Flow-sensing mechanisms and biomimetic potential of seal whiskers

Seals can accurately track fish trails as far as 180 m away solely using ultrasensitive whiskers. A high-aspect-ratio bluff body vibrates due to its shedding vortices when the oncoming flow is present, or it is being towed in still water. However, the undulating morphology of Phocid seal whiskers can reduce vortex-induced vibrations (VIV), rendering seals highly sensitive to flow stimuli. This thesis studied the form and function of seal whiskers, involving 1) geometric parameters (the formulated 3D whisker geometry, length and thickness distributions of all whiskers on the seal muzzle, and reshaped 3D distributions of whiskers), 2) mechanical responses (vibrations in the flow and natural frequencies of seal whiskers), and 3) biomimetic potentials (the bioinspired sensor design and the optimized whisker structure). Through fluid-structure interaction (FSI) studies and experimental investigations involving seal whiskers mounted on 3D-printed microelectromechanical systems (MEMS) sensors, results revealed that neighboring whiskers in an array influenced one another by resulting in greater flow vorticity fluctuation and distribution area, thus causing increased vibrations than an isolated whisker, indicating a vibration-strengthening effect in whisker arrays. Furthermore, it was measured that the ratio (λ) of undulation wavelength to mean diameter of undulating seal whiskers was around 4.36 and 4.63 for harbor and grey seal whiskers, respectively. VIVs of seal whiskers had troughs around λ ~ 4 – 5 for grey seal whiskers, which was around the measured λ value, indicating that the ratio (λ) has evolved to an optimized value and suggesting the biomimetic design of VIV-resistant underwater structures

3D Printed Graphene Piezoresistive Microelectromechanical System Sensors to Explain the Ultrasensitive Wake Tracking of Wavy Seal Whiskers

Many marine animals perform fascinating survival hydrodynamics and perceive their surroundings through optimally evolved sensory systems. For instance, phocid seal whiskers have undulations that allow them to resist noisy self-induced vortex-induced vibrations (VIV) while locking their vibration frequencies to wakes generated by swimming fishes. In this work, fully 3D-printed microelectromechanical systems (MEMS) sensors with high gauge factor graphene nanoplatelets piezoresistors are developed to explain the exquisite sensitivity of whisker-inspired structures to upstream wakes. The sensors are also used to measure natural frequencies of excised harbor (Phoca vitulina) and grey (Halichoerus grypus) seal whiskers and determine the effect of whisker orientation on the VIV, which can explain the possible natural orientation of whiskers during active hunting. Experimental investigations conducted in a recirculating water flume show that whisker-inspired sensors successfully sense an upstream wake located up to 10× the whisker diameter by locking to the frequency of the wake generator, thus mimicking the sensing mechanism of the seal whisker. The combination of VIV reduction and frequency-locking with the upstream wake generator demonstrates the whisker-inspired sensor's high signal-to-noise ratio, indicating its efficiency in long-distance wake sensing as well as its potential as an alternative to visual and acoustic sensors in underwater robots

Creating underwater vision through wavy whiskers:A review of the flow sensing mechanisms and biomimetic potential of seal whiskers

Seals are known to use their highly-sensitive whiskers to precisely follow the hydrodynamic trail left behind by prey. Studies estimate that a seal can track a herring that is swimming as far as 180 m away, indicating an incredible detection apparatus on par with the echolocation system of dolphins and porpoises. This remarkable sensing capability is enabled by the unique undulating structural morphology of the whisker that suppresses vortex-induced vibrations (VIV) and thus increases the signal-to-noise ratio of the flow sensing whiskers. In other words, the whiskers vibrate minimally due to the seal’s swimming motion, eliminating most of the self-induced noise and making them ultra-sensitive to the vortices in the wake of escaping prey. Due to this impressive ability, the seal whisker has attracted much attention in the scientific community, encompassing multiple fields of sensory biology, fluid mechanics, biomimetic flow sensing, and soft robotics. This article presents a comprehensive review of the seal whisker literature, covering the behavioral experiments on real seals, VIV suppression capabilities enabled by the undulating geometry, wake vortex-sensing mechanisms, morphology and material properties, and finally engineering applications inspired by the shape and functionality of seal whiskers. Promising directions for future research are proposed

Bioinspired PDMS-graphene cantilever flow sensors using 3D printing and replica moulding

Flow sensors found in animals often feature soft and slender structures (e.g. fish neuromasts, insect hairs, mammalian stereociliary bundles, etc.) that bend in response to the slightest flow disturbances in their surroundings and heighten the animal's vigilance with respect to prey and/or predators. However, fabrication of bioinspired flow sensors that mimic the material properties (e.g. low elastic modulus) and geometries (e.g. high-aspect ratio structures) of their biological counterparts remains a challenge. In this work, we develop a facile and low-cost method of fabricating high-aspect ratio (HAR) cantilever flow sensors inspired by the mechanotransductory flow sensing principles found in nature. The proposed workflow entails high-resolution 3D printing to fabricate the master mould, replica moulding to create HAR polydimethylsiloxane (PDMS) cantilevers (thickness = 0.5 – 1 mm, width = 3 mm, aspect ratio = 20) with microfluidic channel (150 µm wide × 90 µm deep) imprints, and finally graphene nanoplatelet ink drop-casting into the microfluidic channels to create a piezoresistive strain gauge near the cantilever's fixed end. The piezoresistive flow sensors were tested in controlled airflow (0 – 9 m/s) inside a wind tunnel where they displayed high sensitivities of up to 5.8 kΩ/ms-1, low hysteresis (11% of full-scale deflection), and good repeatability. The sensor output showed a second order dependence on airflow velocity and agreed well with analytical and finite element model predictions. Further, the sensor was also excited inside a water tank using an oscillating dipole where it was able to sense oscillatory flow velocities as low as 16 – 30 µm/s at an excitation frequency of 15 Hz. The methods presented in this work can enable facile and rapid prototyping of flexible HAR structures that can find applications as functional biomimetic flow sensors and/or physical models which can be used to explain biological phenomena

Resonant band engineering of ferroelectric tunnel junctions

We propose energy band engineering to enhance tunneling electroresistance (TER) in ferroelectric tunnel junctions (FTJs). We predict that an ultrathin dielectric layer with a smaller band gap, embedded into a ferroelectric barrier layer, acts as a switch controlling high- and low-conductance states of an FTJ depending on polarization orientation. Using first-principles modeling based on density functional theory, we investigate this phenomenon for a prototypical SrRuO3/BaTiO3/SrRuO3 FTJ with a BaSnO3 monolayer embedded in the BaTiO3 barrier. We show that in such a composite-barrier FTJ, ferroelectric polarization of BaTiO3 shifts the conduction-band minimum of the BaSnO3 monolayer above or below the Fermi energy depending on polarization orientation. The resulting switching between direct and resonant tunneling leads to a TER effect with a giant ON/OFF conductance ratio. The proposed resonant band engineering of FTJs can serve as a viable tool to enhance their performance, useful for device applications

A Thermoplastic Elastomer Belt Based Robotic Gripper

Novel robotic grippers have captured increasing interests recently because of their abilities to adapt to varieties of circumstances and their powerful functionalities. Differing from traditional gripper with mechanical components-made fingers, novel robotic grippers are typically made of novel structures and materials, using a novel manufacturing process. In this paper, a novel robotic gripper with external frame and internal thermoplastic elastomer belt-made net is proposed. The gripper grasps objects using the friction between the net and objects. It has the ability of adaptive gripping through flexible contact surface. Stress simulation has been used to explore the regularity between the normal stress on the net and the deformation of the net. Experiments are conducted on a variety of objects to measure the force needed to reliably grip and hold the object. Test results show that the gripper can successfully grip objects with varying shape, dimensions, and textures. It is promising that the gripper can be used for grasping fragile objects in the industry or out in the field, and also grasping the marine organisms without hurting them

Over 300-km Transmission of 25 Gb/s Optical SSB NPAM-4 Signal with Electronic Dispersion Pre-compensation and Interference Mitigation

We experimentally demonstrate the interference mitigation in direct-detection of optical SSB signals with Nyquist-PAM-4. At 25 Gb/s, we achieve over 300-km and 500-km SSMF with an average BER of 2.7×10-3 (<HD-FEC) and 9.4×10-3 (<SD-FEC), respectively

TL1A–DR3 interaction regulates Th17 cell function and Th17-mediated autoimmune disease

T helper type 17 (Th17) cells play an important pathogenic function in autoimmune diseases; their regulation, however, is not well understood. We show that the expression of a tumor necrosis factor receptor family member, death receptor 3 (DR3; also known as TNFRSF25), is selectively elevated in Th17 cells, and that TL1A, its cognate ligand, can promote the proliferation of effector Th17 cells. To further investigate the role of the TL1A–DR3 pathway in Th17 regulation, we generated a TL1A-deficient mouse and found that TL1A−/− dendritic cells exhibited a reduced capacity in supporting Th17 differentiation and proliferation. Consistent with these data, TL1A−/− animals displayed decreased clinical severity in experimental autoimmune encephalomyelitis (EAE). Finally, we demonstrated that during EAE disease progression, TL1A was required for the optimal differentiation as well as effector function of Th17 cells. These observations thus establish an important role of the TL1A–DR3 pathway in promoting Th17 cell function and Th17-mediated autoimmune disease