Ultrasonic Detection – Basics & Application

Ultrasonic detection is most commonly used in industrial applications to detect hidden tracks, discontinuities in metals, composites, plastics, ceramics, and for water level detection. For this purpose, the laws of physics which are indicating the propagation of sound waves through solid materials have been used since ultrasonic sensors using sound instead of light for detection.

What is the principle of Ultrasonic Detection?

Defining sound wave

Sound is a mechanical wave traveling through the mediums, which may be a solid, or liquid or gas. Sound waves can travel through the mediums with specific velocity depends on the medium of propagation. The sound waves which are having high frequency reflect from boundaries and produce distinctive echo patterns.

Laws of physics for sound waves

Sound waves are having specific frequencies or number of oscillations per second. Humans can detect sounds in a frequency range from about 20Hz to 20 KHz. However, the frequency range normally employed in ultrasonic detection is 100 KHz to 50MHz. The velocity of ultrasound at a particular time and temperature is constant in a medium.

W = C/F (or) W = CT

Where W = Wave length

C = Velocity of sound in a medium

F = Frequency of wave

T=Time Period

The most common methods of ultrasonic examination utilize either longitudinal waves or shear waves. The longitudinal wave is a compression wave in which the particle motion is in the same direction of the propagation wave. The shear wave is a wave motion in which the particle motion is perpendicular to the direction of propagation. Ultrasonic detection introduces high-frequency sound waves into a test object to obtain information about the object without altering or damaging it in any way. Two values are measured in ultrasonic detection.

The amount of time, taking for the sound to travel through the medium and amplitude of the received signal. Based on velocity and time thickness can be calculated.

The thickness of material = Material sound velocity X Time of Fight

Transducers for Wave Propagation and particle detection

For sending sound waves and receiving an echo, ultrasonic sensors, normally called transceivers or transducers will be used. They work on a principle similar to radar that will convert electrical energy into mechanical energy in the form of sound, and vice versa.

The commonly used transducers are contact transducers, angle beam transducers, delay line transducers, immersion transducers, and dual element transducers. Contact transducers are typically used for locating voids and cracks to the outside surface of a part as well as measuring thickness. Angle beam transducers use the principle of reflection and mode conversion to produce refracted shear or longitudinal waves in the test material.

Delay line transducers are single element longitudinal wave transducers used in conjunction with a replaceable delay line. One of the reasons for choosing a delay line transducer is that near-surface resolution can be improved. The delay allows the element to stop vibrating before a return signal from the reflector can be received.

The major advantages offered by immersion transducers over contact transducers are Uniform coupling reduces sensitivity variations, Reduction in scan time, and increases sensitivity to small reflectors.

Operation of ultrasonic sensors:

When an electrical pulse of high voltage is applied to the ultrasonic transducer it vibrates across a specific spectrum of frequencies and generates a burst of sound waves. Whenever any obstacle comes ahead of the ultrasonic sensor the sound waves will reflect back in the form of echo and generates an electric pulse. It calculates the time taken between sending sound waves and receiving the echo. The echo patterns will be compared with the patterns of sound waves to determine the detected signal’s condition.

3 Applications involving Ultrasonic detection:

The distance of obstacle or discontinuities in metals is related to the velocity of sound waves in a medium through which waves are passed and the time taken for echo reception. Hence the ultrasonic detection can be used for finding the distances between particles, for detecting the discontinuities in metals and for indicating the liquid level.

• Ultrasonic Distance Measurement

Ultrasonic sensors are used for distance measuring applications. These gadgets regularly transmit a short burst of ultrasonic sound to a target, which reflects the sound back to the sensor. The system then measures the time for the echo to return to the sensor and computes the distance to the target using the speed of sound within the medium.

Different sorts of transducers are utilized within industrially accessible ultrasonic cleaning devices. An ultrasonic transducer is affixed to a stainless steel pan which is filled with a solvent and a square wave is applied to it, conferring vibration energy on the liquid.

The ultrasonic distance sensors measures distance using sonar; an ultrasonic (well above human hearing) beat is transmitted from the unit and distance-to-target is determined by measuring the time required for the echo return. The output from the ultrasonic sensor is a variable-width beat that compares to the distance to the target.

8 Features of the Ultrasonic Distance Sensor:

1. Supply voltage: 5V (DC).
2. Supply current: 15mA.
3. Modulation frequency: 40Hz.
4. Output: 0 – 5V (Output high when obstacle detected in range).
5. Beam Angle: Max 15 degrees.
6. Distance: 2cm – 400cm.
7. Accuracy: 0.3cm.
8. Communication: Positive TTL pulse.

Operation of Ultrasonic distance Sensor:

The ultrasonic sensor module comprises of one transmitter and one receiver. The transmitter can deliver 40 KHz ultrasonic sound while the maximum receiver is designed to accept only 40 KHz sound waves. The receiver ultrasonic sensor that is kept next to the transmitter shall thus be able to receive reflected 40 KHz, once the module faces any obstacle in front. Thus whenever any obstacles come ahead of the ultrasonic module it calculates the time taken from sending the signals to receiving them since time and distance are related for sound waves passing through air medium at 343.2m/sec. Upon receiving the signal MC program while executed displays the data i.e. the distance measured on an LCD interfaced with the microcontroller in cms.

Characteristically, robotics applications are very popular but you’ll also find this product to be useful in security systems or as an infrared replacement if so desired.

• Ultrasonic transducer for water level detection

Block diagram for contactless liquid level controller

The above circuit diagram shows the contactless liquid level controller in this diagram the ultrasonic sensor module is interfaced with the microcontroller. Whenever level distance measured in cm falls down below a set point the pump starts by sensing the signal coming out and receiving level coming to the ultrasonic transducer which is fed to the microcontroller. When the microcontroller receives the signal from the ultrasonic transducer it activates the relay through a MOSFET that operated the pump ON or OFF.

• Ultrasonic Obstacle Detection

Ultrasonic sensors are used to detect the presence of targets and to measure the distance to targets in many robotized processing plants and process plants. Sensors with an ON or OFF digital output are available for detecting the presence of objects and sensors with an analog output which changes relative to the sensor to target separation distance are commercially available.

Ultrasonic obstacle sensor consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. The point when something moves in the zone secured the circuit’s fine offset is aggravated and the buzzer/alarm is triggered.

Features:

• Power consumption of 20mA
• Pulse in/out communication
• Narrow acceptance angle
• Provides exact, non-contact separation estimations within 2cm to 3m
• The explosion point LED shows estimations in the advancement
• 3-pin header makes it simple to connect utilizing a servo development link

 Specifications:

• Power supply: 5V DC
• Quiescent current: <15mA
• Effectual angle: <15°
• Ranging distance: 2cm – 350 cm
• Resolution: 0.3 cm
• Output cycle: 50ms

 The sensor detects objects by emitting a short ultrasonic burst and then listening for the eco. Under the control of a host microcontroller, the sensor emits a short 40 kHz explosion. This explosion ventures or travels through the air hits an article and after that bounces once again to the sensor.

The sensor provides an output pulse to the host that will terminate when the echo is detected; hence the width of one pulse to the next is taken into the calculation by a program to provide results in a distance of the object.

Now you have understood the applications and basic concept of ultrasonic detection if any queries on this topic or on the electrical and contactless liquid level controller leave the comments section below.