Lucia Bissi

Automated defect detection in uniform and structured fabrics using Gabor filters and PCA

This paper describes an algorithm for texture defect detection in uniform and structured fabrics, which has been tested on the TILDA image database. The proposed approach is structured in a feature extraction phase, which relies on a complex symmetric Gabor filter bank and Principal Component Analysis (PCA), and on a defect identification phase, which is based on the Euclidean norm of features and on the comparison with fabric type specific parameters. Our analysis is performed on a patch basis, instead of considering single pixels. The performance has been evaluated with uniformly textured fabrics and fabrics with visible texture and grid-like structures, using as reference defect locations identified by human observers. The results show that our algorithm outperforms previous approaches in most cases, achieving a detection rate of 98.8% and a false alarm rate as low as 0.20-0.37%, whereas for heavily structured yarns misdetection rate can be as low as 5%.

A Programmable Interface Circuit for an Ultralow Power Gas Sensor

Abstract-An electronic system based on a microcontroller architecture, devoted to interfacing a three-terminal, ultralow power (ULP) Metal OXide (MOX) gas sensor is presented. The sensor features a novel three-terminal configuration where the microheater is not galvanically isolated with respect to the MOX sensor. The system provides both control of the operating temperature and management of the acquired data. A Pulse Width Modulation (PWM) signal with variable duty cycle is used to provide power to the heating resistor in order to set the desired operating temperature. The heating resistance value is measured in the range (100-300) Ω with a relative error of less than 1%. The circuit devoted to measuring the gas concentration is based on a logarithmic amplifier which measures the current flowing in the sensing layer of the sensor. The measurand range is 30 nA to 60 mA and the relative error of the measured current is less than 0.6%. The data acquisition system was successfully tested by acquiring data of a three-terminal ULP gas sensor located in an automatically controlled environmental chamber under benzene and NO2 flow.

Use of a CMOS Image Sensor for an Active Personal Dosimeter in Interventional Radiology

Interventional radiologists and staff members, during all their professional activities, are frequently exposed to protracted and fractionated low doses of ionizing radiation. Due to skin tissues and peripheral blood irradiation, these exposures can result in deterministic effects (radiodermatitis, aged skin, and hand depilation) or stochastic ones (skin and non-solid cancer incidence). The authors present a novel approach to perform online monitoring of the staff during their interventions by using a device based on an Active Pixel Sensor. The performance of the sensor as an X-ray radiation detector has been evaluated with a proper experimental setup: the number of photons and the generated charge have been assessed as dosimetric observables from the frames acquired by the sensor using a two-threshold clustering algorithm, the efficiency of which has been evaluated as well. The correlation of these observables with passive dosimeter dose measurements has been analyzed: a good linearity has been demonstrated, and the response difference between pulsed and continuous operational modes is reduced to less than 10%, marking a distinct improvement with respect to commercial Active Personal Dosimeters.

A Multi-Standard Reconfigurable Viterbi Decoder using Embedded FPGA Blocks

This paper presents a Viterbi decoder (VD) architecture for a reprogrammable data transmission system, implemented using a field programmable gate array (FPGA) device. This VD has been conceived as a building block of a software defined radio (SDR) mobile transceiver, reconfigurable on user request and capable to provide agility in choosing between different standards. UMTS and GPRS standards decoding is achieved by choosing different coding rates and constraint lengths, and the possibility to switch, at run time, between them guarantees a high degree of reconfigurability. The architecture has been tested and verified with a Xilinx XC2V2000 FPGA, to provide a generalized co-simulation/co-design testbed. The results show that this decoder can sustain an uncoded data rate of about 2 Mbps, with an area occupation of 45%, due to the efficient resource reuse

Interface circuit for an ultra low power gas sensor

An electronic system based on a microcontroller architecture devoted to interfacing an Ultra Low Power (ULP) Metal OXide (MOX) gas sensor is presented. The circuit controls the operating temperature and manages the acquired data. A Pulse Width Modulation (PWM) signal with variable duty cycle is used to provide power to the heating resistor in order to set the desired operating temperature. The heating resistance value is measured in the range [100 Ω - 500 Ω] with a relative error less than 1%. The circuit devoted to measure the gas concentration is based on a logarithmic amplifier which measures the current flowing in the sensing layer of the sensor. The measurand range is [30 nA - 60 μA] and the relative error on the measured current is less than 0.6%.

A Configurable Mixed-Signal Architecture for Label-Free Smart Biosensor Applications

The authors present a novel approach to perform the readout of a genetic sensor by using a low-frequency impedance-sensing technique based on phase-shift measurements. The proposed architecture is sufficiently simple to be fit into an off-the-shelf programmable system-on-chip (PSoC) and yet has been demonstrated to be powerful enough to measure a wide range of capacitance values (100 pF-10 muF ) with a relative error smaller than 2% compared with a high-cost laboratory instrumentation. Field measurements on real sensing structures demonstrated the functionality of the system in saline solutions characterized by different molarities. In this case, the sensor model could not be reduced to a simple capacitance, and the acquired phase shifts were fitted by exploiting a constant-phase element (CPE) model of the sensor. The worst-case relative error on the extracted capacitance for a given molar concentration is 16% for the 0.1-M solution and 11% for the 0.5-M solution. Since DNA hybridization should cause a capacitance change on the order of 25%, our conclusion is that, in principle, the proposed measurement procedure is able to discriminate between single-stranded and hybridized DNAs. The measured phase shifts as a function of frequency allowed us to extract the parameters of the CPE model with an error on the phase that is smaller than 0.4deg .

Patch based yarn defect detection using Gabor filters

This paper describes a simple and effective algorithm for texture defect detection in uniform and structured fabrics. The proposed approach is structured in two phases: feature extraction and defect identification. The texture features extraction phase relies on a complex symmetric Gabor filter bank and Principal Component Analysis for dimensionality reduction. Differently from most previous works, our analysis is performed on a patch basis, which has been more effective than simply considering raw pixels as features. The defect identification phase is fast as it is based on the evaluation of the Euclidean norm of the patch feature vectors, and on the comparison with fabric type specific parameters. A calibration procedure, performed offline, is adopted in order to estimate the optimal parameters. The performance of the algorithm has been extensively evaluated, via computer simulations, on the TILDA image database. The results show that our algorithm outperforms previous approaches in most of the considered cases, achieving a detection rate of 98.8% and a false alarm rate as low as 0.37%.

A Viterbi decoder architecture for a standard-agile and reprogrammable transceiver

This paper presents a Viterbi decoder (VD) architecture for a programmable data transmission system, implemented using a Field Programmable Gate Array (FPGA) device. This VD has been conceived as a building block of a software defined radio (SDR) mobile transceiver, reconfigurable on request and capable to provide agility in choosing between different standards. UMTS and GPRS Viterbi decoding is achieved by choosing different coding rates and constraint lengths, and the possibility to switch, at run time, between them guarantees a high degree of programmability. The architecture has been tested and verified with a Xilinx XC2V2000 FPGA for providing a generalized co-simulation/co-design testbed. The results show that this decoder can sustain an uncoded data rate of about 2Mbps, with an area occupancy of 46%, due to the efficient resources reuse.

Personnel real time dosimetry in interventional radiology

Interventional radiology and hemodynamic procedures have rapidly grown in number in the past decade, increasing the importance of personnel dosimetry not only for patients but also for medical staff. The optimization of the absorbed dose during operations is one of the goals that fostered the development of real-time dosimetric systems. Indeed, introducing proper procedure optimization, like correlating dose rate measurements with medical staff position inside the operating room, the absorbed dose could be reduced. Real-time dose measurements would greatly facilitate this task through real-time monitoring and automatic data recording. Besides real-time dose monitoring could allow automatic data recording. In this work, we will describe the calibration and validation of a wireless real-time prototype dosimeter based on a new sensor device (CMOS imager). The validation measurement campaign in clinical conditions has demonstrated the prototype capability of measuring dose-rates with a frequency in the range of few Hz, and an uncertainty smaller than 10%.

Smart Capacitive Biosensor Based on a Programmable System-on-Chip, Featuring a Novel Method for Improving the Performance of its Analog Blocks

The authors present a novel approach to perform the readout of a capacitive genetic sensor by using an impedance sensing technique. The proposed architecture is sufficiently simple for being fitted in an off-the-shelf programmable system on chip (PSoCTM) from Cypress semiconductors and yet powerful enough for measuring a great range of capacitance values (100 pF - 10 muF).