SMART EYE IN NANO TECHNOLOGY

SMART EYE  

IN

NANO TECHNOLOGY

 (AN INNOVATIVE APPROCH ON E-EYE)

Abstract:

In conventional electronic eye,micro photodiode is used for converting the light energy to electrical pulses.for that there are 50-100 electrodes are used.but the amount of diode used here are not enough to view the clear image.To get clear image 1000 of electrodes are required.If we increase the number of electrodes in amount  the size of the device become large.this will be a drawback of an electronic eye.we presents a smart eye that eliminates the drawback of an conventional electronic eye.Instead of  using microphotodiode,nanowires [300nm-500nm] are used in smart eye.since the nanowires having a verygood opto electronic property,it is used for detection and transmission of light and the size of the nonowire is very less as compare to microphotodiode.we can insert  1000 nanowires within the prescribed space allotted for inserting the [50-100] microphotodiode.Here nanolens is used instead of microlens to get high resolution.Hence the slightless person gets the clear image of the particular object  through smart eye.Key words:

electronic eye, microphotodiode, electrodes,nanowire, smart eye.

Introduction:

Research on microelectronics, magnetic, nanotechnology, on-board data processing, etc has now made itpossible to manufacture a new generation of sensors and other electronics devices .further the research works on integration and imaging technology has led to the development of very small size devices that    overcome functional complexity of earlier generation equipment .the technology has a range of application in detection of diseases and abnormalities in medical fields. These new generation biomedicalequipment are not only very small and userfriendly    but work with great precision and produce images of excellent resolutio even  a few years ago people could not think of such equipment .one of suchdevice is smart eye.

An electronic eye:

an effective navigation system would improve the mobility of millions of blind people  all over the world. a new “eye” developed which will allow blind people to cross busy  roads in total safety for the first time. the “electronic eye”, which would be mounted on a pair of glasses, will be capable of detecting the existence and location of a pedestrian crossing, and at the same time measure the width of the road to the nearest step and detect the colour of the traffic lights. but in most of the the time  the image produced by the  electronic eye is not clear  due to  the microphotodiode electrodes which is less in amount.

 

The eyeball is an optical device for focusing light :

The mammalian eyeball  is an organ that focuses a visual scene onto a sheet of specialized neural tissue, the retina, which lines the back of the eye. Light from a scene passes through the cornea, pupil, and lens on its way to the retina. The cornea and lens focus light from objects onto photoreceptors, which absorb and then convert it into electrical signals that carry information to the brain. Two pockets of transparent fluid nourish eye tissues and maintain constant eye shape: these are the aqueous and vitreous humors, through which the light also passes. The lens projects an inverted image onto the retina in the same way a camera lens projects an inverted image onto film; the brain adjusts this inversion so we see the world in its correct orientation. To control the images that fall upon our retinas, we can either turn our heads or turn our eyes independently of our heads by contracting the extraocular muscles, six bands of muscles that attach to the tough outside covering, or sclera, of the eyeball and are innervated by cranial nerves.

 

The cornea and lens bend or refract light rays as they enter the eye, in order to focus images on the retina. The eye can change the extent to which rays are bent and thus can focus images of objects that are various distances from the observer, by varying the curvature of the lens. The ciliary muscle accomplishes this by contracting to lessen tension on the lens and allowing it to round up so it can bend light rays more, or relaxing for the opposite effect. This ciliary muscle is smooth or non-voluntary muscle-you cannot "decide" to contract or relax it as you do the skeletal muscle in a finger or facial muscle.

Colour filter:

A color filter array (CFA) is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information
Color filters are needed because the typical photosensors detect light intensity with little or no wavelength specificity, and therefore cannot separate color information.Since sensors are made of semiconductors they obeysolid-statephysics.The color filters filter the light by wavelength range, such that the separate filtered intensities include information about the color of light. For example, the Bayer filter gives information about the intensity of light in red, green, and blue wavelength regions. The raw image data captured by the image sensor is then converted to a full-color image  by a demosaicing algorithm. The sensor uses a different structure such that a pixel utilizes properties of multi-junctions to stack blue, green, and red sensors on top of each other. This arrangement does not require a demosaicing algorithm because each pixel has information about each color

The retina originates from the brain and contains photoreceptors for detecting light :

The eye is formed during embryonic development by a combination of head ectoderm and neural tube tissue, the latter forming the retina. Thus, the retina is not a peripheral sensory organ like skin touch receptors or taste buds on the tongue, but rather it is an outgrowth of central nervous tisse. Because of this origin, the retina has layers of neurons, internal circuits, and transmitters characteristic of the brain: it is a bit of the brain that has journeyed out, literally, to have a look at the environment.

The photoreceptors in the retina are of two types: rods and cones, so named because of their shapes. These cells are actually specialized neurons that detect light. Embedded in stacks of cell membranes in the distal portions of rods and cones are molecules that absorb certain wavelengths of light. These molecules are called photopigments and are composed of two parts: a large trans-membrane protein, an opsin, and a smaller chromophore, which is a metabolite of Vitamin A called 11-cis-retinal. The chromophore, which is embedded in the opsin, absorbs light; in so doing it undergoes a shape change. This shape change in turn activates the opsin, setting off a cascade of events that leads to a change in the electrical state of a rod or cone cell

 

membrane. This change in the rod conecell membrane is then conducted via the rod or cone axon to other neurons in the retina, and from there to the brain.

Rods function in dim light:

In dim light, we use our rods, which cannot work in bright light. Rods outnumber cones (120 million rods and about 6 million cones in each retina) and they amplify a light signal much more than cones.  the  absorption of even a single quantum  of light can trigger a chromophore shape change in one molecule of rhodopsin in a rod, leading to signal transmission. For transmission to occur, this initial tiny event must be amplified: the activated molecule of rhodopsin converts several thousand molecules of the next enzyme in the cascade to the active form, and this amplification continues until the electrical potential of the cell membrane changes and neurotransmitter release is affected. Cones, on the other hand, must each absorb hundreds of photons in order to send signals.

Another retinal mechanism that helps us to see in dim light or to see a tiny amount of light in the dark is the convergence of rod cell signals onto other retinal neurons. Many rods (up to 150) synapse onto the same target neurons, where the signals are pooled and reinforce one another, increasing the ability of the brain to detect a small amount of light. (A synapse is a contact between a neuron and another cell where an electrochemical signal [most commonly] is transmitted to the second cell.) This convergence amplifies weak signals, but spatial resolution is lost becauseresponses are averaged.

In order for our eyes to make the transition to dim light, rods must adapt after being saturated with light in brighter conditions. Dark adaptation of rods takes seven to ten minutes: during this time rhodopsin molecules, in which the chromophore components have changed to the activated state, return to the non-activated state so that they are able once again to register changes in illumination. Other changes also occur in adaptation to dark or dim conditions, including enlarging or dilating of the pupil, which is controlled by the autonomic nervous system.

Cones mediate day vision:

Our vision in bright or moderate light is completely mediated by cones, which provide color vision, black and white vision, and high acuity, the ability to discern fine detail. Like rods, cones contain an opsin and the chromophore 11-cis-retinal, but the opsins differ from rhodopsin so that each cone is responsive to one of three colors: red, green or blue. Cones are spread throughout the retina but are especially concentrated in a central area called the macula. At the center of the macula is the fovea, where only cones (no rods) are found, and these are densely packed. When we want to read or inspect fine detail, we move our heads and eyes until the image of interest falls onto the fovea. Because the fovea lacks rods, it is easier to see in dim light by looking to the side of an object instead of directly at it. You can test this by looking to the side of a faint star so that its image falls on rods, rather than on the fovea where it probably will not register. When you look directly at the faint star, it disappears.

In contrast to the wiring of rods, only a few cones converge onto other retinal neurons to average their signals, so cones provide better spatial resolution. In fact, each cone in the fovea synapses onto only one neuron in the next relay in the retina. This gives this area the ability to transmit fine detail, such as we use in reading.

Thus, cones mediate day vision and rods take over in dim light and at night. Both rods and cones can operate at the same time under some conditions: in dim or dark conditions, rods are most sensitive, but cones respond to stimuli that are sufficiently bright. This is why we can see the colors of neon lights on dark nights.

Nanolens:
 

Nanoscale lenses with superhigh resolution using a novel self-assembly method. So far, they've demonstrated that the tiny lenses can be used for ultraviolet lithography, for imaging objects too tiny for conventional lenses, and for capturing individual photons from a light-emitting nanostructure called a quantum dot.

 

Self-assembly line: The spherical nanolenses shown in this electron microscope image have separated from the crystalline nanotubes underneath them. The structures spontaneously form when a solution of cup-shaped organic molecules is allowed to evaporate. The limits on the resolution of both light microscopes and the photolithographic instruments used by the semiconductor industry are a consequence of light's fundamental properties. Because of the way light scatters, or diffracts, even a perfect lens cannot distinguish two objects that are closer together than half the wavelength of the light used to image them. nanolens overcome the diffraction limit because of their size. The lenses are flat on one side and spherical on the other and range in diameter from about 50 nanometers to three micrometers. Nanolens makes color imaging of nano objects possible Optical imaging of materials is full with rich physical, chemical and biological information about the sample, because the optical energies in the visible range coincide with the atomic and molecular transition energies of many materials. Apart from the topographical information, the optical image therefore contains information about intrinsic properties of a material. However, the wave nature of light prevents the light to focus in a volume smaller than half of the wavelength, which is about 200-300 nm for visible light. Therefore, it is almost impossible to image nanomaterials, which could be a few nanometers in size, using optical imaging process.

This metallic nanolens is capable of manipulating light in such a way that an optical image of nanoscale objects can be obtained in the visible range.

"We have demonstrated that our nanolens can transfer color images of nanoscale objects over distances of at least micrometer scale with a sufficient amount of magnification for far-field observation "We believe that, in principle, the image can be transferred over even longer distances without any significant loss. The proposed nanolens could potentially be a strong imaging tool, for example, for observing individual viruses and other nano-entities in the far field."

A metal always has free change carriers – called plasmons – moving collectively on the surface of the metal. Plasmons play a large role in the optical properties of metals since they can interact with light, and somehow manipulate the predicted nature of light.

One of the most important restriction was that only one particular wavelength that resonates with the plasmons can be used in imaging, which essentially means that a normal colored object – which emits many wavelengths – would not make a sharp image. The other problem was that the plasmons lose energy quite quickly as they propagate, making it impossible to have a long distance image transfer. Last, but not the least, the size of the image remained the same as the object (in the nanometer scale), and thus it was impossible to record these images."The design of a nanolens that involves a tapered stacked arrangement of silver nanorods. The layers are separated by nano-gaps, which prevents the propagation of plasmons, resulting in extremely low loss of energy and thus making long distance imaging possible. It appears that a gap size of 10 nm gives the optimum value for efficient imaging.

.Color imaging requires the resonance to be broad, so that a large part of the visible spectrum can be covered. "Our simulation results show that with an increasing number of layers, the number of resonant modes also increases, and they tend to gather in the vicinity of the fundamental mode of the corresponding unit rod"  "Moreover, the nanolens can also magnify the image so that the image can be large enough for normal viewing."

This technique has the potential to be an indispensable imaging tool, in particular, for bio-medical applications, where individual viruses and other nano-objects of different colors could be simultaneously imaged at a long distance and could be detected at sufficient magnification with usual microscopes and detectors, such as a CCD camera."A potential challenges lies in the accurate growth of silver nanorods with precise geometry, which involves growth of stacked arrays of silver nanorods where the arrays are separated with specific nano-gaps and are arranged in a tapered manner.

NANOWIRE:

In order to rectify this problem nanowires are used in smart eye .  semiconductor nanowires of high purity and crystallinity hold promise as building blocks for opto-electronical devices at the nanoscale.. they are commonly grown via a vapor-liquid-solid (vls) mechanism in which metal (nano) droplets collect the semiconductor precursors to form a solution which, when saturated, leads to the growth of a wire underneath the droplet.

 

after a brief discussion of this general mechanism, the growth of inp and zno nanowires is detailed. the grown inp nanowires have an integrated alloy particle and have on average diameters of 50 nm and lengths of 10 μm. zno nanowires grown on silicon oxide covered substrates exhibit an integrated alloy particle, have diameters in the 50-100 nm range and lengths of up to 50 μm. in contrast, under the same growth conditions, zno nanowires grown epitaxially on al2o3 substrates do not have an integrated gold particle and exhibit diameters mostly in the 100-300 nm range with lengths of up to 10 μm. finally it is shown that using a method that is widely applicable for nanostructures, zno nanowires can be doped with cobalt ions which is an important step towards room-temperature ferromagnetic semiconducting nanowires for spintronic applications.

nanowire-as  a  detector:

as humans, we are all born equipped with a pair of single-photon detectors-our eyes. actually, the story is a bit more complicated because, while the rod cells on the retina respond to the absorption of a single photon by generating a small current, the brain requires about ten photons to be absorbed before registering a flash of light.

for the applications in communications and metrology that we are interested in, however, the eye would not be a very good choice for a photodetector. first of all, the eye is insensitive to infrared (ir) light and responds to visible light only on millisecond timescales. in addition, high optical loss due to reflection and transmission at the ocular interfaces of the cells lowers the detection efficiency. finally, the eye requires an integrated, highly sophisticated, and thermally stable package-the human body-to maintain its performance. these same challenges-sensitivity, speed, optical loss, and packaging-must be addressed by any photodetector technology for it to be of use.

Infrared Detection:

though other ir single-photon detectors exist, they also have shortcomings. avalanche photodetectors (apds) exhibit impressively low jitter (the error in the time-of-arrival information of the photon) and good detection efficiencies, but are plagued by relatively long (microsecond timescale) reset times and high dark-count rates (the rate at which the detector fires even when a photon is not incident). photomultiplier tubes (pmts) can provide very fast reset times, but suffer from low detection efficiencies in the technically important-to the communications industry-ir region of the spectrum around 1550 nm.

Operation of the Nanowire Detector:

The currently theorized operating principle of the nanowire detector is surprisingly straightforward. when a photon is absorbed by a superconducting wire it creates a hot spot-a small region where the superconductor becomes resistive. a current running through the wire will avoid that hot spot, preferring instead the zero-resistance regions outside the perimeter and on either side of the spot-regions we call the “sidewalks” of the device. the current density in these sidewalks therefore increases. but superconductors also have the interesting and useful property that they only superconduct up to a maximum current density, known as the critical current density. above this current, they become resistive. if the biasing current is initially set very close to the critical current, the absorption of a photon will trigger the entire cross section of the wire to switch into the resistive state and a voltage will appear across the device terminals.

 

figure: operation of the superconducting nanowire single-photon detector is based on how the niobium nitride nanowire responds to an incident photon as it creates a resistive “hot spot” on the detector surface.

while this mechanism of operation may seem simplistic, great care must be taken to realize a device with the observed performance. the starting material for our work (and the majority of the experimental work on this kind of detector to date) is 4-nm-thick niobium nitride material grown epitaxially on a sapphire substrate. state pedagogical university.

after material growth, we pattern the substrates using electron-beam lithography and a series of custom-developed nanometer-length-scale etching, deposition, and optical-lithography steps. the electron-beam lithography is a particularly challenging aspect of the work, as the variation in the device linewidth must be kept below a few percent. this is accomplished using hydrogen silsesquioxane (hsq), an electron-sensitive spin-on-glass resist with very low line-edge roughness and high resolution. the hsq material has the very useful property that after exposure and development it is also a good optical material-similar to silicon dioxide (sio2)-and so we use it throughout the process as part of the final integrated optical device, as well as an electron resist.

 

figure: a conceptual illustration (top) of a superconducting-nanowire single-photon detector being illuminated with laser light shows the microcavity consisting of a nanowire layer, a silicon-like optical-material spacer (above the nanowire layer), and a gold mirror (above the spacer). the laser beam should be smaller in width than the final detector (although the laser beam is currently somewhat wider). a scanning-electron micrograph (bottom) shows a 90-nm-wide niobium nitride nanowire pattern.

device testing is as challenging as fabrication: we have screened several hundred devices in the course of this work at temperatures down to 1.7 k. the detectors must also be packaged carefully, to reduce electrical noise in the readout and biasing circuits, and to couple light efficiently onto the detector surface.

SCANNING TUNNELING MICROSCOPE:

 
An instrument for producing surface images with atomic-scale lateral resolution, in which a fine probe tip is scanned over the surface at a distance of 0.5–1 nanometer, and the resulting tunneling current, or the position of the tip required to maintain a constant tunneling current, is monitored.

Scanning tunneling microscopes have pointed electrodes that are scanned over the surface of a conducting specimen, with help from a piezoelectric crystal whose dimensions can be altered electronically. They normally generate images by holding the current between the tip of the electrode and the specimen at some constant value by using a piezoelectric crystal to adjust the distance between the tip and the specimen surface, while the tip is piezoelectrically scanned in a raster pattern over the region of specimen surface being imaged. By holding the force, rather than the electric current, between tip and specimen at a set-point value, atomic force microscopes similarly allow the exploration of nonconducting specimens. In either case, when the height of the tip is plotted as a function of its lateral position over the specimen, an image that looks very much like the surface topography results.

It is becoming increasingly possible to record other signals (such as lateral force, capacitance, scan-related tip displacement, temperature, light intensity, or magnetic resonance) as the tip scans. For example, modern atomic force microscopes can map lateral force and conductivity along with height, while image pairs from scanning tunneling microscopes scanning to and fro can provide information about friction as well as topography.

Scanning tunneling microscopes make it possible not just to view atoms but to push them and even to rearrange them in unlikely combinations (sometimes whether or not these rearrangements are desirable). A few considerations of scale are important in understanding this process. Atoms comprise a positive nucleus and a surrounding cloud of negative electrons. These charges rearrange when another atom approaches, with unlike charges shifting to give rise to the van der Waals force of attraction between neutral atoms. This force makes gravity (and most accelerations) ignorable when contact between solid objects in the micrometer size range and smaller is involved, since surface-to-volume ratios are inversely proportional to object size.

The electric field in the scanning tunneling microscope allows plucking as well, in which adsorbed or substrate atoms are removed and transferred to the electrode tip with a suitable voltage pulse. Because the electric field from the tip falls off less rapidly with separation than do van der Waals forces, the most weakly attached nearby atom rather than the nearest may end up being removed. One solution to this problem is a hybrid approach. By invoking the tip electric field for bond breaking only when the tip is sufficiently close to the target atom that the van der Waals forces contribute as well, atoms on silicon could be singly removed and redeposited at will.
A third kind of selective bond breaking was also demonstrated. It involved the selective breaking of silicon-hydrogen bonds using electron energies below those necessary to break bonds directly. Since the desorption probability was observed to vary exponentially with the tip-specimen current, it is believed that vibrational heating from inelastic electron tunneling mediated the chemical transition in this work. This work involves bond alteration at the level of signal atoms, the ultimate frontier for lithographic miniaturization.Visual information travels from retinal ganglion cells to the brain:After converting light into electrical signals in their cell membranes, rods and cones transmit this information to other neurons in internal circuits in the retina for processing. From these cells, messages go to the final retinal station, the ganglion cells, whose axons exit the eyeball at the optic disc and form the optic nerve, which contains about one million axons. Because all the nerve fibers converge at the optic disc, no rods or cones are in this area and it forms a "blind spot" on the retina:

 

Within the optic nerve, a defined group of axons from each eye crosses over to join the opposite optic nerve at the optic chiasma
so each side of the brain receives visual information from both eyes. After the chiasma, retinal axons go to one of three areas: two of these are in the midbrain and one is in the thalamus. The information going to the midbrain does not reach conscious levels but rather produces pupillary reflexes (which are controlled by the autonomic nervous system) and eye movements. In the thalamus, ganglion cell axons transmit signals to neurons in the lateral geniculate nucleus (LGN) where information is processed and then carried by LGN axons to the primary visual cortex in the occipital lobe of the cerebrum. These cortical cells then send messages to other "higher" cortical areas.

OPERATION:

The external image is capture by the CCD sensors placed in the eye glasses then it sends  the  digital pulse through  laser beam to the colour filter which  is the first part in retina implant it allows the particular colour to the nano lens .nano lens focus the images and that image will be send to nanowires..

..

nanowires detect  the input image signal and simulate the phosphenes this result the electric signal is producerd at the output  of nanowires .this electrical signal is amplified and it is given to STM tip .it has sharp tip at one end the electrical signal activates the cell in retina then this signal is send to brain through nerves  so the blind person can able to see the image.

CONCLUSION:

Sufficiently advanced technologies developed to treat diseases will inevitably morph into the technologies that will enhanced function .research on artificial implant for blindness is laying the groundwork for the eventual development of vastly superior, artificially enhanced eyesight. The smart eye can also be used in camera for remote monitoring for safety, identification and biometrics purposes. The amazing optical properties of nanowires enhance the efficiency of electronic eye. So there is no doubt that smart eye plays a major role in enhancing the eyesight of sightless person .

REFERENCES:

 1.g.n.goltsmam,o.okunuv”picosecond superconducting single photon optical dectector.

2.s.denny,”medical electronics “-fourth edition

3.www.opticinfobase.com