Sensor Technologies MEMS Fabrication Technique MEMS Accelerometer MEMS Dust
Eskew, Mike, Faculty Advisor has reference to this Academic Journal, PHwiki organized this Journal Sensor Technologies Phase Linearity Describe how well a system preserves the phase relationship between frequency components of the input Phase linearity: f=kf Distortion of signal Amplitude linearity Phase linearity Sensor Technology – Terminology Transducer is a device which trans as long as ms energy from one type to another, even if both energy types are in the same domain. Typical energy domains are mechanical, electrical, chemical, magnetic, optical in addition to thermal. Transducer can be further divided into Sensors, which monitors a system in addition to Actuators, which impose an action on the system. Sensors are devices which monitor a parameter of a system, hopefully without disturbing that parameter.
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Categorization of Sensor Classification based on physical phenomena Mechanical: strain gage, displacement (LVDT), velocity (laser vibrometer), accelerometer, tilt meter, viscometer, pressure, etc. Thermal: thermal couple Optical: camera, infrared sensor Others Classification based on measuring mechanism Resistance sensing, capacitance sensing, inductance sensing, piezoelectricity, etc. Materials capable of converting of one as long as m of energy to another are at the heart of many sensors. Invention of new materials, e.g., smart materials, would permit the design of new types of sensors. Paradigm of Sensing System Design Zhang & Aktan, 2005 Instrumentation Considerations Sensor technology; Sensor data collection topologies; Data communication; Power supply; Data synchronization; Environmental parameters in addition to influence; Remote data analysis.
Measurement Measurement output: interaction between a sensor in addition to the environment surrounding the sensor compound response of multiple inputs Measurement errors: System errors: imperfect design of the measurement setup in addition to the approximation, can be corrected by calibration R in addition to om errors: variations due to uncontrolled variables. Can be reduced by averaging. Sensors Definition: a device as long as sensing a physical variable of a physical system or an environment Classification of Sensors Mechanical quantities: displacement, Strain, rotation velocity, acceleration, pressure, as long as ce/torque, twisting, weight, flow Thermal quantities: temperature, heat. Electromagnetic/optical quantities: voltage, current, frequency phase; visual/images, light; magnetism. Chemical quantities: moisture, pH value Specifications of Sensor Accuracy: error between the result of a measurement in addition to the true value being measured. Resolution: the smallest increment of measure that a device can make. Sensitivity: the ratio between the change in the output signal to a small change in input physical signal. Slope of the input-output fit line. Repeatability/Precision: the ability of the sensor to output the same value as long as the same input over a number of trials
Accuracy vs. Resolution Accuracy vs. Precision Precision without accuracy Accuracy without precision Precision in addition to accuracy Specifications of Sensor Dynamic Range: the ratio of maximum recordable input amplitude to minimum input amplitude, i.e. D.R. = 20 log (Max. Input Ampl./Min. Input Ampl.) dB Linearity: the deviation of the output from a best-fit straight line as long as a given range of the sensor Transfer Function (Frequency Response): The relationship between physical input signal in addition to electrical output signal, which may constitute a complete description of the sensor characteristics. B in addition to width: the frequency range between the lower in addition to upper cutoff frequencies, within which the sensor transfer function is constant gain or linear. Noise: r in addition to om fluctuation in the value of input that causes r in addition to om fluctuation in the output value
Attributes of Sensors Operating Principle: Embedded technologies that make sensors function, such as electro-optics, electromagnetic, piezoelectricity, active in addition to passive ultraviolet. Dimension of Variables: The number of dimensions of physical variables. Size: The physical volume of sensors. Data Format: The measuring feature of data in time; continuous or discrete/analog or digital. Intelligence: Capabilities of on-board data processing in addition to decision-making. Active versus Passive Sensors: Capability of generating vs. just receiving signals. Physical Contact: The way sensors observe the disturbance in environment. Environmental durability: will the sensor robust enough as long as its operation conditions Strain Gauges Foil strain gauge Least expensive Widely used Not suitable as long as long distance Electromagnetic Interference Sensitive to moisture & humidity Vibration wire strain gauge Determine strain from freq. of AC signal Bulky Fiber optic gauge Immune to EM in addition to electrostatic noise Compact size High cost Fragile Strain Sensing Resistive Foil Strain Gage Technology well developed; Low cost High response speed & broad frequency b in addition to width A wide assortment of foil strain gages commercially available Subject to electromagnetic (EM) noise, interference, offset drift in signal. Long-term per as long as mance of adhesives used as long as bonding strain gages is questionable Vibrating wire strain gages can NOT be used as long as dynamic application because of their low response speed. Optical fiber strain sensor
Strain Sensing Piezoelectric Strain Sensor Piezoelectric ceramic-based or Piezoelectric polymer-based (e.g., PVDF) Very high resolution (able to measure nanostrain) Excellent per as long as mance in ultrasonic frequency range, very high frequency b in addition to width; there as long as e very popular in ultrasonic applications, such as measuring signals due to surface wave propagation When used as long as measuring plane strain, can not distinguish the strain in X, Y direction Piezoelectric ceramic is a brittle material (can not measure large de as long as mation) Courtesy of PCB Piezotronics Acceleration Sensing Piezoelectric accelerometer Nonzero lower cutoff frequency (0.1 1 Hz as long as 5%) Light, compact size (miniature accelerometer weighing 0.7 g is available) Measurement range up to +/- 500 g Less expensive than capacitive accelerometer Sensitivity typically from 5 100 mv/g Broad frequency b in addition to width (typically 0.2 5 kHz) Operating temperature: -70 150 C Acceleration Sensing Capacitive accelerometer Good per as long as mance over low frequency range, can measure gravity! Heavier (~ 100 g) in addition to bigger size than piezoelectric accelerometer Measurement range up to +/- 200 g More expensive than piezoelectric accelerometer Sensitivity typically from 10 1000 mV/g Frequency b in addition to width typically from 0 to 800 Hz Operating temperature: -65 120 C
Accelerometer Force Sensing Metal foil strain-gage based (load cell) Good in low frequency response High load rating Resolution lower than piezoelectricity-based Rugged, typically big size, heavy weight Courtesy of Davidson Measurement Force Sensing Piezoelectricity based ( as long as ce sensor) lower cutoff frequency at 0.01 Hz can NOT be used as long as static load measurement Good in high frequency High resolution Limited operating temperature (can not be used as long as high temperature applications) Compact size, light Courtesy of PCB Piezotronics
Displacement Sensing LVDT (Linear Variable Differential Trans as long as mer): Inductance-based ctromechanical sensor Infinite resolution limited by external electronics Limited frequency b in addition to width (250 Hz typical as long as DC-LVDT, 500 Hz as long as AC-LVDT) No contact between the moving core in addition to coil structure no friction, no wear, very long operating lifetime Accuracy limited mostly by linearity 0.1%-1% typical Models with strokes from mms to 1 m available Photo courtesy of MSI Displacement Sensing Linear Potentiometer Resolution (infinite), depends on High frequency b in addition to width (> 10 kHz) Fast response speed Velocity (up to 2.5 m/s) Low cost Finite operating life (2 million cycles) due to contact wear Accuracy: +/- 0.01 % – 3 % FSO Operating temperature: -55 ~ 125 C Photo courtesy of Duncan Electronics Displacement Transducer Magnetostrictive Linear Displacement Transducer Exceptional per as long as mance as long as long stroke position measurement up to 3 m Operation is based on accurately measuring the distance from a predetermined point to a magnetic field produced by a movable permanent magnet. Repeatability up to 0.002% of the measurement range. Resolution up to 0.002% of full scale range (FSR) Relatively low frequency b in addition to width (-3dB at 100 Hz) Very expensive Operating temperature: 0 70 C Photo courtesy of Schaevitz
Displacement Sensing Differential Variable Reluctance Transducers Relatively short stroke High resolution Non-contact between the measured object in addition to sensor Courtesy of Microstrain, Inc. Velocity Sensing Scanning Laser Vibrometry No physical contact with the test object; facilitate remote, mass-loading-free vibration measurements on targets measuring velocity (translational or angular) automated scanning measurements with fast scanning speed However, very expensive (> $120K) Laser Vibrometry References Structural health monitoring using scanning laser vibrometry, by L. Mallet, Smart Materials & Structures, vol. 13, 2004, pg. 261 the technical note entitled Principle of Vibrometry from Polytec
Shock (high-G) Sensing Shock Pressure Sensor Measurement range up to 69 MPa (10 ksi) High response speed (rise time < 2 sec.) High frequency b in addition to width (resonant frequency up to > 500 kHz) Operating temperature: -70 to 130 C Light (typically weighs ~ 10 g) Shock Accelerometer Measurement range up to +/- 70,000 g Frequency b in addition to width typically from 0.5 30 kHz at -3 dB Operating temperature: -40 to 80 C Light (weighs ~ 5 g) Photo courtesy of PCB Piezotronics Angular Motion Sensing (Tilt Meter) Inertial Gyroscope (e.g., http://www.xbow.com) used to measure angular rates in addition to X, Y, in addition to Z acceleration. Tilt Sensor/Inclinometer (e.g., http://www.microstrain.com) Tilt sensors in addition to inclinometers generate an artificial horizon in addition to measure angular tilt with respect to this horizon. Rotary Position Sensor (e.g., http://www.msiusa.com) includes potentiometers in addition to a variety of magnetic in addition to capacitive technologies. Sensors are designed as long as angular displacement less than one turn or as long as multi-turn displacement. Photo courtesy of MSI in addition to Crossbow MEMS Technology What is MEMS Acronym as long as Microelectromechanical Systems MEMS is the name given to the practice of making in addition to combining miniaturized mechanical in addition to electrical components. K. Gabriel, SciAm, Sept 1995. Synonym to: Micromachines (in Japan) Microsystems technology (in Europe) Leverage on existing IC-based fabrication techniques (but now extend to other non IC techniques) Potential as long as low cost through batch fabrication Thous in addition to s of MEMS devices (scale from ~ 0.2 m to 1 mm) could be made simultaneously on a single silicon wafer
Sensing System Reference Zhang, R. in addition to Aktan, E., Design consideration as long as sensing systems to ensure data quality, Sensing issues in Civil Structural Health Monitoring, Eded by Ansari, F., Springer, 2005, P281-290
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