Analysis methodology for the design of start-up rheostats on thermo-dependent polycrystalline resistances

The article provides a brief analysis of the starting processes of electrical devices in autonomous systems of limited power. The existing methods of automatic start-up and regulation of the operation of electrical machines and apparatus are considered, which are a multi-link system, the reliability of which is determined by a number of intermediate links, and the stepping is one of the biggest drawbacks that negatively affect the dynamics of the starting process. In addition, the issues of simplicity, low cost and small dimensions of the automatic control system for electrical installations are of particular importance in the problem of energy saving. The use of low-power thermistors as part of starting devices requires intermediate equipment and various components, which significantly reduces the reliability of the equipment. The increase in currents flowing through the ballasts simplifies the electrical control and regulation circuits. For the use of polycrystalline semiconductor thermistors in circuits with high currents, it is necessary to use special designs in order to prevent overheating of the thermistor material. The article provides algorithms for the synthesis of starting rheostats. A number of restrictions are considered and formulated, on which the nature of the processes of starting electric motors with the help of thermistor rheostats, which ensure the fulfillment of certain restrictions, depends. Recommendations are given for the formation of optimal starting processes using rheostats built on semiconductor polycrystalline thermistors.

High sensitivity bolometers based on metal nanoantenna dimers with a nanogap filled with vanadium dioxide

One critical factor for bolometer sensitivity is efficient electromagnetic heating of thermistor materials, which plasmonic nanogap structures can provide through the electric field enhancement. In this report, using finite element method simulation, electromagnetic heating of nanorod dimer antennas with a nanogap filled with vanadium dioxide (VO2) was studied for long-wavelength infrared detection. Because VO2 is a thermistor material, the electrical resistance between the two dimer ends depends on the dimer’s temperature. The simulation results show that, due to the high heating ability of the nanogap, the temperature rise is several times higher than expected from the areal coverage. This excellent performance is observed over various nanorod lengths and gap widths, ensuring wavelength tunability and ultrafast operating speed, thereby making the dimer structures a promising candidate for high sensitivity bolometers.

MEMS Based Differential Scanning Calorimeter for Biomolecular Study

This paper presented a MEMS based differential scanning calorimeter (DSC) for biomolecular characterization. In this MEMS based DSC, PDMS (Polydimethylsiloxane) and Flexdyne thin film were used to construct the microfluidic chamber. Polyimide were used to fabricate the flexible substrate and temperature sensitive vanadium oxide was used as the thermistor material. A heating stage was used to heat the sample and reference up at a certain rate. The resolution study and step response characterization indicated the high sensitivity (6.1V/W) of the device. The test with Bovine Serum Albumin (BSA) samples showed clear phase transitions and the data was confirmed to be reasonable by comparing it with the results of commercial DSC’s test. This device used 0.63uL sample amount and could complete the scanning process in 3 minutes, significantly increasing the throughput of the biomolecular thermodynamics study like protein denaturation process compared to the traditional DSC (1 to 2 hours).

Low-temperature sintered NTC ceramics for thick film temperature sensors

Printed thick film NTC thermistors and multilayer devices are frequently used for temperature control in hybrid circuits. NiMn2O4 and substituted spinels are the most established materials for this application. For low-temperature sintering at 900 °C the shrinkage behavior of the thermistor material has to be adjusted by the addition of proper sinter additives. We investigated the chemical stability of NiMn2O4 and substituted spinels in air between 25 °C and 1200 °C. The compound NiMn2O4 is stable from 700 °C to 970 °C only and interacts with the sinter additives. Stable cubic spinels were found in the system ZnxNi0,5Co0,5Mn2-zO4. Addition of liquid phase sintering additives to the spinel powders results in complete densification at 900 °C. No chemical interaction between spinel and additive was observed. The effect of Cu-substitution into the spinel was also investigated. Functional NTC pastes were printed on alumina substrates and post-fired at 900 °C. The NTC thermistor films have a sheet resistivity of about 300 kOhm/sq and B = 3300 K. The firing behavior, microstructure formation and electric properties of NTC thick films will be reported.

Fabrication of Lead-Free Semiconducting Ceramics Using BaTiO3-(Bi1/2Na1/2)TiO3 System by Sintering in Air Atmosphere

BaTiO3–(Bi1/2Na1/2)TiO3(abbreviated as BT-BNT) solid solution ceramics, as a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor material usable over 130°C, were synthesized in air atmosphere. By conventional processes, La-doping was not effective in giving semiconducting property to the BT-BNT ceramics because of volatilization of sodium and bismuth during sintering. By preventing the volatilization by lowering the sintering temperature using very fine TiO2powder and by adding calcium oxide to calcined BT-BNT powders, we obtained BT-BNT semiconducting ceramics which shows a resistivity change near Curie temperature.

Characterization of Grain Boundaries of Lead-Free Semiconducting Ceramics Using BaTiO3-(Bi1/2K1/2)TiO3 System

BaTiO3–(Bi1/2K1/2)TiO3 (abbreviated as BT-BKT) solid solution ceramics, as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130°C, has been synthesized by sintering in N2 atmosphere and after annealing in air over 1200°C. In the BT-BKT ceramics with PTC property, the impedance/modulus spectroscopic plots have revealed that a third resistance-capacitance (RC) response besides grains and grain boundaries. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers in the BT-BKT semiconducting ceramics.

Intrinsic resistivity of sintered Nickel Manganite vs. powder activation time and density

In this work the DC resistivity of sintered nickel manganite NiMn2O4 (NTC thermistor material) was studied as a function of additional powder activation time in a planetary ball mill (0, 5, 15, 30, 45 and 60 min). The activated powders and non-activated powder were sintered at different temperatures (900, 1050 and 12000C) for an hour. Structural changes were analyzed using XRD. Sample density, porosity and DC resistivity were measured on the same sintered samples. Correlations between sample density, porosity, and intrinsic DC resistivity vs. additional powder activation time and the sintering temperature were made. It was noticed that the resistivity falls with the increase of sample density (or increase of the sintering temperature).