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Prepared by: Brad Neumann Dept. of Electrical and Computer Engineering Utah State University

ECE5320 Mechatronics Assignment #1 : Literature Survey on Sensors and Actuators Topic: Piezo -resistive Accelerometer Sensor. Prepared by: Brad Neumann Dept. of Electrical and Computer Engineering Utah State University

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Prepared by: Brad Neumann Dept. of Electrical and Computer Engineering Utah State University

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  1. ECE5320 MechatronicsAssignment #1: Literature Survey on Sensors and Actuators Topic: Piezo-resistive Accelerometer Sensor Prepared by: Brad Neumann Dept. of Electrical and Computer Engineering Utah State University E: b.neumann@aggiemail.usu.edu; T: (435) 890-0038; F: (435)797-3054 (ECE Dept.) 3/7/2008

  2. Outline • Reference list • To explore further • Major applications • Basic working principle illustrated • A typical sample configuration in application • Major specifications • Mounting and Response relations • Pricing • Other Considerations • Limitations ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  3. Reference list • http://search.digikey.com/scripts/DkSearch/dksus.dll • http://content.honeywell.com/sensing/sensotec/accelerometer_faq.asp?category=All • http://en.wikipedia.org/wiki/Accelerometer • http://commons.wikimedia.org/wiki/File:Delta_IV_Medium_Rocket_DSCS.jpg • http://i.cmpnet.com/planetanalog/2009/10/C0454-Figure5.gif ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  4. References Cont’d • “CMOS compatible bulk micromachined silicon piezoresistive accelerometer with low off-axis sensitivity” by S. Kal, S. Das, D.K. Maurya, K. Biswas, A. Ravi Sankar and S.K. Lahirihttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V44-4H6GPX0-1&_user=464852&_coverDate=01/31/2006&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1239826270&_rerunOrigin=google&_acct=C000022310&_version=1&_urlVersion=0&_userid=464852&md5=d090a512e014211e71789d7038e3cde7 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  5. References Cont’d • “A High-Performance Planar Piezoresistive Accelerometer” by Aaron Partridge, Student Member, IEEE, J. Kurth Reynolds, Benjamin W. Chui, Eugene M. Chow, Alissa M. Fitzgerald, Lian Zhang, Nadim I. Maluf, Member, IEEE, and Thomas W. Kennyhttp://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=825778 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  6. To explore further (Survival pointers of web references) • http://en.wikipedia.org/wiki/Accelerometer • http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1966355&k=accelerometer • “A High-Performance Planar Piezoresistive Accelerometer” by Aaron Partridge, J. Kurth Reynolds, Benjamin W. Chui, Eugene M. Chow, Alissa M. Fitzgerald, Lian Zhang, Nadim I. Maluf, and Thomas W. Kennyhttp://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=825778 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  7. Major Applications • Accelerometers can be found anywhere movement needs to be measured. • Examples include: • Package monitoring for safe delivery • Direction sensing for electronic handheld devices and modern video game controllers • Apogee detection for rockets • Stability feedback for UAV airplanes • Vibration sensing for earthquake proof testing of buildings ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  8. More Applications • Monitoring health of industrial machinery • Testing acceleration specifications on a new vehicle • Some laptops have accelerometers that detect a fall and lock the hard drive heads before impact. • Airbag deployment systems also rely on accelerometers to detect an impact ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  9. Basic Working Principle • An inertial mass is suspended in a chamber connected to a material very sensitive to strain. • In a piezo-resistive accelerometer, displacements are reflected by a change in the materials resistance ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  10. Working Principle Cont’d • Piezo-resistive accelerometers are very similar to piezo-electric accelerometers with the only difference being the voltage-inducing crystal is replaced with a piezo-resistive substrate. • This substrate is integrated into a whetstone bridge that can detect the changes in the resistance of the substrate when it is subject to an acceleration. • The greatest benefit over the crystals is that it can measure accelerations down to zero Hertz. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  11. Typical Configuration • The whetstone bridge would be integrated into circuitry to amplify the signal • Unless the application is radioactive in nature or high temperature, this circuitry can be part of the accelerometer itself. • The signal can be amplified using a power source and corresponding circuitry. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  12. Material and Dimensions • Material used in piezo-resistive accelerometers is most commonly etched silicon • The silicon can be “bulk micro-machined” using a hydroxide-based anisotropic etchant • These parts can be as small as 20 microns wide and 2 microns thick. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  13. Types of Configuration • Accelerometers can be one, two or three dimensional • Accelerometers can have up to 6 axes. • Can have two or three output wires • Can be magnetically mounted, adhesively mounted, or mounted using a set screw (Set screws provide the maximum working range, increasing the natural frequency to its maximum) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  14. Multi-Dimensional Construction • Using deep reactive ion etching, inertial masses are created in a way to self contain themselves and ensures an in-plane mode of sensing. These can be stacked together to form multidimensional accelerometers in the same substrate ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  15. Major Specifications • Acceleration range (measured in G’s typically) • Axes that the accelerometer can measure • Voltage rating • Sensitivity (measured in mV/g) • Analog or Digital output (Sample rate if digital) • Bandwidth • Type of mount • Coefficients for sensitivity and drift due to temperature ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  16. Type of mounts • Set screw/stud is the most efficient method of mounting Frequency Response ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  17. Frequency Response • The portion of the frequency response that is linearly constant is the usable range, usually to the point of deviation of 5% or +/- 3 dB. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  18. Natural Frequency • The higher the natural frequency the bigger the frequency range that can be used with easily interpreted results. Frequencies required to be measured must fall below this frequency ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  19. Pricing • Keep in mind what you pay is what you get: the more money you pay in general will yield a more robust, yet sensitive accelerometer. • Common accelerometers can be in the price range of $2 to $5 dollars • Extremely sensitive accelerometers can easily be hundreds of dollars • There are a number of stores with online catalogs to find just the accelerometer you need. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  20. Things to Consider • Noise will be reduced in the output signal if all the components share the same ground • Further signal conditioning may also be necessary • Accelerometers have a cross axis sensitivity ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

  21. Limitations • Temperature dependence affects sensitivity • Significant temperature changes can cause a drift in the output of the accelerometer • An increase in temperature causes a decrease in voltage at constant acceleration with a larger effect at higher accelerations • Piezo-resistive accelerometers can’t handle very high frequencies. They have a high risk of breaking due to fatigue failure. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

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