To address the problem of low signal-to-noise ratio (SNR) and poor spatial resolution of cracks detection of the angled SV wave electromagnetic acoustic transducer (EMAT), pulse compression technique (PCT) and line-focusing technique are introduced into the angled SV wave EMAT. A finite element (FE) model of the line-focusing (LF) EMAT detection process based on the Barker code excitation was established, and the effects of the design parameters of magnet and meander-line coil (MLC) on the main lobe amplitude and width of the defect echo after pulse compression were analysed. The optimal combination of LF-EMAT design parameters and excitation parameters was obtained, and it was compared with the traditional angled SV wave EMAT and the tone-burst excitation method by experimental measurements. The results shows that compared with angled SV wave EMAT with tone-burst excitation, LF-EMAT can improve the SNR by 14.9 dB with no synchronous average and be processed by PCT. The SNR from LF-EMAT with PCT is10 dB at 1.5 mm lift-off, while the SNR of the angled SV wave EMAT with tone-burst excitation is less than 0 dB at 1 mm lift-off. When the Barker code PCT is applied to the LF-EMAT detection, we can achieve the purpose of increasing EMAT lift-off and reducing the synchronous averages to meet the demand of online, rapid, and high-temperature detection.

A Pd-Ni alloy thin-film coated surface acoustic wave (SAW) device is proposed for sensing hydrogen. The Pd-Ni thin-film was sputtered onto the SAW propagation path of a SAW device with a delay line pattern to build the chip-sized hydrogen sensor. The prepared sensor chip was characterized by employing a differential oscillation loop. The effect of the Pd-Ni film thickness on sensing performance was also evaluated, and optimal parameters were determined, allowing for fast response and high sensitivity. Excellent working stability (detection error of 3.7% in half a year), high sensitivity (21.3 kHz/%), and fast response (less than 10 s) were achieved from the 40 nm Pd-Ni alloy thin-film coated sensing device.

A laser-electromagnetic acoustic transducer (Laser-EMAT) Rayleigh wave (RW) detection based on surface constraint mechanism and its optimisation design are proposed to solve the low signal-to-noise ratio (SNR) of its application in aluminium alloy detection at high-temperature. We established a finite element (FE) model of aluminium alloy’s Laser-EMAT RW detection process based on the surface constraint mechanism and investigated the effect of the surface constraint mechanism on laser-excited RW . We also studied the effects of laser parameters and meander-line coil (MLC) EMAT parameters on the ultrasonic wave amplitude and spectral composition. Finally, the enhancement effect of the surface constraint mechanism on RW amplitude was analysed by Laser-EMAT RW detection experiments on aluminium alloy at room temperature and high temperatures. The results show that the optimised MLC-EMAT can increase the RW amplitude by 1.97 times. When the laser line source width equals the MLC-EMAT turn spacing, the echo SNR is the highest. The enhancement effect of the surface constraint mechanism on the RW amplitude gradually decreasesas the specimen temperature increases. The RW amplitude can increase by 1.43 times when the surface constraint mechanism is applied at room temperature, and for the aluminium alloy specimen at 430°C, the RW amplitude can increase by 32%.

In order to solve the difficulty in localization and poor signal-to-noise ratio (SNR) of the angled shear vertical wave (SV wave) electromagnetic acoustic transducer (EMAT) in cracks detection of high-temperature carbon steel forgings, a finite element (FE) model of the angled SV wave EMAT detection process was established, and the influence of specimen temperature on the EMAT excitation, propagation, and reception processes was analyzed. A high-temperature resistant angled SV wave EMAT was designed to detect carbon steel from 20 °C to 500 °C, and the influence law of the angled SV wave at different temperatures was analyzed. Then a circuit-field coupled FE model of angled SV wave EMAT in the carbon steel detection process based on the Barker code pulse compression technique was established, and the effects of the Barker code element length, impedance matching method, and matching component parameters on the pulse compression effect were analyzed. In addition, the noise suppression effect and the SNR of the crack-reflected wave in the tone-burst excitation method and the Barker code pulse compression technique were compared. The results show that the amplitude of the block-corner reflected wave decreases from 556 mV to 195 mV, and the SNR decreases from 34.9 dB to 23.5 dB when the specimen temperature increases from 20 °C to 500 °C. When the temperature is 500 °C, the SNR of the crack-reflected wave obtained by the Barker code pulse compression technique can be improved by 9.2 dB compared to the tone-burst excitation method with 16 synchronous averages. The study can provide technical and theoretical guidance for online crack detection for high-temperature carbon steel forgings.