Seamless Monolithic Design for Foam Based, Flexible, Parallel Plate Capacitive Sensors

Comparative investigation of interdigitated and parallel-plate capacitive gas sensors based on Cu-BTC nanoparticles for selective detection of polar and apolar VOCs indoors

The parallel plate capacitive humidity sensor based on the grid upper electrode is considered to be a promising one in some fields which require a humidity sensor with better dynamic characteristics. To strengthen the structure and balance the electric charge of the grid upper electrode, a strip is needed. However, it is the strip that keeps the dynamic characteristics of the sensor from being further improved. The numerical method is time- and cost-saving, but the numerical study on the response time of the sensor is just of bits and pieces. The numerical models presented by these studies did not consider the porosity effect of the polymer film on the dynamic characteristics. To overcome the defect of the grid upper electrode, a new structure of the upper electrode is provided by this paper first, and then a model considering the porosity effects of the polymer film on the dynamic characteristics is presented and validated. Finally, with the help of software FLUENT, parameter effects on the response time of the humidity sensor based on the microhole upper electrode are studied by the numerical method. The numerical results show that the response time of the microhole upper electrode sensor is 86% better than that of the grid upper electrode sensor, the response time of humidity sensor can be improved by reducing the hole spacing, increasing the aperture, reducing film thickness, and reasonably enlarging the porosity of the film.

A new parallel plate capacitance sensor was built consisting of two metal sheets. The sensor – a capacitor and the whole oscillating circuit was driven at 27 MHz frequency. Dynamic laboratory experiments were performed with grass from a natural meadow in order to evaluate the possibility of the forage mass flow determination by means of this sensor. The results revealed a relatively strong linear relationship between the feed rates of the wet forage crop material passing through the sensor between its plates and the measured capacitance sensor circuit output frequency. The coefficients of determination (R<sup>2</sup>) varied from 0.9 to 0.96. Further improvement of the electronic circuit connection and further investigation of the sensor can be recommended.

The paper presents analytical modelling and Finite Element Method (FEM) based simulation of clamped circular capacitive pressure sensors for Intraocular Pressure (IOP) measurement. The parallel plate capacitive pressure sensor consists of a fixed backplate and a circular shaped clamped thin diaphragm made of silicon material. The plates are separated by a vacuum media. MATLAB® and COVENTORWARE® are used for analytical and FEM simulations, respectively, and a comparison of maximum deflection in the diaphragm, capacitance after pressure application and sensitivity is carried out. A pressure range of 0-60 mmHg is used for IOP measurement.

The aim of our work was to establish whether very good to excellent UV (ultraviolet) protective properties of fabrics can be obtained through a suitable fabric construction and yarn colour, at the same time ensuring suitable air permeability. For this purpose, six different fabric structures divided into three groups were employed. The samples were made in blue and red combinations of weft with different sequences and proportions between the upper and lower weave threads. A comparison of different fabric structures and colours was attempted to enable the assessment of the impact of the mentioned parameters on both, UV protective properties and air permeability of fabrics. The analysis comprised the investigation of physical and permeability properties, as well as the colour measurements on twelve different cotton fabrics. The research indicated excellent UV protection (>60) in all samples. UV protection depended on their construction and in a sufficiently closed structure, also on the colour of the used yarn. There was no significant difference between the samples in blue and red. In addition to excellent UV protection, four samples (one double-weft and three double fabrics) also demonstrated very high air permeability, which was 3–5 times higher than in the one-layer sample, which demonstrated the best UV protective properties. The research has shown that fabrics with a very high ultraviolet protective factor value and good air permeability can be made by using a suitable construction and yarn colours that sufficiently absorb UV light; the latter being particularly important for light summer cotton clothes.

Micromachined sensor structures with linear capacitive response

This study describes a low‐cost sensor‐based scheme for online moisture measurement in transformer oil. Considering a harsh environment, moisture measurement of oil at ppm level is challenging, so the sensor should be highly sensitive and thermally and chemically stable. The conventional methods are mostly offline, have long test times and are costly. A thin‐film parallel plate capacitive moisture sensor has been fabricated using inexpensive materials to measure the moisture of fresh, aged and 0.5% water content oil samples. The moisture sensing film is highly hydrophilic and is made of alumina oxide, a very stable material. Experiments were conducted to determine the response parameters of the sensor in the presence of moist nitrogen gas, the concentration of which was measured by a commercial SHAW dew point meter. Experiments were also performed to measure the moisture of different oil samples in the laboratory. Results show that the output of the sensor is sensitive (6 pF/ppm moisture), has negligible hysteresis (∼1% at 1 kHz) and has fast response and recovery times ( T res = 70 s, T rec = 170 s).

Biomimetic-inspired highly sensitive flexible capacitive pressure sensor with high-aspect-ratio microstructures

Capacitive sensors are used in products and systems in which stability, low power consumption and the ability to calibrate without removing it from the product are the main parameters. These areas and areas include the missile, aviation and nuclear industries. Low power consumption and the ability to manufacture capacitive sensors using thin-film technology, which sharply reduces their dimensions, is a promising direction for unmanned samples. Stable operation of capacitive thin-film sensors requires thorough preparation of working surfaces and proven technologies for applying composite coatings. It is very important when assembling and adjusting the absence of distortion and displacement of the topology on the moving and stationary electrodes of the sensors. This makes it possible to significantly reduce errors due to the influence of non-parallelism of the electrodes in the sensor. In addition, the developed designs and models allow significant movement of the movable electrode without increasing the measurement error. And this is important for capacitive sensors designed to measure low pressures.

Novel planar sensor using stretchable vapor phased polymerized PEDOT/PDMS film

To clarify differences in air permeability of the hose cloth of different types of pantyhose on the market in Japan, cylindrical model experiments and wearing experiments were conducted. The former was made to determine fundamental performance of the air permeability, and the latter, to evaluate the practical performance of worn pantyhose. Zokki, kohhen, sheer, wooly, and conjugate types of pantyhose were used as samples. There were large differences in air permeability among these fabrics when elongation was low or moderate. In around the maximum elongation state, almost the same high air permeability was shown regardless of pantyhose types. There were some pantyhose with lower air permeability while being worn, or other ones which have higher air permeability, regardless of posture, body shape, and sites of legs.

To address the resource-competing issue between high sensitivity and wide working range for a stand-alone sensor, development of capacitive sensors with an adjustable gap between two electrodes has been of growing interest. While several approaches have been developed to fabricate tunable capacitive sensors, it remains challenging to achieve, simultaneously, a broad range of tunable sensitivity and working range in a single device. In this work, a 3D capacitive sensor with a seesaw-like shape is designed and fabricated by the controlled compressive buckling assembly, which leverages the mechanically tunable configuration to achieve high-precision force sensing (resolution ~5.22 nN) and unprecedented adjustment range (by ~33 times) of sensitivity. The mechanical tests under different loading conditions demonstrate the stability and reliability of capacitive sensors. Incorporation of an asymmetric seesaw-like structure design in the capacitive sensor allows the acceleration measurement with a tunable sensitivity. These results suggest simple and low-cost routes to high-performance, tunable 3D capacitive sensors, with diverse potential applications in wearable electronics and biomedical devices.

This paper put forward the design and modeling pertaining to a wireless pressure sensor that can monitor blood pressure within the coronary artery with the help of a capacitive pressure sensor. To adjust the resonance frequency (26.78–27.09 MHz) with regards to this sensor’s applied pressure (0–30 KPa), sensor’s dimension as well as human blood pressure (0–220 mmHg), a variable capacitor in the pressure sensor has been put forward. The shape of the capacitive pressure sensor was designed to look like an Ellipse and a circle, which were assessed for their performance with regards to capacitive sensitivity and diaphragm deflection. Also, the diaphragm thickness pertaining to the capacitive pressure sensor with Ellipse and circular shapes was altered (0.1μm to 0.5μm) while the cross-section area was kept constant at 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . As per the results, an invasive sensor with circular and Ellipse capacitive pressure shape that had smaller size (1) mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> displayed high sensitivity. The sensitivity readings for Ellipse and circular shape capacitive pressure sensor were 7.73 ff mmHg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 9.94 ff mmHg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. Diaphragm deflection was simulated based on the COMSOL Multiphysics software, while MATLAB was employed for simulation with regards to changes in resonance frequency, capacitance, and capacitive sensitivity.

This paper describes initial development and testing of a novel high temperature capacitive pressure sensor system. The pressure sensor system consists of two 4H-SiC 11-stage ring oscillators and a SiCN capacitive pressure sensor. One oscillator has the capacitive pressure sensor fixed at one node in its feedback loop and varies as a function of pressure and temperature while the other provides a pressure-independent reference frequency which can be used to temperature compensate the output of the first oscillator. A two-day repeatability test was performed up to 500C on the oscillators and the oscillator fundamental frequency changed by only 1. The SiCN capacitive pressure sensor was characterized at room temperature from 0 to 300 psi. The sensor had an initial capacitance of 3.76 pF at 0 psi and 1.75 pF at 300 psi corresponding to a 54 change in capacitance. The integrated pressure sensor system was characterized from 0 to 300 psi in steps of 50 psi over a temperature range of 25 to 500C. The pressure sensor system sensitivity was 0.113 kHzpsi at 25C and 0.026 kHzpsi at 500C.

Measurement of moisture at ppm or ppb level is very difficult and the fabrication of such sensors at low cost is always challenging. High sensitivity is an important parameter for trace level (ppm) humidity sensors. Anelectronic detection circuit for interfacing the humidity sensor with high sensitivity requires a simple hardware circuit with few active devices. The recent trends for increasing the sensitivity include fabricating nanoporous film with a very large surface area. In the present work, the sensitivity of a parallel plate capacitive type sensor with metal oxide sensing film has been significantly improved with an aim to detect moisture from 3 to 100 ppm in the industrial process gases used to fabricate semiconductors and other sensitive electronic devices. The sensitivity has been increased by (i) fabricating a nanoporous film of aluminum oxide using the sol-gel method and (ii) increasing the cross-sectional area of a parallel plate capacitor. A novel double sided capacitive structure has been proposed where two capacitors have been fabricated—one on the top and one on the bottom side of a flat alumina substrate—and then the capacitors are connected in parallel. The structure has twice the sensitivity of a single sensor in the same ppm range but the size of the structure remains unchanged. The important characteristics of the sensors such as the sensitivity (S = Δ C Δ p p m × 100 ), the response time (tr), and the recovery time (tc) are determined and compared with a commercial SHAW, UKdew point meter. The fabricated double sided sensor has comparable sensitivity (S = 100%, tr (s) = 28, tc (s) = 40) with the commercial meter (S = 100.5%, tr (s) = 258) but has a faster response time. The proposed method of sensitivity enhancement is simple, and mass producible.