A. Vasquez Quintero

Large-area compatible fabrication and encapsulation of inkjet-printed humidity sensors on flexible foils with integrated thermal compensation

This work presents the simultaneous fabrication of ambient relative humidity (RH) and temperature sensors arrays, inkjet-printed on flexible substrates and subsequently encapsulated at foil level. These sensors are based on planar interdigitated capacitors with an inkjet-printed sensing layer and meander-shaped resistors. Their combination allows the compensation of the RH signals variations at different temperatures. The whole fabrication of the system is carried out at foil level and involves the utilization of additive methods such as inkjet-printing and electrodeposition. Electrodeposition of the printed lines resulted in an improvement of the thermoresistors. The sensors have been characterized and their performances analyzed. The encapsulation layer does not modify the performances of the sensors in terms of sensitivity or response time. This work demonstrates the potential of inkjet-printing in the large-area fabrication of light-weight and cost-efficient gas sensors on flexible substrates.

Design and Development of Sensing RFID Tags on Flexible Foil Compatible With EPC Gen 2

Taking advantage of the sensor interface capabilities of a radio frequency identification (RFID) chip, the integration of different types of sensors on printed ultrahigh frequency (UHF) RFID tags is investigated. The design, development, and testing of printed smart sensing tags compatible with the RFID standard electronic product code Gen 2 is presented. Two different strategies are employed to interface the sensors: 1) passive single-chip and 2) semipassive architectures. Both strategies provide sensor data by directly answering to the RFID reader inquiries or using a data logging mechanism to store the sensor data in the RFID chip memory. Temperature readout is measured using the embedded sensor in the RFID chip. Additionally, a light sensor and pressure sensor interfaced to a microcontroller are implemented in the passive and semipassive tags versions, respectively. For the employed RFID chip, two different UHF antennas are designed and printed using inkjet and screen printing to compare their radio frequency performances. Finally, the fabricated smart tags are fully validated through measurements in an anechoic chamber and their behaviors are compared with numerical simulation. The screen printed semipassive RFID tag with loop antenna shows a better reading range than the inkjet-printed one, whereas the passive tag can be considered as the most cost-effective system.

Smart RFID Label with a Printed Multisensor Platform for Environmental Monitoring

This work reports on the design, fabrication and characterization of an inkjet-printed multisensing platform on flexible polymeric substrates integrated into a printed semi-passive high frequency radio frequency identification (HF RFID) smart label. The printed platform was integrated after fabrication to the main RFID carrier, which contained an NFC RFID chip, a microprocessor, a readout frontend and a screen-printed circuitry and antenna. The multisensing platform has channels for capacitive vapor detection (i.e. humidity), two channels for resistive-based vapor detection (i.e. ammonia) with heating capability, and one resistive channel for temperature detection (RTD). A modular approach was employed where the sensing platform was integrated to the base RFID label carrier using foil-to-foil integration techniques compatible with large area fabrication. Besides wireless communication, the semi-passive label possesses data logging and the possibility of measuring all the sensors simultaneously through a direct readout circuitry. In addition to individual sensor characterization, the full functionality of the smart label was successfully demonstrated by measuring different temperature, humidity and ammonia levels.

Vibration energy harvesters on plastic foil by lamination of PZT thick sheets

This paper presents a low-complexity and low temperature (85°C) fabrication process for vibration energy harvesters. The process employs lamination steps to transfer thinned PZT thick sheets onto flexible polymeric substrates, using dry film photoresist. The influence of geometrical parameters on the device performance were assessed by FEM simulations (using COMSOL) and supported by experiments. Optimization of the output power was performed by modifying the neutral plane within the device and by using a localized seismic mass at the tip, which has resulted in an output power of 30 μW at 52 Hz and an acceleration of 1g. Finally, a low-complexity and fully polymeric package is proposed, which together with the harvester process are compatible with large area fabrication methods.

P1.8.6 All-additive Inkjet Printed Humidity and Temperature Sensors Fabricated and Encapsulated at Foil Level

We present the simultaneous fabrication at foil level of ambient relative humidity (R.H.) and temperature sensors printed on flexible substrate. These sensors are based on capacitors and resistors and their combination allows the compensation of the R.H. signals variations at different temperatures. The whole fabrication of the system is carried out at foil level and involves the utilization of additive methods, namely inkjet printing and electrodeposition, as well as the final encapsulation of the sensors for protection. The sensors have been characterized and their performances analyzed. The sensitivity of the humidity sensor ranged from 1 fF / 1% R.H. in differential mode operation to 3.5 fF / 1% R.H. in single mode actuation. The thermal coefficient of temperature (TCR) of the thermoresistor was 4.3 x 10 °C. This work demonstrates the potential of inkjet printing in the fabrication at foil level of flexible, light-weight and cost-efficient large arrays of gas sensors.

Feasibility of Printing Woven Humidity and Temperature Sensors for the Integration into Electronic Textiles

We demonstrate a woven textile with an integrated humidity and temperature sensor on flexible PI substrates. We discuss the fabrication process of the smart textile and compare two methods of sensor fabrication, first conventional photo lithography and second printing using ink jet. The humidity sensor is based on a capacitive interdigitated transducer covered with a sensing layer while the temperature sensor is made of a resistive metallic meander. An encapsulation method protecting the sensors during dicing, weaving and operation has been successfully implemented. The fabricated structures are tested to bending strain, a main source of failure during the fabrication of textiles. We were able to bend bare electrodes and complete sensors down to a minimal bending radius of 100 μm without loss of functionality. The woven temperature sensor has a temperature coefficient of 0.0027 /°C for lithography made and 0.0029 /°C for printed sensors. The humidity sensor shows a repeatable behaviour in the tested humidity range between 20 to 70 %RH. The weaving process does not damage or change the behaviour of the fabricated sensors. This contribution will highlight the challenges and promises of printing and laminating processes for the large scale fabrication of smart polymeric stripes to be woven into textiles.

Flexible and Robust Multilayer Micro-Vibrational Harvesters for High Acceleration Environments

This paper presents the fabrication and characterization of multilayer PVDF resonant micro-vibrational energy harvesters designed to withstand environments in which high levels of acceleration are present. The multilayer cantilevers are fabricated by combining two folded PVDF stacks into a multilayered, bimorph structure. This acts to increase the overall capacitance of the harvester, a problem that plaques PVDF cantilevers as a result of its low dielectric constant. Moderate powers (7 mu W) are produced from the cantilevers even at high acceleration levels (20 g) due to the limited piezoelectric coefficient of PVDF; however, as a result of the high tensile strength and low elastic modulus of PVDF, the cantilevers are able to survive extremely high accelerations (> 4000 g) without breakage - a critical problem for harvesters based on brittle piezoelectric materials and substrates.

Multiphysics finite element model of a frequency-amplifying piezoelectric energy harvester with impact coupling for low-frequency vibrations

This paper presents experimentally-verified multiphysics finite element model of a wideband vibration energy harvester with impact coupling, which operates on the principle of frequency up-conversion: under low-frequency harmonic base excitation a cantilever-type resonator (with resonant frequency of 18.8 Hz) impacts a high-frequency piezoelectric cantilever, which starts freely vibrate at its resonant frequency of 374 Hz. Such input frequency amplification enables efficient power generation under low-frequency ambient excitations. The model was implemented in COMSOL and the contact between the cantilevers was formulated by using a nonlinear viscoelastic model. Reported results of dynamical and electrical testing of the fabricated vibration energy harvester confirm the accuracy of the model as well as reveal some operational characteristics of the device under varying impact and excitation conditions.