Download - ULTRASONIC SENSORS
ULTRASONIC SENSORSSemih ÖztürkMechatronicsInstructor: Associate Prof. İsmail Lazoğlu26/05/2011
OUTLINEUltrasonic SensorsCharacteristics ControlSample SchematicApplications Conclusion
Ultrasonic SensorsUltrasonic Sensors generate high
frequency sound waves.Elavulate the echoTime interval between sending
the signal andreciving is calculated to determine the distance to an object.
WORKING PRINCIPLETransducer: device that converts
energy into ultrasound.Dog wistle: mechanical energy ->
ultrasonic sound waves in the form of air pressure.
Used in the training of dogs and cats 16 – 22 kHz
Piezoelectric TransducersElectrical energy Sound Piezoelectric crystals: change
size with voltageOscillation with applied AC
(above 20kHz)
Scheme
Paralax Ping)))
Paralax Ping)))
Characteristics of Ultrasound Inaudible to humans
◦ Sound pressure over 100dB = jet engineHigh directivity
◦ Due high frequency low energy level (kindey stone)
Compressional vibration of matter◦ Can be used to examine the characteristic of the
matter (organ in a body)Low propagation speed
◦ 340m/s in the air. ◦ Low speed signal processing.
Directivity Size and shape of the vibrating surface
• Frequency at which the trancducer vibrates.
• Narrower directivity • Higher frequency• Large size
In electromagnetics, directivity is a figure of merit for an antenna. It measures the power density the antenna radiates in the direction of its strongest emission, versus the power density radiated by an ideal isotropic radiator (which emits uniformly in all directions) radiating the same total power.
Directivity
Difference in detection distance with varying frequency
Prevent False ReadingsTemperature
◦T ̴ ◦0.6 m/sec change for 1 degree Celsius
Reflection◦Echo ◦Liquids or solids with large and hard particles
◦Angle of reflection = Angle of incidence
Echo
a) is more than 3 meters awayb) that has its reflective surface at a shallow angle so that sound
will not be reflected back towards the sensorc) is too small to reflect enough sound back to the sensor.
Prevent False ReadingsPropagation
◦Dispersion loss of intensity◦Intensity of sound decreases with
Absorption◦Fluff and loose dirt◦In substance in which it travels ( 1-3
dB decrease for 1 m of dry and dust free air)
ApplicationsDistance Measurement
Sensors with an on or off digital output are available for detecting the presence of objects
Sensors with an analog output which varies proportionally to the sensor to target separation distance
Ultrasonic Testing Finding flaws in materials (nondestructive
testing
ApplicationsUltrasound (In Medicine)
References http://www.parallax.com/Store/
Sensors/ObjectDetection/tabid/176/CategoryID/51/List/0/SortField/0/Level/a/ProductID/92/Default.aspx
Munenori Hikita. Murata's European products
Ultrasonic sensor. In Wikipedia, The Free Encyclopedia. from http://en.wikipedia.org/w/index.php?title=Ultrasonic_sensor&oldid=359643539