NSF Award
2235789
A serious shortcoming of conventional antennas is that their efficiencies plummet when they are made much smaller than the wavelength of the electromagnetic radiation they transmit. This is an impediment to building ultra-small antennas that can be medically implanted in a patient or embedded in a stealth device for defense or crime-fighting. This roadblock has been recently overcome by a novel genre of antennas implemented with magnetostrictive nanomagnets built on a piezoelectric substrate. A periodic electric field applied to the substrate periodically strains the nanomagnets, which makes their magnetizations oscillate in time and emit electromagnetic waves. The phenomenon that underlies this effect is phonon-magnon-photon coupling. The efficiencies of these novel antennas were found to exceed the theoretical limits on the efficiencies of traditional antennas by more than 100,000 times. The present research will introduce an additional feature by coupling electric charge oscillations (called plasmons) into the antennas by modifying their structure, which can significantly improve the antenna performance. Moreover, by manipulating the direction of the periodic electric field applied to the substrate, the direction of the strain wave propagating in the substrate can be changed, which may allow capability to steer the radiated electromagnetic beam in space, thereby implementing an active electronically scanned antenna (AESA). These antennas will have the potential to open up many new embedded applications, e.g., medically implanted devices that communicate with external monitors while consuming miniscule amounts of energy, ultra-small stealthy listening devices, personal communicators and wearable electronics. Apart from the fundamental knowledge and technological impact the proposed research will benefit society by producing graduate and undergraduate students trained in nanofabrication, characterization and measurement, as well as in device simulation and design. Particular attention will be paid to entrepreneurship opportunities, increasing K-12 and minority participation through various programs, and educating public through popular lectures and internet blogs.<br/><br/>Recently it has been demonstrated in the PI’s group that periodic arrays of magnetostrictive nanomagnets deposited on a piezoelectric substrate (a two-dimensional artificial multiferroic crystal), can generate a novel genre of spintronic electromagnetic nano-antennas whose gain and radiation efficiency exceed by several orders of magnitude reaching theoretical limits as compared to traditional (electromagnetically actuated) antennas of the same dimensions. A low frequency (~100 MHZ) surface acoustic wave (SAW) launched into the substrate excites magnetization precession in the nanomagnets via the Villari effect and the precessing magnetization radiates electromagnetic waves in the surrounding medium at the SAW frequency, thereby resulting a novel antenna A high frequency (~10 GHz) SAW, on the other hand, resonantly excites confined spin wave modes in the nanomagnet via phonon-magnon coupling and these spin waves then radiate electromagnetic waves (photons) into the surrounding medium via magnon-photon coupling at the same frequency as the SAW. This constituted tripartite phonon-magnon-photon coupling. The proposed research will extend the concept by introducing surface plasmons into the mode mixing to study four-way phonon-plasmon-magnon-photon coupling which is expected to enhance the mode conversion efficiency from phonons to plasmons to magnons to photons, thereby enhancing antenna properties. Additionally, it has been observed that the antenna radiation pattern changes if the direction of SAW propagation changes with respect to the easy axes of the nanomagnets. The goal of this project is to exploit this feature to electronically steer the radiated beam by changing the direction of SAW propagation in an effort to implement an active electronically scanned antenna (AESA).<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
