HIGH-FREQUENCY ELECTRICAL MEASUREMENTS OF ADHESIVE-BONDED STRUCTURES - AN INVESTIGATION OF MODEL PARALLEL-PLATE WAVE-GUIDE STRUCTURE

Analysis using a network analyser of the electrical response between 3 00 kHz and 200 MHz for a range of model waveguide structures is discus sed. The structures chosen illustrate the variations to be expected in real adhesive bonds and include changes in bond line thickness, width and electrical conductivity of the substrate. A simple theoretical mo del was used to simulate the time domain data and very good agreement between experiment and theory was observed. Deficiencies in the model appeared when it was used to simulate frequency domain data, and the l imitations of these calculations ave critically discussed. The accurac y to which this method can be used to calculate the dielectric permitt ivity was assessed from a study of a number of polymers with well-defi ned dielectric characteristics. Parallel plate structures were fabrica ted using low density polyethylene (LDPE), high density polyethylene ( HDPE), polypropylene (PP), polystyrene (PS), polycarbonate (PC) and po lymethyl methacrylate (PM MA). Good agreement between literature and e xperiment was observed in all cases, validating the dielectric permitt ivity values obtained using this approach. This paper illustrates the potential of nondestructive electrical measurements to provide structu ral and quantitative permittivity information on adhesive joint struct ures. (C) 1997 Elsevier Science Ltd.