Mixing Uniformity Measurement of Solidified/Modified Soil With Dielectric Lens-Coupled Circular Waveguide Microwave Sensor

The microwave method can measure the mixing uniformity of solidified/modified soil based on the variation of transmittance with dielectric constant of circular waveguide microwave sensors. However, conventional circular waveguide microwave sensors conduct the mixing uniformity measurement only when the spherical wave is converted into planar waves in the far field, leading to rapid attenuation of microwave intensity and decreased measurement accuracy. In this paper, a dielectric lens-coupled circular waveguide microwave sensor is proposed to convert the spherical wave into the planar wave in the near field, thereby enhancing the microwave intensity and measurement precision of the mixing uniformity of solidified/modified soil. The radiation performance of the dielectric lens-coupled circular waveguide microwave sensor is numerically simulated at a center frequency of 5.8 GHz and the influence of the distance between the circular waveguide microwave sensor and the dielectric lens on the radiation performance is analyzed. Subsequently, a circular waveguide microwave sensor measurement system coupled with the dielectric lens is developed, and the feasibility of enhancing microwave intensity is experimentally confirmed by measuring the received microwave signal strength. Finally, the developed measurement system is experimentally evaluated by measuring the mixing uniformity of solidified/modified soil. Results demonstrated that the dielectric lens-coupled circular waveguide microwave sensor is capable of achieving the better received signal strength when the distance between the dielectric lens and the sensor is exactly the focal length of the lens. The corresponding maximum gain of the microwave sensor is 28.9 dB, which is much better than the 14.5 dB gain of the conventional circular waveguide microwave sensors. Besides, the half-power beam widths of the E-plane and H-plane are 6.2° and 6.1° with the sidelobe powers of -19.9 dB and -30.0 dB, respectively. The uniformity of solidified/modified soil from tannery-contaminated soil remediation site is measured as 90.3% for sample A1, 87.3% for sample A2, 76.1% for sample B1, and 78.6% for sample B2, which is highly consistent with on-site sampling test results.