23 research outputs found

    Design and Implementation of Bio-inspired Underwater Electrosense

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    Underwater electrosense, manipulating underwater electric field for sensing purpose, is a growing technology bio-inspired by weakly electric fish that can navigate in dark or cluttered water. We studied its theoretical foundations and developed sophisticated sensing algorithms including some first-introduced techniques such as discrete dipole approximation (DDA) and convolutional neural networks (CNN), which were tested and validated by simulation and a planar sensor prototype. This work pave a solid way to applications on practical underwater robots

    Animal-Robot Interactions: Electrocommunication, Sensory Ecology, and Group Dynamics in a Mormyrid Weakly Electric Fish

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    Mormyrid weakly electric fish possess a specialized electrosensory system. During the process of active electrolocation, these animals perceive self-generated electric organ dis-charges (EOD) and are thereby able to detect objects in their nearby environment. The EOD is a short, biphasic pulse, which is simultaneously used to communicate with conspe-cifics. There are two principles according to which information exchange occurs during electrocommunication. The waveform of the EOD constitutes a relatively stable identity marker that signals species, gender, and status of an individual. In contrast, the temporal sequence of inter-discharge intervals (IDI) is highly variable and encodes context-specific information. Modifications of IDI-duration not only alter the instantaneous discharge fre-quency but also enable the generation of specific signaling patterns and interactive dis-charge sequences. One such interactive discharge behavior is the so-called echo response, during which a fish responds with a constant latency of only a few milliseconds to the EOD of a conspecific. Animals can synchronize their signaling sequences by mutually generating echoes to each other's signals over a coherent period. Although active electrolocation and electrocommunication are mediated by different types of electroreceptor organs and neural pathways, an unambiguous assignment of electromotor behavior to only one of the two functions is often problematic. In this thesis, the significance of IDI-based signaling sequences during motor and electro-motor interactions of the mormyrid fish Mormyrus rume proboscirostris were investigated. To this end, different electrical playback sequences of species-specific EODs were generated via mobile fish dummies, and the motor and electromotor responses of live fish were analyzed. In Part One of this thesis, electrocommunication strategies of the fish were analyzed, and particularly the functions of double pulses, discharge regularizations, and echo responses were examined in an adaptive context. Double pulses were classified as an aggressive mo-tivation signal, whereas regularizations may have a communicative function during the early stages of the sequential assessment of a potential opponent. In this context, discharge synchronization by means of echo responses may enable a mutual assessment for the net benefit of both contestants. Because echo responses occur in various behavioral contexts, and artificial echoes of the dummy evoked increased echoing by the fish, it was hypothesized that the echo response serves a more general purpose by enabling mutual allocation of social attention between two fish. In Part Two of this thesis, a biomimetic robotic fish was designed to investigate the senso-ry basis on which fish followed the dummy. It was shown that electrical playback signals induced following-behavior in live fish, whereas biomimetic motility patterns had no ef-fect. By subsequently reducing the mobile dummy to only the electric signaling sequence from the perspective of the fish, it could be shown that passive perception of electrical communication signals is also involved in mediating the spatial coordination of social in-teractions. This passive perception is likely mediated by the same electroreceptor organs that are used during electrocommunication. The EOD can therefore be considered to be an essential social stimulus that makes it possible to integrate a dummy into a group of weak-ly electric fish as an artificial conspecific. The influence of an interactively signaling mobile dummy fish on small groups of up to four individuals was investigated in Part Three of this thesis. Typical schooling behavior was a rare occurrence in this context. However, EOD-synchronizations through mutual echo responses between two fish, or between a fish and the interactive dummy, were fre-quently observed during social interactions in small groups. Motor interactions during synchronization episodes supported the hypothesis that mormyrids may use discharge synchronizations between individuals to allocate social attention, and the echo response may thus adopt a particularly useful function during communication in groups.Schwach elektrische Fisch aus der Familie der Mormyriden verfügen über ein spezialisier-tes elektrosensorisches Sinnessystem. In einem Prozess, der als aktive Elektroortung be-zeichnet wird, sind diese Tiere in der Lage, selbstgenerierte elektrische Organentladungen (EOD) wahrzunehmen, und dadurch Objekte in ihrer unmittelbaren Nähe zu detektieren. Das EOD ist ein kurzer bipolarer Puls, der gleichzeitig auch zur Kommunikation mit Artge-nossen dient. Informationsaustausch während der Elektrokommunikation basiert auf zwei verschiedenen Prinzipien: Die Wellenform des EOD stellt einen relativ konstanten Identi-tätsmarker dar, der beispielsweise Art, Geschlecht und Status eines Individuums signali-siert. Die zeitliche Abfolge der Intervalle zwischen den EODs ist hingegen höchst variabel und kodiert kontextspezifische Information. Durch Modifikation der Intervalldauer ändert sich nicht nur die Entladungsfrequenz, sondern es können auch spezifische Signalmuster und interaktive Entladungssequenzen generiert werden. Ein interaktives Entladungsver-halten stellt beispielsweise die Echoantwort dar, bei der ein Fisch mit einer konstanten Latenz von wenigen Millisekunden auf das EOD eines Artgenossen reagiert. Zwei Tiere können ihre Entladungssequenzen synchronisieren, indem sie ihre Signale über einen kohärenten Zeitraum gegenseitig mit Echos beantworten. Obwohl aktive Elektroortung und Elektrokommunikation über unterschiedliche Rezeptororgansysteme und neuronale Pfade vermittelt werden, ist eine eindeutige Zuordnung der elektromotorischen Verhal-tensäußerungen der Fische zu nur einer der beiden Funktionen oft problematisch. In der vorliegenden Arbeit wurde die Bedeutung intervallbasierter EOD-Sequenzen für motorische und elektromotorische Interaktionen des Mormyriden Mormyrus rume proboscirostris erforscht. Hierzu wurden verschiedene elektrische Playbacksequenzen artspezifischer EODs generiert und durch mobile Fischattrappen wiedergegeben. Die mo-torischen und elektromotorischen Verhaltensreaktionen der Fische wurden analysiert. Im ersten Teil der Arbeit wurden Elektrokommunikationsstrategien der Fische analysiert und die adaptive Funktion insbesondere von Doppelpulsen, Entladungsregularisierungen und Echoantworten untersucht. Doppelpulse wurden als aggressives Motivationssignal kategorisiert, wohingegen die Kommunikationsfunktion von Regularisierungen im gegen-seitigen Einschätzen zu Beginn einer kompetitiven Begegnung zu liegen scheint. Entla-dungssynchronisation durch gegenseitige Echoantworten kann dabei eine Einschätzung des Gegenübers zum Vorteil beider Parteien erleichtern. Da Echoantworten in verschiede-nen Verhaltenssituationen auftreten und artifizielle Echoantworten der Attrappe vermehrt zu Echos vonseiten der Fische führten, wurde postuliert, dass die Echoantwort eine generellere Funktion bei der Fokussierung gegenseitiger sozialer Aufmerksamkeit über-nehmen kann. Im zweiten Teil der Arbeit wurde ein biomimetischer Fischroboter konstruiert, um zu untersuchen, auf welcher sensorischen Grundlage die Fische der Attrappe folgen. Es konnte gezeigt werden, dass elektrische Playbacksignale, nicht aber biomimetische Bewe-gungsmuster, Folgeverhalten der Fische induzieren. In einem weiteren Schritt konnte durch die Reduktion der Attrappe auf die elektrischen Signalsequenzen aus der Perspektive der Versuchsfische gezeigt werden, dass passive Wahrnehmung elektrischer Kommu-nikationssignale auch bei der räumlichen Koordination sozialer Interaktionen von Bedeu-tung ist. Dies wird mutmaßlich über die gleichen Rezeptororgane vermittelt, die auch für die Elektrokommunikation verantwortlich sind. Das EOD kann daher als ein soziales Signal betrachtet werden, das es ermöglicht, eine Attrappe als künstlichen Artgenossen in eine Gruppe schwach elektrischer Fische zu integrieren. Der Einfluss einer elektrisch interaktiven mobilen Fischattrappe auf kleine Gruppen von bis zu vier Individuen wurde im dritten Teil der Arbeit getestet. Typisches Schwarmver-halten konnte in diesem Zusammenhang nur selten beobachtet werden. In kleinen Gruppen kam es während sozialer Interaktionen jedoch häufig zu EOD-Synchronisationen durch Echoantworten zwischen zwei Fischen, oder zwischen einem Fisch und der interaktiven Attrappe. Motorische Verhaltensinteraktionen im Zeitraum dieser Synchronisationen stützen die Hypothese, dass Mormyriden durch elektrische Entladungssynchronisation soziale Aufmerksamkeit zwischen Individuen herstellen können, und die Echoantwort somit besonders in Gruppen eine nützliche Kommunikationsfunktion übernehmen kann

    Shape recognition and classification in electro-sensing

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    This paper aims at advancing the field of electro-sensing. It exhibits physical mechanisms underlying shape perception for weakly electric fish. These fish orient themselves at night in complete darkness by using their active electrolocation system. They generate a stable, relatively high-frequency, weak electric field and perceive the transdermal potential modulations caused by a nearby target with different electromagnetic properties than the surrounding water. The main result of this paper is a scheme that explains how weakly electric fish might identify and classify a target, knowing in advance that the latter belongs to a certain collection of shapes. The scheme is designed to recognize living biological organisms. It exploits the frequency dependence of the electromagnetic properties of living organisms, which comes from the capacitive effects generated by the cell membrane structure. When measurements are taken at multiple frequencies, the fish might use the spectral content of the perceived transdermal potential modulations to classify the living target. inverse conductivity problem | polarization tensor | shape classification I n the turbid rivers of Africa and South America, some species of fish generate a stable, relatively high-frequency (0.1-10 kHz), weakly electric (≤100 mV/cm) field that is not enough for defense against predators. In 1958, Lissmann and Machin (1) discovered that the emitted electrical signal is in fact used for active electro-sensing. The weakly electric fish have thousands of receptors at the surface of their skins. A nearby target with different admittivity than the surrounding water perturbs the transdermal potential induced by the electric organ discharge (2, 3). Targets with large permittivity cause appreciable phase shifts, which can be measured by receptors called T-type units (4). It is an important input for the fish, and thus it will be the central point in this paper for shape classification. Active electro-sensing has driven an increasing number of experimental, behavioral, biological, and computational studies since Lissmann and Machin's work (5-12). Behavioral experiments have shown that weakly electric fish are able to locate a target (12) and discriminate between targets with different shapes (13) or/and electric parameters (conductivity and permittivity) (14). The growing interest in electro-sensing could be explained not only by the curiosity of discovering a sixth sense, electric perception, that is not accessible by our own senses, but also by potential bio-inspired applications in underwater robotics. It is challenging to equip robots with electric perception and provide them, by mimicking weakly electric fish, with imaging and classification capabilities in dark or turbid environments Mathematically speaking, the problem is to locate the target and identify its shape and material parameters given the current distribution over the skin. Due to the fundamental ill-posedness of this imaging problem, it is very intriguing to see how much information weakly electric fish are able to recover. The electric field perturbation due to the target is a complicated highly nonlinear function of its shape, admittivity, and distance from the fish. Thus, understanding analytically this electric sensing is likely to give us insight in this regard (5-7, 9, 13, 18, 21). Although locating targets from the electric field perturbations induced on the skin of the fish is now understood (17, 22), identifying and classifying their shapes are considered to be some of the most challenging problems in electro-sensing. Although the neuroethology of these fish has been significantly advanced recently (see ref. 23 and references therein), the neural mechanisms encoding the shape of a target are far beyond the scope of our study. Rather, this work focuses on the physical feasibility of such a process, which was not explained before. In ref. 22, a rigorous model for the electro-location of a target around the fish was derived. Using the fact that the electric current produced by the electric organ is time harmonic with a known fundamental frequency, a space-frequency location search algorithm was introduced. Its robustness with respect to measurement noise and its sensitivity with respect to the number of frequencies, the number of sensors, and the distance to the target were illustrated. In the case of disk-and ellipse-shaped targets, the conductivity, the permittivity, and the size of the targets can be reconstructed separately from multifrequency measurements. Such measurements have been used successfully in transadmittance scanners of breast tumors (24-26). The main result of this paper is the presentation and analysis of a scheme that allows to recognize and classify targets from multifrequency measurements of the electric field perturbations induced by the targets. To explain how the shape information is encoded in measured data, we distinguish two cases: recognition of nonbiological targets and recognition of living organisms. Most of the nonbiological objects have very low permittivities, and therefore, their electromagnetic parameters are frequency independent. Living targets have frequency-dependent electromagnetic parameters because their cell membrane structures induce capacitive effects (27), and therefore it is possible to exploit the spectral content of the data. We will mostly focus our attention on the second situation, but we first explain the strategy for the first one. Our model in this paper of the weakly electric fish relies on differential imaging, i.e., by forming an image from the perturbations of the field due to the target. The method is based on the multipole expansion for the perturbations of the electric field induced by a nearby target in terms of the characteristic size of the target. The asymptotic expansion derived in refs. 22 and 28 generalizes Rasnow's equation (29) in two directions: (i) it is a higher-order approximation of the effect of a nearby target, and it is valid for an arbitrary shape and admittivity contrast; and (ii) it also takes into account the body of the fish. As was first shown in ref. 22, one can reduce the Significance Weakly electric fish orient themselves in complete darkness by using their active electrolocation system. They generate a weak electric field and perceive the transdermal potential modulations caused by a nearby target with different electromagnetic properties than the surrounding water. The main result of this paper is a scheme that explains how weakly electric fish might identify and classify living biological organisms. This scheme exploits the frequency dependence of the electromagnetic properties of living organisms, which comes from the capacitive effects generated by the cell membrane structure

    Modeling the sequential pattern variability of the electromotor command system of pulse electric fish

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    This study was supported by AEI/FEDER grants TIN2017-84452-R, PID2020-114867RB-I00, and PGC2018-095895-B-I0

    Mathematics of biomimetics for active echo- and electro-sensing

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    Active sensing animals may inspire the development of new technologies that mimic their sensing behavior. Electric fish, for instance, orient themselves at night in complete darkness by using their active electro-sensing system. They generate a stable, relatively high-frequency, weak electric field and perceive the transdermal potential modulations caused by nearby targets with different electromagnetic properties than the surrounding water. Since they have an electric sense that allows underwater navigation, target classification and intraspecific communication, they are privileged animals for bio-inspiring man-built autonomous systems. Bats, on the other hand, process the reflected echoes due to the presence of acoustic inclusions for echolocation. In general, they use acoustic waves for most of the perceptual tasks, that range from hunting to navigating. This thesis introduces premier algorithms in electro-sensing and echo-sensing. The weakly electric fish is able to retrieve much more information about the target by approaching it. To mimic this behavior, an innovative (real-time) multi-scale method for target classification in electro-sensing is presented. The method is based on a family of transform-invariant shape descriptors computed from generalized polarization tensors (GPTs) reconstructed at multiple scales. The evidence provided by the different descriptors at each scale is fused using Dempster-Shafer Theory. Numerical simulations show that the recognition algorithm we proposed performs undoubtedly well and yields a robust classification. For real-world applications, inhomogeneous targets have to be identified. The shape descriptor-based classification algorithm is extended in order to consider inhomogenous material parameters. The approach is based on new invariants for the contracted generalized polarization tensors associated with inhomogeneous objects. The numerical simulations show that by comparing these invariants with those in a dictionary of precomputed homogeneous and inhomogeneous targets, one can successfully classify the inhomogeneous target. Another problem concerns intraspecific electro-communication for weakly electric fish. In particular, a description on how the fish circumvent the jamming issue for both electro-communication and active electro-sensing is presented. The main result is a real-time tracking algorithm, which provides a new approach to the communication problem. It finds a natural application in robotics, where efficient communication strategies are needed to be implemented by bio-inspired underwater robots. The concept of time-dependent polarization tensors (TDPTs) for the wave equation associated to a diametrically small acoustic inclusion, with constitutive parameters different from those of the background and size smaller than the operating wavelength, is used to mimic the echo-sensing capabilities of a static bat. Firstly, the solution to the Helmholtz equation is considered, and a rigorous systematic derivation of a complete asymptotic expansion of the scattered field due to the presence of the inclusion is presented. Then, by applying the Fourier transform, the corresponding time-domain expansion is readily obtained after truncating the high frequencies. The new concept of TDPTs is shown to be promising for performing imaging. Numerical simulations are presented, showing that the TDPTs reconstructed from noisy measurements allow to image fine shape details of the inclusion

    Engineering derivatives from biological systems for advanced aerospace applications

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    The present study consisted of a literature survey, a survey of researchers, and a workshop on bionics. These tasks produced an extensive annotated bibliography of bionics research (282 citations), a directory of bionics researchers, and a workshop report on specific bionics research topics applicable to space technology. These deliverables are included as Appendix A, Appendix B, and Section 5.0, respectively. To provide organization to this highly interdisciplinary field and to serve as a guide for interested researchers, we have also prepared a taxonomy or classification of the various subelements of natural engineering systems. Finally, we have synthesized the results of the various components of this study into a discussion of the most promising opportunities for accelerated research, seeking solutions which apply engineering principles from natural systems to advanced aerospace problems. A discussion of opportunities within the areas of materials, structures, sensors, information processing, robotics, autonomous systems, life support systems, and aeronautics is given. Following the conclusions are six discipline summaries that highlight the potential benefits of research in these areas for NASA's space technology programs

    Study of sequential information processing in electroreception through modelling and closed-loop stimulation techniques

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    Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Escuela Politécnica Superior, Departamento de Ingenieria Informática. Fecha de Lectura: 20-01-202

    Current efficient integrated architecture for common mode rejection sensitive neural recordings

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    In the last decade we have seen a significant growth of research and potential applications of electronic circuits that interact with the nervous system, in a wide range of applications, from basic neuroscience research to medical clinic, or from the entertainment industry to transport services. The real time acquisition and analysis of brain signals, either through wearable electroencephalography (EEG) or invasive or implantable recordings, in order to perform actions (brain machine interface) or to understand aspects of brain operation, has become scientifically and technologically feasible. This thesis aims to support neural recording applications with low noise, currentefficiency and high common-mode rejection ratio (CMRR) as main features of the recording system. One emblematic example of these applications in the neuroscience domain is the weakly electric fish neural activity recording, where the interference produced by the discharge of the fish electric organ is a key factor. Another example, from the implantable devices domain, is the nerve activity recorded with cuff electrodes, where the desired signal is interfered by electromyographic potentials generated by muscles near the cuff. In these cases, the amplitude of the interfering signals, which mainly appear in common mode, is several orders of magnitude higher than the amplitude of the signals of interest. Therefore, this thesis introduces a novel integrated neural preamplifier architecture targeting CMRR sensitive neural recording applications. The architecture is presented and analyzed in depth, deriving the preamplifier transfer function and the main design equations. We present a detailed analysis of a technique for blocking the input dc component and setting the high-pass frequency without using MOS pseudo-resistors. One of the main contributions of this work is the overall architecture coupled with an efficient and simple single-stage circuit for the preamplifier main transconductor. A fully-integrated neural preamplifier, which performs well in line with the state-ofthe-art of the field while providing enhanced CMRR performance, was fabricated in a 0.5 um CMOS process. Results from measurements show that the measured gain is 49.5 dB, bandwidth ranges from 13 Hz to 9.8 kHz, CMRR is very high (greater than 87 dB), and it is achieved jointly with a remarkable low noise (1.88 uVrms) and current-efficiency (NEF = noise efficiency factor = 2.1). A second version of the preamplifier with one external capacitor achieves a high-pass frequency of 0.1 Hz while keeping the performance of the fully-integrated version. In addition, we present in-vivo measurements made with the proposed architecture in a weakly electric fish (Gymnotus omarorum), showing the ability of the preamplifier to acquire neural signals from high amplitude common mode interference in an unshielded environment. This was the first in-vivo testing of a neural recording integrated circuit designed in Uruguay done in a local lab. Furthermore, signals recorded with our unshielded low-power battery-powered preamplifier perfectly match with those of a shielded commercially-available amplifier (ac-plugged, without power restrictions). To the best of our knowledge, the proposed preamplifier is the best option for applications that simultaneously need low noise, high CMRR and current-efficiency. Furthermore, in this thesis we applied the aforementioned architecture to bandpass biquad filters, specially but not only, to those with differential input. The new architecture provides a significant reduction in consumption (up to 30%) and/or makes it possible to block a higher level of dc at the input (up to the double, without using decoupling capacitors). Next, we applied the novel architecture to the design of the different stages of an integrated programmable analog front-end. Results from simulations shows that the gain is programmable between 57 dB and 99 dB, the low-pass frequency is programmable between 116 Hz and 5.2 kHz, the maximum power consumption is 11.2 uA and the maximum equivalent input-referred noise voltage is 1.87 uVrms. The comparison between our front-end and other works in the state-of-the-art shows that our front-end presents the best results in terms of CMRR and noise, has the greatest value of gain and equals the best NEF reported. Finally, some system-level topics were addressed during this thesis, including the design and implementation of three prototypes of end-to-end wireless biopotentials recording systems based on off-the-shelf components. Developing and applying circuits, systems and methods, for synchronized largescale monitoring of neural activity, sensory images, and behavior, would produce a dynamic picture of the brain function, which is essential for understanding the brain in action. In this context, we hope that the present thesis become our first step to further contribute to this area

    Status of the freshwater fishes of the Philippines

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