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PCRT21ASX Datasheet - Page 4

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Piezoelectric Acoustic Generators
Mounting
The various mounting methods for piezoelectric acoustic
elements are discussed below:
Simple Mounting Method
The simplest method is to stick the piezo acoustic element
to the plate using double-sided adhesive tape. However, the
sound pressure will not be optimum.
PIEZOELECTRIC ELEMENT
BAKELITE OR ACRYL RESIN PLATE
figure 5
Circumference Fixing Method
This method is to fix the outside circumference of the
element to the supporting ring of the plate. Considerable sound
pressure can be obtained covering a wide frequency range
around the resonant frequency.
PIEZOELECTRIC ELEMENT
BAKELITE OR ACRYL RESIN PLATE
SUPPORTING
RINGMMMMMMMMMMMMMM
figure 6
Nodal Mounting Method
This method is to fix the nodal diameter of the element to
the supporting ring of the plate. Loud sound pressure can be
obtained at the resonant frequency. The sound pressure will
drastically drop when the frequency is shifted from the
resonant frequency.
SUPPORTING RING
PIEZOELECTRIC ELEMENT
figure 7
The adhesive agent used between the element and the
support ring should be elastic, such as silicon rubber.
Designing the Fixture
Factors affecting the sound pressure of the piezoelectric
acoustic element are as follows:
1) resonance frequency of the element
2) cavity resonance (cavity design of the case/casing
method)
3) resonance of sound body (mass after casing)
Maximum sound pressure level can be achieved at the
point where the 3 factors overlap. Taking the oscillation
frequency fluctuation into consideration, the fixture is designed
so that peak points are slightly overlapping with one another.
Case Design for Circumference Mounting Method
When designing a case for circumference mounting, the
cavity resonant frequency of the case (fo) is determined by the
following formula:
where: V: cavity volume (m
For example, when KBS-35DA-3A (resonant frequency
fr=2.9 0.5 kHz) is mounted in a case where the size is:
D=33.5mm, d=5.5mm,T=2mm, t=1mm, the formula for f
explained as follows:
BAKELITE OR
ACRYL RESIN PLATE
Then, the cavity resonant frequency shall be 2,807 Hz.
C
S
f
(Hz)
S
V t
3
)
D T
V
S: area of open hole
2
(m
)
d
S
t:
Length of open hole
(m)
C: sound velocity
C=344 m/sec
D
d
S
t
T
figure 8
is
0
Cd
f
D
T t
d
figure 9
3

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