Research has explored miniature radar as a promising sensing technique for the recognition of gestures, objects, users' presence and activity. However, within Human-Computer Interaction (HCI), its use remains underexplored, in particular in Tangible User Interface (TUI). In this paper, we explore two research questions with radar as a platform for sensing tangible interaction with the counting, ordering, identification of objects and tracking the orientation, movement and distance of these objects. We detail the design space and practical use-cases for such interaction which allows us to identify a series of design patterns, beyond static interaction, which are continuous and dynamic. With a focus on planar objects, we report on a series of studies which demonstrate the suitability of this approach. This exploration is grounded in both a characterization of the radar sensing and our rigorous experiments which show that such sensing is accurate with minimal training. With these techniques, we envision both realistic and future applications and scenarios. The motivation for what we refer to as Solinteraction, is to demonstrate the potential for radar-based interaction with objects in HCI and TUI. CCS Concepts: • Human-centered computing → Interaction techniques; Interface design prototyping; Ubiquitous and mobile computing design and evaluation methods;