Markku Rouvala

Nanomaterial-enhanced all-solid flexible zinc--carbon batteries.

Solid-state and flexible zinc carbon (or Leclanche) batteries are fabricated using a combination of functional nanostructured materials for optimum performance. Flexible carbon nanofiber mats obtained by electrospinning are used as a current collector and cathode support for the batteries. The cathode layer consists of manganese oxide particles combined with single-walled carbon nanotubes for improved conductivity. A polyethylene oxide layer containing titanium oxide nanoparticles forms the electrolyte layer, and a thin zinc foil is used as the anode. The battery is shown to retain its performance under mechanically stressed conditions. The results show that the above configuration can achieve solid-state mechanical flexibility and increased shelf life with little sacrifice in performance.

Enhanced supercapacitors from hierarchical carbon nanotube and nanohorn architectures

Supercapacitors fill the power and energy gap between electrolytic capacitors and batteries. The energy density for commercial supercapacitors is currently limited to ∼5 Wh kg−1. Enhancing the energy and power density of supercapacitors is of great interest as it would open up a much wider range of applications. In this work, thin film supercapacitors made of random networks of single-walled carbon nanotubes (SWNTs) were enhanced by the use of carbon nanoparticles of a size ideal to fill the pores in the SWNT network. These nanoparticles, termed carbon nanohorns (CNHs), provide a much enhanced surface area, whilst maintaining high permeability and porosity. We demonstrate the hierarchical use of carbon nanostructures in a controlled fashion, allowing an enhancement provided by both types of materials, high power density by the SWNTs and high energy density from the CNHs. SWNT films serve as an ideal template onto which CNHs are deposited, with a good size match, adhesion and charge transfer between particles of a single chemical species. This combination results in an enhanced specific capacitance and a reduced equivalent series resistance (ESR) compared to a capacitor made of either individual component. Additionally, the good binding properties of the hybrid material and the high electrical conductivity of the SWNTs permit the removal of both the binder and the charge collector, paving the way for thinner and lighter supercapacitors. These electrodes allow the fabrication of supercapacitors with novel properties. As an example, we demonstrate a semitransparent supercapacitor. These results demonstrate the possibilities that may be available for the enhancement of electrodes by tailoring and combining relevant materials hierarchically in multiple scales. Much potential remains in further enhancement through tailored hierarchical nanostructuring.

Flexible solid state lithium batteries based on graphene inks

Different formulations of solution-processable graphene have been characterised as electrode materials for use in electrochemical energy storage devices. Graphene was fabricated by chemical reduction of exfoliated graphene oxide (GO), and modified with either p-type (e.g. polyaniline) or n-type anionic groups (poly(styrenesulfonate) (PSS−) and poly[2,5-bis(3-sulfonatopropoxy)-1,4-ethynylphenylene-alt-1,4-ethynylphenylene] sodium salt (PPE-SO3−) anion). Solutions of these graphene compounds were deposited on charge collecting electrodes and used as battery cathodes. Electrodes using the anionically-modified graphene inks containing anatase titanate (TiO2) nanoparticles show improved performance over pristine graphene ink as well as the p-type conducting polymer modified ones. In addition, the open circuit voltage of batteries based on TiO2 has been boosted over 3 V with good cyclability when mixed with the graphene ink. Combined with a polymer electrolyte, this work suggests a feasible route towards fully printable rechargeable lithium batteries based on graphene inks. This approach is both versatile and scalable and is adaptable to a wide variety of applications.

Significance of Nanotechnology for Future Wireless Devices and Communications

This paper reviews the expected wide and profound impact of nanotechnology for future wireless devices and communication technologies.

Multi-gigabit serial link emissions and mobile terminal antenna interference

Future mobile terminal digital interconnections are introducing spectrum components in cellular frequencies in an increasing manner. Control of interconnection impedance and common mode noise introduced from them are key elements for robust device design. Electromagnetic coupling from multi-gigabit serial links used for display and camera data transmission in mobile device to positioning and cellular wireless communication receivers depends mainly on common-mode content of serial link signal, and on common-mode coupling strength between the serial link interconnection and cellular receiver antenna. Frequency spectrum of common-mode component of serial link output voltage and current are determined by simulations or measurements, and 8-port S-parameters are used in calculations of induced disturbance power coupled to cellular receiver. Minimum required common-mode attenuation was found to be typically −60dB.

Modeling for High-Speed Interconnects in Mobile Device Hinge Structures

Data interconnects have become important functionality determining technology in mobile devices recently. Analysis and modeling of interconnects are integral part of electro-mechanical design of devices that have integrated high pixel count display and mega-pixel camera modules. Several high-speed serial data interfacing solutions have been introduced for data connectivity during last years. Different device form factors create the need for transferring data over hinge using flexible interconnections. The length of the interconnection is highly dependent on the complexity of the hinge structure. The longer interconnect is, the more critical is the electrical performance at high frequencies. Mechanical durability has a major role in the selection of transfer media. Typically flexible printed circuit (FPC) or micro-coaxial (MCX) cables are used. Major design considerations for FPC selection are shielding effectiveness, and selection between different layer structures, from one to three conductor layers. Different shielding materials have been developed to replace the limited bending durability of copper

On the Effect of Mobile Device Shape Characteristics to Interconnection Noise Coupling to an RF Chip Antenna

Digital interconnections in mobile devices can cause radiative coupling to RF antennas and devices. This paper discusses measurements and modeling of coupling from a digital interconnection to an RF chip antenna with various positional and device shape characteristics

Characterization of flexible interconnects in mobile devices

Mobile device application interface specifications have reached the data speed of gigabit per second per differential lane. Together with increased component density, miniaturization, multi-part devices, and increased signaling frequencies overlapping RF bands, the prediction of interface and system level behavior in terms of signal integrity becomes more and more complicated. This paper concentrates on signal quality studies of a gigabit-speed digital serial interface. The test system is implemented considering a mobile device with moving parts, and corresponding simulation models are built using various simulation tools. The study discusses the correlation between measured and simulated results, adducing also the modeling feasibility of the test system.

SPI Proceedings: Analysis of High-Speed Digital Interfaces in Flexible Interconnections

For mobile device applications, the performance of data interconnections has been getting into focus only lately. Requirements for higher performance devices and product miniaturization have been challenging the design of high-speed interconnections, driving the accurate and fast modeling of interconnect circuits. Here the maximum usable data rate analysis of a high-speed serial, camera- and display-like interface on a specific interconnection template is presented. Multiple modelling methods are combined to construct a flexible interconnection concept with various components. The effect of coupled antenna interference on the interconnection signal quality is included in the study.

Nanocarbon based supercapacitors with reduced internal resistance

Supercapacitors, also known as electrical double layer capacitors, are promising candidates to meet the increasing power demands upon energy storage systems. They have an important role in complementing or replacing batteries in the energy storage field, possessing advantages such as high power density, rapid charge/discharge (few seconds), >100 000 cycle life, and intrinsic safety (they contain no heavy metals and have a reduced likelihood of catastrophic failure). The performance of a supercapacitor depends on charge capacitance, operating voltage and internal resistance. In this paper, particular attention is given to methods of decreasing the internal resistance of supercapacitors because for intended use in high current applications, high internal resistances cause unacceptable power loss and voltage drop. We describe two steps to decrease the equivalent series resistance (ESR) of nanocarbon based supercapacitors. First, a thin, conductive carbon layer was coated on a copper current collector to decrease the contact resistance between the active electrodes and the copper. The carbon layer formed on the copper has a rough surface, which increases both the contact area and adhesion ability between the electrode material and the copper surface. In addition, the carbon layer prevents oxidation and corrosion of the metal layer, and therefore prevents ESR increase after extended cycling, thus prolonging the supercapacitor life. Second, multiwall carbon nanotubes (CNTs) were added to the nanocarbon to further decrease the ESR of the device. CNTs have good electrical conductivity and a readily accessible surface area. Scanning electron microscope images show that the added CNTs cover the surface of the nanocarbon particles and bridge the gap between the particles. After surface treatment of the copper and adding CNTs to the active electrodes, the supercapacitor have a significantly reduced ESR and highly enhanced capacitance. Evaluation of capacitor performance by different techniques, such as voltammetry, charge/discharge characteristics is also discussed.