Based on various radiation components in the spectra of lightning return stroke processes, the temperature of the lightning channel is diagnosed by different methods. Combining with the synchronized electric field data and optical pictures of the lightning channel, the radii of the core current channel and the luminous channel are estimated. On the basis of the above mentioned facts, according to the heat conduction equation, the channel temperature distribution along the radial direction of the lightning return stroke channel is also achieved. The results from six lightning return strokes show that for the core current channel and luminous channel, the radii are in the range of 0.66–1.01 cm and 5.03–7.96 cm, respectively, and the corresponding channel temperatures are 27 300–30 300 K and 3300–5800 K, respectively. Within an average radius of around 1.76 cm, channel temperatures are above 20 000 K and fall sharply along the radial direction while gradually decline outside this range. The radii of the glowing edge with a temperature of around 500 K are first estimated, around 6.94–13.0 cm.

Film bulk acoustic wave resonator (FBAR) experienced skyrocketing development in the past 15 years, owing to the explosive development of mobile communication. It stands out in acoustic filters mainly because of high quality factor, which enables low insertion loss and sharp roll off. Except for the massive application in wireless communication, FBARs are also promising sensors because of the high sensitivity and readily integration ability to miniaturize circuits. On the ground of summarizing FBAR’s application in wireless communication as filters and in sensors including electronic nose, bio field, and pressure sensing, this paper review the main challenges of each application faced. The number of filters installed in the mobile phone has being grown explosively, which leads to overcrowded bands and put harsh requirements on component size and power consumption control for each unit. Data flow and rate are becoming increasingly demanding as well. This paper discusses three promising technical strategies addressing these issues. Among which coupled resonator filter is given intense attention because it is able to vigorously reduce the filter size by stacking two or more resonators together, and it is a great technique to increase data flow and rate. Temperature compensation methods are discussed considering their vital influence on frequency stability. Finally, materials improvement and novel materials exploration for band width modulation, tunable band acquisition, and quality factor improvement are discussed. The authors appeal attention of the academic society to bring AlN epitaxial thin film into the FBAR fabrication and have proposed a configuration to implement this idea.

Using high time‐resolved spectra and simultaneous records of the electric field change of three negative cloud‐to‐ground (CG) lightning flashes with multiple return strokes, the correlations between the total intensity of ionic lines in the spectra and the corresponding amplitude of the initial electric field change, as well as between the total intensity of the spectra and the channel apparent diameter, have been analyzed. The analysis shows the following: (1) The amplitude of the initial electric field change is roughly proportional to the total intensity of ionic lines. (2) The total intensity of the spectra shows a significant linear correlation with the apparent diameter of the channel. (3) The total intensity of ionic lines for 17 analyzed return strokes decreases with increasing height along the channel, which is consistent with the current variation along the channel in the modified transmission line model; the Master, Uman, Lin, and Standler model; and the Diendorfer‐Uman model. Meanwhile, the total intensity of ionic lines for other two analyzed return strokes along the channel without attenuation, this is consistent with the current variation along the channel in the Bruce‐Golde model, the transmission line model, and the Traveling Current Source model.

Based on the high time‐resolved spectra of a cloud‐to‐ground lightning flash with seven return strokes captured by a high‐speed slitless spectrograph, this work was the first to use the Saha‐Boltzmann plot method for the determination of the lightning return stroke channel temperature. The channel temperatures of the seven return strokes ranged from 21370 to 26500 K. Compared with the traditional Boltzmann plot method, the Saha‐Boltzmann plot method can provide more reliable temperature estimation for lightning channel. Analysis of several strong return strokes along the channel showed that the temperature changed little and there was no obvious tendency with increasing height. In addition, it was found that the channel temperature in the late stage of a return stroke was only about 3000–4000 K lower than in the initial stage. This means the channel remains >20000 K during nearly the entire period of the return stroke. This sustained high temperature could be the main cause of lightning‐related disasters.