Thermal Microsensor Research Articles

Development of an Energy-Efficient and Highly Sensitive Thermal Microsensor for Measuring Flow Rates of Fluids

Development of an Energy-Efficient and Highly Sensitive Thermal Microsensor for Measuring Flow Rates of Fluids

Use of a drone equipped with microthermal sensors to estimate the quality of the atmosphere for astronomical observation

AbstractA drone was used to obtain thermal profiles to estimate atmospheric turbulence for the purposes of astronomical observation. The first 150 metres above ground level were studied in two areas in the south‐east of the Iberian Peninsula. The preliminary results are promising regarding the use of drones as a suitable means of transport for obtaining microthermal measurements. We have also assessed the influence of the planetary boundary layer on the quality of the image for astronomical purposes. In future research, we intend to check these measurements with fixed microthermal sensors installed in meteorological towers.

Reversible bipolar thermopower of ionic thermoelectric polymer composite for cyclic energy generation

The giant thermopower of ionic thermoelectric materials has attracted great attention for waste-heat recovery technologies. However, generating cyclic power by ionic thermoelectric modules remains challenging, since the ions cannot travel across the electrode interface. Here, we reported a reversible bipolar thermopower (+20.2 mV K−1 to −10.2 mV K−1) of the same composite by manipulating the interactions of ions and electrodes. Meanwhile, a promising ionic thermoelectric generator was proposed to achieve cyclic power generation under a constant heat course only by switching the external electrodes that can effectively realize the alternating dominated thermodiffusion of cations and anions. It eliminates the necessity to change the thermal contact between material and heat, nor does it require re-establish the temperature differences, which can favor improving the efficiency of the ionic thermoelectrics. Furthermore, the developed micro-thermal sensors demonstrated high sensitivity and responsivity in light detecting, presenting innovative impacts on exploring next-generation ionic thermoelectric devices.

High Temperature Gradient Pirani Micro-Sensor Designed and Tested for Aerodynamic Wall Pressure Measurement

This paper presents and discusses the first demonstration of aerodynamic wall pressure measurement using a thermal Pirani effect based micro-sensor. The thermal micro-sensor is designed as a suspended micro-hot-wire separated from the substrate by a nanoscale gap, and mechanically supported by perpendicular micro-bridges. The micro-sensor was calibrated for pressure measurement from 10 kPa to 800 kPa. It was then used as aerodynamic wall pressure sensor in a turbulent boundary layer wind tunnel and successfully measured the 1.1 kPa depression occurring in the wind tunnel when the flow velocity goes up to 40 m/s.

Objective Assessment of Spectacle Wear in Infants and Toddlers Using a Wearable Sensor.

PurposeTo assess the feasibility of using a thermal microsensor to monitor spectacle wear in infants and toddlers, to determine the inter-method reliability of two methods of estimating spectacle wear from sensor data, and to validate sensor estimates of wear.MethodsFourteen children, 3 to <48 months of age, and one adult were provided pediatric spectacles containing their spectacle prescription. A thermal microsensor attached to the spectacle headband recorded date, time, and ambient temperature every 15 minutes for 14 days. Parents were asked for daily spectacle wear reports, and the adult recorded wear using a smartphone app. Sensor data were dichotomized (wear/non-wear) using two methods: temperature threshold (TT) and human judgment (HJ). Kappa statistics assessed inter-method reliability (child data) and accuracy (adult data).ResultsData from two child participants were excluded (one because of corrupted sensor data and the other because of no parent log data). Sensor data were collected more reliably than parent wear reports. The TT and HJ analysis of child data yielded similar reliability. Adult sensor data scored using the HJ method provided more valid estimates of wear than the TT method (κ = 0.94 vs. 0.78).ConclusionsWe have demonstrated that it is feasible to deduce periods of spectacle wear using a thermal data logger and that the sensor is tolerated by children.Translational RelevanceResults indicate that it is feasible to use a thermal microsensor to measure spectacle wear for use in clinical monitoring or for research on spectacle treatment in children under 4 years of age.

Laser multifunctional fabrication of metallic microthermal components embedded in fused silica for microfluidic applications

Microheaters as tiny in-situ heating elements are of great importance for developing many thermal-sensitive microdevice applications. A facile technique for the fabrication of embedded metallic microheaters, microheater arrays, and microthermal sensors based on the combination of femtosecond laser-assisted chemical etching, electroless plating, and mechanical polishing has been proposed. With the proposed technique, uniform and controllable temperature distributions in the central area of fabricated microheaters have been achieved. Moreover, flexible manipulation of localized temperature in a microheater array as well as precise calibration of microheaters based on a simultaneously integrated microthermal sensor has been demonstrated. Furthermore, precise control of temperature in glass channels and acceleration of a chemical reaction in microfluidics using monolithically integrated microheaters have been realized, showing great potential for developing laser manufacturing of multifunctional thermal-control microfluidic devices.

Evaluation of the day-time ground-level turbulence at Mt Wumingshan with a microthermal sensor

ABSTRACT Surface-layer turbulence, especially the turbulence close to the ground (ground-level, GL), critically determines the height at which to locate a ground-based telescope. It is also vital to assess the contribution of the GL to the total turbulence. To characterize the day-time turbulence at the GL at the Mt Wumingshan (Mt WMS) site (a candidate site for the Chinese next-generation large Solar Telescope), a microthermal sensor (MS) was installed to detect fluctuations of the temperature at the GL and estimate the contribution of the GL to the total turbulence. The MSs were placed at six levels on a 22-m-high tower to measure the refractive index $C_{n}^{2}$ configuration constant. This study presents the day-time optical turbulences due to the GL at the Mt WMS site and compares them with the integrated day-time seeing that was obtained by the Wumingshan Mountain Automated Solar Differential Image Motion Monitor (WMA-SDIMM). MS and WMA-SDIMM data were obtained simultaneously for a total of 16 d during June to October 2017. The average r0 of the GL was found to be $r_{0}^{\rm gl}(\rm {1\, m,16\, m})=11.04\, {\rm cm}$ and $r_{0}^{\rm gl}({\rm 16\,m,22\,m})=61.64\,{\rm cm}$. The contribution of the GL (8 to 22 m) to the total turbulence was $13.05{{\ \rm per\ cent}}$ on average, complying with a $8.0{{\ \rm per\ cent}}$ reduction of the total seeing. At the height of 22 m, most of the GL turbulence was produced below 16 m.

A Microthermal Sensor for Cryoablation Balloons.

Treatment of atrial fibrillation by cryoablation of the pulmonary vein (PV) suffers from an inability to assess probe contact, tissue thickness, and freeze completion through the wall. Unfortunately, clinical imaging cannot be used for this purpose as these techniques have resolutions similar in scale (∼1 to 2 mm) to PV thickness and therefore are unable to resolve changes within the PV during treatment. Here, a microthermal sensor based on the "3ω" technique which has been used for thin biological systems is proposed as a potential solution and tested for a cryoablation scenario. First, the sensor was modified from a linear format to a serpentine format for integration onto a flexible balloon. Next, using numerical analyses, the ability of the modified sensor on a flat substrate was studied to differentiate measurements in limiting cases of ice, water, and fat. These numerical results were then complemented by experimentation by micropatterning the serpentine sensor onto a flat substrate and onto a flexible balloon. In both formats (flat and balloon), the serpentine sensor was experimentally shown to: (1) identify tissue contact versus fluid, (2) distinguish tissue thickness in the 0.5 to 2 mm range, and (3) measure the initiation and completion of freezing as previously reported for a linear sensor. This study demonstrates proof of principle that a serpentine 3ω sensor on a balloon can monitor tissue contact, thickness, and phase change which is relevant to cryo and other focal thermal treatments of PV to treat atrial fibrillation.

Investigation on Temperature Rise of a Micro-Thermal Sensor in Helium–Air Gas Mixtures Considering Near-Field Radiation

The thermal response of a micro-thermal sensor at the slider–disk interface filled with helium–air gas mixtures is investigated. The heat transfer due to both the heat conduction in gas films and the near-field radiation is included. The effects of the helium fraction on the sensor temperature are discussed. The results show that due to the evanescent photo tunneling at a small spacing, the near-field radiation generates a large heat flux, resulting in decreases in the sensor temperature. However, at a large spacing over 10 nm, the heat transfer is dominated by the heat conduction in gas films. An increasing helium fraction causes an increase in the heat conduction and a consequent decrease in the sensor temperature.

Design and Testing of a Micro-thermal Sensor Probe for Nondestructive Detection of Defects on a Flat Surface

This paper presents a design and testing of a micro-thermal sensor probe for realizing the proposed concept of non-contact surface defect detection, in which a change in heat flow across the gap between the tip of the micro-thermal sensor probe and a target surface is utilized to recognize the existences of surface defects. In the proposed concept of surface defect detection, the probe tip, where the micro-thermal sensor is embedded, is required to be placed as close as possible to the target surface for highly sensitive surface defect detection. For the purpose, an optical tilt detection assembly based on the laser autocollimation is designed to detect relative tilt of the micro-thermal sensor with respect to a target surface. A sensor probe assembly, in which the fabricated micro-thermal sensor is embedded to the tip of a hollow-shaped piezoelectric actuator by using a homemade sensor mount, is also designed in such a way that the sensor element will face to a target surface. A prototype micro-thermal sensor probe is constructed by integrating the optical tilt detection assembly and the sensor probe assembly, and some experiments have been carried out to verify the basic performances of the prototype micro-thermal sensor probe.

Performance of Fast-Responsive, Porous Crosslinked Poly(N-Isopropylacrylamide) in a Piezoresistive Microsensor

Hydrogel-based microsensors allow us to measure chemical measurands as well as temperature and other quantities. However, long response times due to cooperative diffusion in the hydrogel has thus far prevented the dissemination of this type of sensor. One way to overcome this drawback is to use porous hydrogels. The strong influence of pores on the response time of the sensor was demonstrated exemplarily in a hydrogel-based thermal microsensor setup. Porous crosslinked poly( N -isopropylacrylamide) (PNIPAAm) was synthesized by a surfactant-based template method. The characterization of the hydrogel with scanning electron microscopy proved the formation of macropores with diameters around 3.8m. A piezoresistive microsensor with embedded porous PNIPAAm hydrogel showed the response time $t_{90}$ to be below 20s when increasing the temperature from 25C to 50C, whereas $t_{90}$ is not reached for the sensor with embedded nonporous PNIPAAm hydrogel after several hours. A discussion on much slower response times for decreasing the temperature to 25C is provided. The results can be transferred to other hydrogel-based sensor and actuator systems.

Improvements in the performance of a microthermal flow sensor using asymmetrically located temperature sensors

A microthermal flow sensor was developed using microfabrication techniques. The flow sensor comprised a microheater and three pairs of resistive temperature detector (RTD) sensors. The heater and the sensors were made of platinum thin films, and they were located in the middle of a thin oxide/nitride-layered membrane, which was used for thermal isolation. The operating characteristics of the developed microthermal flow sensor were investigated for various gap distances between the central heater and the upstream/downstream RTD sensors. When the upstream/downstream RTD sensors were placed at asymmetric distances away from the central heater, the performance of the sensor improved for an air flow rate of 0-10 slpm. Our results indicate that an asymmetrical gap distance between the central heater and the upstream/downstream RTD sensors can be a key factor in improving the sensitivity and dynamic range of a microthermal flow sensor. To the best of the authors’ knowledge, these results are the first to experimentally demonstrate that an asymmetrical placement of RTD temperature sensors can improve the sensitivity and dynamic range of a microthermal flow sensor.

High temperature gradient micro-sensor for wall shear stress and flow direction measurements

We present an efficient and high-sensitive thermal micro-sensor for near wall flow parameters measurements. By combining substrate-free wire structure and mechanical support using silicon oxide micro-bridges, the sensor achieves a high temperature gradient, with wires reaching 1 mm long for only 3 μm wide over a 20 μm deep cavity. Elaborated to reach a compromise solution between conventional hot-films and hot-wire sensors, the sensor presents a high sensitivity to the wall shear stress and to the flow direction. The sensor can be mounted flush to the wall for research studies such as turbulence and near wall shear flow analysis, and for technical applications, such as flow control and separation detection. The fabrication process is CMOS-compatible and allows on-chip integration. The present letter describes the sensor elaboration, design, and micro-fabrication, then the electrical and thermal characterizations, and finally the calibration experiments in a turbulent boundary layer wind tunnel.

A micro-thermal sensor for focal therapy applications

A micro-thermal sensor for focal therapy applications

Vanadium oxide thermal microsensor integrated in a microfluidic chip for detecting cholesterol and glucose concentrations

A highly sensitive thermal measurement device based on a vanadium oxide (VOx) microthermistor is developed for detecting biological molecules based on enzymatic reactions. The measurement principle of the VOx thermistor relies on the temperature dependence of its electrical resistance owing to the heat generation of enzymatic reactions. The device comprises a microfluidic channel and chambers, and VOx thermistors on a suspended Si3N4 membrane for thermal insulation. The enzyme is immobilized in silica gel on the sensor. The temperature coefficient of the resistance of the fabricated VOx thermistor is −1.3 %/K. The fabricated device has a temperature resolution of 0.30 mK/√Hz and a temperature response of 4.9 mV/K. Thermal measurements of cholesterol and glucose are demonstrated using the heat production caused by enzymatic reactions. The detectable concentrations of glucose and cholesterol were 30 and 15 µM/√Hz, respectively.

Micro-thermal CMOS-based gas quality sensing for control of spark ignition engines

Abstract Internal combustion engines fueled with natural gas have to be adjusted to the fuel properties in order to achieve maximum efficiency, minimum pollutant emissions and good long-time integrity of all components. Normally, gas quality is neither measured nor used a as control input. Therefore, engines do not necessarily react correctly to changing gas qualities. This paper describes how a micro-thermal CMOS gas quality sensor is used to directly correlate engine parameters (for example knock tendency, and exhaust gas recirculation tolerance) from basic physical properties of a gas mixture. Doing direct correlation for a certain engine, there is no need any more to correlate engine reactions (e.g., knock) to fuel quality parameters determined on completely different engines (e.g., methane number). The formal correlation procedure also offers insight into the underlying physical process when choosing correlation input functions of weighted terms of thermal conductivity, heat capacity and density and re-factoring these terms.

A Micro-Thermal Sensor for Focal Therapy Applications

There is an urgent need for sensors deployed during focal therapies to inform treatment planning and in vivo monitoring in thin tissues. Specifically, the measurement of thermal properties, cooling surface contact, tissue thickness, blood flow and phase change with mm to sub mm accuracy are needed. As a proof of principle, we demonstrate that a micro-thermal sensor based on the supported “3ω” technique can achieve this in vitro under idealized conditions in 0.5 to 2 mm thick tissues relevant to cryoablation of the pulmonary vein (PV). To begin with “3ω” sensors were microfabricated onto flat glass as an idealization of a focal probe surface. The sensor was then used to make new measurements of ‘k’ (W/m.K) of porcine PV, esophagus, and phrenic nerve, all needed for PV cryoabalation treatment planning. Further, by modifying the sensor use from traditional to dynamic mode new measurements related to tissue vs. fluid (i.e. water) contact, fluid flow conditions, tissue thickness, and phase change were made. In summary, the in vitro idealized system data presented is promising and warrants future work to integrate and test supported “3ω” sensors on in vivo deployed focal therapy probe surfaces (i.e. balloons or catheters).

Sensitive thermal microsensor with pn junction for heat measurement of a single cell

A sensitive thermal microsensor based on a pn junction diode for heat measurements of biological single cells is developed and evaluated. Using a fabricated device, we demonstrated the heat measurement of a single brown fat cell. The principle of the sensor relies on the temperature dependence of the pn junction diode resistance. This method has a capability of the highly thermal sensitivity by downsizing and the advantage of a simple experimental setup using electrical circuits without any special equipment. To achieve highly sensitive heat measurement of single cells, downsizing of the sensor is necessary to reduce the heat capacity of the sensor itself. The sensor with the pn junction diode can be downsized by microfabrication. A bridge beam structure with the pn junction diode as a thermal sensor is placed in vacuum using a microfludic chip to decrease the heat loss to the surroundings. A temperature coefficient of resistance of 1.4%/K was achieved. The temperature and thermal resolutions of the fabricated device are 1.1 mK and 73.6 nW, respectively. The heat measurements of norepinephrine stimulated and nonstimulated single brown fat cells were demonstrated, and different behaviors in heat generation were observed.

Multi-instrument characterization of optical turbulence at the Ali observatory

In order to characterize the atmospheric optical turbulence at Ali observatory, we have deployed multi-instruments, which are able to continuously monitor the optical turbulence for site evaluation. These instruments include the DIMM, MASS, Single Star SCIDAR and Polaris seeing monitor, and we also plan to install SNODAR and Micro-thermal sensors for the turbulence on surface layer by the end of this year. This configuration allows us to collect a substantial database and make cross-comparison of the results. We have successfully obtained the profiles of optical turbulence and wind speed with Single Star SCIDAR, as well as the key parameters for adaptive optics application, such as seeing, coherence time, and isoplanatic angle. The DIMM seeing measurements are also carried out simultaneously. The median seeing measured by the DIMM and SSS in 2013 is 0.69 and 0.79 arcsec, respectively.

Modelling and calibration of microthermal sensor for underwater wall shear stress measurement

To measure underwater wall shear stress, a calibration method for a microthermal sensor is studied. In CC (constant current) mode, a mathematical model which quantitatively describes the relationship between the output of the thermal sensor and the wall shear stress is presented. A well-characterised water tunnel was set up to provide a series of known wall shear stresses in the range of 0-5 Pa. Calibration results prove the proposed model and characterise the thermal sensor precisely. The consistency of the parameters indicates that the performance of the thermal sensor keeps stable in water while driven by electricity. The R -squares in all calibrations exceed 0.995. The deviations between the predicted and the generated wall shear stress are about 5%.