Riku Mäkinen

An improved thin-wire model for FDTD

An improved thin-wire model for the finite-difference time-domain method is proposed. The new model can be used to accurately model straight wire sections connected to other metal structures. In addition, the model includes the effect of charge accumulation at wire end caps. The end-cap model is based on conservation of charge and Coulombs law. Using the end-cap model, unconnected wires such as wire antennas are also accurately modeled. The results indicate a significant improvement in predicting the resonance frequency of a dipole antenna.

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.

PERFORMANCE OF PRINTABLE ANTENNAS WITH DIFFERENT CONDUCTOR THICKNESS

This paper shows that L-shaped monopole antenna on PPS manufactured by inkjet printing of nano silver ink is able to produce very competitive overall antenna performance against Rogers copper foil structures if the thickness of the printed conductor layer is about the skin depth at the operating frequency multiplied by four.

Modeling of Lossy Curved Surfaces in 3-D FIT/FDTD Techniques

A conformal first-order or Leontovic surface-impedance boundary condition (SIBC) for the modeling of lossy curved surfaces in a Cartesian grid is presented for the finite-integration technique (FIT). Equivalently, the model can be derived using the contour-path formulation of the finite-difference time domain (FDTD) method. The SIBC is based on a lumped-element representation of the impedance combined with a conformal modeling scheme. The validity of the proposed model is evaluated by investigating the quality factors of rectangular, cylindrical and spherical cavity resonators. The convergence rate of the conformal SIBC model is shown to be of second order

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.

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.

A stabilized resistive voltage source for FDTD thin-wire models

The von Neumann analysis is applied to investigate the stability of a source connected on a wire described by a thin-wire model. Both a soft source and a resistive voltage source (RVS) are shown to limit the stable range of values for wire radius or time step. Using the von Neumann analysis, a stable RVS model for thin wires is developed. The proposed model is verified by comparison with a hard source, an original RVS and NEC-generated reference data. The stabilized RVS introduces no additional stability constraints on those of the wire model while maintaining fast decay of incident fields of the original RVS model.

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.