How is heat produced in dielectric heating?

Dielectric loss in an insulator between electrodes at 10-50 MHz, uniformly through volume

Rotation of water molecules at 2.45 GHz only

Where is heat formed in infrared heating?

Only at the surface, then conducted inward

What does microwave heating mainly act on?

Polar molecules such as water, using a magnetron at 2.45 GHz

2070 Chaitra

Dielectric vs infrared vs microwave heating

Short answer

Dielectric heating uses 10-50 MHz between electrodes to heat insulators uniformly throughout volume. Infrared heating uses lamps to heat surfaces, suitable for paint drying. Microwave heating uses a magnetron at 2.45 GHz to heat polar molecules internally, mainly for food and drying.

Compare dielectric heating, infrared heating and microwave heating.

All three heat the material without direct contact, but they differ in how and where the heat is produced.

Dielectric heating: a non-conducting material placed between two electrodes at high frequency (10–50 MHz) is heated by dielectric loss (molecular polarisation). Heat is produced uniformly throughout the thickness.
Infrared heating: tungsten-filament lamps (about 2300°C) with reflectors radiate infrared energy onto the surface; heat is absorbed at the surface and conducted inward.
Microwave heating: a magnetron produces microwaves (usually 2.45 GHz) that make polar (water) molecules rotate rapidly; heat is produced inside the material, which is placed in a metal cavity.

 Dielectric        Infrared          Microwave
 +---------+        \ | /            +-----------+
 |electrode|        lamp             | magnetron |
 | [work]  |        (IR)             |   ~~~>    |
 |electrode|        v v v            |  [food]   |
 +---------+      [surface]          +-----------+

Point	Dielectric	Infrared	Microwave
Principle	Dielectric loss in electric field	Radiation absorbed at surface	Molecular friction of polar molecules
Frequency/source	10–50 MHz oscillator	IR lamps (about 10¹⁴ Hz)	0.9–2.45 GHz magnetron
Where heat forms	Throughout volume	Surface only	Inside volume (depth limited)
Material	Insulators: wood, plastic, glue	Painted/coated surfaces	Water-containing materials, food
Uniformity	Very uniform	Surface; slow for thick objects	Fairly uniform, hot spots possible
Speed	Fast	Fast for thin layers	Very fast
Efficiency	50–60%	High for surfaces	50–65%
Cost	High equipment cost	Low, simple	Moderate
Applications	Plywood gluing, plastic welding, drying	Paint drying, enamel baking	Cooking, food drying, sterilisation

✓ Answer checked by Claude Opus 5.5 (high effort)

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