High-overtone bulk acoustic resonator as passive sensor acting as buried cooperative target interrogated by Ground Penetrating RADAR

We consider a broadband bulk acoustic resonator architecture — the so called High-overtone Bulk Acoustic Resonator (HBAR) — as a transducer acting as cooperative target to a RADAR interrogation unit. Specifically, we consider the compatibility of such an acoustic device as a passive buried sensor interrogated through a wireless link by an unmodified Ground-Penetrating RADAR (GPR). While the comb of modes is detected as a series of echoes well within the typical interrogation duration of GPRs, with a spacing between adjacent echoes representative of the acoustic velocity and hence the physical quantity under investigation, the poor coupling coefficient of each individual mode due to the spreading of the piezoelectric transducer coefficient over many modes reduces the interrogation range with respect to the acoustic delay line approach. A sensor identification scheme within the clutter of reflections from dielectric buried interfaces is proposed.