Datasheet
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S15E.pdf
08.10.31
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Construction and Operation Principles
2. Enclosed type Ultrasonic Sensor
3. High Frequency Ultrasonic Sensors
Ultrasonic sensors for outdoors use are sealed to protect
them from dew, rain and dust.
Piezoelectric ceramics are attached to the top inside of
the metal case. The entrance of the case is covered with
resin. (See Fig. 4.)
Metal Case
Piezoelectric
Ceramic
Lead Wire
Base
Shielding
Material
Cable
Fig. 4 Construction of Enclosed Type Ultrasonic Sensor
For use in industrial robots, accuracy as precise as 1mm
and acute radiation are required. By flexure vibration
of the conventional vibrator, no practical characteristics
can be obtained in frequencies higher than 70kHz and,
therefore, vertical thickness vibration mode of piezoelec-
tric ceramics is utilized for detection in high frequency.
In this case, the matching of acoustic impedances of the
piezoelectric ceramics and air becomes important.
Acoustic impedance of piezoelectric ceramics is 2.6×
10.7kg/m
2
s, while that of air is 4.3×10.2kg/m
2
s.
This difference of 5 powers causes large loss on the
vibra-tion radiating surface of the piezoelectric ceram-
ics.
Matching the acoustic impedances with air is performed
by bonding a special material to the piezoelectric ceram-
ics as an acoustic matching layer.
This construction enables the ultrasonic sensor to work
in frequencies of up to several hundred kHz.
Ultrasonic Radiation Surface
Acoustic Matching
Layer
Piezoelectric
Ceramics
Metal Case
Base
Shielding
Material
Lead Terminal
Fig. 5 Construction of High Frequency Ultrasonic Sensors