Qiang Zhao

In this study, we have developed an optical fiber ultrasound emitter based on the thermal cavitation effect. A tube filled with a highly absorptive liquid is sealed at the end of an optical fiber pigtail. A continuous-wave laser is transmitted through the fiber, heating the highly absorptive copper salt solution near the fiber end face to its spinodal limit. Using a single-mode fiber, we achieved ultrasound pulses with an amplitude of 330 kPa and a repetition rate of 4 kHz in the frequency range of 5–17 MHz, and a bandwidth of 12 MHz was obtained by using a low laser heating power of 52 mW at a wavelength of 974 nm. This optical fiber ultrasound emitter features a simple fabrication process, low cost, and low optical power consumption. Its flexible design allows for easy integration into medical devices with small dimensions and makes it suitable for non-destructive testing in confined spaces.

Fiber Bragg grating (FBG) has been widely used in many fields for the measurement of temperature, strain, and other parameters, but single-mode FBG has a cross-sensitivity problem between temperature and strain. In this paper, a new scheme is proposed to solve the problem by using parallel core-cladding FBGs, whose grating areas are located at the interface region of the core and cladding of the fiber. The sensing principle of parallel core-cladding FBGs for the simultaneous measurement of temperature and strain is theoretically analyzed. The femtosecond laser point-by-point method of the parallel core-cladding FBGs is experimentally investigated. Two parallel FBGs, namely core FBG and cladding FBG, are formed efficiently and conveniently by a single time inscription. Two transmission peaks have been observed, which are excited by the core mode and the cladding mode, respectively. The experiment results demonstrated that the proposed compact sensor can detect the temperature with sensitivity of 11.043 pm/°C and strain with sensitivity of 1.2101 pm/με up to 1.114×10 ³ με, and the relative errors of temperature and strain are less than 5.8% and 8.3%. The proposed parallel core-cladding FBGs are much more compact as one FBG element compared with the conventional structure with two cascaded FBGs or parallel FBGs. The parallel core-cladding FBGs can overcome the cross-sensitivity problem of single-mode FBG, which has great application value and potential in fiber sensing fields for dual-parameter.

A polarization-maintaining fiber Bragg grating (PM-FBG) is a crucial component of fiber optic sensors, and the inscription method associated with it has garnered significant interest. Compared to alternative technologies, the femtosecond laser point-by-point inscription method offers greater flexibility. However, it is still unclear how the controllable factors of the femtosecond laser point-by-point inscription process relate to the spectral characteristics of PM-FBG. The main factors that affect the spectral properties of PM-FBG inscribed via the femtosecond laser point-by-point method, including the pulse energy, grating length, fiber type, and grating apodization, are investigated experimentally and theoretically in this article. An experimental investigation was conducted to examine the relationship between the pulse energy and side lobe suppression ratio (SLSR), and the optimal pulse energy was approximately 30 nJ to obtain the highest SLSR. The theoretical model of the full width at half maximum (FWHM) is presented, and it is shown that the FWHM tends to saturate with grating lengths greater than 8 mm. There is a linear relationship between the distance of the two reflection peaks and the birefringence of the polarization-maintaining fiber (PMF), regardless of the birefringence induced by the inscription process. The oblique apodization method can decrease the SLSR of the two reflection peaks, but it also broadens their FWHM. This study provides compelling evidence to support the improvement in the spectral performance of PM-FBGs inscribed via the point-by-point femtosecond laser inscription method.

Lithium-ion batteries are widely used in a variety of fields due to their high energy density, high power density, long service life, and environmental friendliness. However, safety accidents with lithium-ion batteries occur frequently. The real-time safety monitoring of lithium-ion batteries is particularly important during their use. The fiber Bragg grating (FBG) sensors have some additional advantages over conventional electrochemical sensors, such as low invasiveness, electromagnetic anti-interference, and insulating properties. This paper reviews lithium-ion battery safety monitoring based on FBG sensors. The principles and sensing performance of FBG sensors are described. The single-parameter monitoring and dual-parameter monitoring of lithium-ion batteries based on FBG sensors are reviewed. The current application state of the monitored data in lithium-ion batteries is summarized. We also present a brief overview of the recent developments in FBG sensors used in lithium-ion batteries. Finally, we discuss future trends in lithium-ion battery safety monitoring based on FBG sensors.

Background: : Induction motor plays a major role in various industries, and its importance is increasing. Due to the environmental temperature or sealed working environment, heat generation is generally severe. The heat exchange with the outside environment does not take place smoothly, and the motor temperature increases. The performance of the induction motor is also significantly influenced by the temperature. Therefore, it is necessary to study the influence of temperature on the performance of induction motor. Objective: This study aimed to analyse the influence of temperature on induction motor. At different temperatures, variation in performance parameters has been observed. Methods: Taking an 11 kW 1500r/min induction motor as an example, a two-dimensional transient electromagnetic field model was established, and the correctness of the model was verified by experiments. The motor starting performance, various losses and efficiencies under different temperatures wereestimated. Results : As the stator and rotor resistance increased, the starting current decreased by 11.99% when the internal temperature rose from 25°C to 150°C. When the internal temperature rose from 25°C to 150°C, the stator copper loss increased by 32.83%, and the rotor copper loss increased by 28.79%. However, the core loss of the motor increased by 3W, and the motor efficiency decreased by 2.12%. Conclusion: When the temperature is different, the starting torque of the motor is almost unchanged, and the starting current decreases with an increase in temperature. The stator copper loss and rotor copper loss of the motor increase with the increase in temperature, while the core loss is almost unchanged. In addition, the efficiency of the motor gradually decreases with the increase in temperature.

Traditional electrical expendable bathythermograph (XBT) is designed to fall at a known rate based on a great deal of experiments so that the depth of the temperature profile can be inferred from the time it enters the water. Unlike the traditional electrical XBT, which derives the depth from fall-rate equations, we propose an all-optical fiber (AOF) XBT (AOF-XBT) based on cascade of two fiber Bragg gratings (FBGs). In the AOF-XBT, the depth data comes from one FBG, which responds in real time to the pressure acting on the diaphragm, and temperature data can be measured via the other FBG simultaneously. First, the pressure and temperature response characteristics of the AOF-XBT are analyzed based on a finite element method. Then, the temperature and pressure calibrations for the AOF-XBT is completed after they are packaged. Results show that the mean-temperature sensitivity of two sensors are 14.765 and 13.705 pm/°C in the range of 5°C–30°C, and the mean-pressure sensitivities are − 2.75586 and − 3.00472 n m / M P a in the range of 0–0.6 MPa, respectively. At last, by comparing the results obtained from the AOF-XBT and the SBE 911plus CTD that tested in the sea area of Weihai, the trends of the temperature-depth profile from the two devices are consistent, which presents a new all-optical technique to provide full ocean temperature-depth profile observations.