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Abstract
A new maskless mesoscale materials deposition technique allows printing with colloidal inks with arbitrary viscosities ranging from 0.7 to 1000 mPa s. Precise structures down to about 10 microns or even below can be written directly on virtually any surface material without the use of masks. The end result is a high-quality mesoscale structure with excellent edge definition and near-bulk electronic properties. In combination with special nanoscaled inks, the technique has potential uses in the electrical and semiconducting applications as well as in the automotive and medical industries.
... Due to the coaxial flow, the sheath gas stream prevents contact of the aerosol stream with the inner cladding of the printhead nozzle. In the printhead, the aerosol stream, which consists of many single droplets in the femtoliter range, is focused down to as small as a tenth of the nozzle diameter [10][11][12][13]. ...
... It enables effective additive manufacturing of microscale devices for various industrial applications (cf. Zollmer et al. 2006;Hedges et al. 2007;Kahn 2007;Christenson et al. 2011;Paulsen et al. 2012;Renn et al. 2017;Wilkinson et al. 2019;Germann et al. 2023). Any liquid material that can be atomized (or aerosolized) into a mist of microdroplets (e.g., with diameters ranging from 1 to 5 m) can be printed with AJ. ...
Continuous ultrasonic atomization in a closed chamber is expected to generate a mist with an equilibrium droplet concentration and size distribution. Such a mist of microdroplets with controllable mist density has been used for Aerosol Jet ® printing in the fabrication of a variety of additively manufactured microscale devices. Despite many unique capabilities demonstrated with the Aerosol Jet ® printing technology, its ultrasonic atomization behavior appears to be rather sensitive to the ink properties with gaps in our understanding of the fundamental physics underlying its operation. In this work, we investigate some basic mechanisms in the Aerosol Jet ® ultrasonic atomizer with a lumped-parameter kinetic coagulation model for highly concentrated mist. To mitigate the difficulty with unavailable knowledge about the complex turbulent flow inside the atomizer chamber, we present results for several orders of magnitude of the turbulent energy dissipation rates in order to examine a range of possibilities. The same approach is taken for analyzing the scavenging effect of the swirling bulk liquid. Our results also demonstrate the theoretical possibility for achieving a mist saturation condition where the mist output from the atomizer can become insensitive to process variables. As observed in experiments, such a saturated mist is highly desirable for Aerosol Jet ® printing with maximized and well-controlled throughput in additive manufacturing.
... The Aerosol Jet® (AJ) direct-write technology has become an effective additive manufacturing tool for fabrication of microscale electronic devices [1][2][3][4][5][6]. It deposits functional ink materials in a form of aerodynamically focused high-speed mist stream of droplets ranging from 1 to 5 microns with an impinging jet flow to the substrate surface typically several millimeters away from the nozzle exit [7][8][9]. ...
As Aerosol Jet® (AJ) printing is becoming more attractive to additive manufacturing, printed electronics, among other applications, reducing or minimizing the amount of ink droplets landing in unintended regions—known as the overspray—has been elevated on the agenda for print quality control and improvement. Many AJ users had discussed the overspray issue associated with AJ printing, while the metrology for quantified evaluation of overspray is still lacking. In this work, the likely physical mechanism for inducing overspray is analyzed along with a set of computational fluid dynamics (CFD) simulations. We then present a 2D image processing method for quantitatively evaluating the severity of overspray in terms of its percent area coverage versus a normalized distance from printed line edge. Our results show that the amount of overspray of AJ printing seems to scale with the printed line width (LW), and usually to become negligible (e.g. percent area coverage of overspray < 1%) beyond 30%–40% of LW from line edges. The overspray is shown to often decrease by increasing the jet velocity and sheath-to-mist ratio. Without loss of generality and for concise illustration, herewith we use only one representative ink to print test samples for the quantitative overspray analysis. The results have been found to bear a resemblance to AJ printed features with many other inks.
... Aerosol jet deposition is a direct-write non-contact deposition process originally developed for the manufacture of electronic circuits and printing of electronic materials. Since then its use as a deposition technology for a wide range of functional materials including metals, polymers and even biologicals has emerged (Zöllmer, et al., 2006). The compatibility of the technique with such a wide range of materials has seen the development of an assortment of novel applications in key research areas including printed electronics and sensors (Zhao, et al., 2012) (Clifford, et al., 2018) (Cantù, et al., 2018), renewable energy (Mette, et al., 2007) and biological/biomedical devices (Marquez, et al., 2001). ...
Aerosol jet deposition is a digital direct-write additive manufacturing technique capable of producing high resolution and highly customisable electronic and biological functional devices on both two-and three-dimensional substrates. This technology offers important market opportunities in the production of consumer electronics, semiconductor packaging, display technology, aerospace and defence, automotive and life sciences. However, for these opportunities to be realised there is a necessity for greater understanding of how deposition process parameters influence deposition quality. This study has explored the effects of a number of these parameters and their influence on the geometry of printed features. The results of this work outline the operating windows for several deposition parameters including carrier gas flow rate, stage speed working distance and stage temperature. Additionally, a number of relationships have been identified linking deposition parameters to the geometry of printed features.
... As an effective additive manufacturing tool, the Aerosol Jet V R direct-write technology of Optomec enables fabrication of microscale functional devices for various applications (cf. Zollmer et al. 2006;Hedges, King, and Renn 2007;Kahn 2007;Christenson et al. 2011;Paulsen et al. 2012;Renn et al. 2017). It deposits functional ink materials in a form of high-speed mist stream with an impinging jet flow, based on the mechanism of inertial impaction of microdroplets of diameters typically ranging from 1 to 5 mm (Renn 2006;Binder, Glatthaar, and Raddlein 2014;Feng 2015). ...
With the microdroplets of water serving as light scattering particles, the mist flow patterns of round micro-jets can be visualized using the Aerosol Jet® direct-write system. The visualization images show that the laminar mist jet (with sheath-to-mist ratio Y = 1:1) appears to extend to more than 20 times the diameter of nozzle orifice D for jet Reynolds number Re < 600, especially with D = 0.3 mm and less. For smaller jets (e.g., with D = 0.15 mm), laminar collimated mist flow might be retained to 40×D for Re < 600 and for Re ∼1500 within 20×D from the nozzle. The laminar part of mist flow associated with larger jets (e.g., with D = 1.0 mm for Re < 600) tends to exhibit noticeable gradual widening due to viscous diffusion. For free jets, their breakdown length—the distance from nozzle where transition from laminar to turbulent mist flow takes place as signaled by a rapid widening of mist stream—is shown to decrease with increasing Re. The presence of impingement wall tends to prevent turbulence development, even when the wall is placed further downstream of the free-jet breakdown length for a given Re. The critical Re for an impinging jet to develop turbulence increases as the standoff S is reduced. The mist flow of impinging jet of D = 1.0 mm seems to remain laminar even for Re > 4000 at S = 12 mm.
Copyright © 2018 American Association for Aerosol Research
... As an effective additive manufacturing tool, the Aerosol Jet ® direct-write technology of Optomec enables fabrication of microscale functional devices for various applications (cf. Zollmer et al., 2006;Hedges et al., 2007;Kahn, 2007;Christenson et al., 2011;Paulsen et al., 2012;Renn et al., 2017). It deposits functional ink materials in a form of high-speed mist stream with an impinging jet flow, based on the mechanism of inertial impaction of microdroplets of diameters typically ranging from 1 to 5 microns (Renn, 2006;Binder et al., 2014;Feng, 2015). ...
With the microdroplets of water serving as light scattering particles, the mist flow patterns of round micro-jets can be visualized using the Aerosol Jet(R) direct-write system. The visualization images show that the laminar mist jet appears to extend to more than 20 times the diameter of nozzle orifice, D, for jet Reynolds number Re < 600, especially with D = 0.3 mm and less. For smaller jets (e.g., with D = 0.15 mm), laminar collimated mist flow might be retained to 40xD for Re < 600 and for Re ~ 1500 within 20xD from the nozzle. The laminar part of mist flow associated with larger jets (e.g., with D = 1.0 mm for Re < 600) tends to exhibit noticeable gradual widening due to viscous diffusion. For free jets, their breakdown length--the distance from nozzle where transition from laminar to turbulent mist flow takes place as signaled by the inception of a rapid widening of mist stream--is shown to decrease with increasing Re. The presence of impingement wall tends to prevent turbulence development, even when the wall is placed further downstream of the free-jet breakdown length for a given Re . The critical Re for an impinging jet to develop turbulence increases as the standoff S is reduced. The mist flow of impinging jet of D = 1.0 mm seems to remain laminar even for Re > 4000 at S = 12 mm.
... It's 5-axis and non-contact capability with substrate-to-nozzle standoff distance between 1 and 5 mm provides freedom to fabricate novel designs and explore complicated designs on arbitrary surfaces [30]. Aerosol jet offers high resolution and conformal printing [31]. ...
Minute pH changes impact all living organisms, and thus facile pH monitoring in environment and on the cellular level is important. A low cost and flexible carbon nanotube based pH sensor is fabricated in this work using Aerosol jet printing technique. The chemiresistive pH sensor is fabricated with a CNT-based miniaturized serpentine sensing element printed on top of the silver electrodes. The trace width of the serpentine sensing element is accurately controlled to about the same size as the gaps between the traces. Aerosol jet parameters are optimized to achieve high resolution printing of 20 μm. The fabricated pH sensor shows good sensitivity (up to 59 kΩ/pH) and repeatability (coefficient of variance <1.15%) with a response time of 20 s the sensor demonstrates excellent biocompatibility required for live cell applications.
... This technology generates and focuses a continuous stream of aerosol droplets. The stand-off distance between nozzle and substrate is several centimetres, typically, which facilitates printing over steps and certain three-dimensional surfaces without tracking the print-head in z-direction [7]. The samples have been prepared by means of a nozzle with 150 µm diameter and printing velocities of 1-2 mm/s in 2-3 layers on top of each other. ...
... With the Aerosol Jet direct-write technology, ink microdroplets generated by a liquid atomization process are deposited onto a substrate in a form of collimated mist stream (which can become less than 10 µm in diameter having the ink droplet concentration typically about 50 nL/cc) with considerable impinging velocity, e.g., 20 to 100 m/s (cf. Renn, 2006;Zollmer et al., 2006;Renn, 2007;Hedges et al., 2007;Kahn, 2007;Renn et al., 2009Renn et al., , 2010Christenson et al., 2011;Paulsen et al., 2012). Therefore, the ink droplets can have sufficient momentum to impact the substrate several millimeters away from the deposition nozzle as directed by the high-speed jet flow (cf. ...
Numerical solutions of high-speed microdroplet impact onto a smooth solid surface are computed, using the interFoam VoF solver of the OpenFOAM CFD package. Toward the solid surface, the liquid microdroplet is moving with an impinging gas flow, simulating the situation of ink droplets being deposited onto substrate with a collimated mist jet in the Optomec Aerosol Jet printing process. The computed values of maximum spread factor, for the range of parameters of practical interest to Aerosol Jet printing, were found in very good agreement with some of the correlation formulas proposed by previous authors in the literature. Combining formulas selected from different authors with appropriate modifications yields a maximum spread factor formula that can be used for first-order evaluations of deposited in droplet size during the Aerosol Jet technology development. The computational results also illustrate droplet impact dynamics with lamella shape evolution throughout the spreading, receding-relaxation, and wetting equilibrium phases, consistent with that observed and described by many previous authors. This suggests a scale-invariant nature of the basic droplet impact behavior such that experiments with larger droplets at the same nondimensional parameter values may be considered for studying microdroplet impact dynamics. Significant free surface oscillations can be observed when the droplet viscosity is relatively low. The border line between periodic free surface oscillations and aperiodic creeping to capillary equilibrium free surface shape appears at the value of Ohnesorge number around 0.25. Droplet bouncing after receding is prompted with large contact angles at solid surface (as consistent with findings reported in the literature), but can be suppressed by increasing the droplet viscosity.
... In this work, the axisymmetric external deforming force is considered to arise from an impinging gas jet, for its importance to the Aerosol Jet direct-write technology. As an additive manufacturing technology for producing a wide range of features (with resolution down to ∼10 µm), the Aerosol Jet printing nozzle deposits material in the form of a mist stream of micron-size ink droplets in a carrier gas impinging onto the substrate at an appreciable speed (typically greater than 25 ms −1 ) [5][6][7]. Therefore, the ink droplets can have sufficient inertia to impact the substrate as directed by the free jet flow. It has been observed that the amount of wet ink deposited on a substrate is sometimes limited for acceptable print quality such as welldefined feature edges, due to free surface deformation by aerodynamic stresses associated with the impinging jet flow. ...
The problem of steady axisymmetric deformations of a liquid sessile drop on a flat solid surface under an impinging gas jet is of interest for understanding the fundamental behavior of free surface flows as well as for establishing the theoretical basis in process design for the Aerosol \({{\rm Jet}^{\circledR}}\) direct-write technology. It is studied here numerically using a Galerkin finite-element method, by computing solutions of Navier-Stokes equations. For effective material deposition in Aerosol \({{\rm Jet}^{\circledR}}\) printing, the desired value of Reynolds number for the laminar gas jet is found to be greater than ~500. The sessile drop can be severely deformed by an impinging gas jet when the capillary number is approaching a critical value beyond which no steady axisymmetric free surface deformation can exist. Solution branches in a parameter space show turning points at the critical values of capillary number, which typically indicate the onset of free surface shape instability. By tracking solution branches around turning points with an arc-length continuation algorithm, critical values of capillary number can be accurately determined. Near turning points, all the free surface profiles in various parameter settings take a common shape with a dimple at the center and bulge near the contact line. An empirical formula for the critical capillary number for sessile drops with \({45^{\circ}}\) contact angle is derived for typical ranges of jet Reynolds number and relative drop sizes especially pertinent to Aerosol \({{\rm Jet}^{\circledR}}\) printing.
... 2) Aerosol Jet: Another technique for dispensing and patterning materials from liquids onto flexible supports is the Aerosol Jet system, developed by Optomec, Inc. (supplementary material, Figure 5) [127]- [130]. In this system, rather than produce individual droplets of ink, an aerosol is produced (supplementary material, Figure S5a, b), focused and directed toward the substrate (supplementary material, Figure S5c). ...
Patterning functional materials is one of the key technologies to enable flexible electronics. In almost every flexible electronic device, individual materials and layers need to be patterned. Moreover, the importance of patterning is probably second only to materials properties in fabricated flexible functional devices. Frequently, patterning is one of the limiting factors in device performance. Flexible electronics depends upon the ability to construct layers of materials having precisely defined architectures and relationships on flexible supports. These structures require the ability to either deposit (additive) or remove (subtractive) materials in a locally controlled fashion (patterning). There are many techniques that have been used to accomplish the patterning of materials on flexible supports. In general, these patterning techniques have either been derived or adapted from conventional electronics processing, from printing processes, or from a hybrid of both. The appropriate choice of patterning technique will depend upon many considerations, including feature size, area of coverage, throughput, registration, environment, position in the overall device structure, and material considerations. Many, if not most device structures will require the use of multiple different patterning techniques. The purpose of this paper is to review the major patterning techniques that have been used for flexible electronics, and to discuss the unique features, advantages, and disadvantages of each. The focus will be on large area, high throughput, additive deposition techniques that can be performed in ambient conditions.
... The viscosity and the size of the generated drops in Ink Jet -printing limit the possibility of miniaturizing structures down to about 50 µm. Aerosol Jet ® enables a further miniaturization of deposited structure below 20 µm, and allows a very flexible packaging with very different materials on a large variety of substrates [1]: ...
Today, printing technologies like Ink Jet - printing or Aerosol Jet® - printing are used not only for printing graphics. The printing of electronic structures using metallic nano-particulate dispersions as so called “functional inks” followed by a thermal consolidation process for full functionality is of special interest. For a customized packaging, also ceramic and organic materials are taken into account, requiring flexible technologies for deposition of different materials. For a further miniaturization, for many electronic and
sensorial applications smaller structures are needed. Non-contact printing technologies are often a suitable solution to generate these functional structures of very different materials for various new applications. INKtelligent printing® combines the structuring possibilities of maskless printing technologies with the functionality of micro- and nano-scaled functional materials to generate functional structures like conductors, resistors and even sensors or sensor arrays, respectively. The functional structures are printed onto different flat or non-planar substrates like wafers, glass substrates, polymer foils or non-planar components. Typically, the structures have to be consolidated after printing, i.e. in a furnace, by use of laser treatment or high energy irradiation.
... In contrast to the hybrid integration approach, these techniques do not need a separate substrate. Methods used may be sputtering, screen printing, inkjet printing [7] or aerosol printing of nanoparticles [8,9]. 3. The third track shown in Fig. 2 makes use of generic sensing possibilities of the material, such as piezoelectricity, piezoresistivity or magnetic properties. ...
Ubiquitous computing is about to become part four everyday lives by integrating hundreds of "invisible" to us computing devices in our environment, so that they can unobtrusively and constantly assist us. This will imply more and smaller "invisible" sensors, homogeneously distributed and at the same time densely packed in host materials, responding to various stimuli and immediately delivering information. In order to reach this aim, the embedded sensors should be integrated within the host material, heading towards sensorial materials. The first step is to omit all parts that are not needed for the sensorial task and to find new solutions for a gentle integration. This is what we call function scale integration. The paper discusses sensor embedding in the human hand as an example of integration in nature, new technological applications and main challenges associated with this approach. (C) 2011 Elsevier B.V. All rights reserved.
... A so called " Atomizer " produces an aerosol from the suspension which is carried to the print head. The aerosol droplet diameter is between 1 – 5 microns which corresponds to a volume of some femtolitres [4]. Inside the print head a sheath gas (nitrogen) is used to focus the aerosol beam and also to prevent clogging of the nozzle. ...
Sensor structures for non-destructive testing could successfully deposited by INKtelligent printing. Metal strain gauges are fabricated by Aerosol Jet technology, starting with deposition of a polymer isolation layer, followed by a printed metal layer and at least an encapsulation to protect the printed sensor. Characterizations of printed and sintered sensors show a good densification of the porous material which allows high electrical conductivity up to 70 % of bulk value. Performance tests of printed sensors show a reproducible and reliable functionality in terms of strain measurements.
Continuous ultrasonic atomization in a closed chamber is expected to generate a mist with an equilibrium droplet concentration and size distribution. Such a mist of microdroplets with controllable mist density has been used for Aerosol Jet® printing in the fabrication of a variety of additively manufactured microscale devices. Despite many unique capabilities demonstrated with the Aerosol Jet® printing technology, its ultrasonic atomization behavior appears to be rather sensitive to the ink properties with gaps in our understanding of the fundamental physics underlying its operation. In this work, we investigate some basic mechanisms in the Aerosol Jet® ultrasonic atomizer with a lumped-parameter kinetic coagulation model for highly concentrated mist. To mitigate the difficulty with unavailable knowledge about the complex turbulent flow inside the atomizer chamber, we present results for several orders of magnitude of the turbulent energy dissipation rates to examine a range of possibilities. The same approach is taken for analyzing the scavenging effect of the swirling bulk liquid. Our results also demonstrate the theoretical possibility for achieving a mist saturation condition where the mist output from the atomizer can become insensitive to process variables. As observed in experiments, such a saturated mist is highly desirable for Aerosol Jet® printing with maximized and well-controlled throughput in additive manufacturing.
As studied by many authors, the behavior of particles in aerosol flow through bent tubes is relevant to a variety of technological developments for practical applications. The present work is no exception, motivated by the need of understanding ink droplet loss during mist transport in Aerosol Jet® printing. While the majority of works in the literature have considered particle deposition in tube bends with the tube-flow Reynolds number Re > 1000, the mist flow in transport channels of Aerosol Jet® printer often has Re < 100. Here, the effects of inertial impaction and gravitational settling with laminar flows in 90° bends are examined using an OpenFOAM® CFD package, for Re ~ 50 to 1000. The computational code is verified by comparing with the experimental result of Pui et al. for Re = 1000. Besides inertial impaction due to the centrifugal forces in bends, the effect of gravitational settling is shown to become increasingly significant with reduction of tube-flow velocity, which can also be quite sensitive to the bend orientation when the mist flow rate is low. For situations of downward bend or upward inlet, where the gravitational force and centrifugal force oppose each other, the effect of gravitational settling appears relatively insignificant. However, the particle deposition efficiency is generally enhanced in upward bends or bends with downward inlet, where the gravitational force and centrifugal force reinforce each other, exhibiting large deviations from the zero-g case, especially at lower flow velocities (i.e., smaller Froude number).
Conductive ink has extraordinary properties. The printing of patterns with conductive inks on polymer surfaces gives them new properties and functionalities, making them ideal for several diverse application areas. These printed polymeric materials can be embedded in a system to perform a given function, e.g., to change their electrical resistivity as a response to an applied deformation.
The use of printed electronics on the fabrication of flexible pressure sensors is of particular
interest. Flexible Pressure Sensor (FPS) technology provides more accurate reading and contact area thanks to its ability to fold/roll, when compared to other traditionally used materials. However, they remain unsatisfactory and inaccessible to the general population. Developing a more intelligent and efficient sensor, capable of being integrated in complex environments, with improved properties, lighter and more robust, elastically deformable with quick back response, which does not sacrifice the freedom of motion, and equally important, economically attractive and suitable for mass production, is essential.
Inkjet Printing Technology (IPT) has evolved in a way that ceased to be known only as a
manufacturing tool in the paper and newspapers industry and it became one of the most importante technologies in organic, flexible electronics and printing polymeric substrates, as well as a topic in scientific research. This technology as attracted the attention of the industrial community over the past due to a number of features, which makes a compelling argument for an interesting alternative to the conventional Printed Electronics (PE) technologies. But, there are many challenges in the use of direct printing. Most polymers are hydrophobic showing a low surface energy. Therefore, they are difficult to adhere to other materials. A new developed method for the surface treatment of polymeric substrates in order to increase their surface energies is presented. This novel surface treatment of thermoplastic polymers was applied to the inkjet printing of Thermoplastic Polyurethane (TPU) substrates with conductive inks, and significant improvements on the printability were obtained.
Still, to reach the spatial geometry of the printed pattern, electrical conductivity, resolution and durability, several studies were performed and depending on the material involved, a specific know-how is required. A compromise between several criteria must be performed in order to select the proper substrate and conductive ink to get the desired sensor performance (achieve the desired sensor characteristics like resolution and bandwidth).
The focus of this thesis is the development of a new generation of good performance and lower cost thin flexible pressure sensors. The applied research was focused from a materials science point of view (selectively applying commercially available and compatible materials or defining viable material alternatives), with resource to a Drop-on-Demand inkjet printer with a piezoelectric printhead to process the materials, and exploring it’s potential to be integrated into electronic applications. Three different inks with different characteristics were studied. After inkjet printing parameters definition and depending on the ink and substrate, the characterization of the printed system was conducted for pattern resolution, adhesion of the ink to the substrate, and electromechanical properties evaluation.
The design, fabrication and experimental results of a FPS system and its readout electronics
interface are also presented here. The developed sensing platform for postural imbalance
monitoring consists of an array of flexible capacitive pressure sensors, in the millimeter range and uses a simple manufacturing process (enabling a reasonable density of sensors in the active zone). Thus, it is possible to achieve good performance results (comparable to existing solutions in the industry), with the particularity of offering an economically viable alternative, allowing its use in rehabilitation activities. The results obtained are very promising and encouraging. The developed pressure platform could be successfully inkjet printed and was fully functional.
Particle deposition patterns on the plate of inertial impactor with circular laminar jet are investigated numerically with a Lagrangian solver implemented within the framework of the OpenFOAM$^{\circledR}$ CFD package. Effects of taper angle of the nozzle channel and jet-to-plate distance are evaluated. The results show that tapered nozzle tends to deposit more particles toward the circular spot edge than straight nozzle. At jet Reynolds number $Re = 1132$, a tapered nozzle deposits particles to form a pattern with a high density ring toward the deposition spot edge, especially for particle Stokes number $St > St_{50}$, which is absent with a straight nozzle. Increasing the jet-to-plate distance tends to reduce the value of particle density peak near deposition spot edge. Reducing $Re$ to $283$ (e.g., for $300$ ccm flow through a $1.5$ mm diameter jet nozzle) yields particle deposition patterns without the high density ring at the deposition spot edge when the same tapered nozzle is used. The particle deposition patterns with the straight nozzle at $Re = 283$ exhibit more reduced particle density around the spot edge such that the particle density profile appears more or less like a Gaussian function. In general, the effect of reducing $Re$ on particle deposition pattern seems to be similar to increasing the jet-to-plate distance. The computed particle deposition efficiency $\eta$ shows the fact that very fine particles with extremely small values of $St$ near the jet axis always impact the center of plate, indicating that the value of $\eta$ does not approach zero with a substantial reduction of $St$. Such a "small particle contamination" typically amounts to $\sim 10\%$ of small particles (with $\sqrt{St} < 0.1$) at $Re \sim 1000$ and $\sim 5\%$ at $Re \sim 300$, which may not be negligible in data analysis with inertial impactor measurement.
Direct laser interference patterning (DLIP) was used to produce periodic patterns on hydroxyapatite. A Nd:YAG laser operating at 266 and 355 nm wavelengths and a pulse duration of 10 ns was used in these experiments. Line- and cross-like patterns with periodical distances of 10 and 20 μm were fabricated with energy densities between 0.6 and 2.4 J/cm2, and pulse numbers from 1 to 100. In the low/middle laser intensity range it was observed that the structure depth increased with the pulse number. However, for higher energies the patterns smudge due to thermal effects. For single pulse laser experiments, increasing of the laser fluence did not produce deeper structures. In addition, the best results were obtained when using low-medium laser intensities (∼0.6–1.2 J/cm2) and moderate number of laser pulses (20–50), depending on laser wavelength. In addition, at a 355 nm wavelength only patterns with 20 μm periods presented a good quality structure. In contrast, 266 nm wavelengths permitted to improve resolution up to periods of 10 μm due to a higher photochemical contribution to the ablation process. X-ray Photoelectron Spectroscopy (XPS) analysis showed that there are no significant changes in the chemical composition of laser-treated hydroxyapatite.
Maskless direct printing is a good candidate for rapid prototyping and even emerging for manufacturing of large scale electronics. Aiming for rapid prototyping of small multi-layer modules the study combines Aerosol Jet® printing and ink jet printing. Conductive silver traces down to 20μm width were printed together with large interconnect areas on isolating layers of inorganic-organic hybrid polymer (ORMOCER®) and on glass substrates. New copper nickel inks and high-k ORMOCER®s filled with barium titanate particles are paving a path to integrated printed resistors and capacitors. Although some issues still need to be resolved for a commercial grade process the detail solutions presented for the first time and the active integrated circuits and devices attached to the same substrate demonstrate a path and the principle technical feasibility of this method for heterogeneous integration.
New technologies have resulted in transmission lines that deviate significantly from the intended rectangular cross sections. Trapezoidal cross sections and roughness that penetrate a significant depth into the surface in comparison to the skin-depth of the conductor can cause a very significant deviation in transmission line parameters from predicted values. Proximity effect further complicates the analysis by increasing losses and changing the impact of surface roughness by changing the current distribution. A skin-effect filament model that combines a traditional skin-effect filament modeling concept with traditional surface roughness modeling concepts is presented that accounts for surface roughness effects and non-ideal cross sections. The new technique models the transmission line non-idealities in a combined way with the current density in the signal and return current paths. This adapted filament model shows an average deviation of less than 2% above 1 GHz with one given transmission line measurement and does not have the computational challenges seen in a 3D full-wave solver.
Purpose
– The purpose of this paper is to highlight INKtelligent printed sensor structures using maskless depositition technologies.
Design/methodology/approach
– This paper begins with a general introduction to INKtelligent printing®. Starting with layout and ink development, the fabrication of printed sensors is described in detail.
Findings
– Printed strain gauges, thermopiles and gas sensitive films are successfully fabricated with maskless deposition technologies, offering advantages for continuous non‐destructive measurement compared to conventional sensors.
Originality/value
– This paper shows a new approach for customized sensor structures. The application of a resource efficient and flexible printing technique for sensor fabrication is demonstrated.
Polymer-based materials are made electrically conductive by compounding with a particulate conductive material. Carbon soot is used most often in anti-static applications and electromagnetic shielding. In this paper another type of filler material comprising highly porous metal powders (nanopowders) is evaluated that leads to improved thermomechanical properties of the composites at reasonably high electrical conductivity levels and at reduced metal contents. Such powders are produced by the inert gas condensation technique. The broad range of applications is exemplified with a cycloaliphatic epoxy matrix for use in electronic packaging. The mechanical properties of the cured polymer/nanopowder composites have been tested under shear loading and -40 °C/150 °C thermal cycling conditions. It is shown that these highly porous powders counterbalance the embrittling effect of a metal filler in polymer matrix composites. The underlying concept is not limited to conductive adhesives for chip-on-board bonding in the microelectronics industry.
Vacuum evaporation on running liquids (VERL) is an established method for the production of metal nanoparticles in low vapor
pressure carrier liquids like silicone oils or resins. Such metal suspensions may be useful, e.g. as additives for functional
metal/polymer composites or for sintering additives in thick film pastes for microelectronics. In this paper we present a
modified VERL-process employing high gas pressure dc magnetron sputtering for the preparation of suspensions of metal nanoparticles
in various carrier liquids. By using magnetron sputtering, materials having high melting points can be evaporated without
harming the liquid substrate. The method was tested for Ag and Fe-suspensions by varying the carrier liquid and the pressure
of the Argon sputtering atmosphere in the range of 1–30 Pa. A narrow particle size distribution is obtained with the mean
particle size 〈d〉 ranging from 2 to 20 nm. For Ag 〈d〉 increases with increasing gas pressure following roughly a power law type p
1/3. The variation of particle size with sputtering gas pressure is consistent with in a model where particle formation takes
place in the gas phase exclusively before introduction into the carrier liquid. In the case of Fe agglomeration could be prevented
effectively by adding two different surfactants to the carrier liquid before starting the sputtering process.