Measurement Method for the Velocity of Acoustic Emission Wave in Liquid Nitrogen

The velocity of acoustic emission (AE) wave at super-low temperatures is important in many fields, such as aerospace, aviation, nuclear power, superconductors, and military industry. Here, we propose a new fiber-optic AE theory, sensor and equipment to measure the velocity of AE wave in liquid nitrogen. In this fiber-optic AE theory, the AE wave is transmitted into an optical phase inside the fiber, and the phase is demodulated. A new fiber-optic ring AE sensor and equipment are built to test the theory. Finally, AE experiments are performed in liquid nitrogen. For the first time, the velocity of the AE wave in liquid nitrogen is measured, which is 870.63 +/- 5.35 m/s. This scheme could provide a route to a new generation of AE sensors for use in harsh environments.