Micro-power Energy Harvesting Research Articles

Supramolecular Organic Ferroelectric Materials from Donor-Acceptor Systems.

Organic ferroelectric (FE) materials, though known for more than a century, are yet to reach close to the benchmark of inorganic or hybrid materials in terms of the magnitude of polarization. Amongst the different classes of organic systems, donor (D)-acceptor (A) charge-transfer (CT) complexes are recognized as promising for ferroelectricity owing to their neutral-to-ionic phase transition at low temperature. This review presents an overview of different supramolecular D-A systems that have been explored for FE phase transitions. The discussion begins with a general introduction of ferroelectricity and its different associated parameters. Then it moves on to show early examples of CT cocrystals that have shown FE properties at sub-ambient temperature. Subsequently, recent developments in the field of room temperature (RT) ferroelectricity, exhibited by H-bond-stabilized lock-arm supramolecular-ordering (LASO) in D-A co-crystals or other FE CT-crystals devoid of neutral-ionic phase transition are discussed. Then the discussion moves on to emerging reports on other D-A soft materials such as gel and foldable polymers; finally it shows very recent developments in ferroelectricity in supramolecular assemblies of single-component dipolar or ambipolar π-systems, exhibiting intra-molecular charge transfer. The effects of structural nuances such as H-bonding, balanced charge transfer and chirality on the observed ferroelectricity is described with the available examples. Finally, piezoelectricity in recently reported ambipolar ADA-type systems are discussed to highlight the future potential of these soft materials in micropower energy harvesting.

Micropower energy harvesting using high-efficiency indoor organic photovoltaics for self-powered sensor systems

Micropower energy harvesting using high-efficiency indoor organic photovoltaics for self-powered sensor systems

Electro‐mechanical properties of poly(vinylidene fluoride‐hexafluoropropylene) reinforced with zinc oxide nanostructure

The piezoelectric poly(vinylidene fluoride-hexafluoropropylene) ((P(VDF-HFP)) has been incorporated with zinc oxide (ZnO) of different forms, i.e. nanoparticles (NPs), nanorods (NRs), and microrods (MRs). The polymer has been activated the piezoelectric phase with the poling filed of 70 MV/m at 90°C for 10 min. ZnO of various particle types is grown into piezoelectric wurtzite. The addition of ZnO has slightly changed the degree of crystallinity of the polymers and clearly increased the elasticity to the best value in the case of inserted MRs. The electroactive phase of the polymer-based film has been enhanced at 2 wt% of ZnO for both NPs and NRs cases. The dielectric constant of the films increased with ZnO concentration. Finally, a cantilever beam structure with the patch of P(VDF-HFP) reinforced with ZnO of 2 wt% NRs shows the best performance as a microsource of the energy of about 1 µW. Development of micropower energy harvesting in P(VDF-HFP) with ZnO NRs has been substantially and highly promising to power small-scale electronics.‏

A Comprehensive Analysis and Modeling of the Self-Powered Synchronous Switching Harvesting Circuit With Electronic Breakers

Self-powered realization for synchronous switching circuits is a hot spot for piezoelectric vibration energy harvesting. As a well-known approach, the electronic breaker is widely used for its simplicity and reliability. It plays an important role on the performance of the piezoelectric generator by affecting the available open-circuit voltage and the switching phase lag. In this paper, a comprehensive model is developed for improved performance analysis with missed factors included in comparison with previous investigations. The combined influence of the envelope resistor and the capacitor on both the phase lag and the open-circuit voltage is newly considered while the additional phase lag effect induced by charging the switch parasitic capacitance with the envelope capacitance is supplemented. Experiments and simulations validate the proposed model with better accuracy and the results show that these supplemented factors are important to the generator performance, especially for the micropower energy harvesting with small piezoelectric capacitance or displacement magnitude. Moreover, more detailed design guidelines are deduced from the proposed model.

Self-adaptive piezoelectric ceramic vibration system based on asymmetric piezoelectric cantilever for energy harvesting

Micropower energy harvesting is one of key technologies for the micromation and practical development of wireless sensor and communication node networks. A self-adaptive piezoelectric vibration system based on modified homogeneous strain asymmetric PZT piezoelectric ceramic cantilever beam for the micropower energy harvesting was designed and prepared. A vertical cantilever was designed at the first time to obtain the homogeneous state of stress which can largely increase the power output and energy harvesting efficiency of piezoelectric cantilevers. In order to achieve the self-adaptive vibration, the asymmetric structure was adopted. Asymmetric cantilevers moved horizontally and changed the length of main cantilevers when affected by the variation in external frequency excitation, thus, the switching of resonant frequency was archived automatically without dissipating additional energy.

A novel MPPT circuit with 99.1% tracking accuracy for energy harvesting

A novel maximum power point tracking (MPPT) circuit based on Buck–Boost converter is presented for micro-power energy harvesting, which efficiently improves the power efficiency and robustness of system. The proposed MPPT uses the low-power analog multiplier and multi-outputs self-powered common-gate comparator to track the input power, and simplifies data calculation and structure greatly. The fast dynamic switching circuit and digital control circuit are introduced to enhance the adaptability and flexibility of system. The performance of whole converter was validated by the simulation results in a 65-nm CMOS process. The minimum starting voltage is 0.15 V. The peak output power is 40.5 µW, with a power loss of 14.1 µW. The peak power efficiency and peak tracking efficiency are 92.1 and 99.1%, respectively. The proposed MPPT has the advantages such as low power, high efficiency, fast tracking speed, simple structure.

Design of Low-Voltage Integrated Step-up Oscillators with Microtransformers for Energy Harvesting Applications

This paper describes the modeling of startup circuits in battery-less micropower energy harvesting systems and investigates the use of bond wire micromagnetics. The analysis focuses on step-up Meissner oscillators based on magnetic core transformers operating with input voltages down to ≈100 mV, e.g, from thermoelectric generators. As a key point, this paper examines the effect of core losses and leakage inductances on the startup requirements obtained with the classical Barkhausen criterion, and demonstrates the minimum transconductance for oscillations to occur. For validation purposes, a step-up oscillator IC is fabricated in a STMicroelectronics 0.32 μm technology, and connected to two bond wire microtransformers, respectively, with a 1:38 MnZn ferrite core and with a 1:52 ferromagnetic low-temperature co-fired ceramic (LTCC) core. Coherently with the proposed model, experimental measurements show a minimum startup voltage of 228 mV for the MnZn ferrite core and of 104 mV for the LTCC core.

High-efficiency passive full wave rectification for electromagnetic harvesters

We compare the performance of four types of full-wave bridge rectifiers designed for electromagnetic energy harvesters based on silicon diodes, Schottky diodes, passive MOSFETs, and active MOSFETs. Simulation and experimental results show that MOSFET-type rectifiers are more efficient than diode-type rectifiers, reaching voltage and power efficiency of 99% for ideal voltage source with input amplitudes larger than 800 mV. Since active MOSFETs require extra components and an external DC power supply, we conclude that passive MOSFETs are superior for micro-power energy harvesting systems. We demonstrate passive MOSFET rectifiers implemented using discrete, off-shelf components and show that they outperform all electromagnetic harvester rectifiers hitherto reported obtaining a power efficiency of 95%. Furthermore, we show that passive MOSFET rectifiers do not affect the center frequency, harvesting bandwidth, or optimal resistance of electromagnetic harvesters. We demonstrate a complete power management module by adding a capacitor to the rectifier output terminal. We found that this configuration changed the optimal resistive load from 40 Ω to 55 Ω and decreased output power efficiency to 86%.

Design and Fabrication of a 29 μH Bondwire Micro-transformer with LTCC Magnetic Core on Silicon for Energy Harvesting Applications

This paper presents the design of a 1: 50 bondwire micro-transformer assembled with IC gold bonding wires and a toroidal LTCC magnetic core with race-track shape. The transformer is fabricated on-top of a standard BCD IC in a 15 mm2 footprint area for micro-power energy harvesting applications. Measurements show a secondary self-inductance up to 29μH with a maximum Q-factor of 11.6 at 1.3MHz, and a coupling coefficient of 0.65 with an effective turns ratio of 19. This miniaturized technology finds also applications in power supply in package (PwrSiP) and power supply on chip (PwrSoC).

An Inductorless DC–DC Converter for Energy Harvesting With a 1.2-$ \mu\hbox{W}$ Bandgap-Referenced Output Controller

We present a fully integrated dc-dc converter for micropower energy harvesting. A 1.2- μW bandgap-referenced output controller provides output regulation at 1.4 V, achieving quiescent power of 3 μW and a maximum overall efficiency of 58% at 11 μW output power. A modified four-phase charge pump provides a 3× voltage boost and a minimum input voltage of 270 mV in free-running mode. Using dual switches driven from both the converter input and output, the chip achieves boost without external excitation or external components.