Multi layer structure for encapsulation of organic transistors

A novel encapsulation structure to protect organic thin film transistors against oxygen and moisture contaminations is presented. The sealing architecture is comprised of three-layers: aluminum oxide deposited by means of Atomic Layer Deposition is the actual capping layer, while cross-linked poly-vinylphenol and poly-vinylphenol prevent the contamination/damage of the underlying organic semiconductor during the oxide growth. The process has negligible impact on device mobility but it enables poly-3-hexylthiophene based transistors to operate with an on/off ratio in excess of 10³ even after 100 days of continuous ambient air exposure.     

Estimation of M-wave scale factor during sustained contractions at high stimulation rate

In this paper, we propose a time-domain index to assess M-wave widening during high-frequency stimulation, as an objective parameter for quantifying muscle fatigue. At high stimulation frequencies, signal truncation, due to the delivery of the electrical stimulus before the M-wave generated by the previous stimulus extinguishes, biases the spectral frequency variables usually computed to estimate M-wave widening. Thus, we propose an estimator of the scale factor between two truncated M-waves. The estimator is derived from the Scale Transforms of the two signals, with an efficient implementation that avoids limits of resolution. The method was tested on both simulated and experimental signals. The simulations showed that the proposed technique is significantly less affected by signal truncation than previous approaches. The experimental recordings were collected from 11 subjects at stimulation frequencies of 20, 40, and 60 Hz. The scale factor estimation assessed M-wave widening in the three conditions, differentiating between the different rates of change of signal widening. The method proved to be significantly superior to M-wave spectral analysis. The technique can be applied to investigate myoelectric manifestations of muscle fatigue at stimulation rates that could not be analyzed in the past and, thus, opens new perspectives in the evaluation of electrical stimulation for training and rehabilitation protocols.     

Fast and air stable near-infrared organic detector based on squaraine dyes

In search for an organic material suitable for the detection of near-infrared electromagnetic radiation and at the same time capable of air stable operation of related devices, so to address the many applications envisaged with this technology (remote control, chemical/biological sensing, optical communication, spectroscopic and medical instruments), we explore the performance of a blend of hydrazone end-capped symmetric squaraines and phenyl C₆₁ butyric acid methyl ester. We succeed in developing air stable solution-processed devices with external quantum efficiency in the NIR as high as 3.5% and response times of few hundreds of nanoseconds. Essential to these achievements has been a detailed characterization of the devices performed by correlating the optoelectronic performances to the morphology of the layers (extracted from AFM measurements) and to the charge carrier mobility (extracted from transistor structures), enabling their optimization at the chemical level, by tailoring the squaraine substitution pattern, and at the device level, by tuning the blend composition. We show that a good balance between holes and electrons mobility is essential for high EQE and fast response speed, and that a smooth morphology is mandatory to achieve long term air stability and operability with no need for encapsulation.     

Image reconstruction using interval simulated annealing in electrical impedance tomography

Electrical impedance tomography (EIT) is an imaging technique that attempts to reconstruct the impedance distribution inside an object from the impedance between electrodes placed on the object surface. The EIT reconstruction problem can be approached as a nonlinear nonconvex optimization problem in which one tries to maximize the matching between a simulated impedance problem and the observed data. This nonlinear optimization problem is often ill-posed, and not very suited to methods that evaluate derivatives of the objective function. It may be approached by simulated annealing (SA), but at a large computational cost due to the expensive evaluation process of the objective function, which involves a full simulation of the impedance problem at each iteration. A variation of SA is proposed in which the objective function is evaluated only partially, while ensuring boundaries on the behavior of the modified algorithm.     

Trapdoor Hard-to-Invert Group Isomorphisms and Their Application to Password-Based Authentication

In the security chain the weakest link is definitely the human one: human beings cannot remember long secrets and often resort to rather insecure solutions to keep track of their passwords or pass-phrases. For this reason it is very desirable to have protocols that do not require long passwords to guarantee security, even in the case in which exhaustive search is feasible. This is actually the goal of password-based key exchange protocols, secure against off-line dictionary attacks: two people share a password (possibly a very small one, say a 4-digit number), and after the protocol execution, they end up sharing a large secret session key (known to both of them, but nobody else). Then an adversary attacking the system should try several connections (on average 5000 for the above short password) in order to be able to get the correct password. Such a large number of erroneous connections can be prevented by various means. Our results can be highlighted as follows. First we define a new primitive that we call trapdoor hard-to-invert group isomorphisms, and give some candidates. Then we present a generic password-based key exchange construction that admits a security proof assuming that these objects exist. Finally, we instantiate our general scheme with some concrete examples, such as the Diffie-Hellman function and the RSA function, but more interestingly the modular square-root function, which leads to the first scheme with security related to the integer factorization problem. Furthermore, the latter variant is very efficient for one party (the server). Our results hold in the random-oracle model.     

Hybrid Bionic Systems for the Replacement of Hand Function

In recent years, thanks to the advancement of robotics and mechatronics, new and more effective devices for the restoration and replacement of sensory-motor function in disabled people have been developed. In all these systems, user acceptability is strictly connected to several issues such as the residual abilities of the subject, the mechatronic characteristics of the robot, and also the interface chosen to link them. It is possible to figure out different "human-interface-device" combinations [also defined as "hybrid bionic systems" (HBSs)] characterized by different properties in terms of level of hybridness, connection, and augmentation. In particular, in HBSs the interface has to be customized according to the characteristics of the robotic artefact to be controlled and to the desires and needs of the final users. In this paper, our attention has been focused on the problem of the replacement of hand function after amputation. Three HBSs characterized by different levels of complexity, dexterity, and sensorization are presented in order to show the possibility of developing acceptable and effective systems by choosing different levels of connection and hybridness (i.e., different interfaces) for different devices and applications. The following case studies are presented: 1) the use of invasive interfaces to the peripheral nervous system to control a dexterous and highly sensorized hand prosthesis; 2) the use of electromyographic signals recorded using surface electrodes to control a compliant adaptive prosthesis; and 3) the use of a foot interface to control a two-degrees-of-freedom prosthesis. The preliminary results achieved so far seem to confirm the idea that the correct choice of the proper interface while developing an HBS can increase effectiveness and usability     

Transmission power requirements for novel ZigBee implants in the gastrointestinal tract

In this paper, a novel multinode wireless monitoring platform, based on ZigBee communication standard, is presented and tested in vivo. The transmission power levels needed to establish a reliable connection from the different gastrointestinal districts are reported and compared with safety levels from international guidelines. These findings can be useful to evaluate the effectiveness of a commercial and standardized approach to implantable and miniaturized monitoring of physiological parameters.     

A fast and reliable technique for muscle activity detection from surface EMG signals

The estimation of on-off timing of human skeletal muscles during movement is an important issue in surface electromyography (EMG) signal processing with relevant clinical applications. In this paper, a novel approach to address this issue is proposed. The method is based on the identification of single motor unit action potentials from the surface EMG signal with the use of the continuous wavelet transform. A manifestation variable is computed as the maximum of the outputs of a bank of matched filters at different scales. A threshold is applied to the manifestation variable to detect EMG activity. A model, based on the physical structure of the muscle, is used to test the proposed technique on synthetic signals with known features. The resultant bias of the onset estimate is lower than 40 ms and the standard deviation lower than 30 ms in case of additive colored Gaussian noise with signal-to-noise ratio as low as 2 dB. Comparison with previously developed methods was performed, and representative applications to experimental signals are presented. The method is designed for a complete real-time implementation and, thus, may be applied in clinical routine activity.     

Breakdown kinetics at nanometer scale of innovative MOS devices by conductive atomic force microscopy

The breakdown (BD) kinetics of dielectrics represent a crucial issue for the reliability of microelectronics devices. In this paper, we report on an innovative and practical approach based on Conductive Atomic Force Microscopy (C-AFM) for the determination of the BD kinetics on a bare insulator surface. This technique has been applied to Pr₂O₃ films grown by Metal-Organic Chemical Vapour Deposition (MOCVD) on Si(0 0 1) and to thermally grown SiO₂ on 4H-SiC substrates. C-AFM clearly visualizes single breakdown spots under constant voltage stresses. The stress time on the C-AFM tip was varied from 1 × 10⁻³ to 1 × 10⁻¹ s. The density of BD spots, upon increasing the stress time, exhibits in both cases an exponential trend. The Weibull slope of the dielectric BD statistics has been determined by direct measurements at nanometer scale on different dielectrics having different physical thicknesses. The comparison of the Weibull slopes obtained for different dielectric thicknesses with literature data points out intrinsic and extrinsic BD events in the SiO₂/SiC system and Pr₂O₃ based layers, respectively. In the case of the SiO₂/SiC system, BD kinetics have been demonstrated to follow the percolation model, while the role of extrinsic phenomena in the BD of Pr₂O₃ films has been proved.