Radio frequency energy harvesting (RFEH) and wireless power transmission (WPT) are two emerging alternative energy technologies that have the potential to offer wireless energy delivery in the future. One of the key components of RFEH or WPT system is the receiving antenna. The receiving antenna's performance has a considerable impact on the power delivery capability of an RFEH or WPT system. This paper provides a well-rounded review of recent advancements of receiving antennas for RFEH and WPT. Antennas discussed in this paper are categorized as low-profile antennas, multi-band antennas, circularly polarized antennas, and array antennas. A number of contemporary antennas from each category are presented, compared, and discussed with particular emphasis on design approach and performance. Current design and fabrication challenges, future development, open research issues of the antennas and visions for RFEH and WPT are also discussed in this review.

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We would like to acknowledge the support of Food Agility CRC Ltd, funded under the Commonwealth Government CRC Program. The CRC Program supports industry-led collaborations between industry, researchers and the community.

A highly efficient and compact quad-band energy harvester (QBEH) circuit based on the extended composite right-and left-handed transmission lines (E-CRLH TLs) technique is presented. The design procedure based on E-CRLH TLs at four desired frequency bands is introduced to realize a quad-band matching network. The proposed QBEH operates at four frequency bands: f 1 = 0.75 GHz; f 2 = 1.8 GHz; f 3 = 2.4 GHz; and f 4 = 5.8 GHz. The simulations and experimental results of the proposed QBEH exhibit overall (end to end) efficiency of 55% and 70% while excited at four frequency bands simultaneously with −20 dBm (10 µW) and −10 dBm (100 µW) input power, respectively. Due to applying multitone excitation technique and radio frequency (RF) combining method in the QBEH circuit, the sensitivity is improved, and sufficient power is generated to realize a self-sustainable sensor (S 3 ) using ambient low-level RF signals. A favorable impedance matching over a broad low input power range of −50 to −10 dBm (0.01 to 100 µW) is achieved, enabling the proposed QBEH to harvest ambient RF energy in urban environments. Moreover, an accurate theoretical analyses based on the Volterra series and Laplace transformation are presented to maximize the output dc current of the rectifier over a wide input power range. Theoretical, simulation and measurement results are in excellent agreement, which validate the design accuracy for the proposed quad-band structure. The proposed new energy harvesting technique has the potential to practically realize a green energy harvesting solution to generate a viable energy source for low-powered sensors and IoT devices, anytime, anywhere. Index Terms-Ambient energy harvesting, electromagnetic (EM) energy, high efficiency, Internet of Things (IoTs), quad-band rectifier, rectenna (rectifying antenna), wide input power range. NOMENCLATURE Acronym Description η effectiveEffective efficiency η ocOverall (end-to-end) efficiency of the circuit η osOverall (end-to-end) efficiency of the EH system or rectenna efficiency Manuscript