The UK's critical infrastructure---bridges, tunnels, railways, offshore platforms---is aging rapidly. Many assets are unmonitored or inspected infrequently due to the high cost and complexity of traditional structural health monitoring (SHM) systems, which require wired power, network access, and regular maintenance. This puts public safety, service continuity, and environmental goals at risk. EchoNet offers a transformative solution: a zero-maintenance, battery-free structural monitoring system using passive RF (radio frequency) resonators. These small, low-cost devices are embedded or attached to infrastructure surfaces. When the structure experiences strain, corrosion, or fatigue, the resonators' RF echo signature shifts in measurable ways. These changes are detected remotely using a portable software-defined radio (SDR) scanner---mounted on drones or handheld devices---allowing real-time diagnostics without physical access, wiring, or batteries. An AI model is trained to interpret the returned echo signals, classifying the condition of the structure (e.g., healthy, fatigued, degraded) with high accuracy. This enables continuous monitoring and predictive maintenance---preventing failures before they happen, while reducing inspection costs and environmental impact. Over the course of this 6-month Innovate UK Growth Catalyst project, we will: 1)Design and simulate new RF resonator geometries responsive to mechanical strain. 2)Build and test them in lab conditions using controlled stress rigs. 3)Collect RF echo data and train a lightweight AI classifier. 4)Integrate the SDR interrogation setup and deploy a prototype in a real-world outdoor setting. 5)Develop a follow-on plan for a full-scale field pilot and IP protection. EchoNet has the potential to make UK infrastructure smarter, safer, and more sustainable. By enabling low-cost, maintenance-free sensing in remote or high-risk locations, it directly supports Net Zero ambitions and public safety. It also creates a new exportable class of UK-made digital infrastructure technology. Target sectors include transport (bridges, tunnels), energy (offshore and wind), and defence. We are in early discussions with industry stakeholders and plan to build partnerships through the demonstration phase. EchoNet is more than a sensor---it's an intelligent echo-twin for national infrastructure.