Bioinspired Feature Extraction for the Electric Field-based Determination of Object Size and Position

Abstract

1. Fish Sensory Systems

A few fish species can actively generate weak electric fields and use them to explore their environment. The ability to locate objects within about twice their body length is called active electrolocation (Von der Emde 1999). A well-studied fish species that uses active electrolocation is the weakly electric fish Gnathonemus petersii, Peter's elephant-nose fish. During active electrolocation, this fish generates a three-dimensional dipole-like electric field surrounding its body through specialized muscle cells located in its tail (Von der Emde 1999). The fish perceives the self-generated electric field with electroreceptors, called mormyromasts, which are distributed on the skin surface (Von der Emde 2006). The presence of a conductive object in the vicinity of the fish's self-generated electric field results in a two-dimensional image on the fish's electroreceptive skin. This image is also referred to as an electric image (Engelmann et al. 2008). Based on the concept of electric imagery, there is a correlation between object properties and perceived signal parameters.

2. Measurement Scenarios to Determine Size and Position

The simple analytical simulation model (Hunke et al. 2022) of the bio-template consists of an electrical dipole and a sensor line that represents the fish’s electroreceptive skin. This model is utilized to identify various features from the voltage profile, which can be used to determine the size and position of an object. The model distinguishes between static (Hunke et al. 2022) and dynamic (Hunke et al. 2021) localization features. These features were categorized based on their suitability for two measurement scenarios: one with a stationary sensor line and one with a moving sensor line.

2.1 Static Localization Features

The symmetrical shape of the voltage profile allows the evaluation of localization features such as amplitude, maximum slope, and full width at half maximum (FWHM). The object distance can be determined from the slope to amplitude ratio (Von der Emde 2006) or with the FWHM (Chen et al. 2005). However, if the slope and amplitude are considered separately, both object distance and object size can be derived (Hunke et al. 2022).

2.2 Dynamic Localization Features

The movement of the sensor line along an object, creates a voltage profile with a maximum (peak) that appears and disappears again (left position to right position). This results in an imaginary maximum trace (Peak Trace) with different widths for objects at different vertical distances from the sensor line. The peak trace (Hunke et al. 2021) is therefore a localization feature for object distance and position.