Adrian Klein

Determination of object position, vortex shedding frequency and flow velocity using artificial lateral line canals

Summary The lateral line system of fish consists of superficial neuromasts, and neuromasts embedded in lateral line canals. Lateral line neuromasts allow fish to sense both minute water motions and pressure gradients, thereby enabling them to detect predators and prey or to recognize and discriminate stationary objects while passing them. With the aid of the lateral line, fish can also sense vortices caused by an upstream object or by undulatory swimming movements of fish. We show here that artificial lateral line canals equipped with optical flow sensors can be used to detect the water motions generated by a stationary vibrating sphere, the vortices caused by an upstream cylinder or the water (air) movements caused by a passing object. The hydrodynamic information retrieved from optical flow sensors can be used to calculate bulk flow velocity and thus the size of the cylinder that shed the vortices. Even a bilateral sensor platform equipped with only one artificial lateral line canal on each side is sufficient to determine the position of an upstream cylinder.

Artificial lateral line canal for hydrodynamic detection

Fish use their lateral line system to detect minute water motions. The lateral line consists of superficial neuromasts and canal neuromasts. The response properties of canal neuromasts differ from those of superficial ones. Here, we report the design, fabrication, and characterization of an artificial lateral line canal system. The characterization was done under various fluid conditions, including dipolar excitation and turbulent flow. The experimental results with dipole excitation match well with a mathematical model. Canal sensors also demonstrate significantly better noise immunity compared with superficial ones. Canal-type artificial lateral lines may become important for underwater flow sensing.

The functional significance of lateral line canal morphology on the trunk of the marine teleost Xiphister atropurpureus (Stichaeidae)

We investigated the filter properties of the highly branched trunk lateral lines of the stichaeid Xiphister atropurpureus and compared them to the filter properties of simple lateral line canals. For this purpose artificial canals were constructed, some of which were fitted with artificial neuromasts. In still water, the response of a simple canal versus two types of Xiphister-like canals to a vibrating sphere stimulus were similar, as was the decrease in the responses as a function of sphere distance. Also comparable was the mechanical coupling between neighboring parts of the main canal. However, compared to the simple canal, the Xiphister-like canals showed a lower spatial resolution. Equipping artificial lateral line canals with artificial neuromasts revealed that Xiphister-like canals, i.e., lateral lines canals with tubuli that contained widely spaced pores, improve the signal-to-noise ratio in a highly turbulent environment. Even though a reduced spatial resolution is the price for this improvement, Xiphister may compensate for this compromise by having four instead of the usual single trunk lateral line canal. We suggest that lateral line canals with tubuli that contain widely spaced pores and multiple lateral line canals on each body side are an adaptation to a highly turbulent aquatic environment.

μ-biomimetic flow-sensors—introducing light-guiding PDMS structures into MEMS

In the area of biomimetics, engineers use inspiration from natural systems to develop technical devices, such as sensors. One example is the lateral line system of fish. It is a mechanoreceptive system consisting of up to several thousand individual sensors called neuromasts, which enable fish to sense prey, predators, or conspecifics. So far, the small size and high sensitivity of the lateral line is unmatched by man-made sensor devices. Here, we describe an artificial lateral line system based on an optical detection principle. We developed artificial canal neuromasts using MEMS technology including thick film techniques. In this work, we describe the MEMS fabrication and characterize a sensor prototype. Our sensor consists of a silicon chip, a housing, and an electronic circuit. We demonstrate the functionality of our μ-biomimetic flow sensor by analyzing its response to constant water flow and flow fluctuations. Furthermore, we discuss the sensor robustness and sensitivity of our sensor and its suitability for industrial and medical applications. In sum, our sensor can be used for many tasks, e.g. for monitoring fluid flow in medical applications, for detecting leakages in tap water systems or for air and gas flow measurements. Finally, our flow sensor can even be used to improve current knowledge about the functional significance of the fish lateral line.

Station Holding of Trout: Behavior, Physiology and Hydrodynamics

Trout commonly experience unsteady flows such as those caused by a stationary object exposed to running water. Instead of avoiding these flows, trout often use flow fluctuations for station holding. The behaviors associated with station holding are entraining, Karman gaiting and bow wake swimming. We investigated the swimming behavior of trout in the vicinity of a stationary or moving 2-D shaped cylinder. To uncover the sensory modalities used for station holding, we studied the behavior of intact trout and of trout whose lateral line system was partially or totally impaired in the light or under infrared illumination. We also studied the activity of the axial red swimming muscles of entraining, Karman gaiting and bow wake swimming trout and the neuronal processing of vortex information in the hindbrain of fish. Further studies showed that small motions of the caudal and/or pectoral fins are necessary to stay in preferred areas irrespective of the unsteadiness imposed by the wake of an object. Computational Fluid Dynamics simulations were carried out to uncover the forces that allow trout station holding with a minimum of energy expenditure.

Micro-machined flow sensors mimicking lateral line canal neuromasts

Fish sense water motions with their lateral line. The lateral line is a sensory system that contains up to several thousand mechanoreceptors, called neuromasts. Neuromasts occur freestanding on the skin and in subepidermal canals. We developed arrays of flow sensors based on lateral line canal neuromasts using a biomimetic approach. Each flow sensor was equipped with a PDMS (polydimethylsiloxane) lamella integrated into a canal system by means of thick- and thin-film technology. Our artificial lateral line system can estimate bulk flow velocity from the spatio-temporal propagation of flow fluctuations. Based on the modular sensor design, we were able to detect flow rates in an industrial application of tap water flow metering. Our sensory system withstood water pressures of up to six bar. We used finite element modeling to study the fluid flow inside the canal system and how this flow depends on canal dimensions. In a second set of experiments, we separated the flow sensors from the main stream by means of a flexible membrane. Nevertheless, these biomimetic neuromasts were still able to sense flow fluctuations. Fluid separation is a prerequisite for flow measurements in medical and pharmaceutical applications.

Function of lateral line canal morphology.

Fish perceive water motions and pressure gradients with their lateral line. Lateral line information is used for prey detection, spatial orientation, predator avoidance, schooling behavior, intraspecific communication and station holding. The lateral line of most fishes consists of superficial neuromasts (SNs) and canal neuromasts (CNs). The distribution of SNs and CNs shows a high degree of variation among fishes. Researchers have speculated for decades about the functional significance of this diversity, often without any conclusive answers. Klein et al. (2013) examined how tubules, pore number and pore patterns affect the filter properties of lateral line canals in a marine teleost, the black prickleback (Xiphister atropurpureus). A preliminary mathematical model was formulated and biomimetic sensors were built. For the present study the mathematical model was extended to understand the major underlying principle of how canal dimensions influence the filter properties of the lateral line. Both the extended mathematical model and the sensor experiments show that the number and distribution of pores determine the spatial filter properties of the lateral line. In an environment with little hydrodynamic noise, simple and complex lateral line canals have comparable response properties. However, if exposed to highly turbulent conditions, canals with numerous widely spaced pores increase the signal to noise ratio significantly.

Lateral line canal morphology and signal to noise ratio

The lateral line system of fish is important for many behaviors, including spatial orientation, prey detection, shoaling, intra specific communication and entraining. The smallest sensory unit of the lateral line is the neuromast that occurs free standing on the skin and in fluid filled canals. With aid of the lateral line fish perceive minute water motions. In their natural habitat fish are not only faced with biotic water motion but also with the abiotic fluctuations caused by various inanimate sources. The detection of meaningful signals is crucial for survival, and therefore animals should be able to separate meaningful signals from noise. Fishes live in various habitats (e.g. in still water or in running water). Therefore it is not surprising that the number and distribution of neuromasts as well as canal dimension, canal shape and canal branching patterns differ among fish species. We studied how lateral line canal parameters influence the filter properties of lateral line canals. To do so we exposed artificial lateral line canals, equipped with artificial neuromasts (sensors), to the vortex street shed by a submerged cylinder and to air bubble noise. We found that certain canal parameters significantly can enhance the signal to noise ratio.

Computational Fluid Dynamics Analysis of the Fossil Crinoid Encrinus liliiformis (Echinodermata: Crinoidea)

Crinoids, members of the phylum Echinodermata, are passive suspension feeders and catch plankton without producing an active feeding current. Today, the stalked forms are known only from deep water habitats, where flow conditions are rather constant and feeding velocities relatively low. For feeding, they form a characteristic parabolic filtration fan with their arms recurved backwards into the current. The fossil record, in contrast, provides a large number of stalked crinoids that lived in shallow water settings, with more rapidly changing flow velocities and directions compared to the deep sea habitat of extant crinoids. In addition, some of the fossil representatives were possibly not as flexible as today’s crinoids and for those forms alternative feeding positions were assumed. One of these fossil crinoids is Encrinus liliiformis, which lived during the middle Triassic Muschelkalk in Central Europe. The presented project investigates different feeding postures using Computational Fluid Dynamics to analyze flow patterns forming around the crown of E. liliiformis, including experimental validation by Particle Image Velocimetry. The study comprises the analysis of different flow directions, velocities, as well as crown orientations. Results show that inflow from lateral and oral leads to direct transport of plankton particles into the crown and onto the oral surface. With current coming from the “rear” (aboral) side of the crinoid, the conical opening of the crown produces a backward oriented flow in its wake that transports particles into the crown. The results suggest that a conical feeding position may have been less dependent on stable flow conditions compared to the parabolic filtration fan. It is thus assumed that the conical feeding posture of E. liliiformis was suitable for feeding under dynamically changing flow conditions typical for the shallow marine setting of the Upper Muschelkalk.

The impact of infrared radiation in flight control in the Australian “firebeetle” Merimna atrata

Infrared (IR) receptors are rare in insects and have only been found in the small group of so-called pyrophilous insects, which approach forest fires. In previous work the morphology of the IR receptors and the physiology of the inherent sensory cells have been investigated. It was shown that receptors are located on the thorax and the abdomen respectively and show an astounding diversity with respect to structure and the presumed transduction mechanism. What is completely missing, however, is any behavioral evidence for the function of the IR receptors in pyrophilous insects. Here we describe the responses of the Australian “firebeetle”, Merimna atrata to IR radiation. Beetles in a restrained flight were laterally stimulated with IR radiation of an intensity 20% above a previously determined electrophysiological threshold of the IR organs (40 mW/cm2). After exposure, beetles always showed an avoidance response away from the IR source. Reversible ablation experiments showed that the abdominal IR receptors are essential for the observed behavior. Tests with weaker IR radiation (11.4 mW/cm2) also induced avoidance reactions in some beetles pointing to a lower threshold. In contrast, beetles were never attracted by the IR source. Our results suggest that the IR receptors in Merimna atrata serve as an early warning system preventing an accidental landing on a hot surface. We also tested if another fire specific stimulus, the view of a large smoke plume, influenced the flight. However, due to an unexpected insensitivity of the flying beetles to most visual stimuli results were ambiguous.