Since the first aeroplane flight more than 100 years ago, aeroplanes have been propelled using moving surfaces such as propellers and turbines. Most have been powered by fossil-fuel combustion. Electroaerodynamics, in which electrical forces accelerate ions in a fluid1,2, has been proposed as an alternative method of propelling aeroplanes—without moving parts, nearly silently and without combustion emissions3–6. However, no aeroplane with such a solid-state propulsion system has yet flown. Here we demonstrate that a solid-state propulsion system can sustain powered flight, by designing and flying an electroaerodynamically propelled heavier-than-air aeroplane. We flew a fixed-wing aeroplane with a five-metre wingspan ten times and showed that it achieved steady-level flight. All batteries and power systems, including a specifically developed ultralight high-voltage (40-kilovolt) power converter, were carried on-board. We show that conventionally accepted limitations in thrust-to-power ratio and thrust density4,6,7, which were previously thought to make electroaerodynamics unfeasible as a method of aeroplane propulsion, are surmountable. We provide a proof of concept for electroaerodynamic aeroplane propulsion, opening up possibilities for aircraft and aerodynamic devices that are quieter, mechanically simpler and do not emit combustion emissions. A solid-state propulsion system can sustain powered flight, as demonstrated by an electroaerodynamically propelled heavier-than-air aeroplane.

Flight of an aeroplane with solid-state propulsion

Recent advances in soft materials enable robots to possess safer human-machine interaction ways and adaptive motions, yet there remain substantial challenges to develop universal driving power sources that can achieve performance trade-offs between actuation, speed, portability, and reliability in untethered applications. Here, we introduce a class of fully soft electronic pumps that utilize electrical energy to pump liquid through electrons and ions migration mechanism. Soft pumps combine good portability with excellent actuation performances. We develop special functional liquids that merge unique properties of electrically actuation and self-healing function, providing a direction for self-healing fluid power systems. Appearances and pumpabilities of soft pumps could be customized to meet personalized needs of diverse robots. Combined with a homemade miniature high-voltage power converter, two different soft pumps are implanted into robotic fish and vehicle to achieve their untethered motions, illustrating broad potential of soft pumps as universal power sources in untethered soft robotics.

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Customizing a self-healing soft pump for robot.

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series–parallel ( LCC ) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor ( RC ) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers.

Unified Equivalent Steady-State Circuit Model and Comprehensive Design of the LCC Resonant Converter for HV Generation Architectures

Soft robotics revolutionized human-robot interactions, yet there exist persistent challenges for developing high-performance soft actuators that are powerful, rapid, controllable, safe, and portable. Here, we introduce a class of self-contained soft electrofluidic actuators (SEFAs), which can directly convert electrical energy into the mechanical energy of the actuators through electrically responsive fluids that drive the outside elastomer deformation. The use of special dielectric liquid enhances fluid flow capabilities, improving the actuation performance of the SEFAs. SEFAs are easily manufactured by using widely available materials and common fabrication techniques, and display excellent comprehensive performances in portability, controllability, rapid response, versatility, safety, and actuation. An artificial muscle stretching a joint and a soft bionic ray swimming in a tank demonstrate their effective performance. Hence, SEFAs offer a platform for developing soft actuators with potential applications in wearable assistant devices and soft robots.

Self-contained soft electrofluidic actuators.

Recent studies in electro-aerodynamic (EAD) propulsion have stimulated the need for lightweight power converters providing outputs at tens of kilovolts and hundreds of watts [1] [2]. This paper demonstrates a design of a lightweight high-voltage converter operating from a 160–200 V dc input and providing dc output of up to 600 W at 40 kV. It operates at around 500 kHz and achieves a specific power of 1.2 kW/kg. This is considerably lighter than comparable industrial and academic designs at this power level. High voltage converters generally comprise an inverter, a step-up transformer and a rectifier, with the large needed voltage gain distributed among these stages. Several means of realizing these stages are compared in terms of weight. The weight of the converter is minimized by properly selecting and optimizing the design and the voltage gain of each stage within the constraints of device limitations and losses. A prototype circuit is developed based on this approach and used to drive an EAD-propulsion system for an unmanned aerial vehicle (UAV). In addition to addressing the power conversion needs for EAD, this research can potentially benefit the development of lightweight high-voltage converters in many other applications where weight and size are important.

Design and implementation of a lightweight high-voltage power converter for electro-aerodynamic propulsion

A novel voltage-doubling circuit with parallel-resonant dc–dc converter is proposed. The converter consists of full-bridge inverter, resonant tank, high-frequency high-voltage transformer, and voltage-doubling circuit. In the high-voltage applications, low-output voltage ripple has been given much attention. The output voltage step-up ratio is increased by two parts. One is a high-frequency high-voltage transformer and the other is a voltage-doubling circuit. The novel voltage-doubling circuit can not only reach a higher output voltage but also reduce output ripple to a lower level than the conventional one. Therefore, while maintaining the same output voltage, the transformer's turn ratio can be reduced compared with the conventional voltage-doubling circuit. The output power can be adjusted by the phase-shift control technique. In addition, combining this technique with the parallel resonant tank can make all the switches achieve zero voltage turn on (ZVS). The operating principles, steady-state analysis, and the parameter designs are discussed in this paper. Finally, a prototype circuit with 400-V input voltage, 40-kV output voltage, and 300-W output power is developed in the laboratory to verify the performance of the proposed converter.

Wen-Chien Hsu

Papers

Design and Steady-State Analysis of Parallel Resonant DC–DC Converter for High-Voltage Power Generator