(Dr. Jacek Jarzynski, advisor)

"Fiber Optic Sensor for Ultrasound"

Abstract

In ultrasonic nondestructive testing and in acoustic emission measurements, there is a need for sensors which respond preferentially to the in-plane (tangential) component of surface displacement, as opposed to the out-of-plane (normal) component.  Such a sensor would provide better discrimination against environmental noise since environmental noise produces, in many structures (plates, shells), mainly out-of-plane surface vibrations.  The objective of this study is to develop an interferometric fiber optic sensor for measuring in-plane surface displacements at ultrasonic frequencies in the range 50-200 kHz.

 Several fiber optic sensor designs have already been tested.  The most successful design to date consists of a large number of concentric optical fiber wraps which have been laid flat and bonded to a thin aluminum base.  Experimental measurements of this “spiral-wrap” sensor’s response and a quasi-static model of the sensor are presented.  Future work will involve developing a dynamic model of the spiral-wrap sensor, optimizing the sensor, and comparing the in-plane and out-of-plane response of the sensor to that of a piezoelectric sensor.