Abstract: An apparatus for and a method of determining the material properties of a dielectric and/or conducting radar target by deciphering the backscattered signals returned from the target is disclosed. The resonance "code" of the echo signals from the target is a function of the width and spacing of the resonant spectral lines in the transverse electric (TE) and transverse magnetic (TM) modes of the returned signals. The resonances present in any TE or TM mode become uniformly spaced and of uniform width at high frequencies. The uniform spacing between adjacent resonances is used to uniquely determine the dielectric constant of the material comprising the target, and their uniform width is used to uniquely determine its thickness.

Abstract: An apparatus and method for determining the material properties characterizing a fluid contained in a cavity inside a solid comprises analyzing the resonances in the amplitude of elastic waves scattered by the cavity. Specifically, the resonance positions and their widths are used to determine the sound speed and the density of the cavity filler. The sound speed is found from the spacing between two consecutive overtones of any mode, which asymptotically becomes uniform for the higher-index overtones. The density is obtained from the width of any high order resonance and accordingly, all the information about the material composition of the filler is contained, and can be extracted, from the high-frequency asymptotic region.

Abstract: The shear absorption of a viscoelastic material is determined by directing acoustical energy at the viscoelastic material and sampling the backscattered signals that result when compressional waves propagate through the material and are scattered by either a fluid-filled or evacuated cavity contained therein. The backscattered signals are converted to a resonance amplitude versus frequency domain and the shear absorption of the viscoelastic material is determined from the frequency and the half-width of the resonance peaks.