  This letter investigates a multiple-input multiple-output (MIMO) wireless
power transfer (WPT) system under practical non-liner energy harvesting (EH)
models. We propose a new generic energy receiver (ER) architecture consisting
of $N$ receive antennas and $L$ rectifiers, for which one power splitter is
inserted after each antenna to adaptively split the received radio frequency
(RF) signals among the $L$ rectifiers for efficient non-linear RF-to-direct
current (DC) conversion. With the proposed architecture, we maximize the total
harvested DC power at the ER, by jointly optimizing the transmit energy
beamforming at the energy transmitter (ET) and the power splitting ratios at
the ER. Numerical results show that our proposed design by exploiting the
nonlinearity of EH significantly improves the harvested DC power at the ER, as
compared to two conventional designs.
