Ultra-low-loss tunable piezoelectric-actuated metasurfaces achieving 360° or 180° dynamic phase shift at millimeter-waves

Abstract

Phase shifting metasurfaces typically consist of an ordered metallic geometry that is patterned onto a dielectric substrate and incorporate active devices or materials that enable dynamic tuning. Existing methods at mm-wave and submillimeter bands typically suffer from high losses, which are predominantly produced by the inherent limitations of the tuning elements or materials. This report presents a new, ultra-low-loss and phase-tunable, reflection type metasurface design, which outperforms previously reported technologies in terms of phase shifting and loss. The proposed technique utilizes a variable air cavity, formed between a periodic array and a ground plane, which is controlled by means of a piezoelectric actuator. Two metasurface designs are presented and experimentally tested. Firstly, a square patch element metasurface that is capable of achieving a continuous 180° phase shift across a wide bandwidth, between 35 and 65 GHz. Also presented is a double-cross element metasurface that provides full 360° phase control between 57 and 62 GHz. The variable air cavity is controlled by means of a piezoelectric actuator that supports and varies the height of a ground plane, providing highly accurate, millisecond, displacement. Unlike conventional tuning methods, the tuning mechanism, in this case the moving ground plane, introduces no additional sources of loss and enables an average loss performance of 1 dB. Full-wave simulations are presented and experimentally validated with measurements of both metasurface prototypes. The proposed approach is scalable from microwave up to THz frequencies, due to the electro-mechanical and low loss nature of the tuning.

Steer by Image Technology for Intelligent Reflecting Surface Based on Reconfigurable Metasurface with Photodiodes as Tunable Elements

“…This approach is called phase-gradient and is divided into two sub-approaches: continuous and discrete (digital coding) tuning. Components for continuous tuning of the metasurface, such as Liquid Crystal materials [24], piezoelectric materials and MEMS [25,26] and varactor diodes [19,[27][28][29][30][31], require complicated wiring of DC bias, control boards and RF circuits.…”

Millimeter Wave Reconfigurable Metasurface Intelligent Reflecting Surface Based on Piezoelectric Crystal for 5<sup>th</sup> and 6<sup>th</sup> Generation of Wireless Communication

“…Piezoelectric materials enable continuously change the unit cell thickness depending on the DC voltage [10]. Thus, the properties of the MS continuously change as well.…”

“…Using the piezoelectric method is limited because it involves a physical change in the unit cell size and in the structure as can be seen in Figure 5. In addition, a high voltage of up to 200 V is needed for control [10]. As can be seen in Figure 5 the unit cell structure measuring 0.8 mm × 0.8 mm.…”

“…This IRS will be based on metasurface principle and piezoelectric (PE) crystal as the tunable element. The possibility of using a piezoelectric crystal for the purpose of adjusting the return beam for high frequency is shown in [10]. Moreover, mention that the active elements add an extra, and dynamically variable, degree of freedom in any of the metasurface parameters to produce a tunable reflected response.…”

Air-bridged Schottky diodes for dynamically tunable millimeter-wave metamaterial phase shifters

“…As emerging applications such as 5G/6G and satellite communications 2 , 3 begin to explore the use of the mmWaves, there is a large body of research being established in different tunable materials and devices for use at these frequencies. These include liquid crystals 4 , 5 , ferroelectric substrates 6 , microelectromechanical systems 7 – 9 , vanadium dioxide 10 , 11 , graphene 12 , 13 and piezoelectric actuators 14 , 15 . Each of these technologies have their own merits and drawbacks, in terms of switching speed, ease of fabrication, reliability and loss performance 16 .…”