Microelectronic pill

Microelectronic Pill Introduction

1. INTRODUCTION

We are familiar with a wide range of sensors in the field of electronics. They

are used widely in the various experiments and research activities too. This microelectronic

pill is such a sensor with a number of channels and is called as a multichannel sensor. As the

name implies this sensor is a pill. That is it is meant to go inside the body and to study the

internal conditions.

Earlier it was when transistor was invented, that radiometry capsules were first put into

use. These capsules made use of simple circuits for studying the gastrointestinal tract. Some of

the reasons that prevented their use was their size and their limitation of not to transmit through

more than a single channel. They had poor reliability and sensitivity. The lifespan of the sensors

were also too short. This paved the way for the implementation of single channel telemetry

capsules and they were later developed to overcome the demerits of the large size of laboratory

type sensors.

The semiconductor technologies also helped in the formation and thus finally the

presently seen microelectronic pill was developed. These pills are now used for taking remote

biomedical measurements in researches and diagnosis. The sensors make use of the micro

technology to serve the purpose. The main intention of using the pill is to perform an internal

study and recognize or detect the abnormalities and the diseases in the gastrointestinal tract. In

this GI (Gastro Intestinal) tract we cannot use the old endoscope as the access is restricted. A

number of parameters can be possibly measured by these pills and they include conductivity, pH

temperature and the amount of dissolved oxygen in the gastrointestinal tract.

Dept.CSE,BRECW Page 1

Microelectronic Pill Introduction

Figure 1: Microelectronic Pill


Microelectronic Pill Block Diagram

2. BLOCK DIAGRAM

The design of the microelectronic pill is in the form of a capsule. The encasing it

has is biocompatible. Inside this are multichannel (four channels) sensors and a control

chip. It also comprises of a radio transmitter and two silver oxide cells. The four sensors

are mounted on the two silicon chips. In addition to it, there are a control chip, one access

channel and a radio transmitter. The four sensors commonly used are a temperature

sensor, pH ISFET sensor, a dual electrode conductivity sensor and a three electrode

electrochemical oxygen sensor. Among these the temperature sensor, the pH ISFET

sensor and the dual electrode conductivity sensor are fabricated on the first chip. The

three electrode electrochemical cell oxygen sensor will be on chip 2. The second chip

also consists of a NiCr resistance thermometer which is optional.



Figure 2: Block diagram

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- type1-7, type2-crystal type-10), silver

oxide batteries (8), 1-access channel, 3-capsule, 4- rubber ring, 6-PCB chip carrier.

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. The

fabricated sensors were each attached by wire bonding to a custom made chip carrier

made from a 10pin, 0.5pitch 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 down. Thus, the oxygen sensor on chip 2 had to be connected to the top face by

three 200nm 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, 1.27mm 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).

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

PCB chip carrier was attached to the front section of the capsule (fig 2). 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 3mm

diameter 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 13mm 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*55mm & weighs 13.5g including the

batteries.


Microelectronic Pill Basic Components

3. BASIC COMPONENTS

1. Sensors

Figure 3: Sensors

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 Ni Cr resistance thermometer (5).



i. Sensor chip 1

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

the wafer and 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 connection tracks, electrode bonding pads are defined. Bonding pads provide

electrical contact to the external electronic circuit.

Lithography 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 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

water color-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 temperature sensor silicon diode,

while RHS unit comprises the pH ISFET sensor.

DT-670-SD Silicon Diode Features

Figure 4: DT-670-SD

It measures the body core temperature.

Also compensates with the temperature induced signal changes in other sensors.

It also identifies local changes associated with tissue inflammation & ulcers.

ISFET

Figure 5: ISFET


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

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


Ion Selective Field Effect Transistor ISFET; 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 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.

ii. Sensor chip 2

The Level 1 pattern (electric tracks, bonding pads, and electrodes) was defined in

0.9µm UV3 resist by electron beam lithography. A layer of 200nm gold (including an

adhesion layer of 15nm titanium and 15nm palladium) was deposited by thermal

evaporation. The fabrication process was repeated.

Oxygen sensor detection principle

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.

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 case 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 5oF (-20oC). 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 the 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.

Figure 6: Capillary pore type oxygen sensor



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.

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 sulphuric 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 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 7: 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 sulphide, sulphur 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 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 0.1ppm. 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 sulphide 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.

2. Control Chip

ASIC (Application-Specific Integrated Circuit) is the control chip that connects

together the external components of the micro system.



Figure 8: Interfacing of ASIC with external components of the system

Application-Specific Integrated Circuit (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.

The analog module is based on the AMS (Automated Manifest System), 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 with respect to reference. The analog signals were sequenced through a MUX prior

to being digitized by the ADC. The bandwidth for each channel was limited by the sampling

interval of 0.2ms.

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.

3. Radio Transmitter

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

components on a single-sided PCB. The footprint of the standard transmitter measured

8*5*3mm including the integrated coil (magnetic) antenna. It’s designed to operate at a

transmission freq. of 40.01MHz at 20˚C generating a signal of 10kHz band width. A

second crystal stabilized transmitter was also used. This unit is similar to the free

running STD transmitter, having a transmission frequency limited to 20.08MHz 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 1m & the modulation scheme FSK (Frequency Shift Keying), with a data rate

of 1kb/s.


Microelectronic Pill Performance

4. PERFORMANCE

Figure 9: a) Temperature Channel Performance, b) pH channel performance

1. Temperature Channel Performance

The linear sensitivity was measured over a temperature 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 a), once integrated in the


Microelectronic Pill Performance

pill, gave a linear regression of 11.9 bits/˚C , with a resolution limited by the noise

band of 0.4˚C (Fig 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 temporary channel to drift. Thus, it was seen that o/p

signal changed by 1.45mV change in supply expressed in mV, corresponding to a drift

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

2. 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 b), corresponded to 14.85 bits/pH

which give a resolution of 0.07pH/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 –

6mV/h (0.14pH), of 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 b).


Microelectronic Pill Advantages

5. ADVANTAGES

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

Therefore it is also called as MAGIC PILL FOR HEALTH CARE.

Adaptable for use in corrosive & quiescent environment.

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

fermentation process control & inspection of pipelines.

Micro Electronic Pill utilizes a PROGRAMMABLE STANDBY MODE, So power

consumption is very less.

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

High sensitivity, Good reliability & Life times.

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

(12.1mW, 3.9mA, 3.1 V).

Less transmission length & hence has zero noise interference.


Microelectronic Pill Other Applications

6. OTHER APPLICATIONS

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

corrosive environments related to environmental & industrial applications, such as the

evaluation of water quality, pollution detection, fermentation process control & inspection of

the pipelines. The integration of radiation sensors & 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.


Microelectronic Pill Limitations

7. LIMITATIONS

It cannot perform ultrasound & impedance tomography.

Cannot detect radiation abnormalities.

Cannot perform radiation treatment associated with cancer & chronic inflammation.

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

Still its size is not digestible to small babies.

Further research is being carried out to remove its draw backs.


Microelectronic Pill Conclusion

8. CONCLUSION

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

implemented in remote biomedical using micro technology, the microelectronic 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.


Microelectronic Pill Future Developments

9. FUTURE DEVELOPMENTS

Further developments focus on the photo pattern able gel electrolyte and

oxygen and cation 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.


Microelectronic Pill Future Challenges

10. 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.


Microelectronic Pill References

11. REFERENCES

http://www.lib.udel.edu/ud/spec/exhibits/color/lithogr.htm

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

http://www.globalspec.com/specification/spechpal?

name=IonSelectiveElectrodes&comp=309

http://www.sentron.nl/nieuw/index.php?id=86

http://www.biosystems.com/appnotes/howoxyge.htm

http://computing_dictionary.thefreedictionary.com/applicatio_specific%20integrated

%20circuit


http://computing_dictionary.thefreedictionary.com/applicatio_specific%20integrated%20circuit

http://computing_dictionary.thefreedictionary.com/applicatio_specific%20integrated%20circuit

http://www.biosystems.com/appnotes/howoxyge.htm

http://www.sentron.nl/nieuw/index.php?id=86

http://www.globalspec.com/specification/spechpal?name=IonSelectiveElectrodes&comp=309

http://www.globalspec.com/specification/spechpal?name=IonSelectiveElectrodes&comp=309

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

http://www.lib.udel.edu/ud/spec/exhibits/color/lithogr.htm

CONTENTS

Page No

1. Introduction 1

2. Block Diagram 3

3. Basic Components 6

4. Performance 17

5. Advantages 19

6. Other Applications 20

7. Limitations 21

8. Conclusion 22

9. Future Developments 23

10. Future Challenges 24

11. References 25

ABSTRACT

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

used simple circuits for the internal study of the gastro-intestinal (GI) 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 PILL".

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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Microelectronic pill