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Pixelated metasurfaces integrating both the functions of linear polarization and circular polarization filters on a single platform can achieve full-Stokes polarization detection. At present, the pixelated full-Stokes metasurfaces mainly face the following problems: low transmission, low circular dichroism (CD) of circular polarization filters, and high requirements in fabrication and integration. Herein, we propose high performance ultracompact all-dielectric pixelated full-Stokes metasurfaces in the near-infrared band based on silicon-on-insulator, which is compatible with the available semiconductor industry technologies. Circular polarization filters with high CD are achieved by using simple two-dimensional chiral structures, which can be easily integrated with the linear polarization filters on a single chip. In addition, the dielectric materials have higher transmission than metal materials with intrinsic absorption. We experimentally demonstrated the circular polarization filter with maximum CD up to 70% at a wavelength of 1.6 μm and average transmission efficiency above 80% from 1.48 μm to 1.6 μm. Therefore, our design is highly desirable for many applications, such as target detection, clinical diagnosis, and polarimetric imaging and sensing.

Pesticide application by unmanned agricultural aerial vehicles (UAVs) has rapidly developed in China and other Asian counties. Currently, tank-mix spray adjuvants are usually added into pesticide solutions to reduce spray drift and facilitate droplet deposition and control efficacy. The currently used tank-mix adjuvants are all derived from conventional ground sprays, and their mechanisms of action in aerial applications are still unclear. In order to clarify the spraying characteristics and control efficacy of those adjuvants in aerial sprays, the performances of various types of tank-mix adjuvants were compared by analyzing droplet spectrum, drift potential index (DIX) in a wind tunnel, field deposition and control efficacy on wheat rust and aphids. The atomization results showed that the addition of adjuvants could change the droplet spectrum of liquid, and the results suggest that droplet size is an effective indicator of spray drift potential. In the field application, the meteorological conditions are complex and uncontrollable, and the effects of adjuvants on droplet deposition and distribution were not significant. Compared with the control solution, there was no significant difference in the deposition amount of each adjuvant solution, and the CVs of deposition were higher than 30%. Adding adjuvants to the spray solution can significantly improve the control efficacy of pesticides on wheat aphids and rust and also prolong the duration of the pesticide. Our results suggest that tank-mix adjuvants should be added when UAVs are used for aerial application. This study can be used as a reference to the research and development or selection of adjuvants in aerial sprays of UAVs.

During different growth periods, canopy size and density in orchards are variable, which need application conditions (flow rate and air flow) to be adjusted to match the canopy's characteristics. In order to improve orchard sprayer's automatic operating performance, an automatic variable-rate orchard sprayer (VARS) fixed with 40 electromagnetic valves and 8 brushless fans was developed based on the canopy's spatial dimensions. Each solenoid valve and brushless motor can be individually adjusted in real-time through pulse width modulation (PWM) signals emitted by a control system to adjust each nozzle's spout and fan rotation speed. A high-precision laser scanning sensor (light detecting and ranging, LIDAR) was adopted as the detector to measure the canopy volume using the variable rate algorithm principle. Field experiments were conducted in an apple orchard, and conventional air blast sprayer (CABS) and directed air-jet sprayer (DAJS) were tested as a comparison. Results showed that on average, 46% less spraying solution was applied compared to conventional applications, while penetration rate was similar to DAJS. Normalized deposition in the canopy with variable application was higher than that of conventional applications, indicating that electronic sprayers are more efficient than conventional sprayers. It was also observed that VARS could significantly reduce off-target loss. The field experiment showed that the newly developed variable-rate sprayer can greatly reduce pesticide use and protect the environment for the orchard fruit production, and also provide a reference for design and performance optimization for plant protection machinery.

An analytical formula for the cross-spectral density matrix of the electric field of anisotropic electromagnetic Gaussian-Schell model beams propagating in free space is derived by using a tensor method. The effects of coherence on those beams are studied. It is shown that two anisotropic stochastic electromagnetic beams that propagate from the source plane z=0 into the half-space z>0 may have different beam shapes (i.e., spectral density) and states of polarization in the half-space, even though they have the same beam shape and states of polarization in the source plane. This fact is due to a difference in the coherence properties of the field in the source plane.