A group of researchers are currently using Ultrasonic Nondestructive Testing (NDT), which involves amplification of photoacoustic laser source signals using a nanoparticle array of candle soot and polydimethylsiloxane. The laser absorbs the patch. Their research was published in the journal Applied Physics Letters.
Their method was one of the first NDT systems to combine contact and non-contact ultrasonic testing elements. The use of photoacoustic patches to produce such ultrasound results also demonstrates the promise of a wide range of non-contact NDT applications.
Taeyang Kim, author of the paper, said: "The laser-based non-destructive testing method has almost no temperature-dependent measurement advantages, as well as a wide range of monitoring areas, and can easily change the position of the device. This technology is non-contact and remotely generated. Ultrasonic surface waves offer a very flexible and simple method"
Ultrasonic waves can be generated when a high power laser strikes the surface. The heat generated by the pulse causes expansion and compression on the illuminated area, thereby generating an ultrasonic signal. The resulting wavelength, called the Lamb wave, then passes through the relevant material to become an elastic wave.
The team used candle soot nanoparticles, plus polydimethylsiloxane to absorb the laser. They use candle soot because it is easy to achieve efficient absorption of the laser and can form the elastic expansion required to produce photoacoustic conversion, which can produce lamb waves.
By placing the particles in the patch in an online array, they are able to reduce the bandwidth of the wavelength, filter out unwanted wave signals and improve analysis accuracy. The researchers chose to use an aluminum sensing system in the receiving transducer. The use of the patch increased the amplitude by more than two times compared to the absence of patches and proved to be narrower than the bandwidth produced by other conditions.
Kim said that the durability of the method in industrial environments and the performance of patches on curved and rough surfaces still exist. He pointed out: "The new NDT system will attract more attention in order to explore the best materials for various applications in the patch or NDT industry."
Next, the team wanted to test the system in a high temperature non-destructive test scenario.