Energy is one of the key enablers for robotic swarms. The feasibility of heterogeneous swarms to perform complex missions depends upon the energy stored in the robot batteries. Allowing multiple access energy transfer (MAET) in robot swarms provides more flexibility to accomodate uncertain missions. In this paper, we present a MAET solution for heterogeneous swarms using code division multiple access wireless power transfer (CDMA-WPT). CDMA-WPT allows robots in heterogeneous swarms to exchange energy while in motion, allows faster charging rates by enabling multiple robots to exchange energy, is easily scalable, offers power flow selectivity to enable energy encryption, and does not require a centralized controller. The encoding scheme, power flow model, and code construction algorithm for a particular implementation of CDMA-WPT is presented. The proof of concept is verified using a hardware implementation for a heterogeneous swarm of four robots. Finally, the application of CDMA-WPT to a heterogeneous swarm with 30 robots is presented.

The availability of energy is one of the major hindrances to unlocking the massive potential of electronic devices. Powering a highly connected network of devices requires multiple access and a wireless power transfer (WPT) solution that is scalable and capable of maintaining a constant power flow regardless of reconfiguration (mutability) and electromagnetic environment (power flow selectivity). In this paper, we present a framework for the implementation of code division multiple access wireless power transfer (CDMA-WPT) for enabling WPT among multiple transmitters and multiple receivers simultaneously. CDMA-WPT maintains power flow selectivity and is easily scalable. An inverter/rectifier topology is presented for the hardware implementation of CDMA-WPT. A design process for practical co-design of high-performance hardware and obtaining a code set is also presented. We demonstrate the hardware implementation of CDMA-WPT using two transmitters and two receivers maintaining a nearly constant 5 W operation with nearly 75 % dc-dc efficiency, and four transmitters and four receivers maintaining a constant 4 W operating with greater than 70 % dc-dc efficiency. . This paper is accompanied by a video hardware demonstration in real-time the difference between using orthogonal codes in CDMA versus conventional single-frequency WPT using 4 transmitter-receiver pairs; conventional single-frequency WPT shows up to a 100 % deviation from the intended transfer power as opposed to 8.1 % for orthogonal codes in CDMA.INDEX TERMS Wireless power transfer (WPT), code division multiple access (CDMA), current-mode class-D (CMCD), internet of things (IoT), power amplifier, high-efficiency, resonant converter.

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