  Molecular communication via diffusion (MCvD) is a method of achieving nano-
and micro-scale connectivity by utilizing the free diffusion mechanism of
information molecules. The randomness in diffusive propagation is the main
cause of inter-symbol interference (ISI) and the limiting factor of high data
rate MCvD applications. In this paper, an apertured plane is considered between
the transmitter and the receiver of an MCvD link. Either after being
artificially placed or occurring naturally, surfaces or volumes that resemble
an apertured plane only allow a fraction of the molecules to pass. Contrary to
intuition, it is observed that such topology may improve communication
performance, given the molecules that can pass through the aperture are the
ones that take more directed paths towards the receiver. Furthermore, through
both computer simulations and a theoretical signal evaluation metric named
signal-to-interference and noise amplitude ratio (SINAR), it is found that the
size of the aperture imposes a trade-off between the received signal power and
the ISI combating capability of an MCvD system, hinting to an optimal aperture
size that minimizes the bit error rate (BER). It is observed that the trend of
BER is accurately mirrored by SINAR, suggesting the proposed metric's
applicability to optimization tasks in MCvD systems, including finding the
optimal aperture size of an apertured plane. In addition, computer simulations
and SINAR show that said optimal aperture size is affected by the location of
the aperture and the bit rate. Lastly, the paper analyzes the effects of radial
and angular offsets in the placement of the apertured plane, and finds that a
reduction in BER is still in effect up to certain offset values. Overall, our
results imply that apertured plane-like surfaces may actually help
communication efficiency, even though they reduce the received signal power.
