Weakly electric fish sense their surroundings in complete darkness by their active electrolocation system. For biologists, the active electrolocation system has been investigated for near 60 years. And for engineers, bio-inspired active electrolocation sensor has been investigated for about 20 years. But how the amplitude information response will be affected by frequencies of detecting electric fields in the active electrolocation system was rarely investigated. In this paper, an electrolocation experiment system has been built. The amplitude information-frequency characteristics (AIFC) of the electrolocation system for sinusoidal electric fields of varying frequencies have been investigated. We find that AIFC of the electrolocation system have relevance to the material properties and geometric features of the probed object and conductivity of surrounding water. Detect frequency dead zone (DFDZ) and frequency inflection point (FIP) of AIFC for the electrolocation system were found. The analysis model of the electrolocation system has been investigated for many years, but DFDZ and FIP of AIFC can be difficult to explain by those models. In order to explain those AIFC phenomena for the electrolocation system, a simple relaxation model based on Cole-Cole model which is not only a mathematical explanation but it is a physical one for the electrolocation system was advanced. We also advance a hypothesis for physical mechanism of weakly electrical fish electrolocation system. It may have reference value for physical mechanism of weakly electrical fish active electrolocation system.
Underwater active electrolocation technology is a new kind of technology for underwater detection and environmental perception, whose discovery was inspired by the active electrolocation systems of weakly electric fish. The amplitude information-frequency characteristics (AIFC) obtained by an underwater active electrolocation system (UAES) can effectively assess information about probed objects, such as their material composition, shape, and conductivity. Traditionally, single-frequency excitation has been employed in a UAES, which can make object detection inefficient and timeconsuming. We employed multi-frequency signals for excitation in a UAES, to improve the efficiency of detection. We used three kinds of multi-frequency excitation signals-square wave, single pulse, and biphasic pulse, to detect objects under water. To improve the accuracy of measurements, we developed an AIFC recognition algorithm. The experimental results showed that the multifrequency excitation detection method is effective and feasible. We demonstrated that the electrodes are strongly coupled to the UAES and can result in non-negligible errors that have often been previously ignored. In addition, graphite electrodes performed much better than titanium electrodes for multi-frequency signal detection, and bio-inspired multi-frequency pulse excitation signals gave more accurate results than the square-wave signal.
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