Shady Keyrouz

Co-Design of a CMOS Rectifier and Small Loop Antenna for Highly Sensitive RF Energy Harvesters

In this paper, a design method for the co-design and integration of a CMOS rectifier and small loop antenna is described. In order to improve the sensitivity, the antenna-rectifier interface is analyzed as it plays a crucial role in the co-design optimization. Subsequently, a 5-stage cross-connected differential rectifier with a 7-bit binary-weighted capacitor bank is designed and fabricated in standard 90 nm CMOS technology. The rectifier is brought at resonance with a high-Q loop antenna by means of a control loop that compensates for any variation at the antenna-rectifier interface and passively boosts the antenna voltage to enhance the sensitivity. A complementary MOS diode is proposed to improve the harvesters ability to store and hold energy over a long period of time during which there is insufficient power for rectification. The chip is ESD protected and integrated on a compact loop antenna. Measurements in an anechoic chamber at 868 MHz demonstrate a -27 dBm sensitivity for 1 V output across a capacitive load and 27 meter range for a 1.78 W RF source in an office corridor. The end-to-end power conversion efficiency equals 40% at -17 dBm.

Ambient RF energy harvesting from DTV stations

In the framework of wireless power transmission and RF energy harvesting, the main objective is to design a harvester that collects ambient Radio Frequencies (RF) broadcasted from DTV (Digital TV) stations. This paper summarizes the main challenges experienced, when designing such a harvester. The distance and the free space path loss between the transmitting station and the harvesting location are calculated. Using Friis equation, the available power at the harvesting location is predicted. A novel broad-band Yagi-Uda antenna that covers the DTV broadcasting frequencies (470 MHz-810 MHz) is presented. The antenna design is based on integrating a wide-band strip dipole into a Yagi-Uda antenna. Moreover, The rectifier part, which converts the harvested RF power into DC is discussed, the simulated and measured input impedance and the output voltage of different commercial rectifiers are shown. A voltage multiplier is used to maximize the output voltage, and a matching network is presented to match the impedance of the multiplier to that of the antenna.

Radiative RF power transfer solutions for wireless sensors

Two rectennas are presented. One consists of a printed 5Ω antenna, connected to a loaded voltage doubling rectifier through a LC impedance matching network. The other one consists of a printed loop antenna, complex conjugately impedance-matched to the same rectifier. The second rectenna is reduced in size by a factor of more than four with respect to the first rectenna and showing a 55% RF-to-DC power conversion efficiency at an input power level of -10 dBm. This is a 5% improvement with respect to the 5Ω-based rectenna.

Optimizing RF energy transport: Channel modelling and transmit antenna and rectenna design

For powering wireless sensors in buildings rechargeable batteries may be used, being charged remotely by dedicated RF sources. RF energy transport suffers from path loss and therefore the RF power available on a rectenna will be very low. As a consequence, the RF-to-DC conversion efficiency will also be very low. By optimizing not only the subsystems of a rectenna but also taking the propagation channel into account and using this information to adapt the transmit antenna radiation pattern, the RF energy transport efficiency will be improved.

Far-field energy harvesting rectifier analysis

An accurate equivalent circuit model to predict the power conversion efficiency (PCE) of a Schottky Barrier Diode (SBD) is presented in this paper. By making use of good insight into the used SBD models and careful analysis of circuit behavior, more efficient rectifier circuits have been identified. An increase in circuit efficiency of 18-25% is shown compared to state of the art, resulting in 20-180% more available energy from the rectifying circuit. Also the accuracy of the simulation results has increased significantly. All the simulations in this paper are performed in a conjugately matched environment, which allows for an objective comparison of different Schottky diodes.

Towards the design of a RF-harvesting EBG ground plane

Electromagnetic Band Gap (EBG) structures may be used to create magnetic conductors that can be used as ground planes for dipole and loop-like antennas without annihilating the radiation as electrically conducting ground planes would do. An EBG ground plane may be created by placing a Frequency Selective Surface (FSS) on a grounded dielectric slab. Since RF harvesting FSS structures have been demonstrated recently, we expect to be able to realize RF harvesting EBG ground planes too. In this paper the feasibility of this concept is presented through full-wave simulations. These results will be updated at the conference with modeling and measurement results.

Far-Field Wireless Power Transfer for IoT Sensors

For employing large IoT wireless sensor networks, powering the sensors by cabling or primary batteries is not feasible. Using radiated fields seems to be a possible alternative. However, the expected power densities from ambient radio frequency (RF) sources (Global System for Mobile communication (GSM), digital television (DTV), WiFi) are too small for a practical use. Using dedicated transmitters in a wireless power transfer setup, using the (power-restricted) license-free ISM frequency bands will increase the levels by an order of magnitude. Then through a careful co-design of the rectifier, receive antenna and the power management, the powering of low-power, duty-cycled wireless IoT sensors becomes feasible. The models employed for the rectifier are outlined. Then working from the core (the rectifier) toward both extremeties (the antenna and the power management circuit), the design procedure for a rectifying antenna or rectena is outlined. Future perspectives for increasing the rectenna’s efficiency and the amount of power being received are outlined, using transient arrays and multisine signals.