Influence of Skin-electrode Interface at Spectroscopic Measurements Of

8/8/2019 Influence of Skin-electrode Interface at Spectroscopic Measurements Of

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EBI is a measure of the opposition to the flow ofelectrical charges through biological tissue, ishow well the body impedes electric current

flow, and its value depends on the structureand the intrinsic composition of tissue. BIS allows the determination of the human

body content by measuring the bodyimpedance of a person. In comparison with

other body composition measurementmethods, BIS has two major advantages:

x It is a non-invasive procedurex It is easy to use at home.


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This FDP has followed 3 steps

Measurements: We made use of the spectrometerImpediMed SFB7. We used 2 methods;

the 2 - electrodes method the 4 - electrodes method.

We took ranges of 10 measurements separated atthe time domainby 4 minutes (t0, t4, t8, t12, t wet,)

Themeasurementswererepitedforthetwomethods and forfourpeople. Wewrotethename of themeasurement files in a textdocumentin ordertochecklaterwith files names at thecomputer. Thispointwasdeveloped in

collaborationwith Helena Ballesteros


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Matlab:TheaquiredmeasurementswereprocessedwithMatlab in ordertohavethe mean value andthestandarddeviation of thespectrums ofResistance and Reactance. Two scriptswereprogrammedforgeneratinggraphics of

theevolution of foursubjects and twokind ofelectrodes in comparisonwiththereferenceone.

Weshowed in a graphicfor a determinedsubjectfora determinedelectrodetheevolution of the meanvalue and the SD at the time domain in

comparisonwiththereferenceelectrode

Written work: A Microsoft Word Document of morethan 50 pageswaselaborated


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The body is composed by many different tissues. Themost important unit of the tissue is the cell:

The cell membranes are considered to have a highcapacitance and very low but complicated patternconductivity. At DC and low frequencies most of thecurrent passes around the cells with a little portionflowing through the membrane channels. At higher

frequencies the membrane capacitance letA

Ccurrent pass by charge displacement

The skin electric comportment is similar to acapacitor, for DC currents it has high impedance, butfor alternated signals this value decreases

proportionally to the applied frequency.


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The electrode is one of the most influential elements in an EBImeasurement system, because electrodes do not onlyfunction as potential sensing elements but also as electricalcharge interface between the measurement system and thebody. Dry Textile electrodes do not have an electrolyte to

facilitate the charge transfer, electrons or ions, from thecurrent injecting leads to the biological tissue and this mayinfluence the EBI measurement.

To pick up electrical signals by intelligent textiles one essentialcomponent of a system design is using an appropriateelectrode-design. They must have sufficient electricalproperties, show long-term robustness and should not require

any interaction with the end user. The textile integration of sensors and electronic components

will play an important role in the future within the medical-technical area.

The continuous monitoring of elderly humans living on theirown could be facilitated through the integration of

monitoring systems into everyday textiles, e.g. clothing.


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Types of usedelectrodes

Velcro tapesWidth: 2.5 cm & length: adjustable, velcro fastener.

Inner surface, sensor: Synthetic wrap knitted textile

material with silver fibre as a conductive element.

Sensor Manufactured by Clothing+ and developed

by ElinaVlimki.Application: body monitoring in medical andhealthcare applications.Outer material, garment: knitted cotton

Wrist-ankle band (Bracelet)Manufactured by Textronics Inc.

Made of: polyamide (nylon) 15%, conductive fibers 30%,

Spandex 20% and polypropylene 35%. The conductive textile

material is knitted in the inner surface of the cuff electrode.

Electrolytics (Thereference)Area: 10.1cm2 with a snap-button connector.

Outer surface: flexible non-woven polypropylene covered with

polyethylene film.Inner surface: hydro gel conductive adhesive

type.with elastane. Application: diagnostic ECG measurements


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The SFB7 is the EBI spectroscopy measurement devicemanufactured by Impedimed we have used.The impedance spectrometer is used to do amultifrequencybioimpedance analysis, to measure total bodywater composition and for assessing arm limphoedema. Therange frequency used to measure is from 3 kHz to 1000 kHz.


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The electrical stimulus is applied with a pair of electrodes andthe resulting response is measured with a different pair ofelectrodes, the current injected through the electrodes is notcontained in the sensing voltage, an extra pair of electrodesis used. The current through the sensing electrodes is zero

therefore the sensing voltage came only from the tissue


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Resultsanalysis. Measurement of Resistance vsFrequencytakenbyVelcro tapes electrodes

0 0.5 1 1.5 2 2.5 3300

320

340

360

380

400

420

440

460

480Resistance progression at Subject1s measurement with velcro tapes

log10(F)

Resistance

t0

reference

t4

t8t1 2

t wet


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Resultsanalysis. Measurement of Resistance vsFrequencytakenbywrist-ankle band electrodes

(bracelet)

0 0.5 1 1.5 2 2.5 330 0

35 0

40 0

45 0

50 0

55 0R

3s wrist-ankle band measurement

log10(F)

Resistance

t0

reference

t4

t8

t12

t wet


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Resultsanalysis. Measurement of Reactance vsFrequencytakenbyvelcro tapes electrodes

0 0.5 1 1.5 2 2.5 3

-70

-60

-50

-40

-30

-20

-10

0

10

20Reactance progression at Subject1s measurement with velcro tapes

log10(F)

Reactance

t0

reference

t4

t8

t12

t wet


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Results analysis. Measurement of Reactance vsFrequency taken by wrist-ankle band electrodes

(bracelet)

0 0.5 1 1.5 2 2.5 3-70

-60

-50

-

0

-30

-20

-10

0Reactance pr

ression at Subject1s wrist-ankle band measurement

log10(

)

Reactance

t0

reference

t

t

t12

t we t


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Results analysis. Standard Deviation

measurement. Resistance progression with velcro tapes

0 0.5 1 1.5 2 2.5 30

1

2

3

4

5

6

7

Resistance progression at Subject2 s measurement with velcro tapes

log10(!

)

Resistance

t0

reference

t4

t

t12

t we t


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Results analysis. Standard Deviation

measurement. Resistance progression with wrist-ankle b

0 0.5 1 1.5 2 2.5 30

0. 2

0. 4

0. 6

0. 8

1

1. 2

1. 4Resistance progression at Subject2 s wrist-ankle band measurement

log10("

)

Resistance

t0

reference

t4

t8t12

t we t


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Results analysis. Standard Deviation measurement.Reactance progression with velcro tapes

0 0.5 1 1.5 2 2.5 30

0. 5

1

1. 5

2

2. 5

3

3. 5

4Reactance progression at Subject2 s measurement with velcro tapes

log10(#

)

Reactance

t0

reference

t4

t8t12

t we t


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Results analysis. Standard Deviation measurement.Reactance progression with wrist-ankle band electrodes

0 0.5 1 1.5 2 2.5 30

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7Reactance progression at Subject1s wrist-ankle band measurement

log10($

)

Reactance

t0

reference

t4

t8t12

t we t


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BIS still lacks a wearable character

It demands the measurements to be undertaken under controlled

conditions, so the measurement should be only accomplished bytechnical personnel

A wearable system should allow an easy use, so that the user can

wear the system without supervision, but at the same time it shouldhave enough precision to detect small physiological changes

Textile sensors, when embedded into clothing, can provide new

ways of monitoring physiological signals, and improve the usabilityand comfort of such monitoring systems in the areas of medical,

occupational health and sports.

However, good electrical and mechanical contact between theelectrode and the skin is very important, as it often determines thequality of the signal.

Wearable measurement systems are emerging.

Monitoring and recording body postures and gestures has becomemore feasible, as textile materials allow a greater freedom of

movement than the older recording systems.


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The skin-electrode interface and its

impedance have been studied in this

final degree project. The skin-electrodeimpedance varies at the time domain

with the sweat evolution and also with

the use of abrasive conductive

paste.These effects minimize theimpedance interfaces value. The lower

is the skin electrode impedance the

more reliable is the measurement.

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Influence of Skin-electrode Interface at Spectroscopic Measurements Of