Hannu Sillanpää

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.

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.

Application of wide-band material parameter extraction techniques to printable electronics characterization

Material characterization is an important part of printable electronics design, since material properties depend strongly on the manufacturing process. This paper reviews application of wide-band extraction techniques to printable electronics characterization. The extraction methods are validated using full-wave simulation data with exactly known reference for material parameters. Suitable test structures are evaluated and applied to printable electronics characterization.

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.

A multiline material parameter extraction method

Material characterization is an important part of printable electronics design since material properties depend strongly on the manufacturing process. This paper introduces a novel multiline material characterization method that is applicable to the characterization of printable electronics structures as well as integrated microwave devices. The proposed technique eliminates the half-wave resonances, decrease the sensitivity to small variations in the lines and provide a weighted average from individual line pair data. The multiline extraction method is validated using full-wave simulation data, and is subsequently applied to test structures manufactured with inkjet technology.

RADIO INTERFACE DESIGN FOR INKJET-PRINTED BIOSENSOR APPLICATIONS

Biomedical wireless sensors require thin, lightweight, and ∞exible single-layer structures operating in immediate proximity of human body. This poses a challenge for RF and antenna design required for wireless operation. In this work, the radio interface design for a 2.4GHz wireless sensor including a discrete fllter balun circuit and an antenna operating at 0.3mm distance from the body is presented. Thin, lightweight single-layer structure is realized using printed electronics manufacturing technology. The RF and antenna designs are validated by measurements, and a sensor with a fully functional radio interface is implemented and verifled. At 0.3mm from the body, 2.4dB insertion loss and i10dBi realized gain at 2.4GHz were achieved for a discrete fllter balun and antenna, respectively. The received power level on a Bluetooth low energy (BLE) channel was above i80dBm at 1m distance from the body, indicating capability for short-range ofi-body communications. The paper also provides guidelines for printed electronics RF and antenna design for on-body operation.

HUMAN BODY EFFECTS ON INKJET-PRINTED FLEXIBLE RF INTERCONNECTIONS

The efiect of human body on inkjet-printed ∞exible single- layer transmission lines in immediate proximity of body is investigated by simulations and measurements up to 9GHz. A multiline extraction method is used to obtain efiective material parameters allowing detailed analysis of body efiects. Already at 1mm distance from the body, the line properties converge toward the free-space values. However, at smaller distances and in direct contact with the body, often required in biosensor applications, there is a signiflcant change in characteristic impedance and increase in losses. The results of the paper can be used to evaluate the body efiects at difierent frequencies and at difierent small distances from the body.

Wide-band Electrical Characterization of printable nano-particle copper conductors

Copper nano-particle ink suitable for printing is a promising substitute for silver- or gold-based inks for consumer electronics applications. However, oxidization must be controlled during the manufacturing and sintering processes. In this work conductors created from a copper nano-particle ink are characterized. In order to mitigate oxidation effects, the ink was formulated in inert atmosphere. Sintering is achieved by exposure to a short light pulse, which, due to the short time scales (ms) and added benefit of photoreduction, can be done in air. Wide-band electrical characterization results up to 20 GHz for copper nano-particle conductors are presented. Structural analysis using scanning-electron microscope (SEM) complements the characterization. Based on high-frequency measurements, wide-band material parameter extraction techniques, and modeling-based analysis of measurement results, the conductivity was found to be of the order of 0.7·107 S/m. All loss mechanisms including impurities deposited within the metal, porosity, surface roughness, and variation in structure geometry are attributed to the conductivity. The electrical performance was found almost comparable to that of silver-based inks. Also the average measured direct-current (dc) conductivity 1.37·107 S/m is similar to that of typical nano-metal conductors.

State-of-the-art in characterization-based printed electronics RF design

Printed electronics manufacturing technology is well suited for thin, flexible wireless sensor applications. This work summarizes a state-of-the-art design methodology for printed electronics including recent advances in wide-band electrical material characterization process, characterization-based RF design, optimized antenna design for inkjet printing, and an example of an inkjet-printed wireless sensor. The research is relevant for modeling-based design of flexible wireless sensors.

Modeling-based printed electronics characterization

A wide-band characterization process for printed electronics materials is presented. A parallelized 2-D eigenmode solver is developed and successfully applied to extract actual material parameter values from measurements. This information is critical for both process development and modeling-based design.