Sequential Lamination Research Articles

Multi‐Modal Modular Textile Sensor for Physical Human–Robot Interaction Using Band‐Stop Filters

AbstractFor safe coexistence between robots and humans, it is important for robots to detect the presence of nearby humans as well as any physical contacts made to its body. The design of a modular textile sensor array and an algorithm for multi‐modal sensing of human touches and other contacts with their contact forces proposed. Each sensor module in the array is capable of multi‐modal sensing, and the entire array with multiple modules requires only two wires to read the outputs from all the modules using band‐stop filter circuits. The proposed sensor system shows the structural modularity, achieved by simple fabrication of sequential lamination of conductive and non‐conductive textile materials, realizing electrical connections through conductive snap buttons that connect the modules to the circuit. The functional modularity is also achieved through the compensation algorithm, derived from the analysis of the transfer function in the frequency domain. The algorithm significantly reduces signal interferences between modules. The multi‐modality, the textile‐based design, and the structural and functional modularity of the proposed system enable practical applications to various robotic systems, including robotic skin for a collaborative robot, a wearable sensor, a robot hand sensor, and a human–computer interface, as demonstrated in this study.

Highly Durable Solid Oxide Fuel Cells: Prevention of Chemical Inter-Diffusion By Introducing a 4-Layered Structure

Solid oxide fuel cell (SOFC) poses great potential for stationary power generation. Nevertheless, its full-scale commercialization has lagged due to the inadequacy of long-term durability. Along with diverse background of performance deterioration, the inter-diffusion between the cathode and electrolyte have been identified as a leading fatal factor. Herein, we introduced a robust GDC layer by sequential lamination approach that completely suppresses the detrimental phase of SrZrO3 at electrolyte interface during high temperature operation. This buffer layer is fabricated via green film sequential lamination, in which the anode support, anode functional layer, electrolyte and GDC layers were sequentially co-laminated by iso-static pressing and co-sintered at 1300-1400°C. The enhanced interfacial connectivity and desired packing density of electrolyte and buffer layer were attained by controlling the shrinkages behaviors of each component. Thus, the formation of detrimental secondary phases (SrZrO3) at interface of electrolyte and decomposition of cathode are successfully restrained during fabrication and operation at critical current density. The scale-able and mass production are also confirmed through the fabrication of large area cells (144cm2) having active area 100cm2. The sequentially co-laminated GDC layer exhibited extreme low degradation rate of 0.2%/khr, which fulfils the critical longevity benchmark for commercialization of technology. This work features a cost-effective, scalable, and reproducible method for larger scale production of robust multi-layer anode supported SOFC.Keywords: Durability, Sequential lamination, life expectancy, Detrimental phases, iso-static pressing

Toward millimeter thick cellulose nanofiber/epoxy laminates with good transparency and high flexural strength

While cellulose nanofiber-based bioplastics are of great interest for replacing synthetic polymer and glass materials, the main limitation is their low thickness, which makes them difficult for various applications. In this study, we fabricated millimeter-scale thick bioplastic composites, based on 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (TEMPO-CNF) and epoxy resin, via sequential lamination processes. The glycerol as softener was added to TEMPO-CNF dispersion to prepare a thick TEMPO-CNF layer without shrinkage. It was discovered that the total thickness of TEMPO-CNF/epoxy laminates can be easily controlled by changing the thickness and number of TEMPO-CNF layers and the total thickness can also be easily increased up to 2.4 mm. Furthermore, these TEMPO-CNF/epoxy laminates have high flexural strength (272 MPa) as well as good transmittance (85% % at 600 nm). We anticipate that our approach will significantly broaden the strategies for fabricating nanocellulose-based bioplastics for use as a replacement for transparent synthetic polymers and glass materials.

De Novo Synthesis of Free-Standing Flexible 2D Intercalated Nanofilm Uniform over Tens of cm2.

Of a variety of intercalated materials, 2D intercalated systems have attracted much attention both as materials per se, and as a platform to study atoms and molecules confined among nanometric layers. High-precision fabrication of such structures has, however, been a difficult task using the conventional top-down and bottom-up approaches. The de novo synthesis of a 3-nm-thick nanofilm intercalating a hydrogen-bonded network between two layers of fullerene molecules is reported here. The two-layered film can be further laminated into a multiply film either in situ or by sequential lamination. The 3 nm film forms uniformly over an area of several tens of cm2 at an air/water interface and can be transferred to either flat or perforated substrates. A free-standing film in air prepared by transfer to a gold comb electrode shows proton conductivity up to 1.4× 10-4 S cm-1 . Electron-dose-dependent reversible bending of a free-standing 6-nm-thick nanofilm hung in a vacuum is observed under electron beam irradiation.

Nanomembranes as a substrate for ultra-thin lightweight devices

We propose to utilize a giant nanomembrane as a substrate for an ultra-thin lightweight device. The giant nanomembrane used in this research is a robust nanometer thick film consisting of highly cross-linked epoxy resins. We fabricated organic thin-film solar cells on the nanomembrane, and monitored the performance of the cells. Successful solar cell fabrication on a nanomembrane by just a sequential lamination of thin films proved that nanomembranes showed enough physical stability, chemical resistance, and surface wettability, to be utilized as a substrate for an ultra-lightweight device. In addition, we tried to detach the nanomembrane solar cell from a solid substrate by dissolving an expendable nanomembrane layer, which had been created solely for this purpose, and scooped it up with our fingers. The total thickness and weight of the detached device were less than 500 nm and 0.8 g·m−2 respectively, which are comparable to the corresponding characteristics of the thinnest and lightest devices in the world. This demonstration will expand the possibility of nanomembranes as substrates for various wearable electronic and optical devices.

Novel Fabrication Process for Micro Thermoelectric Generators (μTEGs)

A cost effective bottom-up process for the fabrication of micro thermoelectric generators (μTEGs) was developed. It is based on a novel fabrication method involving a selectively sacrificial photoresist for the sequential galvanostatic electrodeposition of thermoelectric materials. The use of an industrial pick and placer (P&P) for dispensing the second photoresist allows for accurate and flexible μTEG designs. The process makes use of Ordyl® as a negative dry film photoresist template and sequential lamination steps for shaping all thermoelectric legs and contacts. All structures of the μTEG are generated in one photoresist multi-layer - this represents the most significant advantage of the process. The process uses a minimum of clean room processing for the preparation of pre-structured substrates for electrodeposition and therefore provides a cost-effective, highly flexible fabrication platform for research and development.

A laminate‐based modelling approach for rate‐dependent switching in ferroelectric materials

AbstractThis contribution focuses on the sequential laminate‐based modelling approach for the numerical simulation of the complex electromechanical material behaviour of ferroelectric single crystals. The construction of engineered domain configurations by using the method of sequential lamination in order to study the domain evolution and polarisation switching in ferroelectric single crystals has recently been carried out in the works of [1–4]. By fulfilling the kinematic and polarisation compatibility conditions between the domain structures in a crystal, the proposed laminate‐based formulation is governed by an energy‐enthalpy function and by a dissipation potential. The mixed energy‐enthalpy, written in terms of the total strains, electric field and a set of internal variables, here the multi‐rank laminate volume fractions, governs the dissipative electromechanical response of the ferroelectric crystal, whereas the rate‐dependent dissipation potential formulated in terms of the flux of the internal variables describes the time‐dependent evolution of the multi‐rank laminate volume fractions, subjected to inequality constraints. The model reproduces experimentally observed hysteresis and butterfly curves, characteristic for single crystal ferroelectric materials, when subjected to homogeneous electromechanical loading conditions. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

PWB Z Interconnect Technology - Electrical Performance

Driven mainly by Moore's law, there is an ever accelerating drive for smaller, lighter, higher function, and lower power electronics. For PWBs this translates into higher wiring and component densities with ever increasing electrical performance requirements. As high speed serial data rates reach 30 Gbps and beyond, design considerations to promote signal integrity become ever more important. These tighter signal integrity constraints put increased emphasis on via stub effects, via to trace crosstalk in BGA escapes, and adequate ground stitch vias around layer transition vias. With the maturation of sintered paste VIAs in PWBs, VIA structures can be assembled to span only the layers to be connected. This paste technology allows vias to be specifically tailored to only connect the required layers. VIA stubs and their adverse SI effects for high speed signaling are completely eliminated. The elimination of via stubs also makes PWB fabrication easier by removing the need to backdrill or counterbore high speed signal vias. This increases yields and reduces costs associated with this complex and tight tolerance process. In addition to manufacturing advantages provided by Z technology, increased wireability is enabled by opening up area above and below the layers being connected, as well as the ability to use smaller diameter VIAs. These smaller vias also help to reduce crosstalk between high speed wiring channels. Z Interconnect technology also reduces BGA escape crosstalk by the ability to route in areas where via stubs have been removed, and also allows for the tailoring of ground stitch vias to only connect the ground planes associated with the specific stripline environments. However, Z VIAs usually require more pads within the padstack than conventional VIAs (cannot strip pads from non-connection layers) and the resistivity of the paste can be as much as 30 times greater than copper. This paper will quantify the high frequency signal characteristics associated with a PWB design using i3 Electronics sintered paste Z-VIAs. Results are presented based on modeling which is correlated with test vehicle measurements. Modeling also addresses manufacturing tolerances. Suggestions are made for optimizing passive channel structures to use this technology in support of high speed serial interconnects. Integration of i3's 2s1p Cores into new compact high speed stripline structures, which can be built without expensive subassemblies and sequential lamination processes, is also presented. These cores implement the positive aspects of Z Interconnect technology to eliminate via stubs and increase wireability in dense areas. Comparisons of Z Interconnect technology are also made to alternate methods of PWB construction to explain the risks and benefits of this technology.

All-plastic solar cells with a high photovoltaic dynamic range

We report on semitransparent air-processed all-plastic solar cells, fabricated from vacuum-free processes, comprising two polymer electrodes, a polymeric work-function modification layer and a polymer:fullerene photoactive layer. The active layer and the top PEDOT:PSS electrode were prepared by sequential film-transfer lamination on polyethylenimine-modified PEDOT:PSS bottom electrodes. The transferring of films offers ease of layer patterning and the misalignment of defects in the different layers resulting from the additive film transfer lamination process yields high shunt resistance values of 108 ohm cm2. Consequently, all-plastic solar cells fabricated with this process exhibit very low reverse bias dark current and can operate in the photovoltaic quadrant with light irradiance varying over five orders of magnitude. The analysis of the values of the open-circuit voltage as a function of light irradiance over that wide dynamic range points toward an ideality factor of n = 1.82 and a reverse saturation current density of 6.2 × 10−11 A cm−2 for solar cells with an active layer comprised of a blend of poly(3-hexylthiophene) and an indene fullerene bis-adduct.

Bonding of 2 mm thick silicon wafers using LTCC as an intermediate layer

For the fabrication of a micro fluidic high pressure oil sensor (400 bar) based on an infrared transmission measuring principle the bonding of 2 mm silicon wafers is necessary. Conventional bonding techniques such as silicon fusion bonding or anodic bonding are not suitable for bonding thick and inflexible silicon wafers, because these techniques can not compensate for the wafer bow. We present a new bonding procedure for silicon substrates thicker than 1 mm using a silicon adapted LTCC tape as an intermediate leveling layer. The wafers are preprocessed by etching a nano structured silicon surface on the internal side. The silicon wafers are aligned and stacked with pre-structured green LTCC tapes by an optical stacking unit. During the hot isostatic lamination at 55 bar the structured LTCC tape is adjusted to the silicon. A subsequent pressure assisted sintering leads to a wafer bonding strength up to 5000 N/cm2. With the bonding technique it is possible to create cavities and channels between the thick wafers by the use of punched and laser cut LTCC. The fabrication steps of the sandwich build-up especially the sequential lamination and the optical adjusting procedure of the flexible (LTCC) and inflexible (2 mm Wafer) substrates will be explained in detail. A method to reduce the shrinkage and distortion of the green LTCC during handling is demonstrated. The distribution of the bonding and bursting strength of the single fluidic systems on a complete sandwich substrate is analyzed.

On the modelling of time-interleaved sequential lamination micromixers

We develop a novel and simple theoretical model of time-interleaved sequential lamination micromixers that improves the model proposed by Nguyen and coworkers (Microfluid Nanofluid 1:373–375, 2005a, Lab Chip 5:1320–1326, b, J Phys Conf Ser 34:136–141, 2006) based on the Taylor–Aris dispersion theory. The Nguyen model takes into account the non uniform structure of the velocity profile through an effective dispersion coefficient. However, it is essentially a one-dimensional model that is not suitable to describe (i) neither the behavior of mixing occurring at short length-scales, and characterized by the growth of a mixing boundary layer near the channel walls, (ii) nor the exponential decay of the concentration field occurring at larger length-scales. The model we propose, which is based upon the theory of imaginary potential developed by Giona et al. (J Fluid Mech 513:221–237, 2004, Europhys Lett 83:34001, 2008, J Fluid Mech 639:291–341, 2009a), is able to provide quantitative predictions on the evolution of the L 2-norm of the concentration fields as function of the axial coordinate ξ, both for short and asymptotic lengthscales. The quantitative comparison with respect to the Nguyen model is illustrated and discussed. Finally, the coupling between parallel lamination and sequential segmentation is analyzed, and leads to unexpected and apparently counter-intuitive findings.

Interaction between Reelin and Notch Signaling Regulates Neuronal Migration in the Cerebral Cortex

Neuronal migration is a fundamental component of brain development whose failure is associated with various neurological and psychiatric disorders. Reelin is essential for the stereotypical inside-out sequential lamination of the neocortex, but the molecular mechanisms of its action still remain unclear. Here we show that regulation of Notch activity plays an important part in Reelin-signal-dependent neuronal migration. We found that Reelin-deficient mice have reduced levels of the cleaved form of Notch intracellular domain (Notch ICD) and that loss of Notch signaling in migrating neurons results in migration and morphology defects. Further, overexpression of Notch ICD mitigates the laminar and morphological abnormalities of migrating neurons in Reeler. Finally, our in vitro biochemical studies show that Reelin signaling inhibits Notch ICD degradation via Dab1. Together, our results indicate that neuronal migration in the developing cerebral cortex requires a Reelin-Notch interaction.

Embedding capacitors and resistors into printed circuit boards using a sequential lamination technique

Embedding capacitors and resistors into printed circuit boards (PCBs) offers many benefits over surface mount technology (SMT) and through-hole packaging (PTH). These benefits include improvements in electrical performance and reliability, and potential cost reduction. Embedded devices also enable signal integrity at speeds over 1 GHz. Also, replacement of surface mounted discrete passives with an embedded passives layer allows for tighter component spacing, fewer holes and a larger routing area. All these are essential for board miniaturization. However, the goals of reliability improvement, space conservation, performance enhancement and solder joint reduction by using embedded passives can only be realized if the PCB fabricator can produce high quality boards in a practical production environment in a timely manner. This paper describes an investigation of the manufacturing of embedded resistors and capacitors on a prototype basis and the possibility of extending this technique to normal mass production. The proposed sequential lamination technique (SLT) was applied to form a PCB with embedded passives. Then, to verify the manufacturing capability, samples of integrated planar resistors and buried capacitors were fabricated on specially designed PCB test panels. The component readings are also presented in this paper.

Effects of a tert‐butylphenylene substituent on the structure and optical, fluorescent and thermal properties of the poly(p‐phenylenevinylene) derivatives

AbstractTwo soluble fluorescent polymers, poly(2‐decyloxy‐5‐(4′‐tert‐butylphenyl)‐1,4‐phenylenevinylene) (DtBP‐PPV) and poly(2‐decyloxy‐1,4‐phenylenevinylene) (DO‐PPV), were prepared by a method similar to the Gilch procedure. The DtBP‐PPV and DO‐PPV have a same chemical structure except for the conjugated tert‐bytulphenyl substituents in the former. The polymers are characterized by using 1H NMR, FTIR, UV–vis, photoluminescence (PL), and electroluminescence (EL) spectroscopies and thermogravimetric analysis (TGA). The 1H NMR spectra show no tolane‐bis‐benzyl (TBB) structure defects in DtBP‐PPV but some in DO‐PPV. Both UV–vis absorption and PL emission peaks of the DtBP‐PPV exhibit a red‐shift phenomenon as compared with those of the DO‐PPV. Moreover, with the DtBP‐PPV and DO‐PPV acting as light‐emitting polymers separately, EL devices were fabricated with a sequential lamination of ITO/PEDOT/DtBP‐PPV (or DO‐PPV)/Ca/Ag. The DtBP‐PPV‐based device shows a lower turn‐on voltage, a longer EL emission wavelength, and a higher brightness than the DO‐PPV‐based device. The maximum brightness of DtBP‐PPV‐based device is 57 cd/m2 at an applied voltage of 12 V. POLYM. ENG. SCI., 47:1380–1387, 2007. © 2007 Society of Plastics Engineers

Synthesis of Poly[2‐decyloxy‐5‐(4′‐tert‐butylphenyl)‐1,4‐phenylenevinylene] as a Light Emitting Material

In this study, a new electroluminescent poly(2‐decyloxy‐5‐(4′‐tert‐butylphenyl)‐1,4‐phenylene‐vinylene) (designated as DBP‐PPV) with no tolane‐bis–benzyl (TBB) structure defect was prepared by dehydrohalogenation of 1,4‐bisbromomethyl‐2‐decyloxy‐5‐(4′‐tert‐butyl‐phenyl) benzene (as monomer). The monomer bearing decyloxy and 4′‐tert‐butylphenyl substituents was synthesized via alkylation, bromination and Suzuki coupling reactions. The two asymmetric substituents of the monomer can suppress the formation of TBB defect during polymerization process and make the resultant polymer be soluble in common organic solvents. The structure and properties of DBP‐PPV were examined by 1H‐NMR, FT‐IR, UV/Vis, TGA and photoluminescence (PL) analyses. Moreover, with the DBP‐PPV acting as a light‐emitting polymer, a device with sequential lamination of ITO/PEDOT/DBP‐PPV/Ca/Ag was fabricated. The electroluminescence (EL) spectrum of the device showed a maximum emission at around 546 nm, corresponding to a yellowish‐green light. The device showed a turn‐on voltage of about 8.4 V and a maximum luminescence efficiency of 0.11 cd/A at an applied voltage of 12 V.

Development of High Reliability Via on IVH (VONI) for High Density Interconnect Circuit Boards

Via on interstitial via hole (VONI) technique is a complex set of technologies for blind and buried vias in traditional sequential lamination cycles with external layers, and micro via holes (MVH) for true high-density packaging. However, when VONI is repeatedly subjected to thermal stress, the interstitial via hole (IVH) in its structure often creates problems such as IVH barrel cracks, and layer-layer delamination. To solve VONI's reliability problems, such as IVH barrel crack and layer-layer delamination, the authors have investigated the relationship between the CTE difference and the effect of moisture. Through using different types of plugging inks, it was clearly indicated that delamination was related to the chemical properties of the plugging inks. For example delamination was dominated by the inks property of water adsorption, which induced vapor pressure when it undergoes thermal shock testing. The authors have solved the delamination problem by reducing the ratio of water adsorption in the plugging ink.

Synthesis and Characterization of the Luminescent Poly[2-decyloxy-5-(2′,5′-bis(decyloxy)phenyl)-1,4-phenylenevinylene

A new soluble luminescent poly[2-decyloxy-5-(2′,5′-bis(decyloxy)phenyl)-1,4-phenylenevinylene] (DBDP-PPV) is prepared by the dehydrohalogenation of 1,4-bis(bromomethyl)-2-decyloxy-5-(2′,5′-bis(decyloxy)phenyl) benzene (as monomer) in this study. The above monomer bearing decyloxy and 2′,5′-bis(decyloxy)phenyl substituents was prepared via such chemical reactions as alkylation, bromination, and Suzuki coupling reactions. The two asymmetric substituents on the phenylene ring make the DBDP-PPV soluble in organic solvents and eliminate the tolan-bis-benzyl (TBB) structure defects. The structure and properties of the DBDP-PPV are examined by 1H-NMR, FT-IR, UV/Vis, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The DBDP-PPV film exhibits a PL peak at 519 nm. With the DBDP-PPV acting as a light-emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DBDP-PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 507 nm. The turn on voltage of the device is about 15.6 V. Its maximum brightness is 4.67 cd/m2 at a voltage of 16.8 V.

Synthesis and characterization of the soluble fluorescent poly[2‐decyloxy‐5‐(2′‐(6′‐dodecyloxy)naphthyl)‐1,4‐phenylenevinylene

AbstractA new soluble fluorescent polymer, poly[2‐decyloxy‐5‐(2′‐(6′‐dodecyl‐oxy)naphthyl)‐1,4‐phenylenevinylene] (DDN‐PPV), with no tolane‐bisbenzyl (TBB) structure defects is prepared by the dehydrohalogenation of 1,4‐bis(bromomethyl)‐2‐decyloxy‐5‐(2′‐(6′‐dodecyloxy)naphthyl)benzene (as monomer) in this study. The aforementioned monomer is synthesized via such chemical reactions as alkylation, bromination, and Suzuki coupling reactions. The structure and properties of the DDN‐PPV are examined by 1H NMR, FTIR, UV/vis, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The two asymmetric decyloxy and 6′‐dodecyloxynaphthyl substituents on the phenylene ring make the DDN‐PPV soluble in organic solvents and eliminate the TBB structure defects. With the DDN‐PPV acting as a light‐emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DDN‐PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 538 nm. The turn on voltage of the device is about 16.6 V. Its maximum brightness is 14 cd/m2 at a voltage of 18.2 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2734–2741, 2007

In Vivo Imaging Reveals Dendritic Targeting of Laminated Afferents by Zebrafish Retinal Ganglion Cells

Targeting of axons and dendrites to particular synaptic laminae is an important mechanism by which precise patterns of neuronal connectivity are established. Although axons target specific laminae during development, dendritic lamination has been thought to occur largely by pruning of inappropriately placed arbors. We discovered by in vivo time-lapse imaging that retinal ganglion cell (RGC) dendrites in zebrafish show growth patterns implicating dendritic targeting as a mechanism for contacting appropriate synaptic partners. Populations of RGCs labeled in transgenic animals establish distinct dendritic strata sequentially, predominantly from the inner to outer retina. Imaging individual cells over successive days confirmed that multistratified RGCs generate strata sequentially, each arbor elaborating within a specific lamina. Simultaneous imaging of RGCs and subpopulations of presynaptic amacrine interneurons revealed that RGC dendrites appear to target amacrine plexuses that had already laminated. Dendritic targeting of prepatterned afferents may thus be a novel mechanism for establishing proper synaptic connectivity.

Synthesis and characterization of the soluble luminescent poly[2-decyloxy-5-(4’-ethoxyphenyl)-1,4-phenylenevinylene

A new soluble luminescent poly[2-decyloxy-5-(4′-ethoxyphenyl)-1,4-phenylene-vinylene] (DEP-PPV) is prepared by the dehydrohalogenation of 1,4-bis(bromo-methyl)-2-decyloxy-5-(4′-ethoxyphenyl) benzene in this study. The structure and properties of the DEP-PPV are examined by 1H NMR, FT-IR, UV/VIS, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The incorporation of a decyloxy substituent in the 2-position of phenylene ring makes the DEP-PPV soluble in organic solvents and eliminates tolan-bis-benzyl structure defects. The energy band gap of DEP-PPV in tetrahydrofuran is 2.36 eV. The PL peak of DEP-PPV solution shifts to higher wavelength as the solution concentration increases. The PL spectrum of the DEP-PPV film shows a peak at 546 nm and the one of the pristine PPV film does at 540 nm. This red shift of PL peak for the DEP-PPV as compared with that for the PPV indicates that the incorporation of a conjugated ethoxyphenyl group on the phenylene ring can increase the conjugation length of phenylenevinylene units in the DEP-PPV. With the DEP-PPV acting as a light-emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DEP-PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 530 nm, which corresponds to the yellowish-green light. The turn-on voltage of the device is about 16 V. Its maximum brightness is 46 cd/m2 at a voltage of 18 V.