Detection of a subsurface flaw with the total Internal Reflection Ultrasonic Sensor

A novel ultrasonic sensor aimed specifically at detecting subsurface flaws is developed and investigated experimentally. The sensor exploits the phenomenon of frustrated total internal reflection and operates as a two-port device whose insertion loss is affected by a flaw beneath the surface of a tested object. It is designed as a prism of a TeO₂ single crystal, which in the experiment was put in contact with tested specimens using an optical contact technique. An artificial “defect” in the defected specimen of fused quartz was an epoxy layer of 28 μm in thickness. Testing the flawless and defected specimens has shown a distinctive difference between the sensor responses that proves the sensor capability to detect a subsurface flaw.