  In this paper we present a passive and cost-effective method for increasing
the frequency range of ultrasound MEMS microphone arrays when using beamforming
techniques. By applying a 3D-printed construction that reduces the acoustic
aperture of the MEMS microphones we can create a regularly spaced microphone
array layout with much smaller inter-element spacing than could be accomplished
on a printed circuit board due to the physical size of the MEMS elements. This
method allows the use of ultrasound sensors incorporating microphone arrays in
combination with beamforming techniques without aliases due to grating lobes in
applications such as sound source localization or the emulation of bat HRTFs.
