Nannan Chen

Design and Characterization of Artificial Haircell Sensor for Flow Sensing With Ultrahigh Velocity and Angular Sensitivity

We report the development of an artificial hair cell (AHC) sensor with design inspired by biological hair cells. The sensor consists of a silicon cantilever beam with a high-aspect-ratio cilium attached at the distal end. Sensing is based on silicon piezoresistive strain gauge at the base of the cantilever. The cilium is made of photodefinable SU-8 epoxy and can be up to 700-mum tall. In this paper, we focus on flow-sensing applications. We have characterized the performance of the AHC sensor both in water and in air. For underwater applications, we have characterized the sensor under two flow conditions: steady-state laminar flow (dc flow) and oscillatory flow (ac flow). The detection limit of the sensor under ac flow in water is experimentally established to be below 1 mm/s. A best case angular resolution of 2.16deg is also achieved for the sensors yaw response in air.

Distant touch hydrodynamic imaging with an artificial lateral line

Nearly all underwater vehicles and surface ships today use sonar and vision for imaging and navigation. However, sonar and vision systems face various limitations, e.g., sonar blind zones, dark or murky environments, etc. Evolved over millions of years, fish use the lateral line, a distributed linear array of flow sensing organs, for underwater hydrodynamic imaging and information extraction. We demonstrate here a proof-of-concept artificial lateral line system. It enables a distant touch hydrodynamic imaging capability to critically augment sonar and vision systems. We show that the artificial lateral line can successfully perform dipole source localization and hydrodynamic wake detection. The development of the artificial lateral line is aimed at fundamentally enhancing human ability to detect, navigate, and survive in the underwater environment.

Artificial lateral line with biomimetic neuromasts to emulate fish sensing

Hydrodynamic imaging using the lateral line plays a critical role in fish behavior. To engineer such a biologically inspired sensing system, we developed an artificial lateral line using MEMS (microelectromechanical system) technology and explored its localization capability. Arrays of biomimetic neuromasts constituted an artificial lateral line wrapped around a cylinder. A beamforming algorithm further enabled the artificial lateral line to image real-world hydrodynamic events in a 3D domain. We demonstrate that the artificial lateral line system can accurately localize an artificial dipole source and a natural tail-flicking crayfish under various conditions. The artificial lateral line provides a new sense to man-made underwater vehicles and marine robots so that they can sense like fish.

Biologically inspired design of hydrogel-capped hair sensors for enhanced underwater flow detection

Using a precision drop-casting method, a bioinspired hydrogel-capped hair sensory system was created, which enhanced the performance of flow detection by about two orders of magnitude and endowed the sensors with threshold sensitivities that rival those of fish.

Multi-Walled Carbon Nanotube Filled Conductive Elastomers: Materials and Application to Micro Transducers

We report a detailed study investigating the use of multi-walled carbon nanotube (MWNT) filled elastomers to enable sensitive and yet robust MEMS devices. This work is contrasted with previous work using carbon black filling, showing an 8-fold improvement in performance through the use of MWNT. The percolation behavior of MWNT in polydimethylsiloxane (PDMS) and polyurethane (PU) elastomers is presented. We have also developed and characterized two devices: (1) MWNT-based force sensitive resistors (FSRs), analogous to polymer piezoresistors; (2) robust collapsible capacitive tactile sensors using soft conductive elastomers.

Flexible Skin with Two-Axis Bending Capability Made Using Weaving-By-Lithography Fabrication Method

In this paper, we report the general design of a two-axis bendable flexible skin and its companion fabrication method. Conventional flexible skins can only bend along one axis. For example, they may be rolled onto a circular cylinder conformally but not onto a sphere. Our flexible skin features a novel interwoven structure inspired by cloth fabric. The horizontal and vertical threads of the skin are not connected; they are free to slide and rotate against each other, therefore enabling the skin to adjust its shape to conform to complex curvatures. To demonstrate the potential for future applications, we have embedded passive RF elements (planar coil inductors) inside the skin. The inductance value is experimentally determined to be 106 µ H.

From artificial hair cell sensor to artificial lateral line system: Development and application

We report the development and application of an artificial hair cell (AHC) flow sensor inspired by biological systems. With optimized design and fabrication process, the AHC is characterized in terms of sensitivity, calibration, and robustness. Especially, an AHC can discern variations of water flow down to 0.1 mm/s and survive 55deg deflections. The sensor has been applied to flow field measurements, matching perfectly with analytical and previous experimental results. By employing arrays of such AHC sensors, an artificial lateral line is constructed for biomimetic studies on localizing and tracking hydrodynamic events.

Artificial Lateral Line And Hydrodynamic Object Tracking

We report the development of biologically inspired artificial lateral line sensor for underwater flow field imaging. The artificial lateral line is based on an array of integrated, elevated hotwire elements. The static and dynamic behavior of the array, packaged as superficial sensors or canal embedded ones, are discussed. We have developed a complete system and demonstrated mimicking the functions of “ soft touch” of real biological lateral line. The sensor array can track the distance and location of an oscillating dipole source.

Flexible Multimodal Tactile Sensing System for Object Identification

This work presents results towards realizing a flexible multimodal tactile sensing system for object identification. Using polymer substrates and simple fabrication, robust devices are made that can identify objects based on texture, temperature, as well as material properties such as hardness and thermal conductivity. These capabilities are possible using signal processing techniques and physical models along with individual sensing structures inspired by the specialization found in biological skin. These structures are used to sense various object parameters, and array-wide processing to identify texture using a Maximum Likelihood decision rule. 80% texture classification is achieved. In blind object identification tests, over 90% correct identification was achieved by measurement of material properties.

Development and characterization of an artificial hair cell based on polyurethane elastomer and force sensitive resistors

The performance of polyurethane (PU) and polydimethylsiloxane (PDMS) elastomers are compared in a battery of tests showing that the two PU formulations tested compare very favorably with PDMS mechanically and in terms of adhesion, while sacrificing some resistance to solvents and chemicals. PU is then used to form the structure and sensing elements of an all-polymer artificial hair cell. The demonstrated artificial hair cells are composed of a PU cilium on top of force sensitive resistors (FSRs) that detect cilium motion. The FSR is a mixture of carbon nanoparticles and PU, patterned using a newly developed method. Sensitivity of the demonstrated device (245 ppm/mum of tip deflection) is improved by an order of magnitude over previous single-axis polymer AHCs with additional improvements in robustness. Both carbon black and multi-walled nanotubes are tested as conductive fillers, with MWNT providing increased sensitivity