Conventional planar coils in an asymmetric structure cannot provide stable mutual inductance over a wide range. To address this issue, a novel asymmetric flat cross -shaped solenoid magnetic coupler (FCSMC) with high lateral misalignment tolerance for a multiple-receiver wireless power transfer (WPT) system is proposed in this article, which can achieve freer charging positions for multiple automated guided vehicles (AGVs) at a single wireless charging station. Moreover, the analytical model of FCSMC is analyzed to simplify the design process based on the air-core mutual inductance equations. Then, a general design process is proposed for larger-scale FCSMC, which greatly reduces the workload of finite-element analysis (FEA) simulations. Finally, a 200/400 W prototype is built to verify the validity of the system within a $\pm$ 90-mm misalignment. In single-receiver cases with a 10 mm air gap, the comparisons with conventional planar square coils show that FCSMC's (planner square coils') output power fluctuates within 5% (27%) with maximum efficiency of 88.55% (92.01%), indicating that FCSMC sacrifices about 3% efficiency for 22% improvement in power stability. At the highest $\pm$ 90-mm misalignments, the output power fluctuates within 1% (19%), improving about 18%. In multiple-receiver cases for FCSMC, the charging positions are free with maximum efficiency of 87.96% when the shortest distance between ferrites of receivers is 20 mm or more.

In this study, a microwave-sensitive solid acid catalyst was successfully synthesized from sweet potatoes via a simple process. The catalyst was proven to have superior microwave-sensitive and homogeneous properties. The physicochemical properties were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectra (FT-IR), thermogravimetric (TGA), scanning electron microscope (SEM) and elemental analysis (EA). Results showed that the total acid density and specific surface area for the catalyst were 6.35 mmol/g and 78.35 m²/g, respectively. The elemental sulfur content reached 7.449% after sulfonation and the catalytic activity could reach over 91% within 30 min with microwave power density of 1.0 W/mL. The catalytic reaction temperature should not exceed 200 °C, as shown in TGA curve, and the moisture content in the oil raw material should be within 1%–2%. The catalyst deactivated gradually to 64.38% after reutilization five times, but the catalytic activity could be simply regenerated by re-sulfonation, albeit slightly reduced (87.56%). The shift of diffraction peaks in the XRD patterns and new absorption peaks at 619.98 and 1190.49 cm⁻¹ of FT-IR spectra demonstrated that the –SO₃H group was effectively attached to the catalyst. The SEM images displayed a loose and porous amorphous structure in the end catalyst.