H-Field Electromagnetic Heating System for Fusion Bonding: 5,710,413

An H-field electromagnetic heating system for fusion bonding, particularly useful in the sealing of telecommunications cables and closures, comprises a composite bonding material having a bonding matrix and susceptors, the susceptors being magnetically reactive at a frequency above 50 MHz, and an applicator for applying radiant electromagnetic energy to the composite bonding material, at a frequency above 50 MHz (preferably 75-500 MHz). The applicator may take the form of a quarter-wave resonator having an inner conductor and an outer conductor which at least partially surrounds the inner conductor, the two conductors being shorted at a common end. The material to be heated is placed between the conductors. The inner conductor may include a resonator tube which is capacitively coupled to the power supply by a capacitive probe connected to the center conductor of a coaxial connector. Different applicators (having different geometries) may be used with the same power supply, or a variety of heater adapters may be provided which can be removably attached to the applicator base. An alternative applicator employs many wires, electrically insulated from one another, each forming a coil with a common axis, and all of the wires being electrically connected in parallel. Several of these wires are stacked to form multiple layers of coils, such that the effective resistance of said applicator is reduced and the current-carrying capacity is increased. Individual capacitors may be connected in series with a respective one of the wire coils, to make the current in the coils more uniform for coil circumferences which are greater than 0.1 of the wavelength of the radiant electromagnetic energy.