A novel
porous polydimethylsiloxane (PDMS)-based capacitive pressure
sensor was fabricated by optimizing the dielectric layer porosity
for wide-range pressure sensing applications in the sports field.
The pressure sensor consists of a porous PDMS dielectric layer and
two fabric-based conductive electrodes. The porous PDMS dielectric
layer was fabricated by introducing nitric acid (HNO3)
into a mixture of PDMS and sodium hydrogen bicarbonate (NaHCO3) to facilitate the liberation of carbon dioxide (CO2) gas, which induces the creation of porous microstructures within
the PDMS dielectric layer. Nine different pressure sensors (PS1, PS2,...,
PS9) were fabricated in which the porosity (pore size, thickness)
and dielectric constant of the PDMS dielectric layers were varied
by changing the curing temperature, the mixing proportions of the
HNO3/PDMS concentration, and the PDMS mixing ratio. The
response of the fabricated pressure sensors was investigated for the
applied pressures ranging from 0 to 1000 kPa. A relative capacitance
change of ∼100, ∼323, and ∼485% was obtained
by increasing the curing temperature from 110 to 140 to 170 °C,
respectively. Similarly, a relative capacitance change of ∼170,
∼282, and ∼323% was obtained by increasing the HNO3/PDMS concentration from 10 to 15 to 20%, respectively. In
addition, a relative capacitance change of ∼94, ∼323,
and ∼460% was obtained by increasing the PDMS elastomer base/curing
agent ratio from 5:1 to 10:1 to 15:1, respectively. PS9 exhibited
the highest sensitivity over a wide pressure sensing range (low-pressure
ranges (<50 Pa), 0.3 kPa–1; high-pressure ranges
(0.2–1 MPa), 3.2 MPa–1). From the results,
it was observed that the pressure sensors with dielectric layers prepared
at relatively higher curing temperatures, higher HNO3 concentrations,
and higher PDMS ratios resulted in increased porosity and provided
the highest sensitivity. As an application demonstrator, a wearable
fit cap was developed using an array of 16 pressure sensors for measuring
and mapping the applied pressures on a player’s head while
wearing a helmet. The pressure mapping aids in observing and understanding
the proper fit of the helmet in sports applications.
This work presents a solution-processed gravure printed antenna on robust transparent nanopaper for potential Radio Frequency Identification (RFID) application. The nanopaper, having excellent dimensional stability in water, was obtained by glutaraldehyde treatment with hydrochloric (HCl) acid as a catalyst. For the first time, a device consisting of RF components for RFIDs was printed on stable nanopaper via a well-developed scalable method: gravure printing. Insertion losses of -37.9 dB and -38.85 dB for the 100 lpi and 120 lpi antennas respectively were demonstrated at the maximum gain of 683.75 MHz. The RF-based responses from the printed antenna demonstrated the feasibility of using printing technology, such as gravure printing, to fabricate flexible RFID antennas for various electronic device applications. This study paves the way for the development of low cost, disposable devices comprised of biodegradable and earth abundant materials to promote greener electronics.
Chronic wounds affect over 6.5 million Americans and are notoriously difficult to treat. Suboptimal oxygenation of the wound bed is one of the most critical and treatable wound management factors, but existing oxygenation systems do not enable concurrent measurement and delivery of oxygen in a convenient wearable platform. Thus, we developed a low-cost alternative for continuous O2 delivery and sensing comprising of an inexpensive, paper-based, biocompatible, flexible platform for locally generating and measuring oxygen in a wound region. The platform takes advantage of recent developments in the fabrication of flexible microsystems including the incorporation of paper as a substrate and the use of a scalable manufacturing technology, inkjet printing. Here, we demonstrate the functionality of the oxygenation patch, capable of increasing oxygen concentration in a gel substrate by 13% (5 ppm) in 1 h. The platform is able to sense oxygen in a range of 5–26 ppm. In vivo studies demonstrate the biocompatibility of the patch and its ability to double or triple the oxygen level in the wound bed to clinically relevant levels.
This work presents a more realistic study on the potential
of titanium
carbide MXene (Ti3C2T
x
) for gas sensing, by employing first principle calculations.
The effects of different ratios of different functional groups on
the adsorption of NH3, NO, NO2, N2O, CO, CO2, CH4, and H2S gas molecules
on Ti3C2T
x
were
analyzed. The results indicated that Ti3C2T
x
is considerably more sensitive to NH3, among the studied gas molecules, with a charge transfer
of −0.098 e and an adsorption energy of −0.36 eV. By
analyzing the electrostatic surface potential (ESP) and the projected
density of states (PDOS), important physical and mechanical properties
that determine the strength and nature of gas-substrate interactions
were investigated, and also, the significant role of electrostatic
effects on the charge transfer mechanism was revealed. Further, the
Bader charge analysis for the closest oxygen and fluorine atoms to
NH3 molecule showed that oxygen atoms have 60% to 180%
larger charge transfer than fluorine atoms, supporting that Ti3C2T
x
substrate with
a relatively lower ratio of fluorine surface terminations has a stronger
interaction with NH3 gas molecules. The calculations show
that in the presence of water molecules, approximately 90% smaller
charge transfer between NH3 molecule and the Ti3C2T
x
occurs. Ab initio molecular dynamics simulations (AIMD) were also carried out to evaluate
the thermal stabilities of Mxenes. The comprehensive study presented
in this work provides insights and paves the way for realizing sensitive
NH3 sensors based on Ti3C2T
x
that can be tuned by the ratio of surface termination
groups.
This review provides an outlook on some of the significant research work done on printed and flexible sensors. Printed sensors fabricated on flexible platforms such as paper, plastic and textiles have been implemented for wearable applications in the biomedical, defense, food, and environmental industries. This review discusses the materials, characterization methods, and fabrication methods implemented for the development of the printed and flexible sensors. The applications, challenges faced and future opportunities for the printed and flexible sensors are also presented in this review.
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