Resistive Sensor Applications Research Articles

Sustainable antibacterial collagen composites with silver nanowires for resistive pressure sensor applications

Considering the circular economy and the increasing need of smart materials for the digitalization of society, it is essential that these materials are based on bio-resources. Thus, in order to replace synthetic by natural polymers in multifunctional composites, this work reports on the development of collagen/silver nanowires (Ag NWs) composites for resistive sensor applications. It is demonstrated the physical interactions of hydroxyl groups in collagen with the Ag NWs and that the Ag NWs are well dispersed within the collagen matrix. Further, the addition of Ag NWs to the collagen matrix increases the thermal stability of collagen and the Ag NW content does not affect the triple helix structure of the polymer matrix. The mechanical, electrical and antibacterial properties depend on Ag NW content and the best electric conductivity of 0.0515 S cm−1 is obtained for composites with 6 wt% of Ag NWs. This composite presents suitable resistance variations under pressure and bending allowing the development of sustainable multifunctional sensing composites with antibacterial activity that can be applied in next generation touch sensing electronic devices.

A Modified Impedance-Frequency Converter for Inexpensive Inductive and Resistive Sensor Applications.

In this paper an exceptionally simple transducer is presented that is developed for experimental and custom-made sensors with inductive or resistive impedance output. It is based on a venerable 555 Integrated Circuit in a modified astable configuration. Due to single supply 5 V operation, it is directly compatible with most modern microcontroller systems, such as the popular Arduino platform. Various exemplary sensor characteristics are presented, including displacement, force, magnetic field, temperature and light sensing applications. While the transducer is not designed for high accuracy, it allows for fast and inexpensive application of various experimental sensors, such as magnetoelastic or GMI (Giant Magneto Impedance) sensors.

Tuning electrical resistivity anisotropy of ZnO thin films for resistive sensor applications

This work reports on the preparation and characterization of Zinc Oxide (ZnO) thin films, exploring their anisotropic electrical resistivity behaviour evolution as a function of the different preparation conditions. Results show that by increasing the oxygen content in the work gas flow, the electrical resistivity increases from about 2.4 × 10−2 Ω·cm (common in fairly conductive-like materials) to values in order of MΩ·cm, which is typical of materials that vary from semiconducting to roughly insulating type. Regarding the thin films structural behaviour, a relatively clear evolution of the preferential growth becomes clear when preparing the films within the three different regimes. The X-ray diffraction (XRD) patterns revealed the development of a polycrystalline hexagonal-like structure, confirmed by the presence of dominant and very intense ZnO (002) and ZnO (101) diffraction peaks. A change in preferential growth was noticed with the change in the preparation conditions.By in-air annealing the samples from room temperature (RT) up to 200 °C and cooling down to RT again, the differences between the resistivity values along the xx and yy directions become significant, a clear sign of the anisotropic nature of the films. The anisotropy obtained during the annealing cycles of the films increased from 0.98 to 1.10 and, consequently, the Temperature Coefficient of Resistance, TCR, increased in both xx and yy directions, from TCRxx and yy ~9.0 × 10−4 to TCRxx = 6.82 × 10−3 and TCRyy = 5.97 × 10−3 °C−1. Important also to note is that the increase of the grain size of the films showed to have a significant effect in the effective anisotropy, revealing to be a major factor to take into account.

Low power, area efficient, and temperature-variation tolerant bidirectional current source for sensor applications

This paper presents a novel temperature invariant, low power, and area efficient bidirectional current source. The current source can be used as an analog front end R–V converter for different types of resistive sensor applications. The current source is based on weighted sum of thermal voltages and difference of threshold voltages. High VTH transistors operating in sub-threshold region along with regular VTH transistors in strong inversion region form a temperature invariant current source. A current switching technique is presented in this paper for producing a periodic bidirectional current source, fabricated in 180nm CMOS technology for low cost sensor applications. The maximum total current variation simulated is 13nA (±0.5%) for typical value of ±715nA reference current over the temperature range of 25–125°C. The fabricated test circuit lies in SNFP corner and shows ±1% variation in positive and ±1.67% variation over the temperature range of 25–125°C. Total area consumed by the circuit is 100µm×35µm. The behavior of the bidirectional current source has been tested using a piezo-resistive cantilever based explosive detector sensor, with 20ppb TNT vapor concentration and 10 parts per billion resolutions with sensitivity of 10µV/ppb.

A new 0.35 μm CMOS electronic interface for wide range floating capacitive and grounded/floating resistive sensor applications

In this paper we propose a novel interface circuit suitable for the read-out of both wide range floating capacitive and grounded/floating resistive sensors. This solution, employing only two Operational Amplifiers (OAs) as active blocks and some passive components, is based on a square-wave oscillating circuit topology which, instead of a voltage integration typically performed by other solutions in the literature, operates a voltage differentiation. Therefore, the proposed circuit, performing an impedance-to-period (Z–T) conversion, results to be suitable as first analog front-end for both wide variation capacitive (e.g., relative humidity) and resistive (e.g., gas) sensors. Its sensitivity and dynamic range can be easily set through external passive components. Preliminary experimental measurements, which have characterized and validated this solution, have been conducted through a suitable prototype PCB fabricated with discrete commercial components. Then, the proposed interface has been also designed at transistor level, in a standard CMOS technology (AMS 0.35um), developing a single-chip integrated circuit with low-voltage (1.8V, single supply) low-power (about 350μW) characteristics in a very small silicon area (lower than 0.6mm2) which results to be suitable for sensor array configurations and portable applications. Further experimental results, achieved utilizing commercial sample resistors and capacitors to emulate sensor behavior, have shown a linear trend and a satisfactory accuracy in the evaluation of floating capacitive (in the range 10pF–1μF), grounded resistive (in the range 150kΩ–1.5MΩ) and floating resistive (in the range 10MΩ–1GΩ) variations, also when compared to other solutions presented in the literature. The satisfactory interface behavior has been also confirmed by the measurement of both relative humidity through the commercial sensor Honeywell HCH-1000 (capacitive) and carbon monoxide CO through the commercial air quality sensor FIGARO TGS-2600 (resistive).

A 1.2-V CMOS $RC$ Oscillator for Capacitive and Resistive Sensor Applications

An accurate self-adjusting CMOS RC oscillator for capacitive and resistive sensor applications has been designed and manufactured. The oscillator operates with supply voltages from 1.2 to 3 V and achieves an internal accuracy of plusmn0.7% with a temperature range from -20degC to 60degC. The RC oscillator was fabricated in a 0.35-mum standard n-well CMOS process with threshold voltages of 0.5 and -0.65 V. Its design and operation are described, and results of measurements performed on the fabricated chips are presented.