Power-optimized waveforms (POWs) are the enabling technology for realizing an internet-of-things (IoTs). An IoT will require billions or trillions of sensors, which must rely on passive, backscatter communication to facilitate the wireless transfer of information. Passive, backscatter sensors are uniquely suited for an IoT because of their ease of installation, low-cost, and lack of potentially toxic batteries. POW's primary benefit is that they can greatly improve the energy-harvesting efficiency of passive sensors, which increases their range and reliability. An overview of POWs is presented followed by measured results validated by a theoretical model and computer simulations. These measured results conducted at 5.8 GHz demonstrate the highest reported efficiency of a low-power, microwave energy-harvesting circuit of 26.3% at an input power of −10.2 dBm when using an excitation signal with a peak-to-average-power ratio of 12.

Power transfer efficiency in loosely coupled inductive systems can be enhanced by resonance. Primary and secondary can be tuned to same resonant frequency. In this paper, MOSFET-based Varactors and switchable capacitors are used for re-tuning of such a system at 13.56 MHz. This is achieved either using each cap structure alone or as a hybrid model. These techniques are designed for 13.56 MHz wireless power transfer system.

This work presents the design of a system for wireless power transmission based on a compact rectenna array able to supply low-power electronic devices such as wireless sensors. The receiving section is realized with an array of 12 rectangular patch antennas. Each elements of the array is connected with a suitable harmonic filter and a rectifying circuit by means of a coaxial feeding point. The transmitting section is realized with a one-dimensional prime focus parabolic reflector antenna, with a linear feeder composed by four dipole antennas. The rectenna array, the harmonic filter, the rectifying circuit of the receivers, and the transmitting section were optimized to reach the maximum operative range and efficiency, in term of power transfer. A system prototype has been designed, optimized, fabricated, and experimentally assessed. In particular, a prototype operating in the S band and able to provide a supply power of about 50 mW serves as proof-of-concept. Moreover, theoretical guidelines for the design of wireless power transmission are provided. The obtained experimental results are quite promising and demonstrated the capabilities of wireless power transmission systems as alternative power supply sources.

In this paper, a technology based on thin flexible polyimide substrate (Kapton) to develop antennas for millimeter wave wireless power transmission is presented. Firstly, we characterize the Kapton polyimide (relative permittivity and loss tangent) using a ring resonator method up to V band. A 60 GHz patch antenna is designed, fabricated, and measured to validate our technology. Crossed-dipoles array antennas at Ku band and K band for energy harvesting are also designed, fabricated, and measured. Then a prototype of crossed-slot dipole antenna at V band is proposed. Finally, a resistivity characterization of Au bump used in flip-chip packaging is done, which leads us one step further toward aheterogeneous integration on flexible substrate of different components for Wireless Sensor Network nodes.

In this work, a high-efficiency radio-frequency energy-harvesting system that takes use of the Portuguese Digital Television signal (750–758 MHz) to obtain DC power is proposed. To be useful, it is optimized to operate at low-power conditions. For the rectifier, three different solutions are presented: a single-series diode, a single-shunt diode, and a voltage-doubler configuration. The efficiency is similar for the three rectifiers – about 54% with a sine-wave excitation and −10.5 dBm of input power. Field measurements with the voltage-doubler have shown 63% efficiency for the same input power.

In this paper, some theoretical aspects and experimental results are discussed with the aim to provide supplementary dc energy to radio frequency identification (RFID) tags by exploiting the nonlinear nature of rectifier devices. Three nonlinear phenomena are treated: (i) the impedance power dependence, (ii) the harmonic production, and (iii) the dependence on the radio frequency waveform. The novelty of the work relies on proposing a double rectifier composite system in where the nonlinearity of each rectifier is exploited to enhance the global powering performance of the system. Using the passive RFID technology as a beacon for the implementation, the approach considers combining the internal rectifier circuit of a commercial RFID chip operating at 868 MHz with an external rectifier circuit operating at 2.17 GHz. The solution triggers in a composite system RFID tag-harvester integrated in a single-feed dual-band antenna. The experimental validation shows 5 dB of tag sensitivity enhancement when it is empowered by the external harvester. The enhanced sensitivity produces an increase in the theoretical reading range distance from 3.3 to 6.1 m.

Capacitive power transfer (CPT) technology can achieve wireless power transfer based on electric field coupling. However, practical CPT systems often have cross-coupling between coupling plates of the capacitive-coupling interface, which makes accurate system analysis and compensation design tedious and complicated. In this paper, an accurate steady-state equivalent circuit model of the capacitive-coupling interface with cross-coupling is established. The model includes a parallel input capacitor linked with a series output capacitor by an ideal transformer whose turns ratio reflects the extent of cross-coupling between the plates. Effects of coupling variation on the model are analyzed in detail. The model is used for primary and secondary tuning design to achieve the maximum power transfer of a CPT system with cross-coupling. The effectiveness of the proposed model is demonstrated by both simulations and experimental results.

This paper focuses on non-radiative wireless power transfer implemented by means of a resonant magnetic coupling. The case of one transmitter and two receivers is considered and a rigorous analytical procedure is developed demonstrating that maximum power transfer or maximum efficiency can be achieved by appropriately selecting the load values. Both cases of coupled and uncoupled receivers are solved; closed formulas are derived for the optimal loads, which maximize either power or efficiency. It is shown that the resistances that realize maximum power transfer are always greater than the resistances that realize maximum efficiency. According to this observation, an optimal range of operation for the load resistances is also determined. Furthermore, it is demonstrated that in the case where the receivers are coupled the introduction of appropriate compensating reactances allows retrieving the same results corresponding to the uncoupled case both for powers and efficiency. Theoretical data are validated by comparisons with numerical results.