Abstract: In this paper the gas sensing properties of Ag-K-hollandite prepared by K-Ag ion exchange are investigated. The proposed material was used as the active layer of micromachined conductometric gas sensors and tested in different environmental conditions with a number of target gases such as CO and NO x. The response to test gases was evaluated in a temperature interval from 200 to 350 C where surface phenomena can completely explain the sensor behavior. The proposed material was studied also by means of XPS and thermal analyses. The investigated material is a p-type semiconductor and shows a reproducible response and a complete recovery. Data obtained are discussed and a model based on surface states describing the material behavior is proposed. © 2014 Elsevier B.V.

Abstract: In this paper the authors discuss a measurement method based on the zero-crossing demodulation technique of FM signals to estimate the angular velocity vibrations of a rotating shaft. The demodulation algorithm is applied without any filtering to the direct voltage output issued by some probes sensing the passages of arbitrarily shaped targets installed on the rotating shaft. The authors discuss a theoretical approach to analyze the measurement problem taking into account the chief nonidealities related to the measurement setup, i.e., they have investigated the effects of both the shaft side vibrations and the irregular shape of the targets. On the basis of the theoretical results, the authors propose a measurement method that can reject the effects of these mentioned nonidealities, exploiting the measurements of two or more probes properly positioned around the shaft.

Abstract: We propose the design of Physically Unclonable Functions (PUFs) exploiting the nonlinear behavior of Cellular Neural Networks (CNNs). Our work derives from some theoretical results achieved within the theory of CNNs, adapted to a simpler case. The theoretical analysis discussed in this work has a general validity, whereas the presented basic hardware solution (i.e., the PUF electronic implementation) has to be understood as a reference demonstrating circuit to be further optimized and developed for a profitable use of the proposed approach. Theoretical results have been validated experimentally.

Abstract: We propose to exploit a two-neurons Cellular Neural Network (CNN) to design a basic 1-bit Physically Unclonable Function (PUF). The analysis discussed in this work, derived from the general theory of CNNs, has been validated by experimental results.

Abstract: A measurement system designed for the development of novel conductometric gas sensors and of new gas sensing materials is described. The system allows to simultaneously characterize up to 8 sensors. Prototype sensors can be easily realized thanks to an ad hoc structure based on an alumina substrate equipped with electrodes, a heater and an accurate temperature sensor, on this structure the studied material can be deposited by screen printing, spin coating or dip coating. The system is designed to study the behavior of the sensors by accurately setting the operating conditions in terms of chemical environment composition, gas flow, humidity and temperature. The system is fully programmable and it individually controls the film temperatures or measures them with a resolution lower than 0.1 °C. Both chemical transients and thermal transients can be studied. These features make the system suitable for determining the principal performance indexes of a gas sensing device (e.g., sensitivity, stability, selectivity, response/recovery times, etc.) as functions of various combinations of measurement conditions (e.g., gas concentrations, temperature, humidity, flow). The proposed measurement system will find also useful applications in sensor model validation.

Abstract: The materials exploited for the development of gas conductometric sensors are often n-type semiconductors as in the case, e.g., of SnO2. Several materials studied in the last years for this application behave as p-type semiconductors (e.g. CuO, Cr2O3, Kor AgHollandites). In this work the authors present a novel surface state model for p-type, large grained, thick film materials, with a specific reference to Kor Ag- Hollandites, which accounts for the material response to CO in dry and humid N2, and in dry and humid air. A reliable and compact model of this type is of the utmost utility from several points of view, including the development of measurement systems based on gas sensors. The availability of a simulation tool able to accurately predict the sensor behavior enables the replacement of experimental tuning with simulations, and can significantly speed-up sensor-based system development and guarantee better performance.

Abstract: Silicon Physical Unclonable Functions (PUFs) are innovative circuit primitives whose digital output strictly depend on the manufacture random physical variations introduced during the fabrication process of integrated circuits. In this paper we discuss the statistical characterization of a simple PUF module based on ring oscillators to implement challenge-response FPGA authentication. Differently from other approaches, in our proposed solution the challenge bits play a role in changing the time dynamics involved in the chip response measurement. The experimental results show that considering proper values for the challenge bits the repeatability error rate is smaller than 5% at given chip temperature and supply voltage, obtaining a PUF module working with 4 challenge bits whereas exhibiting an high sensitivity to the manufacture random physical variations. The obtained results are comparable to that ones presented for other solutions, with a limited consumption of hardware resources.

Abstract: In this paper we discuss a measurement method based on the zero-crossing demodulation method of FM signals to estimate the angular velocity vibrations of a rotating shaft. The demodulation algorithm is applied without any filtering to the direct output voltage of probes sensing the tooth passing of a geared wheel installed on a rotating shaft. The proposed method rejects the effects on the measurements due to the irregular cogwheel shape profile.

Abstract: This paper presents a compression method that exploits pseudo-chaotic systems, to be applied to True Random Bit Generators (TRBGs). The theoretical explanation of the proposed compression scheme required the projection of some results achieved within the Ergodic Theory for chaotic systems on the world of digital pseudo-chaos. To this aim, a weaker and more general interpretation of the Shadowing Theory has been proposed, focusing on probability measures, rather than on single chaotic trajectories. The design of the compression scheme has been theoretically discussed in order to assure the final entropy of the compressed TRBG to be arbitrarily close to the maximum limit of 1 bit/time-step. The proposed solution requires extremely low-complex hardware circuits for being implemented, assures a constant throughput and is based on theoretical results of general validity.

Abstract: We propose a compression method for True Random Bit Generators (TRBGs) that exploits pseudo-chaotic systems. The compression scheme requires extremely low-complex hardware circuits for being implemented whereas its theoretical explanation is based on a weaker and more general interpretation of the Shadowing Theory, focusing on probability measures, rather than on single chaotic trajectories. We prove theoretically how to design the overall compression scheme, in order to assure the final entropy of the compressed TRBG to be arbitrarily close to the maximum theoretical limit of 1 bit/time-step.

Abstract: In this paper a probabilistic feedback technique to maximize the throughput of a generic True Random Bit Generator (TRBG) circuit, under a given constraint on the entropy, is discussed. In the proposed solution, the throughput of the device is dynamically and adaptively varied by an on-line entropy detector, such to obtain, with an arbitrary confidence level, an entropy greater than a given worst-case value. The approach, which has a general validity, introduces a method for making maximum use of the TRBG random bit generation capabilities, maximizing the generation throughput while preserving its entropy. It is different from the classical "open loop" TRBG design approach, in which the circuit parameter variability determines an uncertainty about the actual entropy of the device, with the proposed techniques the TRBG generation speed is varied under a given constraint on the entropy. The method can be applied to all those integrated TRBG circuits proposed in the literature and based on the uniform sampling of, e.g., random physical processes or chaotic dynamical systems.

Abstract: In this paper we discuss the efficient implementation of pseudochaotic piecewise linear maps with high digitization accuracies, taking the Rényi chaotic map as a reference. The proposed digital architectures are based on a novel algorithmic approach that uses carry save adders for the nonlinear arithmetic modular calculations arising when computing piecewise linear maps with a finite precision. As a result, the system can be implemented by digital circuits obtaining high throughputs, which are not dependent on the digital resolution while involving a hardware complexity linearly proportional to the number of bits used for representing the discretized state. The proposed solutions result to be particularly suitable for the implementation of pseudorandom number generators based on pseudochaos, or for the definition of efficient digital blocks that can be integrated in most of the pseudochaotic cyphers proposed in the
literature.

Abstract: In this paper we discuss a probabilistic feedback technique to maximize the throughput of a generic True Random Bit Generator (TRBG) circuit, under a given constraint on the entropy. In the proposed approach, the throughput of the device is dynamically and adaptively varied by an on-line entropy detector, such to obtain, with an arbitrary confidence level, an entropy greater than a given worst-case value. The method can be applied to all the integrated TRBG circuits proposed in the literature that are based on the uniform sampling of, e.g., random physical processes or chaotic dynamical systems.

Abstract: In this paper we discuss the possible use of chaotic signals for testing Analog to Digital Converters (ADCs). In detail, exploiting a chaos-based discrete-time noise generator, a method for generating test samples with a distribution arbitrarly close to the uniform one is proposed, and their use for the Code Density Test (also known as Histogram Test) of ADC is discussed.

Abstract: In this paper, a theoretical approach for studying the robustness of the chaotic statistics of piecewise affine maps with respect to parameter perturbations is discussed. The approach is oriented toward the study of the effects that the nonidealities derived from the circuit implementation of these chaotic systems have on their dynamics. The ergodic behavior of these systems is discussed in detail, adopting the approach developed by Boyarsky and Gora, with particular reference to the family of sawtooth maps, and the robustness of their invariant measures is studied. Although this paper is particularly focused on this specific family of maps, the proposed approach can be generalized to other piecewise affine maps considered in the literature for information and communications technology applications. Moreover, in this paper, an efficient method for estimating the unique invariant density for stochastically stable piecewise affine maps is proposed. The method is an alternative to Monte Carlo methods and to other methods based on the discretization of the Frobenius-Perron operator.

Abstract: In this paper we discuss an efficient iterative method for the estimation of the chief dynamical invariants of chaotic systems based on stochastically stable piecewise affine maps (e.g., the invariant measure, the Lyapunov exponent as well as the Kolmogorov-Sinai entropy). Referring to the theory developed by C. Liverani, we provide a theoretical tool for determining a priori a sufficient number of iterations that guarantees a given estimation accuracy.
The proposed method represents an alternative to the Monte-Carlo methods and to other methods based on the discretization of the Frobenius-Perron operator, such as the well known Ulam's method.
Our estimation method converges not slower than exponentially and it requires a computation complexity that grows linearly with the iterations. The proposed approach can be used to efficiently estimate any order statistics of a symbolic source based on a piecewise affine mixing map.

Abstract: This paper deals with state-dependent open Markovian (or exponential) queuing networks, for which arrival and service rates, as well as routing probabilities, may depend on the queue lengths. For a network of this kind, following Mandelbaum and Pats, we provide a formal definition of its associated fluid model, and we focus on the relationships which may occur between the network stochastic dynamics and the deterministic dynamics of its corresponding fluid model, particularly focusing on queuing networks whose fluid models have global periodic attractors.

Abstract: The generation of random numbers is required in several applications, including Monte Carlo simulations, testing of digital circuits, noise generation, telecommunication systems, and cryptography. In this paper we discuss a technique to obtain efficient digital hardware implementations of a class of pseudo random number generators derived from the Renyi chaotic map.

Abstract: In this paper an efficient and accurate method for computing the invariant measure of piecewise affine chaotic maps is proposed. As an application example, the method is used to evaluate for a chaos-based true random bit generator the robustness of the entropy with respect to small map parameters variations.

Abstract: In this paper, a family of nonlinear congruential generators (NLCGs) based on the digitized Reacutenyi map is considered for the definition of hardware-efficient pseudorandom number generators (PRNGs), and a theoretical framework for their study is presented. The authors investigate how the nonlinear structure of these systems eliminates some of the statistical regularities spoiling the randomness of sequences generated with linear techniques. In detail, in this paper, a necessary condition that the considered NLCGs must satisfy to have maximum period length is given, and a list of such maximum period PRNGs for period lengths up to 231-1 is provided. Referring to the NIST800-22 statistical test suite, two PRNG examples are presented and compared to well-known PRNGs based on linear recurrencies requiring a similar amount of resources for their implementation

Abstract: In this paper a family of maximum-period nonlinear congruential generators based on the digitized Renyi map is considered for the definition of hardware (or software) efficient pseudo random number generators (PRNGs). A list of such maximum period PRNGs for period lengths up to 231-1 is provided. Referring to the NIST800-22 statistical test suite, a PRNG example is presented and compared to well known PRNGs based on linear recurrences requiring a similar amount of resources for the implementation.

Abstract: In this paper a novel family of maximum-period nonlinear congruential generators (NLCGs) based on the digitized sawtooth map is considered for the definition of hardware and software efficient pseudo random number generators (PRNGs). A list of such maximum period NLCGs for period lengths up to 231-1 is provided. Referring to the NIST800-22 statistical test suite, a PRNG example based on the combination of two of the proposed NLCGs is presented and discussed

Abstract: In this paper a novel family of maximum-period Nonlinear Congruential Generators (NLCGs) based on the digitized Renyi chaotic map is considered for the definition of hardware-efficient Pseudo Random Number Generators (PRNGs). In detail, a theoretical result is provided about the periodicity of the output sequences generated by the proposed NLCGs. Moreover, the distribution of the generated numbers is discussed, comparing the results obtained the proposed NLCGs with those obtainable from traditional PRNGs based on linear recurrences methods.

Abstract: In this paper, the guidelines to design a true random bit generator (TRBG) circuit with a predefined minimum entropy are discussed. The approach is proposed for a TRBG based on a one-dimensional piecewise-linear chaotic map; it does not require bit throughput reduction, and it is suitable for the development of integrated TRBG circuits. In particular, the proposed design strategy is based on a feedback control procedure that allows to dynamically change the system parameters for the correction of the circuit "nonidealities" (e.g., the circuit offsets). The correction algorithm does not require a direct measurement of the system "nonidealities" or of the effective value of the map parameters, but only a dynamic estimation of these quantities based on the observation of the TRBG output. The design approach is validated by a hardware prototype implemented on a field-programmable analog array. The results of the NIST FIPS 140-2 test suite, the DIEHARD test suite, and the Coron's Universal test, applied to the TRBG output sequences before and after a simple post processing without throughput reduction, are reported and discussed.

Abstract: In this brief, a family of discretized one-dimensional chaotic maps derived from the Sawtooth map is analyzed to evaluate its suitability for the integrated implementation of low-complexity digital pseudorandom bit generators (PRBGs). The proposed PRBGs, classifiable as nonlinear congruential generators, are investigated in terms of period length, statistical properties of the generated sequences, hardware complexity, and are compared with traditional PRBGs.

Abstract: In this paper, the discretized Tent map is analyzed as a source of pseudorandom bits. To evaluate the performance of the proposed pseudorandom bit generators (PRBGs), different issues were considered, such as the period length, the statistical characteristics of the generated bit sequences, and the hardware complexity required in digital circuit implementations. The results show that, under proper design conditions, the Tent-map-based PRBGs represent a suitable alternative to other traditional low-complexity PRBGs such as the linear feedback shift registers

Abstract: In this paper the theoretical bases to design a true random bit generator (TRBG) circuit with a predefined minimum entropy are discussed. The approach is tailored to TRBGs based on a one-dimensional piecewise-linear chaotic map, and it is based on a feedback control procedure that allows to dynamically changing the system parameters. For this purpose, the procedure just exploits the TRBG output observation without requiring bit throughput reduction. The design approach was validated by an hardware prototype implemented on a field programmable analog array (FPAA)

Abstract: In this paper, the guidelines to design a true random number generator (TRNG) circuit of uniform distributed numbers. The approach is proposed for a TRNG based on a one-dimensional piecewise-linear chaotic map and it is suitable for the development of integrated TRNG circuits. In particular, the proposed design strategy is based on a feedback control procedure that allows to dynamically change the system parameters for the correction of the circuit "non-idealities" (e.g. the circuit offsets). The correction algorithm does not require a direct measurement of the system "non-idealities" or of the effective value of the map parameters, but only a dynamic estimation of these quantities based on the observation of the TRNG output. The design approach is validated by a hardware prototype implemented on a field programmable analog array (FPAA)

Abstract: In this paper we propose an efficient low-hardware complexity post-processing module for a feedback-corrected chaos-based True Random Bit Generator (TRBG) with high Average Shannon Entropy (ASE). The design of the postprocessing module was based both on the theoretical analysis of the information generation mechanism of the considered source and on numerical simulations. A prototype of the module was tested on an implementation of the TRBG with an actual ASE slightly lower than 1 bit/time step, obtaining random sequences that fully pass all the well-known statistical tests of the Diehard suite.

Abstract: In this paper the theoretical bases to design a true random bit generator circuit with a predefined minimum entropy are discussed. The approach is tailored to generators based on the Sawtooth chaotic map, and it is based on a feedback control system designed for the optimization of the system parameters. The design approach was validated by an hardware prototype implemented on a Field Programmable Analog Array.

Abstract: In this paper we consider state-dependent Markovian queueing networks and we provide a formal definition of their associated fluid model. We particularly consider queuing networks whose fluid models have global periodic attractors, focusing on the relationships which may occur in such cases between the network stochastic dynamics and the deterministic dynamics of its corresponding fluid model.

Abstract: In this paper, the digital implementation of the Sawtooth map is analyzed as a source of pseudo random bits. In particular, a special family of discretized maps derived from the Sawtooth map is introduced, and theoretical aspects on the periodicity of the system are discussed. To evaluate the performance of the obtained pseudo random sources, different statistical parameters and tests that measure the characteristics of the output bit sequences are considered. The results show that, under specific design conditions, the discretized Sawtooth map can be proposed as a suitable solution for the implementation of integrated long period pseudo random bit generators.

Abstract: In this paper, a digital implementation of the Tent map is analyzed as a source of pseudo-random bits. In particular, several solutions are investigated, taking into account the numerical errors due to the approximation strategy used (truncation/rounding off). To evaluate the performance of the obtained pseudo-random sources, a number of statistical parameters and tests that properly measure the characteristics of the output bit sequences are considered. Results show that, under specific design conditions, the discretized Tent map can be proposed as a suitable solution for the implementation of an integrated pseudo random bit generator.

Abstract: In this paper, two families of digital maps derived from the sawtooth map and from the tent map are analyzed in terms of suitability for pseudo-random bit generation. In particular, several solutions are investigated taking into account the numerical errors due to the approximation strategy used (truncation/rounding off). To evaluate the performance of the obtained pseudo-random sources a number of statistical parameters and tests that properly measure the characteristics of output bit sequences are considered. Results show that, under specific design conditions, the discretized sawtooth and tent maps are suitable for generating long-period bit sequences with an adequate randomness quality.