Focal type electromagnetic acoustic transducer and flaw detection system and method

A system for detecting a flaw in an object comprising:

• a focusing electromagnetic acoustic transducer to be placed on said object comprising:
• a first insulation sheet;
• a first meander coil formed on a first surface of said first insulation sheet;
• a second meander coil formed on a second surface of said first insulation sheet, said first and second meander coils positioned so as to be coincident with each other, each of said meander coils comprising a plurality of coil segments wherein intervals between adjacent coil segments vary sequentially from one end to another end of said meander coils;
• a second insulation sheet attached to said first meander coil so as to sandwich the first meander coil between said first and second insulation sheets;
• a third insulation sheet attached to said second meander coil so as to sandwich the second meander coil between said first and third insulation sheets;
• a magnet having opposite surfaces exhibiting,, opposite magnetic poles, said opposite surfaces being positioned above said second insulation sheet, a source configured to supply a high frequency current to one of said meander coils to transmit ultrasonic SV waves into said object the frequency of said current being variable to vary a focal point in said object;
• and
• a detection mechanism configured to detect a flaw in said object in accordance with amplitudes and phases of signals detected by the other meander coil.

A method of detecting a flaw in an object comprising the steps of:

• preparing, a focusing electromagnetic acoustic transducer having transmission and reception meander coils;
• placing said transducer on said object;
• supplying a high frequency current to said transmission meander coil to transmit ultrasonic SV waves into said object;
• varying the frequency of said current in time sequence thereby changing a position of a focal point of said transducer;
• and
• detecting a flaw in said object in accordance with amplitudes and phases of signals detected by said reception meander coil.