More Myths Exposed

Among the many dielectric projects completed to date are a 8kW/27.12MHz solid state amplifier and automatic matching system, a 40.68MHz amplifier and matching system for a totally new process and a system using four 2.5kW/40.68MHz amplifiers and matching networks operating into a common load.

If you’re surprised by the reference to 40.68MHz above that might be because many engineers in the plastics industry are under the impression that it is only possible to operate equipment in the 27.12MHz Industrial Scientific and Medical (ISM) band. This is not the case. There are other ISM bands, which may be used and 40.68MHz is one such band.

The myth probably arose because of equipment limitation rather than any practical or legislative constraint. Indeed it is not easily possible to manufacture a cavity oscillator with sufficient frequency stability to meet the very limited bandwidth required to operate in the other ISM bands.

The rationale behind using a different frequency is that some materials weld more efficiently at higher frequency, indeed some materials that are impractical to weld at 27.12MHz become practical at 40.68MHz.