Acoustic emission technology has been applied to many fields for many years. However, the conventional piezoelectric acoustic emission sensors cannot be used in extreme environments, such as those with heavy electromagnetic interference, high pressure, or strong corrosion. In this paper, a novel fiber-optic ring acoustic emission sensor is proposed. The sensor exhibits high sensitivity, anti-electromagnetic interference, and corrosion resistance. First, the principle of a novel fiber-optic ring sensor is introduced. Different from piezoelectric and other fiber acoustic emission sensors, this novel sensor includes both a sensing skeleton and a sensing fiber. Second, a heterodyne interferometric demodulating method is presented. In addition, a fiber-optic ring sensor acoustic emission system is built based on this method. Finally, fiber-optic ring acoustic emission experiments are performed. The novel fiber-optic ring sensor is glued onto the surface of an aluminum plate. The 150 kHz standard continuous sinusoidal signals and broken lead signals are successfully detected by the novel fiber-optic ring acoustic emission sensor. In addition, comparison to the piezoelectric acoustic emission sensor is performed, which shows the availability and reliability of the novel fiber-optic ring acoustic emission sensor. In the future, this novel fiber-optic ring acoustic emission sensor will provide a new route to acoustic emission detection in harsh environments.

Detonation velocity is an important parameter for explosive, and it is crucial for many fields such as dynamic chemistry burn models, detonation propagation prediction, explosive performance estimation, and so on. Dual-channel detonation velocity measurement method and system are described. The CFBG sensors are pasted both on the surface and in the center of the explosive cylinder. The length of CFBG sensors is measured via the hot-tip probe method. The light intensity reflected from the CFBG sensors attached to the explosive is transformed to voltage, and the voltage–time is then measured with the oscilloscope. According to the five experiments results, the relative standard uncertainty of detonation velocity is below 1%.

Fiber Bragg grating (FBG) acoustic emission (AE) sensors have been used in many applications. In this paper, based on an FBG AE sensor, the sensing principle of the interaction between the AE wave and the sensor is introduced. Then, the directionality of the FBG AE sensor on the surface of a thin polymer-bonded explosive (PBX) material is studied. Finally, the time coefficient location method is proposed to correct the AE time detected by the FBG AE sensor, thereby improving the accuracy of location experiments.

Rolling bearings are widely used in many industries and their online diagnosis is very important. However, there is still no effective way to detect small faults online. In this paper, a fiber Bragg grating acoustic emission sensing method is proposed and tested inside an accelerated bearing life tester. The fiber Bragg grating acoustic emission sensors are small, resistant to electromagnetic interference, intrinsically explosion-proof and are thus fit for the inner environment of an accelerated bearing life tester, which is small, has high electromagnetic interference and is full of lubrication oil. Therefore, we could install the fiber Bragg grating acoustic emission sensors inside an accelerated bearing life tester. The experimental system based on the principle of tunable narrowband laser demodulation is built up to collect the acoustic emission signals of faulty rolling bearings with different fault types. Then, with the envelope demodulation algorithm we obtained the fault characteristic frequencies of the bearings which were consistent with the theoretical fault frequencies. The results show that the fiber Bragg grating acoustic emission sensors are sensitive to the small faults of rolling bearings and can be used inside an accelerated bearing life tester.

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.

With the increase of space activities, the safety detection of equipment in supercold environment becomes more and more important. However, the safety detection of equipment in liquid hydrogen environment is an unsolved worldwide problem. In this article, we present a new method to detect acoustic emission (AE) signals in liquid hydrogen environment, which can be used to confirm the safety and reliability of the equipment working in liquid hydrogen. First, the principle of mandrel-based fiber-optic ring (MBFOR) AE sensor and the corresponding demodulation method are introduced. Second, the effects of physical parameters, such as the length of the sensing fiber, the diameter and material of the mandrel, and the number of fiber winding layers on the sensor's sensitivity, are studied by experiment. Finally, the AE source localization accuracy test of the FOR AE detection system at low temperatures and the adaptability test of the proposed method in −252.8 °C liquid hydrogen are carried out. The results show that the proposed MBFOR sensor and the multichannel AE detection system can complete the defects detection of aerospace pressure vessel in liquid hydrogen. Certainly, it can be used for safety detection for other spacecraft equipment in harsh environments.