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A Brief Study on Piezo Actuators and their Feasibility as a Tactile Communication Device

A Brief Study on Piezo Actuators and their Feasibility as a Tactile Communication Device. Abhishek K. Agarwal Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Beckman Institute for Advanced Science and Technology BioMEMS Group 27 April 2000.

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A Brief Study on Piezo Actuators and their Feasibility as a Tactile Communication Device

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  1. A Brief Study on Piezo Actuatorsand their Feasibility as aTactile Communication Device Abhishek K. Agarwal Department of Electrical and Computer Engineering University of Illinois at Urbana-Champaign Beckman Institute for Advanced Science and Technology BioMEMS Group 27 April 2000

  2. Introduction MEMS Technology Potential use of oral tactile communication devices Piezoelectric Materials Background Utilization in project Experimental setup Driving Piezo film Mouthpiece fabrication Testing Results Concerns Closing Remarks DISCUSSION

  3. INTRODUCTION • MEMS Technology • Recent surge • Versatile field with enormous applications • Ink-jet printers • Accelerometers • CMOS / MEMS Integration • Mirror alignment • Microengines

  4. Potential as an oral tactile communication device Advances in nano-fabrication processes Strong motivation New research New mode of communication Auditory and visual External vibrotactile devices Large and consume much power Desire to investigate possibility of mouth-based interface Mouth is one of most sensitive parts of body Military applications Device for disabled INTRODUCTION…

  5. Why tactile? Auditory / visual aids already available Help reduce sensory overload Keep individual’s visual/auditory and hands free Military scenarios Less susceptible to disorientation Directly channeled mode Tactile devices Electrotactile Direct stimulation of nerve/receptor Vibrotactile Electromagnetic transducers Piezoelectric materials (ceramics and PVDF) INTRODUCTION…

  6. Jacques & Pierre Curie Discover Piezoelectric phenomenon in 1880 Mechanical stress induces electric field Lippmann (theoretically) derives converse in 1881 Curies (experimentally) confirm existence thereafter Material is Piezoelectric… If mechanical stress induces an internal dielectric displacement, thereby creating an external surface charge If imposed external surface charge/electric field induces a mechanical stress (the converse) PIEZOELECTRIC MATERIALS

  7. PIEZOELECTRIC MATERIALS… • Why does the phenomena exist? • Some atomic lattice structures have as an essential unit (or “cell”) a cubic or rhomboid cage made of atoms. This cage holds a single semi-mobile ion which has several stable quantum position states inside cell. The ion's post-ion state can be caused to shift by either deforming cage (applied strain) or by applying an E-field. The coupling between the central ion and the cage provides the basis for transformation of mechanical strain to internal E-field shifts, and vice versa.

  8. Mechanical Stress Pressure on electrically neutral crystals polarizes them by slightly separating center of positive charge from that of negative charge Results in development of measurable E-field Electrical Stress Alternating electric fields produce alternating mechanical vibrations of same frequency Cantilever Motion PIEZOELECTRIC MATERIALS…

  9. Project Specifications Stainless steel bending shim Exhibits Cantilever motion 0.7”  0.04”  0.02” Parallel poled Actuator with voltage applied across each ceramic layer individually (3 layer device) How to access device? Make contacts as shown below Center shim must be accessed for deflection PIEZOELECTRIC MATERIALS…

  10. Driving circuit Pulsed voltage needed to actuate bender Methods Design DC power source from 15V source and use amplifier circuit to create pulsed voltage Simple amplifier circuit and DC power source PSpice Simulations done before design of physical circuit below EXPERIMENTAL SETUP

  11. EXPERIMENTAL SETUP… • How to obtain maximum deflection… • Characterization of Actuator • Variables considered • Input DC voltage (100-300 V) • Input current from DC power supply (0-4 mA) • Input frequency from HP Func. Gen. (1-150 Hz)

  12. EXPERIMENTAL SETUP… Deflection High Medium Low Current (mA) Low High Medium Deflection High Medium Low DC Voltage (Volts) Low High Medium Deflection High Medium Low Frequency (Hz) Low High Medium

  13. Concerns Electrical hazard Insulator Properties Easily applicable (uniform coating) Biologically safe (non-toxic) Minimal deterrence of deflection No alteration of physical properties of Piezo strip Not prone to breakdown from mouth environment Most important – high dielectric properties Possible Solutions? ResTech Biwax 9700 Polyimide 2611 Shrink tubing Electrical tape EXPERIMENTAL SETUP…

  14. Coatings Non-uniform coatings Tedious application procedures Medium durability Other solutions Shrink tubing and electrical tape hindered deflection Final Answer 3M Adhesive tape Only 7-8 mils thick Excellent dielectric properties EXPERIMENTAL SETUP…

  15. Device to hold Piezo strip inside mouth Retainer-like device Requirements Small and very versatile to allow full movement Provides linear and rotational motion in mouth for easy placement Does not promote electrical hazard Comfortable for user Possibilities Sport mouthguard Various dental impression compounds Kerr Impression (Type I) Cuttersil Putty Plus (Silicone Impression) SuperGel (Alginate Impression Powder) MOUTHPIECE FABRICATION

  16. MOUTHPIECE FABRICATION… • Physical design • PVC material • Extreme versatility considered • Two-part concept • Mouthpiece / Track • Piezo strip holder

  17. MOUTHPIECE FABRICATION…

  18. TESTING INSIDE MOUTH • First – Safety concerns • Shock hazards • 3M Adhesive tape • Resistors to limit current • Non-conductive epoxy at solder joints • Shrink tubing around wires • Discussion with co-workers

  19. TESTING INSIDE MOUTH… • Results • None (at the moment) – a few more checks needed of entire setup before beginning any testing • Methods • Tangential sweep across surface of mouth • Less stimulation/force required • Tapping force (perpendicular to mouth surface)

  20. Map upper-roof of mouth Obtain sensitivity data Determine difference between tangential and perpendicular contact More versatile mouthpiece Fit Piezo strips into a “sheath” that will conform to roof of mouth Other interests Extension to a two-way communication device Fabrication of piezoceramic devices in polyimide base Wireless system Possibility of creating required power? Circuitry inside mouth? FUTURE WORK

  21. Piezoelectric phenomena Multitude of applications Feasibility of use as an oral tactile communication device? Possible – device is simple and easy to feel Major complication Large power needed for deflection Many opportunities for further study CLOSING REMARKS

  22. ACKNOWLEDGEMENTS • BioMEMS Group • Professor David Beebe • Hui Tang • Beckman / ECE Machine Shop

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