PUB - Publikationen an der Universität Bielefeld

Weakly electric fish use self-generated electric fields for communication, active electrolocation and navigation. Additionally to visual sense, this ability enables them to detect objects and food even in dark or turbid waters. Specialized muscle cells in the tail region actively generate an electric field in the surrounding fluid, shaped like a dipole between tail and head. This dipole field may be distorted depending on environmental parameters such as the presence of objects of different geometry or material properties in the animal's vicinity. Electroreceptors, distributed all over the fish' skin allow to perceive distortions of the field, caused by objects. Furthermore, fish execute stereotyped scanning behaviors to obtain additional sensory information of detected objects.
The development of innovative sensor systems for short-range exploration in fluids is still in its infancy. Also, the use of electric fields in bio-inspired technologies is still at an early stage. Based on the biological model of weakly electric fish, the question has already been examined if an array of electrodes can be used for a contactless object detection and localization and finally for navigation in fluids (Solberg et al. 2008). This examination is performed by analyses of electric field modulations, based on so-called EEVs. An EEV (Ensemble of Electrosensory Viewpoints) is a scalar field representation of the influence of an object on the electric field in the form of potential differences measured between two electrodes for every possible object location.
The first part of this thesis explores the characteristics of the electric dipole field and the resulting EEV by means of numerical simulations to determine the influence of an object placed in the emitted field. It will also be investigated how many receptors are required and which arrangement is to be preferred to uniquely identify the positions of spherical objects in the vicinity of the sensor system. For this, a receptor system composed of a simple biomimetic abstraction of an emitter dipole and an orthogonally arranged pair of sensor electrodes is used. Inspired by the scanning movements of the fish, a fixed, minimal scanning strategy, composed of active receptor system movements is developed. The active electrolocation strategy introduced here is based on the superposition of extracted EEV contour-rings in order to find intersections of these contours.
The second part of this work focuses on the development of an *application* for active electrolocation which is based on a minimal set of scanning movements as a precursor for the partitioning of the later search area in which sensor-emitter movements take place. In this application, EEVs are also used as major components of two localization algorithms. In order to find points within the search space which are part of several contour-rings, intersection points have to found. Due to numerical inaccuracies intersection points may degrade to contour-segments which lie very close to each other but do not touch. For this case, a nearness metric is used to identify such points. However, in this part of the work the EEVs are based on a simplified analytical representation, which renders the corresponding algorithms suitable for embedded computer systems.
In the third part of this thesis, a fitted histogram representation of EEVs is used to compare a large number of different movement sequences to select the optimal composition from this variety. For this, the general shape of an EEV has to be considered, which plays a major role in estimating the best sequence.