錯雜談。

電子皮膚好觸感 Cheap, Pressure-Sensing ‘Electronic Skin’

 原文翻譯自IEEE spectrum—tech talk

http://spectrum.ieee.org/tech-talk/at-work/test-and-measurement/cheap-pressuresensing-electronic-skin-

　　首爾大學多尺寸仿生系統實驗室的科學家們，在原發表於Nature Materials的一系列示範裡展示了一層夠靈敏的感壓模。它能感知落下的水滴、人的腕關節脈搏、甚或是正躡手躡腳跨過這層＂電子皮＂的窈窕小蟲也能感受得到！

　　研究團隊恪守著＂仿生＂信條，從耳內、腸道、以及腎臟的信號傳遞系統裡找到線索───當奈米尺寸的絨毛表面薄膜凹陷、起伏、或是彎曲時，它們能藉由摩擦彼此來製造及聯結信號。研究團隊也受到甲蟲翅翼上的固定機構啟發，加入了自組裝的特性。

　　這個裝置主要由兩片胺酯丙烯酸酯(polyurethane acrylate)薄板構成。每片僅有9´13公分大小，表面覆上由直徑100奈米，長度1000奈米的聚合物細絲所構成的稠密陣列。細絲外鍍有20奈米厚的白金塗層，接種在一層基底膜上，而聚二甲基矽氧烷(polydimethylsiloxane)則被用來增強其導電性。

　　緊接著，這兩片絨毛薄板就如同魔鬼氈一樣地被面對面接合起來。上下層的細絲嚙合在一起。但非是如魔鬼氈一般的機械式嵌合，兩片薄板藉由凡得瓦力緊密（但可逆）的相合。奈米絨毛層能在層板間傳遞電流，而其電阻隨著細絲接觸的面積改變。對基底膜的輕觸、下壓、扭轉都會使得這些奈米絲相互摩擦或彎曲，而電流的改變便告訴我們是發生了啥事。沒錯，由於正向壓力、側面的剪應力、以及扭轉都會造成不同的反應曲線，故此裝置能分辨出壓、揉、或扭絞之間的差別。

　　系統的應變係數───電阻的改變量根據所受應力而改變，對於正向壓力、剪力、扭力，分別各是11.5、0.75、和8.53。其藉由比較由石墨稀薄膜組成的直接壓力偵測器（應變係數6.1）和傳統金屬箔感測器（應變係數2.0）所得到。（請注意這些外加的偵測器只能偵測單一方向的形變，為了要能偵測出壓力、剪力、和扭力，它們必需個別於各個方向安裝。）

　　總結來說，研究者們表示：「這樣的奈米連結機制不需要複雜的奈米尺寸裝配，或是分層結構，因此所製造的感測平台簡單、便宜、且穩定，適合用於實現高表現、大尺寸的應變感測器。」

相片：Changhyun Pang／首爾大學

 Douglas McCormick撰文

譯者：skywind@NCTU (facebook帳號: Chia-Hung Liu)

按：自組裝，形容一無序系統在沒有外部的干預下，由個別部件間之互動（如吸引和排斥，或自發生成化學鍵），而組成一個有組織的結構之過程。近年自組裝特別吸引注意，因它提供自下而上（bottom-up）、可控制的方法組裝原子或分子成較大的結構（像奈米結構、微型機器等）。（以上摘自維基百科）其實大家可以想像成是利用某些物質本身的吸引、排斥特性來建造微型結構，最簡單的例子如DNA，若把成對的單股DNA片段放在一起，兩者便會自發的利用氫鍵形成穩定的雙股螺旋結構，也可以說是自組裝的現象。

原文：http://spectrum.ieee.org/tech-talk/at-work/test-and-measurement/cheap-pressuresensing-electronic-skin-

POSTED BY: Douglas McCormick  /  星期五, 八月 03, 2012

In a series of demonstrations (published in Nature Materials), scientists at Seoul National University’s Multiscale Biomimetic Systems Laboratory showed off a pressure-sensing membrane that is sensitive enough to feel the fall of water droplets, a human pulse in the wrist, and even the whisper-light tread of a lady-bug walking across the “electronic skin.”

True to its “biomimetic” creed, the group took its cue from the signal transduction systems found in the ear, intestines, and kidney—nanoscopic hairs that interlock and produce signals by rubbing one another when their base membranes dent, ripple, or twist. They also added a self-assembly feature inspired by the locking mechanism on a beetle’s wing.

The device features two sheets of polyurethane acrylate. The sheets, which can be as big as 9 by 13 centimeters, are molded onto dense arrays of minute polymer hairs, each 100 nanometers in diameter and 1000 nm tall. Each of the hairs is coated with a 20 nm layer of platinum and bonded to a basement membrane (polydimethylsiloxane treated to enhance conductivity).

The two ciliated sheets are then mated, face to face, like two pieces of Velcro. The fibers in the top layer mesh with those on the bottom. But instead of mechanical hook-and-loop binding, the sheets are held together strongly (but reversibly) by Van der Waals attraction. The nanofiber sandwich conducts current between layers, and the resistance changes as the total contact area between the meshing hairs varies. A touch, push, or twist of the basement membrane makes the meshed nanohairs rub and bend, and the changing current shows what’s going on. Indeed, since orthogonal pressure, lateral shear, and torsion produce different response curves, the device can tell the difference between a push, a rub, and a twist.

The system’s gauge factors—the change in resistance due to changes in strain—were about 11.5 for direct pressure, 0.75 for shear, and 8.53 in response to torsion. By comparison, direct-pressure sensors based on graphene-film  have a gauge factor of about 6.1, and for conventional metal foil sensors, the factor is about 2.0. (Note that these other sensors pick up strain in one direction only. In order for them to detect pressure, shear, and torsion they must be specially fabricated with separate sensors for each direction of strain.)

In sum, the researchers say, the “nano-interlocking mechanism requires no complex integrated nanomaterial assemblies or layered arrays, thus allowing a simple, cheap, yet robust sensing platform for high-performance, large-area strain-gauge sensors.”

Photo:  Changhyun Pang / Seoul National University

TAGS:Changhyun Pang // Kahp-Yang Suh // Seoul National University // biomimetic // pressure sensor // skin