A Research Of Medical Ultrasonic Sensor Based On Fiber Bragg Grating

In recent years,high intensity focused ultrasonic in megahertz frequency range is widely used in the field of medical diagnosis and treatment.To ensure the treatment safety,it is of significance that detecting the ultrasonic field's intensity and distribution precisely.Compared with the piezoelectric sensor which is conventionally used in the medical applications,fiber grating sensor has the advantages of high sensitivity,small size,flexibility and is immunity to electromagnetic interference,so it is particularly suitable for the medical applications.In this thesis,the sensing principle of the fiber Bragg grating was analyzed based on the geometric effect and the elasto-optic effect.Characteristics of fiber Bragg grating spectrum under ultrasonic were simulated by the coupling mode theory and the transmission matrix method.The ultrasonic sensor based on phase-shifted fiber Bragg grating was proposed to improve the sensitivity and detection frequency.The parameters of fiber grating were designed and optimized according to the characteristics of high frequency focused ultrasonic signal.A uniform fiber Bragg grating(FBG)sensor and a phase-shifted fiber Bragg grating(PS-FBG)sensor for detecting high frequency focused ultrasonic field have been designed and fabricated.The sensing system and corresponding experimental setup have been carried out to measure the ultrasonic field's intensity and spatial distribution,and the performance of our sensing system has been investigated.The experimental results show that both the uniform FBG sensor and the PS-FBG sensor are have good linearity.Compared with the uniform FBG sensor,the sensitivity of the PS-FBG sensor is increased about 14.5 times,reaching to 1.05V/MPa.Furthermore,the PS-FBG sensor presents a signal-to-noise ratio of over 32 dB,which is 11.7 dB higher than that of the uniform FBG sensor.The focal spot size and the focal length of the focused transducer were measured by the PS-FBG sensor.The experimental results are consistent with the design parameters,which indicate that the distribution of ultrasonic field can be measured accurately by our sensor.The experimental results show that our ultrasonic sensor has good performance,which presents the potential for medical ultrasonic application.