Touch Mode Capacitive Pressure Sensor Research Articles

An Improved Theory for Designing and Numerically Calibrating Circular Touch Mode Capacitive Pressure Sensors

The design, especially the numerical calibration, of a circular touch mode capacitive pressure sensor is highly dependent on the accuracy of the analytical solution of the contact problem between the circular conductive membrane and the rigid plate of the sensor. In this paper, the plate/membrane contact problem is reformulated using a more accurate in-plane equilibrium equation, and a new and more accurate analytical solution is presented. On this basis, the design and numerical calibration theory for circular touch mode capacitive pressure sensors has been greatly improved and perfected. The analytical relationships of pressure and capacitance are numerically calculated using the new and previous analytical solutions, and the gradually increasing difference between the two numerical calculation results with the gradual increase in the applied pressure is graphically shown. How to use analytical solutions and analytical relationships to design and numerically calibrate a circular touch mode capacitive pressure sensor with a specified pressure detecting range is illustrated in detail. The effect of changing design parameters on capacitance–pressure analytical relationships is comprehensively investigated; thus, the direction of changing design parameters to meet the required or desired range of pressure or capacitance is clarified.

Design and Simulation of PDMS and PMMA Based Touch Mode Capacitive Pressure Sensor: A Comparative Study

Aims: In this research work, a design method and a comparative of a touch mode capacitive pressure sensor (TMCPS) using poly-dimethyl-siloxane (PDMS) and poly-methyl methacrylate (PMMA) is the done. A novel method is proposed to linear the output characteristics of the sensor because planer type capacitive sensors are non-linear.
 Study Design: This method uses a mechanical coupler to convert the deflection of the diaphragm into a linear displacement that helps to linear the output characteristics. The mathematical model of the sensor is designed and simulated the 3D model to validate the mathematically calculated values.
 Place and Duration of Study: This study is done in the Department of Electronics and Communication Engineering, Rajiv Gandhi University, Arunachal Pradesh at COMSOL Simulation Laboratory during 2021 to 2023.
 Methodology: The mechanical and electrostatic components of the sensor are represented mathematically model in two separate parts. For this study, a square diaphragm was used since it exhibits greater deflection than circular or rectangular diaphragms. In order to validate the model equation, a 3D model of a sensor is created in the COMSOL Multiphysics simulator and simulated. For the pressure range of 0.1 [MPa] to 10.1 [MPa], the identical 3D model of the sensor construction with a square diaphragm thickness of 20 µm is simulated for PDMS and PMMA. The different elements influencing the sensor's sensitivity are discovered, and the effects of the materials PDMS and PMMA on the output characteristic are discussed.
 Results: The simulated and calculated sensitivity of the sensors based on PDMS are 0.03685 [fF/MPa] and 0.03467 [fF/MPa] respectively. And the simulated and calculated sensitivity of the sensors based on PMMA are 0.03929 [fF/MPa] and 0.03748 [fF/MPa] respectively. It is observed that the PDMS based TMCPS has more sensitivity then the PMMA based TMCPS.
 Conclusion: The PMMA based TMCPS has higher sensitivity than the PDMS based TMCPS. The various parameters that affect the sensitivity of the sensor are diaphragm shape, size, Poisson’s ratio and Young’s modulus, area covered by the dielectric material, dielectric constant of the polymers dielectric and surface are of the electrode plate.
 Future Scope: Future research for TMCPS can be conducted using composite polymer dielectric materials and new polymer dielectric materials to improve the sensitivity. One can optimize the sensor using different tools as the mathematical model is developed.

A sensitivity enhanced touch mode capacitive pressure sensor with double cavities

A sensitivity enhanced touch mode capacitive pressure sensor with double cavities

Design and Analysis of a Novel MEMS Touch Mode Convex Capacitive Pressure Sensor for Altimeter Applications

The wide applications of Touch Mode Capacitive Pressure Sensors (TMCPS) have led the researchers working more on its performances. TMCPS have more acceptance due to their linearity, sensitivity, and ability to withstand more pressure which make them suitable for harsh environments. This study proposes a novel convex shape substrate to further improve the response of the TMCPS. This work provides a detailed mathematical and analytical modeling which upholds the proposed design. The analysis is compared with the simulation results from the software MATLAB. The simulated results have been compared with those reported in the existing literature. The linear operation range of the sensor is stretched more on the lower side (88[Formula: see text]KPa–2[Formula: see text]MPa) and the sensitivity is improved 2.85 times in touch mode, which completely fits in for the altimeter applications. This work also includes a detailed step-by-step process to be followed during the fabrication of the sensor. Sensor system characteristics such as nonlinearity, hysteresis and temperature dependence are also calculated in this work. The presented theory and simulation analysis fully supports the superior performance of the novel convex substrate square diaphragm TMCPS.

Sensitivity Enhanced Touch-mode Capacitive Pressure Sensor with Double-cavity

Capacitive pressure sensors that consume less power with less temperature sensitivity have undergone many design modifications, in order to improve the performance for meeting the application needs of various fields. In this paper, the sensitivity of micro-pressure capacitive sensor is improved by adding a novel double-cavity structure and a gas hole. The double-cavity feature can amplify the amplitude of the upper diaphragm, and the gas hole can alleviate the repulsive effect of the gas pressure in the chamber on the diaphragm bending deflection. This paper provides an in-depth theoretical analysis model for the designed sensor structure using Finite Element Method Simulations. The simulated results indicate a significant enhancement in linearity range and capacitance in comparison with traditional structure. Besides, the sensor shows an enhanced sensitivity of about 1.83 times when the volume ratio of the upper cavity to the lower is 4:1, compared to the sensor having two cavities with the same volume. It is expected to realize the micro-pressure detection technology, which integrates the characteristics of high sensitivity, large linearity range, and anti-overload technology.

Understanding Influence of Substrate Floor Concavity on Sensitivity and Linearity Through a Parabolic Model: Theoretical Modeling and Analysis of Performance

These microelectromechanical system (MEMS)-based touch mode capacitive pressure sensors (TMCPSs) are popular because of their linear sensor output and mechanical robustness. In this work, we propose a parabolic well substrate TMCPS with a circular diaphragm. The proposed design is modeled mathematically, analyzed, and simulated using MATLAB. The diaphragm of the sensor is modeled using a small deflection model. The sensor is intended to operate until a pressure of 2 MPa. The analysis and simulations indicate an improvement in linearity and sensitivity of the sensor output in the touch mode of operation. The analysis and modeling of the proposed design will be useful for designing TMCPS for performance improvement and understanding its behavior. An analysis of the influence of the sensor substrate’s concavity on the sensitivity and linearity of the sensor’s output is discussed in this work.

Capacitance Response of Concave Well Substrate MEMS Double Touch Mode Capacitive Pressure Sensor: Robust Design, Theoretical Modeling, Numerical Simulation and Performance Comparison

Touch Mode Capacitive Pressure Sensor (TMCPS) is very suitable for industrial applications where pressure sensing is necessary because of their linearity, mechanical robust nature and large overload protection from harsh industrial condition. This work proposes an introduction of a notch in the concave substrate for further improvement of the sensitivity of the sensor. Small deflection mode is utilized for the mathematical analysis of the design proposed and MATLAB is utilized for all the software simulations. The sensitivity of the proposed model is very high compared to other models with flat substrate. The analysis and simulation show significant increase in sensitivity in touch mode. The pressure at which the value of the capacitance saturates is also much higher than other proposed designs. The analysis of concave substrate Double Touch Mode Capacitive Pressure Sensor (DTMCPS) will helpful in designing new sensor for performance increase and evaluate the behaviour of it.

Capacitance response of concave well substrate touch-mode capacitive pressure sensor: Mathematical analysis and simulation

Touch mode capacitive pressure sensor (TMCPS) is focused due to its advantages of good linearity, mechanical robust and large overload protection for harsh industrial environment. This paper proposes a concave well-shaped substrate bottom electrode for further improvement of capacitance response of TMCPS. Small deflection model is utilized for mathematical analysis of proposed design and ANSYS and MATLAB software are utilized for simulation. The simulation result is compared with analysis and the excellent agreements predict the accuracy of analytical modeling. The sensitivity of proposed TMCPS is increased as 1.36 times as in operating pressure range from 0.25 to 2 ​MPa and the linear region of it is expanded as 2.60 times as the normal (flat substrate) one in touch mode, respectively. The analysis and simulation results indicate a significant improvement of sensitivity and linearity in touch mode. The analytical modeling and overall results will be helpful to design TMCPS for performance improvement and predict the behavior of it.

Design of a Fully Integrated Inductive Coupling System: A Discrete Approach Towards Sensing Ventricular Pressure.

In this paper, an alternative strategy for the design of a bidirectional inductive power transfer (IPT) module, intended for the continuous monitoring of cardiac pressure, is presented. This new integrated implantable medical device (IMD) was designed including a precise ventricular pressure sensor, where the available implanting room is restricted to a 1.8 × 1.8 cm2 area. This work considers a robust magnetic coupling between an external reading coil and the implantable module: a three-dimensional inductor and a touch mode capacitive pressure sensor (TMCPS) set. In this approach, the coupling modules were modelled as RCL circuits tuned at a 13.56 MHz frequency. The analytical design was validated by means of Comsol Multiphysics, CoventorWare, and ANSYS HFSS software tools. A power transmission efficiency (PTE) of 94% was achieved through a 3.5 cm-thick biological tissue, based on high magnitudes for the inductance (L) and quality factor (Q) components. A specific absorption rate (SAR) of less than 1.6 W/Kg was attained, which suggests that this IPT system can be implemented in a safe way, according to IEEE C95.1 safety guidelines. The set of inductor and capacitor integrated arrays were designed over a very thin polyimide film, where the 3D coil was 18 mm in diameter and approximately 50% reduced in size, considering any conventional counterpart. Finally, this new approach for the IMD was under development using low-cost thin film manufacturing technologies for flexible electronics. Meanwhile, as an alternative test, this novel system was fabricated using a discrete printed circuit board (PCB) approach, where preliminary electromagnetic characterization demonstrates the viability of this bidirectional IPT design.

Investigation of Ring Touch Mode Capacitive Pressure Sensor With an Electrothermomechanical Coupling Contact Model

Ring touch mode capacitive pressure sensor, characterized by ring stopper and stepped circular diaphragm, is developed to eliminate or greatly alleviate some disadvantages existing in conventional or small-area touch mode capacitive pressure sensor. An electrothermomechanical coupling model is developed to calculate the deformation, stress and so on of the diaphragm, and it is universally available for different touch modes and non-touch mode. The model is with rapid calculation speed and it is verified by a combination of the finite element method (FEM) and boundary element method (BEM). Benefiting from the high calculation speed of the model, optimization designs of the sensor are carried out. By adjusting the height dimensions or radial dimensions, high sensitivity and strength can be achieved by such a sensor in different pressure ranges of interest without changing its planar package size and masks, or achieved in a very wide pressure range by an array composed of such sensors with a same set of process parameters of each sensor. On the other hand, optimal ratios of height dimensions or radial dimensions are acquired, which can suppress significantly the temperature’s influence on sensor operation, and furthermore, the optimal ratios are advisable for different pressure ranges and different material parameters of the sensor.

Design and Simulation of an Integrated Wireless Capacitive Sensors Array for Measuring Ventricular Pressure.

This paper reports the novel design of a touch mode capacitive pressure sensor (TMCPS) system with a wireless approach for a full-range continuous monitoring of ventricular pressure. The system consists of two modules: an implantable set and an external reading device. The implantable set, restricted to a 2 × 2 cm2 area, consists of a TMCPS array connected with a dual-layer coil, for making a reliable resonant circuit for communication with the external device. The capacitive array is modelled considering the small deflection regime for achieving a dynamic and full 5–300 mmHg pressure range. In this design, the two inductive-coupled modules are calculated considering proper electromagnetic alignment, based on two planar coils and considering the following: 13.56 MHz frequency to avoid tissue damage and three types of biological tissue as core (skin, fat and muscle). The system was validated with the Comsol Multiphysics and CoventorWare softwares; showing a 90% power transmission efficiency at a 3.5 cm distance between coils. The implantable module includes aluminum- and polyimide-based devices, which allows ergonomic, robust, reproducible, and technologically feasible integrated sensors. In addition, the module shows a simplified and low cost design approach based on PolyMEMS INAOE® technology, featured by low-temperature processing.

Novel design for performance enhancement of a touch-mode capacitive pressure sensor: theoretical modeling and numerical simulation

Capacitive pressure sensors have undergone a multitude of design modifications to improve their performance for various applications. This paper aims to add a novel feature to increase the capacitance generated by using a convex dome-shaped substrate electrode. The paper provides in-depth mathematical and analytical modeling that supports the proposed design. The results indicate a significant improvement in capacitance, touch-mode range, and linearity for the touch-mode capacitive pressure sensor.

Comprehensive assessment of MEMS double touch mode capacitive pressure sensor on utilization of SiC film as primary sensing element: Mathematical modelling and numerical simulation

Capacitive Pressure Sensors have consistently been an indispensable application of MEMS (Micro Electro Mechanical Systems) because of their utility and precision. Silicon has proven to be a dominant material in MEMS based sensor design but it is unfit for applications operating in harsh environmental conditions. Silicon Carbide is a justified replacement to Silicon in these conditions due to its solitary attribute of robustness and high temperature tolerance. This work introduces a Silicon Carbide and Aluminum Nitride based DTMCPS (Double Touch Mode Capacitive Pressure Sensor) with a substrate notch. Condensed yet exhaustive step by step mathematics of key performance parameters have been detailed for the sensor under study. This is done to provide a detailed understanding of the underlying physical and mathematical principles. It also aims to provide a fast analysis model for prototyping the sensor to bypass the need for bulky simulation software. A Finite Element Analysis (FEM) analysis for the design was conducted using COMSOL and the results agree with the mathematical model. It is evident from numerical simulation and the FEM analysis that the proposed sensor provides better performance than comparable designs reported in literature.

Touch-mode capacitive pressure sensor with graphene-polymer heterostructure membrane

We describe the fabrication and characterisation of a touch-mode capacitive pressure sensor (TMCPS) with a robust design that comprises a graphene-polymer heterostructure film, laminated onto the silicon dioxide surface of a silicon wafer, incorporating a SU-8 spacer grid structure. The spacer grid structure allows the flexible graphene-polymer film to be partially suspended above the substrate, such that a pressure on the membrane results in a reproducible deflection, even after exposing the membrane to pressures over 10 times the operating range. Sensors show reproducible pressure transduction in water submersion at varying depths under static and dynamic loading. The measured capacitance change in response to pressure is in good agreement with an analytical model of clamped plates in touch mode. The device shows a pressure sensitivity of 27.1 0.5 fF Pa−1 over a pressure range of 0.5 kPa–8.5 kPa. In addition, we demonstrate the operation of this device as a force-touch sensor in air.

Investigation of the influence of double-sided diaphragm on performance of capacitance and sensitivity of touch mode capacitive pressure sensor: numerical modeling and simulation forecasting

Microelectromechanical system-based capacitive pressure sensors have seen significant advancements in modeling and design. This paper provides a complete analysis of a novel improvement to existing models of the touch mode capacitive pressure sensor. An in-depth, step-by-step derivation of the capacitance, capacitive sensitivity and mechanical sensitivity is examined for the double-sided touch mode capacitive pressure sensor. The results generated are modeled and examined using MATLAB. Comparisons with previous models clearly delineate the improved performance in terms of capacitance and sensitivity. The analysis conducted dovetail perfectly with the modeled results.

A simple analysis to improve linearity of touch mode capacitive pressure sensor by modifying shape of fixed electrode

In this paper, we simply analyze the change of touched area between the square diaphragm and the fixed bottom electrode of the touch mode capacitive pressure sensor. The virtual radius model of the circular diaphragm is utilized for the analytical analysis. A formula is derived to modify the fixed electrode shape for improvement of linearity based on the analysis. Finite element analysis (FEA) is used for simulation by software ANSYS and the accuracy of the analytical analysis is investigated. Simulation results of the proposed model show good agreement to the analytical analysis. In the model with modified electrode, the linearity is more improved than the typical one, while sensitivity is decreased. The analysis results suggest that the analytical model can be used to design fixed bottom electrode of touch mode sensor.

Hermetic capacitive pressure sensors for biomedical applications

Purpose This paper aims to purpose the new design and fabrication scheme of Touch Mode Capacitive Pressure Sensor (TMCPS), which can be used in a wireless integrated resistor, inductor and capacitor circuit for monitoring pressure in biomedical applications. Design/methodology/approach This study focuses on the design, simulation and fabrication of dynamic capacitors, based on surface micromachining using polysilicon or aluminum films as the top electrode, both structural materials are capped with a 1.5 μm-thick polyimide film. Findings The design of microstructures using a composite model fits perfectly the preset mechanical behavior. After the full fabrication, the dynamic capacitors show complete mechanical flexibility and stability. Originality/value The novelty of the method presented in this study includes two important aspects: first, the capacitors are designed as a planar cavity within a rigid frame, where two walls contain channels which allow for the etching of the sacrificial material. Second, the electromechanical structures are designed using a composite model that includes a polyimide film capping for a precise pressure sensing, which also protects the internal cavity and, at the same time, provides full biocompatibility.

Capacitance and sensitivity calculation of double touch mode capacitive pressure sensor: theoretical modelling and simulation

Touch mode capacitive pressure sensor offer better performance in many applications than other devices. In touch mode operation of a capacitive pressure sensor the diaphragm touches the bottom of the substrate. Due to this several advantages such as near-linear output characteristics, large over range pressure and robust nature of the device was observed, which made it possible to withstand harsh industrial environment. To obtain better performance on the existing single sided touch mode capacitive pressure sensor (STMCPS) a double sided one has been proposed. In double sided touch mode capacitive pressure sensor (DTMCPS) an additional notch was etched at bottom of the substrate. So far in literature the advantage of DTMCPS over single sided has been discussed i.e. linear output characteristics, large over range protection and robust structure but no work is present which elaborates step by step calculation of performance parameters such as capacitance and sensitivity. Here we have completely derived the underlying expressions for performance parameters. The next step has been to validate our claims of higher sensitivity of this structure over single sided one. So MATLAB has been introduced and interpretations have been made. It has been proved that for the same size and touch point pressure as used in STMCPS the linear range of operation can be extended and the sensitivity can be enhanced for DTMCPS. Furthermore by addition of a notch the reliability of the sensor is also improved.

A complete analytical model for clamped edge circular diaphragm non-touch and touch mode capacitive pressure sensor

Capacitive pressure sensor have become good substitute for piezoresistive pressure sensor because of low power consumption. In order to evaluate the characteristic profile for touch mode micro pressure sensor an accurate and simple model needs to be designed. Hence preferable analytical model is necessary to design and characterize the device. Lot of study has been done on touch mode capacitive sensing but no elaborate work has been presented to clearly understand the underlying expressions and the role of key performance parameters. With this step by step theoretical evaluation model the key performance parameter such as deflection, capacitance and sensitivity can be easily studied for both non-touch and touch mode capacitive pressure sensor. The next aspect has been to simulate the findings in order to validate the results and hence MATLAB has been introduced. It also eliminates the need for design using FEM and hence the study becomes lot easier.

Study of High-Temperature MEMS Pressure Sensor Based on SiC-AlN Structure

In the paper, a touch mode capacitive pressure sensor with double-notches structure is presented. The sensor employs a special SiC-AlN-SiC sandwich structure to achieve high-accuracy pressure measurement in hash environment such as high-temperature. The analysis to the relation of capacitance and external pressure of the sensor shows that the sensor has high sensitivity and long linear range simultaneously. In addition, the technical process of the sensor has been designed in detail in the paper. The research shows that the sensor packaged in a high-temperature ceramic AlN can withstand higher temperature. Consequently, the sensor can be applied in high-temperature and harsh environment.