Background: The risk assessment for video display terminal (VDT) operators in occupational settings often relies on indirect estimates, such as self-reported screen time, which may not accurately reflect the true visual workload. The objective is to assess visual workload in VDT workers by measuring active screen fixation time with a non-invasive monitoring system and to explore its relationship with ocular surface alterations and fatigue-related indicators. Methods: An observational cross-sectional study was conducted on 38 administrative workers employed at a hospital booking center. Active VDT screen fixation, as well as shift duration and time spent in front of the VDT screen, were objectively measured using a patented video-based monitoring system. Ophthalmological evaluation included the Ocular Surface Disease Index (OSDI®), tear break-up time (BUT), and slit-lamp examination. Other investigated markers included blink rate, the Percentage of Eyelid Closure over the Pupil over Time (PERCLOS), and the Fatigue Assessment Scale (FAS). Results: Active screen fixation accounted for approximately 60% of the total recorded working time. Ophthalmological assessment identified alterations of the ocular surface in a substantial proportion of workers, with pathological BUT values observed in nearly half (47%) of the study population. No statistically significant associations were found between objectively measured fixation time and ocular or fatigue-related outcomes. PERCLOS80 and blink rate values remained within physiological ranges across the work shift. Conclusions: Objective measurement of screen fixation provides a more accurate characterization of visual workload among VDT workers than indirect exposure estimates and may support occupational health surveillance and risk assessment in VDT-exposed workers.

Background: Occupational risk assessments of VDT users are usually hindered by the variability of tasks that office workers perform. Digital eye strain is related to the amount of work time dedicated to screen fixation. Purpose: This study aimed to improve the risk assessment of VDT workers by introducing an advanced version of software developed at the University of Brescia. Methods: The prototype enables the recording of the times in front of the screen and those in which the operator actively fixes. It was tested on 30 employees from different offices. The system includes a webcam placed over the workers’ screens and connected with a laptop running specifically developed monitoring software. This experiment required worker-to-worker calibration of the system by the investigators. Results: The obtained data allowed us to distinguish between the period of screen fixation and the presence in front of the monitor. The visual activity varied greatly on a daily basis because of the differences between tasks. The mean facial detection time was approximately 48%, whereas the mean eye fixation time was 29%. Conclusions: The results suggest that our prototype is a promising tool for investigating the relative contributions of screen fixation to the development of digital occupational eye strain.

The occupational risk of operators using display screen equipment (DSE) is usually evaluated according to the extent of time spent in active operator-DSE interactions. Risk assessment is based on activity data collected through questionnaires. We evaluated an original and innovative system that can objectively assess active operator-DSE interactions by collecting electrical impulses generated by the activation of mouse, keyboard and a camera that collects attentive eye-screen fixation. The main aim of this study was to evaluate the system's performance on an employee sample involved in the task of active reading and copying at a DSE workstation connected to the system. In the context of mandatory health surveillance at work, we enrolled 38 DSE operators with normal neuropsychological and eye assessments who were required to complete two predefined reading and writing tasks. The obtained results show that the system is able to collect activity data derived from operator-DSE interactions through screen fixation, keyboard tapping and mouse handling. In the copying task, the session duration as recorded by the system was highly related to the screen fixation time. In the copying task, mouse and keyboard activities were more strongly related to session duration than screen fixation. For the copying task, it was also possible to obtain individual profiles of operator-DSE interactions while performing the same standardized tasks. Collected data can allow an objective evaluation of active time spent by DSE operators at their workstations, thus allowing a more accurate occupational health risk assessment and management. Prospective analysis of individual operator-DSE interaction profiles can favor the setup of targeted preventive and organizational interventions from an of even wider worker wellbeing perspective.

This paper presents a contactless measurement system for a mixed array of resistive and capacitive sensors exploiting a low-frequency radio-frequency identification (RFID)-based approach. The system is composed of a reader unit which provides power to and exchanges measurement data with a battery-less sensor unit. The sensor unit is based on a transponder operating at 134.2 kHz and a microcontroller. The microcontroller sequentially measures the elements of the sensor array composed of n capacitive and m resistive sensors which share a common terminal. The adopted technique measures the charging time of a resistor–capacitor (RC) circuit, where the resistor or the capacitor can be either the sensing element or a reference component. With the proposed approach, the measured values of the resistive or capacitive elements of the sensor array are first-order independent from the supply voltage level. A prototype has been developed and experimentally tested with resistive elements in the range 400 kΩ–1.2 MΩ and capacitive elements in the range 200 pF–1.2 nF showing measurement resolution values of 1 kΩ and 5 pF, respectively. Operative distances up to 3 cm have been achieved, with readings taken faster than one element of the array per second.

This paper presents a contactless measurement system for an array of resistive sensors that exploits a low-frequency (LF) RFID-based approach. The system is composed of an interrogation unit (reader) which powers the sensor unit and exchanges measurement data with it. The sensor unit exploits a transponder operating at 134.2 kHz and a microcontroller. The transponder receives power from the reader and transfers data through the RF-link. The microcontroller sequentially measures the elements of a sensor array composed of six resistors with one common terminal. The adopted technique relies on the evaluation of the charging time of a capacitor through the measured resistor. By exploiting a known reference resistor this technique is theoretically independent from the values of the capacitor and of the supply voltage. A prototype has been developed showing operative distances of up to few centimeters and reads faster than one element of the array per second.

The possibility to generate acoustic modes based on FPWs (Flexural Plate Waves) in a generic non-piezoelectric substrate for microfludic applications by means of piezoelectric actuators has been explored and described in this paper. The FPW acoustic modes are generated by means of actuators made of Lead Zirconate Titanate (PZT) layers with InterDigital Transducers (IDTs) screen-printed on alumina (Al2O3) substrate. The experimental results show that, by exciting the resonances of the actuators, circular vortex rotations are obtained in a fluid drop placed on the substrate between the IDTs. Micrometric particles dispersed in the drop allow to demonstrate that standing waves can be generated in the liquid obtaining particle accumulation along circular lines. These results suggest the possibility to employ the proposed actuators for fluid mixing and controlled positioning of dispersed particles.

Energy harvesting from wideband and random vibrations demands for techniques and solutions to overcome limitations of linear converters, which best operate when the frequency of vibrations matches the resonant frequency of the converter. Viable approaches comprise, among others, the use of array of linear harvesters with different resonant frequencies, the adoption of nonlinear techniques or the exploitation of mechanically coupled converters. This work proposes a piezoelectric energy harvester where the combination of such techniques is explored in a unique device. The harvester is composed of an array of four piezoelectric cantilevers fabricated by screen printing lead zirconate titanate (PZT) films on a stainless steel substrate. Nonlinear behavior of the cantilevers is achieved by exploiting the interaction between a magnet and their ferromagnetic steel substrate. Two configurations have been analyzed where the magnet is either fixed on the harvester base, or it is elastically suspended through a spring on the harvester base. The latter configuration introduces a mechanical coupling among the cantilevers. For the experimental characterization, the prototype has been excited by band-pass filtered white-noise mechanical vibrations in the range 10–100 Hz with amplitude in the range 0.1–2.2 g. The obtained experimental results show that the rms values of the open-circuit output voltage for each cantilever increase in the nonlinear configuration and it can be up to 215% higher for the case with the elastically suspended magnet compared to the case of the same array operated in linear regime.

Piezoelectric films fabricated with lead-free piezoelectric inks by means of a mask-less Direct-Writing (DW) technique are presented. A lead-free piezoelectric material, K0.5Na0.5NbO3-δ (KNN), has been produced via Solid State Reaction (SSR) and Molten Citrate (MC) route in order to improve the microstructural properties of powders. The slurry composition and rheology have been optimized in order to obtain inks with physical properties compatible with the DW technique and layers with enhanced mechanical and piezoelectric properties. Experimental results obtained with pellets and films deposited on alumina substrates demonstrate the piezoelectric properties of the fabricated devices. The developed direct-writing technique will be implemented for the realization of precise patterns of piezoelectric sensors or actuators inside microsystems, without the requirement of manufacture expensive masks.

A piezoelectric converter for energy harvesting composed of a rigid ball enclosed among six piezoelectric diaphragms arranged in a cube-shaped structure is presented. When the converter is excited by mechanical vibrations, the ball repeatedly bounces and hits one or more diaphragms, implementing the impact technique in a multi-degree-of-freedom configuration. The structure is isotropic thus the converter is effective irrespective of the vibration orientation. The converter is particularly suitable for energy harvesting from low-frequency random vibrations, such as those provided by human motion. The triaxial ball-impact piezoelectric converter was designed, built and experimentally characterized in the laboratory, and then tied to the ankle of a person and tested during physical activity. While the person is running at 7 km/h, a peak instantaneous power of up to 16 mW is provided by each of the six piezoelectric diaphragms, while the average power is significantly lower. The converter was coupled to a tailored power management circuit which intermittently powers a battery-less wearable temperature sensor module. In about 260 s of walking at 2 km/h, an energy of 1.4 mJ is extracted, stored into a 1-mF capacitor, and used to power the sensor module, which performs a temperature measurement and transmits the data to a receiver through a 433-MHz RF-UART link. (C) 2015 Elsevier B.V. All rights reserved.

In this paper, a portable battery-powered energy-logger circuit to monitor the energy harvested by different piezoelectric converters mounted on selected positions of the human body under typical daily activity is proposed. The circuit logs on an SD memory card both the rms value of the acceleration imparted to the Energy Harvesting (EH) converter under test and the time intervals needed to achieve a predefined amount of energy stored on capacitors. The energy-logger circuit was tested with three different types of piezoelectric EH converters under different excitation conditions allowing to measure an effectiveness index given by the time necessary to accumulate the energy required to power one operating cycle of the autonomous sensor module representing the load.

Zinc oxide (ZnO, n-type) and copper oxide (CuO, p-type) nanowires have been synthesized and preliminarily investigated as innovative materials for the fabrication of a proof-of-concept thermoelectric device. The Seebeck coefficients, electrical conductivity and thermoelectric power factors (TPF) of both semiconductor materials have been determined independently using a custom experimental set-up, leading to results in agreement with available literature with potential improvement. Combining bundles of ZnO and CuO nanowires in a series of five thermocouples on alumina leads to a macroscopic prototype of a planar thermoelectric generator (TEG) unit. This demonstrates the possibility of further integration of metal oxide nanostructures into efficient thermoelectric devices.

The Seebeck effect in ZnO (n-type) and CuO (p-type) nanowire bundles grown on alumina substrates has been investigated. By combining n- and p-type nanostructured elements, a planar thermoelectric device has been proposed and characterized, confirming the feasibility of fabricating planar thermoelectric generators based on metal oxide nanowires with the future aim of powering autonomous sensors and microsystems.

The Seebeck effect of ZnO nanowires has been investigated with the future aim to build thermoelectric devices based on nanowire arrays for energy harvesting and potential use in low-power portable electronics and autonomous sensor systems. Bundles of ZnO nanowires have been deposited on alumina substrates by a thermal evaporation process. The ZnO nanowires have been characterized by means of a purposely-developed experimental set-up, showing a negative Seebeck coefficient as for n-type semiconductors.

A planar ThermoElectric Generator (TEG) containing five thermocouples based on nanostructured metal-oxide elements wired electrically in series and thermally in parallel has been designed and fabricated. The thermoelectric elements consist of ZnO (n-type) and CuO (p-type) bundles of quasi-monodimensional nanowires deposited utilizing shadow masks. The TEG has been experimentally characterized, confirming feasibility of fabricating planar thermoelectric devices based on metal-oxide nanowires with the future aim to powering portable electronics and autonomous sensors and microsystems.

In this paper a dual-chip system for inclination measurement is presented. It consists of a MEMS (microelectromechanical system) piezoresistive accelerometer manufactured in silicon bulk micromachining and a CMOS (complementary metal oxide semiconductor) ASIC (application specific integrated circuit) interface designed for resistive-bridge sensors. The sensor is composed of a seismic mass symmetrically suspended by means of four flexure beams that integrate two piezoresistors each to detect the applied static acceleration, which is related to inclination with respect to the gravity vector. The ASIC interface is based on a relaxation oscillator where the frequency and the duty cycle of a rectangular-wave output signal are related to the fractional bridge imbalance and the overall bridge resistance of the sensor, respectively. The latter is a function of temperature; therefore the sensing element itself can be advantageously used to derive information for its own thermal compensation. DC current excitation of the sensor makes the configuration unaffected by wire resistances and parasitic capacitances. Therefore, a modular system results where the sensor can be placed remotely from the electronics without suffering accuracy degradation. The inclination measurement system has been characterized as a function of the applied inclination angle at different temperatures. At room temperature, the experimental sensitivity of the system results in about 148 Hz/g, which corresponds to an angular sensitivity around zero inclination angle of about 2.58 Hz deg−1. This is in agreement with finite element method simulations. The measured output fluctuations at constant temperature determine an equivalent resolution of about 0.1° at midrange. In the temperature range of 25–65 °C the system sensitivity decreases by about 10%, which is less than the variation due to the microsensor alone thanks to thermal compensation provided by the current excitation of the bridge and the positive temperature coefficient of resistance of the piezoresistors.

A smart system for flow measurement is presented, consisting of a micromachined thermal flow sensor combined with a smart front-end electronic interface. The flow sensor is based on a novel thermal transduction method, which combines the hot-film and calorimetric sensing principles. The sensor consists of four germanium thermistors embedded in a thin membrane and connected to form a Wheatstone bridge supplied with a constant DC current. In this configuration, both the bridge unbalance voltage and the voltage at the bridge supply terminals are functions of the flow offering high initial sensitivity, i.e., near zero flow and wide measurement range, respectively. The front-end interface is based on a CMOS relaxation oscillator circuit where the frequency and the duty cycle of a rectangular-wave output signal are related to the bridge unbalance voltage and the voltage at the bridge supply terminals, respectively. Furthermore, the amplitude of the output signal is a linear function of the operating temperature. In this way, a single output signal advantageously carries two pieces of information related to the flow velocity and provides an additional measurement of the sensor operating temperature, which enables the correction of the temperature dependence of the sensor readouts. The system has been experimentally characterized for the measurement of nitrogen gas flow velocity at different sensor temperatures. The initial sensitivities at room temperature result 13.7 kHz/(m/s) and 23.5%/(m/s), in agreement with FEM simulations, for frequency and duty cycle readouts, respectively, with an equivalent velocity resolution of about 0.5 and 1.3 cm/s.

A thermoelectric microgenerator based on a novel structure, in which the heat flowing in elements with different thermal resistances produces local temperature differences in the device, has been designed, fabricated in BESOI technology and experimentally characterized. The temperature differences in the microgenerator are converted into a voltage by means of the Seebeck effect exploiting planar thermocouples.

The Seebeck effect of ZnO nanowires has been investigated with the future aim of building thermoelectric devices based on nanowire arrays for energy harvesting and using them in low-power portable electronics and autonomous sensor systems. Quasi monodimensional (1D) ZnO nanowires have been deposited on alumina substrates according to the recently proposed thermal evaporation process, which involves Vapour-Phase and Vapour-Liquid-Phase growth mechanisms. The Seebeck coefficient of ZnO nanowires has been successfully measured with a purposely- developed experimental set-up, confirming that the ZnO nanowires exhibit high thermoelectric coefficient.