Mohsen Asadnia

A flexible liquid crystal polymer MEMS pressure sensor array for fish-like underwater sensing

In order to perform underwater surveillance, autonomous underwater vehicles (AUVs) require flexible, light-weight, reliable and robust sensing systems that are capable of flow sensing and detecting underwater objects. Underwater animals like fish perform a similar task using an efficient and ubiquitous sensory system called a lateral-line constituting of an array of pressure-gradient sensors. We demonstrate here the development of arrays of polymer microelectromechanical systems (MEMS) pressure sensors which are flexible and can be readily mounted on curved surfaces of AUV bodies. An array of ten sensors with a footprint of 60 (L) mm × 25 (W) mm × 0.4 (H) mm is fabricated using liquid crystal polymer (LCP) as the sensing membrane material. The flow sensing and object detection capabilities of the array are illustrated with proof-of-concept experiments conducted in a water tunnel. The sensors demonstrate a pressure sensitivity of 14.3 μV Pa−1. A high resolution of 25 mm s−1 is achieved in water flow sensing. The sensors can passively sense underwater objects by transducing the pressure variations generated underwater by the movement of objects. The experimental results demonstrate the arrays ability to detect the velocity of underwater objects towed past by with high accuracy, and an average error of only 2.5%.

Flexible and Surface-Mountable Piezoelectric Sensor Arrays for Underwater Sensing in Marine Vehicles

In an effort to improve the situational awareness and obstacle avoidance of marine vehicles, we fabricate, package and characterize Pb (Zr0.52Ti0.48)O3 thin-film piezoelectric pressure sensor arrays for passive fish-like underwater sensing. We use floating bottom electrode in designing the sensor which made the sensor able to detect very low frequency range (down to 0.1 Hz) in water. The proposed array of sensors is capable of locating underwater objects by transducing the pressure variations generated by the stimulus. The sensors are packaged into an array of 2 × 5 on a flexible liquid crystal polymer substrate patterned with gold interconnects. Experiments in this paper are divided into three main categories. First, in order to evaluate the effect of water on the sensor performance, resonant frequency, and quality factor changes in air and water are investigated theoretically and experimentally. Second, the ability of the array in locating a vibrating sphere (dipole) in water is illustrated through experiments. The sensors demonstrate a high resolution of 3 mms-1 in detecting in detecting oscillatory flow velocity in water. Third, “real-time” experiments are conducted in a swimming pool environment by surface mounting two arrays of sensors on the curved hull of a kayak vehicle. The arrays are self-powered and do not need any external power supply, to operate, which greatly benefits in eliminating the need of bulky power supplies on underwater vehicles.

Touch at a distance sensing: lateral-line inspired MEMS flow sensors

Evolution bestowed the blind cavefish with a resourcefully designed lateral-line of sensors that play an essential role in many important tasks including object detection and avoidance, energy-efficient maneuvering, rheotaxis etc. Biologists identified the two types of vital sensors on the fish bodies called the superficial neuromasts and the canal neuromasts that are responsible for flow sensing and pressure-gradient sensing, respectively. In this work, we present the design, fabrication and experimental characterization of biomimetic polymer artificial superficial neuromast micro-sensor arrays. These biomimetic micro-sensors demonstrated a high sensitivity of 0.9 mV/(m s(-1)) and 0.022 V/(m s(-1)) and threshold velocity detection limits of 0.1 m s(-1) and 0.015 m s(-1) in determining air and water flows respectively. Experimental results demonstrate that the biological canal inspired polymer encapsulation on the array of artificial superficial neuromast sensors is capable of filtering steady-state flows that could otherwise significantly mask the relevant oscillatory flow signals of high importance.

Nanofibril scaffold assisted MEMS artificial hydrogel neuromasts for enhanced sensitivity flow sensing

We present the development and testing of superficial neuromast-inspired flow sensors that also attain high sensitivity and resolution through a biomimetic hyaulronic acid-based hydrogel cupula dressing. The inspiration comes from the spatially distributed neuromasts of the blind cavefish that live in completely dark undersea caves; the sensors enable the fish to form three-dimensional flow and object maps, enabling them to maneuver efficiently in cluttered environments. A canopy shaped electrospun nanofibril scaffold, inspired by the cupular fibrils, assists the drop-casting process allowing the formation of a prolate spheroid-shaped artificial cupula. Rheological and nanoindentation characterizations showed that the Young’s modulus of the artificial cupula closely matches the biological cupula (10–100 Pa). A comparative experimental study conducted to evaluate the sensitivities of the naked hair cell sensor and the cupula-dressed sensor in sensing steady-state flows demonstrated a sensitivity enhancement by 3.5–5 times due to the presence of hydrogel cupula. The novel strategies of sensor development presented in this report are applicable to the design and fabrication of other biomimetic sensors as well. The developed sensors can be used in the navigation and maneuvering of underwater robots, but can also find applications in biomedical and microfluidic devices.

Artificial fish skin of self-powered micro-electromechanical systems hair cells for sensing hydrodynamic flow phenomena

Using biological sensors, aquatic animals like fishes are capable of performing impressive behaviours such as super-manoeuvrability, hydrodynamic flow ‘vision’ and object localization with a success unmatched by human-engineered technologies. Inspired by the multiple functionalities of the ubiquitous lateral-line sensors of fishes, we developed flexible and surface-mountable arrays of micro-electromechanical systems (MEMS) artificial hair cell flow sensors. This paper reports the development of the MEMS artificial versions of superficial and canal neuromasts and experimental characterization of their unique flow-sensing roles. Our MEMS flow sensors feature a stereolithographically fabricated polymer hair cell mounted on Pb(Zr0.52Ti0.48)O3 micro-diaphragm with floating bottom electrode. Canal-inspired versions are developed by mounting a polymer canal with pores that guide external flows to the hair cells embedded in the canal. Experimental results conducted employing our MEMS artificial superficial neuromasts (SNs) demonstrated a high sensitivity and very low threshold detection limit of 22 mV/(mm s−1) and 8.2 µm s−1, respectively, for an oscillating dipole stimulus vibrating at 35 Hz. Flexible arrays of such superficial sensors were demonstrated to localize an underwater dipole stimulus. Comparative experimental studies revealed a high-pass filtering nature of the canal encapsulated sensors with a cut-off frequency of 10 Hz and a flat frequency response of artificial SNs. Flexible arrays of self-powered, miniaturized, light-weight, low-cost and robust artificial lateral-line systems could enhance the capabilities of underwater vehicles.

Development and testing of bio-inspired microelectromechanical pressure sensor arrays for increased situational awareness for marine vehicles

The lateral line found on most species of fish is a sensory organ without analog in humans. Using sensory feedback from the lateral line, fish are able to track prey, school, avoid obstacles, and detect vortical flow structures. Composed of both a superficial component, and a component contained within canals beneath the fish?s skin, the lateral line acts in a similar fashion to an array of differential pressure sensors. In an effort to enhance the situational and environmental awareness of marine vehicles, lateral-line-inspired pressure sensor arrays were developed to mimic the enhanced sensory capabilities observed in fish.Three flexible and waterproof pressure sensor arrays were fabricated for use as a surface-mounted ?smart skin? on marine vehicles. Two of the sensor arrays were based around the use of commercially available piezoresistive sensor dies, with innovative packaging schemes to allow for flexibility and underwater operation. The sensor arrays employed liquid crystal polymer and flexible printed circuit board substrates with metallic circuits and silicone encapsulation. The third sensor array employed a novel nanocomposite material set that allowed for the fabrication of a completely flexible sensor array. All three sensors were surface mounted on the curved hull of an autonomous kayak vehicle, and tested in both pool and reservoir environments. Results demonstrated that all three sensors were operational while deployed on the autonomous vehicle, and provided an accurate means for monitoring the vehicle dynamics.

Optimum surface roughness prediction in face milling X20Cr13 using particle swarm optimization algorithm

Abstract This paper presents an approach to the determination of the optimal cutting parameters to create minimum surface roughness levels in the face milling of X20Cr13 stainless steel. The proposed approach is to use a particle swarm optimization (PSO)-based neural network to create a predictive model for the surface roughness level that is based on experimental data collected on X20Cr13. The optimization problem is then solved using a PSO-based neural network for optimization system (PSONNOS). A good agreement is observed between the predicted surface roughness values and those obtained in experimental measurements performed using the predicted optimal machine settings. The PSONNOS is compared to the genetic algorithm optimized neural network system (GONNS).

Soft polymer membrane micro-sensor arrays inspired by the mechanosensory lateral line on the blind cavefish

This article reports the development of flexible arrays of soft membrane microelectromechanical system pressure sensors that are inspired by the functional implications of the lateral line organ present in the blind cavefish. Being blind, this fish relies on the lateral line of pressure gradient sensors present on its body to sense the surrounding obstacles. A flexible, low-powered, lightweight, sensitive yet robust microelectromechanical system sensor array is fabricated using liquid crystal polymer material. Such arrays can guide an autonomous underwater vehicle to navigate in unsteady and dirty-water environments. The object detection abilities of the blind cave characin fish are investigated through proof-of-concept experiments conducted on the live fish. Similarly, the abilities of the microelectromechanical system array in determining the velocity and distance of an underwater object are investigated by testing them in water tunnel. Experimental results demonstrate the array’s ability to detect the velocity of moving underwater objects with a high accuracy and an average error of only 2.5%.

MEMS sensors for assessing flow-related control of an underwater biomimetic robotic stingray.

A major difference between manmade underwater robotic vehicles (URVs) and undersea animals is the dense arrays of sensors on the body of the latter which enable them to execute extreme control of their limbs and demonstrate super-maneuverability. There is a high demand for miniaturized, low-powered, lightweight and robust sensors that can perform sensing on URVs to improve their control and maneuverability. In this paper, we present the design, fabrication and experimental testing of two types of microelectromechanical systems (MEMS) sensors that benefit the situational awareness and control of a robotic stingray. The first one is a piezoresistive liquid crystal polymer haircell flow sensor which is employed to determine the velocity of propagation of the stingray. The second one is Pb(Zr(0.52)Ti(0.48))O3 piezoelectric micro-diaphragm pressure sensor which measures various flapping parameters of the stingrays fins that are key parameters to control the robot locomotion. The polymer flow sensors determine that by increasing the flapping frequency of the fins from 0.5 to 3 Hz the average velocity of the stingray increases from 0.05 to 0.4 BL s(-1), respectively. The role of these sensors in detecting errors in control and functioning of the actuators in performing tasks like flapping at a desired amplitude and frequency, swimming at a desired velocity and direction are quantified. The proposed sensors are also used to provide inputs for a model predictive control which allows the robot to track a desired trajectory. Although a robotic stingray is used as a platform to emphasize the role of the MEMS sensors, the applications can be extended to most URVs.

Flexible, zero powered, piezoelectric MEMS pressure sensor arrays for fish-like passive underwater sensing in marine vehicles

In an effort to improve the situational awareness of maritime vehicles, flexible MEMS pressure sensor arrays are developed for underwater sensing applications. This paper outlines the development of piezoelectric microdiaphragm pressure sensor arrays that can perform a passive fish-like underwater sensing. Individual sensors have a low footprint of 1.8 × 1.8 mm2 and do not require any power for their operation. An array of 2 by 5 sensors is fabricated, packaged and tested for use on marine vehicle. The proposed array is capable of locating underwater objects by transducing the pressure variations generated by the stimulus.