Monitoring of drying-induced soil moisture loss with PZT-based EMI technique

Air-drying process of soil is a crucial procedure in geological and geotechnical engineering. Drying-induced ground subsidence and damage to overlying buildings is a widespread and urgent problem. Monitoring of drying-induced water evaporation in soil is of great importance. In this paper, soil moisture loss monitoring based on lead zirconate titanate (PZT) transducer using electro-mechanical impedance (EMI) technique was investigated. A physical model test in our laboratory was conducted to study the feasibility and applicability. In the experimental research, three identical PZT transducers that were wrapped with waterproof insulation glue were pre-embedded inside a cohesive soil specimen. In addition, another PZT transducer was embedded in a sandy soil specimen to explore the application effect in soil with different composition. EMI signatures of these four PZT patches during the air-drying process were collected and analyzed. Experimental results indicated that the peak frequency in the conductance signatures presented a rightward shift as the water evaporates. Moreover, the corresponding peak magnitude keep decreasing with the continuous development of soil moisture loss. To better quantify the variations, two statistical metrics including root mean square deviation (RMSD) and mean absolute percentage deviation (MAPD) were employed to study the changing characteristics of the EMI signatures. All these two metrics increase coincidentally in the process. Experimental results demonstrate that cohesive and sandy soil moisture loss monitoring by using the embedded PZT transducer is feasible and reliable. This work also serves as a proof-of-concept study to demonstrate the performance of the EMI technique in monitoring the soil moisture content.

Piezoelectric Nanogenerators based on Lead Zirconate Titanate nanostructures: An insight into the effect of potential barrier and morphology on the output power generation

The high internal resistance of the perovskite materials used in Nanogenerators (NGs) lowers the power generation. It severely restricts their application for mechanical energy harvesting from the ambient source. In this work, we demonstrate a flexible Piezoelectric NG (PENG) with an improved device structure. Hydrothermally grown one-dimensional Lead Zirconate Titanate (Pb(ZrTi)O3) of different morphologies are used as the generating material. The morphology of the PZT nanostructures, engineered from nanoparticles to needle-shaped nanowires to increase the surface to volume ratio, provides effective mechanical contact with the electrode. The reduction of the internal resistance of the PENG has been achieved by two ways: i) fabrication of interdigitated electrodes (IDE) to increase the interfacial polarization and ii) lowering of Schottky barrier height (SBH) at the junction of the PZT nanostructure and the metal electrode by varying the electrode materials of different work functions. We find that lowering of the SBH at the interface contributes to an increased piezo voltage generation. The flexible nano needles-based PENG can deliver output voltage 9.5 V and power density 615 μW/cm2 on application low mechanical pressure (~1 kPa) by tapping motion. The internal resistance of the device is ~0.65 MΩ. It can charge a 35 μF super-capacitor up to 5 V within 20 s. This study provides a systematic pathway to solve the bottlenecks in the piezoelectric nanogenerators due to the high internal resistance.

Wearable Shoe-Mounted Piezoelectric Energy Harvester for a Self-Powered Wireless Communication System

This study covers a self-powered wireless communication system that is powered using a piezoelectric energy harvester (PEH) in a shoe. The lead-zirconate-titanate (PZT) ceramic of the PEH was coated with UV resin, which (after curing under UV light) allowed it to withstand periodic pressure. The PEH was designed with a simple structure and placed under the sole of a shoe. The durability of the PEH was tested using a pushing tester and its applicability in shoes was examined. With periodic compression of 60 kg, the PEH produced 52 μW of energy at 280 kΩ. The energy generated by the PEH was used to power a wireless transmitter. A step-down converter with an under-voltage lockout function was used to gather enough energy to operate the wireless transmitter. The transmitter can be operated initially after walking 24 steps. After the transmitter has been activated, it can be operated again after 8 steps. Because a control center receives signals from the transmitter, it is possible to check the status of workers who work outside at night or mostly alone, to detect emergencies.

Mode Coupling at around M-Point in PZT

The question of the microscopic origin of the M-superstructure and additional satellite peaks in the Zr-rich lead zirconate-titanate is discussed for nearly 50 years. Clear contradiction between the selection rules of the critical scattering and the superstructure was found preventing unambiguous attributing of the observed superstructure either to the rotation of the oxygen octahedra or to the antiparallel displacements of the lead cations. Detailed analysis of the satellite pattern explained it as the result of the incommensurate phase transition rather than antiphase domains. Critical dynamics is the key point for the formulated problems. Recently, the oxygen tilt soft mode in the PbZr0.976Ti0.024O3 (PZT2.4) was found. But this does not resolve the extinction rules contradiction. The results of the inelastic X-ray scattering study of the phonon spectra of PZT2.4 around M-point are reported. Strong coupling between the lead and oxygen modes resulting in mode anticrossing and creation of the wide flat part in the lowest phonon dispersion curves is identified. This flat part corresponds to the mixture of the displacements of the lead and oxygen ions and can be an explanation of the extinction rules contradiction. Moreover, a flat dispersion surface is a typical prerequisite for the incommensurate phase transition.

STRUCTURE CHANGING OF SUBMICRON PZT FILMS WITH A FINE VARIATION OF THE COMPOSITION CORRESPONDING TO MORPHOTROPIC PHASE BOUNDARY

В работе обсуждаются возможности тонкого варьирования состава субмикронных сегнетоэлектрических пленок твердых растворов цирконата-титаната свинца, соответствующих области морфотропной фазовой границы. Варьирование состава осуществлялось путем изменения расстояния от мишени до подложки в диапазоне 30 - 70 мм в установке высокочастотного магнетронного распыления керамической мишени при осаждении пленок на «холодную» подложку платинированного кремния. Это позволило изменять состав осаждаемых пленок (т.е., элементное соотношение атомов Zr и Ti) в диапазоне 0 -1,5% при сохранении однофазности сформированных перовскитовых пленок в процессе отжига при 580°C. При этом пленки характеризовались элементной неоднородностью состава по толщине, достигающей нескольких процентов. Толщина тонких слоев цирконата-титаната свинца составляла 500 нм. Исследовались изменения микроструктуры и параметров кристаллической решетки. Изменения состава пленок сопровождались существенными изменениями характера сферолитовой микроструктуры и ростовой текстуры. Был обнаружен резкий скачок квазикубического параметра кристаллической решетки, причиной которого может являться фазовая трансформация сегнетоэлектрической фазы - от ромбоэдрической модификации к двухфазному состоянию, предположительно состоящему из моноклинной и тетрагональной модификаций. The paper discusses the possibility of a fine variation in the composition of submicron ferroelectric films of lead zirconate titanate solid solutions corresponding to a morphotropic phase boundary. Composition was varied by changing the distance from the target to the substrate in the range of 30 - 70 mm in an installation for radio-frequency magnetron sputtering of a ceramic target, in which films deposition occurred on a «cold» platinized silicon substrate. This made it possible to change the composition of the deposited films (i.e., the elemental ratio of Zr and Ti atoms) in the range of 0 - 1,5% while maintaining the single-phase perovskite films annealed at 580 °С. In this case, the films were characterized by elemental inhomogeneity of the composition over the thickness, reaching several percents. The thickness of thin lead zirconate titanate layers was 500 nm. Changes in the microstructure and crystal lattice parameters were studied. The change in the composition of the films was accompanied by significant changes in the nature of the spherulite microstructure and growth texture. A sharp jump in the quasi-cubic crystal lattice parameter was discovered, which may be caused by the phase transformation of the ferroelectric phase - from the rhombohedral modification to the two-phase state, presumably consisting of monoclinic and tetragonal modifications.

Surface Acoustic Wave-Based Flexible Piezocomposite Strain Sensor

A surface acoustic wave (SAW), device composed of polymer and ceramic fillers, exhibiting high piezoelectricity and flexibility, has a wide range of sensing applications in the aerospace field. The demand for flexible SAW sensors has been gradually increasing due to their small size, wireless capability, low fabrication cost, and fast response time. This paper discusses the structural, thermal, and electrical properties of the developed sensor, based on different micro- and nano-fillers, such as lead zirconate titanate (PZT), calcium copper titanate (CCTO), and carbon nanotubes (CNTs), along with polyvinylidene fluoride (PVDF) as a polymer matrix. The piezocomposite substrate of the SAW sensor is fabricated using a hot press, while interdigital transducers (IDTs) are deposited through 3D printing. The piezoelectric properties are also enhanced using a non-contact corona poling technique under a high electric field to align the dipoles. Results show that the developed passive strain sensor can measure mechanical strains by examining the frequency shifts of the detected wave signals.

Low Cost, Contamination-Free, and Damage-Free Fabrication of PZT MEMS on SOI Substrate

This paper reports a generalised process flow for the fabrication of Lead Zirconate Titanate based Piezoelectric Micro Electromechanical System devices. The optimised process can be used to realise several devices with different 1-D and 2-D geometries on a single wafer. All the state-of-the-art fabrication methods introduce some damage to the active piezoelectric material. This damage entails the need for an additional step of recovery anneal in the fabrication process. Our process was designed and optimised to avoid any such damage to the PZT layer. Remnant polarisation and effective transverse piezoelectric coefficient (e31,f) were used as metrics to quantify the damage to the PZT layer. It is shown that our process does not damage the PZT thin film during the fabrication, and hence no recovery anneal is required. We observe a ~3x improvement in remnant polarisation and ~2x improvement in e31,f of PZT thin film compared to the PZT thin film subjected to our previous fabrication process. Moreover, the process explained here uses only wet chemical methods for patterning of contaminating agents (PZT and platinum), making it a cost-effective process.