  Signature of phase coherence on the electric and magnetic response of non
connected Aharonov-Bohm rings is measured by a resonant method at 350 MHz
between 20 mK and 500 mK. The rings are etched in a GaAs-AlGaAs heterojunction.
Both quantities exhibit a oscillating behaviour with a periodicity consistent
with half a flux quantum $\Phi_0/2=h/2e$ in a ring. Electric screening is shown
to be enhanced when time reversal symmetry is broken by magnetic field, leading
to a positive magnetopolarisability, in agreement with theoretical predictions
for isolated rings at finite frequency. Temperature and electronic density
dependence are investigated. The dissipative part of the electric response, the
electric absorption, is also measured and leads to a negative
magnetoconductance. The magnetic orbital response of the very same rings is
also investigated. It is consistent with diamagnetic persistent currents of
0.25 nA. This magnetic response is an order of magnitude smaller than the
electric one, in qualitative agreement with theoretical expectations.
