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This paper presents a smart sensor patch with flexible strain sensor and a printed temperature sensor integrated with a Near Field Communication (NFC) tag to detect strain or temperature in a semi-quantitative way. The strain sensor is fabricated using conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in a polymer Polydimethylsiloxane microchannel. The temperature sensor is fabricated by printing silver electrodes and PEDOT:PSS on a flexible polyvinyl chloride (PVC) substrate. A customdeveloped battery-less NFC tag with an LED indicator is used to visually detect the strain or temperature by modulating the LED light intensity. The LED shows maximum brightness for relaxed or no strain condition, and also in the case of maximum temperature. In contrast, the LED is virtually off for the maximum strain condition and for room temperature. Both these could be related to food spoilage. Swollen food packages can be detected with the strain sensor, serving as beacons of microbial contamination. Temperature deviations can result in the growth or survival of food-spoilage bacteria. Based on this, the potential application of the sensor system for smart food packaging is presented.

Herein, a novel tactile sensing device (SensAct) with a soft touch/pressure sensor seamlessly integrated on a flexible actuator is presented. The squishy touch sensor is developed with custom-made graphite paste on a tiny permanent magnet, encapsulated in Sil-Poxy, and the actuator (15 μ-thick coil) is fabricated on polyimide by Lithographie Galvanoformung Abformung (LIGA) micromolding method. The actuator can operate in two modes (expansion and contraction/squeeze) and two states (vibration and nonvibration). The sensor was tested with up to 12 N applied forces and exhibited ≈70% average relative resistance variation (ΔR/Ro), ≈0.346 kPa−1 sensitivity, and ≈49 ms response time with excellent repeatability (≈12.7% coefficient of variation) at 5 N. During simultaneous sensing and actuation, the modulation of coil current, due to ΔR/Ro (≈14% at 2 N force) in the sensor, allows the close loop control (ΔI/Io ≈385%) of expansion/contraction (≈69.8 μm expansion in nonvibration state and ≈111.5 μm peak-to-peak in the vibration state). Finally, the soft sensor is embedded in the 3D-printed fingertip of a robotic hand to demonstrate its use for pressure mapping along with remote vibrotactile stimulation using SensAct device. The self-controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.

Integration of sensors with antennas is becoming popular for compact high-performance wireless sensing systems. In this direction, here we present a silver electrodes and Poly(3,4-ethylenedioxythiophene:polystyrene (PEDOT:PSS) based printed temperature sensor on a flexible PVC substrate. The temperature sensor was characterised using a digital multimeter for a temperature range from 25¤C to 90□C. The sensor showed a 70% change in resistance for the tested temperature range. Further, the sensing part was integrated with a Near Field Communication (NFC) tag with the data obtained semi-quantitatively by means of the intensity of an Light Emittign Diode (LED) connected with the antenna system. In this case, the antenna works as an energy harvester to power an LED indicator connected in series to the resistive temperature sensor. The intensity of the LED, which varies with the increase of temperature, was measured using a lux-meter mobile application. The intensity at 70□C was ~42 lux whereas it decreased down to ~14 lux at room temperature (~25□C). The presented system showed potential use as a smart label in applications requiring temperature monitoring.

This paper presents a miniaturized potentiostat readout circuit patch developed for electrochemical or biosensors. The presented patch has been fabricated on a flexible polyimide substrate using off-the-shelf electronics. In contrast to the traditional bulky equipment for electrochemical analysis, the presented patch is conformable and portable. As a proof of concept, the system has been used for pH measurements in buffer solution (6- 8 pH values) with a printed thick film potentiometric pH sensor having platinum counter electrode. The obtained results are in line with a commercially available potentiostat that has been used for benchmarking.

In this work we present a polymer-based flexible strain sensor integrated with an NFC tag to detect strain by means of a visual LED indicator. The sensor was fabricated using conductive polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as an active material inside a flexible and transparent polymer Polydimethylsiloxane (PDMS) microchannel. The strain sensor changes its resistance at different bending conditions, showing up to three order increase in resistance for $\sim 100$ bending. A custom-developed passive NFC tag with an LED connected in series to the strain sensor is powered from an NFC reader to detect strain in a semi-quantitative way. The light intensity of the LED indicator is modulated according to the strain level, showing maximum brightness $(\sim 67$ lux) for relaxed or no strain condition, and being almost OFF $(\sim 8$ lux) for the maximum strain condition. The potential application of the NFC-based strain sensor system in food package for spoilage detection is also presented.

Disposable and flexible sensors are needed in biomedical and healthcare applications because of hygiene requirements. At the same time, they should provide an affordable solution for point-of-care (POC) testing and large-scale deployment. In this view, herein we report flexible polyimide-based disposable sensor patch for the detection of a-amylase in blood serum. The concentration of a-amylase in blood serum is a potential indicator of health issues such as pancreatitis and pancreatic cancer and an affordable solution to detect its concentration could benefit many. Here, the detection is based on thermal Marangoni circulation inside a microfluidic droplet of starch-FeSO 4 salt solution, which detects the a-amylase concentration upon addition of blood serum. It was observed that the temperature difference between the droplet substrate and ambient sets a thermal Marangoni and natural convections motion inside the droplet. The performance of the microdropletbased sensor was best at temperature difference (~18–20°C). The sensor is capable of detecting 20-110 units/liter concentration of α-amylase with ~80% change in the electrical resistance across the microdroplet (at ~40°C substrate temperature), and with a sensitivity of 0.88% (units/liter) -1 . The response of the sensor was also compared with pathological laboratory results and both were found to be in agreement. The presented sensor has the potential to be used as a POC device for detecting α-amylase in real-time.

This paper presents a polymer strain sensor integrated with\ud an NFC tag to detect strain semi-quantitatively. The strain\ud sensor is fabricated using flexible and transparent polymer\ud Polydimethylsiloxane (PDMS) microchannel having\ud conductive polymer poly (3,4-ethylenedioxythiophene)\ud polystyrene sulfonate (PEDOT:PSS) as an active material.\ud The sensor was tested with different bending conditions\ud and it was found that the resistance increases with higher\ud bending. A maximum of 3 order change in resistance was\ud observed for ~100 bending. The sensor was finally tested\ud using a custom-developed passive NFC tag having an LED\ud connected in series with the strain sensor and powered from\ud the reader via the NFC antenna in the tag.

This paper presents poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate polymer microchannel (diameter ≈175 µm) based stretchable strain sensor developed inside polydimethylsiloxane substrate. The microchannel diameter changes when subjected to various strains, leading to change in the resistance of strain sensor. The sensor exhibits about three order (ΔR /R 0 ≈ 1200) increase in the resistance (R ) for 10% applied strain (ΔL /L , L = length of the sensor). This leads to a gauge factor (GF Δ (ΔR /R 0)/(ΔL /L ) of ≈12 000, which is about ≈400 times higher than most of the reported polymer‐based strain sensors. The sensor is evaluated up to a maximum strain of 30%, which is the standard strain limit associated with human body parts such as fingers and wrists. The sensor exhibits a considerably good average degree of hysteresis (

This work was supported in part by the Spanish Research and Development National Program under Project TIN2016-75097P and Project RTI2018-102002-A-I00, in part by "Junta de Andalucia" under Project B-TIC-402-UGR18 and Project P18.RT.4830, and in part by the Predoctoral Grant FPU18/01965., In this brief, we present a low-loss mechanically reconfigurable phase shifter implemented in gap-waveguide technology for mm-wave frequencies. The proposed design gives a practical implementation of tuning elements inside the waveguide providing alternatives to the use of the E-plane split waveguide at high frequencies in order to avoid leakage losses. The depicted phase shifter design is based on a H-plane split waveguide. The phase shift is controlled by means of a tuning screw, which exerts pressure on a flexible metallic strip inserted inside the waveguide. The flexible strip bends with different curvature radii and determines the phase shift at the output port. Cost-effective manufacturing and simple implementation of the flexible metallic strip are achieved by means of the gap-waveguide design. A prototype has been manufactured for validation purposes. Good impedance matching is achieved from 64 GHz to 75 GHz providing a 15.8% impedance bandwidth. The results show a maximum phase shift of 250° with a maximum and mean insertion loss (IL) of 3 dB and 1.7 dB, respectively., Spanish Research and Development National Program TIN2016-75097P RTI2018-102002-A-I00, Junta de Andalucia B-TIC-402-UGR18 P18.RT.4830, FPU18/01965

Thermal sintering has traditionally been the most popular sintering method to enhance conductivity after the printing process in the manufacturing of printed electronics. Nevertheless, in recent years, there has been a growing interest in electrical sintering as an alternative method to overcome some of the limitations of thermal curing. This paper makes a comparative study of both sintering methods in terms of surface morphology, electrical dc conductance, and radiofrequency performance for different applied voltage waveforms. To this end, microstrip transmission lines have been inkjet-printed using nanoparticle-based silver ink on flexible polyimide substrate. The traces have been tested under different sintering conditions, achieving electrical sintering resistivity values only 2.3 times higher than that of bulk silver. This implies a 62% reduction in comparison with the best resistivity value achieved using thermal sintering in our samples. The main novelty of this contribution lies in the analysis of RF behavior as a function of electrical sintering conditions. Lower resistivities have been achieved with slower voltage ramps or allowing higher density current during sintering. It has also been proved that electrically sintered lines have similar RF performance than high-temperature thermally sintered lines in terms of insertion losses, regardless of their very different surface topology. Therefore, we can take advantage of the benefits that electrical sintering offers over thermal sintering regarding significant shorter sintering times maintaining suitable RF performance., This work was supported in part by the Spanish Ministry of Economics and Competitiveness under Grant CTQ2016-78754-C2-1-R.

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 tags with temperature sensing capability, while interdigitated electrode 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; that is, those fitting to human limbs. In the case of the fabricated near field communication tags, a shift in the resonance frequency below 1.7% was found, meaning that the e-textile tag would still be readable by a near field communication-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 40℃. When compared with the 4% variation due to bending, it can be concluded that this capacitive structure can be harnessed as a 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.

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).

The authors would like to acknowledge to the staff of the Hospital Universitario Clínico San Cecilio, Granada, Spain, for their support and use of the facilities. We also thank the reviewers for their useful and constructive comments and suggestions which have improved this paper., Safe quality control of radiotherapy treatments lies in reliable dosimetric sensors. Currently, ionization chambers and solid-state diodes along with electrometers as readout systems are accomplishing this task. In this work, we present a well-known and low-cost semiconductor sensor, the light-dependent resistor (LDR), as an alternative to the existing sensing devices for dosimetry. To demonstrate this, a complete characterization of the response to radiation of commercial LDRs has been conducted in terms of sensitivity, reproducibility and thermal correction under different bias voltages. Irradiation sessions have been applied under the common conditions in radiotherapy treatments using a hospital linear accelerator. Moreover, the same electrometer used for the ionization chamber has also been successfully used for LDRs. In comparison with the sensitivity achieved for the ionization chamber (0.2 nC/cGy at 400 V bias voltage), higher sensitivities have been measured for the proposed LDRs, ranging from 0.24 to 1.04 nC/cGy at bias voltages from 30 to 150 V, with a reproducibility uncertainty among samples of around 10%. In addition, LDR temperature dependence has been properly modeled using the simple thermistor model so that an easy thermal drift correction of dose measurements can be applied. Therefore, experimental results show that LDRs can be a reliable alternative to dosimetric sensors with the advantages of low size, affordable cost and the fact that it could be adopted with minimal changes in routine dosimetry quality control since the same readout system is fully compatible., Junta de Andalucía B-TIC-468-UGR18 PI-0505-2017, European Union (EU)

In this work we present a novel technique to estimate the resonance frequency of LC chipless tags (inductor-capacitor parallel circuit) with improved sensitivity and linearity. The developed reader measures the power consumption of a Colpitts oscillator during a frequency sweep. The readout circuit consists of a Colpitts oscillator with a coil antenna, varactor diodes to change the oscillator frequency, analog circuitry to measure the power consumption and a microcontroller to control the whole system and send the data to a PC via USB. When an LC tag is inductively coupled to the oscillator, without contact, a maximum power peak is found. As shown by an experimental calibration using an LC tag made on FR4 substrate, the frequency of this maximum is related to the resonance frequency. Both parameters, power consumption and resonance frequency, present an excellent linear dependence with a high correlation factor (R 2 = 0.995). Finally, a screen-printed LC tag has been fabricated and used as relative humidity sensor achieving a sensitivity of (−2.41 ± 0.21) kHz/% with an R 2 of 0.946.

This communication presents the design of a two-port electronically tunable phase shifter at K band. The phase shifter consists of a 3 dB hybrid coupler loaded with reflective phase-controllable circuits. The reflective circuits are formed by varactors and non-sequential impedance transformers which increase the operational bandwidth and the provided phase shift. The final phase shifter design is formed by two loaded-coupler stages of phase shifting to guarantee a complete phase turn. An 18 GHz phase shifter design with dynamic range of 600 degrees of phase shift is depicted in this document. The prototype is manufactured and validated through measurements showing good agreement with the simulation results., This work has been partially supported by the TIN2016-75097-P, RTI2018-102002-A-I00, and EQC2018- 004988-P projects of the Spanish National Program of Research, Development, and Innovation and project B-TIC-402-UGR18 of Junta de Andalucía

In this work we describe a passive screen printed flexible tag for gas monitoring that can be used in sealed environments. The developed measurement system is based on chemical sensors that are sensitive to gases concentration presenting optical response, luminescent or colourimetric. The measuring electronics consist of a LED for optical excitation of the sensing membrane and a high resolution digital colour detector for the reading of the optical signal. A microcontroller receives and processes the data enabling the detection threshold for the corresponding gas. The whole system is powered by two miniaturized solar cells that provide 4 V and up to 250 μA each one. This system can run in sunlight or using a bright artificial light as the only energy source. The information of the inner environmental conditions regarding the gas concentration is transmitted to the user through a simple optical code using colour light-emitting diodes. These LEDs are activated to indicate whether the concentration of the monitored gas is within the expected limits, or not. Two prototypes based on this architecture and only changing the sensing module have been developed and applied for the determination of two common gases: oxygen and carbon dioxide. In the first case, a luminescent chemical sensor is used while in the second, the sensing membrane presents a colourimetric response. Both types of sensors can be used in this design. Resulting limits of detection are compatible with assessment of modified atmosphere packaging.

Here, we present a technique for the determination of the gaseous oxygen concentration 2 inside packed food. It is based on the use of a luminescent membrane sensitive to O2 that is optically excited and read by a smartphone. The flash of the smartphone along with an optical filter is used as the light source for the optical stimulation of the membrane. The luminescence generated, which is quenched by the surrounding gaseous oxygen, is registered by the rear camera of the same device. The response parameter is defined by combining the registered intensities at two different wavelength ranges corresponding to the emission and the absorption peaks of the sensitive membrane. Thanks to this novel response parameter, the sensitivity is increased and, more importantly, the thermal dependence of the membrane is significantly reduced. This approach allows the use of a luminescent O2-sensitive membrane for intelligent packaging with no need of any associated electronics for its excitation and reading. This means that an oxygen sensor is developed, where a luminescent compound acts as an indicator, therefore combining the advantages of both schemes, that is, the simplicity and reduced cost of indicators with the high sensitivity and accuracy of selective sensors., This work was supported by the Spanish Ministry of Economics and Competivity through the Project CTQ2016-78754-C2-1-R. The work P. Escobedo Araque was supported by the Spanish Ministry of Education, Culture and Sport under Grant FPU13/05032. The work of I. Pérez de Vargas-Sansalvador was supported in part by the European Union’s Horizon 2020 Research and Innovation Program (Multisens) under Grant 706303, in part by the Talentia Postdoc Program launched by the Andalusian Knowledge Agency, in part by the European Union’s Seventh Framework Program, in part by the Marie Skłodowska-Curie actions (COFUND) under Grant 267226, and in part by the Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía.

Omega (ω) phase is formed in alpha (α) zirconium during dynamic loading and can be retained in the recovered material. The pathway for the α to ω change (or the reverse transformation) is not well understood. Zirconium was shock-loaded and the resulting two-phase microstructure was examined. Electron backscatter diffraction (EBSD) was used to characterize the orientation relationships and habit planes between phases to understand the pathways between α and ω phases and compare to Molecular Dynamics (MD) simulations. Based on key microstructural features, a significant amount of α phase appears to have originated from the reverse transformation from ω-Zr on unloading. Results of microstructural analysis will be discussed, along with implications toward phase transformation pathways.

Materials performance is recognized as being central to many emergent technologies. Future technologies will place increasing demands on materials performance with respect to extremes in stress, strain, temperature, and pressure. In this study, the dynamic ductile damage evolution of OFHC Cu is explored as a test bed to understand the role of spatial effects due to loading profile and defect density. Well-characterized OFHC Cu samples of 30 μm, 60 μm, 100 μm, and 200 μm grain sizes were subjected to plate impact uniaxial strain loading at 1.5 GPa. This spall geometry produced early stage (incipient) damage in the Cu samples that could be correlated to microstructural features in metallographic analysis. The recovered damaged microstructure was examined using traditional 2D metallographic techniques (optical and electron microscopy) as well as 3D x-ray microtomography. Calculated spall strength from the free surface velocimetry (VISAR) showed no change with respect to changes in grain size, however, the magnitude of the peak after the first pull-back as well as rate of reacceleration are dependent on grain size and can be correlated to damage observed in the recovered samples. These results reveal a critical length scale for the transition from a nucleation dominated regime to a growth dominated regime for the damage evolution process. The results show that for samples with small (30 μm) and large (200 μm) grain sizes the growth of voids is dominated by coalescence, whereas for medium (60 μm and 100 μm) grain sizes the growth is restricted to a much slower process of individual void growth. Electron backscatter diffraction reveals that voids preferentially nucleate at grain boundaries with high misorientation angles while special boundaries (low angle Σ1 and high angle Σ3) proved to be resistant to void nucleation. Based on these findings, mechanisms for the void nucleation/growth and coalescence are proposed.

In this paper, we present a passive tag for the determination of gaseous oxygen in intelligent packaging (IP). The power supply for this tag is obtained from thermoelectric energy harvesting taking advantage of the temperature difference between a cooled package and the human body. For this purpose, a compact Peltier module is attached to the surface of the package. This device is able to generate 1.2 mW when a temperature difference of 25 °C is applied between its surfaces. A dc-to-dc boost converter is included to generate an output voltage of 3.3 V and an output current of $225~\mu \text{A}$ from the harvested energy by the Peltier cell, which are used to supply the measurement circuitry. A luminescent membrane sensitive to oxygen is used as a gas detector in the package. The generated signal is compared to a reference value to evaluate if the oxygen concentration inside the package falls below or above a predetermined value. This is shown by turning on a green or a red LED, respectively. The proposed system presents a resolution of 0.02% of the predicted oxygen concentration in the range of interest (0%–5%) and a limit of detection (LOD) of 0.007%, which makes the instrument appropriate to be used in IP and active packaging (AP) technology.