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Microwave characteristics of SUPRAX® 8488

Auer Lighting borosilicate glass SUPRAX® 8488 is a suitable material for microwave applications, e.g. as a lamp cover glass.

Half-Power Depth

The measurement below shows the half-power depth for SUPRAX® 8488, a special borosilicate glass from Auer Lighting. The half-power depth is a widely used indicated value for microwave properties. It describes the depth in an absorbing material at which the power of a propagating TEM (Transversal Electro Magnetic) wave is reduced to 50% of its initial value by deposition as heat. The measurement covers the temperature range from 25 °C to 400 °C and has been taken at 2.466 GHz.

Microwave properties of SUPRAX® 8488

Temperature 20 °C 400 °C
Dielectric constant ε’ 5.1 ± 0.1 5.7 ± 0.1
Dissipation factor ε’’ 0.050 ± 0.005 0.26 ± 0.03
Loss tangent 0.010 ± 0.001 0.045 ± 0.004
TEM half-power depth (mm) 594 ± 50 125 ± 10


For a thin window, the fraction of the travelling wave power deposited in the window can be simply estimated by: 

                                            0.693 · Window Thickness

   PowerFraction  ≈   ____________________________ 

                                                  Half Power Depth

For a 3 mm thick SUPRAX® 8488 window at 20°C this gives a power deposition of ~0.3% of the magnetron output power.

In every case it is still in responsibility of the manufacturer of the microwave oven to design the product in a safe way. He has to take care for avoiding hot spots in the complete system, which will damage every glass material.