Rahman Wagiran

Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

SnO2/Pt thin film laser ablated gas sensor array.

A gas sensor array was developed in a 10 × 10 mm2 space using Screen Printing and Pulse Laser Ablation Deposition (PLAD) techniques. Heater, electrode, and an insulator interlayer were printed using the screen printing method on an alumina substrate, while tin oxide and platinum films, as sensing and catalyst layers, were deposited on the electrode at room temperature using the PLAD method, respectively. To ablate SnO2 and Pt targets, depositions were achieved by using a 1,064 nm Nd-YAG laser, with a power of 0.7 J/s, at different deposition times of 2, 5 and 10 min, in an atmosphere containing 0.04 mbar (4 kPa) of O2. A range of spectroscopic diffraction and real space imaging techniques, SEM, EDX, XRD, and AFM were used in order to characterize the surface morphology, structure, and composition of the films. Measurement on the array shows sensitivity to some solvent and wood smoke can be achieved with short response and recovery times.

Characterization of Mixed xWO3(1-x)Y2O3 Nanoparticle Thick Film for Gas Sensing Application

Microstructural, topology, inner morphology, and gas-sensitivity of mixed xWO3(1-x)Y2O3 nanoparticles (x = 1, 0.95, 0.9, 0.85, 0.8) thick-film semiconductor gas sensors were studied. The surface topography and inner morphological properties of the mixed powder and sensing film were characterized with X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Also, gas sensitivity properties of the printed films were evaluated in the presence of methane (CH4) and butane (C4H10) at up to 500 °C operating temperature of the sensor. The results show that the doping agent can modify some structural properties and gas sensitivity of the mixed powder.

Rapid prototyping asynchronous processor

Asynchronous processors are an attractive research field, since they offer many advantages over synchronous processors. Field-programmable gate arrays (FPGA), one of the dominant media at present for prototyping and implementing digital circuits, is used to construct an 8-bit asynchronous RISC processor. The asynchronous processor employs the conceptual framework of a Sutherland micropipeline, a modular approach to design of asynchronous circuits.

A simple capacitive biosensor device for histamine measurement

Purpose – The purpose of this paper is to describe a capacitive biosensor device consisting of an enzyme electrode and a simple detector which has been developed for histamine measurement.Design/methodology/approach – In this analysis, degradation of histamine through enzymatic reaction produces signal that is monitored using a simple detector equipped with “astable” multivibrator operation circuit (in capacitor‐resistor circuit).Findings – Different frequency (f) readings have been obtained for glucose, alcohol and histamine in different concentration levels, showing the ability of this simple device system to measure their dielectric constant (k) as formulated by the equation f=(1.44d)/ [kA (R1+2R2)]. The analysis using smaller electrode gap (d) produces higher value of f, indicating that d, is directly proportional to f. For histamine, by using immobilized enzyme electrode, the results show that the change of dielectric properties during the 300‐second reaction period could also be monitored. A linear ...

Design of auto control interface circuit for thick film heater gas sensor

In this paper an automated control system of thick film resistive heater for gas sensor applications has been designed using low cost technologies. To control the desired temperature of heater, a programmable voltage with 12 bits resolution applies which can be adjusted to the appropriate temperature. The circuit consists of ADC, DAC, microcontroller, and current buffer. This circuit compensates dropt voltage across the heater which has been resulted from the ambient temperature changes. In particular, using one microcontroller for entire heater process is for the first time introduced to drive the heater, control heater temperature, and compensate ambient temperature of heater all together automatically. Fabrication of this circuit using commercially available technologies and simplicity of the circuit make it a novel and simple design in gas sensor applications. This circuit has the ability to connect to alarms and computers in order to monitoring purposes.

Electrical response of multi-walled carbon nanotubes to ammonia and carbon dioxide

This paper presents the electrical response of Multi-Walled Carbon Nanotube (MWCNT) towards the presence of gases at room temperature. The preparation of MWCNT and the experimental setup are also discussed. The resistance of MWCNT elements is extracted from current-voltage measurements done at room temperature. The results show that there is a change in the resistance when the sensing element is exposed to either ammonia or carbon dioxide gas. Fast response time and recovery time have been achieved.

DSP design using VLIW architecture

Programmable digital signal processors (pDSPs) are microprocessors that are specialized to perform well in digital signal processing intensive applications. A standard microprocessor can do most pDSP operations. However, the pDSP chip has better ability to perform number crunching algorithms in real-time, and pDSPs are highly flexible because they can be reprogrammed. The major objective of this research is to design and implement a general-purpose programmable DSP core (digital signal processor core). The architecture of the pDSP core must be designed in such a way that parallel processing can be exploited and computational units can be integrated into the core with ease. The pDSP designed is a fixed-point DSP based on a very long instruction word (VLIW) architecture. One way to overcome the performance limitation is to use field programmable gate array (FPGA) technology, a technology which gives the designer a higher degree of parallelism and ease of pDSP design.

A fully temperature controlled test chamber for the application of gas sensor characterization

Research and de velopment on gas sensors design and fabrication demands the needs for test chambers as the characterizing and testing of gas sensor are based on its detection of the concentration of different type of gas under the influence of temperature and also humidity. This project, a Fully Temperature Controlled Test Chamber is about the design and development of a system to provide an artificial environment for gas sensor characterization. Th e main part of the designed system is th e temperature feed back loop control system. Its function is to monitor and regulate the environment temperature to the desired value for characterization of gas sensor under test. While the LM35DZ temperature sensor is used for this purpose, the in tended chamber system to be designed is ab le to communicate with control switches from outside of the chambers using keypad and LCD. The user can set the desired temperature in the chamber, and then the PIC16F877A microcontroller which acts the “brain” of this system will analyze and process the input signal from the sensor and key pad to give th e corresponding output to control th e h eater and display on the LCD s creen. When the steady state condition has been reached, the chamber will be ready for the testing of gas sensors under test. The inlet valve, vacuum pump and fan integrated in the chamber are also fully controlled b y the microcontroller. Beside, th e control system can also be controlled manually by using the manual switches. When tested using the sensor under test, the test chamber and the regulation system of the temperature are working successfully as programmed and give the desired outputs.

Design interface circuits for thick film heater for a gas sensor resistor

In this paper an auto calibrated system of thick film resistive heater have been designed which can be adjusted to desired temperature. The circuit is consists of ADC, DAC, microcontroller, and current buffer. This circuit compensates dropt voltage across the heater which has been resulted from ambient temperature changes. Finally this circuit is able to control and adjust the heaters temperature automatically and also drives different resistive heaters for similar gas sensors.