  Airborne 3D imaging using ultrasound is a promising sensing modality for
robotic applications in harsh environments. Over the last decade, several
high-performance systems have been proposed in the literature. Most of these
sensors use a reduced aperture microphone array, leading to artifacts in the
resulting acoustic images. This paper presents a novel in-air ultrasound sensor
that incorporates 1024 microphones, in a 32-by- 32 uniform rectangular array,
in combination with a distributed embedded hardware design to perform the data
acquisition. Using a broadband Minimum Variance Distortionless Response (MVDR)
beamformer with Forward-Backward Spatial Smoothing (FB-SS), the sensor is able
to create both 2D and 3D ultrasound images of the full-frontal hemisphere with
high angular accuracy with up to 70dB main lobe to side lobe ratio. This paper
describes both the hardware infrastructure needed to obtain such highly
detailed acoustical images, as well as the signal processing chain needed to
convert the raw acoustic data into said images. Utilizing this novel
high-resolution ultrasound imaging sensor, we wish to investigate the limits of
both passive and active airborne ultrasound sensing by utilizing this virtually
artifact-free imaging modality.
