Researchers at MIT have created a reconfigurable antenna that adjusts its frequency spectrum by altering its physical configuration, thus providing greater adaptability for communication and sensing compared to conventional, static antennas.
A user has the capability to stretch, bend, or compress the antenna to effect reversible modifications to its radiation characteristics, allowing a device to function across a broader frequency spectrum without the complexity of intricate moving components. With an adaptable frequency range, such an antenna could respond to varying environmental conditions and diminish the necessity for multiple antennas.
The term “antenna” may evoke images of metallic rods resembling the “bunny ears” found on vintage television sets, yet the MIT team worked with metamaterials—engineered materials whose mechanical attributes, like stiffness and strength, are influenced by the geometric configuration of the material’s constituents.
This results in a streamlined design for a reconfigurable antenna suitable for uses such as energy transfer in wearable technology, motion tracking and sensing in augmented reality, or wireless communication across a variety of network protocols.
Additionally, the researchers have created an editing tool that allows users to design customized metamaterial antennas, which can be manufactured using a laser cutter.
“Typically, when we consider antennas, we think of them as fixed — they are designed to possess specific characteristics and that is their limit. However, by utilizing auxetic metamaterials capable of transforming into three different geometric configurations, we can effectively modulate the antenna’s characteristics by altering its shape without needing to create a new device. Furthermore, we can use adjustments in the antenna’s radio frequency characteristics, resulting from changes in metamaterial geometry, as an innovative sensing technique for interactive design,” explains lead author Marwa AlAlawi, a graduate student in mechanical engineering at MIT.
Her co-authors include Regina Zheng and Katherine Yan, both undergraduate students at MIT; Ticha Sethapakdi, a graduate student in electrical engineering and computer science; Soo Yeon Ahn from the Gwangju Institute of Science and Technology in Korea; and co-senior authors Junyi Zhu, an assistant professor at the University of Michigan; and Stefanie Mueller, the TIBCO Career Development Associate Professor within MIT’s departments of Electrical Engineering, Computer Science, Mechanical Engineering, and leader of the Human-Computer Interaction Group at the Computer Science and Artificial Intelligence Lab. The findings will be showcased at the ACM Symposium on User Interface Software and Technology.
Understanding Antennas
While traditional antennas transmit and receive radio frequency signals, this study investigated the potential for these devices to function as sensors. The research team aimed to engineer a mechanical component that could double as an antenna for sensing applications.
To achieve this, they utilized the antenna’s “resonance frequency,” which is the frequency threshold at which the antenna operates most effectively.
An antenna’s resonance frequency will adjust as its shape changes. (Imagine extending the left “bunny ear” to reduce television static.) Researchers can monitor these adjustments for sensing purposes. For example, a reconfigurable antenna might be employed to detect expansion in a person’s chest, thereby tracking their breathing.
To create a versatile reconfigurable antenna, the researchers turned to metamaterials. These engineered substances, capable of being programmed to assume different forms, consist of a periodic arrangement of unit components that can be rotated, compressed, stretched, or deformed.
By manipulating the metamaterial configuration, one can alter the antenna’s resonance frequency.
“In order to induce modifications in resonance frequency, we must either adjust the antenna’s effective length or incorporate slits and holes within it. Metamaterials enable us to achieve these varied states using a single structure,” AlAlawi says.
The device, referred to as the meta-antenna, comprises a dielectric layer of material sandwiched between two conductive layers.
To create a meta-antenna, the researchers cut the dielectric layer from a rubber sheet using a laser cutter. Subsequently, they applied a conductive spray paint to create a resonating “patch antenna” on the dielectric layer.
However, they discovered that even the most flexible conductive materials struggled to endure the extent of deformation expected from the antenna.
“We underwent extensive trial and error to ascertain that coating the structure with flexible acrylic paint safeguards the hinges from premature failure,” AlAlawi elaborates.
A Tool for Makers
With the fabrication challenge addressed, the researchers developed a tool enabling users to design and create metamaterial antennas tailored to specific needs.
Users can specify the antenna patch dimensions, select a thickness for the dielectric layer, and set the length-to-width ratio of the metamaterial unit cells. Subsequently, the system automatically simulates the antenna’s resonance frequency range.
“The beauty of metamaterials lies in their interconnected system of linkages, where the geometric design allows us to simplify the mechanical system’s complexity,” AlAlawi notes.
Utilizing the design tool, the researchers embedded meta-antennas within various smart devices, including a curtain that automatically adjusts household lighting and headphones that transition seamlessly between noise-cancelling and transparent modes.
For the smart headphone, for example, as the meta-antenna expands and bends, it alters the resonance frequency by 2.6 percent, prompting a switch in the headphone’s mode. The team’s tests also revealed that meta-antenna structures can endure over 10,000 compressions without degradation.
Given that the antenna patch can be patterned on any surface, it allows for integration with more complex configurations. For instance, the antenna could be woven into smart textiles designed for noninvasive biomedical sensing or temperature monitoring.
In future work, the researchers aspire to craft three-dimensional meta-antennas for a broader array of applications. They also aim to enhance the functionality of the design tool, improve the durability and flexibility of the metamaterial, explore various symmetric metamaterial configurations, and optimize some manual fabrication procedures.