Abstract
A novel temperature sensor based on nematic liquid crystal permittivity as a sensing magnitude, is presented. This sensor consists of a specific micrometric structure that gives considerable advantages from other previous related liquid crystal (LC) sensors. The analytical study reveals that permittivity change with temperature is introduced in a hyperbolic cosine function, increasing the sensitivity term considerably. The experimental data has been obtained for ranges from −6 °C to 100 °C. Despite this, following the LC datasheet, theoretical ranges from −40 °C to 109 °C could be achieved. These results have revealed maximum sensitivities of 33 mVrms/°C for certain temperature ranges; three times more than of most silicon temperature sensors. As it was predicted by the analytical study, the micrometric size of the proposed structure produces a high output voltage. Moreover the voltage's sensitivity to temperature response can be controlled by the applied voltage. This response allows temperature measurements to be carried out without any amplification or conditioning circuitry, with very low power consumption.
Highlights
Over time temperature monitoring has been an indispensable tool for sensing changes in many different processes and systems, in both research and industrial applications
The liquid crystal (LC) sensor structure is similar to a conventional LC display, that is, a sandwich configuration with the material confined between the control and ground plane electrodes (Figure 2)
In the last step of this process, the polyimide is rubbed using an in-house machine with velvet covering a rubbing wheel. This causes nearly parallel microgrooves in a common direction; when a cell is filled with a nematic LC, the molecules align nearly parallel to the glasses
Summary
Over time temperature monitoring has been an indispensable tool for sensing changes in many different processes and systems, in both research and industrial applications. There are not many studies in the literature that take advantage of the properties of LCs The most broad range LC temperature sensors are based on cholesterics [2,3] These LCs have a helical configuration that results in a material with a high light rotatory power. Despite the fact cholesteric temperature sensors are the most common approach, in the last few years some attempts employing nematic liquid crystals have been carried out Most of these sensors are based on optical properties of a nematic LC and have the LC refraction index, n, as the sensing magnitude. A nematic LC sensor based on the LC electrical properties was first reported in 2012 [17] This system generates a variable frequency as an output signal; the result is a temperature-frequency transducer. A good stability and no hysteresis have been observed in the experimental measurements
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