Pyroelectric Voltage Research Articles

Pyroelectric Energy Harvesting Using Ferroelectric Ba1−xCaxTiO3

The structural and pyroelectric properties of partially Ca‐substituted BaTiO3, Ba1−xCaxTiO3 (0 ≤ x ≤ 0.2), are investigated. Partial Ca‐substitution in BaTiO3 introduced tetragonal distortion in the TiO6 octahedrons and increased the displacement, Δd, of a Ti4+ cation from the center of an octahedron. This increase in Δd led to enhancement of remanent polarization and pyroelectric voltage, Vp. The pyroelectric energy storage behavior is demonstrated for the partially Ca‐substituted BaTiO3. For the Ba0.9Ca0.1TiO3 sample which exhibited the highest Vp, the stored energy in an output capacitor was proven to be sufficient to operate micropower Internet of Things devices.

Long-wave infrared selective pyroelectric detector using plasmonic near-perfect absorbers and highly oriented aluminum nitride

Pyroelectric detectors are desirable for infrared sensing because they operate at room temperature and are easier to fabricate than traditional detectors such as mercury-cadmium-telluride. Unfortunately, they cannot detect specific wavelengths or wavelength bands. Herein, a pyroelectric detector for selective detection in the long-wavelength infrared region will be presented. Pyroelectric aluminum nitride forms a dielectric layer separating a gold plasmonic hole array from a refractory metal, titanium nitride. Infrared radiation incident on the hole array forms a gap plasmon mode whose electric field is confined to the pyroelectric spacer layer. Relaxation of the mode heats the pyroelectric spacer layer, producing a pyroelectric voltage. Using this technique, 18.9 dB of spectral selectivity at λ=9 μm was achieved with a peak responsivity of 1.08 V/W.

Deposition of ZnO thin films by RF&DC magnetron sputtering on silicon and porous-silicon substrates for pyroelectric applications

In this study, the temperature response of ZnO thin film is investigated in an attempt to enhance its pyroelectric performance. The film is formed on PS and Si substrates utilizing RF&DC magnetron sputtering deposition technique. The outcome of study reveals a pyroelectric coefficient observed from ZnO film on PS which is 40 times higher than that on Si and a pyroelectric voltage as high as 2.4V due to PS's profound effect on film formation, large surface to volume area and low thermal conductivity. Thus, this study can lead the way to a robust, reliable and more efficient pyroelectric operation of ZnO with employment of PS structure.

Graphene Ink Laminate Structures on Poly(vinylidene difluoride) (PVDF) for Pyroelectric Thermal Energy Harvesting and Waste Heat Recovery.

Thermal energy can be effectively converted into electricity using pyroelectrics, which act as small scale power generator and energy harvesters providing nanowatts to milliwatts of electrical power. In this paper, a novel pyroelectric harvester based on free-standing poly(vinylidene difluoride) (PVDF) was manufactured that exploits the high thermal radiation absorbance of a screen printed graphene ink electrode structure to facilitate the conversion of the available thermal radiation energy into electrical energy. The use of interconnected graphene nanoplatelets (GNPs) as an electrode enable high thermal radiation absorbance and high electrical conductivity along with the ease of deposition using a screen print technique. For the asymmetric structure, the pyroelectric open-circuit voltage and closed-circuit current were measured, and the harvested electrical energy was stored in an external capacitor. For the graphene ink/PVDF/aluminum system the closed circuit pyroelectric current improves by 7.5 times, the open circuit voltage by 3.4 times, and the harvested energy by 25 times compared to a standard aluminum/PVDF/aluminum system electrode design, with a peak energy density of 1.13 μJ/cm3. For the pyroelectric device employed in this work, a complete manufacturing process and device characterization of these structures are reported along with the thermal conductivity of the graphene ink. The material combination presented here provides a new approach for delivering smart materials and structures, wireless technologies, and Internet of Things (IoT) devices.

Extrinsic size effect of pyroelectric response of ferroelectric films

We have developed the theoretical model for calculation of the main characteristics of pyroelectric response of pyroactive multilayer structures, which are the basic elements of the modern pyroelectric detectors of radiation and other transducers. In the framework of the proposed model, the dependences of the pyroelectric response frequency spectra on the ferroelectric film thickness have been investigated. It was found that a pronounced extrinsic size effect is inherent to the pyroelectric response frequency spectra, such as the strong thickness dependence of the response maximal value and its frequency position. The thickness dependences of the frequency position of the maximum pyroelectric response and the optimal thickness of the pyroactive ferroelectric film have been calculated. The frequency spectra of the pyroelectric current and voltage calculated theoretically are in quantitative agreement with the experimental ones for the Al/P(VDF-TrFE)/Ti/Si pyroactive structure. The developed procedure is important for improving the sensitivity of pyroelectric devices. The obtained analytical expressions allow optimizing the performances of pyroactive elements using the existence of the size effect, which depends on the pyroactive ferroelectric film and substrate thicknesses, as well as on the conditions of heat transfer and exchange at the corresponding boundaries of the pyroactive structure.

Determination of thermal characterisation by photopyroelectric technique: application on textile

In this paper, a thermal performance of textile samples by photopyroelectric technique from only logarithm of amplitude pyroelectric signal is presented. A special case of normalised pyroelectric signal relative to an empty pyroelectric sensor is implemented in order to avoid experimental factor and simplify final expression of pyroelectric voltage. In addition, we have simulated a fault detector based on a microcontroller PIC16F877A in order to provide low cost protection of the lock-in amplifier. Obtained thermal parameters of single jersey knitted fabrics made of 100% cotton, 50% cotton–50% acrylic fibre and 100% acrylic fibre are measured by fitting theoretical curves to experimental ones of photopyroelectric amplitude signal according to modulation frequency root. These measurements were in good agreement with corresponding values extracted from photopyroelectric phase signal and the reported literature values.

A Flexible Piezoelectric-Pyroelectric Hybrid Nanogenerator Based on P(VDF-TrFE) Nanowire Array

The piezoelectric and pyroelectric effects are well known and have been widely used for energy harvesting and self-powered sensing systems. This paper presents a high performance piezoelectric-pyroelectric hybrid nanogenerator based on P(VDF-TrFE) nanowire array that is capable of simultaneously harvesting mechanical and thermal energies. The nanowire array was synthesized by nanoimprinting P(VDF-TrFE) polymer into anodic aluminum oxide (AAO). The ferroelectric β crystalline phase of the aligned P(VDF-TrFE) nanowires has been demonstrated by Fourier transform infrared spectrum and X-ray diffraction measurements. Under periodic mechanical bending, electric signals are repeatedly generated from the hybrid nanogenerator and the measured piezoelectric output reach 4.0 V/65 nA. The cyclic bending-releasing process and impacts of strain rate on the electrical outputs are thoroughly characterized and analyzed. Besides, upon exposure of heat-cool condition with a temperature range of 8 K around room temperature, pyroelectric output up to 3.2 V/52 nA was obtained. There is a linear relationship between the output and the temperature difference across the device. Because the fast response time of 90 ms and high detected sensitivity of 0.8 K, the hybrid nanogenerator can also use as a self-powered temperature sensor. Finally, the piezoelectric and pyroelectric output voltages were successfully integrated together to obtain an enhanced output. These results demonstrate the great potential of the flexible hybrid nanogenerator for self-powered electronic devices.

Electric and pyroelectric properties of AlN thin films deposited by reactive magnetron sputtering on Si substrate

Electric and pyroelectric properties of AlN layers deposited on Si substrates with different resistivities were investigated. The dielectric constant was found to be around 12, while the conductance determined from dc current measurements was found to be in the 10−9 to 10−10S range. The pyroelectric measurements were performed in voltage mode using two types of IR sources: a laser diode with 800nm wavelength and a black body at 700°C. A peculiar behavior was observed for the signal recorded when the laser diode was used as IR source. It was found that the Si substrate is introducing a signal component, due to the photogenerated carriers, which is adding to the pyroelectric signal generated by the AlN layer. This component is strongly dependent on the resistivity of the Si substrate. For strongly doped Si (Si++) the signal generated into the substrate represents only 10% of the recorded pyroelectric voltage. For electronic grade Si the signal generated into the substrate is about 100 times larger than the pyroelectric signal generated in the AlN layer. This effect can be used as an optical amplification of the pyroelectric signal. The frequency dependence observed for the pyroelectric signal recorded when the black body is used as IR source is typical for a pyroelectric detector. A value as large as 12.4μCm−2K−1 was obtained for the pyroelectric coefficient using for estimation the constant signal at low modulation frequencies of the IR beam. However, the value of the pyroelectric coefficient is strongly affected by the electrical conductance of the AlN layer. As the conductance is frequency dependent it results that the value of the pyroelectric coefficient is frequency dependent, the value from above being valid only for very small frequencies of the temperature variation. It was also found that the electric and pyroelectric properties are dependent on the crystalline quality of the AlN layer.

Flexible Polymer-on-Polymer Architecture for Piezo/Pyroelectric Energy Harvesting

An all polymer piezo/pyroelectric device was fabricated using β phase poly(vinylidene fluoride) (PVDF) as the active material and vapor phase polymerized (VPP) poly(3,4-ethylenedioxythiphene) (PEDOT) as the flexible electrode overlay material. Inherent problems usually associated with coating polymeric electrodes onto the low surface energy PVDF were overcome by air plasma treating the film in conjunction with utilizing the VPP technique to simultaneously synthesize and in situ deposit the PEDOT electrode. Strain measurements up to the breaking-strain of PVDF (approximately 35%) indicated that the change in R/Ro was significantly smaller for the PEDOT based electrodes compared to the platinum electrode. Plasma treatment of the PVDF film increased the level of surface oxygenated carbon species that contributed to increased surface energy, as confirmed by confirmed by contact angle measurement. The enhanced adhesion between the two polymers layers contributed to a significant increase in the measured piezoelectric output voltage from 0.2 to 0.5 V for the same strain conditions. Pyroelectric voltage outputs were obtained by placing the film onto and off of a hotplate, for temperatures up to 50 °C above ambient. Finally, as a proof of concept, a simple energy harvesting device (plastic tube with slots for mounting multiple piezo/pyro films) was fabricated. The device was able to generate a usable level of peak output current (>3.5 μA) from human inhalation and exhalation "waste energy".

A 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3-based pyroelectric generator and temperature sensor

We report the extremely-high pyroelectric power generation of a relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) single crystal. The pyroelectric current and voltage of PMN-0.3PT depend on the electric poling voltage, the temperature-variation rate, and the measurement temperature. Near the structural transition temperatures of the rhombohedral-tetragonal transition (~380 K) and the tetragonal-cubic transition (~410 K), the temperature-induced change in the electric polarization results in a sharp enhancement of the pyroelectric power. Near the tetragonal-cubic transition temperature, i.e., the Curie temperature, we observe a pyroelectric current of ~100 nA and voltage of ~11 V. Near room temperature, we observe a pyroelectric current of ~1.4 nA and voltage of ~0.2 V from the touch of a human finger. These results imply that the relaxor ferroelectric PMN-0.3PT should be quite useful for pyroelectric energy-harvesting and temperature-sensing applications.

High pyroelectric power generation of 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal

We report the pyroelectric power generation of a relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) single crystal. For a temperature variation rate of 0.5 K/s, the PMN–PT generated a closed-circuit current of 10 nA and an open-circuit voltage of 1.1 V at room temperature. The pyroelectric current and voltage of the PMN–PT single crystal were proportional to the temperature variation rate and were sharply enhanced near the structural phase-transition temperature. Additionally, the PMN–PT pyroelectric generator produced stable power for excessive thermal cycling and was highly sensitive to random thermal fluctuations. Our results indicate the potential importance of PMN–PT for high-power pyroelectric generator applications.

Enhanced AlN nanostructures for pyroelectric sensors

AbstractMeasurements of the pyroelectric coefficient and pyroelectric voltage response of polycrystalline AlN films are presented. The results were used to calculate pyroelectric detectivity figures of merit in order to compare potential AlN pyroelectric sensor performance to other pyroelectric materials such as epitaxial AlN, PbSc0.5Ta0.5O3, and Ba0.65Sr0.35TiO3 films. We observed substantial enhancement (∼5x) of pyroelectric coefficient and pyroelectric figure of merit in polycrystalline multi‐oriented AlN films when compared to epitaxial monocrystalline AlN films. A mechanism of such augmentation in polycrystalline AlN films is proposed and discussed. Despite the relatively small absolute value of pyroelectric coefficient, AlN presents pyroelectric detectivity figure of merit near the same magnitude as commonly used pyroelectric materials because of its relatively low dielectric constant. The low dielectric constant enables high speed sensor operation >MHz. The results of these studies are suggesting even higher pyroelectric response might be obtainable for the polycrystalline thin film AlN structures. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Self-polarization in ultrathin Langmuir–Blodgett polymer films

Ultrathin copolymer films of vinylidene fluoride and trifluoroethylene were deposited on Al-coated polyimide substrates, by the Langmuir–Blodgett method. A top Al electrode was evaporated onto the polymer film, to form an Al/polymer/Al structured infrared detector. The pyroelectric voltage response of the detector under various polarizing processes was characterized. The detector with only one transferred polymer layer exhibited a preferential polarization direction. This was considered to result from the self-polarization of the ultrathin polymer film. It was due to the preferred alignment of the dipoles on the Al substrates. This process can be applied for designing stable fast-response infrared detectors.

Systematic evaluation of a secondary method for measuring diagnostic-level medical ultrasound transducer output power based on a large-area pyroelectric sensor

A systematic study of the application of a novel pyroelectric technique to the measurement of diagnostic-level medical ultrasound output power is described. The method exploits the pyroelectric properties of a 0.028 mm thick membrane of polyvinylidene fluoride (PVDF), backed by an acoustic absorber whose ultrasonic absorption coefficient approaches 1000 dB cm−1 at 3 MHz. When exposed to an ultrasonic field, absorption of ultrasound adjacent to the PVDF–absorber interface results in heating and the generation of a pyroelectric output voltage across gold electrodes deposited on the membrane. For a sensor large enough to intercept the whole of the acoustic beam, the output voltage can be calibrated for the measurement of acoustic output power. A number of key performance properties of the method have been investigated. The technique is very sensitive, with a power to voltage conversion factor of typically 0.23 V W−1. The frequency response of a particular embodiment of the sensor in which acoustic power reflected at the absorber–PVDF interface is subsequently returned to the pyroelectric membrane to be absorbed, has been evaluated over the frequency range 1.5 MHz to 10 MHz. This has shown the frequency response to be flat to within ±4%, above 2.5 MHz. Below this frequency, the sensitivity falls by 20% at 1.5 MHz. Linearity of the technique has been demonstrated to within ±1.6% for applied acoustic power levels from 1 mW up to 120 mW. A number of other studies targeted at assessing the achievable measurement uncertainties are presented. These involve: the effects of soaking, the influence of the angle of incidence of the acoustic beam, measurement repeatability and sensitivity to transducer positioning. Additionally, over the range 20 °C to 30 °C, the rate of change in sensitivity with ambient temperature has been shown to be +0.5% °C−1. Implications of the work for the development of a sensitive, traceable, portable, secondary method of ultrasound output power measurement, appropriate for clinical diagnostic ultrasound systems, are discussed.

On the heating modulation frequency dependence of the photopyroelectric signal in experiments for liquid thermal characterization

A pyroelectric sensor can be seen as a layered system consisted on a pyroelectric material sandwiched between two thin metal layers acting as electrical contacts for measurements of the voltage drop that can be induced by heating. This kind of sensor can be used as a detector of electromagnetic radiation but also for thermal characterization of materials using the photopyroelectric technique. In this work we perform a theoretical analysis based in the so-called thermal wave approach to show that, when this sensor is heated periodically by the absorption of intensity modulated light by one of the metalized surfaces, while the other metal surface is in contact with a liquid sample, the resulting pyroelectric voltage signal amplitude enhances respecting the one resulting from the bare sensor, for certain values of the modulation frequency. This contradicts the intuitively expectation based in the assumption that the sample provides a new channel for heat conduction, thereby decreasing the pyroelectric temperature. We will show that the back and forth propagation and the superposition of thermal waves through the metal coatings must be taken into account in order to explain the observed behavior. The proposed model was experimentally tested for water and glycerin samples, and using a polyvinylidene difluoride (PVDF) polymer film, with Ni–Cu metal electrodes, as a pyroelectric sensor.

Progress in developing a thermal method for measuring the output power of medical ultrasound transducers that exploits the pyroelectric effect

Progress in developing a new measurement method for ultrasound output power is described. It is a thermal-based technique with the acoustic power generated by a transducer being absorbed within a specially developed polyurethane rubber material, whose high absorption coefficient ensures energy deposition within a few mm of the ultrasonic wave entering the material. The rate of change of temperature at the absorber surface is monitored using the pyroelectric voltage generated from electrodes disposed either side of a 60 mm diameter, 0.061 mm thick membrane of the piezoelectric polymer polyvinylidene fluoride ( pvdf) bonded to the absorber. The change in the pyroelectric output voltage generated by the sensor when the transducer is switched ON and OFF is proportional to the delivered ultrasound power. The sensitivity of the device is defined as the magnitude of these switch voltages to a unit input stimulus of power (watt). Three important aspects of the performance of the pyroelectric sensor have been studied. Firstly, measurements have revealed that the temperature dependent sensitivity increases over the range from approximately 20 °C to 30 °C at a rate of +1.6% °C −1. Studies point to the key role that the properties of both the absorbing backing layer and pvdf membrane play in controlling the sensor response. Secondly, the high sensitivity of the technique has been demonstrated using an NPL Pulsed Checksource, a 3.5 MHz focused transducer delivering a nominal acoustic power level of 4 mW. Finally, proof-of-concept of a new type of acoustic sensor responding to time-averaged intensity has been demonstrated, through fabrication of an absorber-backed hydrophone of nominal active element diameter 0.4 mm. A preliminary study using such a device to resolve the spatial distribution of acoustic intensity within plane-piston and focused 3.5 MHz acoustic fields has been completed. Derived beam profiles are compared to conventional techniques that depend on deriving intensity from acoustic pressure measurements made using the sensor as a calibrated hydrophone.

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.

Method and system for elimination of background in measurements of optical energy by means of pyroelectric detector

A model of a processing system permitting separation of the useful signal from the background interferences of pyroelectric detector voltage response is presented. Elimination of the background is achieved by the differential method. The use of this method enables elimination of the influence of any interference to a sufficient degree.

Enhanced Pyroelectric and Piezoelectric Figure of Merit of Porous Bi0.5(Na0.82K0.18)0.5TiO3 Lead‐Free Ferroelectric Thick Films

Bi0.5(Na0.82K0.18)0.5TiO3(NKBT) lead‐free ferroelectric thick films with various porosities have been produced by screen printing. Their microstructures, pyroelectric and piezoelectric properties were investigated with variation of porosity. The results show that the relative dielectric constant of the resulting 90 μm NKBT thick films with 19% and 32% porosity was down to 161 and 56, respectively. The pyroelectric voltage figure of merit (Fv) and detectivity figure of merit (FD) of NKBT thick films were increased from 10.2 × 10−13 to 19.7 × 10−13 Cm/J and 1.1 × 10−5 to 3.8 × 10−5 Pa−0.5. Moreover, the hydrostatic voltage constant and hydrostatic figure of merit of the NKBT thick films with 32% porosity reached 81 × 10−3 V/mPa and 8200 × 10−15 Pa−1 respectively. The decreasing of relative dielectric constant, volume specific heat, and piezoelectric coefficient with increasing porosity was responsible for the improved pyroelectric and piezoelectric figures of merit of the NKBT thick films. Furthermore, screen printing with the addition of controlled fraction of organic vehicle in pastes has been proved to be an alternative method for fabrication of porous pyroelectric and piezoelectric thick films. Our work demonstrates that introduction of pores in ferroelectric thick films creates a matrix void composite resulting in high figures of merit for pyroelectric and piezoelectric applications.

The effect of ferroelectric polarization on the interaction of water and methanol with the surface of LiNbO 3(0 0 0 1)

Water and methanol temperature programmed desorption (TPD) measurements were performed on the positive ( c +) and negative ( c −) surfaces of poled ferroelectric lithium niobate (LiNbO 3) single crystals. The results indicate that the molecule–surface interactions are both coverage and polarization-dependent. From a comparison of the TPD spectra for the positive and negative surfaces, it is shown that the desorption temperatures of water and methanol are consistently lower on the negative surface by 15 K and 20 K, respectively. The TPD spectra were simulated using the Polanyi–Wigner equation with a coverage-dependent energy term. These calculations show that the polarization dependence of the desorption temperature is due to a difference in the zero-coverage desorption energies on the two surfaces equal to a few kJ per mole. The mechanism for the polarization effect is explored with in situ pyroelectric voltage measurements, which indicate that a surface voltage of ±2 mV develops in the LiNbO 3(0 0 0 1) samples during TPD measurements. The magnitude of the pyroelectric-induced surface charge is heating rate dependent.