Extremely long signal delays from magnetic particles

Magnetic particles generate sonic waves when they are exposed to an AC magnetic field. We call this phenomenon sonic wave emission by simulated magnetic nanoparticles (SWESMAN). We found an extremely long signal delay between the SWESMAN signal and the excitation current: it took 2.9 ms for a sonic wave to propagate 10 mm in a polyacrylamide gel, which is approximately 500 times longer than that expected. X–Y mapping of the signal delays was performed and a linear relationship between the signal delay and the propagation distance was found. Thus, the three-dimensional position can be determined from these signal delays. This study represents the first step toward using SWESMAN in practical applications. The extremely long signal delay has the potential to give a high spatial resolution in such applications.

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► This paper describes the phenomenon by which magnetic nanoparticles emit sonic waves when they are exposed to an AC magnetic field.
► Prior to our studies, there had been no reports of magnetic particles exposed to an AC magnetic field generating acoustic waves. Currently, only our group is studying this phenomenon.
► We found that the position of magnetic particles could be determined utilizing this phenomenon. In this paper, we show that it should be possible to realize magnetic particle imaging by utilizing this phenomenon.