An Ultrasonic Heading Goniometer Intrinsically Robust to Magnetic Interference

An ultrasonic heading measurement method, working under magnetic interference prohibitive for magnetometers, was prototyped, validated, and metrologically characterized. Two capacitive ultrasonic transducers convert the mechanical rotation in two correspondingly time-delayed electrical sine waves. Then, the time delay is estimated using the standard tree parameter sine-fitting algorithm. The prototyped goniometer achieves the same repeatability level (<36 mrad) of a magnetometer-based heading in the range [−437 mrad, 437 mrad]. Simultaneously, a throughput of 505 Sa/s is proven on an STM32F303xC Arm Cortex −M4 32-bit microcontroller. An interference analysis revealed the experimental deterministic error well explained by the combined effect of beacon and receiver directivity, as well as by the relative position of beacon, receiver, and reflective surfaces. Noise robustness was assessed in case of SNR decayed to 9.1 dB from the initial value of 36.6 dB; the maximum deterministic error in the range [−437 mrad, 437 mrad] increased less than 10% (from 21 to 23 mrad in absolute value).