Eerik Halonen

Body-Worn Antennas Making a Splash: Lifejacket-Integrated Antennas for Global Search and Rescue Satellite System

The Cospas (Cosmicheskaya Sistyema Poiska Avariynich Sudov)-Sarsat Search-and-Rescue (SAR) satellite system provides distress alert and location data to assist rescue operations at sea, in the air, or on land. This paper summarizes the design, development, and verification for a body-worn antenna system interfaced with commercial Cospas-Sarsat personal locator beacons (PLBs), where the implemented system is integrated within an inflatable live vest. The modular approach adopted in the work allows different antenna configurations for different platforms. The electrical and mechanical requirements for antenna materials and antennas were derived from the Cospas-Sarsat system requirements, possible antenna platforms, and the maritime operational environments. The antennas were used in field tests organized in cooperation with the local Cospas-Sarsat search-and-rescue authorities. The field tests were a success. In both cases, low-earth orbit search-and-rescue (LEOSAR) satellites detected the distress signal within minutes, and accurately resolved the location. An additional detection by Geostationary Orbit Search and Rescue (GEOSAR) satellite confirmed the successful operation of the body-worn antenna system.

Capability of inkjet technology in electronics manufacturing

The past decade has seen a growing interest in additive manufacturing and printable electronics. The main markets are expected to be among low-cost mass production of radiofrequency identification (RFID) tags, antennas, keyboards, displays, sensors, and smart packages, but also high-performance products. This paper focuses on process improvement and capability analysis of inkjet technology in electronics manufacturing using six sigma methodology. It provides not only tools and roadmaps for technical development and process improvement, but also a systematic program management tools for technology development also in industrial-academic collaboration. This paper focuses on the printing accuracy and quality issues in inkjet printing technology. The scaling of the image and the alignment capability of the process is analyzed by printing several dot matrixes on polyimide substrates and measuring the places of the inkjetted drops from substrates and comparing those onto the locations of the dots in printfile. This data is used to generate a mathematical model, which was used to correct the shifting and scaling of the image yielding to improved process capability.

RF Design for Inkjet Technology: Antenna Geometries and Layer Thickness Optimization

The suitability of local conductive print-layer thickness variation for RF applications is demonstrated on flexible substrates. First, the concept is subjected to printed transmission lines as attenuation of one- and two-layer lines is compared to lines having additional layers only on critical high-current areas. Then, two antenna types are studied by applying local additions to the feed line and radiator with optimized print parameters for each layer utilizing low-temperature ink enabling a variety of substrate materials. For a narrow wire-type antenna, efficiency improvement with local thickness increase is observed both at 868 MHz and 2.4 GHz, reaching the efficiency level of a full two-layer antenna. For a wide monopole-type antenna at 2.4 GHz, the similar efficiency improvement up to the full two-layer level is seen already by increasing the edge thickness on the feed line. Accordingly, the antenna type is promising for printing with satisfactory efficiency only with one-layer print on the antenna element. The printed antennas also show good electrical performance, with only approximately 5%-10% decrease in efficiency compared to thick 18-μm copper reference antennas.

Oven Sintering Process Optimization for Inkjet-Printed Ag Nanoparticle Ink

This paper focuses on optimizing the oven sintering time and temperature for inkjet-printed silver nanoparticle ink on a polyimide substrate. Two basic aspects in fabricating conductor structures in printable electronics are conductivity and adhesion between the ink and the substrate material. Conductivity evolution during oven sintering is monitored with real-time resistance measurements at five different temperatures. Based on conductivity results, adhesion is evaluated at several time points at three temperatures. The higher the sintering temperature, the faster the structures reach their maximum conductivity values. The lowest conductor resistivity values are below 4 μΩ· cm. However, at each sintering temperature, it takes longer to reach the best adhesion values. In this paper, we aim to better understand oven sintering of silver nanoparticles and determine the best oven sintering conditions (temperature, time) for our particular ink-substrate combination. The results can be used to further define optimum sintering conditions for printed nanoparticle inks on polymer substrates.

Sintering of printed nanoparticle structures using laser treatment

Printed intelligence is a promising new technology to produce low-cost electronics. Non-conductive circuits can be printed using nanoscale metal particle inks. Due to the nanoscale size of the particles, the typical sintering temperatures of 100–300 °C are only a fraction of the macroscopic melting point of the corresponding materials, thus allowing the use of paper or plastic substrates.Sintering of printed nanoparticle structures using laser treatment has been investigated at VTT. Laser sintering can be utilized in manufacturing of printed conductor structures such as antennas, circuits and sensors. A drop-on demand printer was used to print patterns with metallo-organic silver nanoparticles on a flexible polyimide substrate. Laser sintering was made with a 940 nm CW fiber coupled diode laser. Process was optimized using different laser power levels, line separation and repetition rounds. Conductivity of laser sintered samples was compared to conductivity of samples sintered in convection oven.Printed intelligence is a promising new technology to produce low-cost electronics. Non-conductive circuits can be printed using nanoscale metal particle inks. Due to the nanoscale size of the particles, the typical sintering temperatures of 100–300 °C are only a fraction of the macroscopic melting point of the corresponding materials, thus allowing the use of paper or plastic substrates.Sintering of printed nanoparticle structures using laser treatment has been investigated at VTT. Laser sintering can be utilized in manufacturing of printed conductor structures such as antennas, circuits and sensors. A drop-on demand printer was used to print patterns with metallo-organic silver nanoparticles on a flexible polyimide substrate. Laser sintering was made with a 940 nm CW fiber coupled diode laser. Process was optimized using different laser power levels, line separation and repetition rounds. Conductivity of laser sintered samples was compared to conductivity of samples sintered in convection oven.

Dynamic bending test analysis of inkjet-printed conductors on flexible substrates

The need to optimize space in electronic devices has made flexible electronics an attractive option for manufacturing electronics. Techniques to fabricate flexible circuits have become more and more common and the processes increasingly more efficient. Printed electronics is a potential technique for manufacturing electronic patterns on flexible substrates. In particular, inkjet printing is an effective way to produce fine, thin, conductive structures without touching the substrate material. This study concentrated on dynamic bending analysis of inkjet-printed silver conductors on a polymer substrate. Because printed electronics is a relatively new manufacturing method, not much research is yet available on mechanical endurance of printed structures. By default, thin layers of inkjet-printed traces may just prove to have good tolerance against bending. However, factors such as adhesion between ink layer and substrate and the effect of the porous structure of sintered nanoparticle ink must be studied. This paper evaluates the capability of the inkjet technique on a flexible substrate and benchmarks the results on conventional flexible copper circuit boards. Measurements were made in real time of the resistance of conductors while bending the sample along two different radii. Results showed that printed conductors were superior in endurance over etched copper circuits.

Inkjet printing in manufacturing of stretchable interconnects

Stretchable circuits have the potential to enable integrating electronics in everyday objects, but also skin-like, imperceptible electronic applications. However, manufacturing stretchable electronics requires developing novel manufacturing methods and using novel materials at least as substrate. Since the elastic materials for stretchable electronics are relatively soft, using traditional manufacturing methods becomes more problematic, whereas contactless material deposition by inkjet-printing is unaffected by such material properties. This study concentrates on feasibility analysis of using inkjet printing in manufacturing of stretchable electronics. First, printing related challenges are evaluated by manufacturing test structures with inkjet-printer using silver nanoparticle ink on elastic thermoplastic polyurethane substrate and sintering structures in convection oven. Adhesion between ink and substrate, but also sheet resistance, is evaluated. A minimum sheet resistance approx. of 26 mΩ/□ was obtained, and peak strains of inkjet-printed conductors are found to be between 1.0 % and 1.5 %, but conductivity is observed to be almost fully reversible when strain is released.

The effect of sintering profile and printed layer variations with inkjet-printed large-area applications

Inkjet-printed conductors with large areas and increased layer thickness may cause challenges with the materials applied. The possibly required increased sintering energy can result in exceeding the heat tolerance of the substrate and cracks in the conductor surface can be formed. The advantages of inkjet print technology can be applied to reduce these challenges by limiting the ink usage by varying the conductor thickness locally or even removing the parts of material from the layout. In this paper, large-area RF applications are studied in terms of varying conductive ink usage and sintering profile. An antenna type with high current density areas is used as a demonstrator of an application requiring larger uniform printed area. The paper shows the advantages of limited local printing on additional layers compared to printing full layers. Two different sintering profiles are applied to differently printed antenna versions fabricated for 868 MHz and 2.4 GHz frequencies. It is shown, that with less sintering energy, the antennas with only local additions perform better than antennas with fully printed antennas with more ink. With longer sintering process time, the local antenna and the fully printed antenna behave equally in terms of total efficiency.

Antenna Applications Corner

Abstract form only given. The Cospas (Cosmicheskaya Sistyema Poiska Avariynich Sudov)-Sarsat Search-and-Rescue (SAR) satellite system provides distress alert and location data to assist rescue operations at sea, in the air, or on land. This paper summarizes the design, development, and verification for a body-worn antenna system interfaced with commercial Cospas-Sarsat personal locator beacons (PLBs), where the implemented system is integrated within an inflatable live vest. The modular approach adopted in the work allows different antenna configurations for different platforms. The electrical and mechanical requirements for antenna materials and antennas were derived from the Cospas-Sarsat system requirements, possible antenna platforms, and the maritime operational environments.