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Helping Hand: EMG prosthetics

Helping Hand: EMG prosthetics . Biomedical applications of filters and amplifiers. Biomedical Applications. http://www.touchbionics.com/products/active-prostheses/i-limb-ultra/. The E lectro M yo G ram (EMG). How to measure the EMG. Filters and Amplifiers. Skin electrodes.

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Helping Hand: EMG prosthetics

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  1. Helping Hand: EMG prosthetics Biomedical applications of filters and amplifiers

  2. Biomedical Applications http://www.touchbionics.com/products/active-prostheses/i-limb-ultra/

  3. The ElectroMyoGram (EMG)

  4. How to measure the EMG Filters and Amplifiers Skin electrodes http://www.vibrationtrainingdevice.com/VG-Evolution-I-Vibrogym.htm http://lowerextremityreview.com/article/unstable-shoe-designs-functional-implications

  5. EMG Main Idea 3 total electrodes 1 positioned over an “electrically quiet” place = ground, Vg 2 signal electrodes measure potential on muscle relative to ground. Instrumentation amplifier computes the difference: Vout = (V1 – Vg) – (V2 – Vg) = V1 – V2 V1-Vg G (V2-V1) V2-Vg

  6. Gain-Bandwidth Product Gain x Bandwidth = constant

  7. Measuring muscle generated voltages on the skin Problem: Skin Resistance Solution: op-amp buffer Voltage lost going across skin: Iskin x Rskin • Buffer blocks current flow, therefore no voltage lost across skin! • Buffer output voltage “follows” the input Measurement Device Muscle-generated signal

  8. Skin-Tissue Interface = DC battery • Metal electrode touching skin looks very similar to an electrochemical cell • Unwanted DC offset voltage generated

  9. Full Signal Chain Buffer/Active Electrodes Account for skin/electrode resistance Account for dc offset (“battery”) offset at electrode-skin interface HPF Differential Amplifier Make voltage signal usable to computers that usually require >1V signal LPF Get rid of unwanted high frequency junk Computer Processing

  10. Sources • AJ Fridlund and JT Cacippo. Guidelines for Human Electromyographic Research. Pscyhophysiology 23(5) 567- 589, retrieved from: http://www.sprweb.org/articles/Fridlund86.pdf • Intan amplifiers: http://intantech.com/amplifier_intro.html • INA126 http://www.ti.com/lit/ds/symlink/ina126.pdf • Delsys: delsys.com

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