Abstract: According to the principle of measuring bioelectrical impedance changes based on magnetic induction， a method was proposed to test the respiratory signal by measuring the change of conductivity in chest. Supposing the thorax as a uniform conductivity sphere， a measuring respiratory signal theoretical model was developed based on the motion characteristics. Some simulations were implemented to analyze the relationship between the thoracic impedance and volume variation， as well as the effect of sensor coil radius on the measurement results. At last， the testing experiments was carried out to discuss the effects of the coil sensor parameters， the conductivity and volume of the NaCl liquid， measuring distance and respiration motion on the measurement circuit. The results showed that the respiratory signal measurement based on magnetic induction will be one of the effective solutions for non-contact， long-term respiratory signal detection and has further research value.

Key words: magnetic induction, bio-impedance, thorax, conductivity, respiration signal