alvise bagolini - Academia.edu (original) (raw)

Papers by alvise bagolini

Journal of Engineering Thermophysics

Several challenges coexist in the field of flow boiling in microchannels, ranging from high super... more Several challenges coexist in the field of flow boiling in microchannels, ranging from high superheat required for boiling incipience to boiling instabilities and early dryouts. The aim of this study is to mitigate or solve some of the challenges and develop an image-processing algorithm for analysis of boiling oscillations in multiple parallel channels. The experimental results were acquired on an array of 64 parallel 25 × 25 μm microchannels using a synchronized highspeed visualization and measuring system. The small cross section of the microchannels allowed only the formation of annular two-phase flow, and a computer algorithm was developed for tracking the meniscus oscillations during boiling. The applied image analysis focuses on reliability with the simultaneous use of brightness variation and brightness derivative along with image subtraction. Moreover, the images were preprocessed to determine the number of microchannels and their orientation with applying different filtering and Radon transformations. The data extracted from the visualization helped determine the peak-to-peak amplitudes and fundamental frequencies of the oscillating meniscus. The results exhibit lower amplitudes and higher fundamental frequencies with increasing heat flux. The mass flux was kept constant at 83 kg/m 2 s, whereas the heat flux varied from 150 kW/m 2 to 250 kW/m 2. The amplitudes and the fundamental frequencies of the meniscus oscillations determine the length and duration of microchannel with periodically alternating liquid and vapor phases.

arXiv (Cornell University), Jun 15, 2020

In the framework of the GLARE-X (Geodesy via LAser Ranging from spacE X) project, led by INFN and... more In the framework of the GLARE-X (Geodesy via LAser Ranging from spacE X) project, led by INFN and funded for the years 2019-2021, aiming at significantly advance space geodesy, one shows the initial activities carried out in 2019 in order to manufacture and test adaptive mirrors. This specific article deals with manufacturing and surface quality measurements of the passive substrate of 'candidate' MEMS (Micro-Electro-Mechanical Systems) mirrors for MRRs (Modulated RetroReflectors); further publications will show the active components. The project GLARE-X was approved by INFN for the years 2019-2021: it involves several institutions, including, amongst the other, INFN-LNF and FBK. GLARE-X is an innovative R&D activity, whose at large space geodesy goals will concern the following topics: inverse laser ranging (from a laser terminal in space down to a target on a planet), laser ranging for debris removal and iterative orbit correction, development of high-end ToF (Time of Flight) electronics, manufacturing and testing of MRRs for space, and provision of microreflectors for future NEO (Near Earth Orbit) cubesats. This specific article summarizes the manufacturing and surface quality measurements activities performed on the passive substrate of 'candidate' MEMS mirrors, which will be in turn arranged into MRRs. The final active components, to be realized by 2021, will inherit the manufacturing characteristics chosen thanks to the presented (and further) testing campaigns, and will find suitable space application to NEO, Moon, and Mars devices, like, for example, cooperative and active lidar scatterers for laser altimetry and lasercomm support.

Micro and Nano Engineering, 2022

2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015

In the past few years, several interesting developments in microstructured solid-state thermal ne... more In the past few years, several interesting developments in microstructured solid-state thermal neutron detectors have been pursued. These devices feature high aspect-ratio cavities, filled with neutron converter materials, so as to improve the neutron detection efficiency with respect to coated planar sensors. In the framework of the INFN HYDE (HYbrid Detectors for neutrons) project, we have designed a new microstructured sensor aimed at thermal neutron detection and imaging, e.g., with a Medipix read-out chip, and featuring a good efficiency (~20%) while minimizing the process complexity. The sensor design and technology are presented, along with selected results from simulations and from the initial characterization campaigns.

This paper describes the design, simulation, construction process and experimental analysis of a ... more This paper describes the design, simulation, construction process and experimental analysis of a microgripper, which makes use of a new concept hinge, called CSFH (Conjugate Surfaces Flexure Hinge). The new hinge combines a curved cantilever beam, as flexible element, and a pair of conjugate surfaces, whose contacts depend on load conditions. CSFHs improve accuracy and guarantee that minimum stress conditions hold within the flexible beam. This microgripper is designed for Deep Reactive-Ion Etching (DRIE) construction process and comb-drive actuation. Theoretical basis and Finite Element Analysis (FEA) simulations have been employed in order to predict the feasibility of the device under construction. Finally, some experimental evidence of the construction process has been provided.

In the last years, the research in the gas sensor field experienced a significant boost. Gas sens... more In the last years, the research in the gas sensor field experienced a significant boost. Gas sensors represent the crucial elements in gas monitoring systems and olfactory systems for several applications: environmental monitoring, safety and security, quality control of food production, medical diagnosis and so on. From the point of view of the gas sensing design, the substrate plays a fundamental role, because acts as a heater, mechanical support and transducer of the sensor response. The application of MEMS technology for the fabrication of silicon device with low power consumption has offered new opportunities for innovative gas sensor design. In this work, we studied different approaches to realize an adapt silicon and quartz microheaters for chemoresistive gas sensors, available for high operating temperatures (650°C) through the MEMS technology. Our study is focused on a fabless approach to microheater fabrication, because of the lack of a cheap CMOS compatible process.

Microsystem Technologies, 2017

In this work, a thin-film packaging was developed to be used for radio-frequency microelectromech... more In this work, a thin-film packaging was developed to be used for radio-frequency microelectromechanical system configurations. The fabricated packages are suspended membranes in the multilayer Si x N y /aSi/Si x N y on conductive coplanar waveguides (CPWs) of different length. Several geometric parameters of the membranes, which are the length, the curvature radius at the vertices of the rectangular base, the density and the diameter of holes on the capping surface, were also varied. The mechanical properties of the suspended membranes were investigated by mechanical simulations and surface profilometry measurements as a function of the geometric parameters. RF characterization was performed to evaluate the impact of the package on the CPW performance. Finally, network analysis was carried out, allowing to clarify the origin of the RF losses measured for the fabricated microdevices.

2016 Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS (DTIP), 2016

In this work, thin film packages were developed for radio-frequency microelectromechanical system... more In this work, thin film packages were developed for radio-frequency microelectromechanical system (RF MEMS) configurations. The fabricated packages are suspended membranes in the multilayer SixNyHz/aSi/SixNyHz on conductive coplanar lines of different length. Several geometric parameters of the membranes, which are the length, the curvature radius at the vertices of the rectangular base, the density and the diameter of holes, were also varied. The mechanical properties of the suspended membranes were investigated by surface profilometry as a function of the geometric parameters. Finally, the RF characterization was performed to evaluate the impact of the package on the coplanar line performance. Hence, the proposed study provides results of crucial importance for the application of thin-film suspended microstructures for the packaging of RF MEMS devices.

2015 XVIII AISEM Annual Conference, 2015

ABSTRACT The aim of this work is to present the main technological developments carried out at FB... more ABSTRACT The aim of this work is to present the main technological developments carried out at FBK for micro machined radiation sensors used in High Energy Physics (HEP) experiments. We report on the main technological issues to integrate silicon etching (wet and dry) techniques in the fabrication flow for silicon detector and we show some examples of innovative detectors realized by means of these technologies.

IEEE Sensors Journal

In this work, a low-temperature fabrication process of thin-film encapsulation (TFE) with silicon... more In this work, a low-temperature fabrication process of thin-film encapsulation (TFE) with silicon nitride/chromium cap is proposed for large-size (750 × 300 µm) packaging of microelectromechanical systems (MEMS). A finite element method (FEM) model was developed to evaluate the shape of TFE as a function of the residual stress and the thickness of the sealing layer, providing useful guidelines for the fabrication process. The low temperature of 200 • C, which was used in the plasma-enhanced chemical vapor deposition (PECVD) of the silicon nitride capping layer, allowed an organic sacrificial material to be employed for the definition of the encapsulation area. Silicon nitride/chromium (1 µm/20 nm) bilayer was demonstrated to be successful to overcome the technological limitations that affect the creation of cap holes with size of ∼2 µm on high-topography substrates, as in the case of MEMS. Plasma focused ion beam (PFIB) and scanning electron microscopy (SEM) techniques were used in combination to gain deeper insight into the sealing process of cap holes. Specifically, a PFIB-SEM serial section procedure was developed, resulting to be a powerful tool to directly observe the sealing profile above cap holes. Hence, the presented results greatly contribute to overcome the main technological/reliability issues of TFE, paving the way for the widespread application of the proposed encapsulation methodology to the most used MEMS devices, such as radio frequency (RF) switches, transducers, actuators, sensors, and resonators.

IEEE open journal of ultrasonics, ferroelectrics, and frequency control, 2022

This paper addresses the assessment of the variability of CMUT arrays' electro-mechanical and aco... more This paper addresses the assessment of the variability of CMUT arrays' electro-mechanical and acoustic performance, as related to the tolerance of the CMUT vertical dimensions due to the microfabrication process. A 3-factors 3-levels factorial sensitivity analysis is carried out to compute the main effects and the interaction effects of the moving plate thickness, the passivation layers thickness, and the sacrificial layer thickness, on the CMUT resonance frequency, collapse voltage, and static capacitance, as well as on the transmission and reception sensitivity amplitude and bandwidth and time delay in watercoupled condition. The analysis is performed by means of FEM simulations of the CMUT static behavior and dynamic response, and the findings are compared to experimental data.

arXiv (Cornell University), Jul 24, 2023

Surfaces capable of delaying the frosting passively and facilitating its removal are highly desir... more Surfaces capable of delaying the frosting passively and facilitating its removal are highly desirable in fields where ice introduces inefficiencies and risks. Coalescence jumping, enabled by highly hydrophobic surfaces, is already exploited to slow down the frosting but it is insufficient to completely eliminate the propagation by ice-bridging. We show how the self-ejection of single condensation droplets can frustrate the ice bridges of all the condensation droplets leading to a frost velocity lower than 0.5 μm/s thus dropping below the current limits of passive surfaces by a factor of at least 2. Arrays of truncated microcones, covered by uniformly hydrophobic nanostructures, enable individual condensation droplets to growth and self-propel towards the top of the microstructures and to self-eject once a precise volume is reached. The independency of self-ejection on the neighbour droplets allows a precise control on the droplets' size and distance distributions and the ice-bridging frustration. The most performant microstructures tend to cones with a sharp tip on which the percentage of self-ejection is maximum. Looking towards applications, tapered microstructures allow maximising the percentage of self-ejecting drops while maintaining a certain mechanical strength. Further, it is shown that inserted pinning sites are not essential, which greatly facilitates manufacturing.

arXiv (Cornell University), Jun 30, 2023

Coalescence-jumping of condensation droplets is widely studied for anti-icing, condensation heat ... more Coalescence-jumping of condensation droplets is widely studied for anti-icing, condensation heat transfer, water harvesting and self-cleaning. Another phenomenon that is arousing interest for potential enhancements is the individual droplet self-ejection. However, whether it is possible from divergent structures without detachment from pinning sites remains unexplored. Here we investigate the selfejection of individual droplets from divergent, uniformly hydrophobic structures. We designed, fabricated and tested arrays of nanostructured truncated microcones arranged in a square pattern. The dynamics of the single condensation droplet is revealed with high speed microscopy: it self-ejects after cycles of growth and self-propulsion between four cones. Adopting the conical pore for simplicity, we modelled the slow iso-pressure growth phases and the surface energy release-driven rapid transients enabled once a dynamic configuration is reached. In addition to easier fabrication, microcones with uniform wettability have the potential to allow self-ejection of almost all the droplets with a precise size while maintaining mechanical resistance and thus promising great improvements in a plethora of applications.

Physics of Fluids

Cactaceae have adapted to harsh environments by resisting intense solar radiation, retaining and ... more Cactaceae have adapted to harsh environments by resisting intense solar radiation, retaining and collecting water. Some cacti species have hairs on them along with distinctive spines to serve different functions. In this study, we characterized the Old Man of Andes cactus (Oreocereus trolli). We examined the surface morphology and estimated roughness and adhesion force of both spines and hairs. They both consist of longitudinal microgrooves. The condensation experiments carried out on spines showed that there is a particular phenomenon of distant coalescence (DC): smaller droplets flow totally or partially into larger ones through the microgrooves with consequent accumulation of water in a few large drops. An earlier study (Bintein et al., 2019) has shown that artificial micro-grooved surfaces that exhibit DC are more efficient than flat ones at collecting and sliding dew, and thus cactus spines could act as soil dew conveyors. The agreement between our analytical model and experime...

2022 IEEE International Ultrasonics Symposium (IUS)

Micromachines

Free space optics laser communication using modulating retroreflectors (MR) is a challenging appl... more Free space optics laser communication using modulating retroreflectors (MR) is a challenging application for an active mirror, due to the high frequencies (>100 kHz) required to enable sufficient data transfer. Micro Electromechanical (MEMS) mirrors are a promising option for high-frequency applications, given the very small moving mass typical of such devices. Capacitive MEMS mirrors are presented here for free space communications, based on a novel fabrication sequence that introduces a single-layer thin film aluminum mirror structure with an underlying silicon oxide sacrificial layer. The use of aluminum instead of gold as a mirror layer diminishes the heating generated by the absorption of the sun’s radiation once the mirrors exit the earth’s atmosphere. Thanks to the novel fabrication sequence, the presented mirror devices have a full range actuation voltage of less than 40 V, and a high operational frequency with an eigenfrequency above 2 MHz. The devices were manufactured ...

Micromachines

Microgrippers are promising tools for micro-manipulation and characterization of cells. In this p... more Microgrippers are promising tools for micro-manipulation and characterization of cells. In this paper, a biocompatible electro-thermally actuated microgripper with rotary capacitive position sensor is presented. To overcome the limited displacement possibilities usually provided by electrothermal actuators and to achieve the desired tweezers output displacement, conjugate surface flexure hinges (CSFH) are adopted. The microgripper herein reported can in principle manipulate biological samples in the size range between 15 and 120 µm. A kinematics modeling approach based on the pseudo-rigid-body-method (PRBM) is applied to describe the microgripper’s working mechanism, and analytical modeling, based on finite elements method (FEM), is used to optimize the electrothermal actuator design and the heat dissipation mechanism. Finally, FEM-based simulations are carried out to verify the microgripper, the electrothermal actuator and heat dissipation mechanism performance, and to assess the v...

Journal of Engineering Thermophysics

Several challenges coexist in the field of flow boiling in microchannels, ranging from high super... more Several challenges coexist in the field of flow boiling in microchannels, ranging from high superheat required for boiling incipience to boiling instabilities and early dryouts. The aim of this study is to mitigate or solve some of the challenges and develop an image-processing algorithm for analysis of boiling oscillations in multiple parallel channels. The experimental results were acquired on an array of 64 parallel 25 × 25 μm microchannels using a synchronized highspeed visualization and measuring system. The small cross section of the microchannels allowed only the formation of annular two-phase flow, and a computer algorithm was developed for tracking the meniscus oscillations during boiling. The applied image analysis focuses on reliability with the simultaneous use of brightness variation and brightness derivative along with image subtraction. Moreover, the images were preprocessed to determine the number of microchannels and their orientation with applying different filtering and Radon transformations. The data extracted from the visualization helped determine the peak-to-peak amplitudes and fundamental frequencies of the oscillating meniscus. The results exhibit lower amplitudes and higher fundamental frequencies with increasing heat flux. The mass flux was kept constant at 83 kg/m 2 s, whereas the heat flux varied from 150 kW/m 2 to 250 kW/m 2. The amplitudes and the fundamental frequencies of the meniscus oscillations determine the length and duration of microchannel with periodically alternating liquid and vapor phases.

arXiv (Cornell University), Jun 15, 2020

In the framework of the GLARE-X (Geodesy via LAser Ranging from spacE X) project, led by INFN and... more In the framework of the GLARE-X (Geodesy via LAser Ranging from spacE X) project, led by INFN and funded for the years 2019-2021, aiming at significantly advance space geodesy, one shows the initial activities carried out in 2019 in order to manufacture and test adaptive mirrors. This specific article deals with manufacturing and surface quality measurements of the passive substrate of 'candidate' MEMS (Micro-Electro-Mechanical Systems) mirrors for MRRs (Modulated RetroReflectors); further publications will show the active components. The project GLARE-X was approved by INFN for the years 2019-2021: it involves several institutions, including, amongst the other, INFN-LNF and FBK. GLARE-X is an innovative R&D activity, whose at large space geodesy goals will concern the following topics: inverse laser ranging (from a laser terminal in space down to a target on a planet), laser ranging for debris removal and iterative orbit correction, development of high-end ToF (Time of Flight) electronics, manufacturing and testing of MRRs for space, and provision of microreflectors for future NEO (Near Earth Orbit) cubesats. This specific article summarizes the manufacturing and surface quality measurements activities performed on the passive substrate of 'candidate' MEMS mirrors, which will be in turn arranged into MRRs. The final active components, to be realized by 2021, will inherit the manufacturing characteristics chosen thanks to the presented (and further) testing campaigns, and will find suitable space application to NEO, Moon, and Mars devices, like, for example, cooperative and active lidar scatterers for laser altimetry and lasercomm support.

Micro and Nano Engineering, 2022

2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015

In the past few years, several interesting developments in microstructured solid-state thermal ne... more In the past few years, several interesting developments in microstructured solid-state thermal neutron detectors have been pursued. These devices feature high aspect-ratio cavities, filled with neutron converter materials, so as to improve the neutron detection efficiency with respect to coated planar sensors. In the framework of the INFN HYDE (HYbrid Detectors for neutrons) project, we have designed a new microstructured sensor aimed at thermal neutron detection and imaging, e.g., with a Medipix read-out chip, and featuring a good efficiency (~20%) while minimizing the process complexity. The sensor design and technology are presented, along with selected results from simulations and from the initial characterization campaigns.

This paper describes the design, simulation, construction process and experimental analysis of a ... more This paper describes the design, simulation, construction process and experimental analysis of a microgripper, which makes use of a new concept hinge, called CSFH (Conjugate Surfaces Flexure Hinge). The new hinge combines a curved cantilever beam, as flexible element, and a pair of conjugate surfaces, whose contacts depend on load conditions. CSFHs improve accuracy and guarantee that minimum stress conditions hold within the flexible beam. This microgripper is designed for Deep Reactive-Ion Etching (DRIE) construction process and comb-drive actuation. Theoretical basis and Finite Element Analysis (FEA) simulations have been employed in order to predict the feasibility of the device under construction. Finally, some experimental evidence of the construction process has been provided.

In the last years, the research in the gas sensor field experienced a significant boost. Gas sens... more In the last years, the research in the gas sensor field experienced a significant boost. Gas sensors represent the crucial elements in gas monitoring systems and olfactory systems for several applications: environmental monitoring, safety and security, quality control of food production, medical diagnosis and so on. From the point of view of the gas sensing design, the substrate plays a fundamental role, because acts as a heater, mechanical support and transducer of the sensor response. The application of MEMS technology for the fabrication of silicon device with low power consumption has offered new opportunities for innovative gas sensor design. In this work, we studied different approaches to realize an adapt silicon and quartz microheaters for chemoresistive gas sensors, available for high operating temperatures (650°C) through the MEMS technology. Our study is focused on a fabless approach to microheater fabrication, because of the lack of a cheap CMOS compatible process.

Microsystem Technologies, 2017

In this work, a thin-film packaging was developed to be used for radio-frequency microelectromech... more In this work, a thin-film packaging was developed to be used for radio-frequency microelectromechanical system configurations. The fabricated packages are suspended membranes in the multilayer Si x N y /aSi/Si x N y on conductive coplanar waveguides (CPWs) of different length. Several geometric parameters of the membranes, which are the length, the curvature radius at the vertices of the rectangular base, the density and the diameter of holes on the capping surface, were also varied. The mechanical properties of the suspended membranes were investigated by mechanical simulations and surface profilometry measurements as a function of the geometric parameters. RF characterization was performed to evaluate the impact of the package on the CPW performance. Finally, network analysis was carried out, allowing to clarify the origin of the RF losses measured for the fabricated microdevices.

2016 Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS (DTIP), 2016

In this work, thin film packages were developed for radio-frequency microelectromechanical system... more In this work, thin film packages were developed for radio-frequency microelectromechanical system (RF MEMS) configurations. The fabricated packages are suspended membranes in the multilayer SixNyHz/aSi/SixNyHz on conductive coplanar lines of different length. Several geometric parameters of the membranes, which are the length, the curvature radius at the vertices of the rectangular base, the density and the diameter of holes, were also varied. The mechanical properties of the suspended membranes were investigated by surface profilometry as a function of the geometric parameters. Finally, the RF characterization was performed to evaluate the impact of the package on the coplanar line performance. Hence, the proposed study provides results of crucial importance for the application of thin-film suspended microstructures for the packaging of RF MEMS devices.

2015 XVIII AISEM Annual Conference, 2015

ABSTRACT The aim of this work is to present the main technological developments carried out at FB... more ABSTRACT The aim of this work is to present the main technological developments carried out at FBK for micro machined radiation sensors used in High Energy Physics (HEP) experiments. We report on the main technological issues to integrate silicon etching (wet and dry) techniques in the fabrication flow for silicon detector and we show some examples of innovative detectors realized by means of these technologies.

IEEE Sensors Journal

In this work, a low-temperature fabrication process of thin-film encapsulation (TFE) with silicon... more In this work, a low-temperature fabrication process of thin-film encapsulation (TFE) with silicon nitride/chromium cap is proposed for large-size (750 × 300 µm) packaging of microelectromechanical systems (MEMS). A finite element method (FEM) model was developed to evaluate the shape of TFE as a function of the residual stress and the thickness of the sealing layer, providing useful guidelines for the fabrication process. The low temperature of 200 • C, which was used in the plasma-enhanced chemical vapor deposition (PECVD) of the silicon nitride capping layer, allowed an organic sacrificial material to be employed for the definition of the encapsulation area. Silicon nitride/chromium (1 µm/20 nm) bilayer was demonstrated to be successful to overcome the technological limitations that affect the creation of cap holes with size of ∼2 µm on high-topography substrates, as in the case of MEMS. Plasma focused ion beam (PFIB) and scanning electron microscopy (SEM) techniques were used in combination to gain deeper insight into the sealing process of cap holes. Specifically, a PFIB-SEM serial section procedure was developed, resulting to be a powerful tool to directly observe the sealing profile above cap holes. Hence, the presented results greatly contribute to overcome the main technological/reliability issues of TFE, paving the way for the widespread application of the proposed encapsulation methodology to the most used MEMS devices, such as radio frequency (RF) switches, transducers, actuators, sensors, and resonators.

IEEE open journal of ultrasonics, ferroelectrics, and frequency control, 2022

This paper addresses the assessment of the variability of CMUT arrays' electro-mechanical and aco... more This paper addresses the assessment of the variability of CMUT arrays' electro-mechanical and acoustic performance, as related to the tolerance of the CMUT vertical dimensions due to the microfabrication process. A 3-factors 3-levels factorial sensitivity analysis is carried out to compute the main effects and the interaction effects of the moving plate thickness, the passivation layers thickness, and the sacrificial layer thickness, on the CMUT resonance frequency, collapse voltage, and static capacitance, as well as on the transmission and reception sensitivity amplitude and bandwidth and time delay in watercoupled condition. The analysis is performed by means of FEM simulations of the CMUT static behavior and dynamic response, and the findings are compared to experimental data.

arXiv (Cornell University), Jul 24, 2023

Surfaces capable of delaying the frosting passively and facilitating its removal are highly desir... more Surfaces capable of delaying the frosting passively and facilitating its removal are highly desirable in fields where ice introduces inefficiencies and risks. Coalescence jumping, enabled by highly hydrophobic surfaces, is already exploited to slow down the frosting but it is insufficient to completely eliminate the propagation by ice-bridging. We show how the self-ejection of single condensation droplets can frustrate the ice bridges of all the condensation droplets leading to a frost velocity lower than 0.5 μm/s thus dropping below the current limits of passive surfaces by a factor of at least 2. Arrays of truncated microcones, covered by uniformly hydrophobic nanostructures, enable individual condensation droplets to growth and self-propel towards the top of the microstructures and to self-eject once a precise volume is reached. The independency of self-ejection on the neighbour droplets allows a precise control on the droplets' size and distance distributions and the ice-bridging frustration. The most performant microstructures tend to cones with a sharp tip on which the percentage of self-ejection is maximum. Looking towards applications, tapered microstructures allow maximising the percentage of self-ejecting drops while maintaining a certain mechanical strength. Further, it is shown that inserted pinning sites are not essential, which greatly facilitates manufacturing.

arXiv (Cornell University), Jun 30, 2023

Coalescence-jumping of condensation droplets is widely studied for anti-icing, condensation heat ... more Coalescence-jumping of condensation droplets is widely studied for anti-icing, condensation heat transfer, water harvesting and self-cleaning. Another phenomenon that is arousing interest for potential enhancements is the individual droplet self-ejection. However, whether it is possible from divergent structures without detachment from pinning sites remains unexplored. Here we investigate the selfejection of individual droplets from divergent, uniformly hydrophobic structures. We designed, fabricated and tested arrays of nanostructured truncated microcones arranged in a square pattern. The dynamics of the single condensation droplet is revealed with high speed microscopy: it self-ejects after cycles of growth and self-propulsion between four cones. Adopting the conical pore for simplicity, we modelled the slow iso-pressure growth phases and the surface energy release-driven rapid transients enabled once a dynamic configuration is reached. In addition to easier fabrication, microcones with uniform wettability have the potential to allow self-ejection of almost all the droplets with a precise size while maintaining mechanical resistance and thus promising great improvements in a plethora of applications.

Physics of Fluids

Cactaceae have adapted to harsh environments by resisting intense solar radiation, retaining and ... more Cactaceae have adapted to harsh environments by resisting intense solar radiation, retaining and collecting water. Some cacti species have hairs on them along with distinctive spines to serve different functions. In this study, we characterized the Old Man of Andes cactus (Oreocereus trolli). We examined the surface morphology and estimated roughness and adhesion force of both spines and hairs. They both consist of longitudinal microgrooves. The condensation experiments carried out on spines showed that there is a particular phenomenon of distant coalescence (DC): smaller droplets flow totally or partially into larger ones through the microgrooves with consequent accumulation of water in a few large drops. An earlier study (Bintein et al., 2019) has shown that artificial micro-grooved surfaces that exhibit DC are more efficient than flat ones at collecting and sliding dew, and thus cactus spines could act as soil dew conveyors. The agreement between our analytical model and experime...

2022 IEEE International Ultrasonics Symposium (IUS)

Micromachines

Free space optics laser communication using modulating retroreflectors (MR) is a challenging appl... more Free space optics laser communication using modulating retroreflectors (MR) is a challenging application for an active mirror, due to the high frequencies (>100 kHz) required to enable sufficient data transfer. Micro Electromechanical (MEMS) mirrors are a promising option for high-frequency applications, given the very small moving mass typical of such devices. Capacitive MEMS mirrors are presented here for free space communications, based on a novel fabrication sequence that introduces a single-layer thin film aluminum mirror structure with an underlying silicon oxide sacrificial layer. The use of aluminum instead of gold as a mirror layer diminishes the heating generated by the absorption of the sun’s radiation once the mirrors exit the earth’s atmosphere. Thanks to the novel fabrication sequence, the presented mirror devices have a full range actuation voltage of less than 40 V, and a high operational frequency with an eigenfrequency above 2 MHz. The devices were manufactured ...

Micromachines

Microgrippers are promising tools for micro-manipulation and characterization of cells. In this p... more Microgrippers are promising tools for micro-manipulation and characterization of cells. In this paper, a biocompatible electro-thermally actuated microgripper with rotary capacitive position sensor is presented. To overcome the limited displacement possibilities usually provided by electrothermal actuators and to achieve the desired tweezers output displacement, conjugate surface flexure hinges (CSFH) are adopted. The microgripper herein reported can in principle manipulate biological samples in the size range between 15 and 120 µm. A kinematics modeling approach based on the pseudo-rigid-body-method (PRBM) is applied to describe the microgripper’s working mechanism, and analytical modeling, based on finite elements method (FEM), is used to optimize the electrothermal actuator design and the heat dissipation mechanism. Finally, FEM-based simulations are carried out to verify the microgripper, the electrothermal actuator and heat dissipation mechanism performance, and to assess the v...