Magnetoelectric Sensors

Though our understanding of the human brain is continually evolving, electroencephalography (EEG), one of the primary tools used to study neural activity, has remained unchanged for decades. Magnetoencephalography (MEG) is a newer technology that provides useful information, but it requires cryogenic conditions to operate, which limits its utility and affordability. With funding from the W.M. Keck Foundation, Northeastern University’s Nian Sun and colleagues set out to combine the best of EEG and MEG capabilities, by devising nano-sized magnetic sensors to measure neural outputs at room temperature. Indeed, the team proceeded to develop ultra-sensitive magnetoelectric (ME) sensors, which measure reflected output voltage as a function of magnetic field.  They have additionally fabricated the sensors onto neural probes, and begun in vivo testing, which is currently ongoing. These devices provide a new way of measuring neural activity that is not voltage-dependent; with additional development, they may lead to transformative advances in brain research and the diagnosis of brain disorders. 

The W.M. Keck Foundation grant generated an additional, unexpected and very important outcome: Professor Sun further used the sensors as the basis for an entirely new antenna technology.  He optimized the Keck funded sensors to create acoustically actuated ME antennas that are roughly 100 times smaller than most state-of-the-art compact antennas. Antennas typically must be similar in length to the electromagnetic wave they are receiving, which are relatively long.  Using the same principles involved in the neural probe sensors, Sun designed magnetic/piezoelectric materials to convert electromagnetic waves into much shorter acoustic waves, which enabled correspondingly smaller antennas. These new compact designs may revolutionize how we receive and transmit information, with potential applications in bioinjectable and bioimplantable sensing systems; portable wireless communication systems; and military and navigation systems. Efforts are already underway to commercialize this technology for the benefit of health and society.

Fig. 1  a Schematic illustration of the magnetoelectric (ME) thin-film bulk acoustic wave resonators (FBAR) and the antenna measurement setup. The horn antenna and ME FBAR are connected to the S 1 and S 2 port of a network analyzer. b Scanning electron microscopy (SEM) images of the fabricated the ME FBAR. The red and blue areas show the suspended circular plate and AlN anchors. The yellow area presents the electrode. c Return loss curve (S 22) of ME FBAR. The inset shows the out-of-plane displacement of the circular disk at resonance peak position. d Transmission and receiving behavior (S 12 and S 21) of ME FBAR. e Return loss (S 22) curve of the non-magnetic Al/AlN control FBAR. f Transmission and receiving behavior (S 12 and S 21) of the non-magnetic Al/AlN control FBAR

T.X. Nan, et al. Nature Comm. 8, 296 (2017).



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