A method for characterizing the biodiversity in bat pinnae as a basis for engineering analysis

A quantitative analysis of the interspecific variability between beamforming baffle shapes in the biosonar system of bats is presented. The data set analyzed consisted of 100 outer ear (pinna) shapes from at least 59 species. A vector-space representation suitable for principal component analysis (PCA) was constructed by virtue of a transform of the pinna surfaces into cylindrical coordinates. The central axis of the cylindrical transform was found by minimizing a potential function. The shapes were aligned by means of their respective axes and their center of gravity. The average pinna of the sample was a symmetrical, obliquely truncated horn. The first seven eigenvalues accounted already for two-thirds of the variability around the mean, which indicates that most of the biodiversity in the bat pinna can be understood in a more low-dimensional space. The first three principal components show that most of the variability of the bat pinna sample is in terms of opening angle, left-right asymmetry, and selective changes in width at the top or the bottom of the pinna. The beampattern effects of these individual components have been characterized. These insights could be used to design bioinspired beamforming devices from the diversity in biosonar.     

Dolphin sonar--modelling a new receiver concept

Observations suggest that dolphin sonars function well in the very shallow, reverberant, near-shore region of the ocean, and significantly out-perform man-made systems under such conditions. The echolocation characteristics of many small cetaceans have been measured directly and the high performance of biosonar systems is not in question, but explanations for their resolution, target detection, localization and tracking abilities are inadequate and deserve further investigation. The dolphin's lower jaw has been identified as part of an echo-receptor, and several hypotheses have been proposed to explain this. In one of these, the regularity of dolphin teeth was considered as a sonar array. This paper explores the physics of such systems with models based on established radar and sonar principles, and using data from various dolphin species. The insights gained from this modelling then lead to speculative proposals for new sonar receiver concepts that may have advantages over more conventional designs in shallow water operation.     

Special section on biomimetics of movement

Movement in biology is an essential aspect of survival for many organisms, animals and plants. Implementing movement efficiently to meet specific needs is a key attribute of natural living systems, and can provide ideas for man-made developments. If we had to find a subtitle able to essentially convey the aim of this special section, it could read as follows: 'taking inspiration from nature for new materials, actuators, structures and controls for systems that move'. Our world is characterized by a huge variety of technical, engineering systems that move. They surround us in countless products that integrate actuators for different kinds of purposes. Basically, any kind of mechatronic system, such as those used for consumer products, machines, vehicles, industrial systems, robots, etc, is based on one or more devices that move, according to different implementations and motion ranges, often in response to external and internal stimuli. Despite this, technical solutions to develop systems that move do not evolve very quickly as they rely on traditional and well consolidated actuation technologies, which are implemented according to known architectures and with established materials. This fact limits our capability to overcome challenges related to the needs continuously raised by new fields of application, either at small or at large scales. Biomimetics-based approaches may provide innovative thinking and technologies in the field, taking inspiration from nature for smart and effective solutions. In an effort to disseminate current advances in this field, this special section collects some papers that cover different topics. A brief synopsis of the content of each contribution is presented below. The first paper, by Lienhard et al [1], deals with bioinspiration for the realization of structural parts in systems that passively move. It presents a bioinspired hingeless flapping mechanism, considered as a solution to the kinematics of deployable systems for architectural structures. The approach relies on structural elasticity to replace the need for local hinges. To this end, the authors have used fibre-reinforced polymers combining high tensile strength with low bending stiffness. The solution favours lower structural complexity as well as higher design versatility. Bioinspiration from the elastic kinetics of plants is a central pillar of the paper, which highlights the interrelation of form, actuation and kinematics in those natural systems. The second paper, by Nakata et al [2], deals with bioinspired systems that actively move, and, more specifically, fly. The paper is about the aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle conceived to fly in a Reynolds number regime used by most natural flyers, including insects, bats and birds. The paper presents a study of the flexible wing aerodynamics of the flapping vehicle by combining an in-house computational fluid dynamic model with wind tunnel experiments. In particular, the developed model is shown to be able to predict unsteady aerodynamics in terms of vortex and wake structures and their relationship with aerodynamic force generation. Simulations are validated by wind tunnel experiments, confirming the effectiveness of the adopted design solutions, as well as the importance of wing flexibility in designing small flapping-wing vehicles. The third paper, by Annunziata et al [3], deals with bioinspired control strategies for systems that move. In particular, the paper describes approaches to increase the stiffness variability in multi-muscle driven joints. Different strategies for simultaneous control of torque and stiffness in a hinge joint actuated by two antagonistic muscle pairs are presented. The proposed strategies combine torque and stiffness control by co-activation with approaches based on activation overflow and inverse modelling. Extensive simulations are performed and described to assess the control efficacy. In the fourth paper, Merker et al [4] present a study on stable walking with asymmetric legs. The authors are concerned with the need to clarify to what extent differences in the leg function of contralateral limbs can be tolerated during walking or running. A bipedal spring-mass model simulating walking with compliant legs is used to show that even remarkable differences between contralateral legs can not only be tolerated, but may also introduce advantages to the robustness of the system dynamics. This study might contribute to shedding light on the stability of asymmetric leg walking, including the potential benefits of asymmetry, with possible implications for design of prosthetic or orthotic systems. The last two papers of this special section deal with active bioinspired systems driven by new actuators made of smart materials. In particular, the paper authored by Rossi et al [5] presents an underwater fish-like robot based on bending structures driven by shape memory alloys. These kinds of actuators are used to bend the backbone of the fish, which in turn causes a change in the curvature of the fish body. The paper describes the mechanisms by which standard swimming patterns can be reproduced with the proposed design, and show characterizations in terms of the actuation speed and position accuracy of prototype systems. The last paper, by Carpi et al [6], presents an overview on ionic- and electronic-type electromechanically active polymer actuators as artificial muscles for bioinspired applications. The electrical responsiveness and numerous functional and structural properties that these materials and actuators have in common with natural muscles are shown to be the key motivation by which they are studied as artificial muscles for a huge variety of possible uses. The authors describe the fundamental aspects of relevant technologies and emphasize how after several years of basic research, electromechanically active polymer actuators are today facing their important initial transition from academia into commercialization. In conclusion, we hope that the selection of papers in this special section might help to provide readers with a balanced overview, through examples on the relevant fundamental aspects, materials, actuators, structures, controls and on their effective integration, in order to develop approaches which will be successful in 'taking inspiration from nature for systems that move'. References [1] Lienhard J, Schleicher S, Poppinga S, Masselter T, Milwich M, Speck T and Knippers J 2011 Flectofin: a hingeless flapping mechanism inspired by nature Bioinsp. Biomim. 6 045001 [2] Nakata T, Liu H, Tanaka Y, Nishihashi N, Wang X and Sato A 2011 Aerodynamics of a bio-inspired flexible flapping-wing micro air vehicle Bioinsp. Biomim. 6 045002 [3] Annunziata S, Paskarbeit J and Schneider A 2011 Novel bioinspired control approaches to increase the stiffness variability in multi-muscle driven joints Bioinsp. Biomim. 6 045003 [4] Merker A, Rummel J and Seyfarth A 2011 Stable walking with asymmetric legs Bioinsp. Biomim. 6 045004 [5] Rossi C, Colorado J, Coral W and Barrientos A 2011 Bending continuous structures with SMAs: a novel robotic fish design Bioinsp. Biomim. 6 045005 [6] Carpi F, Kornbluh R, Sommer-Larsen P and Alici G 2011 Electroactive polymer actuators as artificial muscles: are they ready for bioinspired applications? Bioinsp. Biomim. 6 045006.     

Keeping returns optimal: gain control exerted through sensitivity adjustments in the harbour porpoise auditory system

Animals that use echolocation (biosonar) listen to acoustic signals with a large range of intensities, because echo levels vary with the fourth power of the animal's distance to the target. In man-made sonar, engineers apply automatic gain control to stabilize the echo energy levels, thereby rendering them independent of distance to the target. Both toothed whales and bats vary the level of their echolocation clicks to compensate for the distance-related energy loss. By monitoring the auditory brainstem response (ABR) during a psychophysical task, we found that a harbour porpoise (Phocoena phocoena), in addition to adjusting the sound level of the outgoing signals up to 5.4 dB, also reduces its ABR threshold by 6 dB when the target distance doubles. This self-induced threshold shift increases the dynamic range of the biosonar system and compensates for half of the variation of energy that is caused by changes in the distance to the target. In combination with an increased source level as a function of target range, this helps the porpoise to maintain a stable echo-evoked ABR amplitude irrespective of target range, and is therefore probably an important tool enabling porpoises to efficiently analyse and classify received echoes.     

Click-based echolocation in bats: not so primitive after all

Echolocating bats of the genus Rousettus produce click sonar signals, using their tongue (lingual echolocation). These signals are often considered rudimentary and are believed to enable only crude performance. However, the main argument supporting this belief, namely the click’s reported long duration, was recently shown to be an artifact. In fact, the sonar clicks of Rousettus bats are extremely short, ~50–100 μs, similar to dolphin vocalizations. Here, we present a comparison between the sonar systems of the ‘model species’ of laryngeal echolocation, the big brown bat (Eptesicus fuscus), and that of lingual echolocation, the Egyptian fruit bat (Rousettus aegyptiacus). We show experimentally that in tasks, such as accurate landing or detection of medium-sized objects, click-based echolocation enables performance similar to laryngeal echolocators. Further, we describe a sophisticated behavioral strategy for biosonar beam steering in clicking bats. Finally, theoretical analyses of the signal design—focusing on their autocorrelations and wideband ambiguity functions—predict that in some aspects, such as target ranging and Doppler-tolerance, click-based echolocation might outperform laryngeal echolocation. Therefore, we suggest that click-based echolocation in bats should be regarded as a viable echolocation strategy, which is in fact similar to the biosonar used by most echolocating animals, including whales and dolphins.     

Another Lesson from Plants: The Forward Osmosis-Based Actuator

Osmotic actuation is a ubiquitous plant-inspired actuation strategy that has a very low power consumption but is capable of generating effective movements in a wide variety of environmental conditions. In light of these features, we aimed to develop a novel, low-power-consumption actuator that is capable of generating suitable forces during a characteristic actuation time on the order of a few minutes. Based on the analysis of plant movements and on osmotic actuation modeling, we designed and fabricated a forward osmosis-based actuator with a typical size of 10 mm and a characteristic time of 2–5 minutes. To the best of our knowledge, this is the fastest osmotic actuator developed so far. Moreover, the achieved timescale can be compared to that of a typical plant cell, thanks to the integrated strategy that we pursued by concurrently addressing and solving design and material issues, as paradigmatically explained by the bioinspired approach. Our osmotic actuator produces forces above 20 N, while containing the power consumption (on the order of 1 mW). Furthermore, based on the agreement between model predictions and experimental observations, we also discuss the actuator performance (including power consumption, maximum force, energy density and thermodynamic efficiency) in relation to existing actuation technologies. In light of the achievements of the present study, the proposed osmotic actuator holds potential for effective exploitation in bioinspired robotics systems.     

PORPOISE CLICKS FROM A SPERM WHALE NOSE—CONVERGENT EVOLUTION OF 130 KHZ PULSES IN TOOTHED WHALE SONARS?

ABSTRACT

Small toothed whales of the family Phocoenidae and delphinid genus Cephalorhynchus produce long-duration, narrowband biosonar clicks above 100 kHz, that might be seen as an adaptation for short range echolocation in shallow water. This paper presents data showing that the distantly related, and larger pygmy sperm whale Kogia breviceps (Kogiidae), that is a deep-diving, cephalopod-eating toothed whale, produce narrow-banded high frequency (NBHF) clicks identical to those of Phocoena and Cephalorhynchus (f₀ = 130 kHz, Q_3dB>10, duration > 80 msec). Thus, NBHF biosonar signals have evolved on three independent occasions in the odontocete suborder, but the apparent functional convergence does not relate to anatomical or niche similarity. Rather, it is suggested that a biosonar strategy adapting to a minimum in ocean ambient noise above 100 kHz in concert with high Q auditory filters have led to convergent evolution of the NBHF biosonar clicks. Since these biosonar signals carry all their energy at frequencies above the upper hearing limit of the killer whale Orcinus orca, predator avoidance may also have been a evolutionary shaping factor of the sonar signals from these non-whistling odontocetes.     

Size Constancy in Bat Biosonar? Perceptual Interaction of Object Aperture and Distance

Perception and encoding of object size is an important feature of sensory systems. In the visual system object size is encoded by the visual angle (visual aperture) on the retina, but the aperture depends on the distance of the object. As object distance is not unambiguously encoded in the visual system, higher computational mechanisms are needed. This phenomenon is termed “size constancy”. It is assumed to reflect an automatic re-scaling of visual aperture with perceived object distance. Recently, it was found that in echolocating bats, the ‘sonar aperture’, i.e., the range of angles from which sound is reflected from an object back to the bat, is unambiguously perceived and neurally encoded. Moreover, it is well known that object distance is accurately perceived and explicitly encoded in bat sonar. Here, we addressed size constancy in bat biosonar, recruiting virtual-object techniques. Bats of the species Phyllostomus discolor learned to discriminate two simple virtual objects that only differed in sonar aperture. Upon successful discrimination, test trials were randomly interspersed using virtual objects that differed in both aperture and distance. It was tested whether the bats spontaneously assigned absolute width information to these objects by combining distance and aperture. The results showed that while the isolated perceptual cues encoding object width, aperture, and distance were all perceptually well resolved by the bats, the animals did not assign absolute width information to the test objects. This lack of sonar size constancy may result from the bats relying on different modalities to extract size information at different distances. Alternatively, it is conceivable that familiarity with a behaviorally relevant, conspicuous object is required for sonar size constancy, as it has been argued for visual size constancy. Based on the current data, it appears that size constancy is not necessarily an essential feature of sonar perception in bats.     

Gain control in the sonar of odontocetes

The sonar of odontocetes processes echo-signals within a wide range of echo levels. The level of echoes varies widely by tens of decibels depending on the level of the emitted sonar pulse, the target strength, the distance to the target, and the sound absorption by the water media. The auditory system of odontocetes must be capable of effective perception, analysis, and discrimination of echo-signals within all this variability. The sonar of odontocetes has several mechanisms to compensate for the echo-level variation (gain control). To date, several mechanisms of the biosonar gain control have been revealed in odontocetes: (1) adjustment of emitted sonar pulse levels (the longer the distance to the target, the higher the level of the emitted pulse), (2) short-term variation of hearing sensitivity based on forward masking of the echo by the preceding self-heard emitted pulse and subsequent release from the masking, and (3) active long-term control of hearing sensitivity. Recent investigations with the use of the auditory evoked-potential technique have demonstrated that these mechanisms effectively minimize the variation of the response to the echo when either the emitted sonar pulse level, or the target distance, or both vary within a wide range. A short review of these data is presented herein.     

Acoustic signals and echolocation system of the dolphin

Two-channel recording of acoustic signals from two quasi-stationary dolphins has previously suggested that the dolphin echolocation system is more complex than discussed earlier, and includes at least four sonars. In the present work, two-channel recording of signals, analysis and interpretation of their functions were continued in terms of physical acoustics, signal theory and echolocation. The results indicate that the echolocation system of dolphins involves four organs to produce probing signals of five different types, which implies different mechanisms of their processing by the dolphin hearing; its operation corresponds to as many as six varieties of sonar systems. The results are of importance for studying the echolocation system of Odontoceti and for improving sonars and radars.     

A bioinspired autonomous swimming robot as a tool for studying goal-directed locomotion

The bioinspired approach has been key in combining the disciplines of robotics with neuroscience in an effective and promising fashion. Indeed, certain aspects in the field of neuroscience, such as goal-directed locomotion and behaviour selection, can be validated through robotic artefacts. In particular, swimming is a functionally important behaviour where neuromuscular structures, neural control architecture and operation can be replicated artificially following models from biology and neuroscience. In this article, we present a biomimetic system inspired by the lamprey, an early vertebrate that locomotes using anguilliform swimming. The artefact possesses extra- and proprioceptive sensory receptors, muscle-like actuation, distributed embedded control and a vision system. Experiments on optimised swimming and on goal-directed locomotion are reported, as well as the assessment of the performance of the system, which shows high energy efficiency and adaptive behaviour. While the focus is on providing a robotic platform for testing biological models, the reported system can also be of major relevance for the development of engineering system applications.     

Bats use a neuronally implemented computational acoustic model to form sonar images

This paper reexamines neurophysiological results from echolocating big brown bats to propose a new perspective on FM biosonar processing in the auditory system. Individual auditory neurons are frequency-tuned and respond to brief, 2-10 ms FM sweeps with an average of one spike per sound to register their tuned frequencies, to detect echo arrival, or to register a local null in the echo spectrum. When initiated by the broadcast, these responses comprise a cascade of single spikes distributed across time in neurons tuned to different frequencies that persists for 30-50 ms, long after the sound has ended. Their progress mirrors the broadcast's propagation away from the bat and the return of echoes for distances out to 5-8 m. Each returning echo evokes a similar pattern of single spikes that coincide with ongoing responses to the broadcast to register the target's distance and shape. The hypothesis advanced here is that this flow of responses over time acts as an internal model of sonar acoustics that the bat executes using neuronal computations distributed across many neurons to accumulate a dynamic image of the bat's surroundings.     

A comprehensive computational model of animal biosonar signal processing

Computational models of animal biosonar seek to identify critical aspects of echo processing responsible for the superior, real-time performance of echolocating bats and dolphins in target tracking and clutter rejection. The Spectrogram Correlation and Transformation (SCAT) model replicates aspects of biosonar imaging in both species by processing wideband biosonar sounds and echoes with auditory mechanisms identified from experiments with bats. The model acquires broadband biosonar broadcasts and echoes, represents them as time-frequency spectrograms using parallel bandpass filters, translates the filtered signals into ten parallel amplitude threshold levels, and then operates on the resulting time-of-occurrence values at each frequency to estimate overall echo range delay. It uses the structure of the echo spectrum by depicting it as a series of local frequency nulls arranged regularly along the frequency axis of the spectrograms after dechirping them relative to the broadcast. Computations take place entirely on the timing of threshold-crossing events for each echo relative to threshold-events for the broadcast. Threshold-crossing times take into account amplitude-latency trading, a physiological feature absent from conventional digital signal processing. Amplitude-latency trading transposes the profile of amplitudes across frequencies into a profile of time-registrations across frequencies. Target shape is extracted from the spacing of the object’s individual acoustic reflecting points, or glints, using the mutual interference pattern of peaks and nulls in the echo spectrum. These are merged with the overall range-delay estimate to produce a delay-based reconstruction of the object’s distance as well as its glints. Clutter echoes indiscriminately activate multiple parts in the null-detecting system, which then produces the equivalent glint-delay spacings in images, thus blurring the overall echo-delay estimates by adding spurious glint delays to the image. Blurring acts as an anticorrelation process that rejects clutter intrusion into perceptions.     

Plasticity of dendritic function

The various properties of neuronal dendrites--their morphology, active membrane and synaptic properties--all play important roles in determining the functional capabilities of central nervous system neurons. Because of their fundamental involvement in both synaptic integration and synaptic plasticity, the active dendritic properties are important for both neuronal information processing and storage. The active properties of dendrites are determined by the densities of voltage-gated ion channels located within the dendrites in addition to the biophysical characteristics of those channels. The real power of this system resides in the level of plasticity that is provided by the many forms of channel modulation known to exist in neurons. Indeed, voltage gated ion channel modulation shapes the active properties of neuronal dendrites to specific conditions, thus tailoring the functional role of the single neuron within its circuit.     

Advances in synthetic biology: on the path from prototypes to applications

Synthetic biology combines knowledge from various disciplines including molecular biology, engineering, mathematics and physics to design and build novel proteins, genetic circuits and metabolic networks. Early efforts aimed at altering the behavior of individual elements have now evolved to focus on the construction of complex networks in single-cell and multicellular systems. Recent achievements include the development of sophisticated non-native behaviors such as bi-stability, oscillations, proteins customized for biosensing, optimized drug synthesis and programmed spatial pattern formation. The de novo construction of such systems offers valuable quantitative insight into naturally occurring information processing activities. Furthermore, as the techniques for system design, synthesis and optimization mature, we will witness a rapid growth in the capabilities of synthetic systems with a wide-range of applications.     

Biosonar behaviour of free-ranging porpoises

Detecting objects in their paths is a fundamental perceptional function of moving organisms. Potential risks and rewards, such as prey, predators, conspecifics or non-biological obstacles, must be detected so that an animal can modify its behaviour accordingly. However, to date few studies have considered how animals in the wild focus their attention. Dolphins and porpoises are known to actively use sonar or echolocation. A newly developed miniature data logger attached to a porpoise allows for individual recording of acoustical search efforts and inspection distance based on echolocation. In this study, we analysed the biosonar behaviour of eight free-ranging finless porpoises (Neophocaena phocaenoides) and demonstrated that these animals inspect the area ahead of them before swimming silently into it. The porpoises inspected distances up to 77 m, whereas their swimming distance without using sonar was less than 20 m. The inspection distance was long enough to ensure a wide safety margin before facing real risks or rewards. Once a potential prey item was detected, porpoises adjusted their inspection distance from the remote target throughout their approach.     

The Promises and the Challenges of Biotransformations in Microflow

The challenges of transition toward the postpetroleum world shed light on the biocatalysis as the most sustainable way for the valorization of biobased raw materials. However, its industrial exploitation strongly relies on integration with innovative technologies such as microscale processing. Microflow devices remarkably accelerate biocatalyst screening and engineering, as well as evaluation of process parameters, and intensify biocatalytic processes in multiphase systems. The inherent feature of microfluidic devices to operate in a continuous mode brings additional interest for their use in chemoenzymatic cascade systems and in connection with the downstream processing units. Further steps toward automation and analytics integration, as well as computer‐assisted process development, will significantly affect the industrial implementation of biocatalysis and fulfill the promises of the bioeconomy. This review provides an overview of recent examples on implementation of microfluidic devices into various stages of biocatalytic process development comprising ultrahigh‐throughput biocatalyst screening, highly efficient biocatalytic process design including specific immobilization techniques for long‐term biocatalyst use, integration with other (bio)chemical steps, and/or downstream processing.     

The beluga whale produces two pulses to form its sonar signal

Odontocete cetaceans use biosonar clicks to acoustically probe their aquatic environment with an aptitude unmatched by man-made sonar. A cornerstone of this ability is their use of short, broadband pulses produced in the region of the upper nasal passages. Here we provide empirical evidence that a beluga whale (Delphinapterus leucas) uses two signal generators simultaneously when echolocating. We show that the pulses of the two generators are combined as they are transmitted through the melon to produce a single echolocation click emitted from the front of the animal. Generating two pulses probably offers the beluga the ability to control the energy and frequency distribution of the emitted click and may allow it to acoustically steer its echolocation beam.     

Eugene--a domain specific language for specifying and constraining synthetic biological parts, devices, and systems

Background

Synthetic biological systems are currently created by an ad-hoc, iterative process of specification, design, and assembly. These systems would greatly benefit from a more formalized and rigorous specification of the desired system components as well as constraints on their composition. Therefore, the creation of robust and efficient design flows and tools is imperative. We present a human readable language (Eugene) that allows for the specification of synthetic biological designs based on biological parts, as well as provides a very expressive constraint system to drive the automatic creation of composite Parts (Devices) from a collection of individual Parts.

Results

We illustrate Eugene''s capabilities in three different areas: Device specification, design space exploration, and assembly and simulation integration. These results highlight Eugene''s ability to create combinatorial design spaces and prune these spaces for simulation or physical assembly. Eugene creates functional designs quickly and cost-effectively.

Conclusions

Eugene is intended for forward engineering of DNA-based devices, and through its data types and execution semantics, reflects the desired abstraction hierarchy in synthetic biology. Eugene provides a powerful constraint system which can be used to drive the creation of new devices at runtime. It accomplishes all of this while being part of a larger tool chain which includes support for design, simulation, and physical device assembly.     

A phase-based stereo vision system-on-a-chip

A simple and fast technique for depth estimation based on phase measurement has been adopted for the implementation of a real-time stereo system with sub-pixel resolution on an FPGA device. The technique avoids the attendant problem of phase warping. The designed system takes full advantage of the inherent processing parallelism and segmentation capabilities of FPGA devices to achieve a computation speed of 65megapixels/s, which can be arranged with a customized frame-grabber module to process 211frames/s at a size of 640x480 pixels. The processing speed achieved is higher than conventional camera frame rates, thus allowing the system to extract multiple estimations and be used as a platform to evaluate integration schemes of a population of neurons without increasing hardware resource demands.