美國倫斯勒理工學院最近開發(fā)出一種新式液體鏡頭，能通過超小型的微流體活塞、以電氣方式調(diào)整焦距，不須外加零件。此前，液體鏡頭已經(jīng)被應(yīng)用在浸沒式光刻設(shè)備，用以提升光刻分辨率，使得目前的CMOS工藝得以繼續(xù)向90納米以下的工藝線寬拓展。但必須以人工對焦的方法來消除這種鏡頭中不受控制的空氣液滴。

倫斯勒理工學院表示，他們所開發(fā)的電磁式液體鏡頭適合各種精密影像應(yīng)用，包括浸沒式光刻設(shè)備、人工視網(wǎng)膜以及手機用的超低功耗攝影機。這項技術(shù)是該校教授Amir Hirsa的研究成果，他的工作起始于一項看似漫不經(jīng)心的游戲。Amir Hirsa 以磁場小心翼翼地震蕩飽含鐵納米粒子的流體液滴，液滴內(nèi)部的流體就會像幫浦活塞一樣被上下抽吸，并因此能進行液體鏡頭的對焦。Amir Hirsa發(fā)現(xiàn)這樣做所需的功耗甚至低于采用微機電系統(tǒng)組件(MEMS)的方案。

Microfluidic pumps focus liquid lens

R. Colin Johnson

Liquid lenses are already used in immersion lithography to boost resolution, but the free-air droplets must be manually adjusted for proper focus. Now Rensselaer Polytechnic Institute (RPI) has shown a liquid lens with a focal length that can be electrically adjusted with tiny microfluidic pistons with no moving parts. RPI claims its electromagnetic liquid lens could boost all types of precision imaging applications, from immersion lithography to implantable retinas to the ultra-low power cameras on cell phones.

RPI's technique, developed by professor Amir Hirsa, uses fluids saturated with iron nanoparticles. By carefully oscillating a ferro-fluidic droplet with a magnetic field, the fluids inside can be pumped up-and-down like a piston, allowing the focal length of a lens to be adjusted using even less energy than a micro-electro-mechanical system (MEMS). Because the fields are generated use alternating currents, the lens is constantly cycling between its closest and furthest focal lengths, but the researchers say that software algorithms can easily eliminate any out-of-focus frames. In its demonstrations, the researchers were able to capture in-focus 30 frame-per-second videos as a proof of concept.

The demonstration set-up housed an opaque ferro-fluidic droplet—the piston—in one hole drilled next to another holding the transparent lens droplet in a solid substrate separating two sealed chambers filled with water (see figure). Electromagnetic pulses then forced the piston droplet to vibrate up and and down in its hole. Magnetic, capillary and inertial forces combined to cause the second droplet—the lens—to follow the movement of the piston droplet, setting it to oscillating between its maximum and minimum focal lengths.

Hirsa's collaborators on the project included MIT Lincolm Lab researcher Bernard Malouin, Michael Vogel, a private research consultant, RPI doctoral candidate Joseph Olles, and former postdoctoral researcher Lili Cheng, now at General Electric Global Research. Funding was provided by the Defense Advanced Research Projects Agency (DARPA).

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