Permanent Magnet-Based Superficial Flow Velometer With Ultralow Output Drift

Superficial flow velocity perception is inspired by aquatic organisms and has become increasingly important for underwater robots and vehicles. Existing marine electromagnetic velometers require very large alternating current (ac) coils with high power consumption for excitation, limiting their mobility and underwater applications. Permanent magnet excitation is preferable for miniature flow sensors because of low power consumption, small size, and high sensitivity. However, permanent magnet excitation has not been applicable due to the high output drift caused by electrode polarization voltage. This article proposes a permanent magnet-based flow velocity meter that measures the velocity based on the electrode output current instead of the output voltage. The relationship between the output current and the fluid velocity, fluid conductivity, permanent magnet parameters, and electrode position during permanent magnet excitation is derived, and a finite element simulation is conducted. A signal processing circuit is designed to obtain the current output. The experimental results show that the output drift ratio of the proposed sensor is 92% lower than that of the sensor measuring the voltage output, and the measurement R-2 is 0.998 in the test range of 0-0.875 m/s.