Biopotential Electrodes

Biopotential and Electrodes

• Presented by: Engr. Carl Joseph A. Penuliar, ECE, ECT

Design of Medical Instrument

1. Accuracy

2. Frequency response

3. Hysteresis

4. Isolation

5. Linearity

6. Sensitivity

7. Signal-to-noise ratio

8. Simplicity

9. Stability

10. Precision

Factors in Medical Instrument Design

• When designing medical instruments, it is crucial to consider the factors listed above to ensure that the devices provide precise and reliable measurements.

Accuracy in Biomedical Electronics

• Definition: Accuracy refers to how closely an instrument reading matches the true value of the variable being measured.

• Improving Accuracy:

  • Can be enhanced through proper calibration of the equipment and selection of high-precision devices.

Frequency Response in Biomedical Electronics

• Definition: Frequency response indicates how an instrument reacts to various frequency components present in physiological signals.

• Essential Quality: The instrument must faithfully display the biosignal with high fidelity to retain the signal's integrity.

Hysteresis in Biomedical Electronics

• Definition: Hysteresis is the lag in the movement of an indicating needle caused by mechanical friction in analog meters.

• Impact: This can introduce hysteresis errors in measurements.

• Material Choice: Needles should be made from elastic materials not affected by the surrounding environment.

Isolation in Biomedical Electronics

• Definition: Isolation refers to the electrical separation between the measurement subject and ground, crucial for safety and minimizing interference.

• Implementation: Instruments should use isolated circuits to prevent direct electrical connections between the patient and ground.

Linearity in Biomedical Electronics

• Definition: Linearity indicates how closely the output variations of an instrument correspond to input variations.

• Importance: High linearity is fundamental for accurate data representation across different input levels.

Sensitivity in Biomedical Electronics

• Definition: Sensitivity measures an instrument's ability to detect small changes in input.

• Resolution: Sensitivity is often expressed in terms of resolution, the minimum change that can be accurately measured.

Signal-to-Noise Ratio (S/N) in Biomedical Electronics

• Definition: High S/N ratio is crucial since biosignal magnitudes are typically low.

• Solution: Preamplifiers in biomedical recorders are designed with differential amplifiers to achieve higher S/N ratios for reliable measurements.

Simplicity in Biomedical Electronics

• Importance: Simplicity is vital to reduce human errors and confusion during operation, which can lead to measurement uncertainty.

Stability in Biomedical Electronics

• Definition: Stability reflects the capability of an instrument to provide consistent output for given input.

• Consideration: Stability issues may arise due to drift in amplifiers, which can be mitigated through negative feedback.

Precision in Biomedical Electronics

• Definition: Precision denotes the reproducibility of measurements and the degree of agreement within a measurement group.

Biopotential Electrodes in Biomedical Electronics

• Purpose: Biopotential electrodes act as an interface to connect the human body with electronic measuring apparatus, facilitating measurement of ionic flow.

• Function: Convert ionic potentials generated by the body into electric potentials for accurate readings.

Electrode Types and Their Interface

• Biopotential electrodes can be categorized into various types, each designed for specific applications and characteristics.

• Electrode-Electrolyte Interface: This interface helps understand the passage of electric current from the body to the electrode, integrating body fluids containing ions.

Half-Cell Potential in Biomedical Electronics

• Definition: When a metal contacts a solution, a voltage difference arises at the electrode-electrolyte interface known as half-cell potential or electrode potential.

Electrode Categories

• Perfectly Polarized Electrodes: Have no net charge transfer across the interface.

• Perfectly Non-Polarizable Electrodes: Allow unhindered charge exchange at the interface.

Electrode Paste Use

• Purpose: The outer skin is non-conductive, necessitating electrode paste to establish a good electrical contact.

• Functionality: It decreases contact impedance and minimizes movement artifacts during measurement.

Properties of Bioelectrodes

• Key Features:

  • Good conductivity and low impedance

  • Should not polarize with current flow

  • Establish good body contact without irritation

  • Non-toxic, mechanically rugged, and easy to clean

Types of Electrodes

1. Microelectrodes

2. Needle Electrodes

3. Surface Electrodes

Microelectrodes

• Definition: Small electrodes designed to penetrate a single cell for precise readings.

• Positioning Challenges: Accurate positioning relative to the cell can complicate measurements.

Needle Electrodes

• Purpose: Used primarily for electroneurography to measure action potentials from peripheral nerves.

• Insertion Technique: Needle electrodes create a lumen into which a short metal wire is inserted to detect biological activity.

Surface Electrodes

• Usage: Measure electrical potentials from the body surface, including signals from the heart and brain.

• Types: Include immersion electrodes, plate electrodes, suction cup electrodes, floating electrodes, adhesive type, multipoint type, and disposable electrodes.

Specialized Electrode Types

Disposable Electrodes

• Designed for one-time use to eliminate cleaning and reuse complications, widely adopted in clinical settings.

Ear Clip and Scalp Electrodes

• Essential for EEG measurements, scalp electrodes provide clear signals when applied to a bare head.

Conclusion

• Biomedical electronics is an evolving field necessitating continual advancements in electrode technology and design considerations for improved measurement accuracy and patient safety.

Thank You

• Engr. Carl Joseph A. Penuliar, ECE, ECT