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1 BIONIC EYE

Bionic-eye Org PPT

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Page 1: Bionic-eye Org PPT

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BIONIC EYE

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Overview

Human eye Eye defects History Bonic eye-2 approaches MARC MARC System Functionality ASR Retinal Implants Advantages & Disadvantages Future Scopes

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Human Eye

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Eye Defects .

a.RETINIS PIGMENTOSA Caused by the breakdown in the function of

rods &cones

b.MACULAR DEGENERATION Retinal Pigment Epithelium gradually wears out

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HISTORY

Why bionic eye? .No proven effective remedy for these disorders

. In 1988 ,Dr.Humayun proved that the nerves behind the retina still function even when the retina degenerated

.1990-ArgusII ,bionic eye was developed by U.S company Second Sight

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Bionic Eye:Two Approaches

MARC-Multiple Unit Artificial Retina Chipset

ASR-Artificial Silicon Retina

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Multiple Unit Artificial Retina Chipset (MARC) – The Concept

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MARC System Functionality

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Extra-Ocular CMOS Camera & Video Processing

The CMOS Image Sensor

•Cost Effective for IC’s

•Low Power, less volume

•Easily mounted on a pair of glasses

Video Processing

• Implemented using SRAM Frame buffers, ADC & a FPGA/ CPLD

•Reconfigurable FPGA’s allow flexibility for various Image Processing Algorithms including Artificial Neural Networks

Back

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ASK-PWM Encoding

Alternate Mark Inversion

•Each pulse encodes 1 bit of data

•0’s represented by 50% duty cycle pulses

•1’s represented by pulses with alternating larger or smaller duty cycles (75% & 25% respectively) symmetric around 50%

Back

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Class-E Power Amplifier

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.The class E amplifier is a highly efficient switching power amplifier, typically used at such high frequencies that the switching time becomes comparable to the duty time

.The whole circuit performs a damped oscillation.

.With load, frequency, and duty cycle (0.5) as given parameters the four parameters (L,L0,C,C0) are determined.Back

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RF Telemetry

An Inductive Link consists of 2 resonant circuits

Mutual Inductance M plays a vital role, Maximizing it is very important

As the MARC transmits information via AM/ASK, fluctuations in the coupling constant could potentially be perceived as information by the processing chips

Primary coil is driven with 0.5-10MHz signal for Power accompanied by a 10KHz ASK signal which provides data

It is suitably recovered at the receiving end

Back

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Data, Clock & Power Recovery

Data & Clock Recovery The low frequency data signal is

obtained by a Low Pass filtering The first RF signal conveys the

configuration data which sets the pulse width, height and period Then the actual Image is transmitted

ASK demodulator obtains the PWM scheme.

Delay Locked Loop (DLL) deciphers the PWM wave to obtain the Data transmitted

Clock is defined as the rising edge of the pulse & no explicit clock recovery circuits are required

Power Recovery The high frequency RF carrier

envelope is obtained by filtering the output of receiver coil

The sinusoidal signal is then amplified to suitable levels and then rectified

Rectification provides the required DC voltage power

Back

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Current Controller and Stimulator

20 controlled variable current (CVCS) sources are designed for retinal simulation

Each receive clocking & data info from deciphered PWM wave

Each CVCS is connected to 5 electrodes through a DEMUX

Each current source provides sixteen level (4 bit) linear gray-scale stimulus

Thus each of the 100 electrodes are exited by different currents which form the desired image pattern

Back

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Typical Image Formation

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MARC-3 Chips

The Electrode Array Photograph of MARC-3 Chip

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Important Aspects

Field of View More the number of Ganglion cells stimulated, more is the field of

view Thus large electrodes and the area becomes a trade-off

Changing Scene and Real-time vision The whole process must happen extremely fast so that patients see

in real time This is important as any noticeable lag could stimulate the

"vestibular-ocular reflex", making people feel dizzy and sick.

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REVIEW

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The Resolution Challenge

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Artificial Silicon Retina: The Second Approach

The ASR is a silicon chip2 mm in diameter and 1/1000 inch in thickness.

It contains approximately3,500 microscopic solar cells called "microphotodiodes,“

each having its own stimulating electrode.

These microphotodiodes are designed to convert the light energy from images into thousands of tiny electrical impulses

Adv: Receives power from light entering the eye

Eliminates use of power supplies

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Epiretinal Approach involves a semiconductor based device positioned on the surface of the retina to try to simulate the remaining overlying cells of the retina.

Subretinal Approach involves implanting the ASR chip behind the retina to simulate the remaining viable cells.

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Approaches Towards Retinal Prosthetic Implantation

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Subretinal Implant

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Artifical Retina Component Chip(ARCC)

.02mm thick very small device Placed b/w layers of retina. A secondary device attached to a pair of

eyeglasses directs a laser at the chip's solar cells to provide power. The laser would have to be powered by a small battery pack.

According to researchers, the ARCC will give blind patients the ability to see 10 by 10 pixel images.

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The Images

The top image shows the raw output of the retina chip.

The middle one a picture processed from it.

The third shows how a moving face would appear.

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Advantages

Assit people suffering from RP&AMD Quite durable –last for atleast 10yrs inside eye. Easy surgical methods involved Small component size Reduction of stress upon the retina

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Disadvantages

Donot restore perfect vision but gives sense of surroundings

Only effective for people who once had sight Optic nerves should be functional atleast

partiallly Cost around $30,000

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Future scopes

Face recognition –use of 1000 electrodes Bionic eye to work beyond capability of human

eye. Detect X-ray,infrared,night vsion. Reduced cost Run software algorithms

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References

E.D. Juan, Jr. M. S. Humayun, H. D. Phillips; “Retinal Microstimulation,” M. Humayun, “Is Surface Electrical Stimulation of the Retina a Feasible

Approach Towards The Development of a Visual Prosthesis?” Phillips, “Visual Perception Elicited by Electrical Stimulation of Retina in

Blind Humans by Electrical Stimulation of Retina in Blind Humans,” Arch.

Ophthalmol, pp. 40-46, vol. 114, Jan. 1996. W. Liu, E. McGucken, K. Vichiechom, M. Clements, E. De Juan, and M. Humayun,

“Dual Unit Retinal Prosthesis,” IEEE EMBS97. Mueller, M. Humayun, E. de Juan, “An Implantable Neuro-stimulator Device

for a Retinal Prosthesis,” E. McGucken, “Multiple Unit Artificial Retina Chipset to Benefit The Visually

Impaired and Enhanced CMOS Phototransistors,”

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