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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
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

d iscussion
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
i ntroduction
INTRODUCTION
  • MEMS Technology
    • Recent surge
    • Versatile field with enormous applications
      • Ink-jet printers
      • Accelerometers
      • CMOS / MEMS Integration
        • Mirror alignment
        • Microengines
i ntroduction1
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…
i ntroduction2
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…
p iezoelectric m aterials
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
p iezoelectric m aterials1
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.
p iezoelectric m aterials2
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…
p iezoelectric m aterials3
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…
e xperimental s etup
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
e xperimental s etup1
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)
e xperimental s etup2
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

e xperimental s etup3
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…
e xperimental s etup4
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…
m outhpiece f abrication
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
m outhpiece f abrication1
MOUTHPIECE FABRICATION…
  • Physical design
    • PVC material
    • Extreme versatility considered
  • Two-part concept
    • Mouthpiece / Track
    • Piezo strip holder
t esting i nside m outh
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
t esting i nside m outh1
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)
f uture w ork
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
c losing r emarks
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
a cknowledgements
ACKNOWLEDGEMENTS
  • BioMEMS Group
    • Professor David Beebe
    • Hui Tang
  • Beckman / ECE Machine Shop