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Hydrogen sulfide (H2S) presents many hazardous traits such as corrosive, explosive, toxic, and flammable. It is slightly denser than air, and a mixture of H2S and air can be volatile. Therefore, a reliable and robust measurement system is required to effectively detect and quantify H2S in many applications, such as oil and gas industries. There are several methods available in the literature to quantify H2S in fuel gases; however, only a few are available in case of air samples. Furthermore, array-based sensors are more reliable in the detection of volatile organic compounds (VOCs); however, sensor arrays are more expensive and challenging to produce. To overcome the limitations of producing physical sensor arrays, this article proposes a concept of virtual sensing that enables to augment a single sensing platform into a virtual array, thus, increasing the detection accuracy at no extra cost of producing a large physical sensors array. The merits of the proposed system are as follows: 1) a virtual sensing concept is combined with a physical sensing platform to enhance the proposed model’s estimation power in quantifying H2S in air samples; 2) a new feature extraction method based on fractional derivatives is proposed to further enhance the model’s learning capabilities; 3) an array of four gas sensors is fabricated in the in-house foundry to record and analyze the signature of H2S at various concentration levels; 4) a shallow neural network (NN) model is trained and tested on the recorded data, and based on the NN’s input–output relation, a mathematical model is presented for the quantification of H2S; and 5) the proposed model is a highly sensitive and reliable H2S gas sensing scheme with the ability to detect the gas instantaneously. The proposed gas quantification model has the advantages of being low cost, easy to implement, and fast operation compared with the analytical solutions. Furthermore, it is extensively tested and validated using real gas data. [ABSTRACT FROM AUTHOR]

This paper presents a high linear dynamic range light-to-frequency converter (LFC) with integrated photodiodes (PDs). The high dynamic range with linear response is achieved by two techniques. At first, the NWell/PSubstrate PD is regulated to almost zero voltage drop, in order to minimize the bias-dependent leakage current under a low light irradiance. Secondly, a replica amplifier is implemented to monitor the offset voltage of the regulator against process-voltage-temperature variation. As the result, the systematic and layout-dependent input offset voltage of the regulator can be reduced. The proposed LFC chip is fabricated using 0.35- \mu \textm 2-poly-3-metal nonepitaxy CMOS technology with a die size of $1.02\times 0.83$ mm2. According to the measurement results, the proposed LFC is much less sensitive to temperature variation and it exhibits more than six orders of magnitude linear response under the light irradiance as low as 0.5 nW/cm2 with a temperature range from −25 °C to 125 °C. [ABSTRACT FROM PUBLISHER]

An ultra-low power embedded CMOS temperature sensor based on serially connected subthreshold MOS operation is implemented in a 0.18 µm CMOS process for passive RFID food monitoring applications. Employing serially connected subthreshold MOS as sensing element enables reduced minimum supply voltage for further power reduction, which is of utmost importance in passive RFID applications. Both proportional-to-absolute-temperature (PTAT) and complimentary- to-absolute-temperature (CTAT) signals can be obtained through proper transistor sizing. With the sensor core working under 0.5 V and digital interfacing under 1 V, the sensor dissipates a measured total power of 119 nW at 333 samples/s and achieves an inaccuracy of + 1/-8 °C from -10 °C to 30 °C after calibration. The sensor is embedded inside the fabricated passive UHF RFID tag. Measurement of the sensor performance at the system level is also carried out, illustrating proper sensing operation for passive RFID applications. [ABSTRACT FROM AUTHOR]

Gas recognition is a new emerging research area with many civil, military, and industrial applications. The success of any gas recognition system depends on its computational complexity and its robustness. In this work, we propose a new low-complexity recognition method which is tested and successfully validated for tin-oxide gas sensor array chip. The recognition system is based on a vector angle similarity measure between the query gas and the representatives of the different gas classes. The latter are obtained using a clustering algorithm based on the same measure within the training data set. Experimented results on our in-house gas sensors array show more than 98% of correct recognition. The robustness of the proposed method is tested by recognizing gas measurements with simulated drift. Less than 1% of performance degradation is noted at the worst case scenario which represents a significant improvement when compared to the current state-of-the-art. [ABSTRACT FROM AUTHOR]

This paper presents a time-to-first spike (TFS) and address event representation (AER)-based CMOS vision sensor performing image capture and on-chip histogram equalization (LIE). The pixel values are read-out using an asynchronous handshaking type of read-out, while the HE processing is carried out using simple and yet robust digital timer occupying a very small silicon area (0.1 × 0.6 mm2). Low-power operation (10 nA per pixel) is achieved since the pixels are only allowed to switch once per frame. Once the pixel is acknowledged, it is granted access to the bus and then forced into a stand-by mode until the next frame cycle starts again. Timing errors inherent in AER-type of imagers are reduced using a number of novel techniques such as fair and fast arbitration using toggled priority (TP), higher-radix, and pipelined arbitration. A verilog simulator was developed in order to simulate the effect of timing errors encountered in AER-based imagers. A prototype chip was implemented in AMIS 0.35 μm process with a silicon area of 3.1 × 3.2 mm2. Successful operation of the prototype is illustrated through experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a monolithic 4×4 tin oxide gas sensor array together with on-chip multiplexing and differential read-out circuitry. A robust fabrication process focusing on the integration of the CMOS circuitry and the microelectromechanical systems (MEMS) structure is first described. The gas sensor uses a surface micro-machined micro-hotplate based structure. Platinum is selected as the material of choice for both the micro heater and the sensor’s electrodes, for its good thermal stability and compatibility with the sensing film. Different post-treatments are used to modify the characteristics of the tin oxide gas sensors hence improving the sensor’s selectivity of the overall sensor array. Furthermore, in contrast to the conventional voltage divider read-out technique, a novel differential read-out circuit (DRC) for tin oxide gas sensors is proposed. The DRC applies a constant current to drive the sensor and uses a unit-gain single stage amplifier (inverter) to generate a fully differential output, directly from the voltage drop across the sensor. The output of the DRC is simply proportional to the difference between the voltage on the two electrodes of the sensor but not to the transistor parameters such as mobility and threshold voltage, neither to the supply voltage. The monolithic sensor array and its pre-processing circuitry have been implemented in our in-house 5μm process. Experimental results showed good linearity at the output of the DRC for a wide range of sensor resistance variation (over 20MΩ). The fabricated micro-hotplate sensor array was tested for four target gases. Results show good sensitivity and interesting thermal characteristic leading to only 15.5mW power consumption for 300°C operating temperature. [Copyright &y& Elsevier]

Gas identification represents a big challenge for pattern recognition systems due to several particular problems such as nonselectivity and drift. The purpose of this paper is twofold: 1) to compare the accuracy of a range of advanced and classical pattern recognition algorithms for gas identification for the in. house sensor array signals and 2) to propose a gas identification ensemble machine (GIEM), which combines various gas identification algorithms, to obtain a unified decision with improved accuracy. An integrated sensor array has been designed with the aim of identifying combustion gases. The classification accuracy of different density models is compared with several neural network architectures. On the gas sensors data used in this paper, Gaussian mixture models achieved the best performance with higher than 94% accuracy. A committee machine is implemented by assembling the outputs of these gas identification algorithms through advanced voting machines using a weighting and classification confidence function. Experiments on real sensors' data proved the effectiveness of the system with an improved accuracy over the individual classifiers. An average performance of 97% was achieved using the proposed committee machine. [ABSTRACT FROM AUTHOR]

A CMOS digital pixel sensor (DPS) with programmable resolution and reconfigurable conversion time is described. The chip features a unique architecture based on the pulse width modulation (PWM) technique and operates with either an 8-b or 4-b accuracy. The 8-b conversion mode is used for high-precision imaging while the 4-b conversion mode provides a shorter conversion time and a two times increase in spatial resolution. Two quantization schemes are studied, namely, the uniform and the nonuniform time-domain quantizers, which are referred to as UQ and NUQ, respectively. It is shown that the latter scheme not only permits to linearize the nonlinear response of the PWM sensor, but also allows to significantly speed up the conversion time, particularly for wide dynamic range and low coding resolutions. A prototype of 32 x 32/64 x 32 pixels has been fabricated using 1-poly, 5-metal CMOS 0.35-μm n-well standard process. Power dissipation is 10 mW at VDD = 3.3 V, dynamic range is 90 dB, while dark current was measured at 1 pA. The reconfiguration features of the chip have been verified experimentally. [ABSTRACT FROM AUTHOR]

This paper presents a digital pixel sensor (DPS) array employing a time domain analogue-to-digital conversion (ADC) technique featuring adaptive dynamic range and programmable pixel response. The digital pixel comprises a photodiode, a voltage comparator, and an 8-bit static memory. The conversion characteristics of the ADC are determined by an array-based digital control circuit, which linearizes the pixel response, and sets the conversion range. The ADC response is adapted to different lighting conditions by setting a single clock frequency. Dynamic range compression was also experimentally demonstrated. This clearly shows the potential of the proposed technique in overcoming the limited dynamic range typically imposed by the number of bits in a DPS. A 64 × 64 pixel array prototype was manufactured in a 0.35-μm, five-metal, single poly, CMOS process. Measurement results indicate a 100 dB dynamic range, a 41-s mean dark time and an average current of 1.6 μA per UPS. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we compare the accuracy of a range of advanced density models for gas identification from sensor array signals. Density estimation is applied in the construction of classifiers through the use of Bayes rule. Experiments on real sensors’ data proved the effectiveness of the approach with an excellent classification performance. We compare the classification accuracy of four density models, Gaussian mixture models, Generative topographic mapping, Probabilistic PCA mixture and K nearest neighbors. On our gas sensors data, the best performance was achieved by Gaussian mixture models. [Copyright &y& Elsevier]

This work presents a cost-effective shadow mask printing approach to fabricate flexible sensors. The liquid-state sensing material can be directly brushed on a flexible substrate through a shadow mask. The ink leakage issue which often occurs in printed electronics is addressed with a custom taping scheme. A simple thermal compression bonding approach is also proposed to package the functional area of the sensor. To verify the feasibility and robustness of the proposed fabrication approach, a prototyped strain gauge displacement sensor is fabricated using carbon ink as the sensing material and a flexible polyimide (PI) film as the substrate. Once the substrate is deformed, cracks in the solidified ink layer can cause an increased resistance in the conductive path, thus achieving function of stable displacement/strain sensing. As a demonstration for displacement sensing application, this sensor is evaluated by studying its real-time resistance response under both static and dynamic mechanical loading. The fabricated sensor shows a comparable performance (with a gauge factor of ~17.6) to those fabricated using costly lithography or inkjet printing schemes, while with a significantly lower production cost. [ABSTRACT FROM AUTHOR]

In this letter, a pulse-width modulated digital pixel sensor is presented along with its inherent advantages such as low power consumption and wide operating range. The pixel, which comprises an analog processor and an 8-bit memory cell, operates in an asynchronous self-resetting mode. In contrast to most CMOS image sensors, in our approach, the photocurrent signal is encoded as a pulse-width signal, and converted to an 8-bit digital code using a Gray counter. The dynamic range of the pixel can be adapted by simply modulating the clock frequency of the counter. To test the operation of the proposed pixel architecture, an image sensor array has been designed and fabricated in a 0.35-µm CMOS technology, where each pixel occupies an area of 45 × 45 µm². Here, the operation of the sensor is demonstrated through experimental results. [ABSTRACT FROM AUTHOR]

Highlights • Dual transduction is implemented on a single sensor to achieve gas identification. • Simultaneous detection of the resistance and mass variations in the sensing material is achieved by a single sensor. • The sensing range of the sensing material is expanded through dual transduction. • The dual transduction method can help fully explore the potential of conductive gas sensing materials. Abstract Poor selectivity is one important limitation of gas sensors based on chemisorption or physisorption. This poor selectivity is usually tackled through the use of a gas sensor array, whose individual elements have diverse selectivity. Gas identification can be achieved by analyzing the unique response patterns of the sensor array. However, such an approach is costly due to its complexity. In this paper, we investigate an alternative solution enabling single sensor gas identification through the integration of two transduction mechanisms in one sensor. We demonstrate this approach through the design of a novel dual transduction gas sensor capable of simultaneously detecting gas-induced variations in the mass and resistance of the sensing material. The relative independence of acquired gravimetric and resistive responses is shown to enable subsequent gas identification. In addition, the proposed approach can also improve the overall limit of detection (LOD) to different gases by exploiting the individual responses with the best LODs. The proposed dual transduction gas sensor was implemented by integrating a film bulk acoustic wave resonator (FBAR) together with interdigitated electrodes. A configurable dual-mode oscillator circuit is also proposed to simultaneously read-out both responses from the sensor. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs), a class of two-dimensional (2D) materials with layered structures, have recently gained a lot of attention for highly sensitive humidity sensing applications. Hence, for the first time, it proposes a highly sensitive and fast humidity sensor based on the 2D Zirconium Diselenide (ZrSe 2) material with unique humidity sensing performance via printed technologies. The spin coating technique was used to deposit the 2D ZrSe 2 flakes onto the inter-digital electrodes (IDEs). Herein, the bulk ZrSe 2 powder was exfoliated into the 2D flakes via wet grinding. The proposed sensor shows a high sensitivity of 68 kΩ / %RH (where RH is relative humidity) with a wide detection range of (15–80%) RH having good linearity and stability over 360 min. The sensor showed a transient response of 1 s and 2 s for impedance while 3 s and 6 s for capacitance. Hence, the fabricated sensor can be exhibited an ultra-high sensitivity and quick response in various applications: contactless humidity sensing, water spraying test, and skin humidity test. From these exceptional performances, the proposed sensor can be applied in multiple humidity sensing applications. • This paper proposes a highly sensitive and fast ZrSe2 based humidity sensor through printed technologies. • The proposed humidity sensor exhibits a fast transient response of 1 s and 2 s, and good stability for 360 min. • It has a highly linear relative humidity range of 15 – 80% RH and has been applied in various humidity sensing applications. [ABSTRACT FROM AUTHOR]