We present the use of sub-micron resolution optical coherence tomography (OCT) in quality inspection for printed electronics. The device used in the study is based on a supercontinuum light source, Michelson interferometer and high-speed spectrometer. The spectrometer in the presented spectral-domain optical coherence tomography setup (SD-OCT) is centered at 600 nm and covers a 400 nm wide spectral region ranging from 400 nm to 800 nm. Spectra were acquired at a continuous rate of 140,000 per second. The full width at half maximum of the point spread function obtained from a Parylene C sample was 0:98 m. In addition to Parylene C layers, the applicability of sub-micron SD-OCT in printed electronics was studied using PET and epoxy covered solar cell, a printed RFID antenna and a screen-printed battery electrode. A commercial SD-OCT system was used for reference measurements.
Inkjet deposition is an attractive technology to localize nanomaterials in an area-selective manner on virtually any kind of surfaces. Great advantages of the method are effective usage of materials, low processing temperatures and few required manufacturing steps, thus enabling rapid prototyping and bulk production with reasonably low cost. A number of different electrical devices such as light emitting diodes, transistors and solar cells have already been demonstrated, reflecting the versatility of inkjet printing. In this paper, we collect the contemporary results on inkjet deposited gas sensors and show examples of such gas sensing devices based on surface modified WO3 nanoparticles for efficient discrimination of various gaseous analytes from sub-ppm up to nearly 0.1% concentration levels in air.
We present the use of sub-micron resolution optical coherence tomography (SMR SD-OCT) in volumetric characterization of ink- jet printed color filters, aimed for electronic paper display (EPD). The device used in the study is based on supercontinuum light source, Michelson interferometer centered at 600 nm and employs 400-800 nm spectral region. Spectra are acquired at a continuous rate of 140,000 per second. Color filter array of 143 μm x 141 μm sized and 6 rtm deep ink pools was studied. The volumetric OCT reconstruction was done using the experimental SMR SD-OCT device and a commercial SD-OCT imaging system. The ink layer in the pools was estimated to be 2μm thin. The optical profilometer was used for reference measurements.
In this paper we present, for the first time to our knowledge, the experimental results for determining suspension viscosity in a capillary type viscometer from flow velocity profiles measured by Doppler Optical Coherence Tomography. The suspension of 0.3?m polystyrene microspheres in a glycerol-water solution was used as a model fluid. The viscosity of the suspension was controlled by glycerol concentration. The shear rate and the shear stress at the capillary wall were measured at six flow rates. The corresponding viscosities were calculated. The comparison of the measured shear rates with the values calculated according to the flow rate of the syringe precision pump was performed. Additionally, the viscosities of the studied suspensions were measured by a rotational viscometer. Full Text: PDFReferences K.A. Hayes, M.R. buckley, I. Cohen, L.A. Archer, "High Resolution Shear Profile Measurements in Entangled Polymers", Phys. Rev. Lett. 101, 218301 (2008)[CrossRef] N. Willenbacher, H. Hanciogullari, H.G. Wagner, "High shear rheology of paper coating colors ? more than just viscosity", Chem. Eng. Technol. 20, 557 (1997)[CrossRef] M. Iotti, O.W. Gregersen, S. Moe, M. Lenes, "Rheological Studies of Microfibrillar Cellulose Water Dispersions", J. Polym. Environ. 19, 137 (2011)[CrossRef] M.T. Roberts, A. Mohraz, K.T. Christensen, J.A. Lewis, "Direct Flow Visualization of Colloidal Gels in Microfluidic Channels", Langmuir 23, 8726 (2007)[CrossRef] M. Schmidt, E. Wassner, H. Münstedt, "Setup and Test of a Laser Doppler Velocimeter for Investigations of Flow Behaviour of Polymer Melts", Mech. Time-Depend. Mater. 3, 371, (1999)[CrossRef] S. Schuberth, H. Münstedt, "Simultaneous measurements of velocity and stress distributions in polyisobutylenes using laser-Doppler velocimetry and flow induced birefringence", Rheol. Acta 47, 111 (2008)[CrossRef] Th. Wunderlich, P.O. Brunn, "A wall layer correction for ultrasound measurement in tube flow: comparison between theory and experiment", Flow Meas. Instrum. 11, 63 (2000)[CrossRef] J. Wiklund, I. Shahram, M. Stading, "Methodology for in-line rheology by ultrasound Doppler velocity profiling and pressure difference techniques", Chem. Eng. Sci. 62, 4277 (2007)[CrossRef] S. Yazdanfar, M.D. Kulkarni, J.A. Izatt, "High resolution imaging of in vivo cardiac dynamics using color Doppler optical coherence tomography", Opt. Express 1(13), 424 (1997)[CrossRef] Y. Zhao et al., "Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity", Opt. Lett. 25(2), 114 (2000)[CrossRef] J. Moger, S.J. Matcher C.P. Winlove, A. Shore, "Measuring red blood cell flow dynamics in a glass capillary using Doppler optical coherence tomography and Doppler amplitude optical coherence tomography", J. Biomed. Opt. 9(5), 982 (2004)[CrossRef] S. Tamborski et al., "Simultaneous analysis of flow velocity and spectroscopic properties of scattering media with the use of joint Spectral and Time domain OCT", Phot. Lett. Poland 1(2), 49 (2009) B. Povazay et al., "Submicrometer axial resolution optical coherence tomography", Opt. Lett. 27(20), 1800 (2002)[CrossRef] M. Harvey, T.A. Waigh, "Optical coherence tomography velocimetry in controlled shear flow", Phys. Rev. E 83, 031502 (2011)[CrossRef] J. Lauri, M. Wang, M. Kinnunen, R. Myllylä, "Measurement of microfluidic flow velocity profile with two Doppler optical coherence tomography systems", Proc. SPIE 6863, 68630F (2008)[CrossRef]
Hybrid structural electronics (HSE) consists of printed electronics, conventional rigid electronics, and load-bearing supporting parts of a device (plastic, glass etc.). Extra-large area and flexible lighting elements with embedded light-emitting diodes (LEDs) are an example of such applications. LEDs can be used, for example, as light sources, to create smart surfaces for the architectural or automotive industry. Once the LEDs are embedded into the structure, they cannot be replaced. To make sustainable HSE products with long lifetime, the new type of designs is needed. The elements of HSE undergo conditions with elevated thermal stresses while in operation. That is known to have an impact on their performance and lifetime, thus making a proper heat management of the LED crucial. Due to the novel additive manufacturing methods, structures, and unconventional material combinations, many thermal management related aspects are not known. In this study, a two-step hybrid method, including thermal modeling and measurements, is used to estimate the thermal behavior of a surface-mounted LED on polymer substrate used in HSE. The model is created and simulated in COMSOL Multiphysics. The validity and accuracy of the model's thermal behavior are verified through measurements with thermal transient measurements. Based on the experimental verification, the proposed simulation model only has small (less than 2%) temperature variations when compared with measurements. Hence, the developed model can be used as a basis for designing structural LED elements and predicting their performance characteristics in different user cases.
We describe a new measurement technique to determine the refractive index (RI) of solid particles by monitoring the simultaneous scattering of light from suspension with a camera and the value of the RI with a refractometer. Our immersion solid matching method is based on the solidification process of the liquid continuously changing the RI as a function of time. The principle of the determination is based on finding the RI matching point of the particle and the liquid during the solidification. The traditional liquid immersion method is based on a set of immersion liquids with different refractive indices, while the proposed method requires only a small amount of a single immersion liquid. The method was tested using calcium fluoride (CaF 2 ) particles with a varnish immersion liquid. The RI value of CaF 2 was obtained to be consistent with the literature values, thus indicating the proper functioning of the proposed procedure.
Roll-to-roll (R2R) process is an emerging technology to manufacture printed electronics, microfluidics, biochemical sensors etc. The requirements for high quality and small tolerances at the manufacturing phase are of the essence for such products. To verify the quality and guarantee the high production yield, high speed, non-destructive testing methods are needed. In this paper, optical coherence tomography (OCT) device is used at the R2R-line to measure online hot embossed microchannel structures at speed of 1 m/min, which is typical for the hot embossing process. The channel's width and shape are determined along the web. The applicability of OCT for topography measurements is demonstrated in an actual R2R environment.
