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FIR energy penetrates very little, almost all the energy being converted to heat at the surface of the food,
NIR wavelength region (wavelength < 1.25 µm), approximately 50% of the radiation is reflected back, while less than 10% radiation is reflected back at the FIR wavelength region.
However NIR penetrates deeper.
A study using NIR-I imaging reported a maximum penetration depth through tissue of ~3.2 cm. (1.25")
[Deep-tissue optical imaging of near cellular-sized features | nature.com]
Table 4—. Penetration depth of NIR (0.75 to 1.4 μm) into food products.
Product | Spectral peak (μm) | Depth of penetration (mm) |
---|---|---|
Dough, wheat | 1.0 | 4 to 6 |
Bread, wheat | 1.0 | 11 to 12 |
Bread, biscuit, dried | 1.0 | 4 |
0.88 | 12 | |
Grain, wheat | 1.0 | 2 |
Carrots | 1.0 | 1.5 |
Tomato paste, 70% to 85% water | 1.0 | 1 |
Raw potatoes | 1.0 | 6 |
Dry potatoes | 0.88 | 15 to 18 |
Raw apples | 1.16 | 4.1 |
1.65 | 5.9 | |
2.36 | 7.4 |
A Comprehensive Review on Infrared Heating - Applications in Food Processing
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