Electrostatics and Noise Reduction Techniques

Electrostatic Shield

• An electrostatic shield is used to reduce electric noise.
• The total electric field inside a conductor is zero.
• This applies to the space surrounding the conductor.
• A conductor does not have to be solid; a mesh can be used instead.
• Positioning a biological object inside a Faraday cage can reduce the influence of electric fields on recording signals.

Filtering

• Filters can be low-pass (LPF), high-pass (HPF), or band-pass (BPF).
• Filters can abolish signals of some particular frequencies and conduct other frequency signals.
• Use filters if you know the frequencies of your recording signals and noises.
• If the noise frequency is higher than the recording signal frequency, use a low-pass filter.
• If the noise frequency is lower than the signal frequency, use a high-pass filter.

Grounding to Reduce Noise

• Grounding uses the body's natural capacitance.
• Objects with high capacitance are less affected by external electric fields.
• Grounding creates a high-capacitance system where external electric fields have less effect.

Differential amplifier

• A differential amplifier has two voltage inputs (V1 and V2) and one output (Vout).
• Output voltage is the difference between input voltages.
• Noise often originates from sources distant from the recording process.
• If noise affects both electrodes equally, the noise cancels out.

Biosignals

• Biosignals can be written as s(t), where s is the signal and t is time.
• A simple sine wave can be described as:
  • A = Amplitude
  • ω = Frequency
  • φ = Phase

Biosignal Acquisition

• Sensors convert non-electrical signals to electrical signals.
• Sensors can be amplified, filtered, and processed by electronic systems.
• Biosignals are then stored and analyzed.
• Sensors act as a bridge between biological signals and instruments.
• Sensors are often called transducers, converters, or detectors.
• Active sensors generate an electrical current or voltage.
• Passive sensors detect a change in a physical quantity (e.g., temperature, pressure).

Biosignals (Deterministic)

• Periodic signals have a repeating pattern.
• Almost Periodic signals are almost regular and repeating.
• Transient signals are brief and short-lived.

Biosignals (Random)

• Stationary signals have properties that stay the same over time.
• Non-Stationary signals have properties that change over time.

Electrodes Used in Biomedical Purposes

• Electrodes convert ionic currents from biological objects to electronic currents.

Types of Electrodes

• Microelectrodes are small conducting wires inserted into glass pipettes filled with electrolyte solutions.
• Small Metal Wire Electrodes have diameters of approximately 1mm and record summary potentials from many cells.
• Large Metal Electrodes are used for ECG recordings.

Noise During Recording

• Noise can stem from both internal and external sources.
• External noise sources:
  • Recording devices (sensors, amplifiers)
  • Electromagnetic interference from power lines and nearby operating electrical equipment.
• Internal noise sources:
  • Other signals originating within the organism unrelated to the targeted recording signal.

Biosignals Assessment

• All living things produce biosignals.
• Biosignals are useful for diagnosing health conditions, monitoring patients, and conducting biomedical research.
• Biosignals are a way to describe a physiological process or change happening in the body.
• Biosignals can be categorized by their origin:
  • Electrical: Like the depolarization of a nerve cell or heart muscle.
  • Mechanical: Such as the sound produced by heart valves.
  • Chemical: Like the concentration of $CO_2$ in the blood.

Two types of Biosignals

• Continuous signals: Are defined at every moment in time.
• Discrete signals: Are only defined at specific intervals or points in time.

Biological Processes and Signals

• Biological processes that repeat create repetitive signals, usually with a predictable pattern.
• These signals are called deterministic waveforms.
• Deterministic signals can be:
  • Periodic: Regular or repeating.
  • Aperiodic: Irregular.
• Aperiodic signals can be:
  • Quasiperiodic: Almost regular.
  • Transient: Brief and short-lived.
• In living organisms, perfectly periodic signals don't occur naturally.
• Random signals are created during random or stochastic processes.
• Random signals can be:
  • Stationary: Properties stay the same over time.
  • Nonstationary: Properties change over time.

This quiz covers essential concepts related to electrostatic shields, filtering techniques, and grounding methods to reduce noise in electronic systems. Explore how these principles can help to manage electric fields and improve the quality of recording signals. Test your understanding of these fundamental topics in electrostatics.