Imaging of electromagnetic properties via acoustic excitation

A variety of piezoelectric and magnetic materials are studied through acoustically stimulated electromagnetic (ASEM) response. The ASEM signals are found in polycrystalline plastic materials, ferrite magnets, and a biological tissue of bone as well as single-crystalline GaAs. Since ASEM signals will be canceled in amorphous or randomly oriented polycrystals, small signals emitted from plastic materials imply the presence of crystalline domains within a spot size (about 1 mm) of the focused ultrasonic beam. We also performed ASEM imaging for single crystalline GaAs. A striking stripe pattern is found in GaAs (100) substrates. This will be attributed to resonant modes of acoustic waves confined in the substrates, yielding specific patterns affected by antenna configuration and detection frequency.