  We derive and discuss general physical bounds on the electromagnetic
scattering and absorption of passive structures. Our theory, based on passivity
and power conservation, quantifies the minimum and maximum allowed scattering
for an object that absorbs a given level of power. We show that there is a
fundamental trade-off between absorption and overall scattering suppression for
each scattering harmonic, providing a tool to quantify the performance of
furtive sensors, regardless of the applied principle for scattering
suppression. We illustrate these fundamental limitations with examples of light
scattering from absorbing plasmonic nanoparticles and loaded dipole antennas,
envisioning applications to the design of cloaked sensors and absorbers with
maximized absorption efficiency.
