  Piezoelectric transducers applied on or integrated in structures, combined
with appropriate circuits have been extensively investigated as a smart
approach to the mitigation of resonant vibrations with high relative
amplitudes. \cmt{A resonant shunt circuit consisting of the capacitive
piezoelectric transducer and an inductance can be configured to target specific
eigenmodes of a structure, if appropriately placed and tuned. Their effect is
expressed in terms of mechanical impedance of the host structure, allowing for
the exchange of energy between the mechanical and electrical domain, to
dramatically affect the dynamic response of the structure. By re-framing the
function of resonant shunted piezoelectric transducers as frequency dependent
variable stiffness elements, this paper investigates their capability to
realize a frequency dependent structural mechanical connectivity, where the
load path within a lattice structure can be interrupted at will for specific
frequencies by tunable null-stiffness components. Here, we offer the numerical
and experimental verification of this idea, by demonstrating the ability to
significantly affect the dynamic response of a unit cell of an adaptive lattice
metamaterial, even away from a structural resonance. In the latter case, the
null-stiffness shunt leads to an additional resonance peak in the truss'
dynamic response.} Its realization as additively manufactured component points
to the feasibility of such structures in real life.
