Why ultrasonic frequency more than 3MHz cannot be produced by magnetostriction generator?

Ultrasonic frequencies above 3 MHz cannot effectively be produced by magnetostrictive generators due to the limitations in the magnetostrictive materials and their mechanical properties. At higher frequencies, the energy losses due to internal damping and material imperfections increase, making efficient transduction difficult. Additionally, the physical size and design constraints of the magnetostrictive elements often limit their operational frequency range, resulting in diminished performance beyond this threshold. Consequently, alternative transduction methods, such as piezoelectric transducers, are typically employed for higher frequency applications.