PRESENTED BY:
Jeevan Kamdini,
Kishore Kumar T

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Abstract- Science and engineering have crossed conventional horizons and today, one's imagination is one's limit. The Bionic Lens is the brain child of those visionaries who have transformed the way one looks at the world. A bionic lens is a new generation of contact lens built with microcircuits and LEDs which superimpose computer graphics like images, text, charts etc onto real-world objects. They promise a wide arena of applications ranging from projecting information onto the wearer's field of vision to noninvasive monitoring of the biomarkers.
Keywords- Bionic, lens, Light emitting diode (LED), virtual image, optoelectronics.
I. INTRODUCTION
The human eye is a perceptual powerhouse. It can see millions of colors, adjust easily to shifting light conditions, and transmit information to the brain at a rate exceeding that of a high-speed Internet connection.
But why stop there?
In the Terminator movies, Arnold Schwarzenegger’s character sees the world with data superimposed on his visual field—virtual captions that enhance the cyborg’s scan of a scene. In stories by the science fiction author Vernor Vinge, characters rely on electronic contact lenses, rather than smartphones or brain implants, for seamless access to information that appears right before their eyes. These visions might seem far-fetched, but a contact lens with simple built-in electronics is already within reach. Control and communication circuits and miniature antennas are integrated into the lens using custom-built optoelectronic components to convert a conventional lens into a functional system.
A team of engineers headed by Babak.A.Parviz at the University of Washington have produced first generation versions of the bionic lens.
II. HUMAN EYE
The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways.
The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The structure of the human eye is as shown in Fig. 1.
A. Process of vision
Light waves from an object enter the eye first through the cornea. The light then progresses through the pupil, circular opening in the center of the iris. Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens(located immediately behind the iris and the pupil), to a nodal point located immediately behind the back surface of the lens. At that point, the image becomes inverted. The light continues through the vitreous humor and then back to a clear focus on the retina, behind the vitreous.
Within the layers of the retina, light impulses are changed into electrical signals. Then they are sent through the optic nerve, along the visual pathway, to the brain. Here, the electrical signals are interpreted by the brain as a visual image.
III. STRUCTURE OF BIONIC LENS
The bionic lens has the following components, shown in Fig. 2:
1. Semitransparent display and micro lens array.
2. Telecommunication and power reception antenna.
3. Display control circuit.
4. Solar cell module.
5. Energy storage module.
6. Biosensor module.
7. Sensor readout and control circuit.
8. Radio and power conversion circuit.
9. Electrical interconnects.
10. Polymer Substrate (polyethylene terephthalate).
IV. FABRICATION TECHNIQUE
All the components mentioned above have to be crammed onto a single lens:
• Metal microstructures to form antennas.
• Compound semiconductors to make optoelectronic devices.
• Advanced complementary metal–oxide- semiconductor(CMOS) silicon circuits for low-power control and RF telecommunication.
• Microelectromechanical system (MEMS) transducers and resonators to tune the frequencies of the RF communication.
• Surface sensors that are respond to the biochemical environment.
The conventional semiconductor fabrication processes used for making many of the lens components will not work because they are both thermally and chemically incompatible with the flexible polymer substrate of the contact lens and with one another . To get around this problem, all the components are independently fabricated from scratch. Most of the micro components are fabricated on silicon-on-insulator wafers, and the LEDs and some of the biosensors on other substrates.
To fabricate the components for silicon circuits and LEDs, high temperatures and corrosive chemicals are used, which means one cannot manufacture them directly onto a lens. All the key components of the lens need to be miniaturized and integrated onto about 1.5 square centimeters of a flexible, transparent polymer. And therefore, a specialized assembly process, which enables integration of several different kinds of components onto a lens is devised.
The first step in the fabrication process is preparation of the substrate- a 100 µm thick slice of polyethylene terephthalate which will hold the micro components. The substrate has photo lithographically defined metal interconnect lines and binding sites. These binding sites are tiny wells, about 10 µm deep, where electrical connections will be made between components and the template. At the bottom of each well is a minuscule pool of a low-melting-point alloy that will later join together two interconnects in what amounts to micrometer-scale soldering.
over it. The binding sites are cut to match the geometries of the individual parts so that a triangular component finds a triangular well, a circular part falls into a circular well, and so on. When a piece falls into its complementary well, a small metal pad on the surface of the component comes in contact with the alloy at the bottom of the well, causing a capillary force that lodges the component in place. After all the parts have found their slots, the temperature is dropped to solidify the alloy. This step locks in the mechanical and electrical contact between the components, the interconnects, and the substrate. Hence each part has metal interconnects and is etched into a unique shape. The end yield is a collection of powder-fine parts that we then embed in the lens.
Finally we need to ensure that all the potentially harmful components that have been assembled are completely safe and comfortable to wear. Take an LED, for example. Most red LEDs are made of aluminum gallium arsenide, which is toxic. So before an LED can go into the eye, it must be enveloped in a biocompatible substance. Hence, the functional parts are encapsulated with poly(methyl methacrylate), the polymer used to make earlier generations of contact lenses.
V. WORKING OF THE BIONIC LENS Conventional contact lenses are polymers formed in
specific shapes to correct faulty vision. To turn such a lens into a functional system, control circuits, communication circuits, and miniature antennas are integrated into the lens using custom-built optoelectronic components as explained previously. These components will eventually include hundreds of LEDs, which will form images in front of the eye, such as words, charts, and photographs. Much of the hardware is semitransparent so that wearers can navigate their surroundings without crashing into them or becoming disoriented. In all likelihood, a separate, portable device will relay displayable information to the lens’s control circuit, which will operate the optoelectronics in the lens.
A.Principle of Operation
In the bionic lens, an antenna in the periphery collects incoming RF energy from a separate portable transmitter. Power conversion circuitry provides DC power to other parts of the system and sends instructions to the display control circuit. The display, at the centre might consist of LEDs which would turn on and off, or LCD-like elements, whose transparency would be modulated by the control circuit. An energy-storage module, perhaps a large capacitor is connected to a solar cell, which would provide a boost to the lens.
The plastic lens substrate is then submerged in a liquid medium and flow the collection of micro components
Fortunately, the human eye is an extremely sensitive photo detector. At high noon on a cloudless day, lots of light streams through your pupil, and the world appears bright indeed. But the eye doesn’t need all that optical power—it can
perceive images with only a few microwatts of optical power passing through its lens. An LCD computer screen is similarly wasteful. It sends out a lot of photons, but only a small fraction of them enter your eye and hit the retina to form an image. But when the display is directly over your cornea, every photon generated by the display helps form the image.
The beauty of this approach is obvious: With the light coming from a lens on your pupil rather than from an external source, you need much less power to form an image. But how to get light from a lens? Two basic approaches have been considered. One option is to build into the lens a display based on an array of LED pixels; called an active display. An alternative is to use passive pixels that merely modulate incoming light rather than producing their own. Basically, they construct an image by changing their color and transparency in reaction to a light source. (They are similar to LCDs, in which tiny liquid-crystal ”shutters” block or transmit white light through a red, green, or blue filter.) For passive pixels on a functional contact lens, the light source would be the environment. The colors wouldn’t be as precise as with a white-backlit LCD, but the images could be quite sharp and finely resolved.
The active approach has been mainly pursued and lenses that can accommodate an 8-by-8 array of LEDs have been produced . For now, active pixels are easier to attach to lenses. But using passive pixels would significantly reduce the contact’s overall power needs—if we can figure out how to make the pixels smaller, higher in contrast, and capable of reacting quickly to external signals.
B. Image Perception
By now you are probably wondering how a person wearing a bionic contact lens would be able to focus on an image generated on the surface of the eye. After all, a normal and healthy eye cannot focus on objects that are fewer than 10 centimeters from the corneal surface. The LEDs by themselves merely produce a fuzzy splotch of color in the wearer’s field of vision. Somehow the image must be pushed