How Do Ultrasonic Transducers Work

How Do Ultrasonic Transducers Work

Date:Aug 19, 2019

Ultrasonic transducers are used in many industrial and medical applications. Read on to know their main parts and how they work.

Transducer

Transducers are special instruments that have the ability to turn one energy type into another. A transducer is a vital component of sonography or ultrasonic imaging. In sonography, the camera is a transducer. When an electric charge is applied to the camera, the camera converts this energy into vibrations. This is known as piezoelectric effect. The vibrations are in the form of sound waves. The camera is made of various components. Each of these components plays a role in the production of sound waves, transmission of these sound waves into the body, and reception of echoes from the body.

Piezoelectric Crystals

The camera’s main components are piezoelectric crystals. The crystals in an ultrasonic transducer are usually synthetic crystals made of PZT (lead zirconate titanate). The crystals produce vibrations when voltage is applied to them. The vibration frequency depends on the amount of voltage applied to the crystals and the sound waves’ frequency depends on the vibration frequency.

Focus

The crystal used in an ultrasonic transducer has a shape that is similar to a circular lens. A sound beam is projected from the crystal. At first, the diameter of the sound beam is same as that of the crystal. When the beam’s diameter reduces to half of its original diameter, the focus is reached. The diameter increases again after the focus. To be able to generate an image that is two dimensional, an ultrasonic transducer utilizes lots of piezoelectric crystals.

Settings

It is important to adjust the settings on an ultrasound machine.That is because the beam’s natural focus is not enough to get an accurate image of particular parts. The required focus depends on the distance between the transducer and the part. To improve focusing, instruments such as mirrors and lenses are utilized. The sonographer adjusts the settings on the ultrasonic machine to control electronic focusing. When the focus is changed, the ultrasonic transducer applies voltage at varying times to different crystals. This is how the beam’s focus is changed.

Acoustic Impedance

Acoustic impedance is caused by the sound wave’s velocity and the material’s density. The sound wave’s velocity depends on the type of material it passes through. It is hard to have a sonogram reading when materials do not have the same acoustic impedance. That is because the sound will be reflected back to the instrument. The amounts of sound that will be reflected and will be transmitted through the body depend on the difference in the materials’ acoustic impedances. Air and crystal have very different acoustic impedances. Therefore, no ultrasound will be transmitted beyond the ultrasonic transducer’s surface.

Matching Layer

Matching layers are used to make the acoustic impedance between the body and the piezoelectric crystal as little as possible. A couple of these layers are put in the middle of the transducer and the crystal. The acoustic impedances of the first layer and the crystal are almost the same. The last layer’s acoustic impedance is almost the same as the skin’s acoustic impedance. More sound is transmitted into the body because of this strategy.

Ultrasonic Gel

Air is not a good conductor of sound. And so, ultrasonic gel is used to eliminate the air between the skin and the transducer. The gel is put on the skin. With the help of ultrasonic gel, the sound waves are easily transmitted into the body.

Ultrasonic Imaging

An ultrasonic image is produced with the help of ultrasonic transducers and ultrasonic sound waves. When the sound waves hit tissues, they get reflected off. This is called echoing. The sound waves go back to where they came from. They pass through the gel, layers, and crystal again. Once the waves reach the crystal, they are converted into electro potential energy (voltage). The electro potential energy is then processed and converted into an ultrasonic image by the other components of the ultrasonic machine.


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