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Microwave Soil Heating with Evanescent Fields from Slow-Wave Comb and Ceramic Applicators
| Content Provider | MDPI |
|---|---|
| Author | Brodie, Graham Torgovnikov, Grigory |
| Copyright Year | 2022 |
| Description | Microwave soil heating deactivates weed seeds; however, in many modern agricultural settings, weed seeds are mostly found in the top 1–2 cm of the soil profile. Until recently, microwave soil heating has been achieved using various antennas, which project the microwave energy deeply into the soil. The aim of this research was to develop new microwave applicators that provide shallow heating (less than 50 mm). This paper presents two applicator designs, one based on a comb slow-wave structure and the other on the frustrated total internal reflection (FTIR) principle, which utilise evanescent microwave fields to restrict the depth of microwave heating. The background theory to their performance is presented, followed by experimental evidence of their constrained heating performance under different soil moisture scenarios. Experimental measurements of the heating performance of these applicators, in soils of varying moisture content, demonstrate that the evanescent microwave fields restrict the depth of heating, so that most of the energy is manifested in the top 50 mm of soil. The evanescent field decay rate for the FTIR applicator changes from 44.0 ± 0.7 $m^{−1}$ to 30 ± 1.2 $m^{−1}$ as the soil moisture changes from 32% to 174% (dry weight basis). This is higher than the evanescent field decay rate for the comb slow-wave applicator (17.6 ± 0.7 $m^{−1}$ to 19.9 ± 1.5 $m^{−1}$). The FTIR applicator has a wider and shallower heating pattern than the comb slow-wave applicator. Because of the double heating lobes of the FTIR applicator, the effective half temperature heating width is approximately 150 mm. This is wider than the half temperature heating width of the comb slow-wave applicator (95 mm). |
| Starting Page | 1068 |
| e-ISSN | 19961073 |
| DOI | 10.3390/en15031068 |
| Journal | Energies |
| Issue Number | 3 |
| Volume Number | 15 |
| Language | English |
| Publisher | MDPI |
| Publisher Date | 2022-01-31 |
| Access Restriction | Open |
| Subject Keyword | Energies Agricultural Engineering Microwave Evanescent Fields Soil Heating Slow-wave Frustrated Total Internal Reflection |
| Content Type | Text |
| Resource Type | Article |
