In theory, sub-terahertz (sub-THz) communication offers the potential for near-field beam focusing, that can far surpass conventional far-field beam steering by directing energy to a specific point in space rather than a broad angular direction. In this paper, we introduce TeraFocus, the first adaptive beam focusing system for sub-THz wideband communication. Moreover, we present the first experimental demonstration of a wideband focusing link, in contrast to prior experiments with monochromatic sources. With TeraFocus, we demonstrate how metasurfaces with thousands of radiating elements (81 by 81 for a total of 6,561), can create the non-linear phase gradient required for precise beam focusing, achieving a 60 GHz 3-dB bandwidth. Moreover, TeraFocus maximizes link capacity by addressing the inherent spectral asymmetry in metasurface responses. Finally, for mobile clients, TeraFocus dynamically compensates for misalignment by leveraging the frequency-dependent focal length characteristic, allowing it to adapt to radial mobility without relying on traditional localization algorithms, which can be time-consuming, computationally expensive, and error-prone. Instead, TeraFocus re-localizes the client by analyzing the received spectral signature of a misaligned focusing beam, achieving a maximum error of less than 0.2 cm.

The next generation of wireless networks will utilize highly directional beams to overcome the path loss at high frequencies, requiring angle inference during link establishment. Furthermore, the integration of location-based services into the wireless infrastructure is rapidly increasing, bringing in a significant demand for an integrated fast localization scheme. In this work, we present a first-of-its-kind one-shot angular localization method that is carried out with a re-configurable architecture that unlocks ISAC functionality. Specifically, we use an electrically tunable metasurface with broadband response to generate wavefronts that are randomized across the angular space with diverse wideband amplitude and phase observations, corresponding to a collection of angle-unique one-shot beacons. Our results show down to 0.26° mean absolute error at 20 dB SNR, an order of magnitude improvement over the recently proposed one-shot solutions based on leaky-wave antennas (LWAs), in addition to having wider area coverage and less stringent bandwidth requirements.