Power supply for Internet of Things (IoT) devices is one of the bottlenecks in IoT development. To provide perpetual power supply to IoT devices, resonant beam charging (RBC) is a promising safe, long-range and high-power wireless power transfer solution. How long distance can RBC reach and how much power can RBC transfer? In this paper, we analyze the RBC's consistent and steady operational conditions, which determine the maximum power transmission distance. Moreover, we study the power transmission efficiency within the operational distance, which determines the deliverable power through the RBC energy transmission channel. Based on this energy transmission channel modeling, we numerically evaluate its impacts on the RBC system performance in terms of the transmission distance, the transmission efficiency, and the output electrical power. The analysis leads to the guidelines for the RBC system design and implementation, which can deliver multi-Watt power over multi-meter distance wirelessly for IoT devices.

Aerosol deposition (AD) is a novel ceramic film preparation technique exhibiting the advantages of room-temperature operation and highly efficient film growth. Despite these advantages, AD has not been used for preparing humidity-sensing films. Herein, room-temperature AD was utilized to deposit BaTiO films on a glass substrate with a Pt interdigital capacitor, and their humidity-sensing performances were evaluated in detail, with further optimization performed by postannealing at temperatures of 100, 200, ..., 600 °C. Sensor responses (i.e., capacitance variations) were measured in a humidity chamber for relative humidities (RHs) of 20-90%, with the best sensitivity (461.02) and a balanced performance at both low and high RHs observed for the chip annealed at 500 °C. In addition, its response and recovery were extremely fast, respectively, at 3 and 6 s and it kept a stable recording with the maximum error rate of 0.1% over a 120 h aging test. Compared with other BaTiO-based humidity sensors, the above chip required less thermal energy for its preparation but featured a more than 2-fold higher sensitivity and a superior detection balance at RHs of 20-90%. Cross-sectional transmission electron microscopy imaging revealed that the prepared film featured a transitional variable-density structure, with moisture absorption and desorption being promoted by a specific capillary structure. Finally, a bilayer physical model was developed to explain the mechanism of enhanced humidity sensitivity by the prepared BaTiO film.

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In this study, a high-sensitivity and low-hysteresis porous metal–insulator–metal-type capacitive humidity sensor is investigated using a functional polymer mixed with TiO2 microparticles. The humidity sensor consists of an optimally designed porous top electrode, a functional polymer humidity sensitive layer, a bottom electrode, and a glass substrate. The porous top electrode is designed to increase the contact area between the sensing layer and water vapor, leading to high sensitivity and quick response time. The functional polymer mixed with TiO2 microparticles shows excellent hysteresis under a wide humidity-sensing range with good long-term stability. The results show that as the relative humidity ranges from 10% RH to 90% RH, the proposed humidity sensor achieves a high sensitivity of 0.85 pF/% RH and a fast response time of less than 35 s. Furthermore, the sensor shows an ultra-low hysteresis of 0.95% RH at 60% RH, a good temperature dependence, and a stable capacitance value with a maximum of 0.17% RH drift during 120 h of continuous test.