Explore the vast range of titles available.

With the combination of micropumps and flow sensors, highly accurate and secure closed-loop controlled micro dosing systems for liquids are possible. Implementing a single stroke based control mode with piezoelectrically driven micro diaphragm pumps can provide a solution for dosing of volumes down to nanoliters or variable average flow rates in the range of nL/min to μL/min. However, sensor technologies feature a yet undetermined accuracy for measuring highly pulsatile micropump flow. Two miniaturizable in-line sensor types providing electrical readout—differential pressure based flow sensors and thermal calorimetric flow sensors—are evaluated for their suitability of combining them with mircopumps. Single stroke based calibration of the sensors was carried out with a new method, comparing displacement volumes and sensor flow volumes. Limitations of accuracy and performance for single stroke based flow control are described. Results showed that besides particle robustness of sensors, controlling resistive and capacitive damping are key aspects for setting up reproducible and reliable liquid dosing systems. Depending on the required average flow or defined volume, dosing systems with an accuracy of better than 5% for the differential pressure based sensor and better than 6.5% for the thermal calorimeter were achieved.

Micro-electro-mechanical system (MEMS) devices integrate various mechanical elements, sensors, actuators, and electronics on a single silicon substrate in order to accomplish a multitude of different tasks in a diverse range of fields. The potential for device miniaturization made possible by MEMS micro-fabrication techniques has facilitated the development of many new applications, such as highly compact, non-invasive pressure sensors, accelerometers, gas sensors, etc. Besides their small physical footprint, such devices possess many other advantages compared to their macro-scale counterparts, including greater precision, lower power consumption, more rapid response, and the potential for low-cost batch production. One area in which MEMS technology has attracted particular attention is that of flow measurement. Broadly speaking, existing micro-flow sensors can be categorized as either thermal or non-thermal, depending upon their mode of operation. This paper commences by providing a high level overview of the MEMS field and then describes some of the fundamental thermal and non-thermal micro-flow sensors presented in the literature over the past 30 years or so.

This paper presents a short response time, all-silica, gas-flow-velocity sensor. The active section of the sensor consists of a 16 µm diameter, highly optically absorbing micro-wire, which is heated remotely by a 980 nm light source. The heated microwire forms a Fabry–Perot interferometer whose temperature is observed at standard telecom wavelengths (1550 nm). The short response time of the sensor allows for different interrogation approaches. Direct measurement of the sensor’s thermal time constant allowed for flow-velocity measurements independent of the absolute heating power delivered to the sensor. This measurement approach also resulted in a simple and cost-efficient interrogation system, which utilized only a few telecom components. The sensor’s short response time, furthermore, allowed for dynamic flow sensing (including turbulence detection). The sensor’s bandwidth was measured experimentally and proved to be in the range of around 22 Hz at low flow velocities. Using time constant measurement, we achieved a flow-velocity resolution up to 0.006 m/s at lower flow velocities, while the resolution in the constant power configuration was better than 0.003 m/s at low flow velocities. The sensing system is constructed around standard telecommunication optoelectronic components, and thus suitable for a wide range of applications.

A tube-integrated flow sensor is proposed in this study by integrating a micro-electro mechanical systems (MEMS) flow-sensing element and electrical wiring structure on the same copper on polyimide (COP) substrate. The substrate was rolled into a circular tube with the flow-sensing element installed at the center of the tube. The signal lines were simultaneously formed and connected to the Cu layer of the substrate during the fabrication of the sensing structure, thus simplifying the electrical connection process. Finally, by rolling the fabricated sensor substrate, the flow sensor device itself was transformed into a circular tube structure, which defined the airflow region. By implementing several slits on the substrate, the sensing element was successfully placed at the center of the tube where the flow velocity is maximum. Compared to the conventional sensor structure in which the sensor was placed on the inner wall surface of the tube, the sensitivity of the sensor was doubled.

This paper introduces a novel MEMS-based thermal flow sensor designed for high sensitivity and linearity across a wide range of gas flow velocities. The sensor incorporates a single microheater and two pairs of thermistors symmetrically arranged around the heater, with strategically placed obstacles to enhance performance. To ensure accuracy under varying flow conditions, the sensor is divided into two functional regions: one optimized for low flow velocities (0–1 m/s) and the other for high flow velocities (1–6 m/s). Simulations conducted using COMSOL Multiphysics reveal that including obstacles improves heat transfer and increases the interaction time between the heated surface and the flow, particularly in the high-flow region. In the low-flow regime, the sensor achieves a sensitivity of 2.5 SK/m with 91% linearity. In contrast, in the high-flow regime, the sensitivity increases to 6.5 SK/m with similarly high linearity. This dual-region design highlights the sensor’s versatility in handling a broad range of flow velocities, making it suitable for applications in medical, industrial, and environmental monitoring. These findings underscore the advantages of the dual-region design and obstacle integration, providing a robust solution for accurate flow measurement under diverse operating conditions.

Detection and control of flow separation is a key to improving the efficiency of fluid machinery. In this study, we developed a flexible MEMS (microelectromechanical systems) sensor for measuring the wall shear stress and flow angle in subsonic airflow. The developed sensor is made of a flexible polyimide film and a microheater surrounded by three temperature sensor pairs. The sensor measures the wall shear stress from the heater output and the flow angle from the temperature gradient around the heater. The geometry and design of the heater and temperature sensors were determined based on numerical simulations. To evaluate the validity of the sensor, we conducted an experiment to measure the wall shear stress and the flow angle in a wind tunnel in different velocities ranging from 30 m/s to 170 m/s, equivalent to Mach numbers from 0.1 to 0.5. The heater output was proportional to one-third power of the wall shear stress. Additionally, the bridge output correlating the temperature difference between two opposing temperature sensors showed sinusoidal variation depending on the flow angle. Consequently, we have clarified that the developed sensor can measure both the wall shear stress and flow direction in subsonic flow.

This paper proposes new combination of material and take on model evaluation in development of membrane anemometric gas flow sensor. We propose study of flow rate dependence for membrane-based thermal flow sensor composed with TaN/FeNi/TaN thermistors based on SiO 2 /Si 3 N 4 /SiO 2 membrane. The purpose of this research is to develop a thermal flow rate sensor with advanced range of gas flow velocity measurement with increased accuracy and sensitivity. Currently presented as-is sensor is capable of measuring gas flow in the range from 150 to 300 L/min for low humidity preferably clean not reactive gases such as noble gases or air, supplied for clean room. In calculation the significant influence on the shape of the dependence of resistance on temperature was discovered from the heat capacity of the Si 3 N 4 film on which the sensor is located. Observed dependence can serve as a justification for selecting film materials with lower thermal conductivity to increase the difference in resistance depending on the increase in gas flow, which will lead to a decrease in error and simplify signal detection.

Mechanical ventilation systems require a device for measuring the air flow provided to a patient in order to monitor and ensure the correct quantity of air proportionated to the patient, this device is the air flow sensor. At the beginning of the COVID-19 pandemic, flow sensors were not available in Peru because of the international supply shortage. In this context, a novel air flow sensor based on an orifice plate and an intelligent transducer was developed to form an integrated device. The proposed design was focused on simple manufacturing requirements for mass production in a developing country. CAD and CAE techniques were used in the design stage, and a mathematical model of the device was proposed and calibrated experimentally for the measured data transduction. The device was tested in its real working conditions and was therefore implemented in a breathing circuit connected to a low-cost mechanical ventilation system. Results indicate that the designed air flow sensor/transducer is a low-cost complete medical device for mechanical ventilators that is able to provide all the ventilation parameters by an equivalent electrical signal to directly display the following factors: air flow, pressure and volume over time. The evaluation of the designed sensor transducer was performed according to sundry transducer parameters such as geometrical parameters, material parameters and adaptive coefficients in the main transduction algorithm; in effect, the variety of the described results were achieved by the faster response time and robustness proportionated by transducers of nanostructures based on Anodic Aluminum Oxide (AAO), which enhanced the designed sensor/transducer (ST) during operation in intricate geographic places, such as the Andes mountains of Peru.

Improving the thermal insulation performance of buildings is crucial for saving energy. Currently, the insulation performance can be quantified based on the thermal resistance and thermal transmittance (U-value). However, for owners, these data are not readily available for the verification of different insulation methods. To address this, a solution could involve establishing a connection between specialized evaluation indicators and temperature, a common physical quantity. In this study, static and dynamic heat-transfer experiments were performed using an environmental simulation chamber and heat-flow sensors. Based on the tests, a simple predictive formula for the heat-flow density over time was established. After analyzing a full-scale building model, six cases of the heat-flow density versus temperature rise in indoor environments were obtained. This approach may aid owners in visually assessing the insulation performance of buildings by establishing a conversion relationship between the heat-flow density and temperature. In addition, the performance of 14 experimental specimens, including self-developed and code-documented thermal insulation materials and construction methods, was evaluated. In the simulations, after turning off indoor cooling equipment for 6 h during hot summers, the average indoor temperature increase for a roof with insulation was only 52% of that without insulation.

Experiments devoted to evaluate the performance of a MEMS thermal flow sensor in measuring gas volumes are described. The sensor is a single-chip platform, including several sensing structures and a low-offset, low-noise readout interface. A recently proposed offset compensation approach is implemented obtaining low temperature drift and excellent long time stability. The sensor is fabricated by applying a simple micromachining procedure to a chip produced using the BCD6s process of STMicroelectronics. Application of a gas conveyor allowed inclusion of the sensing structure into a channel of sub-millimeter cross-section. The results of measurements performed by making controlled air volumes pass through the sensor channel in both directions at rates from 0.1 to 5 mL/min are described.