Different kinds of optical ammonia concentration sensors, based on monitoring the absorption or fluorescence characteristics of sensing films deposited onto an optical fiber, have been reported [8-9]. An integrated optical ammonia sensor based on a Y-junction has been reported in [10]. This sensor employs a deposited sensing film whose absorbance (dependent on ammonia concentration in the surrounding ambient) is continuously measured and exhibits a detection limit around 1ppm. Ammonia concentration estimation by this sensor implies an optical power differential measure at the output of the two Y-junction arms.In recent years, integrated optical sensors have attracted considerable attention because of their immunity to electromagnetic interference, high sensitivity, good compactness and robustness and high compatibility with fiber networks [11].

A great variety of guided-wave optical sensors has been proposed, such as those based on directional couplers [12], Mach�CZehnder interferometers [13], grating-assisted couplers [14], and optical microcavities [15].In particular, optical microring resonators, widely used in add�Cdrop filters, optical switches, ring lasers and WDM multiplexers, are showing very attractive features for sensing applications, permitting to realize highly sensitive immunochemical optical biosensors [16-18]. In this paper we design, optimize and 3D simulate an integrated optical microring resonator-based ammonia sensor. Device sensitivity dependence on waveguide optical and geometrical parameters is investigated. Sensor detection limit is also analyzed.

2.?Sensing PrincipleThe architecture of a very compact microring resonator-based sensor in Silicon on Insulator (SOI) technology is sketched in Figure 1(a). A ridge structure has been adopted as waveguide (this kind of sub-micrometer guiding structure is also indicated as silicon photonic wire), as in Figure Brefeldin_A 1(b), and Polymethylmethacrylate (PMMA) doped with Bromocresol Purple (BCP) has been used as cladding layer.Figure 1.(a) Ammonia sensor architecture. (b) Ridge guiding structure adopted in sensor design.Optical absorption changes of PMMA-BCP system, due to interaction with ammonia, has been proved [19] either when PMMA-BCP is exposed to dry ammonia (in this case PMMA-BCP sample is put in a chamber filled by ammonia diluted with pure nitrogen to a molar concentration of 5%) or when PMMA-BCP is exposed to a vapor of conventional medical ammonia spirit (65% alcohol).

The use of capacitive sensing [5] is another possible sensing method, but it requires attaching a mesh-shape to achieve the interaction between transmitter and receiver. One of the most widespread multi-touch technologies uses the Frustrated Total Internal Reflection (FTIR) proposed by Jeff Han [6]. A comparison of multi-touch technologies is given in Table 1. The most common systems are expensive because they use special control hardware and require bulky equipment. A few studies, such as those done by Apple and N-trig [7,8], have focused on projected-capacitive technology for portable devices. A capacitive coupling between neighboring electrodes changes its capacitance as an object approaches the field lines projected from one electrode to another.

However, projected-capacitive technology has a limited maximum size because the number of sensor electrodes needs to increase geometrically as the screen size increases. In multi-touch sensors, there is no organic resistance material between the two electrodes. It is very difficult to correctly identify which element was really touched because the mutual conduction of column and row electrodes is easily confused during the column and row scanning processes. In addition, multi-touch screens are mostly made of glass, which is difficult to bend.Table 1.Comparison of multi-touch characteristics.Therefore, we propose a novel flexible multi-touch sensor design that prints organic thixotropic resistance materials on a top polyimide (PI) film. We also use an algorithm matrix and control system scanning to solve the array matrix for multi-touch switch identification in the tactile sensors.

Flexible electronics actuators for realizing large scale and low-cost applications have been gradually developed in recent years [11,12]. Especially, flexible displays [13,14] and flexible organic transistors [15-17] have been successfully demonstrated using printing technologies. A few studies on flexible electronics sensors, usually using solid components integrated into polymer materials, have focused on small scale pressure [18], temperature [19,20], and humidity [21] sensors. Fabrication technologies for flexible electronics include screen printing [22], ink-jet printing [23,24], and the roll to roll process [25].We have designed a gap between the bottom electrode and the resistance layer to eliminate erroneous signals during bending actions.

For optimal flexible structure characteristics, a protrusion (bump) on the top membrane is Batimastat used to enhance the sensing sensitivity response. A high viscosity thixotropic material is used to print the thick bump structures to reduce the diffusive effects and dimensional shrinkage after printing and curing. Mechanical properties were investigated by analysis of the deflection and stress distributions using finite element analysis (FEA).