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Bio- Potential Electrodes

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Title: Introduction to Data Communication Networks Author: Administrator Last modified by: SMITHA DEEPAK Created Date: 1/13/2000 5:03:11 PM Document presentation format – PowerPoint PPT presentation

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Title: Bio- Potential Electrodes


1
  • Bio- Potential Electrodes

2
Measurement of Bioelectric potentials
  • To measure bioelectric potentials , a transducer
    is required.
  • Electrical signals produced by various body
    activities are used in monitoring / diagnosis
  • In order to measure and record potentials and,
    hence, currents in the body, it is necessary to
    provide some interface between the body and the
    electronic measuring apparatus.
  • .

3
Bio Potential Electrodes
  • Bio-potential electrodes carry out this interface
    function.
  • A transducer consists of two electrodes, which
    measure ionic potential difference between two
    points.
  • The designation of the Bio potential waveform
    ends with Gram.
  • The name of the instrument bio potential
    normally ends with Graph

4
Bio Potential Electrodes
  • Propagation of action potential through different
    body tissues produces final waveform recorded by
    electrodes
  • Electrical activity is explained by differences
    in ion concentrations within the body (sodium,
    Na cloride, Cl potassium, K)
  • A potential difference (voltage) occurs between 2
    points with different ionic concentrations

5
  • Electrodes Theory

6
Equivalent circuit for bio-potential electrode
Metal Electrode
Body Electrolytes
VhaElectrode potential developed across interface
CCharges at the Interface at the skin metal
interface
7
Polarizable and Non-Polarizable Electrodes
  • Polarizable Electrodes
  • No charge crosses the electrode-electrolyte
    interface when a current is applied. (e.g
    Platinum electrode)
  • Non-Polarizable Electrode
  • Current passes freely across the
    electrode-electrolyte interface. (e.g. Ag/AgCl
    Electrode)

8
Equivalent circuit for bio-potential with two
electrode
9
Bio Potential Electrodes
  • Bio-potential electrodes transduce ionic
    conduction to electronic conduction so that
    bio-potential signals can be obtained
  • They generally consist of metal contacts packaged
    so that they can be easily attached to the skin
    or other body tissues

10
  • Classification of Electrodes

11
Bio Potential Electrodes
  • Micro Electrodes--- Bio electric potential near
    or within a single cell
  • Metal TypeTip must be tungsten or stainless
    steel
  • Micro pipette---It is a glass micropipet with
    size of 1 micron, It is filled with electrolyte
  • Skin surface electrode Measure ECG,EEG,EMG
  • Needle electrode ---Penetrate the skin to record
    EEG

12
Microelectrodes
  • Used to measure bio-potential signals at the
    cellular level
  • Due to small dimensions (mm), impedance levels
    are high
  • So amplifier needs very high input impedance


13
Microelectrodes

14
METAL MICROELECTRODES

15
MICROPIPETTE ELECTRODES

16
Surface electrodes
  • These are placed in contact with the skin of the
    subject
  • Early stages immersion electrodes were used.
  • A bucket of saline water is used
  • An improvement of immersion electrode is the
    plate electrode.
  • Another old type electrode is suction type

17
Immersion electrodes

18
Surface electrodes

19
METAL-PLATE ELECTRODES
  • Historically, one of the most frequently used
    forms of bio-potential sensing electrodes is the
    metal-plate electrode.
  • In its simplest form, it consists of a metallic
    conductor in contact with the skin.
  • An electrolyte soaked pad or gel is used to
    establish and maintain the contact.


20
METAL-PLATE ELECTRODES

21
Floating electrodes
  • Conductive paste reduces effect of electrode
    slippage and resulting motion artifact


22
Needle electrodes
  • Unipolar electrode---Single wire inside a needle
  • Bipolar electrode---Two wires inside a needle
  • Mostly used for contacting with internal body
    tissues
  • (a) Insulated needle electrode .
  • (b) Coaxial needle electrode .
  • (c) Bipolar coaxial electrode .
  • (d) Fine -wire electrode connected to hypodermic
    needle, before being inserted .
  • (e) Coiled fine -wire electrode in place


23
Needle electrodes

24
Implantable electrodes

25
ELECTRODE ARRAYS

26
ELECTRODE ARRAYS

27
  • Transducers

28
Transducers
  • A transducer is necessary to convert one variable
    in to another form
  • Used to measure physiological variables
  • Variable is a quantity that vary with time.
  • The term active and passive has different meaning
    when they are applied to Transducers

29
Transducers
  • Transducer can be classified in to two
  • Active Transducer
  • Known principles is used to convert variables in
    to electrical signal
  • Passive Transducer
  • It involves control of an excitation voltage or
    modulation of a carrier signal

30
Principles used in Active Transducers
  • It can convert electrical signal in to physical
    variables and also in reverse direction.
  • Magnetic Induction
  • Piezoelectric effect
  • Thermoelectric effect
  • Photoelectric effect

31
Passive Transducers
  • Utilize the principles of controlling a DC
    excitation or an AC carrier signal.
  • It consists of a passive circuit element which
    changes it value as a function of physical
    variables to be measured.
  • It cannot convert electrical signal in to
    physical variables
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