Capacitive Temperature Sensor Research Articles

High-accuracy road surface condition detection through multi-sensor information fusion based on WOA-BP neural network

High-accuracy road surface condition detection is crucial for enhancing traffic safety. However, existing methods struggle to comprehensively cover various road surface conditions, and the detection accuracy still requires improvement. In this study, we propose a novel road surface condition detection system integrating the whale optimization algorithm-enhanced backpropagation neural network (WOA-BP) with multi-sensor data, which significantly improves the detection accuracy. An experimental system was established, and the model's performance was validated through multiple experiments across a temperature range of −30℃ to 50℃. The results demonstrate that, compared to traditional machine learning algorithms such as back propagation neural network (BPNN), support vector machine (SVM), and random forest (RF), the WOA-BP neural network model shows superior performance in terms of detection accuracy and model stability. Specifically, it achieves a maximum accuracy rate of 100 % and an average accuracy rate of 98.8 % for detecting dry, wet, icy, and snowy conditions. By employing the WOA to refine the initial weights and thresholds of the BPNN, the issues of susceptibility to local optima and slow convergence are addressed, thereby enhancing the model's classification performance and robustness. Furthermore, the collaboration between the capacitive measurement-based road condition sensor, temperature sensor, and microwave measurement-based water film thickness sensor further enhances detection accuracy. This research delves into high-accuracy road condition detection technology utilizing the WOA-BP neural network, offering valuable insights for improving traffic safety and developing intelligent transportation systems.

Aerosol jet printed temperature sensors using an environmentally friendly bilayer dielectric

With the rise of the internet of things and applications such as smart packaging, the need for low cost, disposable temperature sensors with minimum environmental impact are critical. In this study, we report fully printed capacitive temperature sensors made from bio-degradable dielectric materials. All layers were aerosol jet printed and the areal capacitance was characterized at several temperatures between room temperature (22 ˚C) and 80 °C. Using a bilayer dielectric structure, a layer of poly (vinyl alcohol) (PVA) was encapsulated with polycaprolactone (PCL) through interfacial crosslinking to protect it against humidity. Various concentrations and layer amounts of PVA were investigated, with the most effective capacitors consisting of a single layer of PVA deposited from a 5.0 mg ml−1 solution followed by a layer of the UV-crosslink-able PCL deposited from 2.0 mg ml−1 solution, achieving a 43 ± 6% increase in areal capacitance at 80 °C when compared to room temperature, measured at a frequency of 501 Hz.

Enhanced Sensitivity in Capacitive Temperature Sensors through Synergistic Relaxor/Antiferroelectric Composites

Enhanced Sensitivity in Capacitive Temperature Sensors through Synergistic Relaxor/Antiferroelectric Composites

On-Line Detection Method and Device for Moisture Content Measurement of Bales in a Square Baler

Aiming to address the problems of low detection accuracy and poor stability due to the weak anti-interference ability of the bridge circuit and operational amplifier circuit, and the influence on the capacitance of the bulk density and temperature of the straw bale, an on-line detection device for the moisture content of straw bales in a square baler was developed based on the capacitance method. The device integrates a capacitance sensor, pressure sensor, and temperature sensor. The optimal structure size of the capacitor plate was determined through the simulation test of the capacitor sensor plate structure. A moisture content monitoring system based on the MATLAB language is built, and the moisture content detection model was constructed based on the backpropagation neural network (BPNN) algorithm. Finally, a test bench for a square baling machine was designed, and a performance verification test of the moisture content detection device was carried out. The simulation results of the capacitor plate show that when the length, width, and spacing of the capacitor plate are 148.6, 47.7, and 5.1 mm, respectively, the detection sensitivity of the capacitor plate is the highest. The modeling results show that the R2, RMSE, and RPD of the BPNN model are 0.986, 0.008998, and 5.99, respectively, with solid data fitting ability and high prediction accuracy. The bench test results show that for the samples having moisture content between 13.1 and 28.04%, the coefficient of determination R2 of the fitting curve between the predicted value of moisture content and the actual value is 0.949. The relative error range of the predicted value of moisture content is −6.51–8.66%, and the absolute error range is −1.63–1.72%. The on-line detection device for moisture content of straw bales has good accuracy and stability.

Effect of Additive Manufacturing on β‐Phase Poly(Vinylidene Fluoride)‐Based Capacitive Temperature Sensors

Additive manufacturing, commonly known as 3D printing, significantly simplifies the manufacturing process for soft electronics. This work demonstrates the feasibility of a fully 3D-printed flexible poly(vinylidene fluoride) (PVdF) capacitive temperature sensor. The sensor is constructed using fused deposition modeling (FDM)-printed PVdF film as the dielectric (thickness ≈180–280 μm) sandwiched between two parallel Direct Ink Writing (DIW) printed silver electrodes (entire device thickness ≈200–380 μm). The motion of the nozzle can facilitate mechanical drawing to the molten PVdF filament, which is a necessary condition to increase the β-phase content (critical for the sensitivity of the sensor). With optimized printing parameters, the highest β-phase content (21.30%) is achieved when printing with a nozzle temperature of 200 °C and a print speed of 70 mm s−1. The research demonstrates the application of the device as a temperature sensor by applying heating-and-cooling cycles from room temperature (25 °C) up to 140 °C while measuring the capacitance as a function of frequency under different temperatures. The sensor exhibits a stable sensitivity of 3 pF °C−1 at 102 Hz and higher frequencies and improved sensitivities at frequencies higher than 102 Hz after dielectric polarization via the corona poling method.

Capacitive Temperature Sensing via Displacement Amplification

We propose the realization of capacitive temperature sensors based on the concept of displacement amplification. Our design features two high coefficient of thermal expansion (CTE) metallic layers separated by a low-CTE dielectric layer; conductive and dielectric layers are then separated by a thin air gap and glued together at a few locations. As the temperature increases, the high-CTE layer tends to expand more than the low-CTE one. Owing to the constraint to planar expansion imposed by the low-CTE layer, this results in large out-of-plane displacements of the high-CTE layer – hence the displacement amplification term. In our case, the high-CTE layer buckles and causes a reduction of the gap between conductive and dielectric layers; in turn, this results in a large change of capacitance. First, we illustrate the concept via numerical simulations. Then, we realize a low-cost prototype of such sensor by using aluminum foil as conductor, paper as dielectric, and by gluing the layers together with cyanoacrylate. Our results demonstrate the potential of this simple design as a route towards efficient and low-cost temperature sensors.

Performance improvement of capacitive liquid crystal temperature sensor by doping γ-Fe2O3 nanoparticles

Temperature measurement and control has an extremely important role in both scientific research and manufacturing. Capacitive liquid crystal (LC) temperature sensors can monitor the temperature using the linear variation of the capacitance of LC cell with temperature, but the sensitivity and other properties need to be improved. In order to improve the performance of capacitive LC temperature sensor, we propose to mix twisted nematic LC (1M10600-100) with ferromagnetic nanoparticles γ-Fe2O3 to prepare LC temperature sensor in this paper. The relationship between the capacitance change rate of different concentrations of nano-doped LC materials at 0.1–20 V and different temperatures was tested, the sensitivity of the sensor was calculated, and the mechanism of the effect of doped nanoparticles on the performance of the device was analyzed. The experimental results show that the sensitivity of the capacitive temperature sensor made of nano-doped LC with the concentration of 0.03 wt% is as high as 9.5 pF/°C at 12 V, which is about 14.87% higher than the undoped device, and its recovery and stability remain almost unchanged. The Pearson correlation coefficient only changes by 0.02%. The results of this paper provide some guidance for the improvement of the performance of capacitive LC temperature sensors, and the development of high-sensitivity temperature sensors based on LC materials.

Effect of Cu2O nano-particles on the temperature sensing and optical switching of poly-(dioctyl-flourene)

This paper reports the effect of Cu2O nanoparticles on the temperature sensing properties and optical switching of Poly-(Dioctylfluorene). A surface type capacitive temperature sensor and optical switch has been fabricated by depositing 720 nm thin layer of F8:Cu2O on pre-patterned silver (Ag) electrodes, using optical lithography and shadow masking followed by vacuum thermal deposition. The effect of temperature on the electrical resistance for sensor and as optical switch by exposing light has been investigated. The sensor responded exponentially with increasing temperature, also exposing to light it work as an optical switch. The on off of this optical switch is will explained by graph. Scanning Electron Microscopy has been employed to study the morphology of F8:Cu2O thin film. These results demonstrated that the temperature sensor and optical switch made of F8:Cu2O have excellent accuracy and performance.

Wireless Passive LC Temperature and Strain Dual-Parameter Sensor.

There is an increasing demand for bearing temperature and strain monitoring in high-speed rotating systems. This study proposes a new multiresonance, multiplexing, wireless, passive inductance capacitance (LC) temperature and strain sensor. The sensor has two capacitors connected at different locations (turns) on the same inductor to achieve simultaneous temperature and strain measurements. The plate capacitor is connected to the inner part of the inductor and the other interdigital capacitor is connected to the outer part of the inductor to form two LC loops. The structure of the sensor is optimized through High Frequency Structure Simulator (HFSS) simulations to realize frequency separation of the two parameters and avoid mutual interference between the two signals. The sensor is fabricated on a polyimide film using electroplating technology. The experimental results show that the temperature–strain sensor can operate stably from 25 °C to 85 °C with an average sensitivity of 27.3 kHz/°C within this temperature range. The sensor can detect strains in the range of 1000–5000 με with a strain sensitivity of 100 Hz/με at 25 °C. Therefore, the proposed wireless passive LC temperature-strain sensor exhibits stable performance. In addition, the use of a single inductor effectively reduces the sensor’s area. The flexible substrate provides advantageous surface conformal attachment characteristics suitable for monitoring high-temperature rotating parts in adverse environments.

A Novel Linear Capacitive Temperature Sensor Using Polydimethylsiloxane

A linear, simple, and reliable capacitive temperature sensor is fabricated with inexpensive materials. The sensor is a parallel plate capacitor, in which the dielectric material polydimethylsiloxne (PDMS) is sensitive to temperature. The sensor works on the principle that the density of sensing layer decreases with an increase in temperature following the Clausius–Mosotti equation, because of which the permittivity also decreases. Moreover, the thickness of the sensing layer also increases with an increase in temperature due to a positive coefficient of linear expansion. The sensor is tested in the range of 20 °C–200 °C and shows a mean sensitivity ( $\mu$ ) of 156 fF/°C with standard deviation ( $\sigma$ )± 0.037 pF. It shows a linear characteristic with the coefficient of correlation ( $R^{2})~0.99$ , and maximum nonlinearity is 1.11% at 10 kHz. The measured resolution of the sensor is 0.08 °C, and the time constant for a unit step input is 0.6 s/°C. The average repeatability index ( $\Re$ ) of the sensor is 0.51% over a month. Finally, an interfacing circuit based on the integrator and instrumentation amplifier is designed, which gives a DC output with a sensitivity of 67.9 mV/°C.

Development of capacitive temperature sensors with high sensitivity using a multiuser polycrystalline silicon process

A MEMS capacitive temperature sensor is presented that displays high sensitivity over a specific temperature range using out-of-plane thermal actuators and capacitive electrodes. The sensor is suitable for applications that require high precision in relatively small temperature range, such as biomedicine, food processing and food safety. The device uses a combination of bilayer, rigid and flexible beams to create a nonlinear capacitance-temperature response over a short temperature range. The bilayer beams act as the out-of-plane thermal actuator and move the top electrode of the sensor up and down to change the capacitance. The capacitance is inversely proportional to the electrodes' gap and a decrease in the gap increases the sensitivity of the capacitance-temperature (C-T) response. Sensors with different geometries have been simulated using ANSYS to show the possibility of geometric modification to shift the temperature range with high sensitivity. Fabricated sensors are used in an experimental set up to demonstrate the applicability of the proposed design concept. The measured data verify the simulation results and demonstrate that the proposed sensor design can provide high sensitivity of 20 fF/°C in a desired range of ambient temperature where low sensitive region display noticeably smaller sensitivity of 5 fF/°C.

Frequency-independent self-powered sensing based on capacitive impedance matching effect of triboelectric nanogenerator

The advance of intelligent Internet of Things (IoT) requires a large number of independent sensors, while the power supply of the sensors has hindered its development. In this work, we present a concept of frequency-independent self-powered sensing technology based on the capacitive impedance matching effect of triboelectric nanogenerator (TENG). When the intrinsic capacitance of the TENG is constant and matched with an external capacitive load, the output voltage is only related to the external capacitive load and not affected by the working frequency of TENG. In a proposed system, the output voltage of a vertical contact-separation TENG distinctly changes from ~140 V to ~5 V only with a load capacitance ranging from 10 pF to 10 nF, while the voltage does not change at different moving frequencies in a wide range. By replacing the external capacitive load with a glycerol-droplet based capacitive temperature sensor, both quantifiable temperature sensing and frequency-independent high temperature alarming system can be realized. Significant progresses in broad selectivity for sensing materials and high reliability under different motion frequencies are present in this self-powered sensing system, revealing the promising application prospects in intelligent wearable sensing electronics.

Very narrow band sensor antenna for accurate data reading

A purely radio-frequency wireless sensor capable of measuring physical parameters with a very low energy consumption is presented. By integrating a capacitive temperature sensor (a change in temperature is traduced by a change in a capacity value) to a very narrowband antenna, the antenna operating frequency band becomes controlled by the surrounding temperature that translates it, depending on its value. By making sure that there is a bijection between the surrounding temperature and the antenna operating band in the considered two ranges, there is no need to use any digital data to wirelessly transmit the information about the temperature. In this case, an important energy consumption reduction could be achieved since the whole wireless sensor would be composed of only a wideband pulse generator and the sensor antenna that selects the band to transmit based on the temperature. To demonstrate the concept, a prototype has been built by modelling the capacitive sensor with a varying capacitance. Both simulated and measured results show a reasonably good agreement which validates the concept.

Passive Wireless Multi-Parameter Sensor System for Hermetic Environment Monitoring

This paper presents a passive wireless multi-parameter sensor system, which is suitable for monitoring the environment in hermetic space like industrial painting room, coal mine, and so on. The system consists of two subsystems: the primary system and the secondary system. The primary system transmits power and receives modulated data through a coupled transformer composed of primary and secondary inductors printed in their subsystems, respectively. The secondary system comprises micro capacitive temperature, pressure and relative humidity sensors and uses a relaxation oscillator to convert capacitance to frequency. Using time division multiplexing unit, it can simultaneously measure multiple sensors. The converted frequency signal is used to vary the amplitude of the waveforms on the coupling inductors. The modulating signal is recovered from the carrier using the envelope detection unit. The measurement results indicate that the pressure, temperature, and relative humidity sensitivities of the passive wireless multi-parameter sensor system are 5.6 fF/hPa, 250fF/°C and 71.4 fF/%RH, respectively. Three sensors linearly response to the change of the environment and the system has good consistency.

A Novel Capacitive Temperature Sensor for Real-Time Monitoring of Temperature in the Silicone Oil Fan Clutch

This paper presents a novel capacitive sensor for real-time monitoring of temperature in the silicone oil fan clutch. The structure of the temperature sensor is designed and fabricated by the Silicon-On-Glass (SOG) process based on the bonding technology. The silicone oil is designed as the temperature sensing materials in the capacitive sensor. The capacitance of the embedded sensor is changing with respect to temperature of the silicone oil fan clutch. Experimental results show that the sensor provides a sensitivity of 27.3fF/°C in the -30 to 40°C range, 58.2fF/°C in the 50 to 110°C rang. It is also demonstrated that the temperature sensitive capacitor can be integrated with a copper inductance antenna and tests as a passive wireless temperature sensor. The resonant frequency of the inductor-capacitor (LC) resonator changes with respect to the changing capacitance. Then temperature changes can be remotely determined towards a frequency spectrum study. Experimental results show that the LC type passive wireless sensor provides a sensitivity of 6.35kHz/°C in the -30 to 110°C range.

Implementation of Multiparameter Monitoring by an <italic>LC</italic>-Type Passive Wireless Sensor Through Specific Winding Stacked Inductors

A traditional LC-type passive wireless sensor has been used for the measurement in sealed environments. Due to the limitation of its operation principle, this method was only suitable for a single parameter monitoring. For most applications, it is desirable for multi-parameters to be monitored. In order to keep the chip area of the sensor as small as possible, multi-level inductors may be coaxially stacked. However, the transmitting signals affect each other due to strong mutual coupling between the stacked inductors. This paper presents a novel inductor structure by using a specific winding to achieve the minimized mutual inductance. Using the partial inductance theory, the mutual inductance of two stacked inductors is analyzed. Simulations of the two stacked inductors coaxially aligned, with each connected in a variable capacitor, show that the mutual inductance between the two inductors can be greatly suppressed. This phenomenon has also been verified through multi-layer PCB inductors. And capacitive temperature and pressure sensors were linked to the two stacked inductor to implement the simultaneous measurements of temperature and pressure. The measurement results indicate that the sensitivity of the temperature sensor is about 41.67 kHz/°C between -20°C to 100°C while the sensitivity of the pressure sensor is about -133.33 kHz/kPa between 50kPa to 110 kPa.

A Wireless Condition Monitoring System Powered by a Sub-100 $\mu$W Vibration Energy Harvester

A wireless sensor network for condition monitoring and its corresponding sensor node powered by a vibration energy harvester producing about 100 μW are presented. The sensor network utilizes an asynchronous beacon-detection based duty cycle control architecture to reduce power consumption and support ID-based TDMA while avoiding the need for timing synchronization between nodes. It also provides FDMA and fixed-time slot TDMA for further network flexibility. The sensor node transceiver includes a duty-cycle timing control unit to minimize power consumption; an LO-less, TDMA-capable, addressable beacon receiver; an FDMA-capable transmitter; and a low-power, universal sensor interface. The proposed sensor node, implemented in 0.13- μm CMOS technology, achieves low power consumption and a high degree of flexibility without requiring calibration or the use of BAW or SAW filters. The sensor node is experimentally demonstrated to operate autonomously from the power provided by a piezoelectric vibration energy harvester with dimensions of 27 × 23 × 6.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> excited by 4.5-m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> acceleration at 40.8 Hz. The WSN condition monitoring behavior is measured with a capacitive temperature sensor, and achieves an effective temperature resolution of 0.36 °C.

Research on Monitoring of Moisture Content in Transformer Oil by Using Sensors

The moisture distribution in the transformer and variation mechanism of moisture in oil is analyzed in this paper, and using relative saturation and temperature as characteristic parameters, a detail scheme of on-line monitoring moisture content in transformer oil is put forward. The polyimide-based capacitive humidity sensor and temperature sensor are employed in on-line monitoring moisture content in oil. Computer is utilized to sample and analyze the data that sensors send out. The experiment on test transformer confirms that the sensors can work reliably, and reflect the moisture content in transformer oil accurately. The method that the paper proposes can realize the purpose of on-line monitoring.

High‐performance bulk silicon interdigital capacitive temperature sensor based on graphene oxide

A high-performance bulk silicon interdigital capacitive temperature sensor based on graphene oxide (GO) is presented. Compared with typical CMOS integrated temperature sensors, the sensitivity of this bulk silicon interdigital capacitive temperature sensor was improved significantly by using GO as sensing material, and this temperature sensor can operate in the range of − 70 to 40°C.

Solar Cell as a Capacitive Temperature Sensor

Spacecrafts in geostationary Earth orbit and low Earth polar orbit experience temperatures in the range of 180°C to 80°C [1, 2] depending on the orbit. Solar cells are mounted on light weight aluminum honeycomb panels which are deployed and Sun pointed in on-orbit operation. Solar panels charge batteries and supply power to the satellite during sunlit period and batteries supply power during eclipse period. The open circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) of a silicon solar cell varies by about -2.5 mV/°C [3] and temperature can bring about a dramatic change in the solar cell characteristic, particularly with reference to operating voltage. PRT mounted on the rare of the solar panel measure the temperature of the solar panel. This introduces errors due to temperature gradients between solar cell blanket and solar panel and slow transient response of PRTs. A method of using solar cell capacitance to measure the temperature of solar cell blanket is proposed. This removes error due to location and transient response of PRT. Solar cell as a temperature sensor for measurement of temperature is demonstrated.