Özge Zorlu

Fully Self-Powered Electromagnetic Energy Harvesting System With Highly Efficient Dual Rail Output

This paper presents a vibration-based energy harvesting system composed of a compact electromagnetic (EM) power generator and highly efficient full-wave interface electronics in a system-on-package. The system harvests energy from ambient vibrations, and delivers a smooth and reliable dual rail DC supply to power up a practical load. The energy harvester module is an in-house double-coil EM transducer which generates AC voltage in response to low frequency ambient vibrations. Voltage regulation is achieved by the interface electronics at the core of the system, which is designed to rectify the input AC voltage with peak amplitude ranging from several hundred mVs to several Volts, with maximum efficiency. The interface electronics contains an active rectifier with high conversion efficiency (>;80%) for a wide range of load currents (0-42 μA). A passive network, built from low threshold-voltage chip diodes and capacitors, generates a dual supply voltage from one of the coils to power up the active rectifier. The autonomous system of 16 cm3 volume (comparable to the size of a C-Type battery), delivers 54 μW to a 37-μA load through a dual rail 1.46 V DC voltage with total system efficiency of 81%, when subjected to low frequency (8 Hz) external vibrations. The maximum overall system power density has been validated to be 6.06 μW/cm3, three times what was previously reported for a batteryless vibration driven system.

A Fully Integrated and Battery-Free Interface for Low-Voltage Electromagnetic Energy Harvesters

This paper presents a fully integrated and battery-free 90 nm interface circuit for ac/dc conversion and step up of low-voltage ac signals generated by electromagnetic (EM) energy harvesters. The circuit is composed of two stages: The rectifier in the first stage utilizes an improved ac/dc doubler structure with active diodes internally powered by a passive ac/dc doubler and custom-designed comparators to minimize the voltage drops. With this, the efficiency is enhanced to 67% while providing 0.61 V to 40 μA load. The second stage is a dc/dc converter utilizing a low-voltage charge pump with an on-chip ring oscillator for further voltage step up. The rectifier stage is functional down to 125 mV input peak voltage, and the full interface circuit can maintain more than 1 V dc at 1 MΩ load for input peak voltages higher than 0.4 V. The circuit delivers 2.48 V to a 4.4 MΩ load, when interfaced to an in-house EM harvester, operating under 10 Hz, 0.5 g vibration.

Reconfigurable Nested Ring-Split Ring Transmitarray Unit Cell Employing the Element Rotation Method by Microfluidics

A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360 ° linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.

A vibration-based electromagnetic energy harvester system with highly efficient interface electronics

This paper presents a vibration-based electromagnetic (EM) energy harvester system utilizing novel and highly efficient interface electronics. The energy harvesting module up-converts the environmental low frequency vibrations for increased AC power output. The interface circuit employs a boot-strap technique to reduce the threshold voltage of the rectifiers further increasing the power conversion efficiency of the overall system. The complete system, composed of an energy harvester module, and a compact 0.35 µm CMOS IC, was fully validated. It is capable of powering a 1.5V, 15µA load with 65% conversion efficiency, and 5% ripple, at an external vibration frequency of 10Hz. The recorded efficiency is the highest achieved value for vibration-based EM energy harvesters with passive rectification to the best of our knowledge.

An interface circuit prototype for a vibration-based electromagnetic energy harvester

This paper describes the interface electronics for a vibration based Electromagnetic (EM) energy harvester, which works on the mechanical frequency-up-conversion principle. The interface electronics is used to step up and rectify the harvested AC signal of the energy harvester through a two-stage charge-pump circuit. Output voltage of 4.5 V with 2.5% ripple has been demonstrated at a load current of 5μA. The maximum power efficiency is 35% with an output voltage and current range of 2–2.5V and 15–20 μA respectively. Furthermore, a synchronous rectifier was powered by the energy harvester to verify usage under active loading conditions.

Hybrid energy harvesting from keyboard

This paper presents a hybrid energy harvester which combines piezoelectric (PZT) and electromagnetic (EM) transduction mechanisms to scavenge vibration energy from a keyboard. The system comprises of improvements to the dome structure presented in previous studies, in which only PZT transduction mechanism was used to harvest 16.95 μW of experimentally verified power. An in-house modeling and simulation tool is first introduced in this work to evaluate the integration of EM transduction into the PZT system. The tool combines analytical mechanical equations and FEM results for magnetic fields for the optimization of the electromagnetically generated power. Two designs of different cost are then compared. It is concluded that the design utilizing the frequency-up-conversion technique at an incrementally higher cost is superior due to significantly higher contribution to the generated power compared to the alternative implementation without frequency-up-conversion. Modeling and simulations show an additional 2.81 μW power can be generated through EM integration to the previous PZT based keyboard energy harvester system.

A novel planar magnetic sensor based on orthogonal fluxgate principle

In this paper, we present a new planar fluxgate magnetometer structure. The sensor has the orthogonal fluxgate configuration which makes the detection part independent of the excitation mechanism. The sensor consists of a ferromagnetic cylindrical core covering an excitation rod, and planar coils for signal detection. The fabricated sensor has a linear range of /spl plusmn/ a sensitivity of 4.3 mV/mT, and a perming below 400 nT for 200 mA peak sinusoidal excitation current at 100 kHz. The effect of demagnetization on the sensitivity, linear range, and perming for this structure is demonstrated by varying the length of the ferromagnetic core.

Auto-calibrating threshold compensation technique for RF energy harvesters

This paper presents the design of a new threshold compensation technique for UHF Dickson rectifiers. The proposed solution addresses the efficiency reduction of previous architectures especially under large input powers. The measurements show that the proposed technique achieves very good efficiency within 10 dBm variation of the input power. Therefore, the technique is suitable for applications where the incident power is not constant. Thanks to the reduction in the reverse leakage current, a peak efficiency of 34% at 433 MHz was measured.

An electromagnetic energy harvester for low frequency and low-g vibrations with a modified frequency up conversion method

This paper presents a MEMS-based electromagnetic (EM) energy harvester for low frequency and low acceleration vibrations. The harvester is an improved version of [1], which operates with the frequency up conversion (FupC) principle. The former structure was composed of a low-frequency diaphragm carrying a magnet and 16 high-frequency cantilevers with coils. In this work, the phase difference between the coil outputs, leading to voltage cancellation in serial connection, has been eliminated by using a single coil placed on a diaphragm. Furthermore, the placement and the volume of the magnetic film have been modified for better magnetic coupling. The RMS values of the generated voltage and delivered power to an equivalent resistive load have been measured as 6.94 mV and 1.2 nW, respectively with 10 Hz, 3 mm peak to peak vibrations (0.6 g acceleration). About 32-fold increase in the peak power output has been demonstrated with the presented energy harvester with respect to the previous work.

Towards a vibration energy harvesting WSN demonstration testbed

This paper presents initial results toward the implementation of a wireless sensor network (WSN) demonstration testbed powered up by vibration energy, as part of the E-CROPS project. The testbed uses MicaZ Motes, supplied by AA batteries. The power drawn by Motes in different modes of operation are measured. Design details of an electromagnetic harvester, and experimental results of charging AA batteries with this harvester at 10 Hz vibration generated in the laboratory, are presented.