With the increase in potential uses of terahertz technology, the need for terahertz transceivers with application-oriented adaptive radiation patterns has emerged. Reconfigurable reflectarrays consisting of actuated sub-wavelength reflectors have been successfully used for terahertz beam steering and beamforming. They do not require a complex feeding network and associated electronics, enabling a compact and power-efficient terahertz beam steering system. However, the current reflectarray-based beam steering is accomplished by forming the reflectarray as a grating structure, which is accompanied by the problems such as grating lobes, limited steering range, and discrete steering angles. Here, we configure a MEMS-based reflectarray with the genetic algorithm to eliminate the grating lobes and open up the possibility of customizing its radiation pattern. We used single- and multi-objective optimization to find the optimal height profile of the reflectarray and verified the results by full-wave electromagnetic simulations. We measured the radiation patterns of four reflectarray phantoms, i.e. reflectarrays without the MEMS actuation systems. The measurement results agree well with the calculated ones, with the main beam deviating at most 2° from the target direction. Our work demonstrates how a genetic algorithm is used to shape a reconfigurable terahertz reflectarray to eliminate the grating lobes and tailor some specific featuress in its radiation pattern.

This contribution presents a design approach as well as characterization results for dielectric slot waveguides fabricated in highly resistive (HR) silicon (HR-Si) designed for operation in the terahertz (THz) frequency range. The authors discuss the fundamentals of dielectric slot waveguides and the respective figures of merit. Furthermore, analytical solutions as well as numerical results from field simulations of the propagating mode are presented and discussed. Prototypes are fabricated in a process for HR-Si microelectromechanical systems (MEMSs), including a silicon-based metamaterial to mechanically support the waveguide while preserving a strong field confinement. In addition, actuator concepts to implement device functionalities, such as phase shifting capabilities, are demonstrated. The prototypes are measured and characterized using vector network analyzer (VNA)-based two-port measurements in the frequency range from 220 to 330 GHz. The devices are characterized in terms of their field confinement, loss, and effective mode index. For the first time, the authors report on the experimental validation of dielectric slot waveguides in this frequency range and provide values for the obtained losses.

We present the design, fabrication, and characterization of a MEMS-based 3-bit Digital-to-Analog Converter (DAC) that allows the generation of large displacements. The DAC consists of electrostatic bending-plate actuators that are connected to a mechanical amplifier (mechAMP), enabling the amplification of the DAC output displacement. Based on a parallel binary-encoded voltage signal, the output displacement of the system can be controlled in an arbitrary order. Considering the system design, we present a simplified analytic model, which was confirmed by FE simulation results. The fabricated systems showed a total stroke of approx. 149.5 ± 0.3 µm and a linear stepwise displacement of 3 bit correlated to 2³ ≙ eight defined positions at a control voltage of 60 V. The minimum switching time between two input binary states is 0.1 ms. We present the experimental characterization of the system and the DAC and derive the influence of the mechAMP on the functionality of the DAC. Furthermore, the resonant behavior and the switching speed of the system are analyzed. By changing the electrode activation sequence, 27 defined positions are achieved upgrading the 3-bit systems into a 3-tri-state (3³) system.

An earlier version of this paper was presented at the 2021 15th European Conference on Antennas and Propagation (EuCAP) and was published in its Proceedings. This paper describes a design, fabrication, and characterization of a planar frequency-coded retroreflector for indoor localization. The retroreflector is fabricated in high-resistive silicon and consists of a Luneburg lens antenna and a photonic crystal high-Q resonator reflective layer, providing ranging and identification within the same tag and bandwidth. The Luneburg lens antenna presents a measured gain of 21.63 dBi at a design frequency of 240 GHz. The frequency-coded retroreflector allows for ranging in a continuous 130 degree angular range in azimuthal plane, with a discrete but repeatable two-resonance identification over multiples of 15 degree. Its maximum measured radar cross-section is −23.48 dBsqm at a frequency of 240 GHz. The retroreflective tag set in ideal line-of-sight situation is compared to a non-line-of-sight arrangement showing the influence of a metallic rod as an obstacle on the overall tag detection parameters. Finally, the successful read-out of the retroreflective tag is discussed in unknown environments, where no a-priori information is available.

We present the design and fabrication of MEMS reflectors intended to be part of a mechanical terahertz (THz) beam steering reflect-array. Each reflector is shifted by a bidirectional stepwise electrostatic actuator system. The design and functionality of actuator system and reflect-array limit and determine the reflector design. In this paper, we adapt a dicing-free Silicon-on-Insulator (SOI) fabrication process to the requirements of a THz MEMS reflector. We present the partial release of the handle layer from the SOI substrate on wafer level, leaving the remaining connected part as a functional system component. To realize an open interface for the interaction of the reflector with the THz beam, the device layer and the handle layer frame surrounding the SOI chip are partially released during hydrofluoric (HF) vapor etching making a mechanical destruction of the surrounding frame obsolete.

We present a micro-electromechanical reflectarray driven by large displacement actuators with multi-point stability that is intended for THz beam steering. The reflectarray consists of a stack of multiple SOI-chips each featuring a movable reflector. The position of each reflector is individually varied by in-plane mechanical digital-to-analog converters (DAC) that address 27 discrete and equidistant positions driven by only three pairs of cascaded tri-stable electrostatic actuators. Generally, the mechanical DAC addresses 3 $^n$ equidistant positions at a minimum number of 2 $n$ actuators. The reflector displacement is enlarged by combining the DAC output with a mechanical leverage. We demonstrate an SOI-fabrication method allowing to stack multiple chips for a one-dimensional array featuring large displacement DACs and large reflector surfaces. The full-wave electromagnetic simulations of the reflectarray verify its feasibility for terahertz beam steering applications. The electro-mechanical characterization shows the high-resolution displacement of single actuation systems as well as the functionality of a stacked 3 $\times$ 1 reflectarray. 2022-0149