2.2. C-scan system
The C-scan system utilised in this work was developed by Amsterdam Technology and is commercially available. A special feature of this equipment is the inbuilt water tank, with special porous membrane that allows sound waves to travel from the transducer to the sample. The scanner covers a standard area of 10×20 mm2, with a resolution of 0.1×0.1 mm2 and scan time of approximately 5 s. Details of the principles behind this system are well described on the manufacturer's website [11]. The ultrasonic C-scan equipment used is shown in Fig. 2, and was set up according to the manufacturer's guidance.