Magnetic Field Induced Ultrasound from Colloidal Superparamagnetic Nanoparticles

Abstract

Generating ultrasound remotely by means of magnetic fields is an important technological development to circumvent the drawbacks of the traditional means of ultrasound generation techniques. In this report, it is demonstrated that ultrasound is generated from colloidal superparamagnetic nanoparticles when exposed to pulsed and alternating magnetic fields. Comparison of the inhomogeneous and homogeneous magnetic fields indicates that both homogeneous and inhomogeneous magnetic fields could be important for efficient ultrasound generation; however, the latter is more important for dilute colloidal dispersion of magnetic nanoparticles. In strong magnetic fields, the ultrasound generated from the colloidal magnetic nanoparticles shows reasonable agreement with the magnetostriction effect commonly observed for bulk ferromagnetic materials. At low magnetic fields, the colloidal magnetic nanoparticle dispersion produces considerable amount of ultrasound when exposed to ac magnetic fields in the 20–5000 kHz frequ...