A. Duff et al. (eds.): Living Machines 2014, LNAI 8608, pp. 408–410, 2014. © Springer International Publishing Switzerland 2014 Soil Mechanical Impedance Discrimination by a Soft Tactile Sensor for a Bioinspired Robotic Root Chiara Lucarotti 1,2 , Massimo Totaro 1 , Lucie Viry 1 , Lucia Beccai 1,* , and Barbara Mazzolai 1 1 Center for Micro-BioRobotics, Istituto Italiano di Tecnologia, Pontedera, Italy 2 The BioRobotics Institute, Scuola Superiore Sant’Anna, Pontedera, Italy lucia beccai@iit.it Abstract. During the penetration into the soil, plant roots experience mechani- cal impedance changes and come into contact with obstacles which they avoid and circumnavigate during their growth. In this work, we present an experimen- tal analysis of a sensorized artificial tip able to detect obstacles and discriminate between different mechanical impedances in artificial and real soils. The conic- al shaped tip is equipped with a soft capacitive tactile sensor consisting of dif- ferent elastomeric and conductive layers. Experimental results show that the sensor is robust yet sensitive enough to mechanical impedance changes in the experimented soils. Keywords: Soft tactile sensor, sensorized tip, plant root, soil impedance. When a plant root comes into contact with obstacles to its growth, it adopts efficient strategies to circumnavigate the barriers and to direct its growth towards low imped- ance pathways [1]. Therefore, the apex must be able to experience changes in me- chanical impedance related to constraints provided by the soil or soil compaction. In a robotic implementation, the artificial root must be equipped with a sensing system able to detect barriers to growth and to discriminate between different mechanical impedances of the soil [2]. To this aim, we developed a soft capacitive tactile sensor, built from a combination of elastomeric and conductive layers. The sensor was inte- grated in a conical artificial tip made of acrylic resin material by rapid prototyping (Fig. 1D), which shape is conical, as recently suggested for a root apex inspired arte- fact [3]. The sensor (Fig. 1A, 1C) consists of two parallel circular electrodes (5mm diameter, 70μm thickness), made of soft and unstretchable copper/tin coated woven fabrics, and separated by a spin coated silicone elastomeric dielectric film (300μm thickness). Similar materials were proven appropriate for highly sensitive soft tactile sensing [4]. However, in this work an additional layer made of a compliant and robust silicone material (Sugru © , FormFormForm Ltd, London, UK) (1.5mm thick) was integrated on top of the capacitor in order to increase the robustness of the final de- vice, allowing its correct operation in the soil during fifty repeated trials (Fig. 1D). When a force is applied to the top electrode, the dielectric layer  ଴ decreases, resulting * Corresponding author.