Microwave Applications of Industrial Free Electron Lasers

The IFEL is a low cost compact source of microwaves producing high powers (~ 10kW) within the frequency range 1 to 100GHz. The Network is investigating microwave applications and in the area of material processing and two main areas have been identified based upon the direct use of microwaves and the conversion of microwaves into plasma and UV radiation.

1. Direct Use of Microwaves

Advantages compared with conventional furnaces.

• Volumetric heating which avoids mechanical stresses from the high thermal gradient used in conventional furnaces.
• Shorter processing time by 1 or 2 orders of magnitude.
• Low energy consumption due to short processing time and the heating of processed materials only.
• Selective heating, can be focussed to a spot size of 1cm².
• Selective absorption by materials by 2 or more orders of magnitude.

2. Microwave Plasma

Advantages compared with conventional plasma sources.

• Can be operated at high powers.
• Power density is high by 1 order of magnitude over the conventional source.
• Microwave frequency can be selected to optimise the plasma processing.
• Plasma can be focussed to provide intense heat source.

3. Microwave UV Sources

Advantages compared with conventional plasma sources.

• Power per unit length is variable and varies between 100 and 1000W per m compared with a fixed value of 30W per m for conventional lamps.
• Can be tuned to select 254nm or 185nm radiation from mercury vapour.
• Will operate efficiently with excimer gases to produce a range of UV emissions e.g. 222nm, 308nm or 345nm.

4. Microwave Applications in connection with Material Processing

4.1 Polymers

- Curing of adhesives.

- Surface treatment.

- Joining of plastics with and without priming agents.

4.2 Inorganic Materials

- New ceramics for the aerospace and automotive industries

- Classic materials with new micro or macro structures such as nano-powders or microporus materials

- Surface treatment

- Casting and sintering of ceramics and piezoceramics

- Ferrite sintering

- Joining of ceramics

- Fibres in various shapes such as fleece, felt/braid, tow, sausage and curly form for a wide range of materials including:-

• Ceramic, glass, aluminium
• Boron nitride and carbide
• Silicon nitride and carbide
• Alumina silica and carbide

4.3 Metals

Use with aerospace materials (e.g. titanium alloys including titanium aluminide) and automotive materials (high strength steels)

- Welding

- Cutting

- Surface cleaning

- Heat treatment

- Surface coating

- Chipless machining

4.4 Clean Technologies

Microwaves Only

- Pattern marking on cloth

- Waste water cleaning and drinking water purification

- Vitrification of nuclear materials

- Decommissioning of concrete structures

Microwave Plasma

- Automotive plasma catalyst for conversion to remove NOx’s exhaust gases

- Efficient lighting for highways, stadiums etc.

Microwave UV

- Waste water cleaning and drinking water purification

- Food processing for longer shelf life

- Air filters for hospitals, aircraft, factories etc.

- Curing printing ink

- Bonding adhesives

- Surface preparation for painting

4.5 Combination of Laser and Microwave Technologies

Microwave plasma is cheap compared with laser produced plasma but cannot be focussed to the small size attainable by lasers. A combined system produces material preheat with the microwave plasma thus allowing material processing with low power lasers thus giving considerable cost saving per product. Applications are with:-

- Pure metals

- Ceramics

- Coated steels for automotive industries to improve cut quality in terms of good finish reduced kerf width and dross.