36 IEEE Instrumentation & Measurement Magazine October 2011 1094-6969/11/$25.00©2011IEEE Bruno Andò O ver the past ten years, the development of low cost graphic technology-based sensors has been pro- ceeding rapidly. The use of innovative materials and substrates has also picked up momentum. The interest in such sensors is justiied by the need for both low cost, rapid prototyping techniques for research laboratories and mass-production processes for the realization of very low cost devices. Examples of addressed devices are RFID tags, antennas, keyboards, displays and especially sensors. The rapid prototyping of inexpensive devices and sensors by printing technologies is of great importance for the ev- eryday activities of the scientiic community including research laboratories and academia. The availability of novel technologies for the development of low cost sensors would move market interest towards new applications, previously not very attractive because of the costs of traditional silicon electronics [1]. Printed sensors could be the “right answer” to such needs. Screen printing and inkjet printing have received more attention for the realization of printed sensors than other printing techniques. In this paper, we provide brief explana- tions of these technologies. Screen Printing on Sensors Screen printing is a technique which requires the use of a mask that acts as a stencil. The stencil delimits areas where ink must be deposited on the substrate by the mechanical pressure ex- erted, typically through a roller. Examples of sensors realized by screen printing are: gas detectors exploiting conductive pat- terns realized by screen printing with nanoparticle inks [2], humidity sensors for smart packaging applications [3], im- pedance sensors applied to biosensors [4], and resistive force sensors [5]. The rapid widespread use of this technology led to the availability of a good choice of conductive, insulating and functional materials compatible with screen printing. The lat- ter reduces the need for custom formulations. Furthermore, screen printing allows for the deposition of thick layers of material, thus increasing the track conductiv- ity and the device reliability. Drawbacks of screen printing techniques are related to the development process which re- quires masks and physical contact with the substrate. These processes are based on photolithography and, in general, tech- niques requiring masks. Inkjet printing does not require masks or micromachining which reduces processing time and costs (see Fig. 1). Inkjet Printing Inkjet printing of polymers and materials is a fairly new tech- nique which could, in speciic contexts, replace traditional techniques (e.g. sputtering, lithography, and post-process- ing). By using this ‘drop-on-demand technique,’ a layer of functional ink can easily be deposited on the substrate in well deined patterns without the need of patterning techniques and thus reducing waste of materials. Small volumes of ma- terial, in the range of 1-30 picoliters, may be used, resulting in high spatial resolution and good reproducibility (see Fig. 1). Moreover, inkjet printing is a contactless deposition technique which makes it applicable to many different sub- strates. Inkjet-based sensors offer the possibility to combine the performance of lexible substrates and functional inks with a very low-cost prototyping technique (see Fig. 2). Examples of devices realized by this technique are avail- able in the literature, such as strain gauges and capacitors Inkjet-Printed Sensors: A Useful Approach for Low Cost, Rapid Prototyping Bruno Andò and Salvatore Baglio instrumentation notes Fig. 1. Layout of inkjet printable sensors.