Self-powered sensors are gaining a lot of attention in recent years due to their possible application in the Internet of Things, medical implants and wireless and wearable devices. Human breath detection has applications in diagnostics, medical therapy and metabolism monitoring. One possible approach for breath monitoring is detecting the humidity in exhaled air. Here, we present an extremely sensitive, self-powered sensor for breath humidity monitoring. As a power source, the sensor uses electromagnetic energy harvested from the environment. Even electromagnetic energy harvested from the human body is enough for the operation of this sensor. The signal obtained using the human body as a source was up to 100 mV with an estimated power of 1 nW. The relatively low amount of energy that could be harvested in this way was producing a signal that was modulated by an interdigitated capacitor made out of electrochemically activated aluminum. The signal obtained in this way was rectified by a set of Schottky diodes and measured by a voltmeter. The sensor was capable of following a variety of different respiration patterns during normal breathing, exercise and rest, at the same time powered only by electromagnetic energy harvested from the human body. Everything happened in the normal environment used for everyday work and life, without any additional sources, and at a safe level of electromagnetic radiation.

TiO₂ and CeO₂ are well known as oxygen sensing materials. Despite high sensitivity, the actual utilization of these materials in gas detection remains limited. Research conducted over the last two decades has revealed synergistic effects of TiO₂-CeO₂ mixed oxides that have the potential to improve some aspects of oxygen monitoring. However, there are no studies on the sensing properties of the TiO₂-CeO₂ obtained by mechanochemical treatment. We have tested the applicability of the mechanochemically treated TiO₂-CeO₂ for oxygen detection and presented the results in this study. The sensing layers are prepared as a porous structure by screen printing a thick film on a commercial substrate. The obtained structures were exposed to various O₂ concentrations. The results of electrical measurements showed that TiO₂-CeO₂ films have a significantly lower resistance than pure oxide films. Mixtures of composition TiO₂:CeO₂ = 0.8:0.2, ground for 100 min, have the lowest electrical resistance among the tested materials. Mixtures of composition TiO₂:CeO₂ = 0.5:0.5 and ground for 100 min proved to be the most sensitive. The operating temperature can be as low as 320 °C, which places this sensor in the class of semiconductor sensors working at relatively lower temperatures.

This study explored the oxygen-sensing mechanism of CeO₂ modified with TiO₂ via high-energy ball milling at different speeds. Different characterization techniques were employed to investigate the obtained materials. Quantitative surface analysis by X-ray photoelectron spectroscopy was conducted to elucidate their sensitivity mechanisms and assess the impact of the introduction of TiO₂. A comparable concentration of oxygen vacancies was found in the samples milled at 350 and 450 rpm. Electrical measurements conducted at temperatures lower than required for semiconductor gas sensors revealed the higher sensitivity of these two samples in comparison to pure CeO₂ at an oxygen concentration above 10%. In contrast, the samples derived from precursors milled at the highest speed exhibited the lowest sensitivity. This may be linked to a slight decrease in the vacancy concentration and the presence of a differentially charged carbon-containing phase. Eventually, the C 1s line provided significant insight into the surface characteristics of the materials. The uniform and non-uniform charging found for pure TiO₂ and CeO₂, respectively, along with the high charging of CeO₂, suggest that TiO₂ promotes the contact between the sensing layer and the overlayer. Sensor testing showed the significantly lower resistance of mixed oxides in comparison to CeO₂, which increases the utility of metal oxide-based sensors.

Respiratory function monitoring is essential for the early detection of respiratory dysfunction and for managing critical care patients. Various techniques have been developed for the monitoring of respiratory function, including non-invasive methods such as breath humidity detection. In this work, we show preliminary results of fabrication and testing of self-powered, flexible and wearable breath humidity detection sensor. The Electrochemical Impedance Spectroscopy was deployed to quantify properties of the screen-printed humidity sensor with possible use in human respiration monitoring.

Surfaces of adsorption-based gas sensors are often heterogeneous, with adsorption sites that differ in their affinities for gas particle binding. Knowing adsorption/desorption energies, surface densities and the relative abundance of sites of different types is important, because these parameters impact sensor sensitivity and selectivity, and are relevant for revealing the response-generating mechanisms. We show that the analysis of the noise of adsorption-based sensors can be used to study gas adsorption on heterogeneous sensing surfaces, which is applicable to industrially important liquid-phase exfoliated (LPE) graphene. Our results for CO₂ adsorption on an LPE graphene surface, with different types of adsorption sites on graphene flake edges and basal planes, show that the noise spectrum data can be used to characterize such surfaces in terms of parameters that determine the sensing properties of the adsorbing material. Notably, the spectrum characteristic frequencies are an unambiguous indicator of the relative abundance of different types of adsorption sites on the sensing surface and their surface densities. We also demonstrate that spectrum features indicate the fraction of the binding sites that are already occupied by another gas species. The presented study can be applied to the design and production of graphene and other sensing surfaces with an optimal sensing performance.

This work presents an asymmetric p-i-p silicon diode structure (a-p-i-p) characterized using the Transient Current Technique (TCT) with a scanning pulsed laser system. The device, fabricated on n-type silicon (3–5 Ω·cm) with two identical p+-doped meandering line electrodes (one of which is obscured by a black resin layer), was tested in photovoltaic mode (zero bias) under laser excitation at 660 nm, 980 nm, and 1064 nm wavelengths. The transient photocurrent response was recorded as the laser spot was scanned across the device surface with 0.01 mm spatial resolution. A pronounced wavelength-dependent response was observed: the shortest wavelength (660 nm) produced the largest transient current signals, while longer wavelengths (980 nm, 1064 nm) yielded progressively weaker responses. This study introduces a fundamentally new design paradigm that enables the p-i-p diode to operate in photovoltaic mode.