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cited By 2; International audience; We deal with the thermal energy which is one of the ambient energy sources surely exploitable, but it has not been much interest as the mechanical energy. In this paper, our aim is to use thermal energy and show that it's an important source for producing the electrical energy through pyroelectric effect which is the property of some dielectric materials to show a spontaneous electrical polarization versus temperature. In this context, we present a concept to harvest a thermal energy using infrared rays and pyroelectric effect. The pyroelectric material used in this work can generate an electrical voltage when it subjected to a temperature change which will be ensured by the use of infrared lamp. Our experimental results show that the electrical voltage, current and harvested power increased significantly when increasing the area of the pyroelectric element. The experimental results show also that with this simple concept we harvested a heavy amount value of power which will certainly be useful in an extensive range of applications, including sensors and infrared detection. These results shed light on the thermoelectric energy conversion by Ceramic lead zirconate titanate (PZT) buzzer having the pyroelectric property. © 2016 Elsevier B.V. All rights reserved.

The field of waste thermal energy harvesting has experienced significant growth over the past few years. This paper presents an experimental study on thermal radiation to electrical energy conversion using pyroelectric material (PbZrxTi1-xO3 (PZT-5H)). Pyroelectric material was exposed to UV lamp with a constant frequency of 0.5 Hz and another surface of sample was continuously cooled via natural air fan (for generation continuous temporal gradient in material). Maximum value of stored energy was 1.75 µJ across 100 µF without load resistance. Maximum power output was found to be 0.76 µW across load resistance of 3 MΩ and 10 µF.

The purpose of this work is to demonstrate a new simple stand-alone method of characterizing the impedance of a pyroelectric cell. This method utilizes a pyroelectric single pole low-pass filter technique. Utilizing the properties of a pyroelectric single pole low-pass filter technique, a known input voltage is applied and using simple equations, capacitance Cp and resistance Rp at a frequency range of 1 mHz to 1 Hz can be calculated. For verification purposes, an LCR meter and an impedance analyzer were exploited at 10 and 100 Hz, respectively. Results showed that Rp values for two materials, lead zirconate titanate-5A and polyvinylidene difluoride, were within 8%, and Cp values were within 7.5%. In addition, to verify the importance of the impedance values in energy harvesting applications, output power was measured with varying impedance values. The optimal load resistances for polyvinylidene difluoride and lead zirconate titanate-5A were consistent with the measured pyroelectric impedance at the particular heat range with 10.9% and 1.4%, respectively. The pyroelectric single pole low-pass filter method presented here demonstrates that for pyroelectric materials the impedance depends on two major factors: (1) average working temperature and (2) the heating rate. Neglecting these two factors can result in inefficient and unpredictable behavior of pyroelectric materials when used in energy harvesting applications.

Pyroelectric materials have been utilized in several ways to harvest waste thermal energy using pyroelectric effect. One basic requirement for pyroelectric materials to work is the presence of temporal temperature variations, i.e., time gradients of temperatures. For practical thermal energy harvesting applications using pyroelectric effect, Olsen cycle has the highest adoption rate amongst various cycles for it has the highest energy density. In accordance to theoretical calculation, an increase in the energy density can be made possible through broadening the electric field span, in turn necessitates sufficiently high dielectric breakdown strength that the pyroelectric materials should have. This chapter serves to offer an overview on progress in pyroelectric effect and pyroelectric materials that have been employed to harvest waste thermal energies.

This review covers energy harvesting technologies associated with pyroelectric materials and systems. Such materials have the potential to generate electrical power from thermal fluctuations and is a less well explored form of thermal energy harvesting than thermoelectric systems. The pyroelectric effect and potential thermal and electric field cycles for energy harvesting are explored. Materials of interest are discussed and pyroelectric architectures and systems that can be employed to improve device performance, such as frequency and power level, are described. In addition to the solid materials employed, the appropriate pyroelectric harvesting circuits to condition and store the electrical power are discussed.

Harvesting energy from such renewable energy resources as solar, vibration, thermal and magnetism in microelectromechanical systems has gained much attention from researchers in recent decades. From among these resources using piezoelectrics and pyroelectrics due to their ease in the design and implementation has attracted more attention. In this paper, a new harvesting technique has been considered, which uses piezoelectrics and pyroelectrics simultaneously. The concept of method and theoretical analysis for hybrid energy harvesting method is presented and then by exerting vibration and heat forces, the average harvested power is determined. This investigation has been done by considering PZT and PMN-0.25PT ceramics as smart elements. Different strategies for switching have been considered in synchronized switch harvesting method and then the best switching between these three strategies—switching on voltage, mechanical displacement or temperature amplitude—is introduced. In each condition, the positive influence of hybrid method has been as compared with piezogenerators for both smart elements. The effect of four important parameters—temperature amplitude, vibration amplitude, inversion coefficient, and equivalent load resistance—is examined. The most effective switching method and material are proposed in the final part of the paper.

Recently, scientists discovered that relaxor-based ferroelectric single crystals, such as (1-x)Pb(Mg1/3Nb2/3)O3 -xPbTiO3 (PMN-xPT, or PMNT) single crystals, exhibit extra-high pyroelectric responses. They are promising candidates for optical power detectors in broad bandwidth at ultraviolet, visible and infrared wavelength.To fabricate high performance infrared detectors with relaxor-based single crystals, the related readout circuit was investigated to increase signal-to-noise ratio, and 8×1 CMOS readout circuit is fabricated to gain very weak current, which provides a solution for uncooled large focal plane arrays devices based on relaxor-based single crystals.

The development of low-cost, uncooled (room temperature operation) thermal detector arrays has been accelerating in recent years and now commercial products are becoming widely available. As costs come down and volumes rise, these devices are entering the consumer marketplace, providing everything from sophisticated security and people-monitoring devices to hand-held thermal imagers for preventative maintenance and building inspection. Two technologies have established significant market shares in uncooled thermal detector array products. These are resistive microbolometers and pyroelectric ceramics. To address the true mass market, the pyroelectric arrays offer significant cost advantage. In this paper, recent developments in a variety of products based on pyroelectric ceramic arrays are described and their performance and applicability are compared and contrasted with competing technologies. This includes the use of low-element-count arrays for applications in people counting and queue measurement, and the drive for cost-effective imaging arrays for mass-market thermal imaging. The technical challenges in materials production, device development, and low-cost manufacture are reviewed and future opportunities and challenges are outlined.

A pyroelectric phenomenon is a manifestation of the temperature dependence of spontaneous polarization on certain solids, which can be either single-crystal or poly-crystalline aggregates. When the temperature of the material is slightly increased, the electrical polarization of the material changes, and voltage can be measured between certain faces of the pyroelectric sample. Conversely, if the temperature of the material is lowered by the same amount, the same magnitudes of polarization and voltage are found with the signs reversed. Thus, pyroelectric materials provide a means of producing infrared (IR) detectors that conveniently operate at room temperature. In this chapter, a number of fundamental aspects of pyroelectricity are described regarding its application in IR detection and energy harvesting. Pyroelectric materials form a subgroup of piezoelectrics, while ferroelectrics form a subgroup of pyroelectrics. Relationships between crystal structure and relevant properties are discussed along with important candidate materials and their applications.

Properties of a new type of pyroelectric ceramic structure containing a layer of known porosity laminated between two dense layers, to form a functionally gradient material (FGM), are reported. The combination of theoretical models for pyroelectric, dielectric, and thermal properties gave a model for the pyroelectric voltage figure of merit (F v ) in good agreement with experiment, which had shown a 20% improvement for an introduced central layer porosity of 27%. Preliminary pyroelectric responsivity measurements on FGM infrared detectors indicated an even better improvement. It is postulated that this is due to the porous layer acting as a thermal barrier in the structure.

Modern CPUs generate considerable wasted heat due to increased power dissipation from high-performance computation. Lots of research effort has extensively focused on using thermoelectric generators (TEGs) to harvest CPU waste heat to increase overall system energy efficiency. To harvest waste heat using TEGs requires a significant temperature differential between the processor as a heat source and the heat spreader/heat sink, as well as a high heat flow. However, the heat-to-electricity conversion efficiency is typically limited to 15 to 20 percent, due to large heat conductivity, low Seebeck coefficient, and low figure of merit of TEGs. In addition, TEGs on a CPU could significantly increase CPU junction temperature compared to the baseline CPU temperature due to its high thermal resistance. Contrary to using TEGs to harvest waste heat from a fixed, spatial temperature differential, this paper presents an approach to harvest CPU waste heat using pyroelectric (PE) materials from the time-varying, temporal temperature differential that is common in current processors. PE materials can generate electricity when subjected to a temporal temperature gradient. The operation of PE materials is distinctly different from TEGs and they have the following advantages. First, the theoretical efficiency is up to 50% using thin films. Second, the overall optimization of PE material is easier than thermoelectric material, since the conversion ratio, the ratio of net harvested energy divided by the heat taken from the hot reservoir, of PE material is independent of the material properties, whereas that of TEG is highly dependent on material properties. Although PE material is also a long-researched energy harvesting material, it is less explored by researchers compared to TEG in the application domain of processor waste heat management. In this paper, we review current PE materials in terms of pyroelectric coefficient and thermal conductivity, and also investigate the harvested power generation from CPU waste heat in a modern computing system.

A simplified photopyroelectric (PPE) configuration that allows the simultaneous determination of the temperature dependent thermal and pyroelectric parameters of pyroelectric materials is described. The thermal parameters (thermal diffusivity, conductivity, effusivity and volumic specific heat) are obtained from the analysis of the phase of the complex photopyroelectric (PPE) signal generated from the pyroelectric sample itself and measured for two different modulation frequencies. The pyroelectric coefficient is obtained from the amplitude of the signal. Experimental results on thermal and pyroelectric parameters of LiTaO 3 single crystal in the 25°C-70°C temperature range are reported.

The photopyroelectric calorimetry, in the standard (back) configuration, is applied in order to measure the thermal parameters of some pyroelectric materials. It is demonstrated that the method is able to simultaneously measure the thermal diffusivity and effusivity of a pyroelectric material. The information is obtained via a frequency scan of the amplitude or the phase of the pyroelectric signal; the measurements need no calibration. A combined amplitude-phase procedure, at a single frequency, leads to the same results. In the mean time, if the thermal parameters of the pyroelectric sensor are known, one can get the thermal effusivity of a sample acting in the experimental cell as a substrate. Investigations and theoretical simulations were performed on a well known pyroelectric material, LiTaO3, with various liquid substrates.

Pyroelectric materials have been fabricated in bulk single crystals, ceramic (polycrystalline), films, and composite forms. This chapter briefly reviews and describes all of the major and relevant techniques for processing key materials.

Pyroelectrics form a very broad class of materials. Any material which has a crystal structure possessing a polar point symmetry—i.e. one which both lacks a centre of symmetry and has a unique axis of symmetry—will possess an intrinsic, or spontaneous, polarisation and show the pyroelectric effect. The pyroelectric effect is a change in that spontaneous polarisation caused by a change in temperature. It is manifested as the appearance of free charge at the surfaces of the material, or a flow of current in an external circuit connected to it. The effect is a simple one, but it has been used in a range of sensing devices, most notably uncooled pyroelectric infra-red (PIR) sensors, and has thus come to be of some engineering and economic significance, enabling a wide range of sensing systems, ranging from burglar alarms through FTIR spectroscopic instruments to thermal imagers.

Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, an existing pyroelectric energy converter can only operate at low frequencies due to a relatively small convective heat transfer rate between the pyroelectric materials and the working fluid. On the other hand, energy transfer by thermal radiation between two semi-infinite solids is nearly instantaneous and can be enhanced by several orders of magnitude from the conventional Stefan–Boltzmann law as the gap separating them becomes smaller than Wien’s displacement wavelength. This paper explores a novel way to harvest waste heat by combining pyroelectric energy conversion and nanoscale thermal radiation. A new device was investigated numerically by accurately modeling nanoscale radiative heat transfer between a pyroelectric element and hot and cold plates. Silica absorbing layers on top of every surface were used to further increase the net radiative heat fluxes. Temperature oscillations with time and performances of the pyroelectric converter were predicted at various frequencies. The device using 60/40 porous poly(vinylidene fluoride–trifluoroethylene) achieved a 0.2% efficiency and a 0.84 mW/cm2 electrical power output for the cold and hot sources at 273 K and 388 K, respectively. Better performances could be achieved with 0.9Pb(Mg1/3Nb2/3)–0.1PbTiO3 (0.9PMN-PT), namely, an efficiency of 1.3% and a power output of 6.5 mW/cm2 between the cold and hot sources at 283 K and 383 K, respectively. These results are compared with alternative technologies, and suggestions are made to further improve the device.

Pyroelectric energy conversion offers a novel, direct energy-conversion technology by transforming time-dependent temperature directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, existing pyroelectric energy converter can only operate at low frequency due to relatively low heat transfer rate between the pyroelectric materials and the working fluid subjected to oscillatory fluid flow between hot and cold sources. On the other hand, energy transfer by thermal radiation between two semi-infinite solids can be enhanced by several orders of magnitude as the gap separating them reduces to subwavelength size thanks to interference and tunneling of electromagnetic waves across the gap. This paper proposes a novel way to harvest nanoscale radiation heat transfer for direct pyroelectric energy conversion of waste heat into electricity. A new device is investigated numerically by accurately modeling nanoscale radiation heat transfer between the pyroelectric materials and hot and cold surfaces. Performance of the pyroelectric converter is predicted at various frequencies. The result shows that rapid energy transfer and higher operating frequency can be achieved to increase efficiency and power density.

The photopyroelectric signal is analyzed in order to simultaneously obtain the thermal diffusivity and effusivity of pyroelectric materials. Two different experimental configurations are described and compared in terms of accuracy and sensitivity. The information is obtained via a frequency scan of the amplitude or the phase of the pyroelectric signal. The methods have been used for the measurement of thermophysical properties of a lead–titanate–zirconate ceramic sample.

A simplified photopyroelectric configuration that allows the determination of the temperature-dependent thermal parameters of pyroelectric materials is described. The procedure is based on a combination of phase and amplitude signal data obtained at a single frequency. Experimental results obtained on the thermal parameters of LiTaO3 single crystal are presented.

Literature data on the characteristics of different types of ferroelectric materials are reviewed together with the results of own studies. The emphasis is made on the performance of these materials in pyrovidicon targets.

An automated system for the pyroelectric imaging of polar substrates has been developed. The principle of operation, details of the optical and mechanical subsystems, and a description of the system hardware, interface, and software for data acquisition and display are given. The automation has made possible routine scans of high resolution and/or large areas of pyroelectric materials, such as LiNbO/sub 3/ and ZnO. Features of the system are highlighted by means of a pyroelectric imaging of proton-exchanged LiNbO/sub 3/, which is an important material for optical waveguides. >

Pyroelectric solar energy harvesting has been a prominent area of research for the past few years. This study is an attempt to compare different pyroelectric materials for harvesting solar energy. Seven different pyroelectric materials including (NH2CH2COOH)3H2SO4 (TGS), Sr0.5Ba0.5Nb2O6 (SBN), Ca0.2(Sr0.5Ba0.5)0.8Nb2O6 (CSBN), Pb(Zr0.5Ti0.5)O3 (PZT), polyvinylidene difluoride (PVDF), BaTiO3 and LiTaO3 were studied and compared using finite-element analysis. SBN was found to be the potential pyroelectric material with the maximum storage voltage of 11.47 V across an optimized load capacitance. SBN was subjected to further analysis, revealing an optimum power output of 4.9 μW at the optimized cycle frequency (0.040 Hz), a load resistance of 50 MΩ and a load capacitance of 4.7 μF, while the stored energy was found to be 576.87 μJ.

Correction for ‘Pyroelectric materials and devices for energy harvesting applications’ by C. R. Bowen et al., Energy Environ. Sci., 2014, 7, 3836–3856.

An understanding of the power that can be harvested from pyroelectric materials and its dependence on material properties, geometry and boundary condition is crucial to the design of energy harvesting devices using these materials. In this paper, simple analytical expressions are developed for ideal voltage, power and power densities as a function of pyroelectric constant, permittivity, surface area, thickness, temperature variation and rate of change for unclamped samples. Experiments are performed to specifically study the effect of geometry and are compared with theoretical predictions.Copyright © 2009 by ASME

An improved quantitative pyroelectric characterization system has been developed in an effort to more thoroughly investigate the dynamic pyroelectric response of selected materials at particular temperatures of interest, such as at transition, or to study electrical aging effects. Specifically, the system is capable of measuring pyroelectric current responsivity of a wide variety of materials ranging from ferroelectric ceramics to polymers at constant temperature utilizing a modulated heating source technique.' Effectiveness of this system was determined through measurements of lithium tantalate and lithium niobate samples of various geometries. The result of the study was a comprehensive evaluation of dynamic pyroelectric current responsivity of these samples with a particularly good signal-to-noise enhancement for evaluating high noise materials such as polymer gels which are extremely difficult to evaluate using other techniques. These measurements revealed a significant dependence of the pyro...

The results of the study of TGS group crystals, physical properties as well as characteristics of pyroelectric vidicons with the targets made of the crystals are presented.

The design of multichannel data acquisition computer controlled setup for the pyroelectric measurement in a wide range of DC bias and ambient temperatures (280-350 K) under different conditions of pyroelectric currents is presented. The ceramic samples of 0.9 Pb Mg1/3Nb2/3O3 - 0.1 PbTiO3 (PMN-PT) solid solutions prepared in Ioffe Physico-Technical Institute were selected for measurements. The figures of merit of this ceramics calculated using the measured dielectric and pyroelectric data are presented in comparison with other pyroelectric materials and IR detectors.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The pyroelectric effect is the phenomenon whereby a change in temperature in a polar dielectric engenders a change in its electrical dipole moment. It can be used to create a flow of current in an external circuit connected to a piece of the material. The effect has been known for many years but it is only since about 1960 that its technological applications have been seriously considered. These have been almost entirely in the field of the detection of electromagnetic radiation, especially in the two “atmospheric window” infrared (IR) bands of 3-5 pm and 8-14 pm. The ambient temperature operation of pyroelectric detectors, leading to low power consumption, low cost, compactness and lack of any requirement for logistical support in the form of cooling fluids or high-pressure gas, gives them a number of important advantages over photon detectors used in these wavebands, such as MCT or InSb. These must be cooled to cryogenic temperatures to obtain optimum performance. Hence, pyroelectric detectors have found a huge range of applications in products ranging from fire alarms to intruder detectors, in instrumentation such as gas analysis and laser beam characterization and in military/paramilitary applications such as thermal imaging. Detectors have been demonstrated which work from the visible [1] through the infrared [2] to sub-millimetre [3,4] and millimetre [5] wavelengths. They have also been used at radiation modulation frequencies from a few Hz [2] to many GHz [6].

A general method based on the combination of electrostatic force microscopy with thermal cycling of the substrate holder is presented for direct, nanoscale characterization of the pyroelectric effect in a range of materials and sample configurations using commercial atomic force microscope systems. To provide an example of its broad applicability, the technique was applied to the examination of natural tourmaline gemstones. The method was validated using thermal cycles similar to those experienced in ambient conditions, where the induced pyroelectric response produced localized electrostatic surface charges whose magnitude demonstrated a correlation with the iron content and heat dissipation of each gemstone variety. In addition, the surface charge was shown to persist even at thermal equilibrium. This behavior is attributed to constant, stochastic cooling of the gemstone surface through turbulent contact with the surrounding air and indicates a potential utility for energy harvesting in applications including environmental sensors and personal electronics. In contrast to previously reported methods, ours has a capacity to carry out such precise nanoscale measurements with little or no restriction on the sample of interest, and represents a powerful new tool for the characterization of pyroelectric materials and devices.

This thesis discusses characterization of two ferroelectric materials and the fabrication of bolometers. Potassium tantalate niobate (KTN) and potassium dihydrogen phosphate (KDP) are chosen because they can be optimized for operation near 100K. Chap. 2 reviews the physics underlying pyroelectric materials and its subclass of ferroelectric materials. Aspects of pyroelectric detection are discussed in Chap. 3 including measurement circuit, noise sources, and effects of materials properties on pyroelectric response. Chap. 4 discusses materials selection and specific characteristics of KTN and KDP; Chap. 5 describes materials preparation; and Chap. 6 presents detector configuration and a thermal analysis of the pyroelectric detector. Electrical techniques used to characterize the materials and devices and results are discussed in Chap. 7 followed by conclusions on feasibility of KDP and KTN pyroelectric detectors in Chap. 8.

A simple amplitude method of measuring the pyroelectric coefficient of pyroelectric materials is described. Intense, short-duration (0.4 μs) light pulses generated by a semiconductor laser diode are absorbed at one surface of a thermally insulated sample of pyroelectric material, resulting in thermal pulses in the sample. The time and amplitude characteristics of the resulting charge pulses from the sample are measured using electronics of the type used with semiconductor charged-particle detectors. Theoretical calculations of the charge pulse shapes expected from samples having various assumed volume polarization distributions and measured charge rise times are used to determine optimum time constants for the pulse shaping electronics. These techniques are applied to a number of pyroelectronic samples of polyvinylidene fluoride and lithium tantalate with thickness in the range 9 μm to 1 mm, and area of 0.07 cm 2 and 0.28 cm 2 . The absolute pyroelectric coefficient of the samples is obtained directly from the measured amplitude distribution of the charge pulses, the measured sample reflectivity, and the photon and electronic calibrations for the system. In addition, useful information regarding the polarization distribution in the sample is directly obtained during measurements. The results of these studies are reported and show that the pyroelectric coefficients determined by this method are in good agreement with previously reported values for these materials.

The thermal impulse produced along the path of an ultraheavy nucleus (e.g., uranium) moving in a pyroelectric material is shown to generate a fast electronic current pulse. Detectors have been made utilizing the pyroelectric response of polyvinylidene fluoride and lithium tantalate. The theory behind this new class of charged particle detectors and experimental results are presented. Polyvinylidene fluoride detectors may become useful in large-area space experiments for detection and trajectory determination of ultraheavy nuclei.

An automated system for measuring the pyroelectric properties of materials is described. This system can simultaneously measure pyroelectric coefficients and permittivities eliminating errors introduced in the figures of merit by temperature uncertainties. Results on deuterated triglycine fluoroberyllate (DTGFB) are presented.

Some limitations of materials used in the pyroelectric vidicon are briefly discussed. Details of improved lead germanate derivatives are given and the vidicon performance of some oxide materials is assessed.

Publisher Summary This chapter describes the various aspects of pyroelectric materials for the operation in a hard vacuum pyroelectric vidicon. The pyroelectric vidicon camera has become a well-established device attracting a great deal of interest for thermal imaging in the 8 to 14 μm thermal wave band. The pedestal is generated either as an ion current in a soft tube or by secondary electrons produced on pulsing the beam to anode potential. The tubes are operated with the target stabilized at cathode potential. It has been shown that when operated in this mode, a positive pedestal current must be supplied to the scanned surface of the pyroelectric target in order for the stabilization to be achieved. Unlike a photoconductive tube where the signal charge is always positive, the pyroelectric signal may be of either polarity depending on whether the target temperature is rising or falling. A uniform pedestal is obtained by running the mesh potential at a slightly higher potential than the wall anode, so that it forms a barrier to ions generated by the undeflected beam on the gun side of the mesh. It has been demonstrated that pyroelectric vidicon tube targets prepared from lead germanate single crystals may be operated at cathode potential with a conduction pedestal.

A simple technique is presented to interface pyroelectric materials with Si-substrates, into which sensor array circuitry is integrated. The pyroelectric material is inter-faced with the substrate via a thin dielectric layer. The feasibility of the technique is demonstrated by the realization of a single element infrared sensor.

The authors report on a novel method for producing the noncentrosymmetric structures necessary for the observation of the pyroelectric effect. The Langmuir-Blodgett technique has been used to fabricate ultrathin films consisting of alternate layers of 22-tricosenoic acid and 1-docosylamine. The pyroelectric coefficient has been determined using both static and dynamic detection techniques, is approximately 0.2 nC cm/sup -2/ K/sup -1/ (static value); this value is independent of the film thickness in the range of 11 to 99 monolayers, but increases slightly if a substrate of lower thermal expansion coefficient is used. The results indicate that there is a piezoelectrically induced secondary effect contributing to the overall pyroelectric activity. >

Summary form only given, as follows. Pyroelectric vidicon camera tubes have been developed and their performance has been reported for thermal imaging in the 8-14 micron band. Present tubes operate with a triglycine sulphate (TGS) sensing layer. These tubes possess some undesirable characteristics partly due to the incompatibility of TGS with the vacuum environment and partly due to the method of generating the positive pedestal current required for cathode potential operation. The pedestal is generated either as an ion current in a soft tube or by secondary electrons produced on publishing the beam to anode potential. Both methods may result in a tube of limited lifetime with cathode or target deterioration. This work reports an alternative method of pedestal generation and surveys suitable materials. The pedestal is leaked through the pyroelectric target itself. The conductivity must satisfy both charge storage and pedestal generation. Such materials have been run in a hard vacuum where the magnitude of the pedestal is simply set with the signal plate bias. Thus these materials operate in such a way as to overcome lifetime problems and in addition to provide a direct "plug-in" replacement tube for the photoconductive tube in a standard camera.

Among the various forms of natural energies, heat is the most prevalent and least harvested energy. Scavenging and detecting stray thermal energy for conversion into electrical energy can provide a cost-effective and reliable energy source for modern electrical appliances and sensor applications. Along with this, flexible devices have attracted considerable attention in scientific and industrial communities as wearable and implantable harvesters in addition to traditional thermal sensor applications. This review mainly discusses thermal energy conversion through pyroelectric phenomena in various lead-free as well as lead-based ceramics and polymers for flexible pyroelectric energy harvesting and sensor applications. The corresponding thermodynamic heat cycles and figures of merit of the pyroelectric materials for energy harvesting and heat sensing applications are also briefly discussed. Moreover, this study provides guidance on designing pyroelectric materials for flexible pyroelectric and hybrid energy harvesting.

Since the very recent discovery of ferroic ordering under two dimensional limit, novel devices based on 2D ferroelectricity or ferromagnetism has attracted a lot of interests and are promising for next generation electronic and optoelectronic applications. We find that, below the transition temperature Tc ~320 K, ultrathin CuInP2S6 (CIPS) nanoflakes down to bilayer are still pyroelectric. Changing the temperature will lead to charge modification at the surface of CIPS. 2D pyroelectric nanogenerator is fabricated which can efficiently convert the pyroelectric charges into electrical current. This work will facilitate novel applications of pyroelectric and ferroelectric materials, including pyroelectric devices, thermal sensors, ultrathin nanogenerators and various van der Waals (vdW) heterostructure at room temperature. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version This work was supported by the National Research Foundation Singapore under NRF award number NRF-RF2013-08, Tier 2 MOE2017-T2-2-136, Tier 2 MOE2016-T2-2-153, MOE2015-T2-2-007, Tier 1 RG7/18, Tier 1 RG4/17. X.F.L thanks the support from the Ministry of Science and Technology (2017YFA0205004 and 2016YFA0200700), National Natural Science Foundation of China (21673054 and 11874130), Natural Science Foundation of Beijing Municipality (4182076 and 4184109).

Flexural and longitudinal wave propagation in a hollow pyroelectric cylinder of crystal class 6 are considered. The frequency equation has been derived for two different cases. Case (i) is for a hollow cylinder whose inner and outer surfaces are traction free, completely coated with electrode which are shorted and thermally insulated. Case (ii) is for a hollow cylinder whose inner surface is clamped, completely coated with electrode which are shorted and thermally insulated while the outer surface is same as in case (i). The frequency equation has been analyzed numerically for Barium titanate ceramic. The results are tabulated and the dispersion curves are presented. ? 1991 Springer-Verlag.

In the last decades the development of new satellite platforms from a smaller to a bigger size goes in parallel with the development of the microelectronics equipment boarded on. Avionics, control systems and payloads equipment exploit the microelectronics in order to reduce the overall dimensions and masses and to increase the performances of each unit for the improvement of goals in each mission. A larger use of electronic elements with the relevant components increases the importance of a carefully equipment designed under different points of view. One of them is the thermal management. It is well known that the Joule Effect causes the heat overstocking which in turn reduces the efficiency of the electronic devices and increases the difficulties to manage the thermal power budget on board. A new design philosophy sees a possibility for a simpler and a more efficient thermal control on the use of the pyroelectric materials. Pyroelectrics are a “special” class of materials that demonstrates a spontaneous capacity to convert thermal fluxes in electrical charge and if applied on a “passive” structure they can “actively” reduce the heat overstocking. The electrical charge could be eventually stored for different purposes such as for instance the auto-feeding, or better the energy harvesting. With the reduction of the temperature of each component, and consequently with the reduction of the heat flux that flows through microelectronics, better efficiency and better performances are ensured. In this way the reliability is increased and the goals of the mission could be achieved easier and easier. In this paper the design of a thermal rig made up of pyroelectric devices and dummy electronics components in order to verify the thermo-electric conversion is presented. Furthermore an experimental campaign has been performed to validate the technology here introduced and the relevant results presented. In particular the characterisation of a typical aerospace pyroelectric material via scanning electron microscope (SEM) and a semi-quantitative analysis will be discussed. In order to verify the trustworthiness of the experimental campaign the results will be compared with the ones coming from an in-house-developed numerical code.

Large pyroelectric and energy harvesting properties have been attracting increasing attentions due to the practical applications in infrared detectors and energy harvesting technologies. Ferroelectric-antiferroelectric (FE-AFE) phase transitions are usually accompanied by a sharp drop in polarization, which will lead to excellent pyroelectric properties and energy harvesting density. Therefore, FE-AFE phase boundary design is an effective strategy to develop new pyroelectric materials. In this paper, Pb(Lu1/2Nb1/2)O3-PbTiO3 (PLN-PT) single crystals with FE-AFE phase transitions were obtained by molten salt growth method. The temperature-induced FE-AFE phase transition was verified by temperature-dependent macrodomain structure, DSC curves and dielectric properties. Obviously, PLN-PT crystals display excellent peak pyroelectric coefficient (∼6.8 μC/(cm2·K)) with a maximum depolarization temperature of 118 °C. Meanwhile, the pyroelectric energy harvesting density is as high as 2.62 J/cm3, which is much higher than other pyroelectric materials. The results reveal that the PLN-PT crystal is a promising candidate for infrared detectors and energy harvesting devices.