Carlos R. Perez

Carbon coated textiles for flexible energy storage

This paper describes a flexible and lightweight fabric supercapacitor electrode as a possible energy source in smart garments. We examined the electrochemical behavior of porous carbon materials impregnated into woven cotton and polyester fabrics using a traditional printmaking technique (screen printing). The porous structure of such fabrics makes them attractive for supercapacitor applications that need porous films for ion transfer between electrodes. We used cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy to study the capacitive behaviour of carbon materials using nontoxic aqueous electrolytes including sodium sulfate and lithium sulfate. Electrodes coated with activated carbon (YP17) and tested at ∼0.25 A·g−1 achieved a high gravimetric and areal capacitance, an average of 85 F·g−1 on cotton lawn and polyester microfiber, both corresponding to ∼0.43 F·cm−2.

Knitted and screen printed carbon-fiber supercapacitors for applications in wearable electronics

The field of energy textiles is growing but continues to face two main challenges: (1) flexible energy storage does not yet exist in a form that is directly comparable with everyday fabrics including their feel, drape and thickness, and (2) in order to produce an “energy textile” as part of a garment, it must be fabricated in a systematic manner allowing for multiple components of e-textiles to be integrated simultaneously. To help address these issues, we have developed textile supercapacitors based on knitted carbon fibers and activated carbon ink. We show capacitances as high as 0.51 F cm−2 per device at 10 mV s−1, which is directly comparable with those of standard activated carbon film electrodes tested under the same conditions. We also demonstrate the performance of the device when bent at 90°, 135°, 180° and when stretched. This is the first report on knitting as a fabrication technique for integrated energy storage devices.

Effect of pore size and its dispersity on the energy storage in nanoporous supercapacitors

This paper focuses on the choice of the optimal pore size and the effect of pore size dispersion, which is important for the rational design of nanoporous supercapacitors. Optimization of the pore size of nanoporous carbon electrodes is discussed in terms of the maximal stored energy density. By applying a previously developed theory, and supporting it by newly performed experiments, we find that the energy density is a non-monotonic function of the pore size of monodisperse porous electrodes. The ‘optimal’ pore size that provides the maximal energy density increases with increasing operating voltage and saturates at high voltages. We also analyse how the pore size distribution affects the voltage dependent capacitance and the stored energy density, and show that the latter is maximized for monodisperse electrodes.

12E-3 Channel-Select RF MEMS Filters Based on Self-Coupled AlN Contour-Mode Piezoelectric Resonators

This paper reports experimental results on a new class of single-chip multi-frequency channel-select filters based on self-coupled aluminum nitride (AlN) contour-mode piezoelectric resonators. For the first time, two-port AlN contour- mode resonators are connected in series and electrically coupled using their intrinsic capacitance to form multi-frequency (94 -271 MHz), narrow bandwidth (~ .3%), low insertion loss (~4 dB), high off-band rejection (~60 dB) and extremely linear (IIP3-110 dBm) channel-select filters. This novel technology enables multi-frequency, high-performance and small form factor filter arrays and makes a single-chip multi-band RF solution possible in the near future.

Bandwidth control in acoustically coupled AlN contour mode MEMS filters

This paper reports a novel method to acoustically couple higher order AlN contour mode resonators and engineer wide bandwidth filters by controlling the number of electrodes, the size of the overhang and the spacing between electrodes. By exciting a higher order resonance mode using multiple metal electrodes on one side of the device and picking up the generated signal on the other, the location of the response poles can be engineered to create a broader band, wider than previously achieved with similar AlN contour-mode devices. CAD-level parameters are experimentally shown to set the location of the poles and therefore the bandwidth.

Microwave Impedance Microscopy of High Specific Surface Area Carbon

Microwave impedance microscopy (MIM) is a novel scanning probe technique used to measure local electrical impedance under an AFM tip operating at some fixed electrical resonant frequency. Each point in the surface scan records sample elevation and power return loss, thus generating a topographical image with an overlaid impedance map. Various high specific surface area (SSA) carbon materials, recently demonstrated to have excellent performance as electrochemical capacitor electrodes, were investigated via MIM. Results of MIM studies on these materials may be used to provide additional understanding of transport properties and complement conventional methods of surface area measurement.