Instrumentation & Measurement Magazine 25-9 - 10

Feature Extraction from a Static and
a Moving One-Dimensional Voltage
Sensor Line for the Electric FieldBased
Determination of Object Size
and Position in Aqueous Media
Kevin Hunke, Jacob Engelmann, and Axel Schneider
B
iological beings perceive different signals from their
environment through their sensory organs to estimate
object size and position. In this work, the
aspect of object localization and size is investigated in a detailed
simulation study based on a simplified, analytical model
of a weakly electric fish. These fishes generate a three-dimensional
dipole-like electric field for object localization and
communication. With the abstracted model of this bio-template,
different features of a voltage profile that is obtained
from an assumed sensor line (representing the voltage-sensitive
skin of fish) were identified for the determination of object
size and position. These features were categorized according
to their suitability for measurement scenarios with a stationary
or moving sensor line. On the one hand, some features are
considered individually to obtain information about the object
size and position, and on the other hand, a combination of
these features create a distance measure which is independent
of the object size.
Fish Sensory Systems
Biological beings perceive different signals from their environment
through their sensory organs by adapting to different
habitats in order to retrieve relevant information. Perception
in the respective biological sensor system therefore depends
on the habitat (the medium) and on the physical propagation
characteristics of the used signal domain. Biological sensor
systems are classically divided into long-range, short-range
and contact-based sensing domains.
Fish evolved various sensory systems of either long- or
short-range. A typical mechanical short-range sensory system
is the lateral line organ, which responds to low-frequency
vibrations and pressure differences resulting from water motions
[1]. A further example of an aquatic sensory system is
based on the ability to perceive low-frequency electric fields,
which is found in aquatic vertebrates [2].
Only a few fish species have the ability to actively generate
weak electric fields and use these to explore their environment.
In the 1950s, this so-called active electrical sense was
discovered by Lissmann who demonstrated that some fish
10
used the self-generated field to identify objects in their vicinity
[3]. Furthermore, these fishes use their self-generated fields
for communication [4]. The ability to localize objects in the
near-range of about twice the body length is called active electrolocation
[5].
A well-studied fish species that uses active electrolocation
is the weakly electric fish Gnathonemus petersii (Peter's
elephant-nose fish), illustrated schematically in Fig. 1a and
Fig. 1b. These nocturnal fish of the Mormyridae family live in
fresh water rivers and lakes of Africa. They use their active
electrical sense for orientation in the dark or in turbid waters,
as well as for foraging [6].
During active electrolocation, this fish generates a three-dimensional
dipole-like electric field surrounding their body by
specialized muscle cells located in its tail, as shown in Fig. 1.
The fish perceives the self-generated electrical signal with electroreceptors,
so-called mormyromasts, which are distributed
on the skin surface [7], as depicted schematically in green in
Fig. 1a. The electroreceptors are distributed with a higher density
on the head and on the chin appendage, also called the
Schnauzenorgan, to measure the characteristics (amplitude and
waveform change) of the electric field local to the skin [8].
In the example shown in Fig. 1a, the electric field (gray) is
distorted by a round, conductive object. The field distortion
depends on the material parameters (conductivity, permittivity)
of the object and of the surrounding fluid, as well as on the
size, shape and lateral distance of the object [8]. However, it is
important to understand that the conditions for using electric
signals for object localization in water are far from ideal, as the
electrical conductivity of water limits the localization range to
roughly twice the body length [9].
The presence of a conducting object in the vicinity of the selfgenerated
electric field of the fish, leads to a two-dimensional
image on the electroreceptive skin of the fish (shown in Fig. 1a
and Fig. 1b in blue). This image is also called an electric image
[6]. Based on the concept of electric imagery, there is a correlation
between object properties and perceived signal parameters.
Object properties such as position, distance, size, shape
and material parameters can be perceived in a complex
IEEE Instrumentation & Measurement Magazine
1094-6969/22/$25.00©2022IEEE
December 2022

Instrumentation & Measurement Magazine 25-9

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