• Biological Signals
    • Biological signals
      • Organ
        • Voltage
          • Frequency (Hz)
      • Heart
        • 1mV
          • 0.05-100
      • Muscle
        • 1mV
          • 1-20,000
      • Brain
        • 50-200μV
          • 0-100
            • δ - 0-4
            • θ - 4-8
            • α - 8-13
            • β - >13
    • Heart
      • Potentials due to cell membrane depolarisation
      • Combine to form a signal of high amplitude
      • Detected at body surface
    • EEG/BIS
      • Input from few electrodes & estimate depth of anaesthesia
    • Interference
      • Mains (50Hz ⇒ interferes mostly with ECG & EMG)
      • Radio
      • Mobile phones
      • Diathermy (0.5-1MHz ⇒ low pass filters used)
    • Filters
      • Enhance quality of signal
      • High pass
      • Low pass
      • Notch filters
      • Bandpass
    • Amplifier
      • Increase amplitude and usually filter out unwanted frequencies
      • Operate at a specific bandwidth
      • Differential amplifier
      • CMMR
        • Unwanted signal:wanted signal
        • Usually 10,000:1