Tomas Unander

Characterization of Printed Moisture Sensors in Packaging Surveillance Applications

This work presents a study on the performance of printed low-cost moisture sensors fabricated using conductive ink on paper substrates. The sensors are intended to add value to the surveillance of packages. Two different kinds of sensors are evaluated and characterized. The two sensors have similar geometrical shapes, but different measuring principles are employed. The first sensor is measuring the moisture content in cellulose-based substrates, while the second is measuring high levels of relative humidity in the surroundings. The sensors have been developed so that they can be integrated into radio frequency identification (RFID) systems for surveillance in logistic chains. A laboratory setup of a RFID tag with sensor capability based on an ordinary passive RFID tag has been shown.

Remote Moisture Sensing utilizing Ordinary RFID Tags

The paper presents a concept where pairs of ordinary RFID tags are exploited for use as remotely read moisture sensors. The pair of tags is incorporated into one label where one of the tags is embedded in a moisture absorbent material and the other is left open. In a humid environment the moisture concentration is higher in the absorbent material than the surrounding environment which causes degradation to the embedded tags antenna in terms of dielectric losses and change of input impedance. The level of relative humidity or the amount of water in the absorbent material is determined for a passive RFID system by comparing the difference in RFID reader output power required to power up respectively the open and embedded tag. It is similarly shown how the backscattered signal strength of a semi-active RFID system is proportional to the relative humidity and amount of water in the absorbent material. Typical applications include moisture detection in buildings, especially from leaking water pipe connections hidden beyond walls. Presented solution has a cost comparable to ordinary RFID tags, and the passive system also has infinite life time since no internal power supply is needed. The concept is characterized for two commercial RFID systems, one passive operating at 868 MHz and one semi-active operating at 2.45 GHz.

Inkjet Printed Silver Nanoparticle Humidity Sensor With Memory Effect on Paper

In this paper, the design and the manufacture of an inkjet printed resistive type humidity sensor on paper are reported. After having been exposed to humidity above a given threshold level, the resistance of the sensor decreases substantially and remains at that level even when the humidity is reduced. It is possible to deduce the humidity level by monitoring the resistance. The main benefit of the printed sensor presented in this case is in relation to its very low production costs. It has also been shown that both the ink type and this paper combination used prove to be crucial in order to obtain the desired sensor effect. More research is required in order to fully understand the humidity sintering effect on the nano particle ink and the role of the substrate. However, the observed effect can be put to use in printed humidity sensors which possess a memory function. The sensor can be used in various applications for environmental monitoring, for example, in situations where a large number of inexpensive and disposable humidity sensors are required which are able to detect whether they have been subjected to high humidity. This could be the checking of transportation conditions of goods or monitoring humidity within buildings.

Designing of RFID-Based Sensor Solution for Packaging Surveillance Applications

In this work, a two-chip battery assisted Radio Frequency Identification (RFID) based sensor platform is presented. The radio frequency communication interface is based on the EPC Gen 2 standard. A laboratory setup of the platform has been shown and characterized for a moisture content sensor application. The laboratory setup of the sensor platform has a reading range of 3.4 meters which is in comparison to commercial available Gen 2 tags. The laboratory platform has an average power consumption of 2.1 μW operating at 3 V, which together with a printed battery gives an estimated lifetime for data logging of several years. The proposed RFID platform provides a tradeoff between, communication performance, compatibility with international standards, and flexibility in on-package customization including type and number of sensors. The proposed architecture separates the high-performance communication circuit and the low-frequency sensor interface logic. In the future, the sensor interface maybe integrated using printed logics to further enhance the flexibility and low-cost customization features of the architecture.

System Integration of Electronic Functions in Smart Packaging Applications

A system integration scheme relevant for smart packaging applications is presented. Recent advances in printed electronics, radio frequency identification tag production, and standardization of communication protocols are factors that increase the design freedom for new applications. As in all new technology fields, the first products are expected to appear in the high-cost segment attracting early adopters in the form of niche products. A reasonable assumption is that these products will come from hybridization of different types of technologies. Such a scenario is likely since no technology solution available can provide all features that these types of applications demand. There is a need of standard solutions for hybridization of silicon devices and printed (or foil-type) components. Conductive ink technology is a powerful tool for hybridization and customization of large-area electronics, providing 3-D integration and large-area customization. However, high-performance communication and advanced processing demand the use of silicon. Smart hybridization solutions allow combination of the best from both worlds. This paper analyzes the requirements on hybridization technologies suitable for smart packaging applications and provides design examples on integration of intrusion surveillance solutions for cellulose-based packaging applications. It shows that even though the current hybridization technologies are far from optimal, they can provide a considerable design freedom and system performance.

Printed Write Once and Read Many Sensor Memories in Smart Packaging Applications

A horizontal printed Write-Once-Read-Many (WORM) resistive memory has been developed for use in wireless sensor tags targeting single-event detection in smart packaging applications. The WORM memory can be programmed using a 1.5-V printed battery. An alternative programming method is to use chemical sintering which allows the development of exposure-time triggered single event tags that can be accessed wirelessly. The new WORM memory has very low losses in the ON-state which allows direct integration into antenna structures. A sensor tag that utilizes the WORM memory functionality and the well established Electronic Article Surveillance (EAS) communication standard has been outlined. Both active and fully passive sensor tag solutions have been proposed. The role of printed electronics in smart packaging applications has been reviewed and discussed. Important enabling factors for the future development have been highlighted, such as the need for hierarchical design and test tools, better printed interconnect technologies as well as better components that allow communication with existing information and communication technology (ICT) standards. This is illustrated and underlined by the presented smart packaging concept demonstrators.

Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips

The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel fo ...

Printed touch sensor for interactive packaging and display

In this work we present a study on the performance of printed touch sensor fabricated using conductive ink on paper substrates. The sensor system is intended to add values in surveillance of packages or in interactive point-of-purchase displays. The printed sensor changes its capacitance when it is touched or manipulated. The capacitance variations are readout using either a wireless or wired communication link. The most advanced system will utilize RFID or ZigBee readout technology while the simplest systems utilize a simple analog wire solution. The sensor technology has been developed to be easily integrated into high quality prints targeting applications such as large area touch sensitive commercial stands, flat keyboards at point-of-purchase and touch and manipulation surveillance in logistic chains.

Investigation of Humidity Sensor Effect in Silver Nanoparticle Ink Sensors Printed on Paper

Thin inkjet-printed tracks of silver nanoparticles have previously been observed to show a non-reversible decrease in resistance when exposed to a high degree of relative humidity and thus providing sensor functionality with a memory effect. This paper provides a more in-depth explanation of the observed humidity sensor effect that originates from inkjet-printed silver nanoparticle sensors on a paper substrate. It is shown that the geometry of the sensor has a large effect on the sensors initial resistance, and therefore also on the sensors resistive dynamic range. The importance of the sensor geometry is believed to be due to the amount of solvent from the ink interacting with the coating of the paper substrate, which in turn enables the diffusion of salts from the paper coating into the ink and thus affecting the silver ink.

Characterization of moisture sensor based on printed Carbon-Zinc energy cell

In this work we present a simple printed moisture sensor fabricated using electronic inks on a multilayer paper structure. The sensor is based on a Carbon-Zinc type energy cell and provides power to a readout electronic circuit when activated by moisture. The sensors are based on a number of our filed patents according to which the sensor is used for both event detection and as a power source for the processing electronics. Typical applications are moisture and leakage detection in buildings, water pipe lines, smart packages and health care systems such as smart incontinence sensors. As the detector is triggered, it powers up an electronic circuit (polymer based or silicon based) that starts communication with the alarm server. In the simplest systems a sound or a light alarm is started to alert the user. In this work we present a characterization of some critical parameters of the sensor such as power driving capability, linearity, internal memory effects and saturation. In addition, we examine a specific application, when sensor is used as defrosting alarm for surveillance of frozen articles during transport.