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Termites have physiological and behavioral immunities that make them highly resistant to pathogen infections, which complicates biocontrol efforts. However, the stimuli that trigger the pathogen-avoidance behaviors of termites are still unclear. Our study shows that workers of Coptotermes formosanus exposed to the conidia of Metarhizium anisopliae exhibited a significantly higher frequency and longer duration of allogrooming behaviors compared with untreated termites. Volatile compounds in the cuticle of control termites and termites previously exposed to a suspension of M. anisopliae conidia were analyzed and compared using a gas chromatography-mass spectrometer (GC-MS). Our results showed that the amount of ergosterol differed between the fungus-exposed and control termites. Choice tests showed that termites significantly preferred to stay on filter paper treated with ergosterol (0.05, 0.1, or 1.0 mg/mL) compared with control filter paper. In addition, termites exposed to ergosterol followed by M. anisopliae conidia were allogroomed at a significantly higher frequency and for a longer duration than termites exposed to alcohol (the solvent used with the ergosterol in the ergosterol trials) alone followed by M. anisopliae conidia. These results showed that ergosterol may enhance the allogrooming behavior of termites in the presence of entomopathogenic fungi.

Purpose This study aimed to develop and validate an ultraperformance liquid chromatography–tandem mass spectrometry to simultaneously determine diquat (DQ) and its two primary metabolites in rat plasma and its application to the toxicokinetic study. Method The chromatographic separation of DQ and its two primary metabolites was performed with hydrophilic interaction chromatography column by adding formic acid and ammonium acetate in mobile phase in stepwise elution mode. DQ and its two primary metabolites were detected by liquid chromatography–tandem mass spectrometry in positive mode. Results The lower limit of quantification ranging from 0.3 to 3.0 ng/mL for DQ and its two primary metabolites was achieved by using only 50 μL of rat plasma. The maximum concentration (Cmax) was 977 ng/mL, half-life (t1/2) was 13.1 h, and area under the plasma concentration–time curve (AUC0–t) was 2770 h*ng/mL for DQ, Cmax was 47.1 ng/mL, t1/2 was 25.1 h, and AUC0–t was 180 h·ng/mL for diquat monopyridone (DQ-M) and Cmax was 246 ng/mL, t1/2 was 8.2 h, and AUC0–t was 2430 h·ng/mL for diquat dipyridone (DQ-D), respectively. Conclusions The validated method was shown to be suitable for simultaneous determination of diquat and its two primary metabolites in rat plasma. This study is the first to study the toxicokinetics of DQ and its two primary metabolites.

Multifrequency wireless power transfer (WPT) is advantageous in facilitating compatibility with different WPT standards. However, implementing a multifrequency transmitter often requires compromises in system size, complexity, power transfer capability, or output regulation. In this paper, a single-inverter-based dual-mode WPT system is proposed. The system employs a multifrequency programmed pulse width modulation scheme. This multifrequency modulated inverter can simultaneously generate and regulate 100-kHz and 6.78-MHz outputs, or multiple frequencies within ranges of 87–300 kHz, which facilitates the development of multistandard WPT technology for consumer electronics. The principle of the proposed modulation is illustrated, where two different frequencies are concurrently modulated using a programmed pulse train of square waveforms for power delivery, while eliminating certain harmonics. Design tradeoffs and constraints are examined through analytical circuit models. Finally, experimental results are provided to verify the method on a gallium-nitride-based WPT prototype.

In order to enable wireless charging of mobile electronics to compete with wired alternatives, wireless receivers need to operate at power levels sufficient to accommodate fast-charging standards. The receiver efficiency, harmonic content and total volume are key design metrics for wireless receivers. In this paper, four candidate topologies are compared, under 20 W fast-changing conditions, with respect to power loss, harmonic distortion, and power density. Each of the metrics are analyzed and verified experimentally. In coordination with the transmitter, a system-level approach to minimizing distortion is presented. Finally, the multilevel switched-capacitor rectifier is demonstrated to be a good candidate for wireless fast charging of mobile devices with high efficiency, small size, and suitable structure for future integration.

High power density is a desirable feature of power electronics design, which prompts economic incentives for industrial applications. In this paper, a gallium nitride (GaN)-based 2-kVA single-phase inverter design was developed for the Google Little Box Challenge, which achieves a 102-W/in $^{3}$ power density. First, the static and dynamic temperature-dependent characteristics of multiple SiC and enhancement-mode GaN FETs are investigated and compared. Based on the device testing results, several topologies of the inverter stage and different power decoupling solutions are compared with respect to the device volume, efficiency, and thermal requirements. Moreover, some design approaches for magnetic devices and the implementation of gate drives for GaN devices are discussed in this paper, which enable a compact and robust system. Finally, a dc notch filter and a hard switching full-bridge converter are combined as the proposed design for the prototype. A 2-kVA prototype is demonstrated, which meets the volume, efficiency, and thermal requirements. The performance of the prototype is verified by the experimental results.

In mobile electronics applications, the high conduction loss on the ac-dc rectifier and the coil is a barrier to the application of wireless charging. In this paper, a wireless charging architecture employing a 7-level switched-capacitor (SC) ac-dc rectifier is investigated, showing a substantial reduction of the conduction losses on the transmitter, the coil and the receiver. The proposed SC rectifier also features a multilevel design with good scalability to accommodate different power ratings, and potentially reduce the harmonic contents of the input voltage. The principle and operation are verified using a 7-level, 20 W, 5–9 Vdc output, 150 kHz prototype. The measured peak dc-to-load system efficiency is above 90%. The high-power density design without bulky magnetic components is suitable for the implementation in low-profile mobile electronics.

Concurrent dual-frequency ac outputs from a single-inverter configuration potentially benefit many industrial applications, such as induction heating and wireless power transfer. In this paper, a phase-shift dual-frequency selective harmonic elimination (DFSHE) method is proposed to simultaneously generate and regulate two ac outputs at different frequencies from a single full-bridge inverter, which expands the family of DFSHEs. With the phase shift operation, all triplen harmonics of the fundamental are inherently suppressed in the inverter output spectrum, which improves the output THD, and may ease filter design. In addition, an evaluation of the unipolar, bipolar and phase-shift DFSHE techniques is presented, which analyzes design tradeoffs for multi-frequency applications. Finally, experimental results from a 50 W dual-output inverter validate the effectiveness of the proposed method, which agree with theoretical predictions and simulation results.

Multi-frequency wireless power transfer (WPT) is advantageous in facilitating compatibility with different WPT standards. However, implementing a multi-frequency transmitter often requires compromises in system size, complexity, power transfer capability, or output regulation. In this paper, a single-inverter based dual-mode WPT system is proposed. The system employs a multi-frequency programmed pulse width modulation (MFPWM) scheme. This dual-frequency modulated inverter can simultaneously generate and regulate 100 kHz and 6.78 MHz outputs, which facilitates the development of multi-standard WPT technology for consumer electronics. In addition, the principle of the proposed modulation is illustrated, where two different frequencies are concurrently modulated in the programmed pulse train of square waveforms, while eliminating certain harmonics in between. Design tradeoffs and constraints are examined through analytical circuit models. Finally, experimental results are provided to verify the effectiveness of the proposed WPT system.

A two-stage power conversion architecture for the transmitter in wireless power transfer applications is introduced. The system achieves high efficiency at output powers up to 100W, and exhibits constant output current over varying load impedance. A front-end bridgeless totem pole rectifier provides power factor correction (PFC), necessary at the designed power level. This rectifier achieves high efficiency by eliminating the conventional diode full bridge and by achieving soft switching operation. A full bridge inverter, switching at 6.78MHz, generates the AC output. Combined with an output passive filter network, the inverter achieves constant output current with load variation without the need for dynamic feedback control. A prototype system is constructed and tested experimentally to verify operation.

Simultaneous generation of two AC outputs at different frequencies from a single-phase inverter offers practical benefits and control flexibility for many industrial applications. In this paper, a dual-frequency selective harmonic elimination (DFSHE) modulation method is proposed to generate and control two individual frequencies in an H-bridge, while diminishing undesired harmonics. Two AC elements are synthesized independently in the modulation scheme, and thus flexible individual power regulation is achieved via the proposed method. In addition, both unipolar and bipolar DFSHE cases are investigated. Characteristics of the two methods are compared and alternatives are provided for different applications. The generation algorithms of the DFSHE are also studied in this paper, and can be applied to a variety of DC/AC topologies without adding extra switching devices. Finally, the experimental results from a 100W dual-load single-phase inverter verify the effectiveness of proposed method, where 50 kHz and 450 kHz AC outputs are generated and individually regulated.

For wireless power transfer (WPT) systems, communication between the primary side and the pickup side is a challenge because of the large air gap and magnetic interferences. A novel method, which integrates bidirectional data communication into a high-power WPT system, is proposed in this paper. The power and data transfer share the same inductive link between coreless coils. Power/data frequency division multiplexing technique is applied, and the power and data are transmitted by employing different frequency carriers and controlled independently. The circuit model of the multiband system is provided to analyze the transmission gain of the communication channel, as well as the power delivery performance. The crosstalk interference between two carriers is discussed. In addition, the signal-to-noise ratios of the channels are also estimated, which gives a guideline for the design of mod/demod circuits. Finally, a 500-W WPT prototype has been built to demonstrate the effectiveness of the proposed WPT system.

For the development of communication systems such as Internet of Things, integrating communication with power supplies is an attractive solution to reduce supply cost. This paper presents a novel method of power/signal dual modulation (PSDM), by which signal transmission is integrated with power conversion. This method takes advantage of the intrinsic ripple initiated in switch mode power supplies as signal carriers, by which cost-effective communications can be realized. The principles of PSDM are discussed, and two basic dual modulation methods (specifically PWM/FSK and PWM/PSK) are concluded. The key points of designing a PWM/FSK system, including topology selection, carrier shape, and carrier frequency, are discussed to provide theoretical guidelines. A practical signal modulation–demodulation method is given, and a prototype system provides experimental results to verify the effectiveness of the proposed solution.

Conventionally, both the primary side and the pickup side need series or shunt capacitor compensation to increase transmission efficiency in a wireless power transfer system. In this paper, a wireless power transfer system with an active resonance circuit is proposed. Comparing the diode based rectifier on the pickup side in traditional wireless power transfer systems, a PWM rectifier is exploited for several advantages. The compensation capacitor on the pickup side is replaced by the active resonance circuit for reactive power compensation. Furthermore, the low power transmission efficiency, which is caused by the compensation capacitor malfunction and the resonance tank detuning, could be alleviated in the proposed system. A phase shift control technique is adopted to regulate output power when input power varies. The mathematic model of the propose system is presented, and the influence of parasitic parameters are also analyzed to reach a more precise performance analysis. A 500W prototype is built, and the experimental results are provided to validate the theoretical model and the effectiveness of the system.

A novel isolated zero-voltage-switching (ZVS) bidirectional DC-DC converter (BDC) with coupled inductors is proposed in this paper. The series half bridge structure in the high-voltage side reduces the switch voltage stress to half of the high-side voltage, which extends the high-side voltage when using power MOSFETs. Furthermore, all the switches can achieve ZVS soft-switching performance at any load condition by adopting the active clamp circuits and the PWM plus phase shift (PPS) control strategy. Thus, the BDC can operate at high frequency to achieve high power density and still with high efficiency for high voltage dc bus applications. Finally, a 1.5kW 100kHz 48V/800V prototype is built to verify the effectiveness of the proposed circuit.

A new method of contactless temperature measurement is presented in this paper. Through analysis of the transient process of the wireless energy transfer, a linear function of the thermistor resistance is obtained, which could be employed to measure the variation of the resistance and the corresponding fluctuation of the temperature. Compared with the conventional temperature measurement, this method provides convenience to measure the environmental variations in the inaccessible or enclosed environment. In the proposed scheme, the sensor circuit consists of only three passive components: a resistance thermometer, a resonant capacitor and a magnetic coupled inductor. It makes the volume of the sensor small and extra battery supply unnecessary. In addition, by applying a variety of resistance sensors, this method has potential to measure other physical quantities including moisture, pressure or lumen without wire connection. The experimental results are provided to verify the effectiveness of the method. An overall resistance resolution of ±1 Ω is realized in experiments, and temperature resolution of ±5°C can be expected with the available thermistor.