Compact readout system for chipless passive LC tags and its application for humidity monitoring

The development of a contactless readout system for High Frequency (HF) tags and its application to relative humidity monitoring is presented. The system consists of a Colpitts oscillator circuit whose frequency response is determined by a built-in logic counter of a microcontroller unit. The novel readout strategy is based on the frequency response change due to the inductive coupling between the coil of the Colpitts oscillator and the load impedance of a parallel LC resonator tag, as a result of the variation of the humidity sensing capacitor. The frequency is monitored with a low cost microcontroller, resulting in a simple readout circuit. This passive LC tag has been directly screen-printed on a humidity-sensitive flexible substrate. The readout circuit experimental uncertainty as frequency meter was 4 kHz in the HF band. A linear temperature drift of (-1.52 ± 0.17) kHz/⁰C was obtained, which can be used to apply thermal compensation if required. The readout system has been validated as a proof of concept for humidity measurement, obtaining a significant change of about 260 kHz in the resonance frequency of the Colpitts oscillator when relative humidity varies from 10% to 90%, with a maximum uncertainty of ±3% (±2 SD). Therefore, the proposed readout system stands as a compact, low-cost, contactless solution for chipless HF tags that avoids the use of bulky and costly equipment for the analog reading of wireless passive LC sensors.This work was supported by project CTQ2016-78754-C2-1-R from the Spanish Ministry of Economics and Competitivity. P. Escobedo wants to thank the Spanish Ministry of Education, Culture and Sport (MECD) for a pre-doctoral grant (FPU13/05032)

Passive UHF RFID Tag with Multiple Sensing Capabilities

This work presents the design, fabrication, and characterization of a printed radio frequency identification tag in the ultra-high frequency band with multiple sensing capabilities. This passive tag is directly screen printed on a cardboard box with the aim of monitoring the packaging conditions during the different stages of the supply chain. This tag includes a commercial force sensor and a printed opening detector. Hence, the force applied to the package can be measured as well as the opening of the box can be detected. The architecture presented is a passive single-chip RFID tag. An electronic switch has been implemented to be able to measure both sensor magnitudes in the same access without including a microcontroller or battery. Moreover, the chip used here integrates a temperature sensor and, therefore, this tag provides three different parameters in every reading.This work was partially funded by the Ministerio de Educación y Ciencia under Projects CTQ2009-14428-C02-01 and CTQ2009-14428-C02-02 and the Junta de Andalucía (Proyecto de Excelencia P10-TIC-5997), Spain. This project was partially supported by European Regional Development Funds (ERDF)

Development of Sensor Integrated and Inkjet-Printed Tag Antennas for Passive UHF RFID Systems

Radio frequency identification (RFID) is a form of automated identification technology that is nowadays widely used to replace bar codes in asset tracking and management. Looking ahead to the future, our lives will be surrounded by small, embedded and wireless electronic devices that provide information about everything for everybody through pervasive computing. At the core of this vision lie two key concepts of ubiquitous sensing and the Internet of Things. RFID technology is seen as one of the most prominent technologies of today for the implementation of these future concepts. Ubiquitous sensing describes a situation, where small embedded sensors monitoring various environmental parameters are found everywhere. The second concept, the Internet of Things, requires that all objects, even the most insignificant everyday items, surrounding us should encompass computing and communication capabilities of some sort. In its simplest form, such computing could be a transponder that allows the unique identification and tracking of the item. Together these future concepts could truly revolutionize our lives by delivering significantly more information from our living environment. The objectives of this thesis are twofold. Firstly, passive ultra-high frequency (UHF) RFID technology is utilized to develop low cost, completely passive, wireless sensor devices for ubiquitous sensing applications. Secondly, inkjet-printed passive UHF RFID tag antennas are developed and optimization techniques are presented to lower the cost of such tag antenna implementations. The latter objective aims to facilitate the advancement of the Internet of Things by enabling tag antennas to be directly printed on or in to various objects. As a result of the research work presented in this thesis, three different passive UHF RFID based sensor tags were developed. Two of these designs monitor temperature and one is developed for relative humidity measurements. For the first time, the applicability and accuracy of such passive sensor tags was demonstrated. The results show that UHF RFID sensor tags have potential to be utilized as low cost sensor devices in ubiquitous applications. In addition, this thesis presents methods to lower the costs of inkjet-printed tag antennas. A technique was developed to reduce the ink consumption significantly to produce high performance tag antennas. Moreover, a special type of tag antenna design consisting of very narrow lines was developed. Finally, novel electronic materials were used as tag antenna substrate materials for inkjet-printed tag antennas. The use of a high permittivity ceramic-polymer composite, wood veneer, paper and cardboard were demonstrated. In each case, it was shown that inkjet-printing is a feasible form of fabrication on such materials, producing passive UHF RFID tags with long read ranges. This shows that tag antennas can be inkjet-printed directly on to various items to advance the realization of the Internet of Things

An Inkjet Printed Chipless RFID Sensor for Wireless Humidity Monitoring

A novel chipless RFID humidity sensor based on a finite Artificial Impedance Surface (AIS) is presented. The unit cell of the AIS is composed of three concentric loops thus obtaining three deep and high Q nulls in the electromagnetic response of the tag. The wireless sensor is fabricated using low-cost inkjet printing technology on a thin sheet of commercial coated paper. The patterned surface is placed on a metal backed cardboard layer. The relative humidity information is encoded in the frequency shift of the resonance peaks. Varying the relative humidity level from 50% to 90%, the frequency shift has proven to be up to 270MHz. The position of the resonance peaks has been correlated to the relative humidity level of the environment on the basis of a high number of measurements performed in a climatic chamber, specifically designed for RF measurements of the sensor. A very low error probability of the proposed sensor is demonstrated when the device is used with a 10% RH humidity level discrimination

Novel Manufacturing Methods and Materials for UHF RFID Tags in Identification and Sensing Applications

The continuously increasing amount of radio frequency identification tags needed in our daily lives, not forgetting the broadly widening concept of the Internet of Things, sets high demands on the tag materials selection and manufacturing processes. The huge amount of needed tags requires environmentally sustainable material selection together with the requirement of very low cost. In addition, the manufacturing capacity needs to be very high, hence high-volume capable production methods are needed. In addition to identification applications, also sensing applications established with radio frequency identification tags are of great interest in many application fields.This thesis reports the possibilities of radio frequency identification tags manufactured on eco-friendly substrate materials using conductive inks and photonic sintering. The used manufacturing methods use raw materials efficiently. Especially brush-painting together with photonic sintering is capable for low-cost high-volume manufacturing. In addition, the possibilities of radio frequency identification tags for humidity sensing applications are studied.The results of this thesis confirmed that the materials and processes studied in this thesis are suitable for environmentally friendly low-cost radio frequency identification tag manufacturing. Especially brush-painting of regular screen printing conductive inks, both silver and copper oxide ink, on wood and cardboard substrates combined with photonic sintering confirmed to be a very good choice for the application area focused in this thesis. Furthermore, especially the use of screen printable copper oxide ink for identification applications is a very low-cost possibility. The results showed that humidity sensing with passive ultra-high frequency radio frequency identification tags, which were manufactured with regular screen printing silver ink on wood substrate without any coating on the tag, is a very promising approach

RF Energy Harvesting Techniques for Battery-less Wireless Sensing, Industry 4.0 and Internet of Things: A Review

As the Internet of Things (IoT) continues to expand, the demand for the use of energy-efficient circuits and battery-less devices has grown rapidly. Battery-less operation, zero maintenance and sustainability are the desired features of IoT devices in fifth generation (5G) networks and green Industry 4.0 wireless systems. The integration of energy harvesting systems, IoT devices and 5G networks has the potential impact to digitalize and revolutionize various industries such as Industry 4.0, agriculture, food, and healthcare, by enabling real-time data collection and analysis, mitigating maintenance costs, and improving efficiency. Energy harvesting plays a crucial role in envisioning a low-carbon Net Zero future and holds significant political importance. This survey aims at providing a comprehensive review on various energy harvesting techniques including radio frequency (RF), multi-source hybrid and energy harvesting using additive manufacturing technologies. However, special emphasis is given to RF-based energy harvesting methodologies tailored for battery-free wireless sensing, and powering autonomous low-power electronic circuits and IoT devices. The key design challenges and applications of energy harvesting techniques, as well as the future perspective of System on Chip (SoC) implementation, data digitization in Industry 4.0, next-generation IoT devices, and 5G communications are discussed

The effect of bending on laser-cut electro-textile inductors and capacitors attached on denim as wearable structures

In this paper we present the design, fabrication and characterization of electro-textile inductor and capacitor patterns on denim fabric as a basis for the development of wearable e-textiles. Planar coil inductors have been harnessed as antenna structures for the development of Near Field Communication (NFC) tags with temperature sensing capability, while interdigitated electrode (IDE) capacitors have been used as humidity sensors for wearable applications. The effect of bending in the electrical performance of such structures was evaluated, showing variations below 5% in both inductance and capacitance values for bending angles in the range of interest, i.e. those fitting to human limbs. In the case of the fabricated NFC tags, a shift in the resonance frequency below 1.7% was found, meaning that the e-textile tag would still be readable by an NFC- enabled smartphone. In respect of the capacitive humidity sensor, we obtained a minimum capacitance variation of 40% for a relative humidity range from 10% to 90%. Measured thermal shift was below 5% in the range from 10 to 40oC. When compared to the 4% variation due to bending, it can be concluded that this capacitive structure can be harnessed as humidity sensor even under bending strain conditions and moderate temperature variations. The development and characterization of such structures on denim fabrics, which is one of the most popular fabrics for everyday clothing, combined with the additional advantage of affordable and easy fabrication methodologies, means a further step towards the next generation of smart e-textile products

Technological Integration in Printed Electronics

Conventional electronics requires the use of numerous deposition techniques (e.g. chemical vapor deposition, physical vapor deposition, and photolithography) with demanding conditions like ultra-high vacuum, elevated temperature and clean room facilities. In the last decades, printed electronics (PE) has proved the use of standard printing techniques to develop electronic devices with new features such as, large area fabrication, mechanical flexibility, environmental friendliness and—potentially—cost effectiveness. This kind of devices is especially interesting for the popular concept of the Internet of Things (IoT), in which the number of employed electronic devices increases massively. Because of this trend, the cost and environmental impact are gradually becoming a substantial issue. One of the main technological barriers to overcome for PE to be a real competitor in this context, however, is the integration of these non-conventional techniques between each other and the embedding of these devices in standard electronics. This chapter summarizes the advances made in this direction, focusing on the use of different techniques in one process flow and the integration of printed electronics with conventional systems

Design and Development of Efficient and Conformal Printed Antennas for Wireless Sensing and Wearable Applications

Future wireless technologies would require flexibility from electronics that will enable the electronic components to adapt according to the everyday use environment. Flexible electronics has been used in many wireless sensing and wearable applications. One of the fastest growing wireless technologies of this decade is Radio Frequency Identification (RFID) which is an automatic identification technology that uses electromagnetic interaction to identify, sense and track people or objects with transponders known as tags. RFID is rapidly replacing the bar code technology in supply chain applications and huge amount of tags are needed to be produced in order to meet the needs of this application. The production method and material selection are few of the key parameters which are under study for the cost-effective and efficient fabrication of RFID tags and wearable antennas. The latest manufacturing technologies such as inkjet, thermal and three dimensional (3D) printing have shown good potential in improving the fabrication process, however they need to be optimized and explored further to get the best possible results.This thesis reports the use of novel manufacturing methods for the development of passive Ultra High Frequency (UHF) RFID tags and wearable antennas on versatile substrates. Commercially available as well as 3D printed flexible substrates along with different conductive inks/pastes are used for the improvement in the fabrication process. The first part of the research compares inkjet and thermal printing for the RFID fabrication in detail and suggests suitable optimizing parameters for the materials under study. The second part of the research focuses on 3D printing of the substrates and then utilizing brush painting, 3D dispensing and embroidery process to improve the overall fabrication. In addition, the fabricated antennas are tested for humidity, bending and stretching for specific applications.The results indicate that the approach and methodologies used have great potential in improving the fabrication of RFID tags and antennas. The fabricated tags show excellent results and achieve the required performance for modern RFID applications such as supply chain, wearable biomedical sensing and environment monitoring. This detailed study will be very helpful to find out appropriate materials for fabricating wireless components with the best possible results, i.e. easy to fabricate, reliable and better wireless performance, for future applications such as Internet of Things (IoT) and smart RFID packaging