A Cold-Startup SSHI Rectifier for Piezoelectric Energy Harvesters with Increased Open-Circuit Voltage

Piezoelectric vibration energy harvesting has drawn much research interest over the last decade towards the goal of enabling self-sustained wireless sensor nodes. In order to make use of the harvested energy, interface circuits are needed to rectify and manage the energy. Among all active interface circuits, SSHI (synchronized switch harvesting on inductor) and SECE (synchronous electric charge extraction) are widely employed due to their high energy efficiencies. However, the cold-startup issue still remains since an interface circuit needs a stable DC supply and the whole system is completely out of charge at the beginning of implementations or after a certain period of time without input vibration excitation. In this paper, a new cold-startup SSHI interface circuit is presented, which dynamically increases the open-circuit voltage generated from the piezoelectric transducer (PT) in cold-state to start the system under much lower excitation levels. The proposed circuit is designed and fabricated in a 0.18 um CMOS process and experimentally validated together with a custom MEMS (microelectromechanical systems) harvester, which is designed with split electrodes to work with the proposed power extraction circuit. The experiments were performed to start the system from the cold state under variable excitation levels. The results show that the proposed system lowers the required excitation level by at least 50% in order to perform a cold-startup. This aids restarting of the energy harvesting system under low excitation levels each time it enters the cold state

Effect of polyethylene glycol-intercalated organoclay on vulcanization characteristics and reinforcement of natural rubber nanocomposites

Organically modified montmorillonite (OMMT) clay was intercalated with low-molecular weight polyethylene glycol (PEG) oligomer at melt stage. The intercalation behaviour of PEG into the OMMT clay galleries and its interaction with clay platelets were characterized with X-ray diffraction (XRD) and differential scanning calorimetric techniques. A natural rubber (NR)-organoclay nanocomposite (NROCN) was prepared by melt-compounding of NR with PEG-treated organoclay (P-OMMT) and other compounding chemicals using a laboratory-scale internal mixer. XRD analysis of the nanocomposites revealed the intercalation of NR molecules into the P-OMMT clay galleries and subsequent exfoliation during the melt-compounding process. Vulcanization characteristics of the NROCN, especially processing safety and optimum curing time, have been interpreted with reference to the organic modifier of the montmorillonite clay, PEG modification and the degree of exfoliation. Solid-state mechanical properties of P-OMMT clay-filled NROCN vulcanizates have shown a significant enhancement in stiffness and strength characteristics whilst without scarifying the elasticity of the nanocomposites. Results have been explained in terms of the degree of exfoliation, dispersibility of the organoclay and strain-induced crystallization of the natural rubber.The author(s) received no financial support for the research, authorship, and/or publication of this article

A Passive Design Scheme to Increase the Rectified Power of Piezoelectric Energy Harvesters

Piezoelectric vibration energy harvesting is becoming a promising solution to power wireless sensors and portable electronics. While miniaturizing energy harvesting systems, rectified power efficiencies from miniaturized piezoelectric transducers (PT) are usually decreased due to insufficient voltage levels generated by the PTs. In this paper, a monolithic PT is split into several regions connected in series. The raw electrical output power is kept constant for different connection configurations as theoretically predicted. However, the rectified power following a full-bridge rectifier (FBR), or a synchronized switch harvesting on inductor (SSHI) rectifier, is significantly increased due to the higher voltage/current ratio of series connections. This is an entirely passive design scheme without introducing any additional quiescent power consumption and it is compatible with most of state-of-the-art interface circuits. Detailed theoretical derivations are provided to support the theory and the results are experimentally evaluated using a custom MEMS PT and a CMOS rectification circuit. The results show that, while a PT is split into 8 regions connected in series, the performance while using a FBR and a SSHI circuit is increased by 2.3X and 5.8X, respectively, providing an entirely passive approach to improving energy conversion efficiency.UK Engineering and Physical Sciences Research Council (EPSRC) (Grant number: EP/L010917/1 and EP/N021614/1

A Nail-Size Piezoelectric Energy Harvesting System Integrating a MEMS Transducer and a CMOS SSHI Circuit

Piezoelectric vibration energy harvesting has drawn much interest to power distributed wireless sensor nodes for Internet of Things (IoT) applications where ambient kinetic energy is available. For certain applications, the harvesting system should be small and able to generate sufficient output power. Standard rectification topologies such as the full-bridge rectifier are typically inefficient when adapted to power conditioning from miniaturized harvesters. Therefore, active rectification circuits have been researched to improve overall power conversion efficiency, and meet both the output power and miniaturization requirements while employing a MEMS harvester. In this paper, a MEMS piezoelectric energy harvester is designed and cointegrated with an active synchronized switch harvesting on inductor (SSHI) rectification circuit designed in a CMOS process to achieve high output power for system miniaturization. The system is fully integrated on a nail-size board, which is ready to provide a stable DC power for low-power mini sensors. A MEMS energy harvester of 0.005 cm3 size, co-integrated with the CMOS conditioning circuit, outputs a peak rectified DC power of 40.6 µW and achieves a record DC power density of 8.12 mW/cm3 when compared to state-of-the-art harvesters

Indoor photovoltaics, The Next Big Trend in solution-processed solar cells

Abstract: Indoor photovoltaics (IPVs) have attracted considerable interest for their potential to power small and portable electronics and photonic devices. The recent advancemes in circuit design and device optimizations has led to the power required to operate electronics for the internet of things (IoT), such as distributed sensors, remote actuators, and communication devices, being remarkably reduced. Therefore, various types of sensors and a large number of nodes can be wireless or even batteryless powered by IPVs. In this review, we provide a comprehensive overview of the recent developments in IPVs. We primarily focus on third‐generation solution‐processed solar cell technologies, which include organic solar cells, dye‐sensitized solar cells, perovskite solar cells, and newly developed colloidal quantum dot indoor solar cells. Besides, the device design principles are also discussed in relation to the unique characteristics of indoor lighting conditions. Challenges and prospects for the development of IPV are also summarized, which, hopefully, can lead to a better understanding of future IPV design as well as performance enhancement

Alginate nanoparticles protect ferrous from oxidation: Potential iron delivery system

A novel, efficient delivery system for iron (Fe²⁺) was developed using the alginate biopolymer. Iron loaded alginate nanoparticles were synthesized by a controlled ionic gelation method and was characterized with respect to particle size, zeta potential, morphology and encapsulation efficiency. Successful loading was confirmed with Fourier Transform Infrared spectroscopy and Thermogravimetric Analysis. Electron energy loss spectroscopy study corroborated the loading of ferrous into the alginate nanoparticles. Iron encapsulation (70%) was optimized at 0.06% Fe (w/v) leading to the formation of iron loaded alginate nanoparticles with a size range of 15-30nm and with a negative zeta potential (-38mV). The in vitro release studies showed a prolonged release profile for 96h. Release of iron was around 65-70% at pH of 6 and 7.4 whereas it was less than 20% at pH 2.The initial burst release upto 8h followed zero order kinetics at all three pH values. All the release profiles beyond 8h best fitted the Korsmeyer-Peppas model of diffusion. Non Fickian diffusion was observed at pH 6 and 7.4 while at pH 2 Fickian diffusion was observed.This research was financially supported by the HETC QIG Win 3 grant, University of Peradeniya, Peradeniya, Sri Lanka

Tailoring carbon nanostructure for high frequency supercapacitor operation

The possibility of enhancing the frequency performance of electrochemical capacitors by tailoring the nanostructure of the carbon electrode to increase electrolyte permeability is demonstrated. Highly porous, vertically oriented carbon electrodes which are in direct electrical contact with the metallic current collector are produced via MPECVD growth on metal foils. The resulting structure has a capacitance and frequency performance between that of an electrolytic capacitor and an electrochemical capacitor. Fully packaged devices are produced on Ni and Cu current collectors and performance compared to state-of-the-art electrochemical capacitors and electrolytic capacitors. The extension of capacitive behavior to the AC regime (~100 Hz) opens up an avenue for a number of new applications where physical volume of the capacitor may be significantly reduced.Peer Reviewe

A Fully Integrated Split-Electrode SSHC Rectifier for Piezoelectric Energy Harvesting

In order to efficiently extract power from piezoelectric vibration energy harvesters, various active rectifiers have been proposed in the past decade, which include Synchronized Switch Harvesting on Inductor (SSHI), Synchronous Electric Charge Extraction (SECE), etc. Although reported active rectifiers show good performance improvements compared to fullbridge rectifiers (FBR), large off-chip inductors are typically required and the system volume is inevitably increased as a result, counter to the requirement for system miniaturization. In this paper, a fully-integrated split-electrode SSHC (synchronized switch harvesting on capacitors) rectifier is proposed, which achieves significant performance enhancement without employing any off-chip components. The proposed circuit is designed and fabricated in a 0:18 μm CMOS process and it is co-integrated with a custom MEMS (microelectromechanical systems) piezoelectric transducer with its electrode layer equally split into four regions. The measured results show that the proposed rectifier can provide up to 8.2 and 5.2 boost, using on-chip and off-chip diodes respectively, in harvested power compared to a FBR under low excitation levels and the peak rectified output power achieves 186 μW

An empirical study on the impact of collaborative R&D networks on enterprise innovation performance based on the mediating effect of technology standard setting

Against the background of economic globalization, high-technology enterprises need to focus on the characteristics of corporate collaboration R&amp;D networks and Standard-Setting. In this paper, theoretical research on corporate collaboration R&amp;D network characteristics, technology standard-setting capability, and technology innovation performance is carried out, and a theoretical model and hypotheses are constructed. We apply Structural Equation Modeling (SEM) to conduct an empirical analysis based on national data surveys of 12 industries. The conclusions are as follows: (1) Corporate collaboration R&amp;D networks and technology standard-setting capability have a positive and significant impact on technology innovation performance; (2) Technology’s standard-setting capability has been identified to play a full intermediary role in the relationship between the breadth of connections and innovation efficiency. This paper provides a practical reference for enterprises to assess the value of collaborative R&amp;D networks and improve their technology standard-setting capability for enhanced economic efficiency.</jats:p

Improved delivery of caffeic acid through liposomal encapsulation

Photoageing resulting from long term exposure of the skin to UV light can be minimized by scavenging the reactive photochemical intermediates with antioxidants. For effective photoprotection, the antioxidant must overcome the barrier properties of the skin and reach the target site in significant amounts. The present study aims to improve the skin penetration of caffeic acid, a very effective free radical scavenger, by encapsulating in liposomes. Caffeic acid loaded liposomes prepared using the reverse phase evaporation technique showed 70% encapsulation efficiency and size around 100 nm with zeta potential of −55 mV.In vitrodiffusion through a dialysis membrane enabled 70% release of encapsulated caffeic acid within 7 h, whereas 95% of free caffeic acid diffused within 4 h in PBS solution (pH 7.4). Liposomal caffeic acid permeation through pig skin epidermis in a Franz cell apparatus was 45 % during 7 h. In contrast, free caffeic acid was almost nonpermeable (&lt;5%) to pig skin during this time. The DPPH assay indicated that skin penetration did not destroy the antioxidant activity of liposomal caffeic acid or free caffeic acid. In conclusion, we confirm that liposomal caffeic acid may be successfully employed as an effective photoprotective agent against UV mediated skin damage.Peer Reviewe