Fabrication of Ferroelectric Liquid Crystal Thermistor

Kishor, Muchenedi Hari; Prabu, N. Pongali Sathya; Mohan, M. L. N. Madhu

doi:10.1109/ted.2020.3020292

Cited by 16 publications

(6 citation statements)

References 21 publications

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“…This method requires less prework since the measured voltage U T is fed directly to the temperature calculation routine based on (15), which only needs some predefined constants that are related to the thermistor and the signal conditioning circuit. During the experiment, only results for the initially presented method with a B 25/100 constant (Figure 12) were monitored, yielding a total calculation time of 5.16 µs (on average, 0.86 µs per one NTC temperature channel).…”

Section: • Analytical Methods Using the B Equationmentioning

confidence: 99%

“…As suggested in [30], we used two temperatures that coincided with the nominal temperature range, i.e., −55 • C and 150 • C and a point between them-we opted for 25 • C-thus resulting in a = 1.139357363 × 10 −3 , b = 2.327048139 × 10 −4 and c = 9.134393411 × 10 −8 . It must be stressed here that, in terms of the required calculation time, notation (17) is not overly complex compared to (15), since, in both cases, a natural algorithm (ln) operation is performed first, followed by one or more multiplications. For a selected set of values, all six temperature calculations resulted in the calculation time of 5.32 µs (on average, each NTC temperature measurement required 0.89 µs), which is comparable to results calculated with the B equation.…”

Section: • Analytical Methods Using the Steinhart-hart Equationmentioning

confidence: 99%

“…It can be seen that relation (15), which is used for the calculation of temperature with the B equation approach, is merely a simplification of (17) if the cubic part is neglected (c = 0) and a and b are calculated from relation (6). For practical implementation in the microcontroller, the procedure for temperature calculation following (17) is not overly complex, after all, provided that the Steinhart-Hart parameters are known.…”

Section: Analytical Approach Using the Steinhart-hart Equationmentioning

confidence: 99%

“…A preventive monitoring based on voltage and current measurement to calculate the temperature of a power switch is reported in [10,11], whereas a direct temperature measurement was studied in [12] to prevent power switch failure and efficiency degradation. As for the temperature measurement, there are mainly four types of sensors used in power electronics: thermocouples [13], resistance temperature detectors (RTD) such as the temperature probe PT100 as reported in [14], thermistors [15] and dedicated integrated circuits (IC) [16]. In contrast to thermocouples, being active elements, the latter three must have a source of excitation.…”

Section: Introductionmentioning

confidence: 99%

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Algorithm Execution Time and Accuracy of NTC Thermistor-Based Temperature Measurements in Time-Critical Applications

2021

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This paper addresses the challenges of selecting a suitable method for negative temperature coefficient (NTC) thermistor-based temperature measurement in electronic devices. Although measurement accuracy is of great importance, the temperature calculation time represents an even greater challenge since it is inherently constrained by the control algorithm executed in the microcontroller (MCU). Firstly, a simple signal conditioning circuit with the NTC thermistor is introduced, resulting in a temperature-dependent voltage UT being connected to the MCU’s analog input. Next, a simulation-based approximation of the actual temperature vs. voltage curve is derived, resulting in four temperature notations: for a look-up table principle, polynomial approximation, B equation and Steinhart–Hart equation. Within the simulation results, the expected temperature error of individual methods is calculated, whereas in the experimental part, performed on a DC/DC converter prototype, required prework and available MCU resources are evaluated. In terms of expected accuracy, the look-up table and the Steinhart–Hart equation offer superior results over the polynomial approximation and B equation, especially in the nominal temperature range of the NTC thermistor. However, in terms of required prework, the look-up table is inferior compared to the Steinhart–Hart equation, despite the latter having far more complex mathematical functions, affecting the overall MCU algorithm execution time significantly.

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Section: • Analytical Methods Using the B Equationmentioning

confidence: 99%

Section: • Analytical Methods Using the Steinhart-hart Equationmentioning

confidence: 99%

Section: Analytical Approach Using the Steinhart-hart Equationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Algorithm Execution Time and Accuracy of NTC Thermistor-Based Temperature Measurements in Time-Critical Applications

2021

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“…Over the past few decades ferroelectric materials [ 1 ] with electrically switchable spontaneous polarization have been utilized in energy storage devices, [ 2,3 ] piezoelectric sensors, [ 4 ] thermistors, [ 5,6 ] nonvolatile memory, [ 7,8 ] and electro‐optic devices. [ 9,10 ] Fluid‐like ferroelectric liquid crystals (FLCs) [ 11,12 ] are promising for sub‐millisecond electro‐optic modulators [ 13–15 ] and display panels.…”

Section: Introductionmentioning

confidence: 99%

Electrically Tunable Reflection Color of Chiral Ferroelectric Nematic Liquid Crystals

Feng

Saha

Körblová

et al. 2021

Advanced Optical Materials

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for sub-millisecond electro-optic modulators [13][14][15] and display panels. [16][17][18] However, until recently ferroelectricity was observed only in smectic [19] and columnar [20] phases, which are fluid only in two and one dimension, respectively. Due to their piezoelectricity, they deform mechanically during electric switching, eventually leading to permanent defects in the layers or columns. [21] 3D nematic fluids with large molecular dipole moments along the long axis of rod-shaped molecules were predicted to be ferroelectric already in the 1910s by Debye [22] and Born; [23] similar predictions were made later for disc- [24] and pearshaped liquid crystals (LCs). [25] In 2017, over a century after Debye and Born's arguments, Nishikawa et al. [26] found the first evidence of ferroelectric nematic phase (N F ) in a strongly polar 1,3-dioxanebased rod-shaped material, DIO. That same year, Mandle et al. [27,28] reported an N−N transition in another highly polar nematic material, 4-[(4-nitrophenoxy)carbonyl]phenyl2,4-dimethoxybenzoate (RM734). The lower temperature phase was later proposed to be a splay nematic, [29] with the splay deformation being the result of polar molecular ordering. [30] Very recently, Chen et al., argued that this polar ordering does not couple to a splay deformation, but instead, the lower temperature phase is a uniform ferroelectric nematic with a spontaneous polarization as high as 6 µC cm −2 . [31] The large polarization values up to 4-6 µC cm −2 measured by Nishikawa et al. [26] on DIO and Chen et al. [31] on RM734 indicate strong polar order, which is the primary order parameter, similarly to the SmAP and SmCP subphases of bent-core smectic LCs. [32,33] The large ferroelectric polarization and dielectric constant, coupled with sub-millisecond switching, offer potential applications such as high-power super capacitors and low voltage driven fast electro-optical devices. The electro-optical properties of RM734 were recently shown to depend strongly on the surface treatments of the samples, [34,35] namely that the polarity of surface anchoring may couple to the bulk polar order parameter and lead to oppositely twisted domains. To obtain a uniform texture, one needs to bias the twist by adding chiral dopants to the system. [40] The presence of molecular chirality in liquid crystals usually leads to a helical director structure. [36,37] In conventional nematic materials the twist elastic constant K 22 is smaller than the splay (K 11 ) and bend (K 33 ) elastic constants and the director n is The recently discovered ferroelectric nematic (N F ) liquid crystals (LCs) with over 0.04 C m −2 ferroelectric polarization and 10 4 relative dielectric constants, coupled with sub-millisecond switching, offer potential applications in highpower super capacitors and low voltage driven fast electro-optical devices. This paper presents electrical, optical, and electro-optical studies of a ferroelectric nematic LC material doped with commercially available chiral dopants. While the N F phase of the undo...

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Detection of phase transitions in liquid crystals through optical, thermal and electrical techniques

Rohini

Mohan

Prabu

2022

Optik

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Fabrication of Ferroelectric Liquid Crystal Thermistor

Cited by 16 publications

References 21 publications

Algorithm Execution Time and Accuracy of NTC Thermistor-Based Temperature Measurements in Time-Critical Applications

Algorithm Execution Time and Accuracy of NTC Thermistor-Based Temperature Measurements in Time-Critical Applications

Electrically Tunable Reflection Color of Chiral Ferroelectric Nematic Liquid Crystals

Detection of phase transitions in liquid crystals through optical, thermal and electrical techniques

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