Libu Manjakkal

A Low-Cost pH Sensor Based on RuO2 Resistor Material

Fresh water deficiency caused by climate change calls for employing novel measures to ensure safety of drinking water supply. Wireless sensor networks can be used for monitoring hydrological conditions across wide area, allowing flow forecasting and early detection of pollutants. While there are no fundamental technological obstacles to implementation of large area sensor networks, their feasibility is constrained by unit cost of sensing nodes. This paper describes a low-cost pH sensor, intended for use in fresh water monitoring. The sensor was fabricated in a standard thick film process, and an off-the-shelf resistive paste was used as a sensing material. For the fabrication of sensor, RuO2 resistive paste was screen printed on the alumina substrate with silver conducting layer. Test solutions with pH ranging from 2 to 10 were prepared from HCl or KOH solutions. The potential difference between reference and sensing electrode (electromotive force emf of an electrochemical cell) should be proportional to the pH of a solution according to the Nernst equation. The fabricated sensor exhibits Nernstian response to pH. Influence of storage conditions on sensing performance was also investigated.

Potentiometric RuO2–Ta2O5 pH sensors fabricated using thick film and LTCC technologies

The paper reports on the preparation, properties and application of potentiometric pH sensors with thick film RuO2-Ta2O5 sensing electrode and Ag/AgCl/KCl reference electrode screen printed on an alumina substrate. Furthermore, it presents fabrication procedure and characterization of a new miniaturized pH sensor on LTCC (low temperature cofired ceramics) substrate, destined for wireless monitoring. The crystal structure, phase and elemental composition, and microstructure of the films were investigated by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Potentiometric characterization was performed in a wide pH range of 2-12 for different storage conditions and pH loops. The advantages of the proposed thick film pH sensors are: (a) low cost and easy fabrication, (b) excellent sensitivity close to the Nernstian response (56mV/pH) in the wide pH range, (c) fast response, (d) long lifetime, (e) good reproducibility, (f) low hysteresis and drift effects, and (g) low cross-sensitivity towards Li(+), Na(+) and K(+) as interfering ions. The applicability of the sensors for pH measurement of river, tap and distilled water, and some drinks was also tested.

Stretchable wireless system for sweat pH monitoring.

Sensor-laden wearable systems that are capable of providing continuous measurement of key physiological parameters coupled with data storage, drug delivery and feedback therapy have attracted huge interest. Here we report a stretchable wireless system for sweat pH monitoring, which is able to withstand up to 53% uniaxial strain and more than 500 cycles to 30% strain. The stretchability of the pH sensor patch is provided by a pair of serpentine-shaped stretchable interconnects. The pH sensing electrode is made of graphite-polyurethane composite, which is suitable for biosensor application. The sensing patch validated through in-depth electrochemical studies, exhibits a pH sensitivity of 11.13 ± 5.8 mV/pH with a maximum response time of 8 s. Interference study of ions and analyte (Na+, K+ and glucose) in test solutions shows negligible influence on the pH sensor performance. The pH data can be wirelessly and continuously transmitted to smartphone through a stretchable radio-frequency-identification antenna, of which the radiating performance is stable under 20% strain, as proved by vector network analyzer measurement. To evaluate the full system, the pH value of a human sweat equivalent solution has been measured and wirelessly transmitted to a custom-developed smart phone App.

TiO 2 -Based Thick Film pH Sensor

Miniaturized electrochemical pH sensors are increasingly in demand for applications such as online monitoring of water quality and health monitoring. The metal oxides are the best candidates for sensing electrodes of such sensors as they offer high chemical stability. In this paper, we present a novel approach to obtain interdigitated conductimetric pH sensor using screen printing of TiO2 thick film on an alumina substrate. The microstructural and crystalline properties of the TiO2 sensitive film were examined with scanning electron microscopy and Raman spectroscopy. The impedance spectroscopic studies of the fabricated thick film sensor were carried out in the frequency range of 5-20 kHz for the test solutions in the pH range of 4-10 and it was observed that the impedance of the film is distinctly dependent on pH. Using the measured impedance data, we have also proposed an equivalent RC network model for the fabricated pH sensor. The physical meaning of the model parameters was determined by electrochemical impedance spectroscopic analysis, and through statistical analysis it was found that all parameters are distinctly pH-dependent.

The Effect of Sheet Resistivity and Storage Conditions on Sensitivity of RuO2 Based pH Sensors

The increasing fresh water deficiency due to environmental pollution demands accurate, reliable and highly sensitive sensors for online monitoring of water pollution. Solid state sensors are helpful for fabricating and implementing low cost wireless sensors for monitoring of pollution. In water pollution determination, the measurement of pH plays an important role. Among the semiconductor sensitive materials RuO2 shows good sensitivity to hydrogen ions, high accuracy and resistance to interferences caused by other dissolved ions. In this work, thick film RuO2 based pH sensitive electrodes are fabricated by screen printing. The sensors were characterized by electromotive force measurements, SEM, optical microscopy and EDS analysis. The effects of sheet resistivity of the material and storage conditions are discussed. The sensor exhibits a sensitivity of 60 mV/pH in wide pH range of 2 to 10. The obtained response was very close to the theoretical Nernstian behavior. The best performance was attained for a sensor fabricated from 10 kΩ/sq. thick film paste and stored at water for 25 days.

Electrical and optical properties of aluminium doped zinc oxide transparent conducting oxide films prepared by dip coating technique

Purpose Aluminium-doped zinc oxide thin films exhibit interesting optoelectronic properties, which make them suitable for fabrication of photovoltaic cell, flat panel display electrode, etc. It has been shown that aluminium dopant concentration and annealing treatment in reduced atmosphere are the major factors affecting the electrical and optical properties of aluminium doped zinc oxide (AZO) film. Here, the authors report the structural, optical and electrical properties of aluminium-doped zinc oxide thin films fabricated by dip coating technique and annealed in air atmosphere, thereby avoiding hazardous environments such as hydrogen. The aim of this paper was to systematically investigate the effect of annealing temperature on the electrical properties of dip-coated film. Design/methodology/approach Aluminium-doped ZnO thin films were prepared on corning substrates by dip coating method. Aluminium concentration in the film varied from 0.8 to 1.4 mol per cent. Films have been characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV-visible spectroscopy and Hall measurements. The deposited films were heat treated at 450-600°C, in steps of 50°C for 1 h in air to study the improvement in electrical properties. Films were also prepared by annealing at 600°C in air for durations of 1, 2, 4 and 6 h. Envelope method was used to calculate the variation of the refractive index and extinction coefficient with wavelength. Findings The electrical resistivity is found to decrease considerably when the annealing time is increased from 1 to 4 h. The films exhibited high transmittance (>90 per cent) in the visible range, and the optical band gaps were found to change as per the Moss–Burstien effect, and this was consistent with the observed changes in the carrier concentration. Originality/value The study shows the effect of annealing in air, avoiding hazardous reduced environment, such as hydrogen, to study the improvement in electrical and optical properties of aluminum-doped zinc oxide films. Envelope method was used to calculate the variation of optical constants with wavelength.

Characterization and applicability of Sm0.9Sr0.1CoO3-δ in oxygen sensors

Purpose – This paper aims to investigate different properties of synthesized perovskite Sm0.9Sr0.1CoO3-δ and its potential for application in potentiometric oxygen sensors. Design/methodology/approach – The powder was obtained through solid-state reaction method and characterized by thermogravimetric/differential thermal analyzer and X-ray diffraction. It was used for both making a paste and pressing into rods for sintering. The prepared paste was deposited on alumina and yttria-stabilized zirconia substrates, by screen printing. Thick film conductivity, bulk conductivity and Seebeck coefficient of sintered rods were measured as a function of temperature. An oxygen concentration cell was fabricated with the screen-printed perovskite material as electrodes. Findings – Electrical conductivity of the bulk sample and thick film increases with the increase in temperature, showing semiconductor-like behavior, which is also indicated by relatively high values of the measured Seebeck coefficient. Estimated values...

Stretchable pH sensing patch in a hybrid package

This work presents a novel stretchable pH sensing patch to detect the pH in body fluid which is one of the most important parameters in human health monitoring. The sensing patch is a hybrid package comprising of polyimide/gold-based stretchable interconnects and graphite composite-based flexible pH sensor. With the integration of stretchable interconnects, the patch is able to withstand external stretching up to 50% longer than its original length. Moreover, the electrical behavior of the patch does not degrade as studied by the real-time resistance investigation. In order to protect the connecting electrodes and wirings from direct contacting with solution under analysis, the sensing patch is encapsulated with elastic polymer with the active sensing area exposed. The fabricated patch reveals a high pH sensitivity of 36.2 μA/pH in the pH range between 5 and 9 which is validated through electrochemical and electroanalytical studies.

Multi-sensor system for remote environmental (air and water) quality monitoring

In this paper realization of the low-power, portable, low-cost multi-sensor system for air and water quality monitoring is described. Developed system is battery-powered with solar panel-based charger unit, and it is intended for use in remote environmental monitoring by collecting information about air temperature (T) and relative humidity (RH), presence of volatile organic compounds (VOC) as well as water temperature and pH level. The hardware of the system is based on the ATmega128 microcontroller which acquires the sensors data and coordinates the work of all peripherals. To establish full standalone operation, peripherals such a TFT color LCD display, embedded keypad and SD card for data storage are included. Air quality parameters are collected with SHT11 (T and RH) and MQ-135 (VOC) sensors, while water temperature is monitored with encapsulated LM35 sensor. For pH level monitoring, TiO2-based thick film pH resistive sensor was fabricated and characterized. The pH sensor readout electronics, based on the integrated circuit AD5933, is designed in such way to ensure reliable in-situ measurements. Discussion of the applications of the proposed system in the more complex, a cloud-based, system for air and water quality monitoring in real-time, with the IBM Watson IoT platform is given as well.

Planar impedancemetric NO sensor with thick film mixed dy-based oxides sensing electrodes

The pastes destined for sensing electrodes were prepared by mixing Dy-based oxides powders with organic vehicle. The sensing electrodes of interdigitated structure were screen printed onto yttria stabilized zirconia substrates, fabricated from commercially available solid electrolyte green tape. The fabricated sensor was placed in a vertical type gas flow apparatus equipped with heating elements. Impedance spectroscopy was performed upon exposing the sensor to gas mixtures containing NO gas in the concentration range from 0 to 400 ppm, while temperature and gas flow rate were kept constant throughout the measurements. For frequencies spanning from 30 mHz to 100 kHz, the impedance response of the fabricated sensor to the NO gas presence was investigated at temperatures in the range from 600 to 750 °C. The study confirmed that the sensor fabricated in thick film technology is sensitive to nitric oxide in the concentration range of measurements, 0-400 ppm, and when phase angle is chosen for a sensing parameter, linear dependency is observed at certain frequencies. The frequencies, at which maximum sensitivity is observed, as well as NO sensitivity values, are found to be dependent on the operating temperature. Impedance arcs found on Nyquist plots were fitted to an equivalent circuit and values of corresponding parameters were determined.