Capacitive Transducer.pdf

GENEREAL DETAILS ON Capacitive Transducer-MUKESH SUNDARARAJAN

1. CAPACITIVE TRANSDUCER
MUKESHSUNDARARAJAN


2. Introduction
“Capacitivetypemeansusingcapacitanceand
transducermeansadevicethatconverts
variationsinaphysicalquantity,intoanelectrical
signal”
▪Moreover,thecapacitivetransduceror
sensorisnothingbutthecapacitorwith
variablecapacitance

3. Workingprinciple
Thecapacitivetransducercomprisesoftwoparallelmetalplatesthatare
separatedbythematerialsuchasair,whichiscalledasthedielectric
material.Inthetypicalcapacitorthedistancebetweenthetwoplatesis
fixed,butinvariablecapacitancetransducersthedistancebetweenthe
twoplatesisvariable.

4. The capacitanceCbetweenthetwoplatesofcapacitivetransducers is
givenby:
Where,
C-The variablecapacitancetransducer
ε0-absolute
permittivity εr-
relative
permittivity
The product of ε0 & εr is also called as the dielectric
constant of the capacitivetransducer.
A-areaoftheplates
D-distancebetween theplates
C=(ε0xεrxA)/d

5. ❑ChangingAreaofthePlatesofCapacitiveTransducers
❑ChangingDistancebetweenthePlatesofCapacitive
Transducers
❑ChangingDielectricConstanttypeofCapacitive
Transducers
ParametersforCapacitive
Transducers

6. Applicationofcapacitive
transducer
Capacitivetypetransducershaswiderangeofapplicationsin
whichs0meofthemare:
➢InMicrophones
➢InSemiconductorIndustries
➢InDetectingDynamicMotion

7. InMicrophones
Anincreaseofdistancebetweentheparallelplateswill
decreasethe capacitancevaluecorrespondingly.
This transduceris used to convert the value of displacement
orchange in pressureintermsoffrequency.

8. •Asshowninthefigure,Acapacitivetransducerhasa
staticplateandadeflectedflexiblediaphragmwitha
dielectricinbetween.Whenaforceisexertedtothe
outersideofthediaphragmthedistancebetweenthe
diaphragmandthestaticplatechanges.Thisproducesa
capacitancewhichismeasuredusinganalternating
currentbridgeoratankcircuit.
•Atankcircuitismorepreferredbecauseitproduces
achangeinfrequencyaccordingtothechangein
capacitance.Thisvalueoffrequencywillbe
correspondingtothedisplacementorforcegivento
theinput.

9. Capacitivesensorsareusedfortheprecise
positioningofsemiconductordowntonanometer
levelforexposureindifferentelectricaland
electroniccircuits.
Semiconductorindustry

10. Capacitivetransducersareidealforthe
measurementofdynamicsofacontinuously
movingtargetsuchasrotatingspindlesor
vibratingelementlikeindiscdrivespindles.
DetectingDynamicMotion

11. ▪Liquidlevelmeasurementbychangingthe
capacitancebetweentwoconductiveplates.
▪Capacitorsarecommonforcesensors.
▪CommonlyusedforThicknessmeasurementina
noncontactfashion.

12. Advantages
➢Highsensitivity
➢Can detectupto10^-14mdisplacements
➢Lowpowerrequirement
➢Highresolution
➢Lowcost
➢EasytointegrateintoICs

13. Disadvantages
➢Performanceisseverelyeffectedbydirtand
othercontaminants.
➢Themetallicpartmustbeinsulatedfrom
eachother.
➢Affectedbytemperatureandhumidity
➢Sensitivitytonoise
➢Difficultiesin designing
➢Non-linearity