Ultrasonic waves are produced by making use of

Ultrasonic waves are primarily produced using piezoelectric materials through the converse piezoelectric effect. When an alternating electric potential is applied across a piezoelectric crystal, it undergoes rapid mechanical vibrations (macroscopic changes in length), thereby emitting ultrasonic waves into the surrounding medium. These materials, such as PZT or quartz, are highly efficient at converting electrical energy into mechanical energy at frequencies exceeding the human hearing range, often reaching up to 20 MHz. While magnetostriction in ferromagnetic materials can also generate ultrasound, piezoelectric transducers are the industry standard for medical imaging, sonar, and industrial cleaning due to their sensitivity and efficiency at high frequencies [1]. Other materials like pyroelectric or ferrimagnetic substances are not the standard primary sources for ultrasonic wave generation in common technological applications [1].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC4223717/