Post on 02-Jan-2016
Biomedical Sensors
Dr. James A. Smith
What’s Important?
• Accuracy
• Operational Range
• Response Time
• Sensitivity
• Resolution
• Reproducibility
Classification
• Breakdown into general categories– Physical
• Goniometer
– Electrical• EMG (electromyographic)
– Chemical• Blood oxygen
Sensor Packaging
• “In vivo”– Inside the organism!– Risky!– Biocompatibility
• Host can affect the sensor & vice versa• Protein absorption / cell. Deposits
– Permeability affected
• Inflamation of tissue (latex!)• Sterilization
– Steam, ethylene oxide, gamma radiation
Electrolyte / Metal Electrodes
• Charge distribution at interface
• Different metals have different potentials
Physical Measurements: Displacement
• Linear Variable Diff. Transformer• Goniometer
– Knee & Elbow
• Strain– Wire length & width– Chest contraction– Force Plates
• Ultrasonics
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Temperature
• Tightly controlled body variable
• 37.0 +/- 0.5 C at core– Too high: disease or infection– Too low: trauma / shock
• Thermistor– Change resistance with temperature– Cavity or closed area
Oxygen Measurement
• Plasma O2: 2% of total oxygen– Clarke Electrode
• Chem. Reaction with Platinum• Electrode Current is prop. To oxygen content• Transcutaneous• Heat releases oxygen through skin
• Hemoglobin– Optical oximeter– Light absorption by blood
pH Electrodes• Acid: excess hydrogen ions• Base: excess hydroxl ions• Normal blood pH: 7.4 (basic)
– CO2 removal by lungs– Kidneys acid-base regulation
• Organic dye strips• Electrodes in solution
– a battery consisting of two electrodes, • each immersed in its respective solution• joined by a salt bridge
– Glass electrodes– Glass membrane can wear out
CO2
• CO2 in solution:– Weak acid
– Carbonic Acid (H2CO3)
• Use electrodes like in pH system
Enzyme Biosensors
• Biological specific mediators– Reagents for reaction or catalyzing
• Enzymes– 2000 proteins w/ biocatalytic properties– Accelerate reactions in cells
• Embed in neutral matrix• Glucose sensor
– Enzyme glucose oxidase– Useful for diabetics– Measure gluconic acid or hydrogen peroxide
Microbial Sensors
• Assimilation of organic compounds by microorganisms
• Look for secretions by micros– H2, CO2, etc.
• Need immobilized microbes
• Examples– Ammonia & Nitrogen Dioxide
EKG / ECG
• Electrocardiogram (ECG)
• Electrokardiogram (EKG)
• Electrode– Polymer & carbon / metal filler– Silver Chloride contact – Electrolytic foam– Motion artifacts!
EMG / EEG
• Electromyogram (EMG)• Nerve & Muscle• Surface are like EKG• Direct
– Needle– Bipolar electrode
• EEG– Brain– Cups (gel)– Subdermal (10mm, 0.5mm)
EMG & Muscles
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Source: http://www.eorthopod.com/images/ContentImages/elbow/elbow_anatomy/elbow_anatomy07c.jpg
EMG: locate muscles
Figure 1
Source: Vernier Inc.
Electrode Placement
Source: Vernier Inc.
Electrical Patterns
Source: http://www.unmc.edu/physiology/Mann/pix_14/emg.gif
EMG Video
• http://www.youtube.com/watch?v=k0uSpYd_Ics
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