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Title: Biomimetic self-powered micro-sensors for underwater disturbance sensing
Authors: Mohsen Asadniaye Fard Jahromi
Keywords: DRNTU::Engineering::Materials::Biomaterials
DRNTU::Engineering::Electrical and electronic engineering::Microelectromechanical systems
Issue Date: 2015
Source: Mohsen Asadniaye Fard Jahromi. (2015). Biomimetic self-powered micro-sensors for underwater disturbance sensing. Doctoral thesis, Nanyang Technological University, Singapore.
Abstract: With the advent of highly-durable and light-weight materials for the production of unmanned underwater vehicles (UUVs), the challenge in UUV research has shifted from development of high-quality vehicles to the precise control of the vehicles using sensors, which enable the vehicles to perform highly controlled and meticulous navigations. In our research, inspired from the lateral-line sensory system of the blind cavefish Astyanax mexicanus fasciatus, we developed artificial lateral-lines to enhance the manuverability of UUVs. The blind cavefish is bestowed with a resourcefully designed lateral-line of sensors that enable the fish to swim dexterously and navigate with great agility in hydrodynamically challenging underwater environments. It is well understood that the blind cavefish accomplishes most of its sensing needs by utilizing dense arrays of biological pressure-gradient and flow sensors present on their bodies called lateral-lines. The individual sensing elements of the lateral-lines are called neuromasts, which respond to the relative motion between the body of the fish and the surrounding water, acting as flow sensors. Biological neuromasts consist of a rather complex yet beautiful intricate sensory architecture. Each neuromast sensor consists of haircells that are embedded into a soft gelatinous material called cupula. The hair cells are connected to the afferent nerves at the base and form the principal sensing elements while the cupula couples the motion of the surrounding water to the embedded haircells and increases the viscous drag and pressure force on the haircells. Each haircell bundle consists of a number of stereovilli (pillar-like structures) that are arranged into columns of increasing height with the longest pillars called the kinocilium. Each stereoville is connected to the next one by tip links, which open and close to allow ion transfer. In this work, two different types of sensors are fabricated that function based on piezoelectric principles. The first one is a microdiaphragm lead zirconate titanate (PZT) pressure sensor. Flexible arrays of proposed sensors are developed on LCP substrate for underwater sensing and deployment on underwater vehicles. These sensors are capable of mapping flows around the bodies of the vehicle and thereby enable an energy-efficient maneuvering of the vehicle. In addition, the sensor arrays provide artificial vision to the vehicles by detecting surrounding obstacles underwater in the near-field. Functioning similar to the lateral-lines, these artificial sensor arrays together with signal processing circuits and algorithms equip the UUVs with hydrodynamic vision that could aid in object avoidance. Awareness of flows around the vehicle generated by the sensors can give cues into achieving an energy efficient manuverability in controlling the vehicle. The second sensor is a NEMS artificial stereovilli sensor which is the closest biomimetic to the superficial neuromast sensor developed so far. We take advantage of MEMS technology to up bring artificial miniaturized sensors that emulate the functionality of the sensory system of the blind cavefish. For the first time, we developed an artificial nano-sensor that imbibes a very similar architecture that has evolved over years to be an ultra-sensitive, robust and multifunctional flow sensor with unfathomable and marvelous sensing abilities. We aim to develop an artificial sensory analogue of the mechanosensory lateral-line system by developing biomimetic nano-sensors that feature materials, sensing principle and sensory structure inspired by the fish’s neuromast sensor. The artificial micro-sensor fabrication infuses the knowledge gained from MEMS fabrication technology, nanofiber generation techniques and soft-polymer material synthesis. The MEMS piezoelectric sensors developed in this thesis are an excellent candidate for sensing flows around the body of UUVs owing to their great intrinsic advantages such as being self-powered, low-cost, extremely light-weight, miniaturized, highly sensitive, surface mountable and fast operating. The NEMS artificial stereoville sensors developed in this work consist of flexible pillars fabricated by double molding polydimethylsiloxane (PDMS) from SU-8 grown pillars of varying aspect ratio. Piezoelectric nano fiber tip links are formed between stereoville through electrospinning process. Translating the knowledge gained from the morphology of the individual biological neuromasts, we developed an artificial hydrogel cupula using Hyaluronic acid-methacrylic anhydride (HA-MA). The artificial cupula encapsulates the PDMS stereovilli and transdues the flows into displacement of the stereovilli pillars. Flow sensing experiments conducted using the artificial cupula sensors demonstrated ultrahigh sensitivity and high accuracy. The presence of the cupula enhanced the sensitivity of the sensor manifold times. As these miniaturized, low-powered, inexpensive, light-weight MEMS sensors become available, sensing, control and maneuvering of underwater vehicles could see a radical transformation. Currently, more experimental studies are in progress to implement various biomimetic approaches to enhance the signal to noise ratio of these sensors.
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