A ferrofluid-based sensor to measure bottom shear stresses under currents 1 and waves 2 ROSARIA E. MUSUMECI, Assistant Professor, Department Civil Engineering and 3 Architecture, University of Catania, Catania, Italy 4 Email: rmusume@dica.unict.it (author for correspondence) 5 VINCENZO MARLETTA, Post-doc, Department of Electric, Electronics and Computer 6 Engineering, University of Catania, Catania, Italy 7 Email: vincenzo.marletta@dieei.unict.it 8 AGUSTIN SANCHEZ-ARCILLA, Full Professor, Laboratori de Enginyeria Maritima, 9 Technical University of Catalunya, Barcelona, Spain 10 Email: agustin.arcilla@upc.edu 11 ENRICO FOTI, Full Professor, Department Civil Engineering and Architecture, University of 12 Catania, Catania, Italy 13 Email: efoti@dica.unict.it 14 15 16 Running Head: Ferrofluid sensor to measure bottom shear stresses. 17 18 19