Pyroelectric Generator Research Articles

Harvesting heat energy from hot/cold water with a pyroelectric generator

Waste heat has been regarded as one of the most important renewable and green energy sources, and its widespread reclamation could help to reduce the negative impacts of global warming and the energy crisis.

Room-temperature ABX3-typed molecular ferroelectric: [C5H9–NH3][CdCl3

Reaction of CdCl2 with cyclopentylamine in the presence of aqueous HCl affords an ABX3-typed perovskite structure compound [C5H9–NH3][CdCl3] (1). Above 300 K, it is in a paraelectric phase with a centrosymmetric space group Cmcm, while below 300 K it has a noncentrosymmetric space group Cc, corresponding to a ferroelectric phase. The temperature-dependent dielectric constant shows a peak at about 300 K with a 12-fold enhancement which is confirmed by differential scanning calorimetry. The normalized pyroelectric and second-harmonic generation effect as functions of temperature are almost overlapped, probably indicating that the trends with temperature basically satisfy the Landau phenomenological theory, revealing a symmetry-breaking occurrence. The ferroelectricity, a spontaneous saturation polarization approximately reaching 1.7 μC cm−2, is further confirmed by piezoresponse force microscopy.

Improving Pyroelectric Energy Harvesting Using a Sandblast Etching Technique

Large amounts of low-grade heat are emitted by various industries and exhausted into the environment. This heat energy can be used as a free source for pyroelectric power generation. A three-dimensional pattern helps to improve the temperature variation rates in pyroelectric elements by means of lateral temperature gradients induced on the sidewalls of the responsive elements. A novel method using sandblast etching is successfully applied in fabricating the complex pattern of a vortex-like electrode. Both experiment and simulation show that the proposed design of the vortex-like electrode improved the electrical output of the pyroelectric cells and enhanced the efficiency of pyroelectric harvesting converters. A three-dimensional finite element model is generated by commercial software for solving the transient temperature fields and exploring the temperature variation rate in the PZT pyroelectric cells with various designs. The vortex-like type has a larger temperature variation rate than the fully covered type, by about 53.9%.The measured electrical output of the vortex-like electrode exhibits an obvious increase in the generated charge and the measured current, as compared to the fully covered electrode, by of about 47.1% and 53.1%, respectively.

Modeling and Simulation for PVDF-based Pyroelectric Energy Harvester

Energy harvesting technology allows the capturing of unused ambient energy such as solar, wind, thermal, strain and kinetic, energy of gas and liquid flows which is then converted into another form of usable energy. This paper focuses on the thermal-electrical energy harvesting based on pyroelectric effect. Pyroelectric materials generate a voltage, when subjected temperature variation. The pyroelectric polyvinylidene fluoride (PVDF) films were fabricated and characterized for pyroelectric and dielectric parameters. Using the foregoing parameters, the energy-harvesting capacity has been theoretically explored by capturing thermal energy available in the environment of Huntsville (pavement), Saudi Arabia (ambient) and MARS (ambient). The predicted maximum cumulative voltage by the end of a 300 hours cycle is approximately 0.13, 0.7 and 7.7 volts for Huntsville and Saudi Arabia and MARS, respectively for the PVDF based 10 cm2 pyro-elements. The results indicate that the electrical energy harvesting via pyroelectricity holds promise for powering autonomous low-duty electric devices. Furthermore, the mathematical modeling and numerical simulations can be helpful in designing of pyroelectric micro-power generators.

A stochastic principle behind polar properties of condensed molecular matter

A statistical mechanics view leads to the conclusion that polar molecules allowed to populate a degree of freedom for orientational disorder in a condensed phase thermalize into a bi-polar state featuring zero net polarity. In cases of orientational disorder polar order of condensed molecular matter can only exist in corresponding sectors of opposite average polarities. Channel type inclusion compounds, single component molecular crystals, solid solutions, optically anomalous crystals, inorganic ionic crystals, biomimetic crystals and biological tissues investigated by scanning pyroelectric and phase sensitive second harmonic generation microscopy all showed domains of opposite polarities in their final grown state. For reported polar molecular crystal structures it is assumed that kinetic hindrance along one direction of the polar axis is preventing the formation of a bi-polar state, thus allowing for a kinetically controlled mono-domain state. In this review we summarize theoretical and experimental findings leading to far reaching conclusions on the polar state of solid molecular matter. “… no stationary state … of a system has an electrical dipole moment.” P. W. Anderson, Science, 1972, 177, 393.

Performance improvement of a micro thermomechanical generator by incorporating Galinstan® micro droplet arrays

In previous research we have demonstrated a micro thermomechanical pyroelectric generator (µTMPG) as an alternative to thermoelectric generators to harvest ambient heat energy. In such a device, a thermal mass oscillates between a hot and a cold side by virtue of the bistability of its mechanical mount, thus generating a temporal thermal gradient over a pyroelectric material in between. The operational frequency as a major factor deciding the power output of the µTMPG is in turn dependent on the thermal contact resistance (TCR) present at the mating regions of thermal mass, hot and cold sides. Hence, we have investigated the incorporation of an array of Galinstan droplets at the mating interfaces to reduce the TCR. These arrays are fabricated by selective deposition of Galinstan on a laser-micromachined silicon substrate. After incorporating such an array the operational frequency of the µTMPG increases by at least 50%.

Pyroelectric crystal D-D and D-T neutron generators

Pyroelectric neutron generators are a recent development utilizing the pyroelectric effect to produce an accelerating electric field and thus enabling creation of small electron and ion accelerators without external high voltage power supply. The principle of operation includes a pyroelectric crystal (LiTaO3 for example) placed in vacuum and simple heating (or cooling) of the crystal to cause a change in polarization. The change in polarization creates free charges on the faces of the clyndrical z-cut crystal and due to its small capacitance this creates a high potential between one crystal face to the other which is placed at ground potential. To produce neutrons the crystal is placed in low pressure deuterium gas and when the crystal is heated or cooled it ionizes the gas and accelerates deuterium ions towards a deuterated or tritated target. A configuration with two crystals can double the acceleration potential and thus increase neutron production. When operating such a device x-rays with energy over 200 keV about 105 neutrons per heating cycle can be produced. Research is focused on improving the neutron yield, the emission reproducibility, and shortening the heating cycle. Neutron generators based on this technology can be made small portable and relatively cheap compared to sealed tube technology. Further development is needed in order to increase the neutron yield closer to the theoretical limit for a specific crystals size.

X‐Ray fluorescence as an assay tool for musculoskeletal nutrition animal research

XRF techniques are well established for the measurement of the presence of lead and heavy metals in osseous tissue. The advent of compact pyroelectric crystal x‐ray generators and silicon drift detectors presents a new opportunity for nutrition research that studies muscular, vascular and epithelial tissue. We compare the measurable ratios of Fe/K, Fe/Ca, and Fe/Cl in different bovine muscle tissues to establish a baseline feasibility study in preparation for in‐vivo measurements. The low power and portability characteristics of new technology XRF systems make it possible to examine epithelial tissue characteristics of animals in‐vivo. Limited initial calculations and models with backscattered x‐rays utilizing non‐imaging optics indicate promise. Non‐imaging optics are used to increase the effective collecting area of the spectral detection system in the backscatter configuration. We propose the concept that strategically selected ion ratios in muscle and vascular tissues can aid in quantifying “nutritional health” in laboratory animals. We acknowledge institutional support.

A Bimetallic Micro Heat Engine for Pyroelectric Energy Conversion

Abstract We present a novel concept of electric power generation from a spatial temperature gradient, achieved by integrating pyroelectric generators (PEGs) into a self-oscillating micro heat engine. The micro heat engine moves the PEGs between a hot and cold reservoir, thus bringing them in an alternating contact with a higher and lower temperature. By their pyroelectric nature, the PEGs convert this periodic temperature variation into electrical energy. The micro heat engine is fabricated from a 280 μm thick bimetallic strip and the PEGs from a 250 μm thick PZT sheet. At an oscillation frequency of 0.19 Hz the device generates 4.4 μW of electrical power from a 96 K temperature difference.

A self-sustaining micro thermomechanic-pyroelectric generator

Pyroelectric generators (PEGs) can be used for thermal energy harvesting and present a potential alternative to thermoelectric generators. However, in contrary to thermoelectric generators, the PEG principle requires thermal transients to stimulate the conversion process. Such suitable thermal transients are rare in nature, hindering the deployment. In this paper, we present a micro thermomechanic-pyroelectric energy generator (μTMPG) that converts a stationary spatial thermal gradient into the required transient temperature profile across the PEG. The measured power output of the μTMPG is 3 μW from a temperature difference of 79.5 K. However, with an optimized design, a power output of 39.4 mW is estimated for the same temperature difference.

Solar micro-energy harvesting with pyroelectric effect and wind flow

This article proposes to harvest solar micro-energy using the pyroelectric effect and low wind flow. The basic concept was presented and validated by laboratory experiments with controlled airflow. The measured temperature variation, subject to the intensity of radiation and wind speed in the environment was demonstrated to reach 16 °C. The time variation of temperature was 0.53 °C s −1 with the speed of airflow at 2 ms −1. The power density with PZT as the pyroelectric material was 4.2 μW cm −3 in laboratory conditions. Both the thermodynamic model and electric model of the pyroelectric generator were established, and a numerical procedure was developed to predict the system performance which was proven to be reliable. The characteristics of such an energy harvesting system were analyzed in detail by simulation, and the results indicated that the proposed idea is promising.

Organic-inorganic compounds with strong nonlinear optical properties based on 2,4,6-trimethylpyridinium and tetrahedral BF4−networks

A different organic-inorganic crystal---[2,4,6-trimethylpyridinium][BF${}_{4}$]---of nonlinear optical properties at room temperature was synthesized and characterized. The compound is built up of the organic [2,4,6-trimethylpyridinium] cations incorporated into inorganic, tetrahedral BF${}_{4}$ anions. It crystallizes at room temperature in the polar space group $\mathit{Pmn}{2}_{1}$, and undergoes three first-order phase transitions at [cooling (heating)] 241 (245) K, 297 (328) K, and 389 (406) K. The lowest temperature ferroic phase transition (ferroelastic; $\mathit{mm}2\ensuremath{\rightarrow}m$ type) is related to the significant pyroelectric effect. The compound was studied by single-crystal x-ray diffraction at several temperatures, using thermal (differential scanning calorimetry and thermogravimetric analysis) methods and dielectric spectroscopy. The piezoelectric, pyroelectric, and second-harmonic generation (SHG) properties were determined. Density-functional theory calculations in two stable phases are given. The [2,4,6-trimethylpyridinium][BF${}_{4}$] crystal exhibits a SHG efficiency of 1.7 times that of KDP. The mechanism of structural phase transitions in the title compound is discussed.

Pyroelectric response of ferroelectric nanowires: Size effect and electric energy harvesting

The size effect on pyroelectric response of ferroelectric nanowires is analyzed. The pyroelectric coefficient strongly increases with the wire radius decrease and diverges at critical radius Rcr corresponding to the size-driven transition into paraelectric phase. Size-driven enhancement of pyroelectric coupling leads to the giant pyroelectric current and voltage generation by the polarized ferroelectric nanoparticles in response to the temperature fluctuation. The maximum efficiency of the pyroelectric energy harvesting and bolometric detection is derived, and is shown to approach the Carnot limit for low temperatures.

Intense pulsed neutron emission from a compact pyroelectric driven accelerator

Intense pulsed D–D neutron emission with rates of >1010 n/s during the pulse, pulse widths of approximately hundreds of nanoseconds and neutron yields of greater than 10 000 per pulse, are demonstrated in a compact pyroelectric accelerator. The accelerator consists of a small pyroelectric LiTaO3 crystal that provides the accelerating voltage and an independent compact spark plasma ion source. The crystal voltage versus temperature is characterized and compares well with theory. Results show neutron output per pulse that scales with voltage as V∼1.7. These neutron yields match a simple model of the system at low voltages but are lower than predicted at higher voltages due to charge losses not accounted for in the model. Interpretation of the data against modeling provides understanding of the accelerator and in general pyroelectric LiTaO3 crystals operated as charge limited negative high voltage targets. The findings overall serve as the proof of principle and basis for pyroelectric neutron generators that can be pulsed, giving peak neutron rates orders of magnitude greater than previous work and notably increase the potential applications of pyroelectric based neutron generators.

X-ray diamond detectors with energy resolution

Polycrystalline diamond detectors with energy resolving capability of the impinging beam were realized and tested by using a miniature pyroelectric x-ray pulse generator. Microstrip structures were defined by photolithography aimed to reduce parasitic capacitances and to perform characterization measurements in a sandwich configuration. Leakage currents as low as 20pA at 500V were measured on a 270μm thick device. Pulse height distributions were carried out around TaLα (8.14keV) and CuKα (8.05keV) characteristic lines of the source. Energy resolution at 200V was found equal to 9% with an increase to 11% at 500 V. When the bias was increased to the maximum voltage the sample shows an Ohmic behavior.

Applications of pyroelectric particle accelerators

The discovery of pyroelectric X-ray generation in 1992 by Brownridge has led to a recent surge of interest in the use of the pyroelectric effect as a means of producing useful radiation. By heating or cooling a pyroelectric crystal such as lithium tantalate (LiTaO3) in a vacuum, a potential on the order of 100kV can be generated. This potential is great enough to eject electrons from the crystal for the production of characteristic or bremsstrahlung X-rays, or to cause field ionization near a tip mounted to the crystal. By using the combined fields of two polarized crystals, the acceleration potential can be doubled, with one crystal acting as a particle emitter and the other crystal serving as a target. Such a paired-crystal system was used to generate X-rays with energies of greater than 200keV, and can be used to fluoresce the K shell of thorium (Z=92). An alternative use of pyroelectric sources is the field ionization of a dilute gas. If the positively-charged crystal is used to ionize a deuterium gas, and the target crystal is coated with deuterated target, the deuterium ions can be accelerated into the target at high enough energy to cause D–D fusion. Results verifying the production of D–D fusion neutrons from a pyroelectric source will be presented. Future applications of pyroelectric accelerator technology, such as the use of the electron beam for materials testing, will also be discussed.

Pyroelectric conversion—Effects of P(VDF–TrFE) preconditioning on power conversion

Large amounts of low-grade heat are emitted from various industries and wasted into the environment. This heat energy can be used as a free source for pyroelectric power generation. We first discuss the principle of pyroelectric conversion based on the differences in crystal structures of copolymer. Then we discuss the pyroelectric conversion of waste heat using copolymer films containing 60% vinylidene fluoride (VDF) and 40% trifluoroethylene (TrFE) and the impact of the preconditioning of the pyroelectric films on the net power output. We discovered that the pre-polarization (poling) of pyroelectric films has a significant beneficial effect by decreasing internal conduction during power conversion. This in turn increased net power output. We were able to reach 95–165 J/L of copolymer used in each cycle even including the internal leakage. We also showed it is critically important to operate the power conversion near the phase transition where electron discharge is the highest.

Electron and positive ion acceleration with pyroelectric crystals

The phenomenon of pyroelectric electron emission has been employed to develop miniature x-ray sources, such as the Cool-X by Amptek (www.amptek.com/coolx.html). The source strength of a pyroelectric x-ray generator is dependent on the emitted electron energy and current. Similarly, the source strength of a pyroelectric neutron generator will be dependent on the energy and production rate of deuterium ions in the fill gas. This paper summarizes our results in experiments directed toward creating high-energy electrons and positive ions with a pyroelectric source. Single-crystal sources are shown to produce positive ions with energies of up to 98keV and electron energies of up to 143keV. X-ray spectra are presented as proof that a paired-crystal source can increase electron energy to at least 215keV. In addition, we offer independent verification of the “bunched” electron emission effect observed by [Brownridge et al., Appl. Phys. Lett. 78, 1158 (2001)].

X-ray fluorescence analysis at mg l−1level with an X-ray source powered by a dry battery

An X-ray generator with a pyroelectric crystal is used for trace quantitative analysis for the first time. Standard solutions are analyzed with this X-ray generator after preconcentration with sodium diethyldithiocarbamate (NaDDTC) or ion-exchange resins. Mn, Pb, Ba, Co, I, Cr and Br at mg l−1 or sub-mg l−1 level can be detected by measurement of filter paper or resins. The minimum detection limit of Mn is 0.1 mg l−1 with the chelate extraction method, and that of Co is 0.3 mg l−1 with the ion-exchange method. The calibration curves of Pb, Ba, and Cr are approximated to straight lines by using Mn and I as internal standards. The preconcentration method makes it possible to estimate the concentrations of trace elements in aqueous solutions by using a pyroelectric generator driven by a dry battery, even though the X-ray output is a few orders of magnitude lower than a conventional X-ray tube. The pyroelectric generator as a portable X-ray source can be used for on-site trace analysis.

Development of a microreactor as a thermal source for microelectromechanical systems power generation

An alumina ceramic 12.5×12.5×5.0 mm microreactor was constructed using a modified stereolith-ography process. The design was based on a “Swiss roll” concept of double spiral-shaped channels to facilitate a high level of heat transfer between the reactants and combustion products and wall surface contact of the flow through the microreactor body. Self-sustained combustion of hydrogen and air mixtures was demonstrated over a wide range of fuel/air mixtures and flow rates for equivalence ratios from 0.2 to 1.0 and chemical energy inputs from 2 to 16 W. Depositing platinum on gamma alumina on the internal walls enabled catalytic ignition at or near room temperature and self-sustained operation at temperatures to 300°C. Catalyst degradation was observed at higher operating temperatures and reignition capabilities were lost. However, sustained operation coul be obtained at wall temperatures in excess of 300 °C. apparently stabilized by a combination of surface and gas-phase reaction phenomena. A global energy balance model was developed to analyze overall reactor performance characteristics. The reactor design and operating temperature range have potential applications as a heat source for thermoelectric and pyroelectric power generation at small scales compatible with microelectromechanical systems applications.