Piezoelectric Conversion Research Articles

A Piezoelectric Wave-Energy Converter Equipped with a Geared-Linkage-Based Frequency Up-Conversion Mechanism.

In this paper, a piezoelectric wave-energy converter (PWEC), consisting of a buoy, a frequency up-conversion mechanism, and a piezoelectric power-generator component, is developed. The frequency up-conversion mechanism consists of a gear train and geared-linkage mechanism, which converted lower frequencies of wave motion into higher frequencies of mechanical motion. The slider had a six-period displacement compared to the wave motion and was used to excite the piezoelectric power-generation component. Therefore, the operating frequency of the piezoelectric power-generation component was six times the frequency of the wave motion. The developed, flexible piezoelectric composite films of the generator component were used to generate electrical voltage. The piezoelectric film was composed of a copper/nickel foil as the substrate, lead–zirconium–titanium (PZT) material as the piezoelectric layer, and silver material as an upper-electrode layer. The sol-gel process was used to fabricate the PZT layer. The developed PWEC was tested in the wave flume at the Tainan Hydraulics Laboratory, Taiwan (THL). The maximum height and the minimum period were set to 100 mm and 1 s, respectively. The maximum voltage of the measured value was 2.8 V. The root-mean-square (RMS) voltage was 824 mV, which was measured through connection to an external 495 kΩ resistive load. The average electric power was 1.37 μW.

About the nonlinear acoustic parameter during deformation of AMG61 alloy

Various acoustic effects are used in the study of deformation processes. Acoustic emission is most often mentioned in such studies, and the effects due to nonlinear properties of a deformable metal are the subject of the present work. These properties of real solids lead to nonlinear acoustic effects of the interaction elastic waves forbidden by the theory of elasticity of a homogeneous isotropic body. The work solves the problem of using the principles of nonlinear acoustics in studying the deformation of AMg61 alloy samples. A surface elastic wave is used to control the alloy condition. The process of the elastic wave propagation in the deformed AMg61 alloy due to nonlinear effects is accompanied by generating the double frequency, both of the longitudinal component of the wave and the shear one, the latter is forbidden by equations of the classical elasticity theory. Excitation and reception in the samples was carried out by piezoelectric converters (PES). A wedge converter with a resonance frequency of 1MHz was used to excite the surfactant. The passing surfactant was recorded by a wedge converter with a resonance frequency of 2 MHz. We justified the control technique of the nonlinear acoustic parameter with respect to amplitudes of the first and second harmonics measured during the whole deformation process. An experimental device has been developed to control the nonlinear acoustic parameter in the process of changing the structural state of the sample metal. The pilot study results of the nonlinear acoustic parameter under Amg61 alloy deformation are given. It is shown that the nonlinear acoustic parameter, as well as the acoustic emission activity, is sensitive to changing mechanisms of the defective structure evolution. The non-linearity jump formation during deformation of alloy AMg61 is recorded, which may indicate adjustment of the metal structure. The presented data demonstrate the increase of acoustic nonlinearity in metal at various deformation stages, both at early stages of elastoplastic deformation and at pre-destruction stage, which can be used as the prognostic criterion.

A comprehensive review on the state-of-the-art of piezoelectric energy harvesting

The global energy crisis and environmental pollutions caused mainly by the increased consumption of nonrenewable energy sources prompted researchers to explore alternative energy technologies that can harvest energies available in the ambient environment. Mechanical energy is the most ubiquitous ambient energy that can be captured and converted into useful electric power. Piezoelectric transduction is the prominent mechanical energy harvesting mechanism owing to its high electromechanical coupling factor and piezoelectric coefficient compared to electrostatic, electromagnetic, and triboelectric transductions. Thus, piezoelectric energy harvesting has received the utmost interest by the scientific community. Advancements of micro and nanoscale materials and manufacturing processes have enabled the fabrication of piezoelectric generators with favorable features such as enhanced electromechanical coupling factor, piezoelectric coefficient, flexibility, stretch-ability, and integrate-ability for diverse applications. Besides that, miniature devices with lesser power demand are realized in the market with technological developments in the electronics industry. Thus, it is anticipated that in near future, many electronics will be powered by piezoelectric generators. This paper presents a comprehensive review on the state-of-the-art of piezoelectric energy harvesting. The piezoelectric energy conversion principles are delineated, and the working mechanisms and operational modes of piezoelectric generators are elucidated. Recent researches on the developments of inorganic, organic, composite, and bio-inspired natural piezoelectric materials are reviewed. The applications of piezoelectric energy harvesting at nano, micro, and mesoscale in diverse fields including transportation, structures, aerial applications, in water applications, smart systems, microfluidics, biomedicals, wearable and implantable electronics, and tissue regeneration are reviewed. The advancements, limitations, and potential improvements of the materials and applications of the piezoelectric energy harvesting technology are discussed. Briefly, this review presents the broad spectrum of piezoelectric materials for clean power supply to wireless electronics in diverse fields. This paper presents the state-of-the-art review of piezoelectric energy harvesting with a special focus on materials and applications. Piezoelectric energy conversion principles are delineated, and the working mechanisms and operational modes of piezoelectric generators are elucidated. Recent researches on the developments of inorganic, organic, composite, and bio-inspired natural piezoelectric materials are reviewed. The applications of piezoelectric energy harvesting at nano, micro and meso-scale in diverse fields are presented. The advancements, limitations, and improvements of the materials and applications of the piezoelectric energy harvesting technology are discussed. • Piezoelectric transduction is prominent energy harvesting mechanism. • Principles, structures, and operational modes are explained. • Inorganic, organic, ceramic, and bioinspired natural materials reviewed. • Broad range of applications are summarized.

Enhancement of the Piezoelectric Cantilever Beam Performance via Vortex-Induced Vibration to Harvest Ocean Wave Energy

Renewable and sustainable energies exhibit promising performance while serving as the power supply of a wireless sensor especially located in marine waters. Various microgenerators have been developed to harvest wave energy. However, the conversion ability from a dynamic oscillating source of wave is crucial to enhance their effectiveness in practical applications. In this paper, a new piezoelectric converter system is proposed to harvest the kinetic energy from ocean waves. The vortex-induced effect in an air channel enhances the vibration performance, improving the energy harvesting efficiency. The system comprises an oscillating water column (OWC) air chamber, a bluff body, and a piezoelectric piece for electromechanical transduction. The fluid–solid–electric coupling finite element method was used to investigate the relation between the output voltage and geometrical parameters, including the size and position of the piezoelectric cantilever beam, which is based on the user-defined function of the ANSYS. It is found that the bluff body in the outlet channel above the air chamber induced high-frequency vortex shedding vibration. The regular wave rushed into the air chamber with a frequency of 0.285 Hz and extruded the air across the bluff body in the outlet channel. This incurred the fluctuation of the air pressure and excited the piezoelectric cantilever beam vibration with a high frequency of 233 Hz in the wake region. Furthermore, a continuous electrical output with a peak voltage of 6.11 V is generated, which has potential applications for the wireless sensors on the marine buoy.

Piezoelectric Energy Harvester Based on LiNbO3 Thin Films.

This paper reports the results of the influence of the energy of laser pulses during laser ablation on the morphology and electro-physical properties of LiNbO3 nanocrystalline films. It is found that increasing laser pulse energy from 180 to 220 mJ results in the concentration of charge carriers in LiNbO3 films decreasing from 8.6 × 1015 to 1.0 × 1013 cm−3, with the mobility of charge carriers increasing from 0.43 to 17.4 cm2/(V·s). In addition, experimental studies of sublayer material effects on the geometric parameters of carbon nanotubes (CNTs) are performed. It is found that the material of the lower electrode has a significant effect on the formation of CNTs. CNTs obtained at the same growth time on a sample with a Cr sublayer have a smaller diameter and a longer length compared to samples with a V sublayer. Based on the obtained results, the architecture of the energy nanogenerator is proposed. The current generated by the nanogenerator is 18 nA under mechanical stress of 600 nN. The obtained piezoelectric nanogenerator parameters are used to estimate the parameters of the hybrid-carbon-nanostructures-based piezoelectric energy converter. Obtained results are promising for the development of efficient energy converters for alternative energy devices based on lead-free ferroelectric films.

Multi-frequency array of nonlinear piezoelectric converters for vibration energy harvesting

Energy harvesting from wideband and random vibrations demands for techniques and solutions to overcome limitations of linear converters, which best operate when the frequency of vibrations matches the resonant frequency of the converter. Viable approaches comprise, among others, the use of array of linear harvesters with different resonant frequencies, the adoption of nonlinear techniques or the exploitation of mechanically coupled converters. This work proposes a piezoelectric energy harvester where the combination of such techniques is explored in a unique device. The harvester is composed of an array of four piezoelectric cantilevers fabricated by screen printing lead zirconate titanate (PZT) films on a stainless steel substrate. Nonlinear behavior of the cantilevers is achieved by exploiting the interaction between a magnet and their ferromagnetic steel substrate. Two configurations have been analyzed where the magnet is either fixed on the harvester base, or it is elastically suspended through a spring on the harvester base. The latter configuration introduces a mechanical coupling among the cantilevers. For the experimental characterization, the prototype has been excited by band-pass filtered white-noise mechanical vibrations in the range 10–100 Hz with amplitude in the range 0.1–2.2 g. The obtained experimental results show that the rms values of the open-circuit output voltage for each cantilever increase in the nonlinear configuration and it can be up to 215% higher for the case with the elastically suspended magnet compared to the case of the same array operated in linear regime.

Oxygen Pressure Influence on Properties of Nanocrystalline LiNbO3 Films Grown by Laser Ablation.

Energy conversion devices draw much attention due to their effective usage of energy and resulting decrease in CO2 emissions, which slows down the global warming processes. Fabrication of energy conversion devices based on ferroelectric and piezoelectric lead-free films is complicated due to the difficulties associated with insufficient elaboration of growth methods. Most ferroelectric and piezoelectric materials (LiNbO3, BaTiO3, etc.) are multi-component oxides, which significantly complicates their integration with micro- and nanoelectronic technology. This paper reports the effect of the oxygen pressure on the properties of nanocrystalline lithium niobate (LiNbO3) films grown by pulsed laser deposition on SiO2/Si structures. We theoretically investigated the mechanisms of LiNbO3 dissociation at various oxygen pressures. The results of x-ray photoelectron spectroscopy study have shown that conditions for the formation of LiNbO3 films are created only at an oxygen pressure of 1 × 10−2 Torr. At low residual pressure (1 × 10−5 Torr), a lack of oxygen in the formed films leads to the formation of niobium oxide (Nb2O5) clusters. The presented theoretical and experimental results provide an enhanced understanding of the nanocrystalline LiNbO3 films growth with target parameters using pulsed laser deposition for the implementation of piezoelectric and photoelectric energy converters.

Kalman filter-based loading rate-dependent hysteresis compensation of flexoelectric torsional responses in polyvinylidene fluoride films for shaft torque sensors

This paper presents a new method of dynamic shaft torque measurement using polyvinylidene fluoride (PVDF) films, one of the new polymer type piezoelectric conversion materials. The measurement method is based on the shear strain gradient and the flexoelectric torsional response of the PVDF films. The loading rate-dependent hysteresis associated with viscoelastic behavior of PVDF film was modeled to estimate the torque input. The torque estimated by the proposed hysteresis model and optimization algorithm (genetic algorithm) can be implemented by the discrete Kalman filter. Because the torque estimated by the real-time Kalman filtering matches well with the actual torque input measured by the commercial in-line torque transducer, a new method of sensing the dynamic shaft torque using the PVDF output signal has been experimentally validated. This study offers potential applications for the development of new torque sensing technology to be widely used in a variety of mechanical engineering areas such as turbines, rotors, automobiles, and robotics.

A Design of mass-spring type piezoelectric energy harvesting

This study describes an experimental power generation system based on piezoelectric energy conversion for low power applications such as wireless sensor nodes. Piezoelectric transducers (PZTs) are especially suitable for energy harvesting from ambiance. A PZT is able to produce an open circuit voltage at hundreds volt level. But acquired current may be achieved at nano – micro scale. Therefore, PZT energy harvesters (PEH) have a very limited power generation capability. In order to generate higher output power, a series of PZT should be used in a PEH with proper electrical connection. In this paper, PEH is presented with a novel circuit topology for increase output power. The experimental system uses 20 diaphragm type PZTs with a 15 cm spring mounted at the center of each transducer. Necessary vibration is produced via a spring – mass structure of each PZT. Mass – spring structure is vibrated by the effect of wind. The maximum output power of the presented experimental generator for a nominal wind speed of 12 m/s is around 10.8 mJ. Results shows that proposed experimental generator is suitable for low power applications and output power of generator can be increased by using more PTZ is connected used circuit topology.

Design of a Unique Unimorph and Bimorph Cantilever Energy Harvesting System

Piezoelectric energy conversion has received considerable attention for vibration-to-electric energy conversion over the past decade. A typical piezoelectric energy harvester is a unimorph or a bimorph cantilever located on a vibrating host structure. This paper presents a comparison between unimorph and bimorph cantilever beam having a number of segmented PMN-PT piezo-elements on the input and output power. The numerical simulation was carried out by applying the finite element analysis (FEA) using COMSOL multi-physics software in order to predict output voltage and power over a frequency range of 60–200 Hz for the first resonant frequencies. The simulation results show maximum output voltage and power harvested of 7.38 V and 135.73 μW, respectively, by the unimorph piezoelectric energy harvester at resonant frequency value of 84 Hz with electromechanical coupling factor (ke) of 77.29%. These results highlight that the highest value of the output electrical power can be obtained when the piezoelectric element is attached on the top of a clamped end of a cantilever piezoelectric beam. Moreover, in an unimorph or bimorph cantilever beam system, increasing the number of piezoelectric elements results in a higher resonant frequency shift and significantly decreasing in the harvested power.

Features of the receiving of piezoelectric thin films by plasma spraying of powdery AlN

Оne of the promising materials in solid state electronics is the AlN compound. A wide range of semiconductor devices are produced from it, such as photodetectors, LEDs, piezoelectric converters, etc. But the widespread use of products based on AlN prevents low manufacturability designs based on it. In this regard, the development of new technologies for the production of devices based on AlN is relevant. The work is devoted to the study of thin AlN films obtained by plasma spraying from AlN powder. The review of existing technologies of production of thin films AlN is carried out. Their advantages and disadvantages are discussed. Information on the modernization of the VUP-5 installation, which allowed to spray the AlN film from the powdered state, is given. One of the significant advantages of the process developed in this work is that the substrate is heated to temperatures no higher than 300 oC, which in turn allows to combine this technology with the technology of silicon semiconductor devices. As a result, films with a thickness of 200 nm on various substrates were obtained and their surface structure was studied. It is shown that AlN films deposited on single crystal substrates such as diamond and silicon have the least roughness, while films on sitall have the worst roughness. The transmission spectra of the obtained AlN films were investigated by IR spectroscopy. With their help, it was shown that a polycrystalline AlN layer oriented in the crystallographic direction 002 is formed on the substrate. The piezoelectric properties of the obtained films were investigated by scanning probe microscopy. It is shown that their piezoelectric coefficient d 33 is 60% of the value for a single-domain single-crystal sample for a diamond substrate, which indicates a sufficiently high quality of the resulting film. It is concluded that, although the quality of the layers strongly depends on the substrate, nevertheless, they exhibit a significant piezoelectric effect, which allows the use of this method for the manufacture of piezoelectric sensors, ultrasonic emitters, etc.

Development and performance of a piezoelectric energy conversion structure applied in pavement

This paper presents a multi-layer cantilever piezoelectric energy conversion structure for pavement, which avoids weakening the electrical output after the mass contact and realizes the coordinated vibration of each cantilever piezoelectric energy harvester and road driving. In order to ensure the structure meets the requirements of power generation and durability when applied in road engineering, based on the power generation theory of energy harvester, the structural parameters related to the electrical output magnitude are clarified. Based on the power generation performance and durability of energy conversion structure under typical road traffic characteristics, the optimal cantilever position and vibration amplitude are determined, which lay the foundation for the development and application of energy harvester in road field. The results indicate that the improved structure has the best power generation performance and durability with the condition of the distance from the piezoelectric material to the fixed end of 7 mm and the vibration amplitude of 4 mm under under typical road traffic conditions. The output voltage of the monolithic energy harvester at 5 Hz vibration frequency is 5.2 V, the output power can reach 3.14 mW, and the power density is 0.0063 mW/mm3. This power level and power density are significantly higher than other mechanisms. The structure will make it possible to co-vibrate with the driving, and the structural parameters avoid the misunderstandings of traditional designs that only the power generation performance is valued and the durability can be ignored, which make the structure can be used for collecting electric energy in pavement.

Progress in Piezoelectric Material Based Oceanic Wave Energy Conversion Technology

Recently, electrical engineers are paying great attention to develop oceanic wave energy conversion technologies based on the piezoelectric materials because of their excellent conveniences. Piezoelectric oceanic wave energy converters (OWECs) have several benefits over the others such as its small size, lightweight, no requirement of using intermediate device as well as having less negative impacts on the oceanic environment. Various review and research papers focus on the piezoelectric devices, their operation and application for oceanic energy conversion. But, to the best of the authors' knowledge, none of the existing research or review papers present detailed scheme of piezoelectric device based power generation covering all the relevant topics as depicted in this review. This article focuses different aspects of piezoelectric device based oceanic wave energy conversion technology including prospect, historical development, classification, operating principle, configuration, arrangement, model, processing, post-processing, and their test setups. In addition, technical challenges, future direction of research and critical review are also illustrated. It is assumed that, this article would play a significant role for the future development of piezoelectric OWECs and the researcher working in this field.

Design of High Efficiency Controller for Wide Input Range DC-DC Piezoelectric Transformer Converter

Owing to the increasing demand for low-power electronic devices, the need for miniaturized, light-weight power supplies with a high power density is growing. A piezoelectric transformer, which is a mechanical resonance-based power transformer, can meet these requirements. However, piezoelectric transformers are based on mechanical resonance, and the resonance characteristics depend on the output current, temperature, and other parameters. Thus, their efficiency may rapidly reduce with changes in the resonance characteristics under specific load and temperature conditions. Therefore, this study proposes a technique that estimating the optimal frequency by using the measurements of the input voltage and current phase difference of the piezoelectric transformer and regulating the output voltage using the duty cycle. Modeling and control system analyses are performed to address the control interference problem caused by the plurality of control variables and control outputs. To demonstrate the proposed technique, a 40 W prototype hardware device is developed. The efficiency improvement is confirmed, and the analysis is validated.

Improvement of the automated seismic and acoustic monitoring system “Prognoz-ADS” main elements

The results of theoretical and experimental studies have established the need to improve and modernize the highly sensitive piezoelectric resonant type PeA12 converters used in the seismic monitoring system, which have been successfully used for more than 30 years in the rock mass at a number of rockburst hazardous mines. The main problem of the accuracy measurement by the geophone PeA12 (and other models based on it) is due to the presence of several resonances in the operating frequency band. The developed upgraded model of the AP2088 converter has successfully passed industrial testing as part of the automated monitoring system “Prognoz-ADS” at rockburst hazardous mine. During the test period (more than 1 year), seismoacoustic events were registered and verified in the rock mass, including rock burst and shocks in the rock mass. Thus, the use of highly sensitive (u10 V/m•s-2) piezoacoustic converters AP2088 as part of the automated system provides registration of acoustic emission in the rock mass in the frequency range from 0.1 to 10 kHz with the energy of seismic events from 10 to 106 J, which will increase the reliability of the forecast of geodynamic phenomena and technogenic seismicity in the control zone of the system.

The simulation analysis of piezoelectric transducer with multi-array configuration

Low frequency energy harvesting using piezoelectric is one of promising method on harvesting energy from a free source. This method offered powering low load and remote device application. However, due to its nature which is inconsistency in providing the magnitude of input, specifically in low frequency harvesting, better solution to stable up and increase the converted output is explored widely. There are a few parameter that influences in the piezoelectric output generation. These parameter includes the type of piezoelectric, piezoelectric array configuration, AC-DC converter and etc. The types of the piezoelectric used in this project are the circular piezoelectric. When there is a force (motion) exerted on the piezoelectric disk, electrical charge was produced which initiated the energy conversion. In this research, the configuration of array connection for piezoelectric were investigated. The system is tested with different load configuration in a range of 10 kΩ to 1 MΩ. The design and development of the piezoelectric array variant were series (S), parallel(P), series parallel (SP) and parallel-series (PS). The observation emphasized on finding the best types of piezoelectric array configuration in producing optimum output of the harvested power. The simulation part consists of designing, simulating and analysing the result are done by using PSIM software. For validation of the simulation result, the implementation design of the hardware prototype that supplies pressure to piezoelectric have been done. In conclusion, a proper implementation of piezoelectric array configuration will produce optimum power output which can fulfil the minimum requirement of energy for powering low load device.

Preparation and characterization of flexible PVDF-HFP film for piezoelectric applications

We report on the preparation of electroactive β-phase in polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) without any electrical poling treatment. The PVDF-HFP film with various mass fractions (wt%) of magnesium chloride hexahydrate salt (MgCh∼6H2O) was fabricated by a solution casting technique. The morphological, mechanical, structural and dielectric properties were investigated. Results founded that the PVDF-HFP composite films show a large number of micro-pores on the top surface as a sponge-like structure. The Young’s modulus and crystallinity values tend to be linearly decreased with the MgCh2⋗6H2O concentration leading to enhance flexibility. The largest β-phase fraction of 87.2% is found in the composite with 1 wt% MgCh2⋗6H2O filler. The obtained value is 4 times higher than the value of unfilled PVDF-HFP. Moreover, the maximum value of dielectric constant is about 19.2 at 10 Hz for 4 wt% MgCh2⋗6H2O filler. Therefore, the modified composites with the excellent flexibility, dielectric constant and β-phase may be a promising material for applications in the field of piezoelectric energy conversion.

Piezoelectric energy conversion by lead-free perovskite BaTiO3 nanotube arrays fabricated using electrochemical anodization

Synthesis approaches for diverse morphologies of 1D piezoelectric ceramic nanomaterials are still challenging to investigate nanoscale properties and applications. In this work, we demonstrated a vertically grown barium titanate (BaTiO3; BT) nanotube (BT NT) arrays fabricated using optimized electrochemical anodization and hydrothermal reaction. The centimeter-scale synthesized BT NT arrays with a high aspect ratio of up to 300 showed the complete perovskite crystal structure and the notable piezoelectric coefficient of ~180 pm·V−1. A single BT NT-based piezoelectric device was fabricated on a flexible plastic substrate using a highly controlled focused ion beam-assisted method. The single BT NT device produced a piezoelectric voltage of ~150 mV and a current of ~3 nA when the NT was mechanically stimulated by bending and releasing, which are higher than previously reported values for 1D piezoelectric nanoscale materials. Finally, a flexible piezoelectric energy harvester (f-PEH) was achieved using vertically grown BT NT arrays with an elastomer as a vertically aligned nanocomposite; its generated maximum open-circuit voltage and short-circuit current were ~1.0 V and ~20 nA, respectively. The approach in this study can propose the vision for more advanced 1D piezoceramic nanomaterials and future piezoelectric nanodevices.

A New Non-Isolated Low-Power Inductorless Piezoelectric DC–DC Converter

We present a new non-isolated low-power inductorless piezoelectric resonant converter. The piezoelectric material is used as an energy storage element like an inductance in a classical buck–boost power electronic converter. As opposed to most existing piezoelectric converters, the proposed topology enables to dynamically adjust the output power and ratio keeping a high efficiency for a large range of output powers and for a large range of conversion ratios taking advantage of piezoelectric high-quality factor and achieving zero-voltage switching. A theoretical analysis of the step-up converter using an energetic approach is introduced and enables a fast and reliable predesign of the piezoelectric component. This analysis is in perfect agreement with the simulation model performed on MATLAB/Simulink. For a given piezoelectric resonator both analytical and simulation models provide very high efficiencies for different output powers. The converter is tested experimentally with a 10 V input voltage using the piezoelectric radial resonance mode. An efficiency higher than 98% for a 160 mW power conversion is achieved, decreasing slowly to 78% at 1.4 W. For a large range of voltage gains, the efficiency remains higher than 90% up to an output power of 750 mW. The experimental results are in perfect agreement with the theoretical analysis until 500 mW.

270-degree arc-shaped piezoelectric energy converter in uniflow fluid environment

Energy harvesting in uniflow fluid environment aims at ambient energy that can be used in water environment for monitor equipment. In this paper, we focus on coupling both bending vibration and torsional vibration to gain better power generation. A novel structure of energy converter(arc-shaped) was designed and manufactured. Meanwhile the influence of vibrator with and without a pelvic fin was tested. Mathematical analyse due to vibration phenomenon and experimental result are reported. The 270-degree arc-shaped ring size piezoelectric ceramic is verified capable of producing an effective voltage over 10 V with the power of 0.5 mW.