micro electronic pill

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Seminar Report Micro Electronic Capsule

ABSTRACT

A micro electronic pill is basically a multi channel sensor used for remote bio

medical measurements using microtechnology this has been developed for the internal study and

detection of diseases and abnormalities in the gastro intestinal GI tract where restricted access

prevents the use of traditional endoscopy the measurement parameters for detection include real

time remote recording of temperature, pH, conductivity and dissolved oxygen in the GI tract

This paper with the design of the micro electronic pill which mainly consists of an outer

biocompatible capsule encasing 4 channel micro sensors a control chip, a discrete component

radio transmitter and 2 silver oxide cells.

In this report, we present a novel analytical micro system which incorporates a four-channel

micro sensor array for real-time determination of temperature, pH, conductivity and oxygen. The

sensors were fabricated using electron beam and photolithographic pattern integration, and were

controlled by an application specific integrated circuit (ASIC), which sampled the data with 10-bit

resolution prior to communication off chip as a single interleaved data stream. An integrated radio

transmitter sends the signal to a local receiver (base station), prior to data acquisition on a computer.

Real-time wireless data transmission is presented from a model in vitro experimental setup, for the

first time.

ECE Department , SRMGPC , Lucknow

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CONTENTS

i. INTRODUCTION

ii. BLOCK DIAGRAM

iii. BASIC COMPONENTS

iv. PERFORMANCE

v. ADVANTAGES/DISADAVNATGES

vi. OTHER APPLICATIONS

vii. FUTURE DEVELOPMENTS

viii. FUTURE CHALLENGES

ix. CONCLUSION

x. REFERENCES


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INTRODUCTION

The invention of transistor enabled the first use of radiometry capsules, which used

simple circuits for the internal study of the gastro-intestinal (GI) [1] tract. They couldn’t be used

as they could transmit only from a single channel and also due to the size of the components.

They also suffered from poor reliability, low sensitivity and short lifetimes of the devices. This

led to the application of single-channel telemetry capsules for the detection of disease and

abnormalities in the GI tract where restricted area prevented the use of traditional endoscopy.

They were later modified as they had the disadvantage of using laboratory type

sensors such as the glass pH electrodes, resistance thermometers, etc. They were also of very

large size. The later modification is similar to the above instrument but is smaller in size due to

the application of existing semiconductor fabrication technologies. These technologies led to the

formation of “MICROELECTRONIC CAPSULE”.

Microelectronic pill is basically a multichannel sensor used for remote biomedical

measurements using micro technology. This is used for the real-time measurement parameters

such as temperature, pH, conductivity and dissolved oxygen. The sensors are fabricated using

electron beam and photolithographic pattern integration and were controlled by an application

specific integrated circuit (ASIC).


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BLOCK DIAGRAM

Fig 1.

Microelectronic pill consists of 4 sensors (2) which are mounted on two silicon chips (Chip 1 & 2), a control chip (5), a radio transmitter (STD- type 1-7, type2-crystal type-10) & silver oxide batteries (8).1-access channel, 3-capsule, 4- rubber ring, 6-PCB chip carrier


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BASIC COMPONENTS

A. SENSORS

Fig 2.

There are basically 4 sensors mounted on two chips- Chip 1 & chip 2. On chip 1(shown in fig 2 a), c), e)), temperature sensor silicon diode (4), pH ISFET sensor (1) and dual electrode conductivity sensor (3) are fabricated. Chip 2 comprises of three electrode electrochemical cell oxygen sensor (2) and optional NiCr resistance thermometer.


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1) Sensor chip 1:

An array consisting of both temperature sensor & pH sensor platforms were cut

from the wafer & attached onto 100-µm- thick glass cover slip cured on a hot plate. The plate acts

as a temporary carrier to assist handling of the device during level 1 of lithography when the

electric connections tracks, electrodes bonding pads are defined. Bonding pads provide electrical

contact to the external electronic circuit.

Lithography [2] was the first fundamentally new printing technology since the

invention of relief printing in the fifteenth century. It is a mechanical Plano graphic process in

which the printing and non-printing areas of the plate are all at the same level, as opposed to

intaglio and relief processes in which the design is cut into the printing block. Lithography is

based on the chemical repellence of oil and water. Designs are drawn or painted with greasy ink

or crayons on specially prepared limestone. The stone is moistened with water, which the stone

accepts in areas not covered by the crayon. Oily ink, applied with a roller, adheres only to the

drawing and is repelled by the wet parts of the stone. Pressing paper against the inked drawing

then makes the print.

Lithography was invented by Alois Senefelder in Germany in 1798 and, within

twenty years, appeared in England and the United States. Almost immediately, attempts were

made to print pictures in color. Multiple stones were used; one for each color, and the print went

through the press as many times as there were stones. The problem for the printers was keeping

the image in register, making sure that the print would be lined up exactly each time it went


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through the press so that each color would be in the correct position and the overlaying colors

would merge correctly.

Early colored lithographs used one or two colors to tint the entire plate and create a

watercolor-like tone to the image. This atmospheric effect was primarily used for landscape or

topographical illustrations. For more detailed coloration, artists continued to rely on hand

coloring over the lithograph. Once tinted lithographs were well established, it was only a small

step to extend the range of color by the use of multiple tint blocks printed in succession.

Generally, these early chromolithographs were simple prints with flat areas of color, printed

side-by-side.

Increasingly ornate designs and dozens of bright, often gaudy, colors characterized

chromolithography in the second half of the nineteenth century. Overprinting and the use of

silver and gold inks widened the range of color and design. Still a relatively expensive process,

chromolithography was used for large-scale folio works and illuminated gift books that often

attempted to reproduce the handwork of manuscripts of the Middle Ages. The steam-driven

printing press and the wider availability of inexpensive paper stock lowered production costs and

made chromolithography more affordable. By the 1880s, the process was widely used for

magazines and advertising. At the same time, however, photographic processes were being

developed that would replace lithography by the beginning of the twentieth century.

Chip 1 is divided into two- LHS unit having the diode while RHS unit comprises the

ISFET.

Fig. 3.

DT-470-SD Features


http://www.lakeshore.com/temp/sen/sd400_po.html

http://www.lakeshore.com/temp/sen/sd670_po.html

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Monotonic temperature response from 1.4 K to 500 K*

Conformance to standard Curve 10 temperature response curve

Useful above 60 K in magnetic fields up to 5 T

The rugged, reliable Lake Shore SD package designed to withstand repeated thermal cycling

and minimize sensor self-heating Variety of packaging options

ISFET: [4]

Ion Selective Field Effect Transistor; this type of electrode contains a transistor

coated with a chemically sensitive material to measure pH in solution and moist surfaces. As the

potential at the chemically active surface changes with the pH, the current induced through the

transistor varies. A temperature diode simultaneously monitors the temperature at the sensing

surface. The pH meter to a temperature compensated pH reading correlates the change in current

and temperature.

This device [5] has an affinity for hydrogen ions, which is the basis for the

determination of the pH. The surface of the sensitive area of the sensor contains hydroxyl groups

that are bound to an oxide layer. At low pH values hydrogen ions in the sample will bind to these

hydroxyl groups resulting in a positively charged surface. In alkaline environments hydrogen

ions are abstracted from the hydroxyl groups, leading to a negatively charged surface.

Thus, each pH change has a certain influence on the surface charge. On its turn, this

attracts or repulses the electrons flowing between two electrodes in the semiconductor device.

The electronics compensates the voltage in order to keep the current between the two electrodes

at its set point. In this way this potential change is related to the pH.

Attachment of a polymer membrane on the ISFET introduces the possibility to go

beyond the measurement of pH toward other ions. In this plastic layer certain chemicals

(ionophores), which can recognize and bind the desired ion, are put in. Now, complex

formations of the ionophore and the ion introduce a charge. The potential change is a measure

for the ion concentration. Typically, these sensors can be used in a concentration range between

app. 10-5 up to 1 mol/l.

2.) Sensor chip2:


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Level 1 pattern was defined in 0.9 µm UV3 resist by electron beam lithography. It

contains three-electrode electrochemical oxygen sensor & NiCr resistance thermometer.

Oxygen sensor detection principle: [6]

Most portable or survey instruments used for workplace evaluation of oxygen

concentrations make use of "fuel cell" type oxygen sensors. "Fuel cell" oxygen sensors consist of

a diffusion barrier, a sensing electrode (cathode) made of a noble metal such as gold or platinum,

and a working electrode made of a base metal such as lead or zinc immersed in a basic

electrolyte (such as a solution of potassium hydroxide).

Oxygen diffusing into the sensor is reduced to hydroxyl ions at the cathode:

O2 + 2H2O + 4e- OH –

Hydroxyl ions in turn oxidize the lead (or zinc) anode:

2Pb + 4OH 2PbO + 2H2O + 4e –

This yields an overall cell reaction of:

2Pb + O2 2PbO

Fuel cell oxygen sensors are current generators. The amount of current generated is

proportional to the amount of oxygen consumed (Faraday's Law). Oxygen reading instruments

simply monitor the current output of the sensor.

An important consideration is that fuel cell oxygen sensors are used up over time.

In the cell reaction above, when all available surface area of the lead (Pb) anode has been

converted to lead oxide (PbO), electrochemical activity ceases, current output falls to zero, and the

sensor must be rebuilt or replaced. Fuel cell sensors are designed to last no more than one to two

years. Even when installed in an instrument which is never turned on, oxygen sensors which are

exposed to atmosphere which contains oxygen are generating current, and being used up.


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Oxygen sensors are also influenced by the temperature of the atmosphere

they are being used to measure. The warmer the atmosphere the faster the electrochemical

reaction. For this reason oxygen sensors usually include a temperature compensating load resistor

to hold current output steady in the face of fluctuating temperature. (Microprocessor based

instrument designs usually provide additional signal correction in software to further improve

accuracy.) Another limiting factor is cold. The freezing temperature of electrolyte mixtures

commonly used in oxygen sensors tends to be about 5 o F (- 20 o C). Once the electrolyte has frozen

solid, electrical output falls to zero, and readings may no longer be obtained. There are two basic

variations on the fuel cell oxygen sensor design. These variations have to do with the mechanism

by which oxygen is allowed to diffuse into the sensor. Dalton's Law states that the total pressure

exerted by a mixture of gases is equal to the sum of the partial pressures of the various gases. The

partial pressure for oxygen is that fraction of the total pressure due to oxygen. Partial atmospheric

pressure oxygen sensors rely on the partial pressure (or pO 2) of oxygen to drive molecules through

the diffusion barrier into the sensor. As long as the pO 2 remains constant, current output may be

used to indicate oxygen concentration. On the other hand, shifts in barometric pressure, altitude, or

other conditions which have an effect on atmospheric pressure will have a strong effect on pO 2

sensor readings. To illustrate the effects of pressure on pO 2 sensors, consider a sensor located at

sea level where atmospheric pressure equals 14.7 PSI (pounds per square inch). Now consider that

same sensor at an elevation of 10,000 feet. Although at both elevations the air contains 20.9

percent oxygen, at 10,000 feet the atmospheric pressure is only 10.2 PSI! Since there is less force

driving oxygen molecules through the diffusion barrier into the sensor, the current output is

significantly lower.

"Capillary pore" oxygen sensor designs include a narrow diameter tube through

which oxygen diffuses into the sensor. Oxygen is drawn into the sensor by capillary action in

much the same way that water or fluid is drawn up into the fibers of a paper towel. While capillary

pore sensors are not influenced by changes in pressure, care must be taken that the sensor design

includes a moisture barrier in order to prevent the pore from being plugged with water or other

fluids.


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Figure 4: Capillary pore type oxygen sensor

1.1. Effects of contaminants on oxygen sensors

Oxygen sensors may be affected by prolonged exposure to "acid" gases such as

carbon dioxide. Most oxygen sensors are not recommended for continuous use in atmospheres

which contain more than 25% CO 2.

1.2. Substance-specific electrochemical sensors

One of the most useful detection techniques for toxic contaminants is the use of

substance-specific electrochemical sensors installed in compact, field portable survey

instruments. Substance-specific electrochemical sensors consist of a diffusion barrier which is

porous to gas but nonporous to liquid, reservoir of acid electrolyte (usually sulfuric or

phosphoric acid), sensing electrode, counter electrode, and (in three electrode designs) a third

reference electrode. Gas diffusing into the sensor reacts at the surface of the sensing electrode.

The sensing electrode is made to catalyze a specific reaction. Dependent on the sensor and the

gas being measured, gas diffusing into the sensor is either oxidized or reduced at the surface of

the sensing electrode. This reaction causes the potential of the sensing electrode to rise or fall

with respect to the counter electrode. The current generated is proportional to the amount of

reactant gas present.

This two electrode detection principle presupposes that the potential of the counter

electrode remains constant. In reality, the surface reactions at each electrode causes them to

polarize, and significantly limits the concentrations of reactant gas they can be used to measure.

In three electrode designs it is the difference between the sensing and reference electrode which


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is what is actually measured. Since the reference electrode is shielded from any reaction, it

maintains a constant potential which provides a true point of comparison. With this arrangement

the change in potential of the sensing electrode is due solely to the concentration of the reactant

gas.

Figure 5: Three electrode electrochemical sensor

The oxidation of carbon monoxide in an electrochemical sensor provides a good

example of the detection mechanism:

Carbon monoxide is oxidized at the sensing electrode:

CO + H2O CO2 + 2H+ + 2e -

The counter electrode acts to balance out the reaction at the sensing electrode by reducing

oxygen present in the air to water:

1/2 O2 + 2H+ + 2e- H 2O

Similar reactions allow for the electrochemical detection of a variety of reactant

gases including hydrogen sulfide, sulfur dioxide, chlorine, hydrogen cyanide, nitrogen dioxide,

hydrogen, ethylene oxide, phosphine and ozone. A bias voltage is sometimes applied to the

counter electrode to help drive the detection reaction for a specific contaminant. Biased sensor


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designs allow for the detection of a number of less electrochemically active gases such as

hydrogen chloride and nitric oxide. Several other contaminants (such as ammonia) are detectable

by means of other less straight forward detection reactions.

Electrochemical sensors are stable, long lasting, require very little power and are

capable of resolution (depending on the sensor and contaminant being measured) in many cases

to 0.1 ppm. The chief limitation of electrochemical sensors is the effects of interfering

contaminants on toxic gas readings. Most substance-specific electrochemical sensors have been

carefully designed to minimize the effects of common interfering gases. Substance-specific

sensors are designed to respond only to the gases they are supposed to measure. The higher the

specificity of the sensor the less likely the sensor will be affected by exposure to other gases

which may be incidentally present. For instance, a substance-specific carbon monoxide sensor is

deliberately designed not to respond to other gases which may be present at the same time, such

as hydrogen sulfide or methane.

Even though care has been taken to reduce cross-sensitivity, some interfering gases

may still have an effect on toxic sensor readings. In some cases the interfering effect may be

"positive" and result in readings which are higher than actual. In some cases the interference may

be negative and produce readings which are lower than actual. Electrochemical sensor designs

may include a selective external filter designed to remove interfering gases which would

otherwise have an effect on the sensing electrode. The size and composition of the filter are

determined by the type and expected concentration of the interfering contaminants being

removed.


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B. CONTROL CHIP:

Fig 6. Interfacing of ASIC with external components of the system

ASIC is the control chip that connects together the external components of the

micro system.

Application-Specific Integrated Circuit [7]

(ASIC) An integrated circuit designed to perform a particular function by defining

the interconnection of a set of basic circuit building blocks drawn from a library provided by the

circuit manufacturer.

ASIC is a novel mixed signal design that contains an analog signal conditioning

module operating the sensors, 10-bit ADC & DAC converters & a digital data processing

module. An RC relaxation oscillator (OSC) provides the clock signal.


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The analog module is based on the AMS OP05B opamp, which offer a lot of power

saving scheme (sleep mode) & a compact IC design. The temperature circuitry biased the diode

at constant current, so that a change in temperature would result in corresponding change in

diode voltage. The pH ISFET sensor was biased as a simple source & drain follower at constant

current with D-S voltage changing with threshold voltage & pH. Conductivity circuit operated at

direct current measuring the resistance across the electrode pair as an inverse function of

solution conductivity. An incorporated potentiostat operated the amperometric oxygen sensor

with a 10-bit DAC controlling the working electrode potential w.r.t. reference. The analog

signals were sequenced through a MUX prior to being digitized by the ADC. The BW for each

channel was limited by the sampling interval of 0.2 ms.

The digital data processing module conditioned the digitized signals through the

use of a serial bit stream data compression algorithm, which decided when transmission was

required by comparing the most recent sample with the previous one. This minimizes the

transmission length & particularly effective when the measuring environment is at quiescent, a

condition encountered in many applications. The entire design is based on low power

consumption & immunity from noise interference. The digital module is clocked at 32 kHz &

employed in sleep mode to conserve power from analog module.


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C. RADIO TRANSMITTER

It’s assembled prior to integration in the capsule using discrete surface mount

components on a single-sided PCB. It’s designed to operate at a transmission freq. of 40.01 MHz

at 20˚C generating a signal of 10 kHz. BW. A second crystal stabilized transmitter was also used.

This unit is similar to the free running STD transmitter, having a transmission freq. limited to

20.08 MHz at 20˚C, due to crystal used. Pills incorporating the STD transmitter are Type 1, where

as the pills having crystal stabilized unit is Type 2. The transmission range was measured as being

1 m & the modulation scheme FSK, with a data rate of 1 kb/s.

Fig 7.

Capsule

The microelectronic pill consists of a machined biocompatible (non-cytotoxic),

chemically resistant polyether-terketone (PEEK) capsule and a PCB chip carrier acting as a

common platform for attachment of sensors, ASIC, transmitter & batteries (fig 1.). The fabricated

sensors were each attached by wire bonding to a custom made chip carrier made from a 10-pin,

0.5-pitch polymide ribbon connector. The connector in turn was connected to an industrial STD.

flat cable plug (FCP) socket attached to the PCB carrier chip of the microelectronic pill, to

facilitate the rapid replacement off the sensors when required. The PCB chip carrier was made

from 2 STD. 1.6 mm-thick fiber glass boards attached back to back epoxy resin which maximized

the distance between the 2 sensor chips. The sensor chips are connected to both sides of the PCB

by separate FCP sockets, with sensor chip 1 facing the top face, with the sensor chip 2 facing


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down. Thus, the oxygen sensor on chip 2 had to be connected to the top face by 3 200 nm copper

leads soldered onto the board. The transmitter was integrated in the PCB which also incorporated

the power supply rails, the connection points to the sensors, as well as the transmitter & the ASIC

& the supporting slots for the capsule in which the carrier is located.

The ASIC was attached with double-sided Cu conducting tape prior to wire

bonding to the power supply rails, the sensor inputs & the transmitter (a process which entailed the

connection of 64 bonding pads). The unit was powered by 2 STD. 1.55V SR44 Silver oxide

(Ag2O) cells with a capacity of 175mAh. The batteries were connected & attached to a custom

made 3-pin, 1.27 mm pitch plug by electrical epoxy. The connection on the matching socket on the

PCB carrier provided a three point power supply to the circuit comprising a negative supply rail

(1.55V).

Fig 8.

The capsule was machined as two separate screw-fitting compartments. The PCB

chip carrier was attached to the front section of the capsule (fig 1.). The sensor chips were exposed

to the ambient environment through access ports & were sealed by 2 stainless steel clamps

incorporating a 0.8 µm thick sheet of Viton fluoroelastometer seal. A 3 mm dia access channel in

center of each of the steel clamps (incl. the seal), exposed in sensing regions of the chips. The rear

section of the capsule is attached to the front section by a 13 mm screw connection incorporating a

Viton rubber O-ring. The seals rendered the capsule water proof, as well as making it easy to

maintain (e.g. during sensor & battery replacement).The complete prototype was 16*55 mm &

weighs 13.5 g including the batteries.


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D. AG2O Batteries

Fig 9.

The unit was powered by two standard 1.55-V SR44 silver oxide (Ag2O) cells with a capacity of

175 mAh. The batteries were serial connected and attached to a custom made 3-pin, 1.27-mm pitch

plug by electrical conducting epoxy. The connection to the matching socket on the PCB carrier

pro-vided a three point power supply to the circuit comprising a negative supply rail (-1.55 V),

virtual ground (0 V), and a positive supply rail (1.55 V). The battery pack was easily replaced

during the experimental procedures.

1. 2 SR44 Ag2O batteries are used.

2. Operating Time > 40 hours.

3. Power Consumption = 12.1 Mw

4. Corresponding current consumption = 3.9mA

5. Supply Voltage = 3.1 V


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PERFORMANCE

Fig 10. a) Temperature Channel Performance, b) pH channel performance

A. Temperature Channel Performance:

The linear sensitivity was measured over a temp. range from 0˚C to 70˚C & found

to be 15.4 mV/˚C. This amplified signal response was from the analog circuit, which was later

implemented in the ASIC. The sensor (Fig 10a) a)), once integrated in the pill, gave a linear

regression of 11.9 bits/˚C , with a resolution limited by the noise band of 0.4 ˚C (Fig 10 a) b)). The

diode was forward biased with a constant current (15 µA) with the n-channel clamped to the

ground, while p-channel was floating. Since the bias current supply circuit was clamped to the

negative V rail, any change in the supply voltage potential would cause the temp. channel to drift.


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Thus, it was seen that o/p signal changed by 1.45 mV/mV change in supply expressed in mV,

corresponding to a drift of – 41.7 mV/h in the pill from a supply voltage change of –14.5 mV/h.

B. pH Channel Performance:

The linear performance from pH 1 to 13 corresponded to sensitivity of –41.7mV/pH

unit at 23˚C. The pH ISFET sensor operated in a constant current mode (15 µA), with drain

voltage clamped to positive supply rail & the source voltage floating with the gate potential. The

Ag/AgCl reference electrode, representing the potential in which the floating gate was referred to,

was connected to ground. The sensor performance, once integrated in the pill (Fig 10 b)a)),

corresponded to 14.85 bits/pH which give a resolution of 0.07 pH/ data point. The sensor exhibits

a larger responsivity in alkaline solutions.

The sensor life time of 20h was limited by Ag\Agcl reference electrode made from electroplated

silver. The ph sensor exhibited a signal drift of –6 mV /h (0.14ph), o f which –2.5mV/h was

estimated to be due to the dissolution of Agcl from the reference electrode. The temperature

sensitivity of the ph sensor was measured as 16.8mV/˚c. The changing of the ph of the solution at

40˚c from ph 6.8 to 2.3 and 11.6 demonstrated that the two channels were completely independent

of each other and there was no signal interference from the temperature channel (Fig 10. b (b))

C. Conductivity sensor performance

The prototype circuit exhibited a logarithmic performance from 0.05 to 10 ms cm -1 which

conformed to a first-order regression analysis expressed in millivolts. The sensor saturated at

conductivities above 10 ms cm-1 due to the capacitive effect of the electric double layer, a

phenomena commonly observed in conductimetric sensor systems.


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D. Oxygen Sensor performance

The electrodes were first characterized using the model redox compound FMCA, showing that the

oxygen sensor behaved with classic microelectrode characteristics. The reduction potential of water

was subsequently measured at -800 mV (versus the integrated Ag|AgCl) by recording the steady-

state current in oxygen-depleted PBS, t hereby excluding any interfering species.

In order to calibrate the sensor, a three point calibration was performed (at saturated oxygen,

and with oxygen removed by the injection of Na2SO3 to a final concentration of 1 M). the steady

state signal from the oxygen saturated solution was recorded at a constant working electrode

potential of -700 mV(versus Ag|AgCl).which was below the reduction potential for water. This

generated a full-scale signal of 65 nA corresponding 8.2 mg O2L-1. The injection of Na2S03 into the

PBS after 90 s provided the zero point calibration. This fall in the reduction current provided

corroborative evidence that dissolve oxygen was being recorded, by returning the signal back to the

base line level once all available oxygen was consumed. A third, intermediate point was generated

through the addition of 0.01 M Na2SO3. The resulting calibration graph form a linear regression

expressed in nanoamperes. The sensitivity of the sensor was 7.9 nA mg-1 O2,with the resolution of

0.4mg L-1 limited by noise or background drift. The lifetime of the integrated Ag|AgCl reference

electrode, made from thermal evaporated silver, was found to be to 45 h, with an average voltage

drift of -1.3 mVh-1 due to he dissolution of the AgCl during operation. Both measurements of FMCA

and oxygen redox behavior indicated a stable Ag|AgCl reference.

Fig. 11. Recording of pH and temperature in vitro using the electronic pill


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E. Control Chip

The background noise from the ASIC corresponded to a constant level of 3-Mv peak-to-peak, which

is equivalent to one least significant bit (LSB) of the ADC. Since the second LSB were required to

provide an adequate noise margin, the 10-bit ADC was anticipated to have an effective resolution of

8 bits.

F. Dual Channel Wireless Signal Transmission

Dual channel wireless signal transmission was recorded from both the pH and temperature

channels at 230c, with the pill immersed in a PBS solution of changing pH. The calibration graphs for

the temperature and pH channel were used to convert the digital units from the MATLAB calculated

routine to the corresponding temperature and pH values.

The signal from the pH channel exhibited an initial offset of 0.2 pH above the real value at pH

7.3. In practice, the pH sensor was found to exhibit a positive pH offset as the solution became more

acidic, and a negative pH offset as the solution became more alkaline. The temperature channel was

unaffected by the pH change, confirming the absence of crosstalk between the two channels.

Fig. 12 .Long term in vitro pH measurements in response to a changing pH from the initial pH

4 to pH 7 (2 h) and pH 10.5 (4 h) at 36.50C


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RANGE AND ACCURACY

Range

1. Temperature from 0 to 70 Ã‚Â° C

2. pH from 1 to 13

3. Dissolved Oxygen up to 8.2 mg per liter

4. Conductivity above 0.05 mScm-1

5. Full scale dynamic Range analogue signal = 2.8 V

Accuracy

1. pH channel is around 0.2 unit above the real value

2. Oxygen Sensor is Ã‚Â±0.4 mgL.

3. Temperature & Conductivity is within Ã‚Â±1%.


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ADVANTAGES AND DISADVANTAGES

Advantages

1. It is being beneficially used for disease detection & abnormalities in human body. Therefore

it is also called as MAGIC PILL FOR HEALTH CARE.

2. Adaptable for use in corrosive & quiescent environment.

3. It can be used in industries in evaluation of water quality, Pollution Detection, fermentation

process control & inspection of pipelines.

4. Micro Electronic Pill utilizes a PROGRAMMABLE STANDBY MODE, So Power

consumption is very less.

5. It has very small size, hence it is very easy for practical usage’

6. High sensitivity, Good reliability & Life times.

7. Very long life of the cells(40 hours), Less Power, Current & Voltage requirement (12.1 mW,

3.9 mA, 3.1 V)

8. Less transmission length & hence has zero noise interference

Disadvantages

1. It cannot perform ultrasound & impedance tomography. Tomography is imaging by sections

or sectioning, through the use of any kind of penetrating wave.

2. Cannot detect radiation abnormalities.

3. Cannot perform radiation treatment associated with cancer & chronic inflammation.

4. Micro Electronic Pills are expensive & are not available in many countries.

5. Still its size is not digestible to small babies.


http://en.wikipedia.org/wiki/Wave

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OTHER APPLICATIONS

Apart from the detection of real time remote recording of temperature, pH, conductivity and

dissolved oxygen in the GI tract the Micro electronic Capsule can also be used for many other uses

in the real world.

The generic nature of microelectronic pill makes it adaptable for use in corrosive

environments related to environmental & industrial applications, such as

A. Evaluation of Water Quality – Just like the pill is used for detection of amount of

dissolved oxygen in the stomach or GI tract similarly it can be used to detect if the water

is suitable for drinking and suitable for survival of the plants and animals.

B. Pollution Detection

C. Fermentation Process Control

D. Inspection of the pipelines.

E. The Integration of Radiation Sensors

F. The application of indirect imaging technologies such as ultrasound & impedance

tomography will improve the detection of tissue abnormalities & radiation treatment

associated with cancer & chronic inflammation.


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FUTURE DEVELOPMENTS

Further developments focus on the photo pattern able gel electrolyte and oxygen

and cat ion selective membranes. Also in the future, these measurements will be used to perform

physiological analysis of the GI tract. For e.g., Temperature sensors can be used to measure the

body core temperature, also locate any changes corresponding to ulcers or tissue inflammation; pH

sensors may be used for determination of presence of pathological conditions associated with

abnormal ph levels etc.

In the future, one objective will be to produce a device, analogous to a micro total analysis

system (TAS) or lab on a chip sensor which is not only capable of collecting and processing data, but

which can transmit it from a remote location. The overall concept will be to produce an array of

sensor devices distributed throughout the body or the environment, capable of transmitting high-

quality information in real-time.

In future another objective will be to develop a micro electronic pill with a camera to study

the internal structure of GI tract visually , with the imaging technology added it will help the doctors

to view the internal abnormalities or tumors without any operation so it will benefit both the patients

and as well as the doctors.

After recent significant technology improvements, design of small size camera and battery

could have been possible. Thus in the last ten years some research projects looking at developing

electronic pills have concentrated mostly on the visual sensor system. Thus a high frequency link is

required for better resolution and a miniaturized system.

Another category of electronic pill technology is to use fluorescence spectroscopy and

imaging, similar to those that are commercially available. Kfouri, et al., studied a Fluorescence based

electronic pill system that uses UV light with illumination LEDs to obtain clearer images . This is

like flash based digital camera widely used by people.


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FUTURE CHALLENGES

In the future, one objective would be to produce a device, analogous to a

micro total analysis system (µTAS) or lab on a chip sensor which is not only capable of

collecting & processing data, but which can transmit it from a remote location. The overall

concept would be to produce an array of sensor devices distributed throughout the body or

environment, capable of transmitting high-quality information in real time.

Some other challenges will be to make the capsule even more small in size

so that they can be digested easily by small children . Moreover in present time the capsules are

really expensive thus cannot be used readily so the future challenge include the reducing the

pricing of the pill so it can be also used in rural areas and hospitals/doctors can afford it for use.

Also the capsule is not available in many counties so in future arrangements has to be made so

that it can be available in more and more places around the world.

Micro electronic pill also cannot detect radiation abnormalities as it has no

sensor to predict or know about the abnormalities due to radiation , with the nuclear age on the

rise many people often suffer from radiation diseases which cannot be detected easily so the

micro electronic pill has to be made such that it also has sensor to know something about the

radiation abnormalities caused in a person’s body.

With the start of use of camera in the capsule ,thus in the last ten years some

research projects looking at developing electronic pills have concentrated mostly on the visual sensor

system. Thus a high frequency link is required for better resolution and a miniaturized system. So the

challenge is to Improve the methodology used to transmit the images with high precision and

accuracy.


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CONCLUSION

We have therefore described about the multichannel sensor, which has been

implemented in remote biomedical using micro technology, the micro electronic pills, which is

designed to perform real time measurements in the GI tract providing the best in vitro wireless

transmitter, multi channel recordings of analytical parameters.

We have developed an integrated sensor array system which has been incorporated in

a mobile remote analytical microelectronic pill, designed to perform real-time in situ measurements

of the GI tract, providing the first in vitro wireless transmitted multichannel recordings of analytical

parameters. Further work will focus on developing photopatternable gel electrolytes and oxygen and

cation selective membranes. The microelectronic pill will be miniaturized for medical and veterinary

applications by incorporating the transmitter on silicon and reducing power consumption by

improving the data compression algorithm and utilizing a programmable standby power mode.

The generic nature of the microelectronic pill makes it adaptable for use in corrosive

environments related to environ-mental and industrial applications, such as the evaluation of water

quality, pollution detection, fermentation process control and the inspection of pipelines. The

integration of radiation sensors and the application of indirect imaging technologies such as

ultrasound and impedance tomography, will improve the detection of tissue abnormalities and

radiation treatment associated with cancer and chronic inflammation.


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