Ales Hamacek

An Electrochemical NO2 Sensor Based on Ionic Liquid: Influence of the Morphology of the Polymer Electrolyte on Sensor Sensitivity

A systematic study was carried out to investigate the effect of ionic liquid in solid polymer electrolyte (SPE) and its layer morphology on the characteristics of an electrochemical amperometric nitrogen dioxide sensor. Five different ionic liquids were immobilized into a solid polymer electrolyte and key sensor parameters (sensitivity, response/recovery times, hysteresis and limit of detection) were characterized. The study revealed that the sensor based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][N(Tf)2]) showed the best sensitivity, fast response/recovery times, and low sensor response hysteresis. The working electrode, deposited from water-based carbon nanotube ink, was prepared by aerosol-jet printing technology. It was observed that the thermal treatment and crystallinity of poly(vinylidene fluoride) (PVDF) in the solid polymer electrolyte influenced the sensitivity. Picture analysis of the morphology of the SPE layer based on [EMIM][N(Tf)2] ionic liquid treated under different conditions suggests that the sensor sensitivity strongly depends on the fractal dimension of PVDF spherical objects in SPE. Their deformation, e.g., due to crowding, leads to a decrease in sensor sensitivity.

Comparison of the surface properties of power electronic substrates

This paper deals with thick film copper technology (TFC) and its comparison with other power electronic substrates such as a printed silver or direct bonded copper (DBC) on alumina substrates. The research activities were concentrated on surface properties of power substrates and its solderability. The solderability of thick film copper is comparable with other power electronic substrates such as DBC, but it is necessary to ensure proper firing condition or remove oxides from the surface after firing and use a proper flux. The main advantages of thick film copper in comparison with common power electronic substrates are a high resolution of conductive pattern, higher reliability at thermal cycling and a possibility to create a different local thickness of copper layer on substrate. Maximal thickness of copper layer can reach 300 μm.

Organic based sensors: Novel screen printing technique for sensing layers deposition

This paper presents a research focused on development of low-cost manufacturing process which enables fabrication of accurate organic humidity sensors, where only screen printing is used for all layers deposition. It means that not only the interdigital structures with 50 μm line and space, but also phatolocynine sensing film and protective polymer layer are screen printed. The interdigital structures are printed by advanced screen printing in order to replace complex an expensive vacuum processes. In the frame of this research a novel screen printing technique for deposition of low viscose organic sensing film was also developed, where non-standard precise stainless steel Beta mesh was used for screens.

Printed passive components for RFID labels

This paper deals with the research and development of printed flexible capacitors and inductors predominantly designed for the construction of RFID labels. These printed RF passive components are required for the construction of fully printed low cost passive RFID labels. The passive components are directly printed on PET substrate by the screen printing technique. The printing process was optimized in order to achieve a high yield and good electrical parameters at the frequency of 13,56 MHz. Electrical parameters of printed capacitors, such as impedance to frequency characteristic, capacity to temperature characteristic, capacity to bias voltage characteristic were measured in detail. The bending tests were also performed for verifying of printed capacitors flexibility. The performance of capacitors was verified in the real sample of resonant circuit at 13,56 MHz.

Implementation of AODV routing protocol in sensor wireless networks

This paper presents an implementation of the Ad hoc On-Demand Distance Vector (AODV) routing protocol in conditions of sensor wireless networks. AODV is a reactive on-demand distance vector protocol and utilizes partially connected mesh network topology. Designed stack is intended for purposes of applications that require quick adaptation to dynamic link conditions. Protocol implementation was primarily focused on embedded systems with constrained memory and computational resources and was intended to be easy portable to other platforms. For testing purposes, designed stack was attached to link layer of SimpliciTI stack and compiled for CC430 microcontroller with on-chip sub-1-GHz RF transceiver supplied by Texas Instruments Company. This work was motivated by the need of a simple implementation of the routing protocol intended for tiny systems and utilizing mesh network topology which will quickly adapt on fast node position changes.

Sensorial characteristics of conductive polymers

This paper deals with the investigation of intrinsic conductive polymer PEDOT-PSS and development of vapour sensors. These sensors are based on the specific vapours influence on the electrical parameters. The designed sensors consist of glazed ceramic substrate with gold interdigital electrodes covered by a thin layer of conductive polymer. The insulation gap between electrodes was investigated in the range of 50 – 200 µm in order to achieve the maximal sensitivity. Temperature and humidity dependences of PEDOT-PSS layers were measured in the climatic chamber, influence of particular vapours on electrical parameters were measured in the special gas chamber. Except for temperature, humidity and vapour sensitivity, long term stability was also studied.

Organic materials for humidity sensors

This paper deals with research and development of organic humidity sensors. These sensors are based on gold interdigital electrodes placed on the glass substrate covered by the thin layer of organic sensitive material. The sulfonated aluminium phtalocyanine was used as the prospective sensitive material. The advantage of organic sensitive materials instead of inorganic is the easier deposition of thin films, their higher modifiability and lower cost. Electrical parameters of organic sensors were measured at variable relative humidity and temperature. The influence of aging and frequency behaviour was also measured in detail.

Smart textile-based protective system for firefighters

This paper presents a research focused on a smart textile-based protective system which is intended to bring more safety to firefighters facing hazardous conditions. The system is fully integrated into a firefighter protective suit and it is able to monitor heart rate (HR), to detect movements of a firefighter, to detect toxic and combustible gases in the environment and to measure temperature (T) and relative humidity (RH) inside and outside of the suit. The protective system consists of developed integrated sensor modules, e-textile wiring harnesses, body control unit (BCU), central processing unit (CPU), body area network (BAN) and wide area network (WAN). The measured data are wirelessly transmitted over a wide area network with automatic routing algorithm to the central processing unit, which is checked by a firefighter operation chief, who is kept informed about an actual state of individual fire fighters. In case that some monitored parameter oversteps pre-set threshold values the BCU will automatically inform a fire fighter by means of acoustic alarm about oncoming risk.

Potentiostat solution for electrochemical amperometric gas sensor

This study deals with intrinsic parameters of electrochemical amperometric gas sensors with a solid-state polymeric electrolyte. An experimental electrochemical NO2 sensor based on organic ionic liquid was developed. Subsequently, electrical and mechanical parameters of the sensor were studied and an appropriate potentiostat circuit was designed for the evaluation of a sensor response to the particular gas. The description of the sensor, measurement procedures and results of experiments will be presented in more detail.

Perspective methods of creating conductive paths by Aerosol Jet Printing technology

This paper presents a research focused on four-wire resistivity measurement of the selected materials printed by Aerosol Jet Printing system (AJP) with different process parameters. The aerosol jet printing technology is an additive deposition technique which is based on the idea of the formation the aerosol mist from the printed ink and its transportation on the substrate by gas flow. The aerosol formation - the atomization process can be made by two different ways. One way is the pneumatic atomizer which smashes the ink on the wall of the jar and so creates the aerosol. The inks of viscosity from 1 to 1000 mPa·s can be used. The second way is the ultrasonic atomizer which creates the aerosol by smashing the ink by ultrasonic waves. In ultrasonic one, the viscosity of the ink should be in the range from 1 to 5 mPa·s. Three different conductive inks based on nanoparticles were printed to the form of the test pattern. Printing parameters were optimized in order to achieve highest conductivity of printed line. The impedance measurement and used inks are described in this paper. The main application of such aerosol jet printed materials could as follows: organic electro-chemical transistors (OECT), gas sensors, smart ID cards or RFID antennas.