Miniaturization and modeling of a folded beam-based microelectromechanical intraocular pressure sensor

Glaucoma is an eye disease that is caused by abnormal high intraocular pressure (IOP) in the eye. If the disease becomes serious, it is recommended to use the implant device that decreases the IOP. Though conventional glaucoma implants have the capability to regulate pressure, these implants cannot maintain the IOP desired for different patients. To solve this problem, an active implant is needed that is capable of actively controlling the IOP for personal differences between patients. The active glaucoma implant consists of a valve actuator, a pressure sensor, a pressure controller, and a power supply. The focus of this work is mainly on the valve actuator and pressure sensor. For the valve actuator, different design are presented. These designs consider actuation principles, fluidic resistance elements, control methods, and energy supplies. Based on the analysis, an optimal design of the valve actuator is determined. For the implant’s pressure sensor, sensing principles, measurement methods, and the signal-to-noise ratio are considered for both piezoresistive and capacitive sensors that have been used to monitor the IOP. As an example, the design of a pressure sensor is presented that considers a bridge type sensor that uses piezoresistive materials on a membrane that is strained under pressure. An optimal design of the piezoresistive pressure sensor is determined that takes into account the signal to noise ratio of the sensor. In vitro/vivo experiments are conducted to illustrate how the performance of the fabricated valve/sensor can be obtained and verified under a similar environment for an implant in the human eye.

The authors report their initial clinical results with a novel wireless ocular telemetry sensor (OTS) (Sensimed AG, Switzerland) for continuous intraocular pressure (IOP) monitoring in patients with open angle glaucoma....

Micro Electro Mechanical Systems (MEMS) are a small-scale technology that was largely adopted by the IC industry and applied to miniaturize of all systems (electrical systems, mechanical, optical, fluidic, magnetic, etc.). Minimization has been accomplished with small manufacturing processes. A Capacitive pressure sensor is simply a diaphragm-type device in which the diaphragm displacement is determined by measuring the capacitance change between the diaphragm and a metal plate that is close to it.
 For this purpose, intraocular pressure sensors are important in detection and treatment of an incurable disease called glaucoma. To improve the sensitivity of the capacitive pressure sensor, low stress doped polysilicon material is used as a biocompatible material. Glaucoma is a group of eye diseases that occurs by high intraocular pressure (IOP). IOP is the pressure exerted by the ocular fluid called aqueous humor (the clear fluid inside the eye) that fills the anterior chamber of the eye
 The results Shows the simulated relation between capacitance and pressure for clamped ++silicon and polysilicon clamped. It can be seen from figure that the initial capacitance for clamped p++ silicon is about 1.81 pF the capacitance varies from 1.81 to 2.162 pF for clamped p++silicon and clamped polysilicon diaphragm, respectively, so the total variation of the capacitance. This result shows the use of poly silicon material in diaphragm is high sensitivity than the p++ silicon.

In this paper, Poly-crystalline silicon carbide (poly-sic) Micro-electromechanical systems (MEMS) capacitive pressure sensor operating in harsh environment in touch mode is proposed, The principle of the paper is to design, obtain analytical solution and compare the results with the simulation for a circular diaphragm deflection before and after touch point. The sensor demonstrated a high temperature sensing capability up to 400°C, the device achieves a linear characteristic response and consists of a circular clamped-edges poly-sic diaphragm suspended over sealed cavity on a silicon carbide substrate. The sensor is operating in touch mode capacitive pressure sensor, The advantages of a touch mode are the robust structure that make the sensor to withstand harsh environment, near linear output, and large over-range protection, operating in wide range of pressure, higher sensitivity than the near linear operation in normal mode, The material is considered to be used for harsh environment is SiC (Silicon Carbide), Because of SiC owing excellent electrical stability, mechanical robustness, and chemical inertness properties and the application of pressure sensors in harsh environments are, such as automotive industries, aerospace, oil/logging equipments, nuclear station, and power station. We are simulating MEMS capacitive pressure sensor to optimize the design, improve the performance and reduce the time of fabricating process of the device. The proposed touch mode MEMS capacitive pressure sensor demonstrated diaphragm ranging from 150 μm to 360 μm in diameter, with the gap depth from 0.5 μm to 7.5 μm and the sensor exhibit a linear response with pressure from 0.05 Mpa to 10 Mpa.

Micro electro-mechanical systems (MEMS) based capacitive pressure sensors are typically fabricated using silicon micromachining techniques. In this paper, novel liquid crystal polymer (LCP) based capacitive pressure sensors, fabricated using printed circuit processing techniques, are reported. LCP exhibits good dimensional stability, material flexibility, high chemical resistance, and extremely low moisture absorption, which makes it suitable for MEMS applications. The pressure sensor comprises of a cylindrical cavity formed by a sandwich of LCP substrate, LCP spacer layer with circular holes and LCP top layer. The bottom electrode and the top electrode of the capacitive pressure sensor are defined on the top surface of the LCP substrate and the bottom surface of the top LCP layer, respectively. A typical pressure sensor with a diaphragm diameter of 3.2 mm provides a total capacitance change of 0.7627 pF for an applied pressure in the range of 0-170 kPa.

To evaluate the efficacy of a novel contact lens sensor system (CLS) in detecting continuous intraocular pressure (IOP) variations following positional transitions, and to explore these IOP variation patterns among normal subjects, untreated glaucoma patients, and untreated ocular hypertension (OHT) subjects. This prospective comparative study included 20 normal subjects, 14 high tension glaucoma (HTG) patients, 16 normal tension glaucoma (NTG) patients, and 14 OHT subjects. Participants wore the CLS for continuous IOP monitoring while undergoing sequential body position changes: from sitting to supine to a 10° head-down tilt (HDT), with each position maintained for ten minutes. Continuous IOP parameters, including mean, peak, and fluctuation (peak minus valley) in each position, as well as increment (peak minus starting value), interval (time to arrive peak), and velocity (increment divided by interval) after two position transitions, were compared among different positions and groups, respectively. Normal subjects, HTG and NTG patients exhibited higher CLS IOP mean and peak in supine/HDT positions compared to sitting (P < 0.05), but the mean or peak in HDT did not significantly differ from that in supine (P > 0.2). In OHT, all IOP parameters showed no significant difference among various positions (P > 0.1), except for velocity. Comparisons among groups revealed that during the transition from sitting to supine, HTG demonstrated higher IOP increment than other three groups and higher velocity than normal subjects (P < 0.05). NTG patients exhibited no significant differences in IOP increment, interval and velocity, compared to normal subjects (P > 0.05). The CLS proved effective in continuously recording IOP responses following positional changes in normal and glaucomatous eyes. Transitioning from sitting to supine resulted in increased IOP among normal subjects, HTG and NTG patients, but not in OHT. Compared to normal subjects, this IOP increase was more pronounced and rapid in HTG, but comparable in NTG. WHAT IS KNOWN : Positional transitions can induce IOP variations, which differ among normal subjects and glaucoma patients, and potentially relate to glaucomatous neuropathy. However, prior findings are constrained by the discontinuity of traditional tonometry. This study utilized a novel contact lens sensor system (CLS) to continuously monitor IOP during positional transitions in normal subjects and untreated glaucoma/OHT subjects. Continuous IOP outcomes revealed that normal subjects, HTG patients, and NTG patients exhibited an increase in IOP when transitioning from sitting to supine, whereas OHT did not. Compared to normal subjects, this increase in IOP was more pronounced and rapid in HTG patients, but similar in NTG.

A microelectromechanical system capacitive pressure sensor with a differential configuration (patent pending), including a reference and sensitive capacitor, is presented. A single cavity includes both reference and sensitive electrodes. This implementation is achieved by a size reduction of the sensitive electrode. A reduction of the 40% on the sensible electrode area represents a decrease in the sensor sensitivity of only 12.5%, and allows the reference capacitor implementation in the area commonly used only for the sensitive capacitor. A tridimensional model of the sensor was simulated using a finite-element solver considering coupled mechanical and electrostatic models. The simulations show that this pressure sensor has a sensitivity of 4.2 fF/bar. The proposed pressure sensor designs use only materials available in complementary metal oxide silicon (CMOS) standard processes. A CMOS compatible post-process, based on the sacrificial material technique and its restrictions is presented.

MEMS (microelectromechanical systems) is an enabling technology that has been used in high volume automotive applications such as pressure sensors and accelerometers for a variety of applications such as that control the engine performance as well as the safety of the occupants. MEMS sensors require an interface circuit to convert the input mechanical signal to the equivalent electrical signal that is used to generate the required control function. The integration of the MEMS sensor with the interface circuit can be achieved either in the same piece of silicon or in the package. The challenges in this integration are discussed in the paper with specific examples for piezoresistive pressure sensors, capacitive accelerometers and capacitive pressure sensors. The effects of the application environment on the performance of these sensors are also discussed in the paper. Examples of system partitioning and integration are described using a satellite accelerometer system and a tire pressure monitoring system.

Skin mountable flexible pressure sensors are crucial for the next generation technologies. Capacitive pressure sensors bring several advantages and hence, they have been preferred over piezoelectric and piezoresistive alternatives. Flexible electrode and dielectric material are the fundamental components of the capacitive flexible pressure sensors. Hence, solution processable silver nanowires (AgNWs) are highly promising as electrode material or filler material in dielectric layer, owing to their superior inherent conductivity and flexibility. This article reviews recent progress on fabrication of flexible capacitive pressure sensors with AgNWs used as electrode and dielectric material. Performance of the sensors based on AgNWs is comprehensively discussed and emerging applications, as well as future outlook, are presented in detail.

This paper presents the design, fabrication and characterization of a wireless capacitive pressure sensor with directional RF chip antenna that is envisioned for the health monitoring of aircraft engines operating in harsh environments. The sensing system is characterized from room temperature (25 C) to 300 C for a pressure range from 0 to 100 psi. The wireless pressure system consists of a Clapp-type oscillator design with a capacitive MEMS pressure sensor located in the LC-tank circuit of the oscillator. Therefore, as the pressure of the aircraft engine changes, so does the output resonant frequency of the sensing system. A chip antenna is integrated to transmit the system output to a receive antenna 10 m away.The design frequency of the wireless pressure sensor is 127 MHz and a 2 increase in resonant frequency over the temperature range of 25 to 300 C from 0 to 100 psi is observed. The phase noise is less than minus 30 dBcHz at the 1 kHz offset and decreases to less than minus 80 dBcHz at 10 kHz over the entire temperature range. The RF radiation patterns for two cuts of the wireless system have been measured and show that the system is highly directional and the MEMS pressure sensor is extremely linear from 0 to 100 psi.

Capacitive pressure sensors measure changes in pressure typically by the deflection of a flexible conducting membrane towards a fixed electrode. The deflection in the membrane produces a quadratic change in capacitance, which often yields higher sensitivity to changes in pressure compared to piezo-resistive pressure sensors, which measures the resistance changes proportional to the applied pressure. However, residual stresses in the membrane can provide a substantial resistance to deformation compared to the driving force created by the applied pressure, which decreases the sensitivity at low pressures and produces a nonlinear signal. If the membrane is made compliant enough to increase sensivitiy, pull-in of the membrane can occur, reducing the effective pressure range of the capacitive manometer type pressure sensor. Hence, these type of sensors are typically not used to measure very low pressure differences over several hundred Pascals. To overcome this limitation, a capacitive pressure sensor was developed that operates in a peeling mode while under applied electrostatic actuation, which counters the residual stresses. The changes in capacitance can be detected if the pressure is just enough to overcome the interfacial electrostatic pressure. This type of pressure sensor can potentially be used for very low differential pressure differences, well below 100 Pa, over ~ 1 kPa range.

A highly sensitive and wide-range pressure sensor based on orientated and strengthened TPU nanofiber membranes fabricated by a conjugated electrospinning technology

Porous dielectric materials based wearable capacitance pressure sensors for vital signs monitoring: A review

Flexible capacitive pressure sensors are becoming increasingly significant in wearable electronic devices. The conventional form of pressure sensors, however, focuses primarily on microstructure design. While this approach can enhance sensitivity, it can also compromise the reliability of the sensor device. Here, we present a flexible pressure sensor according to the capacitance effect using the high dielectric P(VDF-TrFE)/MXene polymer as the capacitive pressure sensor dielectric layer. The P(VDF-TrFE)/MXene film has a high dielectric constant, making it an ideal choice for the dielectric layer of the flexible capacitive pressure sensor, resulting in rapid response and high sensing sensitivity. We also examine the impact of dielectric layer thickness on the sensor’s performance and find that increasing the thickness from 0.5 to 1.5 mm leads to a continuous improvement in sensitivity, reaching a maximum sensitivity of 0.42 kPa−1 and a wide sensing amplitude (3 Pa–25 kPa). Moreover, the response time of the capacitive pressure sensor can reach 47 ms. In addition, the sensor can be utilized to monitor human physiological information such as respiration and heartbeat. Its flexibility makes it ideal for application in sports, particularly for monitoring the movement posture of football players. Our findings can drive the wider adoption of pressure sensors in football motion monitoring.

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.