Milica Kisic

Passive Wireless Sensor for Force Measurements

The goal of this paper is to investigate fabrication and design of a wireless passive sensor, and its application for measuring normal forces. The proposed force sensor consists of a single coil as an essential part, realized in printed circuit board technology, commercially available elastomer, and ferrite core. Measurements are done wirelessly for variable values of applied force by phase-dip technique, using an external coil antenna. By applying force to the sensor, the elastomer deforms and ferrite approaches to the coil, causing changes to the inductance of the coil. As a result, the resonant frequency of the antenna-sensor system shifts toward lower frequencies. The experimental setup is conducted to test and characterize the developed force sensor. A high sensitivity of 311 kHz/N is achieved in the measured force range from 0 to 75 N. The measurement results proved the theoretical and analytical calculations, as well as the electrical simulations.

Ink-jet printed strain sensor on polyimide substrate

This paper describes a method for measuring strain on a specimen with flexible strain sensor. The sensor is made by ink-jet printing of silver ink on polyimide substrate, in that manner providing a combination of electrical conductivity and mechanical flexibility. When a force is applied on the free end of cantilever beam, three different strain gauges are used to measure flex of the beam. The gauge is taped at the fixed end of the beam, on the top side. To determine the strain, it requires accurate measurement of small resistance change, therefore strain gauge is connected to the Source Meter Keithley 2410. This work will consolidate the research on theoretical, technological and experimental aspect of design, development and validation of resistive sensors that are flexible, bendable and stretchable.

Flexible inkjet printed sensor for liquid level monitoring

In this work a method for liquid level measurement is presented, with a support of experimental results. The presented liquid-level measurement method uses two sensors: level and reference interdigital capacitors. Proposed sensors are fabricated in low-cost inkjet printing technology with nanoparticle silver ink on a Novele™ coated polyethylene terephthalate (PET) substrate. The sensors comprise a two interpenetrating comb electrodes with 1.5 mm width of comb electrode, 1.5 mm spacing between each comb and 15 fingers with length of 135 mm and 8 fingers with length of 19 mm for level and reference sensor, respectively. Capacitance of the level sensor fixed on a test tube increases as the liquid level increases (up to 43.5 mm). The sensor characteristics for three liquids with different permittivity are presented. The reference sensor at the bottom of the tube is completely covered by liquid and its capacitance changes as the permittivity of the liquid changes. Experimental results for three different liquids confirmed simple liquid level measurement method which enables the measurement regardless of the liquid type.

Design and simulation of 13.56 MHz RFID tag in ink-jet printing technology

This paper presents design, modeling and simulation cost-effective RFID (Radio Frequency Identification) tag using ink-jet printing technology. Passive 13.56 MHz RFID tag is based on an inductive-capacitive resonant circuit. Designed RFID tag is part of the ID (Identification) card, which has standard ISO ID1 size (85.60 mm × 53.98 mm). It consists of rectangular spiral planar inductor (antenna) and interdigital capacitor. The modeling and optimization of RFID tag are discussed. At the first step, inductor and capacitor were designed using in-house developed simulation tools AntInd and INDICON, respectively, in order to provide proper electrical characteristics of tag. After that, the designed geometrical structures are modeled and simulated using CST Microwave Studio software. A radiation pattern at operational frequency of 13.56 MHz simulated in CST of the RFID tag insulated in free spaces is presented.

Design of RFID antenna in ink-jet printing technology

In this paper design of 125 kHz RFID antenna is presented. The optimization and improvement of electrical characteristics, including inductance and Q-factor, is also discussed. Designed RFID antenna is part of the ID card, which has standard ISO ID1. It consists of two spiral coils in two layers. Comparison of antenna in flexible and PCB technology is presented. The aim of this work is to introduce novel cost-effective antenna in flexible technology instead of conventional RFID antenna in PCB technology.

Fully inkjet printed CPW meander inductors on PET flexible substrate

This paper presents continued research on CPW (coplanar waveguide) meander inductors. The inductors were made in inkjet printing technology. They were printed on polyethylene terephthalate (PET) based substrate (Novele IJ-220), 140 μm thick. Water-based nanoparticle silver ink (Metalon® JS-B25HV) is used for printing. The fabricated inductors have a great value of quality factor (up to 4.2) and high frequency operating range between 1 GHz ÷ 7 GHz for three turn, and 1 GHz -19 GHz for one turn structure. Those characteristics made them suitable for application in flexible electronics.

Inductive Displacement Sensor of Novel Design Printed on Polyimide Foil

Displacement sensors play a key role in many applications. In this paper, an inductive structure is presented which changes its inductance with deformation, which serves as a measure of displacement. The structure itself is produced by ink-jet printing on a flexible polyimide foil, using a conductive silver-based nanoparticle ink. The foil is subsequently cut in such a way to allow for extending in a direction perpendicular to the foil plane. The resulting dependence of the inductance on the amount of extension is analyzed both in calculation and experimental measurement. Calculation is done using a variation of the Neumann formula adjusted to calculating self-inductance. A simple mathematical model of the structure deformation is introduced which proved to give results very close to the results obtained by measurement. The displacement range of the experimentally verified structure is up to 25 mm; however, the structure is expected to be scalable and therefore it should be possible to adapt it to various measurement ranges.

Electrical properties of inkjet printed graphene patterns on PET-based substrate

In this paper, electrical properties of inkjet printed graphene patterns on a PET-based (Novele™ IJ-220) substrate are presented. Water-soluble graphene conductive ink (Phene plus I3015) was used. Tested samples were printed with up to 12 layers. Desktop inkjet printer with 2000 dpi resolution was used for printing. After that, structures were sintered at 100 °C for 30 minutes. Printed patterns surface topography and profiles were observed using atomic force microscope (AFM) NTEGRA prima (NT-MDT). According to the results of AFM characterization, the thickness of 12 printed layers is ~750 nm. Measurements of electrical properties were performed with Hall effect measurement system at 0.37 T. Carrier mobility is 2330 cm2/Vs, while the conductivity is 389.11 1/Ωcm. All patterns are printed successfully with uniform structure and they are showing excellent compatibility with flexible PET-based substrate.

Influence of coil design on sensing performance of pressure sensor with polyimide membrane

The objective of this research is to study various coil designs and to propose the pattern that can improve the performance of the pressure sensor. Wireless pressure sensor, based on polyimide foil, is designed, fabricated and tested. The proposed sensor is realised in heterogonous integration process and consists of PCB (Printed Circuit Board) coil, spacer and polyimide membrane with attached LTCC (Low Temperature Co-fired Ceramic) ferrite. Pressure variations are wirelessly detected in system antenna-sensor resonant frequency, by a phase-dip technique. The distance between the coil and the ferrite varies with an applied external pressure and consequently membrane deflection, so the inductance of the coil increases and the resonant frequency of the system decreases. The effect of coil designs with different number of turns is examined and sensor performances are compared. Experimental measurements are determined and confirmed by analytical calculations and simulated results.

A flexible polyimide based device for displacement sensing

The goal of this work is to investigate design and fabrication of a passive displacement sensor based on flexible polyimide membrane. Proposed sensor is realized in heterogeneous integration process of Printed Circuit Board (PCB) technology, flexible substrate, and Low Temperature Co-fired Technology (LTCC) ferrite core. The sensor uses the self-resonant frequency modulation of a planar coil by the relative displacement of a ferrite core attached to a polyimide foil. Displacement variations are presented with micrometre translation stage (MTS) and detected by impedance and phase dip modulation. Measurements were performed on Impedance Analyzer (Agilent HP 4191A) and simulation results are in agreement with measurement results. The proposed sensor design has various options and applications in many fields. The realized sensor and its fabrication present several advantages concerning the possibility of direct modification and integration with the corresponding electronics, the simplicity of the process and packaging systems.