KEYWORDS: Gas sensors, Nitrogen dioxide, Sensors, Nanomaterials, Resistance, Graphene, Metals, Electrodes, Signal to noise ratio, Oxides, Stretchable electrodes, Health sciences, Structural health monitoring
Measurements from the gas-sensitive nanomaterials typically involve the use of interdigitated electrodes. A separate heater is often integrated for fast recovery. However, their use increases fabrication complexity. Here, a novel gas sensing platform based on a highly porous laser-induced graphene (LIG) pattern is reported. The LIG gas sensing platform consists of a sensing region and a serpentine interconnect region. A thin film of metal coated in the serpentine interconnect region significantly reduces its resistance, thereby providing localized healing in the sensing region. Dispersing nanomaterials with different selectivity results in an array to potentially deconvolute various components in the mixture. Systematic investigations of various nanomaterials demonstrate the feasibility of the LIG gas sensing platform. Taken together with the stretchable design in the serpentine interconnects, the demonstrated system could open new opportunities in bio-integrated electronics.
Due to its multidisciplinary nature, the power behavior of a piezoelectric vibration energy harvester depends on system properties in multiple domains such as material, mechanical and electrical. This paper presents a dimensionless maximum power equation that integrates these effects into a simple model, which serves as a convenience tool for the design and analysis of piezoelectric vibration energy harvesters. The model is given as a closed-form relationship between the dimensionless maximum power (maximum power normalized by the power limit) and the normalized electromechanical coupling coefficient with respect to the critical coupling coefficient, which is the minimum coupling to reach the power limit of a system. In addition, this integrated design equation can be applied to different energy harvesting interface circuit types such as resistive and standard AC-DC with a simple change of the critical coupling expression in the equation. The application of this equation is illustrated by a detailed design example of a bimorph beam harvester for fixed target natural frequency and length given a base motion excitation. It is found that under the same level of excitation, there is an optimal PZT thickness for maximum power. In addition, overall, it is beneficial to make the system of low damping to yield a larger structural response and more power. However, this also leads to a higher bending stress, which is an important design consideration due to the relatively brittle nature of PZT materials.
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