The temperature dependence of the thermo-optic coefficient for crystalline silicon has been measured in the temperature range between room temperature and 550 K at the wavelength of 1523 nm by means of an interferometric technique. This technique, which requires a very simple experimental setup, is based on the observation of the fringe pattern produced by temperature changes in a Fabry–Perot resonator. Measurement results indicate that the thermo-optic coefficient is independent on the sample doping and crystal plane orientation. The experimental data appear to be in agreement with the few values reported to date at this important wavelength. The temperature dependence of the excitonic band gap is also calculated by fitting these data with a recently introduced model of $\mathrm{\partial n/\partial T.}$

The thermo-optic coefficient ∂n/∂T has been measured from room temperature to 600 K at the wavelength of 1523 nm in three important semiconductors for fiber-optic device fabrication, namely, InP, GaAs, and 6H–SiC. The adopted technique is very simple and is based on the observation of the periodicity of the signal transmitted, at the desired wavelength, by an étalon made of the material under test, when it experiences a temperature variation. The values of ∂n/∂T measured in InP and GaAs at room temperature are in agreement with previously reported ones, but increase with temperature with a weak quadratic dependence. SiC conversely shows a lower thermo-optic coefficient (2.77×10−5 K−1) at 300 K, which, however, doubles for a 300 K temperature increase.

The temperature dependence of the thermo-optic coefficients of lithium niobate has been measured in the temperature range between 320 and 515 K for both wavelengths of 632 and 1523 nm and for ordinary and extraordinary refractive indices. The experimental data, carried out by means of a simple interferometric technique, have been compared with two theoretical models that follow different approaches for treating the thermo-optic effect. The experimental results show good agreement with the theoretical ones.

The thermo-optic coefficient $\mathrm{(dn/dT)}$ of crystalline silicon has been critically analyzed in the temperature range 300–600 K, at the fiber optic communication wavelength of 1.5 μm. The temperature dependence has been attributed to the variation of the interband transition energies at some critical points of the silicon band structure. The experimental data have been fitted using single and double oscillator models. In particular, the double oscillator model, which is physically correlated to the silicon band structure, has been exploited to extrapolate the temperature dependence of the interband transition energies at some points (critical points) of the combined density of states. The extracted parameters are in good agreement with the data reported in the literature. Finally, in connection with both of the oscillator approximations, an analysis based on thermodynamic considerations is carried out, and electron–hole formation entropy and specific heat are calculated. The consistency of the obtained results validate the reliability of the proposed analysis.

A high-performance temperature sensor based on coupled 4H-SiC Schottky diodes is presented. The linear dependence on temperature of the difference between the forward voltages appearing on two diodes biased at different constant currents, in a range from 30 °C up to 300 °C, was used for temperature sensing. A high sensitivity of 5.11 mV/°C was measured. This is, to the best of our knowledge, the first experimental result about a proportional-to-absolute-temperature sensor made with SiC diodes, showing both a good degree of linearity and long-term stability performance.

The number of older people needing healthcare is a growing global phenomenon. The assistance in long-term care comprises a complex of medical, nursing, rehabilitation, and social assistance services. The cost is substantial, but technology can help reduce spending by ensuring efficient health services and improving the quality of life. Advances in artificial intelligence, wireless communication systems, and nanotechnology allow the creation of intelligent home care systems avoiding hospitalization with evident cost containment. They are capable of ensuring functions of recognition of activities, monitoring of vital functions, and tracking. However, it is essential to also have information on location in order to be able to promptly intervene in case of unforeseen events or assist people in carrying out activities in order to avoid incorrect behavior. In addition, the automatic detection of physical activities performed by human subjects is identified as human activity recognition (HAR). This work presents an overview of the positioning system as part of an integrated HAR system. Lastly, this study contains each technology’s concepts, features, accuracy, advantages, and limitations. With this work, we want to highlight the relationship between HAR and the indoor positioning system (IPS), which is poorly documented in the literature.