The evaluation of elbow joint motion using bio-impedance signal

Electromyography (EMG) method is widely used in motion detection based on physiological phenomenon. However, EMG technique doesn't fit to measure the dynamic parameter of motion. For instance, EMG is difficult to measure the joint angle changing. Bio-impedance method is a non-invasive, high performance method. This article evaluates the elbow joint movement using Bio-impedance, the correlation between the elbow joint angle changing and the upper arm bio-impedance changing has been calculated. A one-channel Bio-impedance measurement device with a goniometer has been designed in this study. The bio-impedance device generates high-frequency, low-intensity alternating constant current to human body and measure the bio-impedance signal. 20-kHz, 45-kHz, 50-kHz and 70-kHz has been investigated in the experiment. The one-channel bio-impedance measurement device includes of Wein oscillator, Howland constant current source, high-pass filter, the instrument amplifier INA 128, rectifier, low-pass filter and direct current coupling. Three electrode configurations were applied to compare the influence from each electrode configuration to the correlation calculation. Four male and two female have participated in the experiment of 70-kHz with three electrode configuration. In the experiment of 20-kHz, 45-Khz and 50-kHz, only one subject has participated in these experiments. The motion setting of 45-kHz is different with other frequency condition, it consists of 9 stages. Subject lifted their arms from 0 degrees to 80 degrees and kept their arm at each 10 degrees. The other motion setting consists of 4 stages. Subject lifted their arms from 0 degrees to 90 degrees and kept their arm at each 30 degrees. In multi-frequency with different electrode configurations condition, the result of 45-kHz, 50-kHz and 70-kHz contribute high correlation between the elbow joint angle changing and upper arm bio-impedance changing. However, the result of the 20-kHz condition is not stable. In the multi-subject experiment, each subject contributes high correlation result in the 70-kHz condition with three electrode configurations.