Piezoelectric energy harvesters have proven to have the potential to be a power source in a wide range of applications. As the harvester dimensions scale down, the resonance frequencies of these devices increase drastically. Proof masses are essential in micro-scale devices in order to decrease the resonance frequency and increase the strain along the beam to increase the output power. In this work, the effects of proof mass geometry on piezoelectric energy harvesters are studied. Different geometrical dimension ratios have significant impact on the resonance frequency, e.g., beam to mass lengths, and beam to mass widths. A piezoelectric energy harvester has been fabricated and tested operating at a frequency of about 4 kHz within the audible range. The responses of various prototypes were studied, and an optimized T-shaped piezoelectric vibration energy harvester design is presented for improved performance.

This paper aims at comparing micromachined cantilever structures with the purpose of providing design guidelines towards high performance energy harvesters such that they provide a good output power, resonant frequency and volume trade-off, while considering microfabrication process limitations. Increasing the power output of piezoelectric energy harvesters by tapering the beams has been presented as promising solution in the literature. This paper investigates the power output of several geometric variations of cantilever beams, and examines the advantages of balancing the strain distribution throughout the beam. A comparison of the impact of different geometries is presented, and recommendations are given. Namely, eight rectangular and trapezoidal T-shaped designs are fabricated and benchmarked. Their resonant frequencies and power outputs are compared for the same available area (1800 μm× 800 μm). Measurements show that the trapezoidal designs can have a higher output power depending on the beam length to mass length ratio, in comparison to the rectangular T-designs that have lower frequencies. Resonant frequencies ranging from 2.9 to 7.2 kHz and power outputs ranging from 2.2 to 7.1 nW are reported.

In this study, Silicon Carbide (SiC) nanoparticle-based serigraphic printing inks were formulated to fabricate highly sensitive and wide temperature range printed thermistors. Inter-digitated electrodes (IDEs) were screen printed onto Kapton^® substrate using commercially avaiable silver ink. Thermistor inks with different weight ratios of SiC nanoparticles were printed atop the IDE structures to form fully printed thermistors. The thermistors were tested over a wide temperature range form 25 °C to 170 °C, exhibiting excellent repeatability and stability over 15 h of continuous operation. Optimal device performance was achieved with 30 wt.% SiC-polyimide ink. We report highly sensitive devices with a TCR of −0.556%/°C, a thermal coefficient of 502 K ($\beta$-index) and an activation energy of $0.08$ eV. Further, the thermistor demonstrates an accuracy of ±1.35 °C, which is well within the range offered by commercially available high sensitivity thermistors. SiC thermistors exhibit a small 6.5% drift due to changes in relative humidity between 10 and 90%RH and a 4.2% drift in baseline resistance after 100 cycles of aggressive bend testing at a 40° angle. The use of commercially available low-cost materials, simplicity of design and fabrication techniques coupled with the chemical inertness of the Kapton^® substrate and SiC nanoparticles paves the way to use all-printed SiC thermistors towards a wide range of applications where temperature monitoring is vital for optimal system performance.

With the rise of the Internet of Things (IoT) and the ever-increasing number of integrated sensors, the question of powering these devices represents an additional challenge. The traditional approach is to use a battery; however, harvesting energy from the environment seems to be the most practical approach. To that end, the use of piezoelectric MEMS energy has been proven as a potential power source in a wide range of applications. In this work, a proof of concept for a new architecture for MEMS energy harvesters is presented. The influence of the dimensions and different characteristics of these designs is discussed. These designs have been proven to be resilient to process variation thanks to their unique architecture. This work presents the use of vibration enhancement petals in order to widen the bandwidth of the energy harvester and provide a non-linear frequency response. The use of these vibration enhancement petals has allowed the fabrication of three design variations, each using an area of 1700 µm by 1700 µm. These designs have an operating bandwidth between 3.9 kHz and 14.5 kHz and can be scaled to achieve other targeted resonant frequencies.

This study provides a comprehensive comparison of two leading direct-write manufacturing technologies: Aerosol Jet Printing (AJP) and Micro Dispensing Technology (MDT). The investigation examines their capabilities, limitations, and performance characteristics for printing on both 2D and 3D substrates. The findings offer valuable insights into the suitability of each printing method for flexible electronics based on the morphology and electrical performance of the deposited inks. The results reveal distinct advantages for each technique: AJP excels in resolution, while nScrypt’s micro dispensing offers superior 3D conformality, greater material versatility, and higher throughput.

Humidity sensors are essential components in modern technology, spanning applications from residential appliances to the Internet of Things (IoT). However, conventional commercial sensors are typically rigid, constrained by narrow relative humidity (%RH) operating ranges, and require complex fabrication processes. In this study, we present a highly sensitive cubic silicon carbide (3C–SiC) nanoparticle-based relative humidity sensor, fabricated via serigraphic printing on to 5 mil thick flexible polyimide (Kapton^®) substrate. Devices are tested across a broad humidity range of 10–90%RH at ambient temperature and their performance is evaluated in a controlled humidity chamber. The sensor exhibits a robust response of 45.2% R/R₀, with a sensitivity of 5.34 Ω/%RH, an adsorption time of 18 seconds, and a desorption time of 46 seconds. Additionally, the device demonstrates low hysteresis of 6.5% at 60%RH, with excellent repeatability and stability over 3.5 hours of continuous cycling. To showcase their potential for real-world applications, the printed sensors are integrated into a commercial KN95 mask for monitoring respiration parameters, such as respiration rate. This integration highlights the potential for future exploration in human health monitoring, utilizing fully printed, low-cost sensing devices.