Alberto Roncaglia

Fiber Optic Broadband Ultrasonic Probe for Virtual Biopsy: Technological Solutions

An ultrasonic probe was developed by using, in conjunction, opto-acoustic and acousto-optic devices based on fiber optic technology. The intrinsic high frequency and wide bandwidth associated both to the opto-acoustic source and to the acousto-optic receiving element could open a way towards a “virtual biopsy” of biological tissue. A Micro-Opto-Mechanical-System (MOMS) approach is proposed to realize the broadband ultrasonic probe on micromachined silicon frames suited to be mounted on the tip of optical fibers.

Adaptive K-NN for the detection of air pollutants with a sensor array

The field of air-quality monitoring is gaining increasing interest, with regard to both indoor environment and air-pollution control in open space. This work introduces a pattern recognition technique based on adaptive K-nn applied to a multisensor system, optimized for the recognition of some relevant tracers for air pollution in outdoor environment, namely benzene, toluene, and xylene (BTX), NO/sub 2/, and CO. The pattern-recognition technique employed aims at recognizing the target gases within an air sample of unknown composition and at estimating their concentrations. It is based on PCA and K-nn classification with an adaptive vote technique based on the gas concentrations of the training samples associated to the K-neighbors. The system is tested in a controlled environment composed of synthetic air with a fixed humidity rate (30%) at concentrations in the ppm range for BTX and NO/sub 2/, in the range of 10 ppm for CO. The pattern recognition technique is experimented on a knowledge base composed of a limited number of samples (130), with the adoption of a leave-one-out procedure in order to estimate the classification probability. In these conditions, the system demonstrates the capability to recognize the presence of the target gases in controlled conditions with a high hit-rate. Moreover, the concentrations of the individual components of the test samples are successfully estimated for BTX and NO/sub 2/ in more than 80% of the considered cases, while a lower hit-rate (69%) is reached for CO.

Smart integration of silicon nanowire arrays in all-silicon thermoelectric micro-nanogenerators

Micro and nanotechnologies are called to play a key role in the fabrication of small and low cost sensors with excellent performance enabling new continuous monitoring scenarios and distributed intelligence paradigms (Internet of Things, Trillion Sensors). Harvesting devices providing energy autonomy to those large numbers of microsensors will be essential. In those scenarios where waste heat sources are present, thermoelectricity will be the obvious choice. However, miniaturization of state of the art thermoelectric modules is not easy with the current technologies used for their fabrication. Micro and nanotechnologies offer an interesting alternative considering that silicon in nanowire form is a material with a promising thermoelectric figure of merit. This paper presents two approaches for the integration of large numbers of silicon nanowires in a cost-effective and practical way using only micromachining and thin-film processes compatible with silicon technologies. Both approaches lead to automated physical and electrical integration of medium-high density stacked arrays of crystalline or polycrystalline silicon nanowires with arbitrary length (tens to hundreds microns) and diameters below 100 nm.

Material Properties Measurement and Numerical Simulation for Characterization of Ultra-Low-Power Consumption Hotplates

The results of a thorough thermoelectric characterization, performed both in a vacuum chamber and at atmospheric pressure, of ultra-low-power hotplates based on suspended structures with different layouts are presented in this work and compared with thermoelectric 2D and thermal 3D finite elements simulations. Electrical and thermal properties of the thin films used in the devices have been also measured, involving appropriate on-chip test structures, and their values were employed in both 2D and 3D model. Temperature vs. heating power experimental curves showed the great influence of conduction through air on power consumption and an excellent agreement with the simulated results.

Robotic intelligent vision and control for tunnel inspection and evaluation - The ROBINSPECT EC project

Recent developments in robotics and the associated fields of computer vision and sensors pave the floor for automated robotic solutions, exploitable in the wider field of inspection of civil infrastructures and particularly transportation tunnels, the latter ageing urgently requiring inspection and assessment. Currently, tunnel inspections are performed via visually by human operators. This can result into slow, labour expensive and subjective process often requiring lane shutdown during the inspection, parameters that need to be lowered while having safety requirements and tunnel uptimes increasing.

Fabrication of fiber-optic broadband ultrasound emitters by micro-opto-mechanical technology

A micro-opto-mechanical system (MOMS) technology for the fabrication of fiber-optic optoacoustic emitters is presented. The described devices are based on the thermoelastic generation of ultrasonic waves from patterned carbon films obtained by the controlled pyrolysis of photoresist layers and fabricated on miniaturized single-crystal silicon frames used to mount the emitters on the tip of an optical fiber. Thanks to the micromachining process adopted, high miniaturization levels are reached in the fabrication of the emitters, and self-standing devices on optical fiber with diameter around 350 µm are demonstrated, potentially suited to minimally invasive medical applications. The functional testing of fiber-optic emitter prototypes in water performed by using a 1064 nm Q-switched Nd-YAG excitation laser source is also presented, yielding broadband emission spectra extended from low frequencies up to more than 40 MHz, and focused emission fields with a maximum peak-to-peak pressure level of about 1.2 MPa at a distance of 1 mm from the devices.

Thermofluid Analysis of Ultra Low Power Hotplates for a MOX Gas Sensing Device

This work presents a full three-dimensional finite-element multiphysics simulation of the conjugate heat transfer for a gas sensing device composed by a two-element array of ultra low power (ULP) metal oxide semiconductor (MOX) sensors operated in a miniaturized sampling chamber. The heat equation in a solid, the Poisson equation for the electric potential and the incompressible Navier-Stokes and energy equations for a fluid have been solved in a coupled manner. Validation of the simulation results has been performed comparing the simulated power dissipated by the array with a set of experimental data under different operating conditions. A maximum relative error of less than 7% between the simulations and the experiments has been obtained without application of any fitting strategy on the physical properties. A negligible effect on the power dissipated by the sensor, in presence of volumetric fluxes in the sampling chamber, has been observed both numerically and experimentally. Finally, a real operational condition has been simulated and examined.

Influence of Grain Size on the Thermoelectric Properties of Polycrystalline Silicon Nanowires

The thermoelectric properties of doped polycrystalline silicon nanowires have been investigated using doping techniques that impact grain growth in different ways during the doping process. In particular, As- and P-doped nanowires were fabricated using a process flow which enables the manufacturing of surface micromachined nanowires contacted by Al/Si pads in a four-terminal configuration for thermal conductivity measurement. Also, dedicated structures for the measurement of the Seebeck coefficient and electrical resistivity were prepared. In this way, the thermoelectric figure of merit of the nanowires could be evaluated. The As-doped nanowires were heavily doped by thermal doping from spin-on-dopant sources, whereas predeposition from POCl3 was utilized for the P-doped nanowires. The thermal conductivity measured on the nanowires appeared to depend on the doping type. The P-doped nanowires showed, for comparable cross-sections, higher thermal conductivity values than As-doped nanowires, most probably because of their finer grain texture, resulting from the inhibition effect that such doping elements have on grain growth during high-temperature annealing.

Fabrication and testing of a high resolution extensometer based on resonant MEMS strain sensors

A novel type of linear extensometer with exceptionally high resolution of 4 nm based on MEMS resonant strain sensors bonded on steel and operating in a vacuum package is presented. The tool is implemented by means of a steel thin bar that can be pre-stressed in tension within two fixing anchors. The extension of the bar is detected by using two vacuum-packaged resonant MEMS double- ended tuning fork (DETF) sensors bonded on the bar with epoxy glue, one of which is utilized for temperature compensation. Both sensors are driven by a closed loop self-oscillating transresistance amplifier feedback scheme implemented on a PCB (Printed Circuit Board). On the same board, a microcontroller-based frequency measurement circuit is also implemented, which is able to count the square wave fronts of the MEMS oscillator output with a resolution of 20 nsec. The system provides a frequency noise of 0.2 Hz corresponding to an extension resolution of 4 nm for the extensometer. Nearly perfect temperature compensation of the frequency output is achieved in the temperature range 20–35 °C using the reference sensor.

Fabrication of DETF sensors in SOI technology with submicron air gaps using a maskless line narrowing technique

We report about the fabrication of double-ended tuning fork (DETF) single-crystal silicon sensors starting from SOI substrates in which a novel line narrowing technique is adopted in order to shrink the electrostatic coupling gaps between the moving and fixed electrodes. By using conventional near-UV lithography, this solution provides the possibility to control gaps scaled down to 200 nm on an oxide hard mask realized on the structural silicon layer, yielding air gaps with minimum feature size between 400 and 600 nm after the subsequent silicon deep reactive ion etching (DRIE) step. With the proposed process, DETF structures with length varying between 100 and 500 mum have been realized, with a process yield around 85% on a 4-inch SOI substrate. DC testing of the realized prototypes, performed in a SEM-based setup, and vacuum AC testing are also presented, providing a first evaluation of the device pull-in voltage, resonance frequency and Q factor.