Smart lenses zoom in a blink

Materials World magazine
,
29 Aug 2019

A lens that can zoom using electrical signals from the eye looks promising for robotics. Alex Brinded reports.

A soft lens that mimics and responds to the human eye has been created by scientists at the University of California San Diego, USA. The proof-of-concept and biomimetic lens changes shape, and therefore focus, in direct response to movements of the eyeball.

To produce the lens, thin layers of dielectric elastomer (DE) film were sandwiched with a soft central layer, in between two electrodes. When exposed to a change in voltage, the film expands and reduces in thickness. In real-world use, the films would be controlled by electro-oculographic signals, which are electrical signals caused by eye movement due to the electric potential between the front and back of the eye.

Encapsulated salty water at the centre of this soft, tuneable lens provides the transparent fluid, much like the crystalline lens of an eye, and also functions as an electrode. The second electrode is formed by a circle of carbon grease on the top film.

When electric potential was applied to the top, the film became more convex and changed the focal length. This centre lens was connected to two more DE films and eight more areas applied with carbon grease in the same way extraocular muscles around the eye work. Each of these separate areas can move independently to produce a different motion of the lens, with different parts of the film expanding at a time.

During testing, five electrodes were attached around the eye, much like smaller versions of pads attached to a patient’s chest to monitor their heart. Depending on the movement of the eyeball, a signal was sent to a different part of the prototype, changing the focus with the eye.

As well as left-right and up-down actions, the lens changed focal length when the user double blinked.

Eyes on progress

While certain parts operate independently, the lens as a whole is more akin to a human-machine interface. The researchers listed three potential applications in the study paper, A biomimetic soft lens controlled by electrooculographic signal, published in Advanced Functional Materials.

It is primarily intended for the manufacture of adjustable, responsive glasses that could be tuned by blinking motions, but the team believes the emerging field of soft robotics also stands to benefit.

‘In recent years, people have developed a lot of soft robots,’ Lead Author Professor Shengqiang Cai told Materials World. ‘In contrast to conventional hard robotics, a soft robot is mainly made up of soft material, is highly deformable and very good at interaction with humans and fragile objects. If you want to develop a soft robot that can see things, you probably want a soft lens.’

The third potential use is as a visual prosthesis. Some people who cannot see clearly still have functional eye muscles, which would generate enough electrical signal to operate the lens. According to Cai, the device could be used as a model for study, such as for biomedical students.

Although the lens was designed around the mechanics of human eyes, Cai said it could be controlled by any other bio-signals. ‘It can be the signal generated by your heartbeat, it can be the signal generated by your motion – whatever signal you have it can be used in here,’ Cai said.

The prototype lens was built using commercial and accessible electrodes, but the team believes it could be quickly improved by integrating better existing technologies. ‘We can use a more comfortable and flexible electrode which captures the signals in high accuracy that would be more compatible to human beings. There are many aspects we can further improve this device,’ Cai confirmed.

Another option would be to go wireless. ‘The signal from the eyes has to be transmitted to the signal processor and further to the lens through wires but, technically, it is possible to make the whole structure wireless’.

The lens has been demonstrated via a human-machine interface using soft robotics, a key area of interest for Cai and his team, and research into improving the system for the market is ongoing.