Shear Stress Sensor Research Articles

Experimental study on the bed shear stress under breaking waves

The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1:15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.

Role of Piezo Ion Channels in Mechanosensation

Mechanotransduction is perhaps the last sensory modality not understood at the molecular level. Proteins/ion channels that sense mechanical force are postulated to play critical roles in sensing touch/pain (somatosensation), sound (hearing), sheer stress (cardiovascular function), etc.; however, the identity of ion channels involved in sensing mechanical force has remained elusive. We identified Piezo1 and Piezo2, mechanically-activated cation channels that are expressed in many mechanosensitive cell types. We demonstrated that Piezos constitute an evolutionarily conserved family of mechanically-activated cation channels. We further showed that Piezo1 is a shear stress sensor in vascular endothelial cells, while Piezo2 is the major transducer of mechanical forces for touch sensation in mice. Current efforts focus on understanding structure-function relationship of Piezo proteins, and elucidating their physiological roles in various biological processes and diseases that depend on mechanotransduction. Finally, we are searching for novel mechanosensors.

Abstract WMP36: Inhibition of the Endothelial Shear Stress Sensor, P2x4 Purinoceptor Drastically Reduces Cerebral Aneurysm Formation

Background and purpose: Although the assumption that wall shear stress-related hemodynamics is closely involved in cerebral aneurysm formation is now widely accepted, direct evidence still remains to be presented. Here, we examine a role of shear stress in cerebral aneurysm development, focused on a vascular endothelial shear sensor, P2X4 purinoceptor. Methods: P2X4 knockout mice and wild type mice were subjected to cerebral aneurysm-generating surgery with ligation of unilateral common carotid artery and renal hypertension. Damage to the internal elastic lamina, early phase aneurysm development, and the incidence of aneurysm induction were examined by light microscope. The expression of biochemical contributors to aneurysm formation was immunohistochemically examined. Additionally, the P2X4 purinoceptor inhibitor, paroxetine (10mg/kg/day) was administered to Sprague-Dawley rats after aneurysm-inducing surgery, and the incidence of aneurysm formation was examined. Results: Damage to the internal elastic lamina and the frequency of CA induction were significantly diminished in P2X4 knockout mice compared to control wild-type mice after CA-inducing surgery ( p =0.027 and 0.018, respectively). Expression levels of known contributors to aneurysm formation, iNOS, MCP-1, cathepsin L, and COX-2, were immunohistochemically weakened in P2X4 KO mice compared to wild-type mice. Moreover, paroxetine significantly attenuated the incidence of induced aneurysms in rats ( p =0.031). Conclusions: Disruption of the endothelial shear stress sensor, P2X4 purinoceptor drastically reduces cerebral aneurysm formation, suggesting that shear stress-related hemodynamics initiates cerebral aneurysm formation. The P2X4 purinoceptor inhibitor paroxetine, which is also prescribed to human as an antidepressant, may be a potential clinical prophylactic agent against cerebral aneurysm formation.

Simulation and testing of a MEMS calorimetric shear-stress sensor

The principle of operation of a new MEMS calorimetric shear-stress sensor is described. The sensor is based on the detection of the thermal wake generated by a heated beam over a cavity. Numerical simulations and wind-tunnel tests are conducted to highlight the effects of the inter-beam distance and the importance of the constant-temperature mode of operation. The calibration of a sensor prototype in a range of ±1.2Pa of wall shear-stress in air is performed and the sensor's capability to measure the mean and fluctuating wall shear-stress and the flow direction in a separation-bubble flow is demonstrated. Results of reverse-flow intermittency measurements are compared with those obtained with a classical thermal-tuft probe.

Piezoelectric Floating Element Shear Stress Sensor for the Wind Tunnel Flow Measurement.

A piezoelectric sensor with a floating element was developed for direct measurement of flow induced shear stress. The piezoelectric sensor was designed to detect the pure shear stress while suppressing the effect of normal stress generated from the vortex lift-up by applying opposite poling vectors to the piezoelectric elements. During the calibration stage, the prototyped sensor showed a high sensitivity to shear stress (91.3 ± 2.1 pC/Pa) due to the high piezoelectric coefficients (d 31=-1330 pC/N) of the constituent 0.67Pb(Mg1∕3Nb2∕3)O3-0.33PbTiO3 (PMN-33%PT) single crystal. By contrast, the sensor showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the sensing structure. The usable frequency range of the sensor is up to 800 Hz. In subsonic wind tunnel tests, an analytical model was proposed based on cantilever beam theory with an end-tip-mass for verifying the resonance frequency shift in static stress measurements. For dynamic stress measurements, the signal-to-noise ratio (SNR) and ambient vibration-filtered pure shear stress sensitivity were obtained through signal processing. The developed piezoelectric shear stress sensor was found to have an SNR of 15.8 ± 2.2 dB and a sensitivity of 56.5 ± 4.6 pC/Pa in the turbulent flow.

Surface micromachined differential piezoelectric shear-stress sensors

The ability to measure viscous wall shear stress in high-speed flows is important for verifying simulated results typically obtained from direct numerical simulation in the aerodynamics research community, and robust sensors are required to measure wall shear reliably under such high-speed conditions. This letter summarizes the design, fabrication, and testing of a surface micromachined piezoelectric shear-stress sensor which uses a thin piezoelectric film to generate a voltage proportional to an applied shear stress without additional moving parts. A differential-cell architecture is used to enhance selectivity to shear stress while canceling normal-stress sensitivity. The conceptual design, fabrication details, and experimental measurements of device sensitivity are presented. A finite element model is used to validate the device performance against measurements, and to provide insight into the potential and electric fields underlying the device concept. The potential for understanding device behavior and optimization through modeling is illustrated using finite element analysis results. The minimum detectable shear stress for the sensor is estimated to be 52.9 mPa √Hz−1 at 1.5 kHz.

Spatial frequency content of plantar pressure and shear profiles for diabetic and non-diabetic subjects

How high does pressure and shear stress sensor resolution need to be in order to reliably measure the plantar pressure and shear profiles (PPSPs) under normal and diabetic feet? In this study, pressure and shear stress data were collected from 26 total diabetic and control subjects using new instrumentation that measures vertical and horizontal force vectors of the plantar contact surface during multiple instances in the gait cycle. The custom built shear-and-pressure-evaluating-camera-system (SPECS) performs simultaneous recordings of pressure and both components of the horizontal force vector (medio–lateral and antero–posterior) at distinctive regions under one׳s foot, at a spatial resolution for each sensor equal to 1.6mm by 1.6mm. A linear interpolation method was used to simulate the effect of increasing sensor size on PPSPs. Ten square-shaped sensors were included in the analysis, having edge lengths of: (1.6mm, 3.2mm, 4.8mm, 6.4mm, 8mm, 9.6mm, 11.2mm, 12.8mm, 14.4mm, and 16mm). A two-dimensional Discrete Fourier Transform was performed on each data set, for each of the ten sensor sizes. To quantify the difference between sensor sizes, a comparison was made using the maximum pressure and shear stress data over the entire plantar contact surface, equivalent to the peak of the spatial frequency spectrum. A reduction of 5% of any component of the stress vector (i.e., pressure, or medio–lateral shear stress, or anter–posterior shear stress) due to an increase in sensor size was deemed significant. The results showed that a sensor measuring 9.6mm by 9.6mm caused meaningful reductions in all three stress components (p<0.001), whereas sensors measuring 1.6mm by 1.6mm, up to 4.8mm by 4.8mm, can capture the full range of spatial frequencies in both pressure and shear stress data.

Endothelial Mechanosignaling: Does One Sensor Fit All?

Significance: Forces are important in the cardiovascular system, acting as regulators of vascular physiology and pathology. Residing at the blood vessel interface, cells (endothelial cell, EC) are constantly exposed to vascular forces, including shear stress. Shear stress is the frictional force exerted by blood flow, and its patterns differ based on vessel geometry and type. These patterns range from uniform laminar flow to nonuniform disturbed flow. Although ECs sense and differentially respond to flow patterns unique to their microenvironment, the mechanisms underlying endothelial mechanosensing remain incompletely understood. Recent Advances: A large body of work suggests that ECs possess many mechanosensors that decorate their apical, junctional, and basal surfaces. These potential mechanosensors sense blood flow, translating physical force into biochemical signaling events. Critical Issues: Understanding the mechanisms by which proposed mechanosensors sense and respond to shear stress requires an integrative approach. It is also critical to understand the role of these mechanosensors not only during embryonic development but also in the different vascular beds in the adult. Possible cross talk and integration of mechanosensing via the various mechanosensors remain a challenge. Future Directions: Determination of the hierarchy of endothelial mechanosensors is critical for future work, as is determination of the extent to which mechanosensors work together to achieve force-dependent signaling. The role and primary sensors of shear stress during development also remain an open question. Finally, integrative approaches must be used to determine absolute mechanosensory function of potential mechanosensors. Antioxid. Redox Signal. 25, 373–388.

Flow sensing by buckling monitoring of electrothermally actuated double-clamped micro beams

We report on a flow sensing approach based on deflection monitoring of a micro beam buckled by the compressive thermal stress due to electrothermal Joule's heating. The air stream, convectively cooling the device, affects both the critical buckling values of the electric current and the postbuckling deflections of the structure. After calibration, the flow velocity can be obtained from the deflection measurements. The quasi-static responses of 1000 μm and 2000 μm long, 10 μm wide, and 30 μm high single crystal silicon beams were consistent with the prediction of the model, which couples thermoelectric, thermofluidic, and structural domains. The deflection sensitivity of up to 1.5 μm/(m/s) and the critical current sensitivity of up to 0.43 mA/(m/s) were registered in the experiments. Our model and experimental results demonstrate the feasibility of the sensing approach and further suggest that simple, robust, and potentially downscalable beam-type devices may have use in flow velocity and wall shear stress sensors.

A MEMS thermal shear stress sensor produced by a combination of substrate-free structures with anodic bonding technology

By combining substrate-free structures with anodic bonding technology, we present a simple and efficient micro-electro-mechanical system (MEMS) thermal shear stress sensor. Significantly, the resulting depth of the vacuum cavity of the sensor is determined by the thickness of the silicon substrate at which Si is removed by the anisotropic wet etching process. Compared with the sensor based on a sacrificial layer technique, the proposed MEMS thermal shear-stress sensor exhibits dramatically improved sensitivity due to the much larger vacuum cavity depth. The fabricated MEMS thermal shear-stress sensor with a vacuum cavity depth as large as 525 μm and a vacuum of 5 × 10−2 Pa exhibits a sensitivity of 184.5 mV/Pa and a response time of 180 μs. We also experimentally demonstrate that the sensor power is indeed proportional to the 1/3-power of the applied shear stress. The substrate-free structures offer the ability to precisely measure the shear stress fluctuations in low speed turbulent boundary layer wind tunnels.

An integrated temperature-compensated flexible shear-stress sensor microarray with concentrated leading-wire.

Flexible shear stress sensor is quite important for characterizing curved surface flows. In this work, a novel integrated shear stress sensor microarray is designed with twenty parallel channels, which share the concentrated leading-wire to transmit the ground signal. Electrical pads in rows are easily connected to the circuits with two separate Wheatstone bridges and constant-temperature-difference mode operation is provided for the hot-wires. Temperature crosstalk between adjacent hot-wires is prevented well and the effectiveness of the temperature compensated circuits is verified. Relatively large output response is obtained as the shear stress varies and the sensitivity of the sensors is measured about 0.086 V(2)/Pa(1/3) with nonlinearity lower than 1%, revealing high performance characteristic of the sensors.

Wall Shear Stress and Flow Direction Thermal MEMS Sensor for Separation Detection and Flow Control Applications

We report a study on a wall shear stress and flow direction hot-wire based sensor operating in anemometric mode. The sensor is designed to achieve fast response time and high sensitivity. The sensor structure consists in free hot wires over insulator bridges and exhibits sensitivity to wall shear stress variations and to flow direction. The sensor can be wall-mounted for applications such as flow control or turbulence analysis. Finite elements simulations have been made to demonstrate a fast thermal response time to fluid velocity of about 300 μs in constant current operating mode and a sensitivity to wall shear-stress fluctuations. Electrical characterizations and wind tunnel experiments were performed to analyze the sensor response to respectively heat power and flow velocity.

220 MEMSを用いた熱式壁面せん断応力センサの開発および壁乱流構造に関する研究(OS3-2 乱流現象の実験とシミュレーション(2),OS3 乱流現象の実験とシミュレーション)

220 MEMSを用いた熱式壁面せん断応力センサの開発および壁乱流構造に関する研究(OS3-2 乱流現象の実験とシミュレーション(2),OS3 乱流現象の実験とシミュレーション)

MEMS热膜壁面剪应力传感器标定技术研究现状

流体壁面剪应力的测量对于流动减阻，湍流结构机理研究等方面都具有重要的作用，MEMS壁面剪应力传感器为壁面剪应力的测量提供了一种准确有效的手段。首先介绍了热膜型的MEMS壁面剪应力传感器的测量原理及发展现状；其次着重分析了热膜型的MEMS壁面剪应力传感器的静态和动态标定方法，静态标定方法可分为基于速度，基于流量和基于压力的方法，动态标定方法通常采用斯托克斯层激励方法；最后对标定技术进行了归纳总结及展望。 The measurement of wall shear stress is significant for drag reduction and mechanism study of turbulence structure. MEMS wall shear stress sensor offers an accurate and effective method for wall shear stress measurement. Firstly, measurement principle and development status of thermal based MEMS wall shear stress sensor are introduced. Secondly, static and dynamic calibration methods of thermal based MEMS wall shear stress sensor are stressed. The static method can be based on velocity, flux and pressure measurement, while the commonly used dynamic calibration method is the Stokes-layer excitation method. Finally, conclusion and expectation are made about the calibration method.

Fabrication and flow-sensor application of flexible thermal MEMS device based on Cu on polyimide substrate

A Cu on polyimide (COP) substrate was proposed as a MEMS material, and the fabrication process for a flexible thermal MEMS sensor was developed. The COP substrate application to MEMS devices has the advantage that typical MEMS structures fabricated in a SOI wafer in the past--such as a diaphragm, a beam, a heater formed on a diaphragm--can also be easily produced in the COP substrate in the flexible fashion. These structures can be used as the sensing element in various physical sensors, such as flow, acceleration, and shear stress sensors. A flexible thermal MEMS sensor was produced by using a lift-off process and sacrificial etching of a copper layer on the COP substrate. A metal film working as a flow sensing element was formed on a thin polyimide membrane produced by the sacrificial etching. The fabricated flexible thermal MEMS sensor was used as a flow sensor, and its characteristics were evaluated. The obtained sensor output versus the flow rate curve closely matched the approximate curve derived using King's law. The rising and falling response times obtained were 0.50 and 0.67 s, respectively.

High-Sensitivity Single Thermopile SOI CMOS MEMS Thermal Wall Shear Stress Sensor

In this paper, we present a novel silicon-on-insulator (SOI) complementary metal–oxide–semiconductor (CMOS) microelectromechanical-system thermal wall shear stress sensor based on a tungsten hot-wire and a single thermopile. Devices were fabricated using a commercial 1- $\mu \text{m}$ SOI-CMOS process followed by a deep reactive ion etching back-etch step to release a silicon dioxide membrane, which mechanically supports and thermally isolates heating and sensing elements. The sensors show an electrothermal transduction efficiency of $50~\mu \text{W}$ /°C, and a very small zero flow offset. Calibration for wall shear stress measurement in air in the range of 0–0.48 Pa was performed using a suction type, 2-D flow wind tunnel. The sensors were found to be extremely sensitive, up to 4 V/Pa for low wall shear stress values. Furthermore, we demonstrate the superior signal-to-noise ratio (up to five times higher) of a single thermopile readout configuration compared with a double thermopile readout configuration (embedded for comparison purposes within the same device). Finally, we verify that the output of the sensor is proportional to the cube root of the wall shear stress and we propose an accurate semiempirical formula for its modeling.

Evaluation of a film-based wall shear stress measurement technique in a turbulent channel flow

Mean wall shear stress in a turbulent channel flow has been measured using a film-based shear stress sensor with a working principle based on the deformation of a thin elastic film. A direct comparison was made between the elastic film measurements and those using oil-film interferometry in the same experimental facility to evaluate the capability of the novel technique to measure the mean wall shear stress. The results indicate that the film-based sensor measures the wall shear stress within the uncertainty of the oil film measurement for the range of Reynolds numbers considered here, i.e. 2100–2900 based on the friction velocity and the half channel height.

Flexible Micro-Sensor Array for the Non-Invasive Monitoring of 3D Pressure Fields

Non-invasive pressure / force measurements are needed in many applications involving human body, such as gesture and displacement analysis. They are particularly needed in medical applications for the monitoring of pressure fields, e.g. in the case of plantar lesion detection in neurodegenerative pathologies or in the case of the control of compression bandage therapy dedicated to chronic venous disorders. This type of applications features very demanding specifications. Indeed, they require the development of pressure field measurement devices which are accurate, reliable, easily wearable, and possibly biocompatible. To meet these requirements, polymer based micro-capacitive sensor arrays fabricated on flexible substrates are good candidates to let non-invasive as well as accurate stress measurements to be carried out. Since single-axis pressure measurements may be found incomplete in some applications, capacitive arrays featuring 3-axes pressure sensing capabilities are considered in this study. Here, a sensor array prototype featuring 25 element 3-axes micro-sensors is designed and fabricated. The principle of operation of the sensing array is based on the use of a two electrode networks facing one another and separated with a highly deformable dielectric polymer film (PDMS). In order to foresee the sensitivity of the designed sensors to the applied pressure, a thorough study of the mechanical properties of PDMS thin films is carried out both computationally and experimentally. According to this study, a 3-axes sensing array constituted of a network of top and bottom copper electrodes separated by a 100 µm thick PDMS film is considered. The electrode network is organized so that it constitutes 25 elementary 3-axes sensing units, which are addressed by means of a multiplexed row and column electrical connection system. Each unit is 5 X 5 mm2 large and is constituted of three single-axis capacitive sensors, the design of which being chosen so as to enhance the sensitivity of each single-axis sensor to the desired spatial component of the applied load and to reduce its sensitivity to the other components, while limiting the overall dimensions of the 3-axes sensing unit. They are realized on a flexible substrate (Kapton) using PDMS as a deformable dielectric material, by means of an original transfer of film technique. It enables metallic electrodes to be deposited on deformable and weak adherence material such as PDMS. The fabrication process enables sensor arrays of up to 75 sensors to be realized with a transfer yield of 100%. The alignment of electrodes features an accuracy of 3%, and the fabricated load-free dielectric layer thickness exhibits a thickness accuracy of 5% in load-free conditions. In the realized sample the normal pressure sensors and the shear stress sensors feature 1.3 pF (measured: 1.2 pF) and 2 pF (measured: 2.2pF) load-free capacitances, respectively. Besides, preliminary electro-mechanical characterizations are carried out to estimate the force/pressure sensitivity of the realized sensors. To do so, a dedicated experimental test bench is set up. It includes a three-axis robot together with an integrated commercial pressure sensor (Honeywell micro-force gauge FSG15N) allowing monitoring normal loads on the sensors, a spring loaded set-up allowing the sensor to be linked to the force gauge, and a HP4192A impedance analyzer to measure the sensor capacitance. Preliminary experimental evaluations of the sensor array are presented. It shows that the capacitance changes under applied load up to 7 N are in the order of 10%. These results are discussed according to the expected sensitivity of the designed 3-axis sensor array. Figure 1

Improved sensitivity of micro thermal sensor for underwater wall shear stress measurement

Drive current is an important parameter of thermal shear stress sensor. Increasing drive current is helpful for enhancing its sensitivity. However, there must be an allowable drive current for the sake of safe working temperature of the sensor. How to make full use of drive current to increase the sensor's sensitivity working underwater was studied. If the allowable drive current in still water and the current in stream water are used to drive the sensor in lower and higher shear stress input ranges, respectively, sensitivity of the sensor will be enhanced with the sensor working under a safe temperature. The both currents were separately determined by analyzing I---V characteristic and output voltage-shear stress relationship. We can improve the sensor's sensitivity from 11.8 to 27.5 mV/Pa when shear stress input was 0.4 Pa.

167 TRPV4; a Potential New Target to Increase Placental Blood Flow in Fetal Growth Restricted Pregnancies?

IntroductionFetal growth restriction (FGR) is a pregnancy complication that predisposes to an increased risk of neonatal morbidity and mortality. A low birth weight is also associated with increased risk of...