Polyethylene Terephthalate (PET), renowned for its exceptional physical and chemical properties, finds widespread use in our daily lives. However, conventional PET drying methods are time consuming and energy intensive. Leveraging microwave heating effects, we investigated drying characteristics concerning both microwave parameters and PET permittivity. The PET permittivity variation during heating is related to the microwave reflection at the incident port. Our innovative approach involves frequency and power tuning based on reflection. This method not only significantly improved heating uniformity and reduced temperature covariance (COVT) but also led to a more uniformly distributed temperature profile and a drastic reduction in energy consumption. Integrating precise and rapid frequency tuning, we compared our method’s efficiency with traditional approaches, revealing an impressive time savings of 2 h and an energy consumption limited to approximately less than 3 kWh/kg. Notably, our laboratory system’s logistic models of the Moisture Ratio (MR) related to rotary rates, masses, and powers whose averages of R-square are 0.9972, 0.9982, and 0.9977, respectively, which provide intriguing insights for industrial production forecasts during variable frequency PET drying.

This article presents experimental evidence demonstrating the feasibility of implementing a quasi-dual-frequency microwave signal generator using a 1 kW commercial magnetron. The injection-pulled magnetron may generate quasi-dual-frequency output with nearly identical amplitudes by injecting signal at specific powers and frequencies out of the Adler locking band. This generator offers the advantage of developing a large-power and tunable quasi-dual-frequency signal at low cost and with simple implementation. In the present study, a tunable quasi-dual-frequency signal with a frequency interval ranging from 0.48 MHz to 13.74 MHz is generated experimentally. Furthermore, the effects of anode voltage ripples on the dual-frequency outputs are experimentally investigated. An empirical relationship between the frequency interval and injection ratio is obtained and presented. In addition, neither the output power nor the efficiency of the magnetron in the dual-frequency mode decreases. This research is promising for improving microwave heating uniformity in large-scale industrial applications.

Microwave wireless power transfer (MWPT) is a promising technology for powering dedicated industrial Internet of Things (IoT) devices, enabling battery-free operation. However, in realistic MWPT deployments, the received RF signals fluctuate drastically due to varying transmission distances and multipath fading. Additionally, the equivalent impedance of sensor nodes varies significantly during duty cycles, shifting between a low-resistance active state and a high-resistance sleep state. Consequently, maintaining high rectification efficiency under these dynamic conditions remains a critical challenge. This paper proposes a high-efficiency rectifier with a wide input power and load range based on the suppression of second and third harmonics. The rectifier adopts a dual-diode parallel configuration. By leveraging the impedance compensation characteristics of two short-circuited stubs with distinct electrical lengths, it simultaneously achieves fundamental-frequency impedance matching and harmonic suppression without the need for an additional matching network. Validated through theoretical derivation, simulation analysis, and physical prototype testing, the proposed 2.45 GHz rectifier realizes high-efficiency rectification over a wide dynamic range. Experimental results demonstrate that the power dynamic range reaches 10 dB when the rectification efficiency exceeds 70%, and extends to 17 dB when the efficiency is above 60%. Furthermore, the rectification efficiency is insensitive to load variations (100–1200 Ω), making it highly suitable for powering wireless sensor nodes with varying operating modes in complex electromagnetic environments.

Microwave wireless power transmission (MWPT) applications have attracted worldwide interest and attention in recent years. Rectennas are a crucial component of a MWPT system. The rectenna’s power capacity and output DC power have great significance with regard to the MWPT system’s performance. In this article, a compact 4 × 4 S-band rectangular patch rectenna array for MWPT is proposed and experimentally verified. Firstly, an S-band rectifier with better consistency and lower cost than a traditional output design using parallel capacitors as a filter is achieved. Then, a rectenna array based on the proposed rectifier and a novel design idea is proposed. The rectenna can achieve an output DC power of 117.6 mW/cm³ and an efficiency of 47.6%. Finally, a MWPT verification experiment is conducted. A 12-inch LCD screen powered by the rectenna with a rated power of 12 W successfully works without any other power supply. This article provides a new design of a rectenna for MWPT, and the proposed rectenna array demonstrates its good engineering significance and application prospects.

In this work, a Fabry–Perot (F–P) antenna based on metal integrated suspended lines (MISLs) at the K-band for microwave wireless power transmission (MWPT) is proposed. The antenna’s contribution lies in its adaptation of the MISL structure and its all-metal design, which achieves low loss, high gain, and high-power capability. The entire antenna structure is dielectric-free, further reducing apparent dielectric loss at high frequencies. Meanwhile, the radiation structure is surrounded by a metallic wall to minimize radiation loss. A metal partially reflective surface (PRS) on the top of the antenna, together with a metal ground plane, constitutes an air-filled resonant cavity. The reflection and transmission of electromagnetic waves in the PRS are effectively controlled to be in phase, thereby enhancing its gain by optimizing the PRS and resonant cavity dimensions. A simple slot antenna is employed as the primary source for the F–P resonant cavity. The antenna is processed layer by layer and then assembled to lower machining costs and complexity. Experimental results indicate that the proposed F–P antenna achieves an aperture efficiency over 60% and a measured peak gain of 18.4 dBi at 23.85 GHz with an aperture size of 2.86 λ₀ × 2.86 λ₀.