Weakly electric fish use a process called 'active electrolocation' to orientate in their environment and to localize objects
based on their electrical properties. To do so, the fish discharge an electric organ which emits brief electrical current
pulses (electric organ discharge, EOD) and in return sense the generated electric field which builds up surrounding the
animal. Caused by the electrical properties of nearby objects, fish measure characteristic signal modulations with an
array of electroreceptors in their skin. The fish are able to gain important information about the geometrical properties of
an object as well as its complex impedance and its distance. Thus, active electrolocation is an interesting feature to be
used in biomimetic approaches.
We used this sensory principle to identify different insertions in the walls of Plexiglas tubes. The insertions tested were
composed of aluminum, brass and graphite in sizes between 3 and 20 mm. A carrier signal was emitted and perceived
with the poles of a commercial catheter for medical diagnostics. Measurements were performed with the poles separated
by 6.3 to 55.3 mm. Depending on the length of the insertion in relation to the sender-receiver distance, we observed up to
three peaks in the measured electric images. The first peak was affected by the material of the insertion, while the
distance between the second and third peak strongly correlated with the length of the insertion.
In a second experiment we tested whether various materials could be detected by using signals of different frequency
compositions. Based on their electric images we were able to discriminate between objects having different resistive
properties, but not between objects of complex impedances.
During their nocturnal activity period, weakly electric fish employ a process called "active electrolocation" for
navigation and object detection. They discharge an electric organ in their tail, which emits electrical current pulses,
called electric organ discharges (EOD). Local EODs are sensed by arrays of electroreceptors in the fish's skin, which
respond to modulations of the signal caused by nearby objects. Fish thus gain information about the size, shape, complex
impedance and distance of objects.
Inspired by these remarkable capabilities, we have designed technical sensor systems which employ active
electrolocation to detect and analyse the walls of small, fluid filled pipes. Our sensor systems emit pulsed electrical
signals into the conducting medium and simultaneously sense local current densities with an array of electrodes. Sensors
can be designed which (i) analyse the tube wall, (ii) detect and localize material faults, (iii) identify wall inclusions or
objects blocking the tube (iv) and find leakages. Here, we present first experiments and FEM simulations on the optimal
sensor arrangement for different types of sensor systems and different types of tubes. In addition, different methods for
sensor read-out and signal processing are compared.
Our biomimetic sensor systems promise to be relatively insensitive to environmental disturbances such as heat, pressure,
turbidity or muddiness. They could be used in a wide range of tubes and pipes including water pipes, hydraulic systems,
and biological systems. Medical applications include catheter based sensors which inspect blood vessels, urethras and
similar ducts in the human body.