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