A Revolutionary Breakthrough in Antennas
Researchers at the NSF-funded Nanosystems Engineering Research Center (ERC) for Translational Applications of Nanoscale Multiferroic Systems (TANMS), led by the University of California Los Angeles (UCLA), have created a new class of devices called multiferroic antennas and have observed electromagnetic radiations out of those devices for the first time. Due to the drastically different nature of electromagnetic waves and mechanical vibrations—central to this revolutionary breakthrough—the concerted efforts of a multi-disciplined team, including experts in materials science as well as mechanical and electrical engineering, were required to ensure a successful outcome.
Dimensions of the fabricated multiferroic antennas are ~50μm x 50μm x 3μm, and they create electromagnetic radiation at 1.5GHz, near cellphone frequency bands. Classical antennas for this frequency are on the order of ~5 cm (~50,000μm), which means the breakthrough has resulted in antennas potentially orders of magnitude smaller, shifted the art of antenna design into a completely new paradigm, helped create next-generation “electrically small antennas” (antennas with physical dimensions much smaller than electromagnetic wavelengths), and revolutionized the state of the art in wireless communications for a variety of products, including sensors and medical devices.
It is difficult to create an electrically small antenna using conventional approaches. Multiferroic antennas operate on fundamentally different principles than conventional antennas—in this case propagating electromagnetic waves directly from coupling between the field and mechanical vibrations in composite structures, a paradigm that avoids both energy loss associated with conductor resistance as well as an effect that limits radiation bandwidth.
Because the acoustic wavelength is so small compared to the electromagnetic wavelength, a resonating structure can be orders of magnitude smaller, providing antennas that have minimum footprint and can be integrated on-chip, on a conducting body, or on a flexible surface. Antennas have classically remained the last component to be integrated on-chip in a wireless system, but emergence of electrically small multiferroic antennas will change this approach and offer a new generation of wireless miniature electronics previously thought impossible.
Generating electromagnetic waves via mechanical vibrations and radiating them into free space was predicted years ago from theory, but only recently was such a device fabricated and a significant amount of electromagnetic radiation measured. To create a “pathway” for electromagnetic waves to radiate and receive, TANMS researchers hypothesized a novel device structure consisting of a thin layer of magneto-elastic material sandwiched by two thin layers of piezoelectric material (see figure). Mechanical vibrations are generated through the bottom piezoelectric layer by an electrical excitation and transferred to the magnetic layer through acoustic waves that propagate across the layers. The magnetic layer converts these mechanical vibrations to oscillating magnetic dipoles that radiate electromagnetic waves outward.