Thermal Flow Sensor Research Articles

CMOS-Compatible MEMS 2D Thermal Flow Sensor With High Sensitivity and Low Power Consumption

CMOS-Compatible MEMS 2D Thermal Flow Sensor With High Sensitivity and Low Power Consumption

Fabrication and characterization of high-sensitivity, wide-range, and flexible MEMS thermal flow velocity sensors

With the rapid development of various fields, including aerospace, industrial measurement and control, and medical monitoring, the need to quantify flow velocity measurements is increasing. It is difficult for traditional flow velocity sensors to fulfill accuracy requirements for velocity measurements due to their small ranges, susceptibility to environmental impacts, and instability. Herein, to optimize sensor performance, a flexible microelectromechanical system (MEMS) thermal flow sensor is proposed that combines the working principles of thermal loss and thermal temperature difference and utilizes a flexible cavity substrate made of a low-thermal-conductivity polyimide/SiO2 (PI/SiO2) composite porous film to broaden the measurement range and improve the sensitivity. The measurement results show that the maximum measurable flow velocity can reach 30 m/s with a resolution of 5.4 mm/s. The average sensitivities of the sensor are 59.49 mV/(m s−1) in the medium-to-low wind velocity range of 0–2 m/s and 467.31 mV/(m s−1) in the wind velocity range of 2–30 m/s. The sensor proposed in this work can enable new applications of flexible flow sensors and wearable devices.

Micromachined needle-like calorimetric flow sensor for sap flux density measurement in the xylem of plants

Miniaturized silicon thermal probes for plant’s sap flow measurement, or micro sap flow sensors, have advantages in minimum invasiveness, low power consumption, and fast responses. Practical applications in sap flow measurement has been demonstrated with the single-probe silicon micro sensors. However, the sensors could not detect flow directions and require estimating zero sap flow output that leads to significant source of uncertainty. Furthermore, silicon-needles would break easily during the insertion into plants. We present the first three-element micro thermal sap flow sensor packaged on a durable printed circuit board needle that can measure bidirectional flows with improved dynamics and precision. The performance of the newly designed calorimetric flow sensor was confirmed through precision calibration and field test on tomato stems. A calibration curve for a tomato stem was obtained with a sensitivity of 0.299 K/(µL mm−2 s−1) under the maximum temperature increase of 4.61 K. Results from the field test for one month revealed a correlation between the measured sap flux density and related conditions such as solar radiation, vapor pressure deficit, sunshade and irrigation. The developed sensor will contribute to practical long-term sap flow monitoring for small and delicate plants with minimal physical invasion.

Flow-Independent Thermal Conductivity and Volumetric Heat Capacity Measurement of Pure Gases and Binary Gas Mixtures Using a Single Heated Wire.

Among the different techniques for monitoring the flow rate of various fluids, thermal flow sensors stand out for their straightforward measurement technique. However, the main drawback of these types of sensors is their dependency on the thermal properties of the medium, i.e., thermal conductivity (k), and volumetric heat capacity (ρcp). They require calibration whenever the fluid in the system changes. In this paper, we present a single hot wire suspended above a V-groove cavity that is used to measure k and ρcp through DC and AC excitation for both pure gases and binary gas mixtures, respectively. The unique characteristic of the proposed sensor is its independence of the flow velocity, which makes it possible to detect the medium properties while the fluid flows over the sensor chip. The measured error due to fluctuations in flow velocity is less than ±0.5% for all test gases except for He, where it is ±6% due to the limitations of the measurement setup. The working principle and measurement results are discussed.

Recent Advances of VO2 in Sensors and Actuators.

Vanadium dioxide (VO2) stands out for its versatility in numerous applications, thanks to its unique reversible insulator-to-metal phase transition. This transition can be initiated by various stimuli, leading to significant alterations in the material's characteristics, including its resistivity and optical properties. As the interest in the material is growing year by year, the purpose of this review is to explore the trends and current state of progress on some of the applications proposed for VO2 in the field of sensors and actuators using literature review methods. Some key applications identified are resistive sensors such as strain, temperature, light, gas concentration, and thermal fluid flow sensors for microfluidics and mechanical microactuators. Several critical challenges have been recognized in the field, including the expanded investigation of VO2-based applications across multiple domains, exploring various methods to enhance device performance such as modifying the phase transition temperature, advancing the fabrication techniques for VO2 structures, and developing innovative modelling approaches. Current research in the field shows a variety of different sensors, actuators, and material combinations, leading to different sensor and actuator performance input ranges and output sensitivities.

Reliability of Domestic Gas Flow Sensors with Hydrogen Admixtures.

Static flow sensors (e.g., thermal gas micro electro-mechanical sensors-MEMS-and ultrasonic time of flight) are becoming the prevailing technology for domestic gas metering and billing since they show advantages in respect to the traditional volumetric ones. However, they are expected to be influenced in-service by changes in gas composition, which in the future could be more frequent due to the spread of hydrogen admixtures in gas networks. In this paper, the authors present the results of an experimental campaign aimed at analyzing the in-service reliability of both static and volumetric gas meters with different hydrogen admixtures. The results show that the accuracy of volumetric and ultrasonic meters is always within the admitted limits for subsequent verification and even within those narrower of the initial verification. On the other hand, the accuracy of the first generation of thermal mass gas flow sensors is within the limits of the verification only when the hydrogen admixture is below 2%vol. At higher hydrogen content, in fact, the absolute weighted mean error ranges between 3.5% (with 5%vol of hydrogen) and 15.8% (with 10%vol of hydrogen).

Review of methods and devices for determining the resistance to heat transfer under natural conditions

The purpose of this study is to review modern methods of determining the resistance to heat transfer of building envelopes under natural conditions using experimental equipment. Methods for experimental determination of the resistance to heat transfer given in regulatory documents have been considered. Golunov S.V. and co-authors developed a method of determining the resistance to heat transfer based on thermal imaging examination with the placement of sensors on the surfaces of the building envelopes. Abramova E.V. together with other researchers created a method of thermal non-destructive testing using a thermal imaging system, temperature and heat flow sensors. The possibility of experimentally determining the reduced resistance to heat transfer of external building envelopes under summer operating conditions using the device developed by A.E. Rusanov’s with co-authors has been described. Wang Xin et al. proposed a device for determining the resistance to heat transfer of building envelopes with improved accuracy. As a result of the analytical review, it was concluded that the presented methods make it possible to measure the resistance to heat transfer of external building envelopes when modeling various stationary and non-stationary heat transfer processes.

DEVELOPMENT OF A MATHEMATICAL MODEL OF THE THERMAL FIELD OF AN INTEGRAL STRUCTURE IN THE IMPLEMENTATION OF SENSORS FOR BIOMEDICAL RESEARCH

The paper deals with the implementation of a complex technique for electrothermal modeling of measuring transducers of thermal flow sensors, which combines the synthesis of the impulse temperature relaxation substitution circuit and the method of forming the I-V converters in the mode of their self-heating by the supply current. The issue of assessing the instability of iteration processes in the analysis of I/V measuring converters with negative differential resistance, which is caused by self-heating of these converters, is considered. An express method for determining the limits in which correct electrothermal DC analysis is provided for use in biomedical devices and systems has been developed.

High-Sensitivity Hydrogen Sulfide Electrochemical Gas Sensor Based on CNT/Pt Cluster Electrode

Recently, due to the development of industrial technology, harmful gases discharged from industrial sites are gradually increasing, and as a result, inconvenience and civil complaints due to odor in the community are rapidly increasing. Among several types of harmful gases, hydrogen sulfide (H2S) is a colorless representative harmful gas that can cause pain through irritation of the mucous membranes of the eyes and respiratory tract, and can cause central nerve paralysis and suffocation at the same time when exposed to high concentrations. In addition, H2S is not only harmful to the human body, but also can create an unpleasant feeling by causing an odor even in a very small amount. Therefore, in order to manage H2S, research on a gas sensor capable of quickly and stably detecting H2S has been actively conducted. Most of the sensors that have been studied in the past are metal oxide-based semiconductor H2S gas sensors, which have high sensitivity, but have disadvantages in that low selectivity and high-temperature operating conditions are required. On the other hand, the electrochemical gas sensor can measure H2S gas with high selectivity because a chemical reaction occurs with respect to a specific gas depending on the type of electrolyte and electrode, and a potential difference due to electrons generated thereby is measured. Therefore, in this study, a CNT/Pt-based electrochemical H2S gas sensor capable of detecting at room temperature with high selectivity for H2S was developed. After forming a CNT thin film on a PTFE membrane, Pt was deposited through an E-beam to fabricate a working electrode capable of selectively detecting only H2S, and applied to an electrochemical H2S gas sensor using sulfuric acid (H2SO4) electrolyte. H2S was measured at a concentration of 100 to 10 ppm in units of 10 ppm using the manufactured CNT/Pt-based electrochemical H2S gas sensor. As a result, the amount of current change was confirmed to be 100uA at a concentration of 100 ppm, and the response time and recovery time were confirmed to be about 10 seconds.This work was supported by the Korea Innovation Foundation(INNOPOLIS) grant funded by the Korea government(MSIT) (2020-DD-UP-0348). This study has been conducted with the support of the Korea Institute of Industrial Technology as "Development of a thermal convection-type flow sensor with high-sensitivity for emergency patients breathing monitoring in real-time" (Kitech UI-23-0012).

Monolithic Integration of Ultraslim Flow Sensor and Medical Guidewire by Laser Filament Scanning Sintering for In Vivo Diagnostics of Cardiovascular Diseases.

In this study, an ultraslim thermal flow sensor system integrated onto a 340 μm diameter medical guidewire was developed using a laser filament scanning sintering method for the early diagnosis of cardiovascular diseases. The proposed system is a calorimetric-based micro thermal flow sensor comprising a microheater and two thermistors. Prior to fabrication, the sensor design was optimized through flow simulation, and the patterned sensor was successfully implemented on a thin and curved surface of the medical guidewire using a laser patterning method with Ag nanoparticles. The performance of the ultraslim thermal flow sensor-on-guidewire system (SoW) was evaluated under pulsatile flow by using an artificial heartbeat simulator with differentially induced fluid flow velocities of up to 60 cm/s. The resulting electrical signals generated by the temperature difference between the two thermistors caused by the fluid flow were measured across different velocity ranges. Based on the obtained data, a calibration curve was derived to establish the relationship between the fluid velocity and the sensor output voltage. Furthermore, the SoW was tested on living animals, whereby the measured blood flow velocities were 60-90 cm/s in the left coronary artery of pigs. This research demonstrates the potential of ultraslim microsensors, such as the developed thermal flow sensor system, for various industries, particularly in the medical field.

Finite-Element Simulation of the Performance of a Temperature-Compensated Membrane-Based Thermal Flow Sensor

Finite-Element Simulation of the Performance of a Temperature-Compensated Membrane-Based Thermal Flow Sensor

P045 Noxturnal cRIP: A Comparative Analysis of Sensors for the Identification of Respiratory Events in Polysomnography

Abstract Introduction AASM recommends the use of nasal pressure (NP), oronasal thermal flow (TF), and respiratory inductance plethysmography (RIP) for detecting and characterising respiratory events in polysomnography. The use of both NP and TF sensors is reported to be more accurate in respiratory event identification than either alone. However, these sensors can be unreliable if dislodged and cause discomfort. Noxturnal calibrated RIP flow (cRIPflow), derived from RIP, may provide a non-invasive alternative method for flow measurement in identification of respiratory events. Method Respiratory scoring was performed manually by a single experienced scorer on 10 diagnostic sleep studies under AASM standards. Scoring was repeated using three different measurements for each study: cRIPflow only, Thermistor (Th) only and both Th+NP (AASM recommendation). Apnoea hypopnoea index (AHI), central apnoea index (CAI), obstructive apnoea index (OAI), mixed apnoea index (MAI) and hypopnoea index (HI) were calculated and paired t-test analysis utilised for comparison between measurements. Results No statistical differences were identified in comparison of cRIPflow with Th or Th+NP in respiratory event identification: CAI (cRIPflow 3.2/hr±7.1, Th 3.9/hr±8.9, Th+NP 3.1/hr±7.5), OAI (cRIPflow 6.1/hr±6.8, Th 5.3/hr±8.2, Th+NP 6.7/hr±8.9), MAI (cRIPflow 5.2/hr±9.7, Th 4.3/hr±8.7, Th+NP 4.7/hr±9.2), or HI (cRIPflow 12.5/hr±13.9, Th 11.1/hr±10.5, Th+NP 10.4/hr±10.7). There was a statistical difference for AHI (cRIPflow 26.9/hr±26.6, Th 24.5/hr±26.4, Th+NP 25.0/hr±26.5). Discussion This study suggests cRIPflow may provide an alternative measurement in the detection and characterisation of respiratory events, however further analysis with larger sample size would provide more insight into sensitivity and specificity of this method.

Numerical Simulation of Unsteady Turbulent Flow and Heat Transfer of Dynamic Thermal Flow Sensor

Improving energy efficiency in the building’s design is a priority area. To avoid unnecessary energy consumption, electronic control (intelligent) systems can be used to measure and monitor heat exchange between building walls and the surrounding environment, as (Calorimetric Sensor, Heat Flux Sensor ...). They are ideally suited for research in rationalizing and improving thermal efficiency. The aim of this study was a computational fluid dynamics investigation of unsteady turbulent flow and heat transfer of dynamic heat flux sensor for quantitative description of the heat transfer between the building's walls and the surrounding environment.Using CFD software, we numerically simulated the wind tunnel where the sensor was installed; we used six different air speeds (Vinlet=2m/s to 12m/s) in the inlet. To improve the standard features of the CFD code, the User-Defined Function (UDF) was written in the C language program and integrated into the solver of ANSYS Fluent, in order to determine the thermal flow file applied to the surface of the sensor. Heat transfer coefficient (h0) values are obtained according to each speed. The results obtained were compared to results in previous experimental and theoretical literature. There is a good compatibility of all results that allows dependence on numerical simulations in the future as a way of stewardship when studying energy rationalization.

Thermal Flow Meter with Integrated Thermal Conductivity Sensor.

This paper presents a novel gas-independent thermal flow sensor chip featuring three calorimetric flow sensors for measuring flow profile and direction within a tube, along with a single-wire flow independent thermal conductivity sensor capable of identifying the gas type through a simple DC voltage measurement. All wires have the same dimensions of 2000 μm in length, 5 μm in width, and 1.2 μm in thickness. The design theory and COMSOL simulation are discussed and compared with the measurement results. The sensor's efficacy is demonstrated with different gases, He, N2, Ar, and CO2, for thermal conductivity and thermal flow measurements. The sensor can accurately measure the thermal conductivity of various gases, including air, enabling correction of flow rate measurements based on the fluid type. The measured voltage from the thermal conductivity sensor for air corresponds to a calculated thermal conductivity of 0.02522 [W/m·K], with an error within 2.9%.

Design and analysis of micro thermal mass flow sensor using thin-film-based thermocouples

Design and analysis of micro thermal mass flow sensor using thin-film-based thermocouples

Особливості проектування теплових сенсорів потоку біомедичного призначення

It is shown that thermal flow sensors are characterized by high structural and technological compatibility with biomedical equipment and, compared to other types of flow sensors, they most fully meet the requirements for this equipment. The developed signal converters fully meet the requirements for modern biomedical equipment and energy-saving low-voltage electronics (unipolar 3V power supply), provide a negligible thermal effect on the flow environment and are implemented on the latest element base - high-precision CMOS railto-rail operational amplifiers, bidirectional multiplexers of the type ADG, ADuC type microconverters, powerful D-MOS HEX FET transistors, etc

Microfluidic thermal flow sensor based on phase-change material with ultra-high thermal sensitivity

A microfluidic thermal mass flow sensor with ultra-high thermal sensitivity, based on planar micro-machining technology and a phase-change material is developed.

Integrated membrane-free thermal flow sensor for silicon-on-glass microfluidics.

Lab-on-a-chip (LOC) forms the basis of new-generation portable analytical systems. LOC allows the manipulation of ultralow flows of liquid reagents and multistep reactions on a microfluidic chip, which requires a robust and precise instrument to control the flow of liquids on a chip. However, commercially available flow meters appear to be a standalone option adding a significant dead volume of tubes for connection to the chip. Furthermore, most of them cannot be fabricated within the same technological cycle as microfluidic channels. Here, we report on a membrane-free microfluidic thermal flow sensor (MTFS) that can be integrated into a silicon-glass microfluidic chip with a microchannel topology. We propose a membrane-free design with thin-film thermo-resistive sensitive elements isolated from microfluidic channels and a 4'' wafer silicon-glass fabrication route. It ensures MTFS compatibility with corrosive liquids, which is critically important for biological applications. MTFS design rules for the best sensitivity and measurement range are proposed. A method for automated thermo-resistive sensitive element calibration is described. The device parameters are experimentally tested for hundreds of hours with a reference Coriolis flow sensor demonstrating a relative flow error of less than 5% within the range of 2-30 μL min-1 along with a sub-second time response.

Analysis of development state of the thermal flow sensors of general, biomedical and ecological designation

The paper analyzed the characteristics of microelectronic flow sensors, which made it possible to draw a number of important conclusions, namely: modern microelectronic thermal flow sensors, and in particular biomedical sensors, are characterized by a significant variety of principles of signal formation - from elementary linear converters based on one sensitive element to non-linear ones ( generation, time-dependent) converters based on matrices of functionally integrated elements. The problem of energy consumption of thermal flow sensors remains relevant. This is especially characteristic when powering destination sensors from autonomous, i.e., small-sized, low-power, low-voltage electrochemical cells. A decrease in energy consumption (power and heating temperature) leads to the parasitic effect of signal line resistances and, as a result, to the deterioration of functional characteristics, in particular, to a decrease in the accuracy of flow rate measurement.

Micromachined Thermal Time-of-Flight Flow Sensors and Their Applications.

Micromachined thermal flow sensors on the market are primarily manufactured with the calorimetric sensing principle. The success has been in limited industries such as automotive, medical, and gas process control. Applications in some emerging and abrupt applications are hindered due to technical challenges. This paper reviews the current progress with micromachined devices based on the less popular thermal time-of-flight sensing technology: its theory, design of the micromachining process, control schemes, and applications. Thermal time-of-flight sensing could effectively solve some key technical hurdles that the calorimetric sensing approach has. It also offers fluidic property-independent data acquisition, multiparameter measurement, and the possibility for self-calibration. This technology may have a significant perspective on future development.