# Eco-Friendly Metadome-Antenna Innovations for Wearable Millimeter Wave Radar Sensing
## 1 Introduction
Metasurfaces (2-dimensional counterparts of metamaterials with sub-wavelength thickness) are useful to control the electromagnetic response for a wide scope of applications in RF and microwave sensing [18; 19; 20]. In recent years, metasurfaces have been proposed to be combined with radomes, to reduce their negative effect on antenna performance, or to be used as radomes themselves [21], named metaradomes or metadomes [22]. The increasing amount of waste electrical and electronic equipment (WEEE or E-waste) has become an obstacle in reducing the ecological footprint. Eco-friendly materials [23; 24; 25; 26; 27; 28; 29; 30] and manufacturing technologies are solutions paving the way towards circular economies and green technologies. A few mm-wave antennas on eco-friendly substrates [31; 32] were recently proposed, but the metallic parts were left out of such consideration. Moreover, sensitivity to moisture and low radiation efficiency prevent suitability for wearable applications [31]. Recent research [33; 34] has shown that polypropylene (PP) outperforms widely used commercial antenna materials, such as RO3003, for medium- to long-range anti-collision radar applications. The present contribution aims to show that, in addition, PP can be used to design a metaradome, achieving an advantageous meta-randomized antenna, in this case for short-medium range applications. Accordingly, a wearable meta-randomized grid array antenna (MTR-GAA) for ETA application at 24 GHz, based on eco-friendly materials (Polypropylene (PP) substrate and aluminum conductor), is presented. The development of a 24 GHz grid array antenna protected by a metaradome, both fabricated from eco-friendly materials, represents a significant advancement in radar technology for Electronic Travel Aid (ETA) systems designed to assist visually impaired individuals. This innovative approach leverages polypropylene (PP) as the dielectric substrate and aluminum for metallization, ensuring both environmental sustainability and high performance. The use of eco-friendly materials addresses the growing demand for green technologies, reducing the ecological footprint of electronic devices. Additionally, the integration of a metaradome enhances the durability and reliability of the antenna system, providing robust protection against environmental factors while maintaining optimal signal integrity (it is worth noting that wearable antenna designs in the literature do not include a radome, which makes them very prone to damage or even unusable in realistic applications). This combination of sustainable materials and advanced design not only meets the technical requirements for high-frequency radar applications but also sets a new standard for environmentally conscious engineering in assistive technologies. The proposed solution is particularly novel in its application to ETA systems, offering a practical and sustainable means to improve the mobility and safety of visually impaired individuals. The manuscript is organized as follows: the eco-friendly materials (both dielectric substrate and metallic conductor) selected for the devices are presented first. The design and performance of a metaradome operating at 24 GHz is explained after. Then the design of the antenna is presented. The combination of the antenna with a conventional radome and with the metaradome is analyzed next. Afterwards, the fabrication of prototypes is shown and measurement results are provided, as well as an analysis of their matching with the simulation ones. Then, a comparison with the state of the art on 24 GHz radar antennas is provided to back up the benefits of the featured MTR-GAA ensemble. Finally, some conclusions are drawn.