Inkjet-Printed Transparent Antennas Integrated on Solar Cells

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Marian Fleming
7 years ago
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1 Inkjet-Printed Transparent Antennas Integrated on Solar Cells Tursunjan Yasin, Reyhan Baktur Department of Electrical and Computer Engineering Utah State University, Logan, UT

2 Background Main goal: To integrate optically transparent antennas directly on commercial solarcells for satellite applications. Meshed antenna is a straightforward and cost friendly solution Can easily be optimized for both the optical transparency and the antenna performance Can produce an optically transparency of > 93%, which is higher than most optically transparent conductors A rectangular 93.7% transparent meshed antenna integrated on solar cells (USU 2008)

3 How to Fabricate Meshed Antennas? Off-the shelf electroformed conductor mesh High accuracy High transparency Expensive Screen printing using conductiveink Flexible, mesh is not limited to rectangular geometry Cost friendly Not accurate Hard to reach high transparency due to the printing resolution A strong need for a faster, cheaper, and more accurate fabrication method

4 Background 2-- Design Method To effectively design a highly transparent meshed antenna is another challenge For example, the following geometry can not be easily studied with HFSS using a regular computer. Circular meshed antenna: about 60% transparency, line-width (width of the grid lines) = 0.46 mm Computer Specification: Processor: Intel Core2 Duo CPU 2.93 GHz RAM: 4.00 GB (3.25 GB usable) System Type: 32-bit OS Out of Memory for a relatively simple geometry

5 Another Example In this geometry, there is less number of lines, and the line-width is widened to reduce computation load. Total CPU time spent is 01:25:12 for one simulation Will take at least 4.5 hours to achieve an optimal matching The example geometry has an optical transparency of only 60% 60% transparency, line-width = 0.57 mm Our goal is to have 90% transparency, which means very thin line-width Result: either out of memory, or a very long design period.

6 A better fabrication tool Fast and straight forward Inkjet Printing Capable of printing fine geometries, more accurate than screen printing Cost friendly compared to electroformed mesh A good design tool Traditional process: Software parametric study understanding design parameters validation through experiment. Time consuming for meshed antenna. Instead, inkjet printing allows us directly study and extract design parameters though fast experiments

7 Inkjet Printing Essentials Printer Epson C88+ (< $100.00) Conductive Ink JS-15 silver ink (NOVACENTRIX) Cartridges (prefilled, refillable) Substrates: Paper, Photo paper (at least 4 stars), Transparencies, Kapton, PET (Polyethylene Terephthalate) with extra ink absorbing layer (NOVACENTRIX) Curing Oven or PulseForge 3100 (NOVACENTRIX)

8 Printing Process Printer Printer setup: high resolution Sufficient ink deposit Substrates Thin Good at holding the ink Curing Oven NOVACENTRIX PulseForge 3100

9 More Details The printer used for this inkjet printing method is Epson C88+, only costing around100 dollars. The silver conductive ink (JS-15) prefilled in empty cartridges for Epson C88+ is provided by Novacentrix, a company supplying tools and conductive inks for printed electronics manufacturing; PET (polyethylene terephthalate), which has a special coating for capturing the conductive ink to enhance the conductivity, is used in this experimental study.

10 Curing after Printing Curing can make the conductive ink to form good channels for electrons to flow It is very fast and reliable to use PulseForge, a sepecial equipment from Novacentrix An alternative method of curing is through heating: preheat at around 60 for ten minutes to avoid oxidization of silver particles in the conductive ink, and then heat at high temperature above 100 for ten hours.

11 Choice of Feed Designs Coaxial probe feed: Inconvenient for practical tuning Line feed: Difficult to match to the antenna due to its high impedance (meshing increases input impedance) Insetting changes antenna geometry Proximity coupling: A good option Easy to tune and match

12 Transparency is defined as T-Coupled Feed antenna metal tran = = Aantenna Transparencies are varied by changing the number of lines Number of lines transparency impedance Impedance matching can be achieved by adjusting w and s (e.g. table and figures in below) Trans (%) P A A A A transparent antenna s (mm) w (mm)

13 Verification of Printing Quality Quick test on the conductivity Conductors Without Curing After Curing Copper Relative Resistance(Ω) Open Copper Ink Test print is compared with a copper tape Dimensions: 41.0 mm by 5.6 mm Inkjet printed line on PET Copper tape is also stuck on to the same PET substrate A HP 34401A Multimeter is used for resistance measurement

14 Verification Using a Patch Antenna Initial verification before proceeding to print more complicated mesh geometry Two geometrically identical rectangular patch antennas with inset feed were fabricated One is inkjet printed on PET substrate, then assembled on RO4003C (1.524 mm) The other antenna is fabricated using milling machine on a same Rogers substrate Design for 2.5 GHz Ground size is 40 mm by 32 mm

15 Measurements Copper Difference in S11 is expected because of the additional PEL layer for the printed antenna Overall performance of the inkjet printed antenna is comparable to the copper antenna Ink

16 What s Next? Study the performance of a meshed circular patch antenna Commercial software: challenging for larger number of meshes, and thinner mesh lines We chose to perform experimental study by printing Print and analyze a series of circular meshed patch antennas with different geometries Our interest is to achieve an effective antenna without compromising its transparency

17 Using Inkjet Printing to Study Circular Meshed Antennas Antenna printed on PET Plexiglass Antenna Assembly Copper Tape backing as ground plane An example assembly of a 90% antenna. This antenna can not be simulated with a regular computer using HFSS due to its fine geometry

18 Effect of Number of Mesh Lines 7 circular meshed antennas were assembled and measured When the width of the mesh lines is fixed, the transparency of the antenna can be adjusted by varying the number of lines It is seen that higher transparency results in lower resonant frequency

19 Effect of Line-Width 11 circular meshed antennas were assembled and measured Another parameter that affects transparency is the line-width of meshes It is seen that for a given transparency (60% in this case), finer mesh lines results in higher resonate frequency This means by refining mesh lines, it is feasible to achieve a meshed antenna as effective as a solid patch antenna

20 Summary The feasibility of printing patch type antennas with a commercial inkjet printer is presented Inkjet printing with conductive ink is not only becoming a popular method to produce antennas, but also is an effective tool to analyze antennas with complex and refined geometry Initial studies show that for a circular meshed patch antenna, one can achieve both optical transparency and antenna efficiency by refining the mesh lines It is possible to print antennas with transparency higher than 90% that will allow one to integrate these antennas with solar cells, windows, and LED displays

21 Questions?

Good Boards = Results

Section 2: Printed Circuit Board Fabrication & Solderability Good Boards = Results Board fabrication is one aspect of the electronics production industry that SMT assembly engineers often know little about.