawed primarily due to thermal energy transported through subsurface taliks during individual rain events. Most increases in depth to permafrost occurred below the ∼45 cm thickness seasonally frozen layer, and therefore, expanded existing site taliks. Results highlight the importance of canopy cover and microtopography in controlling soil thermal inputs, the ability of subsurface runoff from individual rain events to trigger warming and thaw, and the acceleration of thaw caused by consecutive wet and snowy years. As northern high-latitudes become warmer and wetter, and weather events become more extreme, the importance of these controls on soil warming and thaw is likely to increase.

Micro-kelvin temperature-stable system for biocalorimetry applications.

Achieving micro-kelvin (µK) temperature stability is critical for many calorimetric applications. For example, sub-nanowatt resolution biocalorimetry requires stabilization of the temperature of the calorimeter to µK levels. Here, we describe how µK temperature stability can be accomplished in a prototypical calorimetric system consisting of two nested shields and a suspended capillary tube, which is well suited for biocalorimetry applications. Specifically, we show that by employing nested shields with µTorr-levels of vacuum in the space between them as well as precise feedback control of the temperature of the shields (performed using high-resolution temperature sensors), the effect of ambient temperature fluctuations on the inner shield and the capillary tube can be attenuated by ∼100 dB. We also show that this attenuation is key to achieving temperature stabilities within ±1 and ±3 µK (amplitude of oscillations) for the inner shield and the capillary tube sensor, respectively, measured in a bandwidth of 1 mHz over a period of 10h at room temperature (∼20.9 ± 0.2 °C). We expect that the methods described here will play a key role in advancing biocalorimetry.

High-resolution temperature sensor fabricated with composed PEDOT: PSS/CuPc for electronic skin

High-resolution temperature sensor fabricated with composed PEDOT: PSS/CuPc for electronic skin

Soliton microcomb-assisted microring photonic thermometer with ultra-high resolution and broad range

Whispering gallery mode resonators (WGMRs) have proven their advantages in terms of sensitivity and precision in various sensing applications. However, when high precision is pursued, the WGMR demands a high-quality factor usually at the cost of its free spectral range (FSR) and corresponding measurement range. In this article, we propose a high-resolution and wide-range temperature sensor based on chip-scale WGMRs, which utilizes a Si3N4 ring resonator as the sensing element and a MgF2-based microcomb as a broadband frequency reference. By measuring the beatnote signal of the WGM and microcomb, the ultra-high resolution of 58 micro-Kelvin (μK) was obtained. To ensure high resolution and broad range simultaneously, we propose an ambiguity-resolving method based on the gradient of feedback voltage and combine it with a frequency-locking technique. In a proof-of-concept experiment, a wide measurement range of 45 K was demonstrated. Our soliton comb-assisted temperature measurement method offers high-resolution and wide-range capabilities, with promising advancements in various sensing applications.

High-resolution silicon photonic sensor based on a narrowband microwave photonic filter

Microwave photonic sensors are promising for improving sensing resolution and speed of optical sensors. In this paper, a high-sensitivity, high-resolution temperature sensor based on microwave photonic filter (MPF) is proposed and demonstrated. A micro-ring resonator (MRR) based on silicon-on-insulator is used as the sensing probe to convert the wavelength shift caused by temperature change to microwave frequency variation via the MPF system. By analyzing the frequency shift with high-speed and high-resolution monitors, the temperature change can be detected. The MRR is designed with multi-mode ridge waveguides to reduce propagation loss and achieves an ultra-high Q factor of 1.01 × 106. The proposed MPF has a single passband with a narrow bandwidth of 192 MHz. With clear peak-frequency shift, the sensitivity of the MPF-based temperature sensor is measured to be 10.22 GHz/°C. Due to higher sensitivity and ultra-narrow bandwidth of the MPF, the sensing resolution of the proposed temperature sensor is as high as 0.019 °C.Graphical

Fiber Optic Temperature Sensor System Using Air-Filled Fabry-Pérot Cavity with Variable Pressure.

We report a high-resolution fiber optic temperature sensor system based on an air-filled Fabry-Pérot (FP) cavity, whose spectral fringes shift due to a precise pressure variation in the cavity. The absolute temperature can be deduced from the spectral shift and the pressure variation. For fabrication, a fused-silica tube is spliced with a single-mode fiber at one end and a side-hole fiber at the other to form the FP cavity. The pressure in the cavity can be changed by passing air through the side-hole fiber, causing the spectral shift. We analyzed the effect of sensor wavelength resolution and pressure fluctuation on the temperature measurement resolution. A computer-controlled pressure system and sensor interrogation system were developed with miniaturized instruments for the system operation. Experimental results show that the sensor had a high wavelength resolution (<0.2 pm) with minimal pressure fluctuation (~0.015 kPa), resulting in high-resolution (±0.32 ℃) temperature measurement. It shows good stability from the thermal cycle testing with the maximum testing temperature reaching 800 ℃.

Internal tidal sloshing and a non-linear wave source away from topography

The ocean-interior shows omnipresent internal wave motions whose importance becomes more and more acknowledged for deep mixing across the stable vertical density stratification for heat and suspended matter redistribution. To observationally study vertical propagation variations of internal tides away from a steep topographic slope, a >1-km long mooring with 760 high-resolution temperature sensors was deployed at 2380 m depth halfway Mount Josephine NE-Atlantic Ocean for 4 months. In the lower 150 m above the seafloor, internal waves slosh, become highly non-linear and break vigorously, every tidal cycle. After signal separation using semidiurnal band-pass and harmonic filters, the vertical phase propagation shows: 1. Phase differences of 90° are observed in isotherms and cross-slope currents over typically 600 m in the vertical, 2. Non-linearity is already found in harmonic records that describe 300-m large-scale internal tides, 3. Non-uniform thin-layer stratification causes about 50% of the semidiurnal variance in small-scales, 4. Upward internal tide propagation starts at the top of non-linear wave breaking, 5. Downward propagation from above leading to energy-focusing at 700 m above the ocean-floor and about 700 m below the nearest seamount-ridge generates interior hydraulic jumps during spring tide.

Preliminary Study on the Stability of High-resolution π-phase Shift FBG Ocean Temperature Sensor

Fiber Bragg gratings are widely used in sensing fields, but few studies about their stability have been reported. A high-resolution π-phase shift FBG (π-FBG) ocean temperature sensor is experimentally demonstrated by using a linearized optical frequency sweeping interrogation system. A gas absorption line from H13C14N (HCN) gas was used to calibrate the laser frequency in real-time, providing long-term stability of the demodulation system. The temperature coefficient of π-FBG is ~14pm/°C, the temperature-resolution is as high as 0.001 °C and the response time is 49.45ms. In order to study the stability of the π-FBG probe, it is placed in a Gallium point bottle with a constant temperature point. Over the course of 4 hours of continuous testing, the probe exhibited a linear drift of approximately 0.09°C.

Convection and intermittency noise in water temperature near a deep Mediterranean seafloor

Turbulent and internal wave motions are important for the exchange of momentum, heat, and suspended matter in the deep sea, which is generally stably stratified in density. Turbulence-generation models involve shear of vertical current differences that deforms stratified waters and convection that is driven by (unstable) buoyancy. In general, shear generation is found more in the interior of the well-stratified ocean, while convection is known to occur near the sea surface, e.g., via nighttime cooling. Far below the surface, the Western Mediterranean Sea is very weakly stratified and offers opportunity to observationally study the deep-sea convection. An opportunistic small set of high-resolution temperature sensors demonstrate not only classic internal-wave-induced turbulence but also convection attributed to geothermal heating and spectral properties that relate to various chaos-theory models, such as 1/σ pink noise (σ denoting frequency), mainly found lying at (0.01 m above) the seafloor, and 1/σ2 Brownian noise, mainly found on a moored line at about 100 m above the seafloor. Near-inertial temperature variations are observed to occur down to the seafloor, thereby disturbing the local convective turbulence regime to shear-dominated one temporarily. The integral turbulence timescale is generally smaller (with dominant higher frequency motions) at the seafloor than about 100 m above it.

ANN-Assisted High-Resolution and Large Dynamic Range Temperature Sensor Based on Simultaneous Microwave Photonic and Optical Measurements

We proposed and demonstrated a temperature sensor with both high resolution and large dynamic range based on simultaneous microwave photonic and optical measurements. To simultaneously increase the sensitivity and dynamic range of optical measurement, two cascaded ring resonators (CRRs) with different temperature sensitivities and free spectral ranges (FSRs) are designed as the sensing probe and fabricated based on silicon-on-insulator (SOI) wafer. Based on the ultrahigh-Q-factor microring in the CRR, a microwave photonic notch filter (MPNF) is obtained and used to achieve a high temperature resolution. Meanwhile, the optical transmission spectrum of the CRR is used to achieve a large dynamic range. Combining the two measurements, a temperature sensor with both high resolution and large dynamic range is realized. To improve the response speed and robustness of the sensing system, the artificial neural network (ANN) is used to directly extract the temperature from the CRR spectrum, which is particularly helpful at low signal-to-noise ratio (SNR). The sensing resolution and dynamic range achieved by our scheme are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.02 \times 10^{-3}$ </tex-math></inline-formula> °C and 106.94 °C, respectively.

KmT, Kilometer-long mooring of high-resolution Temperature measurements results overview

The global oceans show extensive bottom topography above which intensive turbulent mixing is generated by breaking internal waves. Growing evidence suggests that the mixing is sufficient to maintain the ocean’s stable vertical density stratification, thereby preventing the deep-ocean from becoming a stagnant pool of cold water. Observational details of the extent of turbulent mixing away from topography are still scarce however. In this paper, results are presented from 760 high-resolution temperature sensors that were moored between 8 and 1146.5 m above a 2380-m deep sloping seafloor of Mount Josephine NE-Atlantic for 4 months. The local seafloor-slope is supercritical for semidiurnal internal tides under average stratification. The purpose of the > 1-km-long densely instrumented mooring is to provide insight in the variability of coherent scales, and in the connection between seamount-slope and mixing-effects up to 7-km horizontally into the ocean-interior. Largest four-month mean turbulence values are found near the seafloor, decreasing to half an order of magnitude lower values at 500 m above, and remaining steady-high further up. Local increases of mean turbulence values are observed in bands of 100–200 m thickness. Larger internal wave breaking occurs during baroclinic spring tide, which also affects internal waves and turbulent overturning in the interior. Spectrally, a turbulence inertial subrange dominates part of the internal wave band continuum near the seafloor. Coupling between interior- and near-seafloor-mixing is not only via previously suggested isopycnal transport of mixed waters, but also via strong internal wave interactions. Seamount-flow contributes to absolute vorticity so that blue-shifted near-inertial motions interact with internal tides.

A High Temporal-Spatial Resolution Temperature Sensor for Simultaneous Measurement of Anisotropic Heat Flow.

The thermal measurement sensor applied to hypersonic vehicles requires characteristic size in the order of micrometers and characteristic time in the order of microseconds. The measurement criteria of localized detection, high temporal-spatial precision, and long-term stability cannot all be reached by current thermal measuring techniques. This work presents a temperature sensor with excellent temporal-spatial resolution that can measure both in-plane and out-of-plane heat flow. The sensor was made of thin platinum nano-film and an aluminum nitride ceramic sheet. The sensor was calibrated using a thermostatic vacuum chamber and used for in-plane and out-of-plane heat flow measurements. The temperature measurement accuracy of the sensor was estimated to be 0.01 K. The sensor’s resolution for measuring heat flow density is more than 500 W/m2 and its measurement uncertainty is roughly 3%. To ensure the structural stability of the device, the aluminum nitride ceramic sheet was chosen as the substrate of the thermal sensing unit, and the response time became longer due to the high thermal conductivity of aluminum nitride. The suspension platinum nano-film sensor can reach a sub-microsecond response time according to the theoretical derivation. Experimental results of pneumatic thermal effects of high-temperature flames using the sensor prove that the designed sensor has good sensitivity and accuracy.

Internal Wave and Turbulence Observations with Very High-Resolution Temperature Sensors along the Cabauw Mast

Abstract Knowledge about the characteristics of the atmospheric boundary layer is vital for the understanding of redistribution of air and suspended contents that are particularly driven by turbulent motions. Despite many modeling studies, detailed observations are still demanded of the development of turbulent exchange under stable and unstable conditions. In this paper, we present an attempt to observationally describe atmospheric internal waves and their associated turbulent eddies in detail, under varying stable conditions. Therefore, we mounted 198 high-resolution temperature (T) sensors with 1-m spacing on a 200-m-long cable. The instrumented cable was attached along the 213-m-tall meteorological mast of Cabauw, Netherlands, during late summer 2017. The mast has standard meteorological equipment at extendable booms at six levels in height. A sonic anemometer is at 60 m above ground. The T sensors have a time constant in air of τa ≈ 3 s and an apparent drift about 0.1°C month−1. Also due to radiation effects, short-term measurement instability is 0.05°C h−1 during nighttime and 0.5°C h−1 during daytime. These T-sensor characteristics hamper quantitative atmospheric turbulence research, due to a relatively narrow inertial subrange of maximum one order of magnitude. Nevertheless, height–time images from two contrasting nights show internal waves up to the buoyancy period of about 300 s, and shear and convective deformation of the stratification over the entire 197-m range of observations, supported by nocturnal marginally stable stratification. Moderate winds lead to 20-m-tall convection across weaker stratification, weak winds to episodic &lt;10-m-tall shear instability across larger stratification.

High-Resolution Optical Fiber Temperature Sensor Based on Draw Tower Grating Array.

Ocean temperature monitoring is of great significance to marine fishing, aquaculture, and marine operations. Traditional electric sensors lack the potential to multiplex several sensors, and may suffer from electromagnetic interference. Meanwhile, fiber Bragg grating-based sensors have the advantages of high sensitivity, possibility for large-scale multiplexing, and immunity to electromagnetic interference. In this paper, we propose a Fabry–Pérot (FP) interferometer based on the draw tower grating array and combine it with the phase measurement method for demonstration and testing. In the sensor system, two adjacent fiber Bragg gratings (FBGs) are used as mirrors and an optical fiber connects them, forming a sensor unit. The signal was detected through the compensation of the optical path difference via two-arm path differences in an unbalanced interferometer. The sensor is calibrated in the range of 36.00–36.50 °C, and back to 36.00 °C, in steps of 0.10 °C. A thermocouple (DW1222) is used as a reference. Experimental testing demonstrates that under the thermal loop, the temperature and phase can be approximated as a linear relationship, the Pearson square correlation coefficient is 0.9996, and the temperature sensitivity is −9846 rad/°C. To prove that our experimental device can achieve a higher temperature resolution, we measured the background noise of the system. The experimental results indicate that the order of magnitude of our system temperature resolution can reach 10−5 °C. Thus, we believe that the sensor system is promising for the application of ocean temperature detection, and owing to the ultraweak reflection characteristics of the FBG, this method provides the possibility for large-scale multiplexing of the system.

High Resolution Temperature Sensor Based on the Resonance Excitation of Tamm Plasmons

High Resolution Temperature Sensor Based on the Resonance Excitation of Tamm Plasmons

Experimental investigation on the coolability of nuclear reactor debris beds using seawater

During the Fukushima nuclear reactor accident, seawater was injected into the reactor core to cool the decay heat from the heat generating porous debris bed. However, the impact of dissolved salts in water on the coolability of a debris bed is not well understood. This paper is one of the first works to investigate the cooling mechanisms for debris bed using seawater. An experimental system was built where the packed bed test section was volumetrically heated via a high frequency induction heater. The temperature along the axis of the test section was measured using a high resolution temperature sensor based on Optical Frequency Domain Reflectometry. Experimental results show that the dryout heat flux increases with an increase in concentration, with pure water having a dryout volumetric heat flux of 1.8 MW/m3 and salt water of concentration 7% having a dryout volumetric heat flux of 2.8 MW/m3. However, this enhanced coolability using salt water is short term, as the crystallization fouling mechanism becomes significant over time and leads to gradual temperature excursion in the bed. The fouling mechanism eventually leads to a cross section of the debris bed to plug with the deposited salts, and this leads to a pressure build up in the lower regions of the debris bed.

Tracking deep-sea internal wave propagation with a differential pressure gauge array

Temperature is used to trace ocean density variations, and reveals internal waves and turbulent motions in the deep ocean, called ‘internal motions.’ Ambient temperature detected by geophysical differential pressure gauges (DPGs) may provide year-long, complementary observations. Here, we use data from four DPGs fixed on the ocean bottom and a high-resolution temperature sensor (T-sensor) 13 m above the seafloor as a square-kilometer array deployed offshore ~ 50 km east of Taiwan facing the open Pacific Ocean to examine the impact of temperature on DPG signals related to internal motions. The DPG signals correlate with T-sensor temperature variations between 0.002 and 0.1 mHz, but have time shifts partially caused by slow thermal conduction from the ambient seafloor to the DPG chamber and partially by internal motion propagation time across the array. Applying beamforming-frequency-wavenumber analysis and linear regression to the arrayed T-sensor and DPG data, we estimate the propagating slowness of the internal motions to be between 0.5 and 7.4 s m−1 from the northwest and northeast quadrants of the array. The thermal relaxation time of the DPGs is within 103–104 s. This work shows that a systematic scan of DPG data at frequencies < 0.1 mHz may help shed light on patterns of internal wave propagation in the deep ocean, especially in multi-scale arrays.

Design of a metamaterial film with excellent conformability and adhesion for bandage substrates

Developing films with excellent conformability and adhesion has become a research hotspot in many fields, such as medical bandages. The conventional method for enhancing films conformability and adhesion is to make the films thinner or modify the material of the films, which usually compromises the function of the films. In this paper, a novel metamaterial film was proposed to cover the skin area of a human elbow during the rotation of elbow. This structure is composed of unit cells with rectangular perforations, whose Poisson's ratio (PR) is determined by the length of the perforation. With finite element analysis (FEA), relations among the stretch strain, Poisson's ratio and length of the perforation of unit cell was obtained. Then, the proposed film was generated by mapping unit cells with different PR to the target skin surface. With the same deformation behavior as the elbow skin, conformability and adhesion of the generated film can be guaranteed during the entire rotation process of the elbow, which has been verified by both FEA and experimental tests. Theoretically, by changing the arrangement of different PR unit cells, the proposed method can be applied to design films for other complex surface on human body. It also provides a new way to introduce materials with better biocompatibility but poor mechanical properties as bandage substrates. As a possible application, a prototype of smart bandage was developed by installing a high-resolution temperature sensor on the proposed film, which can monitor the inflammation of the wounded skin in real time.

Half a cubic hectometer mooring array of 3000 temperature sensors in the deep sea

AbstractThe redistribution of matter in the deep-sea depends on water-flow currents and turbulent exchange, for which breaking internal waves are an important source. As internal waves and turbulence are essentially three-dimensional ‘3D’, their dynamical development should ideally be studied in a volume of seawater. However, this is seldom done in the ocean where 1D-observations along a single vertical line are already difficult. We present the design, construction and successful deployment of a half-cubic-hectometer (480,000 m3) 3D-T mooring array holding 2925 high-resolution temperature sensors to study weakly density-stratified waters of the 2500-m deep Western Mediterranean. The stand-alone array samples temperature at a rate of 0.5 Hz, with precision &lt;0.5 mK, noise level &lt;0.1 mK and expected endurance of 3 years. The independent sensors are synchronized inductively every 4 h to a single standard clock. The array consists of 45 vertical lines 125 m long, at 9.5 m horizontally from their nearest neighbor. Each line is held under tension of 1.3 kN by a buoyancy element that is released chemically one week after deployment. All fold-up lines are attached to a grid of cables that is tensioned in a 70 m diameter ring of steel tubes. The array is build-up in harbor-waters, with air filling the steel tubes for floatation. The flat-form array is towed to the mooring site under favorable sea-state conditions. By opening valves in the steel tubes, the array is sunk and its free-fall is controlled by a custom-made drag-parachute reducing the average sinking speed to 1.3 m s-1 and providing smooth horizontal landing on the flat seafloor.