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Biomedical Sensors

Biomedical Sensors. A key in knowing what is wrong with you. . What is Measured and How?. Transducible property - that property of a measurand that allows it to be measured. Measurand - a biomedical property that can be measured. .

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Biomedical Sensors

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  1. Biomedical Sensors A key in knowing what is wrong with you.

  2. What is Measured and How? • Transducible property - that property of a measurand that allows it to be measured. Measurand - a biomedical property that can be measured. • Biosensor - converts a measurand into a measurable signal, usually electrical.

  3. Classification of Measurands • Nonbiopotentials, for example, temperature, blood pressure, rate of blood and air flow. Biopotentials, for example, ECG, EEG, etc. That is, those that arise from an electrical signal generated in the body.

  4. Classification of Sensors • Therapeutic- defibrillators, pacemakers Diagnostic - temperature, blood pressure, ECG • Assistive - cochlear implants, functional neuromuscular stimulation

  5. Location of Sensor • Noninvasive/contact - ECG electrodes, temperature, oximetry, etc. Noninvasive/noncontact - blood gases, electrolytes, etc. • Invasive/short-term - EMG electrodes, catheter, etc. • Invasive/long-term - Pacemaker, FES electrodes, etc.

  6. Measuring a Physiological Potential

  7. Measurable Physiological Potentials Voltage (V) 0.1 1 10 100 1,000 10,000 Frequency (Hz)

  8. Electrodes • Metal conductor in an electrolyte solution • Transduces an ion to an electron current • Characterized by electrode potentials

  9. Surface Electrodes Foam Self Adhesive Tan Weave Multi Use

  10. Electrode Potential Metal - - - - - - - - - - - - - - - - - + + + + + + + + + + + Ehc + + + + - + - - + + - - + + - - - - - - - - - - - - - - - + Electrolyte Gel + - - - + - - + + - + - - + - + + - + - - + + + - Skin Half-cell potential

  11. Ag/AgCl Electrodes • Very important clinically and in research. • Cl is the primary charge carrier and is present in tissue. • Low noise electrodes.

  12. PHYSICAL MEASUREMENTS Temperature: systemic, thermography Pressure: blood, pulmonary Force, acceleration, displacement Volume: blood, pulmonary Flow: blood, air Blood oxygen content (oximetry)

  13. Linear Variable Differential Transformer Ferrite Core

  14. Differential Capacitive Transducer

  15. V = potential diff L = vessel width Electromagnetic Flowmeter

  16. Electromagnetic Flowmeters

  17. (a) (b) (a) Signals without noise are uncorrupted. (b) Interference superimposed on signals causes error. Frequency filters can be used to reduce noise and interference.

  18. (b) (c) (a) Figure 1.15 (a) Original waveform. (b) An interfering input may shift the baseline. (c) A modifying input may change the gain.

  19. (a) (b) Figure 1.16 Data points with (a) low precision and (b) high precision.

  20. (a) (b) Figure 1.17 Data points with (a) low accuracy and (b) high accuracy.

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