Method and apparatus for generating and detecting acoustic signals

Abstract

A magnetic/acoustic transducer is disclosed. The transducer can be used in security/smart tag applications. The transducer includes a sensor tag made of magnetic metallic glass having a relatively high magnetostriction and a relatively low coercivity. Driving signals are provided by an rf dipole loop antenna. The tag responds to the rf signals and converts the exciting magnetic field into acoustic signals via magnetoelastic coupling. That is, the tag is forced to vibrate in unison with the incident electromagnetic signals generating longitudinal acoustic waves along a length of the tag. This results in radiation of ultrasound waves in air which can then be detected and characterized using an ultrasound microphone or a piezoelectric sensor. The tag is provided having a length equal to one half or one quarter long of an acoustic wavelength so that an acoustic resonance condition is established to maximize the generation of ultrasound waves in air. The measured ultrasound signal is locked in phase with the excitation or reference signal for sensitive long-range detection. The tag can operate in a magnetized or a demagnetized state to stimulate binary signals for security-tag applications. Tags of different length and/or geometry can be deployed in combination so that the tag transducer produces unique and distinguishable frequency spectrums to be used as smart tags.