University of Cagliari
Control of absorption with resonators by critical coupling
11 April 2017
Nell’ambito del Visiting Professor Program
Control of absorption with resonators by critical coupling
Vincent Pagneux
Laboratoire d’Acoustique de l’Université du Maine
(LAUM – UMR CNRS 6613)
Le Mans, France
When an acoustic wave is reflected by a structured wall with loss, or is both reflected
and transmitted through a screen, there is some part of absorption. The perfect
absorption case, often desirable, corresponds to the complete annulation of the
scattered waves. The method of analysis of acoustic absorption that will be
presented uses the structure of the scattering coefficients in the complex frequency
plane. In the absence of losses, the scattering coefficient supports pairs of poles and
zeros that are complex conjugates and which have imaginary parts linked to the
energy leakage by radiation. When losses are introduced and balanced to the
leakage, the critical coupling condition is satisfied and perfect absorption is obtained.
Several cases will be discussed, using sub-wavelength resonators, displaying perfect
or quasi-perfect absorption for reflection (one port scattering) or
reflection/transmission (two port scattering).
Mercoledì 12 aprile 2017 alle ore 11:00 in Aula M della Facoltà di Ingegneria, via Marengo 2, avrà invece luogo il seminario
PT-symmetric scattering with flow duct acoustics
Vincent Pagneux
Laboratoire d’Acoustique de l’Université du Maine
(LAUM – UMR CNRS 6613)
Le Mans, France
In this talk, theoretical and experimental results will be presented for an acoustical
wave in an air flow duct going through a pair of diaphragms, one with amplification
and another with an equivalent amount of attenuation: this system displays all the
features of a parity-time (PT) symmetric system. With a scattering matrix formalism,
we show the features which reflect the PT-symmetry of the wave scattering. The
results demonstrate the existence of a transition between PT-symmetric scattering
eigenstates, which are norm preserving, and symmetry-broken pairs of eigenstates
exhibiting net amplification and loss. Some extensions to periodic systems will be
presented.