Advancements in wireless technology and miniaturized circuits have transformed how we live and connect. However, as we move toward higher-frequency communication, engineers face challenges from multipath propagation, where a radio signal takes multiple paths to reach an antenna, often with delays and distortion. This can cause issues like TV ghosting and signal fading in wireless networks.
Multipath interference is challenging to fix because:
- These signals share the same frequency as the primary signal, making traditional filtering ineffective.
- Their angles of arrival vary unpredictably, making passive solutions difficult.
Conventional materials can’t adjust for changing signal angles, and filters need active power to work dynamically. Solving these challenges is key to making wireless communication more reliable in an increasingly connected world.
A research team led by Associate Professor Hiroki Wakatsuchi from the Nagoya Institute of Technology in Japan has developed a new filtering system to address signal interference challenges.
Selecting the best communication channel over a wireless network
The team designed a passive metasurface-based shield that selectively transmits only the first incoming wave while blocking delayed signals from different angles without active controls. The system uses metasurface panels with built-in MOSFETs (metal-oxide-semiconductor field-effect transistors) to create a time-varying response.
Each unit cell on the panel contains a MOSFET switch that opens or closes in response to voltage changes. When the first signal arrives, the metasurface maintains resonance to let it through while adjusting circuit configurations to block later signals from different angles.
This breakthrough could significantly enhance wireless communication by reducing interference without requiring additional power.
Researchers tested their passive metasurface filtering system using simulations and experiments. The system uses a hexagonal prism structure containing two interlinked metasurface unit cells. Signals from different transmitters hit adjacent sides of the prism with a time delay, mimicking real-world multipath interference.
In their experiments, the team boosted the first incoming signal by 10 dB while successfully blocking delayed signals, regardless of direction. This marks the first passive filtering system to overcome the challenges of same-frequency interference and unpredictable signal angles.
“This mechanism is completely different from existing designs,” says Professor Wakatsuchi. Unlike traditional methods, it does not require complex calculations or modulation circuits, making it ideal for low-cost applications, such as IoT devices. Unlike adaptive arrays, it also eliminates the need for direct current energy sources.
The current prototype relies on basic antenna designs and commercial diode products, but researchers believe they can enhance performance with advanced semiconductor technologies and optimized configurations.
Beyond solving multipath interference, this interlocking approach could enable autonomous control of electromagnetic devices, potentially transforming wireless communication for IoT, especially in low-power systems with limited computational resources.
According to Professor Wakatsuchi, this passive filter design could pave the way for next-generation radio-frequency technologies, including antennas, sensors, imagers, and reconfigurable intelligent surfaces.
“Our passive interlocking solution is ideal for versatile, low-cost communication devices that cannot use conventional modulation or signal-processing techniques due to their high computational demands and cost,” Wakatsuchi explains.
Journal Reference:
- Kaito Tachi, Kota Suzuki, Kairi Takimoto, Shunsuke Saruwatari, Kiichi Niitsu, Ryo Ikeya, Tayaallen Ramachandran, Atsuko Nagata, Peter Njogu et al. Multipath Signal-Selective Metasurface: Passive Time-Varying Interlocking Mechanism to Vary Spatial Impedance for Signals with the Same Frequency. Physical Review Letters. DOI: 10.1103/PhysRevLett.134.157001
