Complex permittivity monotoring gives us information about abnormal density or glue-overdose or presence of air inclusions in the board at the moment of its occurance. Using dielectric mixing models (e.g. Index of Refraction Mixing Model: IRMM) the effect of change of moisture content, fluctuations in amount of other ingredients can be predicted. It was shown, besides the moisture content, density etc., the mechanical parameters (so the quality) of boards (modulus of elasticity: MOE, modulus of rupture: MOR) can also be forecasted, by the so called density independent parameters.

Industrial tests show that the developed measurement system is suitable for on-line, real-time quality monitoring of large boards (e.g. 3x17 m2). Multifrequency operation is introduced, minimizing the errors caused by distance-variation between material under test and backscatter. The effects of reflected signals from elements of metal parts of machines are also minimized, using our circularly polarized microstrip antennas [3].

In this phase of development the system is installed in industrial environment to collect more measurement data. In addition we make experiments to compare the real mechanical properties to the measured microwave parameters. Then a computer aided correlation analysis is carried out to find empirical formulas between measured values of attenuation, phase shift and the measured mechanical properties. After all an appropriate software can also display graphically the surface distribution of these parameters on the whole board so its quality could be judged simply at a glance.

[1] F.Volgyi, I.Mojzes, M.Kelemen, I.Racz, R.Seller, A.Sonkoly, F.Divos and B.Zombory, Hungarian Patent Application, MSzH, P-9601630, 1996.
[2] F.Volgyi: "Monitoring of Paricleboard -Production using Microwave Sensors" Ch.10, pp. 249-274 in book: Sensors Update,Vol.7, WILEY-VCH,Weinheim,GE,ISBN 3527298215
[3] F.Volgyi: "Microstrip Antenna R&D in Hungary" 10th MICROCOLL, Budapest, Hungary, March 21-24, 1999, Proc. pp. 249-252.