Design and Development of Planar and 3D Rectennas for RF Energy Harvesting and Wireless Power Reception

The Internet of Things (IoT) is a significant technological revolution that improves the quality of human life in various ways, such as smart homes, industrial automation, smart healthcare, education, agriculture, and smart transportation. IoT devices can range from simple lightbulbs controlled through an app on a phone to autonomous vehicles. IoT can be used to monitor air and water pollution in real-time through smart environments and can help minimize losses in natural disasters like forest fires, floods, and earthquakes. The number of IoT devices is rapidly increasing. However, one major barrier to the practical implementation of IoT is the limited battery capacity of these devices. It is challenging to replace the batteries of large number of IoT devices, especially when they are in hard-to-reach environments such as bridges, oil and gas pipelines, oceans, remote forests and inside building materials like concrete, or even embedded within the human body. Additionally, traditional powering methods, such as disposable batteries or wired connections, pose considerable challenges, including environmental harm, increased operational costs, and reduced deployment flexibility. These limitations highlight the need for alternative, sustainable powering solutions for IoT devices.To address the challenges of powering IoT devices sustainably, approaches such as wireless power transmission (WPT) and radio frequency energy harvesting (RFEH) from ambient sources have emerged as viable solutions. RFEH systems recycle the ambient RF energy from different sources in the environment to power IoT sensors. Thus, it provides a promising solution. However, RFEH face several challenges, primarily due to the unpredictable distribution of RF sources in the environment. These sources are randomly positioned, leading to time-varying distances and orientations between the transmitters and the rectenna. As a result, incoming RF waves arrive at the receiving antenna from random angles, which can significantly impact energy collection efficiency. Another key challenge is the presence of RF energy across different frequency bands. Therefore, in addition to leveraging the spatial domain through multidirectional reception, the frequency domain can also be exploited to enhance system performance. By simultaneously harvesting energy from multiple frequency bands, the total collected power can be significantly increased. This approach takes advantage of the diverse RF signals present in the environment, ensuring a more reliable and efficient energy supply for battery-free IoT sensors.To support the development of battery-free IoT sensors, this thesis investigates both planar and 3D rectenna designs, aiming to enhance spatial coverage, frequency utilization, power conversion efficiency, and polarization diversity in RF energy harvesting. The 3D rectennas provide comprehensive spatial coverage in comparison to the 2D rectennas. The third dimension in 3D rectenna arrays enables the deployment of a greater number of antennas within a specified volume. However, planar rectennas are less complex and easy to fabricate. They offer the advantage of easy deployment into existing structures. Their planar layout, in particular, allows for a more seamless integration with compact electronic equipment. The proposed designs optimize rectenna configurations to address the challenge of low ambient RF energy density, thereby improving overall energy harvesting efficiency.The thesis begins by examining the key challenges associated with RF energy harvesting and wireless power transfer, followed by the introduction of various rectenna designs tailored to overcome these limitations. Chapter 4 explores techniques for designing wideband antennas capable of capturing RF energy from diverse sources. Chapter 5 presents a 3D pyramidal rectenna array that enhances energy harvesting by utilizing multidirectional reception in the spatial domain and broad-spectrum utilization in the frequency domain. To mitigate polarization mismatch losses caused by signal reflections and scattering in real-world environments, Chapter 6 proposes a circularly polarized (CP) rectenna that operates over a wide bandwidth while primarily harvesting RF energy from the broadside direction. Finally, to achieve extensive coverage while maintaining a planar structure, a circularly polarized circular rectenna array is proposed in chapter 7. This design effectively captures RF energy across the entire azimuthal plane and over a wide range in the elevation plane, addressing both polarization mismatch losses and spatial coverage constraints. Planar structure, better efficiency and wide coverage, making it a practical choice for future compact sensor applications.