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.
We present the findings from an experimental study of a MEMS flow sensor in which an initially curved, double-clamped bistable microbeam is the primary sensing element. Our research explores how the ...overheat ratio, direct flow loading, and turbulence-induced vibration affect the sequential snap-through (ST) buckling and snap-back (SB) release of an electrostatically actuated beam heated by an electric current. The sensor is fabricated from highly doped single-crystal silicon using a silicon-on-insulator (SOI) wafer. Positioned at the chip’s edge, the microbeam is exposed to airflow, enabling concurrent dynamic response measurements with a laser Doppler vibrometer and a video camera.
Our research demonstrates that the overheat ratio can be significantly lower for this sensing principle than conventional thermal sensing elements, pointing to the potential for substantial energy savings. We also emphasize the significant impact of flow angles and vibrations on the critical ST and SB voltages, which are vital for the flow sensor’s output. Additionally, we introduce the first direct experimental observation of the beam profile’s time history during the snap-through/snap-back transition.
The potential impact of this research lies in developing more robust MEMS flow sensors with enhanced sensitivity and a better understanding of their response to environmental factors, which could have broader applications in fields such as aerospace, environmental monitoring, and industrial process control.
•Bistable flow sensor based on the initially curved double-clamped beam is presented.•Effects of overheat, flow loading, and vibrations on critical voltages are studied.•Asymmetric beam profile during the dynamic snap-through and snap-back is presented.
Autonomous navigation of a flying object requires the measurement of velocity and position in absolute or relative means. A possible approach is to measure the air flow velocity on the object. ...Measurement on a flying object requires low-power and low-weight sensors. Since several decades, flow velocity of fluids in two dimensions can be measured by microsystems, which are inherently low-weight sensors.
Here, we report the design of a low-power 2D flow sensor and present the characteristics of a variety of sensor designs to investigate the effects of several design considerations. We further discuss the error sources in angle measurement with a 2D thermal flow sensor and propose design and measurement approaches to reduce the error. Highly sensitive amorphous germanium thermistors are used in our design to provide a high temperature resolution and to achieve low velocity measurement limits at low power consumption. Using an optimized design for thermistor locations, diaphragm dimensions, and choice of materials, power consumption of our micromachined thermal flow sensors is reduced to the sub-milliwatt level, which has not been shown by the state-of-the-art devices with keeping high resolution. Initial results in flow velocity characterizations show a resolution below 1
cm/s at a power of 0.177
mW
rms. The maximum angle error is determined to be 3.5° in wind channel tests. Theoretical limits indicate that further reduction of the measurement limit to the order of 0.1
mm/s is possible using germanium thermistors.
Thermal flow meters are widely spread in research, industry and daily life because of their simple handling and their cost efficiency. However, the signals of thermal flow meters are highly ...fluid-dependent. In fact, a conventional thermal flow meter can often not distinguish if the fluid or the flow has changed. A fluid-independent thermal flow meter is still a challenge in research. This article presents a new approach of a fluid-compensated thermal flow meter using a combination of the 3ω-method and constant temperature anemometry (CTA). The 3ω-method is used to characterize the fluid properties and CTA is used to characterize the flow. A key element of the proposed method is the combination of the theoretical models of the 3ω-method and CTA to obtain a fluid-compensated flow. This method has been characterized theoretically and experimentally, and it could be shown that it can determine the flow rate within 9%, independent of the type of the fluid.
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•Proposal and investigation of a fluid compensated thermal flow sensor for liquids.•The method is based on constant temperature anemometry and the 3ω-method.•Theoretical models are the base of the compensation routine.•Both theoretical and experimental investigations are shown.
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.
In this paper, the effect of wind-induced vibration on measurement range of microcantilever anemometer is investigated for the first time. The microcantilever anemometer is composed of a flexible ...substrate and a piezoresistor. The wind speed can be detected through the airflow-induced deformation in the flexible substrate. Previous work indicated that the flexible substrate vibrates violently once the wind speed exceeds a critical value, resulting in severe output jitter. This wind-induced vibration limits the measurement range of the anemometer, and the relationship between the anemometer measurement range and its structural parameters has not been explored systematically. Therefore, this paper aims to reveal this relationship theoretically and experimentally, demonstrating that a shorter and thicker cantilever with larger stiffness can effectively suppress the wind-induced vibration, leading to the critical speed rising. By eliminating the wind-induced vibration, the measurement range of the microcantilever anemometer can be increased by up to 697%. These results presented in this paper can pave the way for the design and fabrication of wide-range mechanical anemometers.
This paper starts from a brief revisit of key early published work so that an overview of modern Coriolis flowmeters can be provided based on a historical background. The paper, then, focuses on ...providing an updated review of Coriolis flow measurement technology over the past 20 years. Published research work and industrial Coriolis flowmeter design are both reviewed in details. It is the intention of this paper to provide a comprehensive review study of all important topics in the subject, which include interesting theoretical and experimental studies and innovative industrial developments and applications. The advances in fundamental understanding and technology development are clearly identified. Future directions in various areas together with some open questions are also outlined.
•A brief revisit of key early published work is provided.•An updated review over the past 20 years is presented.•Published research work and industrial Coriolis flowmeter design are both reviewed.•Advances in fundamental understanding & technology development are identified.•Future directions together with open questions are outlined.
Here, we describe the development and characterisation of a flow sensor for microfluidic applications. The flow sensor utilises two miniaturised commercial pressure sensors mounted across a 3D ...printed microfluidic tube to measure the flow rate based on the viscous pressure drop occurring between the two sensors. The operational range of the flow sensor can be modulated by varying the diameter of the microfluidic tube. We demonstrate the suitability of the flow sensor for measuring constant and dynamic flow rates driven by syringe, piezoelectric, and pressure pumps. We characterise the flow sensor against water, water-glycerol solutions, and human blood. We harness the sensitivity of the sensor for measuring the viscosity of human blood at physiologic and room temperatures. We also show the ability of the flow sensor for monitoring the transitory flow rates generated by a manual pipette. The flow sensor is compact, low-cost, and highly responsive. It has no moving elements and can be easily tailored, interfaced, and operated. These features make it appealing for a wide range of applications in microfluidics.
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•Uses 3D printing technologies to create a flow sensor for microfluidic applications.•Utilises two miniaturised, sensitive, and inexpensive pressure sensors.•Flow sensor is capable of measuring constant and highly dynamic flow rates.•Flow sensor is compatible with human blood.•Flow sensor is characterised against commonly used microfluidic pumps.
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 bionic ciliary piezoelectric microsensor in d33 mode is presented for enhancing performance of self-powered hydrodynamic perception.•Based on the receptance method and Kirchhoff plate theory, a ...mathematical model is established to evaluate the resonant frequencies.•The effects of key parameters on the output characteristics of the sensor are numerically investigated by CFD combined with finite element analysis.•Utilizing MEMS technology and stereolithography, sensor prototypes are fabricated for experimental testing, whose results are in good agreement with simulation.•Experimental results indicate a sensitivity as high as 2.483 V/(m/s) and a relatively flat frequency response of the sensor.
This work presents a bionic ciliary piezoelectric microsensor in d33 mode for enhancing performance of self-powered hydrodynamic perception. The sensor is composed of a cylindrical pillar emulating the fish cilium and a piezoelectric sensing diaphragm imitating the hair cell. Interdigital electrodes are designed on both sides of the sensing diaphragm to realize the radial polarization, whose pattern consists of a few semi-circular rings connected to each other. Based on the receptance method and Kirchhoff plate theory, a mathematical model is established to evaluate the resonance frequency of the sensor. The output characteristics of the sensor are numerically obtained by coupling the drag force acquired by computational fluid dynamics into the finite element model. The effects of key structural parameters on the sensor response are further investigated for the purpose of optimizing the device design. Prototypes are fabricated by the microelectromechanical systems technology and stereolithography, characterized using the impedance spectrum and tested employing a dipole stimulus. The experimental values of the sensor response to hydrodynamic flow velocities are in fine agreement with the numerical simulation. The results indicate a high sensitivity of 2.483 V/(m/s) and a relatively flat frequency response of the sensor. This work provides important guidance for designing the more efficient ciliary microsensor that can conduct flow field perception for underwater autonomous vehicles.
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