Academic literature on the topic 'Cantilever Flow Sensor'

Background: Flow stimuli in the natural world are varied and contain a wide variety of directional information. Nature has developed morphological polarity and bidirectional arrangements for flow sensing to filter the incoming stimuli. Inspired by the neuromasts found in the lateral line of fish, we present a novel flow sensor design based on two curved cantilevers with bending orientation antiparallel to each other. Antiparallel cantilever pairs were designed, fabricated and compared to a single cantilever based hair sensor in terms of sensitivity to temperature changes and their response to changes in relative air flow direction. Results: In bidirectional air flow, antiparallel cantilever pairs exhibit an axially symmetrical sensitivity between 40 μV/(m s−1) for the lower air flow velocity range (between ±10–20 m s−1) and 80 μV/(m s−1) for a higher air flow velocity range (between ±20–32 m s−1). The antiparallel cantilever design improves directional sensitivity and provides a sinusoidal response to flow angle. In forward flow, the single sensor reaches its saturation limitation, flattening at 67% of the ideal sinusoidal curve which is earlier than the antiparallel cantilevers at 75%. The antiparallel artificial hair sensor better compensates for temperature changes than the single sensor. Conclusion: This work demonstrated the successive improvement of the bidirectional sensitivity, that is, improved temperature compensation, decreased noise generation and symmetrical response behaviour. In the antiparallel configuration, one of the two cantilevers always extends out into the free stream flow, remaining sensitive to directional flow and preserving a sensitivity to further flow stimuli.

Abstract. Microcantilevers offer a wide range of applications in sensor and measurement technology. In this work cantilever sensors are used as flow sensors. Most conventional flow sensors are often only calibrated for one type of gas and allow an analysis of gas mixtures only with increased effort. The sensor used here is a cantilever positioned vertically in the flow channel. It is possible to operate the sensor in dynamic and static mode. In the dynamic mode the cantilever is oscillating. Resonance frequency, resonance amplitude and phase are measured. In static mode, the bending of the cantilever is registered. The combination of the modes enables the different measured variables to be determined simultaneously. A flow influences the movement behaviour of the sensor, which allows the flow velocity to be deduced. In addition to determining the flow velocity, it is also possible to detect different types of gas. Each medium has certain properties (density and viscosity) which have different effects on the bending of the sensor. As a result, it is possible to measure the mixing ratio of a known binary gas mixture and their flow velocity simultaneously with a single sensor. In this paper this is investigated using the example of the air–carbon-dioxide mixture.

The purpose of this paper is to apply MEMS techniques to manufacture a gas flow sensor that consists with an airflow rate and airflow direction sensing units for detection of airflow states. This study uses a silicon wafer as a substrate which is deposited silicon nitride layers. To form the airflow rate sensing unit, a micro heater and a sensing resistor are manufactured over a membrane that released by a back-etching process. The airflow direction sensing unit is made of four cantilever beams that perpendicular to each other and integrated with piezoresistive structure on each micro-cantilever, respectively. As the cantilever beams are formed after etching the silicon wafer, it bends up a little due to the released residual stress induced in the previous fabrication process. As air flows through the airflow rate sensor, the temperature of the sensing resistor decreases and the evaluation of the local temperature changes determines the airflow rate. On the proposed sensor, the airflow direction can be determined through comparing the resistance variation caused by different deformation of cantilever beams at different directions.

In this study, we propose a microelectromechanical system (MEMS) force sensor for microflow measurements. The sensor is equipped with a flow sensing piezoresistive cantilever and a dummy piezoresistive cantilever, which acts as a temperature reference. Since the dummy cantilever is also in the form of a thin cantilever, the temperature environment of the dummy sensor is almost identical to that of the sensing cantilever. The temperature compensation effect was measured, and the piezoresistive cantilever was combined with a gasket jig to enable the direct implementation of the piezoresistive cantilever in a flow tube. The sensor device stably measured flow rates from 20 μL/s to 400 μL/s in a silicon tube with a 2-mm inner diameter without being disturbed by temperature fluctuations.

In this paper, a self-out-readable, miniaturized cantilever resonator for highly sensitive airborne nanoparticle (NP) detection is presented. The cantilever, which is operated in the fundamental in-plane resonance mode, is used as a microbalance with femtogram resolution. To maximize sensitivity and read-out signal amplitude of the piezo-resistive Wheatstone half bridge, the geometric parameters of the sensor design are optimized by finite element modelling (FEM). The electrical read-out of the cantilever movement is realized by piezo-resistive struts at the sides of the cantilever resonator that enable real-time tracking using a phase-locked loop (PLL) circuit. Cantilevers with minimum resonator mass of 1.72 ng and resonance frequency of ~440 kHz were fabricated, providing a theoretical sensitivity of 7.8 fg/Hz. In addition, for electrostatic NP collection, the cantilever has a negative-biased electrode located at its free end. Moreover, the counter-electrode surrounding the cantilever and a µ-channel, guiding the particle-laden air flow towards the cantilever, are integrated with the sensor chip. µ-channels and varying sampling voltages will also be used to accomplish particle separation for size-selective NP detection. To sum up, the presented airborne NP sensor is expected to demonstrate significant improvements in the field of handheld, micro-/nanoelectromechanical systems (M/NEMS)-based NP monitoring devices.

In this work the application of a self-sensing and self-actuating cantilever for gas-flow measurement is investigated. The cantilever placed in the flow is excited permanently at its first resonance mode. Simultaneously the resonance amplitude, the resonance frequency and the static bending of the cantilever are detected. All three sizes are related to the velocity of the gas-flow.

MEMS are used in acceleration, flow, pressure and force sensing applications on the micro and macro levels. The fundamental part of every sensor is the transducer which converts the measurend of intrest into and interpretable output signal. The most prominent transducer is the piezoresistive cantilever which translates any signal into an electrical signal.This paper presents the deisgn and fabrication of U shaped cantilever with enhanced sensitivity and stiffness which gives better results than other cantilevers. The simulation results of the cantilevers are designed using COMSOL software. MEMS technology becomes more affordable better and easier to fabricate in increasing quantities. Each layer of fabrication process is quite complex and final fabricated product will tested and used for high end applications.

Angular acceleration sensors are attracting attention as sensors for monitoring rotational vibration. Many angular acceleration sensors have been developed; however, multiaxis measurement is still in a challenging stage. In this study, we propose a biaxial angular acceleration sensor with two uniaxial sensor units arranged orthogonally. The sensor units consist of two rotational-symmetric spiral channels and microelectromechanical system (MEMS) piezoresistive cantilevers. The cantilever is placed to interrupt the flow at the junctions of parallelly aligned spirals in each channel. When two cantilevers are used as the resistance of the bridge circuit in the two-gauge method, the rotational-symmetric spiral channels enhance the sensitivity in the target axis, while the nontarget axis sensitivities are canceled. The fabricated device responds with approximately constant sensitivity from 1 to 15 Hz, with a value of 3.86 × 10−5/(rad/s2), which is equal to the theoretical value. The nontarget axis sensitivity is approximately 1/400 of the target axis sensitivity. In addition, we demonstrate that each unit responds according to the tilt angle when the device is tilted along the two corresponding rotational axis planes. Thus, it is concluded that the developed device realizes biaxial angular acceleration measurement with low crosstalk.

This thesis proposes a novel air flow sensor based on PZT material which is used to measure air velocity in an experimental tunnel or indoor ventilation. The work focuses on designing and verifying the sensor model through finite element analysis (FEA) simulation using COMSOL Multiphysics software. This thesis is devoted to developing a sensor model with a focus on a low-velocity range up to 2 m/s and high sensitivity. The design of the sensor should be robust and reliable for different flow patterns, temperature, and atmospheric pressure variation. The sensor model consists of a fixed cylinder which connects with a bilayer cantilever made of PZT and PDMS material. The laminar flow from the sensor inlet is transformed into the turbulent flow when passing by the fixed cylinder. This structure of bilayer cantilever is designed to generate self-induced oscillation on PZT to overcome the charge leakage over the sensor impedance. Resonance optimization of the sensor structure is investigated to obtain better SNR and performance by adjusting the dimension of the cantilever. From the conducted simulation results, the relationship between the dominant frequency of output voltage generated by PZT and air velocity can be described linearly. In conclusion, it is shown that proposed sensor has a sensitivity of 0.1 m/s and a range of 0.2 to 2 m/s.

Design, fabrication and development of polymer microcantilever for flow rate measurement and thermal actuation Research Supervisors: Prof. K. Rajanna and Dr. G. R. Jayanth Microcantilevers are sensitive micromechanical platforms used to detect small forces and surface stresses arising due to changes in physical environment. They are popularly used as mechanical probes in scanning probe microscopy to obtain 3D surface topography of samples upto atomic scale resolution. These microcantilevers find applications in biosensing, environment monitoring, air flow measurement, microbolometry, Atomic Force Microscopy (AFM), etc,. Furthermore, microcantilevers form versatile, compliant platforms for producing mechanical actuation. Microcantilever based actuators are used as RF switches, biomanipulators, microrelays and microfluidic valves. Conventionally, microcantilevers are fabricated using silicon, silicon nitride or silicon dioxide. However, in recent times polymers are being used as alternate materials for fabricating microcantilevers. These polymer microcantilevers offer several advantages and versatilities. The aim of the present thesis work is to the design, fabricate, characterize and evaluate the performance of piezoresistive SU8 microcantilevers for low flow rate measurement and thermal actuation. Finite element (FE) simulation was used to determine the stress distribution across a stressed microcantilever structure. The results of FE simulations enable suitable piezoresistor design for integration with the cantilever. Various surface micromachining techniques were attempted to fabricate freely suspended SU8 microcantilevers with gold thin film piezoresistors. Electrical interconnection was established using ball bump aided epoxy bonding technique. The fabricated SU8 microcantilever sensor was mechanically characterized and its strain sensitivity was evaluated. These sensors were employed for low gas flow rate measurement in the range 0 to 100 mL/min. The sensor response was found to be linear, repeatable and consistent with different flow rates. The fabricated SU8 microcantilever device also exhibited thermomechanical actuation. Hence, the performance of the device due to Joule heating of the piezoresistor was studied in detail. A nonlinear thermomechanical model was proposed to accurately estimate the thermal behaviour of the polymer microcantilever. This study underscores the need to consider nonlinear thermo-elastic properties of polymers while modeling their thermomechanical response. Both finite element simulation and experimental result indicate nonlinear thermomechanical response of the SU8 based thermal actuator. The developed microsystem presents simultaneous sensing and actuation mechanisms. Hence, they are suitable for integration with Lab-on-chip-devices. This thesis in divided into 8 chapters and the brief summary is as follows: Chapter 1 This chapter gives a brief introduction to the state-of-art scenario of MEMS technology and its relevance in the field of sensors and actuators. Later, an overview of micromachining techniques used for the fabrication of MEMS devices is discussed. Microcantilever based devices and their applications are discussed. In particular, their use as non-thermal flow sensors is presented. Also, the need for polymeric microcantilever sensors for low gas flow rate measurement is discussed. At the end, the objective, scope of present work and the organization of the thesis are discussed. Chapter 2 The aspect of SU8 microcantilever design for flow measurement is presented. Relevant piezoresistivity theory required for the design of thin film piezoresistor is explained. Finite element simulation was used to identify regions of maximum stress in the microcantilever due to fluid flow interactions. The geometry and shape of thin film piezoresistor was chosen based on the simulation results. Finally, the optimal design parameters of piezoresistive SU8 microcantilever sensor are summarized. Chapter 3 This chapter describes the processes involved in the fabrication of piezoresistive SU8 microcantilevers. Surface micromachining techniques such as wet oxidation, lift-off, thin film deposition, sacrificial layer etching etc were used during the fabrication. Wet oxidation was used to grow uniform, dense oxide for sacrificial layer. Gold thin films were deposited using RF sputtering technique and patterned using UV photolithography. SU8 microcantilevers were patterned using photolithography and freely suspended SU8 microcantilevers were obtained by selectively etching the sacrificial layer. The issues of residual stress in suspended SU8 microcantilever are discussed. Finally, an optimal fabrication process was obtained to build SU8 microcantilever with integrated piezoresistor. Chapter 4 The fabricated flow sensor needs to be connected with the external circuitry via electrical interconnects. This chapter discusses the process of packaging and electrical interconnection with the fabricated SU8 microcantilever sensor. The issues of making wire bonding onto SU8 chip using conventional wire bonding techniques are described. Alternate wire bonding techniques such as epoxy bonding was attempted. Finally, ball bump aided epoxy bonding technique was developed and used for making electrical interconnection with the sensor. Chapter 5 In this chapter the fabricated and packaged microcantilever sensor was characterized to evaluate its electro-mechanical performance. The sensor response was evaluated experimentally by providing known mechanical displacement via precisely controlled piezostage. At the end, the sensor characteristics such as gauge factor of the piezoresistor, deflection sensitivity of the microcantilever sensor, its hysteresis, linearity and repeatability were also obtained. Chapter 6 This chapter describes the performance study of piezoresistive SU8 cantilever sensor for low gas flow rate measurement in the range 10 to 500 mL/min. The measured flow sensitivity was about 1.103×10-5 mL/min. Finite element simulations were used to estimate the cantilever deflection due to gas flow. The simulation results show quadratic dependence of cantilever deflection on gas flow rate. For a flow rate between 0 to100 mL/min, the experimental results agree well with the simulation results showing a linear trend in this range. Chapter 7 This chapter presents the nonlinear thermomechanical analysis and thermal actuation of fabricated SU8 microcantilevers. The thermomechanical analysis of the actuator incorporates nonlinear temperature-dependent properties of SU8 polymer to accurately model its thermal response during actuation. The issues of residual stress developed within the SU8 microstructure during fabrication are discussed and a novel strategy was proposed to release the residual stress in the fabricated actuators. The thermomechanical response of the actuator was obtained experimentally. The measured average actuation range of about 8.5 μm was produced for an actuation current of 5 mA. It was found that the results of nonlinear thermomechanical analysis agree well with the experimental result. Chapter 8 The chapter summarizes the results and conclusions drawn from the present work. Also, the scope of future work is discussed.

Microelectromechanical systems offer variety of advantages such as small size, higher sensitivity, low cost because of mass fabrication capabilities and ease of implementation. Thin film cantilever based devices have been successfully used for variety of applications not limited to chemical vapors for chemical agents, biological warfare agents, contaminants in water, explosives, acoustics, vibration monitoring, flow sensing, viscosity and density measurements, antibody, pathogen detection, acceleration, shock sensing and magnetic field sensing. Thin film cantilevers can easily realized on silicon and other surfaces. Microcantilevers supported on one edge of the substrate can be designed to demonstrate very high sensitivity to very less force of the order of piconewtons. These structures could be extended for application in gas sensing if chemically sensitive layer is added on to the cantilever. The dimensions of the cantilever determine the sensitivity. Cantilevers as thin as few tenths of nanometer in thickness has been successfully demonstrated. Challenge associated with these devices when used as a sensor is their response to shock and acceleration.

Abstract A new type of MEMS flow sensor has been designed, analyzed, fabricated, and tested. This sensor consists of a surface micromachined switch with a complex cantilever shape. A portion of the sensor is bent at a right angle to the substrate and to the flow direction. The fluid flow produces a pressure on the sensor; sufficient pressure causes the switch to close at the designed flow rate. These flow sensors have been developed for a large multi-university project for the design and construction of a biomimetic underwater lobster robot to be used to search for and destroy mines. However, we envision a variety of other uses for these flow sensors, including biomedical applications such as blood flow measurement. The fabrication process is based on the Northeastern University Metal Micromachining (NUMEM) technology [1]. The NUMEM process has been used to fabricate various surface micromachined metallic structures such as microrelays, microinterferometers, micromirrors, and microaccelerometers. The analysis of these devices consists of using incompressible fluid mechanics to determine the pressure acting on the sensor and beam theory to model the resulting deflection of the switch. The first set of flow sensors was designed to close at flow velocities of 0.5, 1.0, 3.4, and 5.4 m/s. The area of the paddle, which lies in the flow, is varied in order to obtain sensors that close at different flow rates. The results of testing agree well with the analytical predictions. Although these flow sensors are unidirectional, an array of four sensors at each point can be used to determine the flow velocity and direction.

An experimental investigation was conducted to measure skin friction along the chamber walls of supersonic combustors. A direct force measurement device was used to simultaneously measure an axial and transverse component of the small tangential shear force passing over a non-intrusive floating element. This measurement was made possible with a sensitive piezoresistive deflection sensing unit. The floating head is mounted to a stiff cantilever beam arrangement with deflection due to the flow on the order of 0.00254 mm (0.0001 in). This allowed the instrument to be a non-nulling type. A second gauge was designed with active cooling of the floating sensor head to eliminate non-uniform temperature effects between the sensor head and the surrounding wall. The key to this device is the use of a quartz tube cantilever with piezoresistive strain gages bonded directly to its surface. A symmetric fluid flow was developed inside the quartz tube to provide cooling to the backside of the floating head. Tests showed that this flow did not influence the tangential force measurement. Measurements were made in three separate combustor test facilities. Tests at NASA Langley Research Center consisted of a Mach 3.0 vitiated air flow with hydrogen fuel injection at Pt = 500 psia (3446 kPa) and Tt = 3000 R (1667 K). Two separate sets of tests were conducted at the General Applied Science Laboratory (GASL) in a scramjet combustor model with hydrogen fuel injection in vitiated air at Mach = 3.3, Pt = 800 psia (5510 kPa), and Tt = 4000 R (2222 K). Skin friction coefficients between 0.001–0.005 were measured dependent on the facility and measurement location. Analysis of the measurement uncertainties indicate an accuracy to within ±10–15% of the streamwise component.