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Fig. 3. Side-by-side comparison of biological and electronic pressure sensors. (a) The neuromast is a biological water pressure sensor, consisting of a gelatinous
cupula and hair cells whose movement are transmitted as nerve impulses along the afferent nerve fibers [7]. (b) Schematic of a standard piezoelectric water
pressure sensor, which translates water depth and motion into analog or digital signals. (c) Biological underwater stimulus pathway in which water motion
and the mechanical properties of the cupula are translated into electrical nerve impulses sent to a fish's brain. (d) Similar to their biological counterparts,
electromechanical pressure sensors respond to water pressure changes, sending electrical signals to a computer or embedded microcontroller.

flows that help or hinder upstream and downstream migrating fish.
Fish experience the flow around their bodies via a bimodal
sensory system consisting of the inner-ear and lateral line organs. Similar to an electronic inertial measurement unit, the
inner ear senses the linear and angular accelerations of the
body. The lateral line organ is made up of several arrays of neuromasts, which cover the head and run along the body and are
velocity and pressure sensitive. Each neuromast is made up of
a gel-filled cupula which bends depending on the local motion
of the water passing over the fish's body. Pressure-sensitive
neuromasts are embedded in the fish's skin in tiny canals, connected via pores to the surrounding flow. In most fish species,
they are primarily used as high-frequency (50-200 Hz) flow
detectors. Bioinspired artificial lateral lines can be created using an array of underwater pressure sensors. A side-by-side
comparison of a biological neuromast with conventional
piezoelectric pressure sensor is shown in Fig. 3.
The robust flow sensing ability of the biological lateral line
has inspired researchers to develop a wide spectrum of artificial sensing organs. Current approaches include piezoelectric,
April 2020

capacitive, thermal and optical sensors. Although the majority of research and development remains constrained to
laboratory studies, commercial implementations using artificial lateral lines are foreseen which can expand flow sensing
abilities, leading to new methods to measure and explore the
underwater environment. Current variants of pressure-sensing artificial lateral lines are even capable of flow velocity and
turbulence parameter estimation on par with a state-of-the-art
acoustic Doppler velocimeter [8].

Example of Bioinspired Sensing to
Improve Environmental Monitoring:
Fish-like Artificial Lateral Lines
Freshwater ecosystems around the world are in decline, and
fish are especially vulnerable. Fish are excellent indicators of
ecosystem health because they have evolved for specific roles
in their environment. In Europe, the major long-term threats
facing fish populations are river regulation, loss of habitat and
barriers to free migration. To address these threats, bypass
structures around river barriers, called fishways, are built. Ideally, fishways ensure access to habitats by allowing upstream

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