A Symmetric Dual-Slider Architecture for Expandable Smartphones: A Design Study

Every expandable phone on sale is a book: two rigid halves on a hinge, a folding display between them, and a second screen on the outside because the main one is hidden when shut. This design study works through a different shape. The device is a conventional 163 × 78 × 10.6 mm slab that splits symmetrically from a fixed centre spine, each side sliding out 39 mm so that one continuous display grows from 78 mm to 156 mm wide with no crease and no seam. The screen is never wound onto a drum: it makes a single half-turn around a roller at each end and runs back flat inside the body, so every part of it is bent identically on every cycle. A chain of small metal links beneath the panel is rigid wherever it lies flat and free only where it turns, which makes the extended screen solid under a thumb without any latch or actuator. The study gives the dimensional budget layer by layer, the load path in both states, the sealing strategy, and interaction targets in newtons and microns rather than adjectives. It also sets out what it cannot show: the architecture depends on one component that is not publicly available, a rollable panel qualified to a 3.5 mm bend for the device's service life. That bend is gentler than any folding phone on sale, and whether it survives is the question a prototype exists to answer. A closing section lists the alternatives that were considered and rejected, and the claims earlier drafts made that did not survive review.