A thermophone-based FM sonar for airborne ultrasonic sensing under drone flight noise

Bats achieve agile navigation, including obstacle avoidance and prey pursuit in complex environments, using a remarkably simple active sonar system consisting of a single sound emitter and two receivers. Their biosonar highlights the potential of broadband FM pulses in simple sensing architectures. Here, we present a bat-inspired FM sonar system for drones, employing a single ultrasonic transmitter and two receivers. The system integrates a lightweight thermoacoustic emitter (thermophone) capable of generating broadband frequency-modulated (FM) pulses, including echolocation-like signals. Owing to its resonance-free operation, the thermophone provides wideband ultrasonic emission with low voltage input. Using onboard cross-correlation processing, we demonstrate object detection, two-dimensional localization, and low-speed two-dimensional obstacle avoidance using ultrasound alone during autonomous drone flight. The proposed system successfully detects narrow obstacles even under flight conditions in which the raw onboard microphone signals are dominated by drone flight-induced noise. Our results demonstrate the feasibility of thermophone-based FM sonar for airborne ultrasonic sensing during drone flight and establish thermophone technology as a promising platform for future bat-inspired aerial sonar system.