Development of a taste sensor with high sensitivity, stability and selectivity is highly desirable for the food and beverage industries. The main goal of a taste sensor is to reproduce five kinds of senses of humans, which is quite difficult. The importance of knowing quality of beverages and drinking water has been recognized as a result of increase in concern in environmental pollution issues. However, no accurate measuring system appropriate for quality evaluation of beverages is available. A highly sensitive microsensor using horizontally polarized Surface Acoustic Waves (SH-SAW) for the detection and identification of soft drinks is presented in this paper. Different soft drinks were tested using this sensor and the results which could distinguish between two popular soft drinks like Pepsi and Coca cola is presented in this paper. The SH-SAW microsensors are fabricated on 36°-rotated Y cut X propagating LiTaO<sub>3</sub> (36YX.LT) substrate. This design consists of a dual delay line configuration in which one line is free and other one is metallized and shielded. Due to high electromechanical coupling of 36YX.LT, it could detect difference in electrical properties and hence to distinguish different soft drinks. Measured electrical characteristics of these soft drinks at X-band frequency using free space system show distinguishable results. It is clear from these results that the microsensor based on 36YX.LT is an effective liquid identification system for quantifying human sensory expressions.
This paper reports a novel ultra-fast chemosensor array microsystem for the rapid detection of volatile organic compounds (VOCs). The sensing device consists of an array of 80 miniature resistive sensors on a 10 mm by 10 mm silicon substrate, configured in 5 rows of 16 elements. In this application each row has been deposited with a different carbon black/polymer composite nanomaterial. As a result of arranging the sensors in the matrix fashion, we are able to represent the sensor response as an olfactory image. The sensor array was tested with pulses of ethanol, toluene, toluene and ethanol mixture, milk, cream, cypress oil and peppermint oil at two different flow rates (60 and 130 ml/min) and three different pulse widths (10, 25, and 50 secs). Preliminary analysis was performed by comparing different images which showed excellent discrimination between the different analytes. Increasing the pulse width and flow rate improved the discrimination capability of the system. We have also investigated the effect of 'stereo' olfactory imaging by combining mono images measured at different flow rates to form a composite image. Results have shown such scheme can provide additional discriminatory information.
In this paper we report on the characterisation of a smart ASIC chip comprising a pair of room temperature resistive vapour sensors in a ratiometric configuration. This novel design enables the near elimination of several undesirable baseline effects and provides an automatic offset of the output signal. The novel ASIC chip has been designed and fabricated through a standard 0.7 μm CMOS process. The ASIC response has been modelled prior to fabrication as reported elsewhere. There are two main stages in the circuit: one for the processing and conditioning of the sensor signals and the other for temperature control. Two sets of sensor electrodes are positioned in two opposite corners of the chip and are connected in a non-inverting operational amplifier configuration. Carbon black/polymer composite materials have been deposited across the electrodes to create the sensing chemoresistors and illustrate the functionality of the chip. Sample devices were created by depositing either the same nanomaterial on both electrodes and having one active and one passive sensor, or by depositing two different materials, thus creating two active sensors. Following deposition, the responses of the ASIC devices to toluene and ethanol vapours in air have been characterised in an automated mass flow system and presented here.
In this paper we present design, fabrication and integration of a micro fluidic cell for use with the electronic tongue. The cell was machined using microstereo lithography on a Hexanediol Diacrylate (HDDA) liquid monomer. The wet cell was designed to confine the liquid under test to the sensing area and insure complete isolation of the interdigital transducers (IDTs). The electronic tongue is a shear horizontal surface acoustic wave (SH-SAW) device. Shear horizontally polarized Love-waves are guided between transmitting and receiving IDTs, over a piezoelectric substrate, which creates an electronic oscillator effect. This device has a dual delay line configuration, which accounts for the measuring of both mechanical and electrical properties of a liquid, simultaneously, with the ability to eliminate environmental factors. The data collected is distinguished using principal components analysis in conjunction with pre-processing parameters. The experiments show that the micro fluidic cell for this electronic tongue does not affect the losses or phase of the device to any extent of concern. Experiments also show that liquids such as Strawberry Hi-C, Teriyaki Sauce, DI Water, Coca Cola, and Pepsi are distinguishable using these methods.
This paper describes coupled-effect simulations of smart micro gas-sensors based on standard BiCMOS technology. The smart sensor features very low power consumption, high sensitivity and potential low fabrication cost achieved through full CMOS integration. For the first time the micro heaters are made of active CMOS elements (i.e. MOSFET transistors) and embedded in a thin SOI membrane consisting of Si and SiO<SUB>2</SUB> thin layers. Micro gas-sensors such as chemoresistive, microcalorimeteric and Pd/polymer gate FET sensors can be made using this technology. Full numerical analyses including 3D electro- thermo-mechanical simulations, in particular stress and deflection studies on the SOI membranes are presented. The transducer circuit design and the post-CMOS fabrication process, which includes single sided back-etching, are also reported.
In this paper we review recent effort towards the development of both a smart tongue (the so-called `electronic tongue') and a smart nose (or so-called `electronic noise'). The difference being that the smart tongue operates within the solution under test, while the smart nose evaluates the nature of its headspace.
Gas sensors fabricated using conventional silicon microtechnology can suffer from a number of significant disadvantages when compared with commercially available thick-film, screen-printed devices. For example, platinum gate MOSFET devices normally operate only at a temperature of up to 180 degree(s)C and this limits the catalyst activity, and hence their sensitivity and response time. In addition, the fabrication of an integrated, resistive heater poses interesting problems; thus whilst polysilicon heaters are CMOS compatible, they tend to suffer from non-linearity, poor reproducibility and stability; whereas platinum resistive heaters are incompatible with a CMOS process and thus difficult and expensive to manufacture. Here we propose the use of SOI technology leading to a new generation of high-temperature, silicon smart gas sensors (patent pending). Numerical simulations of an n-channel MOSFET structure on a thin SOI membrane have been performed in non- isothermal conditions using a MEDICI simulator. Our results demonstrate that SOI-based devices can operate at temperatures of up to 350 degree(s)C without causing a problem for neighboring CMOS I.C. circuitry. The power consumption of our SOI-based designs may be as low as ca. 10 mW at 300 degree(s)C and so compares favorably with previously reported values for non-SOI based silicon micromachined gas sensors. In conclusion, SOI technology may be used to fabricate novel high-temperature, micropower resistive and catalytic-gate MOSFET gas/odor sensors. These devices can be fabricated in a standard SOI CMOS process at low unit cost and should offer an excellent degree of reproducibility. Applications envisaged are in air quality sensors for the automotive industry and odor sensors for electronic noses.
Conducting polymer films are employed as the active material in both resistive and acoustic waves gas sensors. Here we describe the use of an electroactive conducting polymer as the gate material in a gas-sensitive MOSFET sensor run at ambient temperature and compare it to a conventional catalytic metal gate MOSFET run at 180 degree(s)C.