Design of a Kelvin cell acoustic metamaterial

Advancements in 3D print technology now allow the printing of struc-
tured acoustic absorptive materials at appropriate microscopic scales and
sample sizes. Optimisation of parameter sets associated with a Kelvin Cell
structure have the potential to develop various metabehaviours in the as-
sociated acoustic responses. The repeatability of the fundamental cell unit
also provide a route for the development of viable macro models to simu-
late built up structures based on detailed models of the individual cell units.
This paper describes a process to model, print and test such a sample. Man-
ufacturing restraints will initially guide the optimised design and introduce
response uncertainties associated with surface finishes and critical geomet-
ric dimensions. A ”micro to macro” model is developed using a full visco
thermal acoustic model of a single cell to develop a frequency dependent cell
transfer matrix. The transfer matrices for the repeated cells may then be
combined until sufficient material depth is achieved and efficiently generate
an absorptivity for the material layer. Two prints using different processes
(digital light processing (DLP) and selective laser melting (SLM)) of nomi-
nally the same kelvin cell structure. For the metal print the model predicts
the absorptivity well once an allowance is made for the surface roughness.
The DLP has a smoother finish with a lower geometric fidelity however the
DLP sample is still well modelled by the process.