Analytical Solution of Heat Exchange in Typical Electrocaloric Devices

Most of electrocaloric devices reported so far can be simplified as a multilayer structure in which thermal source and sink are different materials at two ends. The thermal conduction in the multilayer structure is the key for the performance of the devices. In this paper, the analytical solutions for the thermal conduction in a multilayer structure with four layers are introduced. The middle two layers are electrocaloric materials. The analytical solutions are also simplified for a hot/cold plate with two sides being different media - a typical case for thermal treatment of materials. The analytical solutions include series with infinite terms. It is proved that these series are convergent so the sum of a series can be calculated using the first N terms. The equation for calculating the N is introduced. Based on the case study, it is found that the N is usually a small number, mostly less than 40 and rarely more than 100. The issues related to the application of the analytical solutions for the simulation of real electrocaloric devices are discussed, which includes the usage of multilayer ceramic capacitor, influence of electrodes, and characterization of thin film.

Measurements of pyroelectric coefficients of BT and BST ceramics

In the work, the field and temperature dependencies on the pyroelectric coefficients of ceramic capacitor structures were measured. Barium titanate (BT) and solid solutions of barium-strontium titanate (BST) were investigate. At temperatures range from 20 °C to 30 °C, the values of the pyroelectric coefficients of the BST ceramics (p) 10-5 - 10-4 C/m2 K exceeded p for the BT ceramics by an order. The developed measurement technique made it possible to carry out direct pyroelectric coefficients measurements and determine the polarization initial state of the samples, regardless of their phase state.

Bifunctional Europium Doped SrTiO3 Ceramics with Energy Storage and Photoluminescence

Rare-earth ion Eu 3+ was doped into SrTiO 3 ceramic to improve its dielectric energy storage properties and act as luminescence centres. Typically, SrTiO 3 ceramics doped with 0.2% Eu 3+ exhibit high breakdown strength up to 354 kV/cm and a relatively high recoverable energy density of 2.13 J/cm 3 . Compared to those of the undoped sample, the doped ceramic breakdown strength and recoverable energy density are enhanced by about 22% and 58%, respectively. The doping effect can be explained by the inhibition of the long-range movement of carriers. Moreover, the europium doped SrTiO 3 ceramic capacitor exhibits an excellent power density of 37 MW/cm 3 in an ultrafast discharge time of 25 nanoseconds at 200 kV/cm. Meanwhile, the Eu 3+ doped sample exhibits obvious red photoluminescence. The bifunctional ceramics offer an excellent prospect for energy storage and optical applications.

A 300°C High Reliability HALT/HAST Screening/Sorting Procedure for Ceramic Capacitors – Part 2

This is Part 2 of a study initially presented at HiTEC 2018, for context, some introductory material is duplicated. A highly accelerated life test (HALT) and highly accelerated stress test (HAST) procedure for ceramic capacitors developed by the author in the mid 1980’s to early 1990’s, and published in 1994, consists of a 400 Volt biased six (6) hour stress sort at 150°C (423K), a methanol current leakage test that located mechanical and structural cracks, a visual inspection at ten times (10X) magnification, and a capacitance and dissipation measurement before and after the test. In over thirty (30) years of use, there has never been a user reported in-circuit failure in industrial, military, and aerospace application at temperatures as high as 500°C (773K). However, reviewing user feedback, two concerns with the original sorting procedure are the stress is performed at 150°C (423K), and the lack of a more detailed ceramic capacitor electrical model. To address the first, the low aging temperature, the stress temperature was increased from 150°C to 300°C, in order to age ceramic solid state crystal mineral phases that may change with temperature. The test results for X7R and NP0/COG multilayer ceramic capacitors (MLCC) at 300°C, are compared to the test results using the original HALT/HAST procedure at 150°C. Differences between X7R/NP0/COG and porcelain capacitors are discussed when applicable. Further, a more detailed ceramic capacitor electrical model that represents the physical and electrical characteristics of the ceramic capacitors is presented, including the electrical current leakage effects with temperature, and the carbonized residue effects from the manufacturing process.

Construction and calibration of Time Domain Reflectometry probes for assessing soil humidity in distropheric red latosol

Among the indirect methods of assessing soil moisture, Time Domain Reflectometry (TDR) stands out, which uses the soil dielectric constant to provide volumetric moisture efficiently, quickly and non-destructively. Despite a practical and precise method, TDR has a high cost due to the probes and its Data Logger. In view of this, the present work aims to build and calibrate TDR probes to assess moisture in a Dystrophic Red Latosol. The present work was carried out in the experimental area of the hydraulics laboratory of the Federal University of Grande Dourados (UFGD), located in Dourados-MS, at latitude 22⁰ 12 'south, longitude 54⁰ 59' west and altitude of 434 meters. Each probe built consisted of 3 stainless steel rods (Ø = 3 mm; L = 230 mm) RG 98 cable with 90% mesh and 50 ohm impedance, 4.7 pF ceramic capacitor and BNC connector. The construction procedures followed the following steps: 1- Making the cable, 2- Preparing the rods, 3- Welding the rods to the wires, 4 -Operating test and 5 - finishing phase. After construction, they were calibrated with the characteristic soil of the Region, proceeding with the Probe Reading in two depths (10 and 30 cm) and simultaneous collection of deformed soil samples to determine the moisture based on mass in Laboratory. Subsequently, calibrations with cubic polynomial adjustment were performed. The results showed adjustments with high determination coefficients, and the probes developed showed satisfactory performances.