Optimized piezoelectric energy harvesting circuit using step-down converter in discontinuous conduction mode

An optimized method of harvesting vibrational energy with a piezoelectric element using a step-down DC-DC converter is presented. In this configuration, the converter regulates the power flow from the piezoelectric element to the desired electronic load. Analysis of the converter in discontinuous current conduction mode results in an expression for the duty cycle-power relationship. Using parameters of the mechanical system, the piezoelectric element, and the converter; the "optimal" duty cycle can be determined where the harvested power is maximized for the level of mechanical excitation. It is shown that, as the magnitude of the mechanical excitation increases, the optimal duty cycle becomes essentially constant, greatly simplifying the control of the step-down converter. The expression is validated with experimental data showing that the optimal duty cycle can be accurately determined and maximum energy harvesting attained. A circuit is proposed which implements this relationship, and experimental results show that the converter increases the harvested power by approximately 325%.     

基于压电材料的双频段混合能量收集天线

针对环境混合能量收集(天线)的小型化设计目标,设计一种基于聚偏氟乙烯(PVDF)压电材料的双频段共面波导(CPW)天线.天线的主要辐射单元为矩形铜皮贴纸,两侧对称的L型铜皮贴纸形成共面波导馈电结构,并作为微扰单元改变天线的表面电流分布,实现双频的设计要求.天线设计并制造在PVDF压电薄膜上,由于压电材料本身所具备的压电...     

Analysis of piezoelectric energy harvesting device with adjustable resonance frequency

This paper presents an analytic method that adjusts resonance frequency of a piezoelectric vibration energy harvester. A mathematical model that estimates resonance frequency of cantilever is also proposed. Through moving an attached mass and changing its weight on the cantilever beam, resonance frequency of adopted piezoelectric device can be adjusted to match the frequency of ambient vibration sources, which is critical in order to harvest maximum amount of energy. The theoretical results are validated by experiments that move different masses along experimental cantilever beams. The results demonstrate that resonance frequency can be adjusted by an attached mass located at different positions on the cantilever beam. Different combinations of operational conditions that harvest maximum amount of energy are also discussed in this paper.     

一种无源同步开关压电能量收集电路研究

在压电能量收集接口电路中,并联开关同步电感电路在开关断开后电感上所剩余磁能并未得到有效利用。为了克服上述问题,提出一种改进的并联同步开关电感电路,以倍压整流电路取代并联同步开关电感电路中的全桥整流电路,一方面减少整流电路耗能,另一方面在开关过程中构建新的振荡回路,将电感上存储磁能转化成电能传递至负载。再利用无源峰值检测开关电路,降低开关控制电路耗能。仿真及实验结果表明,该电路输出功率为传统并联同步开关电感电路输出功率的130%、为经典电路输出功率的9.6倍。同时,该电路中开关电路耗能仅占所采集能量的12%,可以实现能量自给。     

Energy harvesting using piezoelectric transducers for suspension systems

Energy harvesting by using functional materials in suspension systems bear potential to win-back certain (even if low) amounts of vibrational energy, otherwise dissipated via the conventional (passive) dampers. Piezoelectric (PE) ceramics are functional materials that can be used for transforming mechanical energy into electrical and vice versa. In this paper, we study the capabilities and efficiency of energy harvesting (EH) with PE transducers under two different kinds of external excitation: i) Periodic and ii) stochastic. An appropriate nonlinear lumped parameter electromechanical model (LPEM) is brought into the two-port network notation. Laboratory experiments were conducted under periodic external force-controlled excitation performed on a universal test machine (UTM). The two-port model parameters were identified and the model was validated by comparing results of numerical simulations and experiments. Extended simulations have been conducted to investigate the EH capabilities of PE transducers in automotive applications, i.e. EH in suspension systems under the standardized road conditions. The analysis results of the power conversion and EH efficiency are presented and discussed.     

Adaptive piezoelectric energy harvesting circuit for wireless remote power supply

This paper describes an approach to harvesting electrical energy from a mechanically excited piezoelectric element. A vibrating piezoelectric device differs from a typical electrical power source in that it has a capacitive rather than inductive source impedance, and may be driven by mechanical vibrations of varying amplitude. An analytical expression for the optimal power flow from a rectified piezoelectric device is derived, and an "energy harvesting" circuit is proposed which can achieve this optimal power flow. The harvesting circuit consists of an AC-DC rectifier with an output capacitor, an electrochemical battery, and a switch-mode DC-DC converter that controls the energy flow into the battery. An adaptive control technique for the DC-DC converter is used to continuously implement the optimal power transfer theory and maximize the power stored by the battery. Experimental results reveal that use of the adaptive DC-DC converter increases power transfer by over 400% as compared to when the DC-DC converter is not used.     

Low-frequency piezoelectric energy harvesting prototype suitable for the MEMS implementation

A low-frequency piezoelectric energy harvester based on impact vibration assembled with a compliant driving beam and two rigid generating beams is presented. The ambient low frequency is up-converted to high resonant frequency by the periodic impact between the driving beam and the generating beams. The advantages of the harvester are: restricting the large displacement of the compliant driving beam, improving power density and being especially suitable for a compact MEMS approach. The 1.53 mW average power of the macroscale impact vibration harvester is achieved at 20.1 Hz under 0.4g acceleration. The power density is 93.2 μW/cm³, which is 6.8 times that of conventional counterpart (13.6 μW/cm³). The measured results demonstrate the potential of the device applied to portable and implantable electronics benefited from the MEMS batch-fabrication technology.     

A MEMS-based piezoelectric power generator array for vibration energy harvesting

Piezoelectric power generator made by microelectromechanical system (MEMS) technology can scavenge power from low-level ambient vibration sources. The developed MEMS power generators are featured with fixed/narrow operation frequency and power output in microwatt level, whereas, the frequency of ambient vibration is floating in some range, and power output is insufficient. In this paper, a power generator array based on thick-film piezoelectric cantilevers is investigated to improve frequency flexibility and power output. Piezoelectric cantilevers array has been designed and fabricated. The cantilevers array can be tuned to the frequency and expanded the excited frequency bandwidth in ambient low frequency vibration. Serial connection among cantilevers of the array is investigated. The prototype generator has a measured performance of 3.98 μW effective electrical power and 3.93 DC output voltage to resistance load. This device is promising to support networks of ultra-low-power, peer-to-peer, wireless nodes.     

Energy harvesting from radio frequency propagation using piezoelectric cantilevers

This work reports an induced strain in a piezoelectric cantilever due to radio frequency signal propagation. The piezoelectric actuator is coupled to radio frequency (RF) line through a gap of 0.25 mm. When a voltage signal of 10 Vpp propagates in the line it sets an alternating current in the actuator electrodes. This flowing current drives the piezoelectric cantilever to mechanical movement, especially when the frequency of the RF signal matches the mechanical resonant frequency of the cantilever. Output voltage signals versus frequency for both mechanical vibrational and RF signal excitations have been measured using different loads.     

A self-powered piezoelectric energy harvesting interface circuit with efficiency-enhanced P-SSHI rectifier

The key to self-powered technique is initiative to harvest energy from the surrounding environment.Harvesting energy from an ambient vibration source utilizing piezoelectrics emerged as a popular method.Efficient interface circuits become the main limitations of existing energy harvesting techniques.In this paper,an interface circuit for piezoelectric energy harvesting is presented.An active full bridge rectifier is adopted to improve the power efficiency by reducing the conduction loss on the rectifying path.A parallel synchronized switch harvesting on inductor (P-SSHI) technique is used to improve the power extraction capability from piezoelectric harvester,thereby trying to reach the theoretical maximum output power.An intermittent power management unit (IPMU) and an output capacitor-less low drop regulator (LDO) are also introduced.Active diodes (AD) instead of traditional passive ones are used to reduce the voltage loss over the rectifier,which results in a good power efficiency.The IPMU with hysteresis comparator ensures the interface circuit has a large transient output power by limiting the output voltage ranges from 2.2 to 2 V.The design is fabricated in a SMIC 0.18μm CMOS technology.Simulation results show that the flipping efficiency of the P-SSHI circuit is over 80％ with an off-chip inductor value of 820 μH.The output power the proposed rectifier can obtain is 44.4μW,which is 6.7× improvement compared to the maximum output power of a traditional rectifier.Both the active diodes and the P-SSHI help to improve the output power of the proposed rectifier.LDO outputs a voltage of 1.8 V with the maximum 90％ power efficiency.The proposed P-SSHI rectifier interface circuit can be self-powered without the need for additional power supply.     

Fabrication and performance of MEMS-based piezoelectric power generator for vibration energy harvesting

A MEMS-based energy harvesting device, micro piezoelectric power generator, is designed to convert ambient vibration energy to electrical power via piezoelectric effect. In this work, the generator structure of composite cantilever with nickel metal mass is devised. Micro-electronic-mechanical systems (MEMS) related techniques such as sol-gel, RIE dry etching, wet chemical etching, UV-LIGA are developed to fabricate the device and then its performance is measured on vibration testing setup. The investigation shows that the designed device is expected to resonantly operate in low-frequency environmental vibration through tailoring the structure dimension. Under the resonant operation with frequency of about 608 Hz, a first prototype of the generator result in about 0.89 V AC peak-peak voltage output to overcome germanium diode rectifier toward energy storage, and its power output is in microwatt level of 2.16 μW.     

Multiple block structure-preserving reduced order modeling of interconnect circuits

In this paper, we propose a generalized multiple-block structure-preserving reduced order interconnect macromodeling method (BSPRIM). Our approach extends the structure-preserving model order reduction (MOR) method SPRIM [R.W. Freund, SPRIM: structure-preserving reduced-order interconnect macromodeling, in: Proceedings of International Conference on Computer Aided Design (ICCAD), 2004, pp. 80-87] into more general block forms. We first show how an SPRIM-like structure-preserving MOR method can be extended to deal with admittance RLC circuit matrices and show that the 2q moments are still matched and symmetry is preserved. Then we present the new BSPRIM method to deal with more circuit partitions for linear dynamic circuits formulated in impedance and admittance forms. The reduced models by BSPRIM will still match the 2q moments and preserve the circuit structure properties like symmetry as SPRIM does. We also show that BSPRIM can build the compact models with similar size and accuracy of that produced by traditional projection based methods but using less computation costs. Experimental results show that BSPRIM outperforms SPRIM in terms of accuracy with more partitions and outperforms PRIMA with less CPU times for generating the same accurate models.     

ESEI能量回收接口电路的设计与仿真

具有较大回收功率且回收功率不随负载变化是设计基于压电效应的能量回收接口电路需要考虑的主要因素,标准接口、SECE、串联SSHI、并联SSHI是常用的四种接口电路,其中SECE接口电路的回收功率与负载无关,基于此提出了一种新的压电能量回收接口电路——ESEI(Enhanced Synchronous Charge Extraction and Inversion Interface)接口电路,分析计算了该接口电路在恒定激振位移下的回收功率,并利用电子仿真软件Multisim对ESEI和四种接口电路的回收功率进行了仿真和比较。结果表明当负载大于临界值时,ESEI接口电路的回收功率达到最大值且与负载没有关系,该最大回收功率值约为SECE接口电路的4倍,仅小于并联SSHI接口电路。     

Reliability modeling and planning of energy harvesting based on uncertainty theory

Energy harvesting network is a new form of computer networks.It can convert the environmental energy into usable electric energy,and supply the electrical energy as a primary or secondary power source to the electronic device for network communication.However,the energy harvesting process has great volatility and uncertainty,the traditional analytical method based on probability distribution function to describe the energy collection process can not accurately simulate the actual situation,resulting in higher depletion probability of nodes,then the reliability cannot be guaranteed as a result.For this,the energy harvesting reliability of energy harvesting nodes was defined,represented with the degree of normal operation,respectively set up the node reliability models with no battery and infinite battery.As an example for maximum node achievable rate,the uncertain multilevel programming model based on node reliability was put forward,then the network efficiency was improved under the premise of ensuring node reliability.An energy average allocation (EAA) algorithm was proposed and the upper bound of competitive ratio of the algorithm was proved theoretically.Finally,the actual wind power data was taken as an example to verify the feasibility and effectiveness of the proposed model and method.     

Generation of FDTD subcell equations by means of reduced order modeling

Adapted finite-difference time-domain (FDTD) update equations exist for a number of objects that are smaller than the grid step, such as wires and thin slots. We provide a technique that automatically generates new FDTD update equations for small objects. Our presentation focusses on 2D-FDTD. We start from the FDTD equations in a fine grid where the time derivative is not discretised. This yields a large state-space model that is drastically reduced with a reduced order modeling technique. The reduced state-space model is then translated into new FDTD update equations that can be used in an FDTD simulation in the same way as the existing update equations for wires and thin slots. This technique is applied to a number of numerical problems showing the accuracy and versatility of the proposed method.     

Thermally reused solar energy harvesting using current mirror cells

This paper implements a simultaneous solar and thermal energy harvesting system, as a hybrid energy harvesting (HEH) system, to convert ambient light into electrical energy through photovoltaic (PV) cells and heat absorbed in the body of PV cells. Indeed, a solar panel equipped with serially connected thermoelectric generators not only converts the incoming light into electricity but also takes advantage of heat emanating from the light. In a conventional HEH system, the diode block is used to provide the path for the input source with the highest value. In this scheme, at each time, only one source can be handled to generate its output, while other sources are blocked. To handle this challenge of combining resources in HEH systems, this paper proposes a method for collecting all incoming energies and conveying its summation to the load via the current mirror cells in an approach similar to the maximum power point tracking. This technique is implemented using off-the-shelf components. The measurement results show that the proposed method is a realistic approach for supplying electrical energy to wireless sensor nodes and low-power electronics.