Technology

Electrically active fluid helps new liquid lens change focus

Electrically active fluid help...
Researchers have developed a new liquid lens that uses voltage changes to adjust its focal length
Researchers have developed a new liquid lens that uses voltage changes to adjust its focal length
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Researchers have developed a new liquid lens that uses voltage changes to adjust its focal length
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Researchers have developed a new liquid lens that uses voltage changes to adjust its focal length
A diagram illustrating how the new liquid lens works
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A diagram illustrating how the new liquid lens works
A demonstration of the liquid lens' different focal lengths, at different voltages
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A demonstration of the liquid lens' different focal lengths, at different voltages
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Researchers in China have developed a new type of adaptive liquid lens that changes its focal distance when a voltage is applied. Made using a new electrically responsive fluid, the lens is small, lightweight, and could be easily manufactured for use in smartphones and other cameras.

Existing lenses are solid, and while they work well, they have a limited range of focal lengths. That’s why modern smartphones are packing in two, three, four or more lenses lately, specialized for macro, wide-angle, or telephoto shots.

But liquid lenses are more flexible, allowing them to shift between all of these focal lengths easily. Liquid lenses themselves are nothing new – tech companies have been promising their arrival in consumer electronics since at least 2004 – but the first one only made it to market last year, in Xiaomi’s Mi Mix phone.

The new liquid lens, developed by researchers at Hefei University of Technology, is designed to be simpler than existing tech. The key ingredient is a fluid known as dibutyl adipate (DBA), which has an electronegative molecular structure. That means that its shape will change when a direct current is applied to it.

A diagram illustrating how the new liquid lens works
A diagram illustrating how the new liquid lens works

The lens was created by filling a ring-shaped electrode with this DBA liquid. Because the electrode is coated with a water-repelling layer, the surface of the liquid forms a dome shape. When a voltage is applied to it, the DBA molecules gather at one end of the tube, changing the dome and, as a result, the focal length of the lens. When the electric field is removed, the liquid returns to its original shape.

In tests, the liquid lens was able to change its focal length from 7.5 mm to 13.1 mm, as the voltage was increased from zero to 100 V. Its resolution was almost 29 lines per millimeter, and it could allow about 95 percent of visible light through. The liquid lens also performed well in a range of temperatures, between 20 and 100 °C (68 and 212 °F).

A demonstration of the liquid lens' different focal lengths, at different voltages
A demonstration of the liquid lens' different focal lengths, at different voltages

The team says that the new liquid lens has a simpler structure and better stability than existing liquid lenses. Some require insulating layers between the electrode and the liquid, while others such as Xiaomi’s use tiny motors to manipulate their shape. Without those, the DBA lens should be easier to integrate into smartphones, cameras, endoscopes, and other lenses.

The research was published in the journal Optics Letters.

Source: Optica

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3 comments
3 comments
Aross
sounds like they need to add a little antifreeze for this to work in colder climates.
EH
It could likely benefit from a matched corrector, which would likely need to be another similar such lens, perhaps concave (using hydrophilic coating on the ring electrode). 29 lines / mm is terrible, even 29 line pairs /mm would be 17 micron resolution, or around 200 1.2 micron smartphone pixels. The main interest for such a design would be for rapid changes in focus, but the speed of the fluid response isn't mentioned. 3D scanning / focus stacking cameras with high frame rates would be the main application for rapid focus, but there may be better designs for that, e.g. a resonant vibrating focal group with a voice coil driver.
Bob Flint
Might have to consider gravity, & thermal expansion & contraction even at small scale.