Study On Respiration And EEG Measurement Based On Mach-Zehnder Interferometer

Respiration and electroencephalogram?EEG?monitoring are closely related with personal health status and potential disease diagnosis.Typically,these physiological signals are obtained through independent instruments using electrical/electronic sensors.However,when an anaesthetized patient is in magnetic resonance imaging?MRI?,traditional methods have failed since most of them are susceptible to electro-magnetic interference?EMI?.In addition,electrical devices inevitably introduce external power source,like voltages or currents,which may raise safety concern when contacting with human body.To address the issues of traditional technology,this thesis presents optical methods for respiration and EEG monitoring based on the principle of Mach-Zehnder?M-Z?interference.The signal monitoring systems are separately designed and experimentally tested under different volunteers.Testing results are also analyzed and compared with standard device.Main work of this thesis:1.An optical respiration monitoring method is proposed based on a cascaded single-mode-few-mode-single-mode?SFS?fiber sensor,the principle of LP₀₁ and LP₁₁mode interference is theoretically analyzed,the effect on interference pattern with respect to fiber length and offset values is analyzed,and the curvature sensing principle of the sensor is presented.Through optimal design,the extinction ratio is up to 23.5dB.2.An optical EEG monitoring method is proposed based on a M-Z lithium niobate electro-optic?EO?modulator,the linear EO effect is described,the working principle of the sensor is analyzed theoretically,and the signal processing method is given.Through theoretical analysis,the calculated sensitivity of the sensor is 287.8?W/V in the linear working region.3.The curvature sensitivity and the optimal linear working region of the fiber sensor is determined experimentally.Through packing design,the linear working reign is positioned by an arch structure.The respiratory monitoring system is designed and tested on different individuals.Meanwhile,the instantaneous rate of abnormal respiratory waveform is analyzed,and the tidal volume and minute ventilation is estimated through simultaneous test with a standard spirometer.Through experimental results,the sensitivity of the respiration sensor is up to 8.53dB/m^-1 when working at linear region.Respiration monitoring results are in good agreement with the standard spirometer,the maximum difference of tidal volume estimation is 0.1999L and the overall error of minute volume estimation is less than 5%.4.The sensitivity of the EO modulator is tested,and the optical EEG acquisition system and signal processing system is designed respectively.The minimum threshold for voltage detection is determined and EEG acquisition experiments are conducted on different volunteers in the state of open eyes and closed eyes.Through experiment results,the sensitivity of the modulator is up to 266.4?W/V,which is in agreement with theoretical calculation.The system is able to detect voltage signals as low as10?V.Moreover,EEG monitoring results are correlated with standard Neuroscan device and the signal noise ratio is increased by 2?3dB.