skin

1. NICU Neonatal Monitor: Smart textile based Sensor
Design, Development and Fabrication
Presented by
RESHMA.K
Junior Research Fellow
IIITDM Kancheepuram

2. ELECTRODES IN BIO SIGNAL AMPLIFICATION
WET ELECTRODES TEXTILE ELECTRODES
Ag/AgCl electrodes  textile fabrics
 Eg. Silver , graphene, carbon nanotube
infused textiles , polymeric conductive
fabrics
 Out of these silver fabric is mostly
employed.
• Limited shelf life
• Poor Longevity
• Pre-skin preparation is needed
• Non biodegradable
• Low contact impedance for short
term monitoring
• Long shelf life
• Flexible and reusable-assures longevity
• No pre skin preparation
• Biodegradable
• Lesser weight
• Adaptability
Potential issues in choosing dry
textile electrodes
 Weak Signal pickup-higher delay
 Proper skin electrode interfacing
 low and stable skin contact
impendence
 Motion artifacts
 Biocompatibility and durability

3. SELECTION OF TEXTILE MATERIAL -ELECTRODE
Element Copper Silver
Density 8.92 g/cm3 10.49 g/cm3
Ultimate Tensile
Strength
210 MPa 110 MPa
Young’s Modulus of
Elasticity
120 GPa 83 GPa
Brinell Hardness 250 MPa 210 MPa
Vickers Hardness 350 MPa 251 MPa
Melting Point 1084.62 °C 961.78 °C
Boiling Point 2562 °C 2162 °C
Thermal Conductivity 401 W/Mk 430 W/mK
Thermal Expansion
Coefficient
16.5 µm/mK 18.9 µm/mK
Specific Heat 0.38 J/g K 0.235 J/g K
Heat of Fusion 13.05 kJ/mol 11.3 kJ/mol
Heat of Vaporization 300.3 kJ/mol 250.58 kJ/mol
Material selection
Selection of material depends on electrical and chemical properties like
conductivity, impedance, temperature, pressure, washability,
biocompatibility, reusability, oxidation resistance and antimicrobial
properties
Conductivity:
Silver > Copper > Gold
Mostly employed : Silver->antimicrobial, high conductivity,
But copper can also be used with respect to applications like long term
wearable monitoring devices.
For High Electrical Conductivity: Both are excellent, but silver slightly
edges out copper.
For Flexibility and Durability: Copper might be preferable due to its
higher tensile strength and lower Young’s modulus.
For Lightweight Applications: Copper is less dense.
For High-Temperature Stability: Copper has higher melting and boiling
points.
Cost and Availability: silver is generally more expensive and less
abundant than copper.
Low contact impedance :copper has low contact impedance in different
skin conditions.

4. Electrical equivalent circuit-Skin Electrode

5. Skin Electrode Impedance or Contact impedance:
 Impedance is the measure of resistance and reactance in ac circuits. If impedance is lower ,conductivity
is high and vice versa.
 Understand signal transfer mechanism from electrical equivalent circuit model and study factors
affecting contact impedance.
 Improper contacts or electrode movements variable and high skin electrode impedance
 Variable and high skin electrode impedance increases powerline interference sensitivity, leads to baseline
wandering affects SNR thereby affects signal quality.
Summary
Low contact impedance is desirable.
a) Electrode movements
b) poor skin electrode interfacing
c) low contact pressure variable or high skin electrode contact impedance
d) temperature variations

6. How to overcome?
• Choose high input impedance bio amplifier.
• CMRR>80dB
• Impedance monitor
• Design electrodes according to these factors increasing contact area, contact pressure, shielding,
selection electrode material and its size
• Adaptive selection instrumentation amplifier
• Air gap elimination by shielding.
Work to be done
Measure contact impedance using different textile electrodes and patch electrodes.

7. REFERENCES
• [1] S. M. Lobodzinski, “ ECG Instrumentation: Application and Design.”
• [2] A. H. Umar, M. A. Othman, F. K. C. Harun, and Y. Yusof, “Dielectrics for Non-Contact ECG Bioelectrodes: A
Review,” IEEE Sensors Journal, vol. 21, no. 17. Institute of Electrical and Electronics Engineers Inc., pp. 18353–18367,
Sep. 01, 2021. doi: 10.1109/JSEN.2021.3092233.
• [3] M. R. Miah, M. Yang, M. M. Hossain, S. Khandaker, and M. R. Awual, “Textile-based flexible and printable
sensors for next generation uses and their contemporary challenges: A critical review,” Sens Actuators A Phys, vol. 344, p.
113696, Sep. 2022, doi: 10.1016/J.SNA.2022.113696.
• [4] S. M. M. Rahman, H. Mattila, M. Janka, and J. Virkki, “Impedance evaluation of textile electrodes for EEG
measurements,” Textile Research Journal, vol. 93, no. 7–8. SAGE Publications Ltd, pp. 1878–1888, Apr. 01, 2023. doi:
10.1177/00405175221135131.
• [5] S. Maji and M. J. Burke, “Establishing the Input Impedance Requirements of ECG Recording Amplifiers,” IEEE
Trans Instrum Meas, vol. 69, no. 3, pp. 825–835, Mar. 2020, doi: 10.1109/TIM.2019.2907038.
• [6] K. Goyal, D. A. Borkholder, and S. W. Day, “Dependence of Skin-Electrode Contact Impedance on Material and
Skin Hydration,” Sensors, vol. 22, no. 21, Nov. 2022, doi: 10.3390/s22218510.
• [7] R. Cardu, P. H. W. Leong, C. T. Jin, and A. McEwan, “Electrode contact impedance sensitivity to variations in
geometry,” Physiol Meas, vol. 33, no. 5, pp. 817–830, 2012, doi: 10.1088/0967-3334/33/5/817.
• [8] T. W. Wang and S. F. Lin, “Negative Impedance Capacitive Electrode for ECG Sensing through Fabric Layer,”
IEEE Trans Instrum Meas, vol. 70, 2021, doi: 10.1109/TIM.2020.3045187.

8. NOISES IN BIOSIGNALS
• Baseline wandering
• Powerline interference
• Instrumentation noises
• Muscle artifacts
• Channel noises
• Flicker noise
• Thermal noise
Noises Reasons Frequency range
Baseline wandering Respiration, body movements, poor
electrode contact, and skin-electrode
impedance
ranges between 0.05 and 1 Hz
Power-line interference inductive and capacitive couplings
of ubiquitous power lines in the
signal acquisition circuitry
narrowband noise centred at
50/60 Hz with a bandwidth <1 Hz
Muscle artifacts electrical activity of muscles during
periods of contraction or due to a
sudden body movement
bandwidth ranges between 20 and
1000 Hz