Toward metrological trustworthiness for automated and connected mobility

The mobility of people and goods is moving into a new era of more automated services based on sensors networks and Artificial Intelligence. At present, Automated Mobility, in the broadest meaning of the terms includes Advanced Driver Assistance System (ADAS) and Autonomous Vehicle (AV), beyond being attractive for many practical advantages, ranging from safety to traffic flow manage- ment, still presents several concerns on the trustworthiness of sen- sor networks integrated into vehicles, especially regarding sen- sors calibration, data uncertainty and data fusion approaches. Currently, the trustworthiness of ADAS and AV functions is assessed with virtual and physical simulation of functions relying on synthetic sensor models, simulated and measured sensor data and equivalent environmental conditions. During the lifespan of vehicles, environmental effects including possible accidents and common usage, can have significant impact on the performance of ADAS sensors and customer functions. Current approach is to consider ADAS sensors output nominal, disregarding the uncer- tainty of sensors data and including all the possible tolerances and variability at sensors/system testing stage. At present day, market offers several facilities and commer- cial set-up promoted as being able to do ADAS calibration: usu- ally are modular equipment allowing alignment and sensitivity check of different ADAS sensors, especially front sensors and camera. However, sensor calibration involves specific calibration facilities, procedures to establishing sensors sensitivity and most of all, associated uncertainty. Accuracy and traceability of ADAS sensors beyond being fundamental requirements in measurement science, allow the quantitative evaluation of the trustworthiness of sensors and customer functions. This paper suggests an approach to lay the foundation of Metrology of Trustworthiness for ADAS and AV complex sensors systems and provide a case study of IMU sensor trustworthiness

Sound Insulation of Building Elements at Low Frequency: A Modal Approach

In typical laboratory volumes (50-80 m(3)) and at low frequencies (50-100 Hz), the acoustic field is non-diffuse due to the presence of source and receiving room modes. Under such conditions, standard sound insulation measurements and descriptors are not adequate to correctly characterize the insulating property of partitions or flooring systems. The "modal approach" allows to evaluate the airborne sound insulation by the determination of modal transmission loss, or modal sound insulation, of a single mode passing through the partition. Proper normalization terms and an extension method to one-third octave bands are also introduced. The same approach is applied to impact sound insulation measurement. (C) 2015 The Authors. Published by Elsevier Ltd

A MODAL APPROACH FORREVERBERATION TIME MEASUREMENTS IN NON-DIFFUSE SOUND FIELD

In recent years the extension of reverberation time measurements to frequencies below 100 Hz is becoming more and more important due to the increase of low frequency sources. In ordinary rooms with volumes smaller than 200 m3the low frequency sound field is non-diffuse due to the presence of modes, which are also the main cause of bad quality of listening in terms of clarity and rumble effects. Since standard measurements according to ISO 3382 fail to achieve accurate and precise values in third octave bands due to non-linear decays of room modes, a new ap-proach based on reverberation time measurements of single resonant frequencies (the modal re-verberation time) is introduced. Two measurementmethods based on the relation between mod-al decays and resonant half bandwidths are proposed: the direct method, based on the direct evaluation of modal sound decays with interrupted source signals, and the indirect method based on half bandwidth measurements. Proper measurement procedures, with microphones placed at rectangular room corners and anti-resonant sine waves and sweep source signals for direct and indirect measurement methods respectively, are proposed. Comparison between direct and indi-rect methods shows good and significant agreement. Comparing modal reverberation times with standard ones, the inadequacy of standard procedure to get accurate and precise values at low frequencies with respect to the modal approach becomes evident. In the future, further investi-gations are necessary in more rooms toimprove uncertainty evaluation

Reverberation time measurements in non-diffuse acoustic field by the modal reverberation time

partially_open3mixedPrato, A.; Casassa, F.; Schiavi, A.Prato, A.; Casassa, F.; Schiavi, Alessandr

Indentation Modulus, Indentation Work and Creep of Metals and Alloys at the Macro-Scale Level: Experimental Insights into the Use of a Primary Vickers Hardness Standard Machine

open5In this work, the experimental method and the calculation model for the determination of indentation moduli, indentation work, and indentation creep of metallic materials, by means of macroscale-level forces provided by a primary hardness standard machine at the National Institute of Metrological Research (INRIM) at the at room temperature were described. Indentation moduli were accurately determined from measurements of indentation load, displacement, contact stiffness and hardness indentation imaging and from the slope of the indentation unloading curve by apply-ing the Doerner-Nix linear model; indentation work, representing the mechanical work spent dur-ing the force application of the indentation procedure, was determined by calculating the areas un-der the loading–unloading indentation curve, through fitting experimental data with a polynomial law. Measurements were performed with a pyramidal indenter (Vickers test). The applied force was provided by a deadweight machine, and the related displacement was measured by a laser inter-ferometric system. Applied forces and the occurring indentation depths were simultaneously meas-ured: the resulting loading–unloading indentation curve was achieved. Illustrative tests were per-formed on metals and alloy samples. Discussion and comments on the suitability of the proposed method and analysis were reported.openAlessandro Schiavi, Claudio Origlia, Alessandro Germak, Andrea Prato, Gianfranco GentaSchiavi, Alessandro; Origlia, Claudio; Germak, ALESSANDRO FRANCO LIDIA; Prato, Andrea; Genta, Gianfranc

Bundle-o-graphy: improving structural connectivity estimation with adaptive microstructure-informed tractography

Tractography is a powerful tool for the investigation of the complex organization of the brain in vivo, as it allows inferring the macroscopic pathways of the major fiber bundles of the white matter based on non-invasive diffusion-weighted magnetic resonance imaging acquisitions. Despite this unique and compelling ability, some studies have exposed the poor anatomical accuracy of the reconstructions obtained with this technique and challenged its effectiveness for studying brain connectivity. In this work, we describe a novel method to readdress tractography reconstruction problem in a global manner by combining the strengths of so-called generative and discriminative strategies. Starting from an input tractogram, we parameterize the connections between brain regions following a bundle-based representation that allows to drastically reducing the number of parameters needed to model groups of fascicles. The parameters space is explored following an MCMC generative approach, while a discrimininative method is exploited to globally evaluate the set of connections which is updated according to Bayes' rule. Our results on both synthetic and real brain data show that the proposed solution, called bundle-o-graphy, allows improving the anatomical accuracy of the reconstructions while keeping the computational complexity similar to other state-of-the-art methods

Perspectives and limits on the use of commercial low-cost digital MEMS accelerometers in gravimetry

The value of the acceleration due to gravity is of interest in a wide range of fields, from geophysics, geodesy, water-floor monitoring, and hazard forecasting to oil, gas and mineral exploration. For this purpose, relative or absolute gravimeters have been developed and used for decades. While absolute gravimeters are mainly used in monitoring stations or as reference, relative gravimeters are those actually used to determine the relative variations of the local gravitational field given their smaller dimension, lighter weight, and better reading resolution, despite the high costs and the difficulty in being used under severe environmental conditions. In the last years, the advent of micro-electromechanical-systems (MEMS), in particular MEMS accelerometers, has opened up the doors to new measuring possibilities at very low-costs. As a consequence, different international research groups focused their efforts to develop relative MEMS gravimeters and showed that this technology might be really useful for monitoring the gravitational field. However, their current production is limited to a few specimens and prototypes that cannot be exploited on a large scale at the present day. For this reason, this work investigates the possibilities and the limits in the use of commercial digital MEMS accelerometers as relative gravimeters. The digital MEMS accelerometers investigated in this work are two commercial low-cost digital MEMS accelerometers (STM, model LSM6DSR, and Sequoia, model GEA). The first is composed of an accelerometer sensor, a charge amplifier, and an analog-to-digital converter and is connected by a serial cable to a separated external microcontroller (ST, model 32F769IDISCOVERY), in which other electronic components are integrated. The second is composed of the sensing element and the analog-to-digital converter. Both are connected to the computer via USB cable. The two devices are included in a thermally insulated case, in which a resistive heater and a resistance thermometer (PT1000), connected in loop, are placed in order to guarantee temperature stability during use. The system, installed on a tilting table to ensure higher accuracy in the evaluation of local g, is calibrated in static conditions by comparison to the absolute gravimeter IMGC-02 at a specific measurement location at INRIM. Calibration is repeated several times over a period of a few weeks in order to evaluate repeatability, reproducibility and stability over time. Despite the promising future prospects of this technology, at present, the levels of precisions are low compared to the ones required by most of geodynamics applications

Calibration of tri-axial MEMS accelerometers in the low-frequency range – Part 2: Uncertainty assessment

Abstract. A comparison among three methods for the calibration of tri-axial accelerometers, in particular MEMS, is presented in this paper, paying attention to the uncertainty assessment of each method. The first method is performed according to the ISO 16063 standards. Two innovative methods are analysed, both suitable for in-field application. The effects on the whole uncertainty of the following aspects have been evaluated: the test bench performances in realizing the reference motion, the vibration reference sensor, the geometrical parameters and the data processing techniques. The uncertainty contributions due to the offset and the transverse sensitivity are also studied, by calibrating two different types of accelerometers, a piezoelectric one and a capacitive one, to check their effect on the accuracy of the methods under comparison. The reproducibility of methods is demonstrated. Relative uncertainty of methods ranges from 3 to 5 %, depending on the complexity of the model and of the requested operations. The results appear promising for low-cost calibration of new tri-axial accelerometers of MEMS type