Abstract: A cooking surface has a thickness between 0.05 and 3.0 mm to optimize between highest efficiency, lowest magnetic stray field, and desired surface material. In the thickness range of 0.05 to 0.2 mm, a top layer may consist of plasma sprayed hard ceramic such as alumina which can be impregnated with poly-tetra-fluor-ethylene. In the thickness range of 0.2 to 2.0 mm, the top layer may consist of glass fibre reinforced material which can be impregnated with poly-tetra-fluor-ethylene and can be of a hardened quality. In the thickness range of 1.00 to 3.00 mm, the top layer may consist of a vitroceramic or glass material.

Abstract: For use in the heating of foodstuffs by induction, use is made of an energy converter between energy taken from the mains supply via a rectifier and a high frequency oscillation. Such a converter is frequently based on the maintenance of an oscillation in a parallel resonant circuit (CR, LR) which may be disposed in a converter bridge (S1, S2, S3, S4) of controlled switches. It has turned out to enhance the efficiency considerably to let the parallel resonant circuit be series connected to a self-inductance L1 which connects it to the DC source UDC. A series resonant circuit is thereby created which is active during supply of energy and which in a simple fashion reduces the load on the participating switches.

Abstract: Circuits for high frequency energy supply for cooking pots, etc. utilize resonant circuits in which the coil for the energy transfer forms a part. Furthermore circuits of the inverter type are used. It has turned out to be advantageous to use an extra circuit which gives the current feed from the rectifier of the power supply unit to the inverter a period of oscillation which is less than or equal to the period of oscillation of the resonant circuit. In this manner an efficient control of the supplied power is obtained, and the losses are reduced. Furthermore measuring signals may be derived which may be used for increasing the safety with respect to incorrect use.