The use of modulated radiation pressure in target detection and classification

Both acoustic and electromagnetic waves exert forces of radiation on targets in their path of propagation. The radiation force (pressure) results from the change in wave momentum due to scattering by the target, averaged over one period of oscillation.  Modulated radiation pressure (MRP) utilizes the acoustic radiation force by using a double-sided suppressed carrier modulated (DSB-SCM) incident signal, which when averaged over one period of the carrier frequency, results in a signal that oscillates at the modulation frequency.  Target detection and classification can be facilitated by using the high carrier frequency to create a narrow beam with surgical accuracy, which can be used to probe the target with the ability to ’shake’ it at the modulation frequency. A frequency scan can reveal target resonances, while a physical scan along the length of the target can reveal the mode shapes corresponding to those resonances, which can be used to estimate target size and its content. The purpose of this effort is to investigate the use of MRP in detection, classification and identification of underwater targets.  In the last five years we have been investigating the use of MRP with scaled targets using funding from ONR.  We plan to build on this experience to design and fabricate a prototype transducer that will eventually be modified for use with real-size targets.