Datasheet
2
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S15E.pdf
08.10.31
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Characteristics of Ultrasonic Waves
4. Attenuation
3. Effects of Temperature
2. Reflection
1. Wavelength and Radiation
Velocity of wave propagation is expressed by multipli-
cation of frequency and wavelength. The velocity of an
electromagnetic wave is 3×10
8
m/s, but the velocity of
sound wave propagation in air is as slow as about 344m/
s (at 20°C). At these slower velocities, wavelengths are
short, meaning that higher resolution of distance and
In order to detect the presence of an object, ultrasonic
waves are reflected on objects.
Because metal, wood, concrete, glass, rubber and paper,
etc. reflect approximately 100% of ultrasonic waves,
these objects can be easily detected.
Cloth, cotton, wool, etc. are difficult to detect because
they absorb ultrasonic waves. It may often be difficult,
also, to detect objects having large surface undulation,
because of irregular reflection.
direction can be obtained.
Because of the higher resolution, it is possible to get
higher measurement made large accuracy. The sur-
face dimension of the ultrasonic device can be easily to
obtain accurate radi-ation.
Velocity of sound wave propagation “c” is expressed by
the following formula.
c=331.5+0.607t (m/s) where t=temperature (°C)
That is as sound velocity varies according to circumfer-
The strength of ultrasonic waves propagated into the air
attenuate proportionally with distance. This is caused
by diffusion loss on a spherical surface due to diffrac-
tion phenomenon and absorption loss, that energy is
absorbed by medium.
As shown in Fig.1, the higher the frequency of the ultra
-
sonic wave, the bigger the attenuation rate and the
shorter the distance the wave reaches.
Ultrasonic waves are sounds which cannot be heard by
humans and are normally, frequencies of above 20kHz.
The basic characterisitics of ultrasonic waves are
explained below.
ential temperature, it is necessary to verify the temper-
ature at all times to measure the distance to the object
accurately.
-
10
-
20
-
30
-
40
-
50
-
60
0.1 0.5 1.0 5.0 10.0
(t
=
20ϒC)
Distance (m)
Frequency
Attenuation (dB)
20 (kHz)
40 (kHz)
80 (kHz)
200 (kHz)
Fig. 1 Attenuation Characteristics of Sound Pressure by
Distance