To study the effect of frequency on the attenuation characteristics of acoustic emission signals in wood, in this paper, two types of hard wood and soft wood were studied separately, and the energy attenuation model of the propagation process of AE sources with different frequencies was established. First, using the piezoelectric inverse effect of the AE sensor, an arbitrary waveform generator was used to generate frequency-tunable pulses in the range of 1 kHz to 150 kHz as the AE source, where the AE source energy could be regulated by the output voltage level. Then, five AE sensors were placed at equal intervals of 100 mm on the surface of the specimen to collect AE signals, and the sampling frequency was set to 500 kHz. Finally, the energy value of AE signal of each sensor was calculated based on the AC principle, and the energy attenuation model was established by exponential fitting. The results showed that both the amplitude and energy of the AE signals of different frequencies showed negative exponential decay with the increase of propagation distance, and, at the same frequency, the change of AE source energy level had no significant effect on its attenuation rate. Compared with hard wood, the energy attenuation of the AE signal of soft wood was more sensitive to the change of frequency, and, at the same frequency, the attenuation rate of soft wood was smaller than that of hard wood.

To investigate the effect of Zelkova schneideriana surface cracks on the longitudinal wave propagation characteristics of acoustic emission (AE). Different sizes and numbers of cracks were made on the surface of the specimen, the propagation characteristics of AE longitudinal waves along wood texture direction were studied. Firstly, five regular cracks with the same length, different width, depth and equidistant distribution were fabricated on the surface of thespecimen. Theburst and continuous AE sources were generated by lead core breakage and signal generator, and the AE signals were acquired by 5 sensors with sampling frequency was set to 500 kHz. Then, the propagation speedof AE longitudinal wave was calculated by Time Difference of Arrival (TDOA) based on lead core breakage. Finally, the 150 kHz pulse signals of different voltage levels generated by the signal generator were used as AE sources to study theinfluence of cracks on the attenuation of AE longitudinal wave energy. The results showed that the AE longitudinal wave propagation speedunder the crack-free specimen was 4838.7m.s-1. However, after the regular crack was artificially made, the longitudinal wave speedreduced to a certain extent, and the relative error of the change was not more than 9%. Compared with the energy decay rate of 1.29 in the crack-free specimen, the decay rate gradually increased to 2.08 with the increase of the crack cross-sectional area.

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To explore the propagation characteristics of acoustic emission (AE) signals in wood at different angles. The AE signals at different angles were obtained by changing the angle of incidence by sawing the inclined surfaces at different angles. The Zelkova schneideriana specimen was sawn 5 times with an increment of 15°, and 5 different incidence angles were obtained. AE signals were collected by 5 sensors arranged equally on the surface of the specimen, AE energy and energy attenuation rate were calculated. The reflection signals corresponding to different angles were collected on the uncut specimen by changing the position of the sensors, and the propagation speed of the AE signals at different angles was calculated. The results showed that the kinetic energy provided by the external excitation is small, and the AE energy is mainly provided by the displacement potential energy. With the change of the incidence angle, the AE kinetic energy changes significantly. With the increase of the reflection angle, the speed of the reflected wave also continued to increase, and finally stabilized at 4600 m/s.

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