INSTITUTE OF PHYSICS PUBLISHING CLASSICAL AND QUANTUM GRAVITY Class. Quantum Grav. 19 (2002) 2013–2019 PII: S0264-9381(02)29134-0 A wideband and sensitive GW detector for kHz frequencies: the dual sphere Livia Conti 1 , Massimo Cerdonio 1 , Michele Bignotto 1 , Michele Bonaldi 2 , William Duffy Jr 3 , Paolo Falferi 2 , Antoine Heidmann 4 , J Alberto Lobo 5 , Francesco Marin 6 , Antonello Ortolan 7 , Michel Pinard 4 , Giovanni Andrea Prodi 8 , Luca Taffarello 9 , Stefano Vitale 8 and Jean-Pierre Zendri 9 1 INFN Padova Section and Department of Physics, University of Padova, via Marzolo 8, I-35100 Padova, Italy 2 CeFSA, ITC-CNR and INFN Gruppo Coll. Trento, I-38050 Povo, Trento, Italy 3 Department of Physics, Santa Clara University, Santa Clara, CA 95053, USA 4 Laboratoire Kastler Brossel, 4 place Jussieu, F75252 Paris, France 5 Departamento de F´ ısica Fonamental, Universidad de Barcelona, Diagonal 647, 08028 Barcelona, Spain 6 INFN Firenze Section and Department of Physics, University of Firenze, Lgo E Fermi 2, I-50125 Firenze, Italy 7 INFN, Laboratori Nazionali di Legnaro, via Romea 4, I-35020 Legnaro, Padova, Italy 8 INFN Gruppo Coll. Trento and Department of Physics, University of Trento, I-38050 Povo, Trento, Italy 9 INFN Padova Section, via Marzolo 8, I-35100 Padova, Italy E-mail: conti@lnl.infn.it Received 25 September 2001, in final form 26 October 2001 Published 18 March 2002 Online at stacks.iop.org/CQG/19/2013 Abstract We discuss the new concept of a sensitive and wide-band detector, consisting of a solid sphere nested inside a hollow one: the dual sphere. The advantage is that it would be possible to keep both the omni-directionality and high sensitivity of the spherical geometry without giving up the wide band. In the few kHz range the dual sphere would be complementary to ‘advanced’ interferometers. We also discuss the main technological and scientific challenges that the construction of such a system poses, particularly regarding material choice, fabrication, cooling, suspension and readout. PACS numbers: 0480N, 9555Y 1. Introduction Gravitational wave (GW) detectors aim at measuring tiny strains δl/l of test masses where δl/l = h/2 and h is the wave amplitude. In order to get a significant rate event,experimentalists 0264-9381/02/072013+07$30.00 © 2002 IOP Publishing Ltd Printed in the UK 2013