How are ultrasound waves produced in the transducer?

How are ultrasound waves produced in the transducer?

• A. Taking alternating current strikes the crystal causing it to compress and expand
• B. Passing direct current through the crystal
• C. Heating the crystal to cause emission
• D. Rubbing the crystal surface

Answer: (A)

The ultrasound transducer relies on the piezoelectric effect: a piezoelectric crystal changes shape when an electric field is applied. When an alternating current drives the crystal, the electric field repeatedly reverses, causing the crystal to rapidly expand and contract at the drive frequency. This mechanical vibration sends out longitudinal sound waves into the tissue and, on reception, converts returning echoes back into electrical signals. Using direct current would produce a static deformation with no ongoing vibration, heating the crystal wouldn’t create a controlled ultrasound wave, and rubbing the crystal would generate charges without producing a coherent, driven oscillation. Hence, alternating current is what produces the ultrasound waves.

The ultrasound transducer relies on the piezoelectric effect: a piezoelectric crystal changes shape when an electric field is applied. When an alternating current drives the crystal, the electric field repeatedly reverses, causing the crystal to rapidly expand and contract at the drive frequency. This mechanical vibration sends out longitudinal sound waves into the tissue and, on reception, converts returning echoes back into electrical signals. Using direct current would produce a static deformation with no ongoing vibration, heating the crystal wouldn’t create a controlled ultrasound wave, and rubbing the crystal would generate charges without producing a coherent, driven oscillation. Hence, alternating current is what produces the ultrasound waves.