Scientists have now invented ‘Smart Glasses’, that use liquid lenses to change focus in real time! Find out more..

It’s time to say your goodbyes to all the trouble of buying a new pair of glasses every time your eye power changes, or buying two different set of glasses for viewing close things like when reading, and other for looking at far away things, or using a bifocals lens which let us all except are a bit uncomfortable. Liquid lenses have come to our rescue. Liquid lenses are an emerging technology that is revolutionizing the field of optics with their advantage of having variable focus, and thus extensively used in telescopes, cameras, and other optical systems.

Liquid lenses make use of the property to change the curvature of the liquid to vary the focal length

Liquid lenses use a single liquid or a mixture of liquids, and the property of infinitely variable focus is achieved by varying the curvature of the meniscus or the surface of the liquid. Since focal length of the lens is related to the curvature, by changing the shape of the surface the focal length also changes. There are many methods implied to change the curvature which we shall know about below.

A black-structured liquid lens telescope pointing towards the ceiling in Univ. Of British Columbia.

In reflective type liquid lenses, a single liquid is used in a container. When this container is rotated, due to centrifugal force, the liquid spreads out from the centre, and thus a curved surface is formed and depending on the speed of rotation, this extend of curvature can be varied. These types of liquid lens are mostly used in telescopes, and the liquid used is mostly mercury. It has the advantage of achieving any desired focus plus unlike traditional glass mirrors, these don’t need to be polished for  a smooth surface, because mercury already a liquid has that property. This saves a lot of money and is thus really a cost-effective alternative. The 6-meter Liquid Mirror Telescope, built by the University of British Columbia, is the 13th largest telescope in the world and the normal rotation speed of the lens is 5 RPM. Plus, the telescope costs only $1 million which is 10 times less from what would have cost to build the normal glass mirror telescope of the same properties and dimensions.

Transmissive type: See how the use of voltage can provide us with variable focus

Another type of liquid lens is the transmissive type, which uses a mixture of two liquids, of the same density, one of which is an insulator oil and the other is an electrolytic aqueous mixture. The container is a tube fitted with two transparent caps on both sides, one of which is made of a hydrophobic material. This forces the surface of the mixture on the opposite side to be curved in shape of a lens. Using the process of electrowetting, by applying dc voltage on the material, the surface tension of the liquid is adjusted by increasing or decreasing the level of hydrophobic nature of the material, which thus changes the curvature of the lens and hence changing the focal length. These type of liquid lenses find use mostly in optical sensors, endoscopy, and imaging devices.

Schematic of transmissive liquid lens. The cap above is coated with a hydrophobic material.
Image Courtesy: Professor Carlos Mastrangelo and Nazmul Hassan from University of Utah. The creators of the ‘Smart Glasses’ with their invention.

Now, coming to topic under concern, that is the use of liquid lenses in spectacles, professor  Carlos Mastrangelo and doctoral student Nazmul Hasan, along with other electrical and computer engineers of the University of Utah, have used the liquid lens technology to make ‘Smart Glasses’. They used glycerine (the liquid medium), in a stretchable transparent rubber or plastic container, liquid lens system to achieve a self focusing lens. The rear rubber surface has three actuators attached to it, which through dc electricity form a battery, adjust or change the surface of the glycerine lens in the container and thus changing focus. The user first feeds data into an smart-phone app, which then analysis the data and sends the result to the glasses using bluetooth and based on the parameters the acutators adjust the shape of the lens surface to give the desired power. The ‘smart glasses’ are also fitted with an infrared laser in the centre which measures the distance of the object the glasses are facing and thus changing the focus of the lens in realtime in order of 14 milliseconds. The battery that powers this, is hidden in the frame and is said to run for more than 24 hours. At the moment the glasses seem a bit geeky and bulky, but the team is working on the frame size and portability, and the device is expected to be released soon.

A prototype lens used by Carlos Mastrangelo. Look at the electrically controlled actuators that control the liquid meniscus. Image Courtesy : University of Utah.

Another startup from Israel, Deep Optics, is working on glasses whose liquid lens use optic sensors to measure the curvature and other parameters of the pupil when focused on an object and thus changing the curvature of the liquid lens using electricity from a battery source to autofocus the lens. They are using a type of liquid crystal in their lens. Similar to Mastrangelo, Dr. Ronald Blum, chief-executive of e-Vision claims to have made a prototype glass using polymer or liquid crystal in a glass frame to achieve variable focus, and using the same infrared technology to measure the distance of an object under observation. The frame though is still in designing stage to tackle its bulkiness.

The structure of eye. Look at the ciliary muscles that control the curvature of the eye lens.

Our eyes use ciliary muscles to change the curvature of the lens, but as we age, the ability of variable focus of eye looses effectiveness, and at some point we feel the need to use a pair of glasses. For people like me, who are always in front of a mobile or laptop screen, this problem comes fast and with this a need to buy new set of glasses every time our eye power changes. So, the release of these ‘Smart Glasses’ can be a relief for us and our pockets, but we might need to adjust our fashion sense for the beginning, but hey, Nerdy is the new cool *wink*. Till next time, take care of your eyes, read another of the blog posts, review, like and share, and be ready to buy your very own set of liquid lenses soon.  Happy Reading!

-The Cosmogasmic Person



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