# Ultrasound synthetic aperture non-line-of-sight imaging

## TL;DR

This paper introduces an ultrasound-based system for non-line-of-sight imaging that achieves high-resolution 3D reconstructions of hidden scenes.

## Contribution

The novel ultrasound-based NLOS imaging system achieves performance comparable to optical methods with low-power, eye-safe hardware.

## Key findings

- The system achieves ~1 cm lateral and depth resolution at distances up to 2 meters.
- Measurements of the NLOS modulation transfer function confirm the spatial resolution.
- The method uses f-k migration and phase-sensitive synthetic-aperture techniques.

## Abstract

Non-line-of-sight (NLOS) imaging typically relies on the use of ultrashort laser pulses and time-resolved detection to then reconstruct 3D environments that are hidden from the direct line-of-sight. However, the same scattering mechanism and wall-reflections that allow light to propagate into the hidden environment and back again ultimately limit both resolution and imaging distances even at high laser powers. Non-optical, such as acoustic and radio-wave approaches promise to solve some of these issues but have yet to achieve results comparable to optical systems. We present an ultrasound-based NLOS imaging system based on a scanning ultrasound emitter and receiver operating in a frequency range similar to common bats that demonstrates high-resolution 3D reconstruction of hidden scenes. We successfully image multiple targets and complex scenes with  ~ cm depth resolution at distances up to 2 m away from the scattering surface. Measurements of the NLOS modulation transfer function quantify the spatial resolution to also be  ~ 1 cm, which is comparable to traditional optical NLOS techniques.

Optical non-line-of-sight imaging demands ultrafast detectors and suffers steep power loss, limiting range and practicality. Here, the authors realize a phase-sensitive synthetic-aperture ultrasound platform that exploits specular wall reflections and f-k migration to reconstruct 3D hidden scenes with 1 cm lateral resolution at meter-scale ranges, attaining performance comparable to optical approaches with low-power, eye-safe hardware.