Abstract
Monitoring apple fruit growth directly in the orchard is essential for precision orchard management. By accurately estimating the final fruit size, growers can fine-tune agronomic practices such as fruit thinning and irrigation to optimise harvest quality. This study focuses on tools used for fruit growth measurement. Traditionally, this has been performed manually using vernier calipers. More recently, fruit dendrometers have allowed for continuous monitoring. However, neither method is widely adopted: the former is labor-intensive, and the latter is often expensive and bulky. In this work, we explore a stretchable, printed resistive strain sensor as an innovative alternative to current state-of-the-art solutions. A stretchable carbon-based ink was printed in a meander pattern on thermoplastic polyurethane (TPU). This approach aim to address key limitations of existing methods by offering a lightweight, low-cost sensor that adheres directly to the fruit surface. By adopting a field-oriented perspective, the lab characterisation was designed to closely replicate real-world operating conditions. Under these conditions, the sensor, tested using a custom-made stretching setup, demonstrated a sensitivity of 0.153 ± 0.0032/%. These preliminary results are promising and suggest that this approach can offer a scalable, maintenance-free solution for smart orchard monitoring.