2010.03.19 9307PIEVOL04E

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8 Piezoelectric Ceramics Vol.04

NEP

b)

VoItage output constant

This is the intensity of the electric field caused when

a specified amount of stress is applied to a material

that is in the condition of zero displacement. Voltage

output constant is calculated with Eq. 16.

This is the temperature at which polarization

disappears and the piezoelectric qualities are lost. It is

also the temperature at which the value of the

dielectric constant becomes maximum.

g

d

Vm N

=⋅

(

)

ε

/

7) Curie temperature

· · · · · · · · · · · · · · · · · · · · · · · · (16)

The temperature coefficient is a measure of the

variation of the resonant frequency and static

capacitance with change in temperature. Temperature

coefficient is calculated with Eqs. 17 and 18.

Where TK(f) : Temperature coefficient of resonant

: Resonant frequency at temperature

TK(C) : Temperature coefficient of static

Δt

)

8) Temperature coefficient

· · · · (17)

· · (18)

The aging rate is an index of the change in resonant

frequency and static capacitance with age. To

calculate this rate, after polarization the electrodes of a

transducer are shorted together, and are heated for a

specified period of time. Measurements are taken of

the resonant frequency and static capacity every 2

n

days. (That is, at 1, 2, 4, and 8 days.) The aging rate

is calculated with Eq. 19.

Where

(AR) : Aging rate for resonant frequency or

static capacitance

polarization

()

log

log

AR

tt

Xt

Xt

Xt

=

−

⋅

−

1

21

2

1

1

The density is calculated with Eq. 20, after

determining the volume and weight of the specified

ceramic material.

Where W : Weight (kg) of ceramic material

D

W

V

kg m

=

(

)

/

3

9) Aging rate

10) Density

· · · · · · · · · · · · (19)

· · · · · · · · · · · · · · · · · · · · · · · · · (20)

TK f

t

ft

ft

f

PPm C

TK C

t

Ct

Ct

C

PPm C

()

()

( )

(/

)

()

()

( )

(/

)

=⋅

−

×°

=⋅

−

×°

1

10

1

10

12

20

12

20

6

6

Δ

Δ