Wireless Passive Pressure Sensor Research Articles

LC dynamic signal modeling and analysis of resonant frequency measurement error under rapid eye movements interference

Abstract LC resonant wireless passive intraocular pressure (IOP) sensors measure IOPs by mapping them to LC resonance frequencies. However, during the sweeping acquisition process of each LC signal frame, possible rapid eye movement (REM) can interfere with the wireless mutual inductance coupling, leading to the signal distortion and resulting in the error of resonance frequency measuring. Currently, there is a lack of modelling analysis of the errors generated by REM effect, resulting in an absence of guidance for reducing the impact. Therefore, here, we start from the perspective of the signal model and establish the LC dynamic signal model for sweeping acquisition. By means of the limit state analysis and Monte Carlo simulation, we analyze the influence of external REM parameters (including REM range and velocity) and internal parameters of the LC sensing system (including the quality coefficient of LC sensor, diameter, and number of turns of the reader coil, signal sweep acquisition speed and period) on the errors. We demonstrated theoretical relationship between the extreme errors with these parameters and verify it through a computer simulation. Based on the results, we propose to optimize the internal parameters of the LC sensing system to reduce the REMs effect on errors, safeguarding the quality of signal acquisition and improving the measurement accuracy.

A wireless multiparameter cryogenic monitoring method using passive backscatter sensors

In this paper, we proposed the first wireless multiparameter monitoring method for cryogenic environments (−196 ℃). Present-day cryogenic industries implement a large array of wired sensors to monitor key parameters in fabrication processes. The wirings for a large sensor array greatly complicate the monitoring system. We presented the first wireless multiparameter monitoring method for cryogenic environments by making two efforts. First, a novel wireless passive vibration and pressure sensor is developed. We transfer vibrations and pressures to a relative displacement between a magnet and a tunnel magnetoresistor (TMR). This affects the magnetic field at the TMR and changes the TMR’s resistance. By integrating the TMR on a backscattering antenna, the antenna’s wireless return loss is modulated by both vibrations and pressures. We proposed a decoupling method for simultaneously monitoring vibration and pressure by a single sensor. Second, we demonstrated and evaluated the first wireless multiparameter cryogenic monitoring system. A wireless passive temperature sensor is developed by integrating a resistance temperature detector (RTD) on a backscattering antenna. The developed vibration and pressure sensor and temperature sensor are tuned to separate frequency bands, embedded in cryogenic environments, and calibrated in situ. Vibrations, pressures, and temperatures in cryogenic environments are synchronously obtained by our wireless cryogenic monitoring system, with an accuracy of 80∼90 %. This research provides a wireless option in large-scale automated cryogenic monitoring, thus it is desirable in implementing the Internet of Things in cryogenic industries.

Theoretical and Experimental Investigation of a Wireless Passive Pressure Sensor Based on Flexible Printed Circuit Board Technology

Theoretical and Experimental Investigation of a Wireless Passive Pressure Sensor Based on Flexible Printed Circuit Board Technology

Design and Research of SIW Wireless Passive High-Temperature and Pressure Sensor

Design and Research of SIW Wireless Passive High-Temperature and Pressure Sensor

Iontronic capacitance-enhanced LC wireless passive pressure sensor for high-performance flexible sensing

Wireless passive sensors based on inductor-capacitor (LC) circuits have been an area of intense research in wearable electronics because of their battery-free and wirelessly connected operation. However, significant challenges remain in achieving high sensitivity and long-range performance for such device. In this study, we present a bilayer coils LC wireless passive iontronic pressure sensor (BWIPS) that overcomes these limitations. The bilayer coils strategy enhances the coupling effect and extends the operating distance up to 20 mm. Meanwhile, the capacitive iontronic pressure sensor (IPS) achieves high sensitivity (0.54 kPa−1) and a broad sensing range (400 kPa). By integrating bilayer coils and IPS, the BWIPS exhibits a remarkable sensitivity of −37.4 kHz kPa−1. Furthermore, the flexibility of the sensor allows it to maintain its resonant frequency regardless of various bending radius, making it suitable for use in prosthetic devices. Our BWIPS technology holds great potential for advancing the development of wireless passive sensors in the future, particularly in applications that require high sensitivity, broad sensing range, and non-contact detection at a distance.

Radio Frequency Resonator-Based Flexible Wireless Pressure Sensor with MWCNT-PDMS Bilayer Microstructure.

Flexible pressure sensors have been widely applied in wearable devices, e-skin, and the new generation of robots. However, most of the current sensors use connecting wires for energy supply and signal transmission, which presents an obstacle for application scenarios requiring long endurance and large movement, especially. Flexible sensors combined with wireless technology is a promising research field for realizing efficient state sensing in an active state. Here, we designed and fabricated a soft wireless passive pressure sensor, with a fully flexible Ecoflex substrate and a multi-walled carbon nanotube/polydimethylsiloxane (MWCNT/PDMS) bilayer pyramid dielectric structure. Based on the principle of the radio-frequency resonator, the device achieved pressure sensing with a changeable capacitance. Subsequently, the effect of the pyramid density was simulated by the finite element method to improve the sensitivity. With one-step embossing and spin-coating methods, the fabricated sensor had an optimized sensitivity of 14.25 MHz/kPa in the low-pressure range. The sensor exhibited the potential for application in limb bending monitoring, thus demonstrating its value for long-term wireless clinical monitoring. Moreover, the radio frequency coupling field can be affected by approaching objects, which provides a possible route for realizing non-contact sensing in applications such as pre-collision warning.

Improving Water Pressure Measurement Using Temperature-Compensated Wireless Passive SAW Bidirectional RDL Pressure Sensor

Currently pressure sensors utilized for water pressure measurement need batteries for direct power supply. However, batteries are lifespan-limited and not so reliable in the buried water pipe environment. The maintenance work due to battery failures leads to high cost to utility owners. Wireless passive surface acoustic wave (WP-SAW) sensors do not need direct power supply from batteries and can work in harsh environment. They are low-cost and compatible with micro-electromechanical systems (MEMS) technologies. This study investigates a temperature-compensated WP-SAW bidirectional reflective delay line (RDL) pressure sensor and its feasibility in improving water pressure measurement. The linear temperature-compensated pressure sensing functional model between the output phase shifts and the pressure change is established theoretically and verified by experiments. An experimental framework for testing the sensor node is built. The water pressure sensing adaptor is proposed. Experimental results: the experimental data show good linearities, which fits the established functional relationship; the numerical functional relationship has been derived and expressed; the sensor node has a good performance in the range of pressure difference from 0 to 0.5 MPa, which meets the normal 28-meter water pressure sensing requirements; the accuracy of this sensor is 7.22 kPa, which can be utilized for the water pressure sensing tasks in water distribution systems.

An LC Wireless Passive Pressure Sensor Based on Single-Crystal MgO MEMS Processing Technique for High Temperature Applications.

An LC wireless passive pressure sensor based on a single-crystalline magnesium oxide (MgO) MEMS processing technique is proposed and experimentally demonstrated for applications in environmental conditions of 900 °C. Compared to other high-temperature resistant materials, MgO was selected as the sensor substrate material for the first time in the field of wireless passive sensing because of its ultra-high melting point (2800 °C) and excellent mechanical properties at elevated temperatures. The sensor mainly consists of inductance coils and an embedded sealed cavity. The cavity length decreases with the applied pressure, leading to a monotonic variation in the resonant frequency of the sensor, which can be retrieved wirelessly via a readout antenna. The capacitor cavity was fabricated using a MgO MEMS technique. This MEMS processing technique, including the wet chemical etching and direct bonding process, can improve the operating temperature of the sensor. The experimental results indicate that the proposed sensor can stably operate at an ambient environment of 22–900 °C and 0–700 kPa, and the pressure sensitivity of this sensor at room temperature is 14.52 kHz/kPa. In addition, the sensor with a simple fabrication process shows high potential for practical engineering applications in harsh environments.

An Innovative LC-C Resonant Pressure Sensor Based on Capacitive Feedthroughs

LC resonant wireless passive pressure sensor has been receiving increased attention nowadays. In this paper, an innovative LC-C resonant wireless passive pressure sensor based on dual capacitors was designed and manufactured to replace the traditional LC device. In addition to the inductor and capacitor structure required by the traditional LC device, this paper innovatively designs the fixed capacitor as the inter-layer interconnection structure. The key structural dimensions of the sensor were determined through the numerical analysis of the planar inductor theory and the electromechanical coupling simulation of the dual capacitors model in the previous stage, and the processing of the sensor was carried out through MEMS technology. The final test results showed that within the pressure range of 5kPa to 100kPa, the sensor’s average sensitivity was greater than 69.0 kHz/kPa, while the maximum linear fitting error was smaller than 4.18%. The temperature drift in atmospheric environment was 2.7kHz/°C, and the sensitivity temperature drift was 0.0062kHz/(kPa·°C).

Flexible Wireless Passive LC Pressure Sensor with Design Methodology and Cost-Effective Preparation.

Continuous monitoring of physical motion, which can be successfully achieved via a wireless flexible wearable electronic device, is essential for people to ensure the appropriate level of exercise. Currently, most of the flexible LC pressure sensors have low sensitivity because of the high Young’s modulus of the dielectric properties (such as PDMS) and the inflexible polymer films (as the substrate of the sensors), which don’t have excellent stretchability to conform to arbitrarily curved and moving surfaces such as joints. In the LC sensing system, the metal rings, as the traditional readout device, are difficult to meet the needs of the portable readout device for the integrated and planar readout antenna. In order to improve the pressure sensitivity of the sensor, the Ecoflex microcolumn used as the dielectric of the capacitive pressure sensor was prepared by using a metal mold copying method. The Ecoflex elastomer substrates enhanced the levels of conformability, which offered improved capabilities to establish intimate contact with the curved and moving surfaces of the skin. The pressure was applied to the sensor by weights, and the resonance frequency curves of the sensor under different pressures were obtained by the readout device connected to the vector network analyzer. The experimental results show that resonant frequency decreases linearly with the increase of applied pressure in a range of 0–23,760 Pa with a high sensitivity of −2.2 MHz/KPa. We designed a coplanar waveguide-fed monopole antenna used to read the information of the LC sensor, which has the potential to be integrated with RF signal processing circuits as a portable readout device and a higher vertical readout distance (up to 4 cm) than the copper ring. The flexible LC pressure sensor can be attached to the skin conformally and is sensitive to limb bending and facial muscle movements. Therefore, it has the potential to be integrated as a body sensor network that can be used to monitor physical motion.

Flat Film Structure Wireless Passive Pressure Sensor based on SiCN materials

In order to solve the measurement of air pressure in harsh environment, a new kind of wireless passive pressure sensor based on the amorphous SiCN material with high heat resistance was proposed. Ansoft HFSS software was used to study the relationship between the size of the rectangular resonator with the resonant frequency and quality factors. By optimizing the position and size of the sloped antenna, a wireless passive pressure sensor with high performance was designed. The sensitivity is 0.25mpa/GHZ and the bandwidth is 0.85GHZ of the pressure sensor at the working frequency of 6.8GHZ. This indicates its potential application in the harsh environment with high temperature.

A wireless passive pressure sensor using microstructured ferromagnetic films with tunable effective permeability

This paper presents a novel LC-based passive wireless flexible pressure sensor that employs microstructured ferromagnetic films with tunable effective permeability. The proposed device consists of a micromachined planar spiral coil and a polymer film with cilia arrays (CAs) realized by the ferrofluidic instability principle. The effective permeability of the polymer film can be tuned by deforming the CAs with externally applied pressure, which can be estimated in turn by detecting the resonant frequency of the device using the phase-dip technique. The fabrication parameters for synthesizing different dimensions and densities of CAs were investigated as well. Devices of different CA densities were measured and discussed. The measured results showed that the device quality factor and phase change both increased with applied pressure. Due to this characteristic, the proposed device is advantageous over typical capacitive LC-based devices and performs better in wireless interrogation while maintaining the sensitivity of pressure sensing.

Effect of the graphitization level of the free carbon on the temperature sensitivity of silicon carbonitride‐based pressure sensors

AbstractPolymer‐derived ceramics (PDCs) have recently attracted an increasing attention because of their applications for wireless passive pressure sensors in the harsh environment. However, due to the effect of temperature on the frequency of PDC‐based wireless passive pressure sensors, it is not beneficial to accurate measurement of pressure. In this paper, a dense polymer‐derived silicon carbonitride (SiCN) ceramic was prepared by precursor infiltration and pyrolysis (PIP) technique to reduce the temperature sensitivity of PDC–SiCN‐based pressure sensor. The open porosity and density of SiCN ceramics varied from 13.34% and 1.89 g/cm3 without PIP process to 3.24% and 2.09 g/cm3 after three PIP cycles, respectively. Raman spectroscopy revealed that the level of graphitization of free carbon in dense SiCN ceramics is higher than that in porous SiCN ceramics, which would lead to an increase in the conductivity of dense SiCN ceramics. After three PIP cycles, the conductivity increased by almost two orders of magnitude from 3.01E − 10 to 1.28E − 08 S/cm. In addition, SiCN ceramic discs after PIP cycles and without PIP were applied to wireless passive pressure sensor based on resonator, which were tested at high temperature, respectively. Results confirmed that the temperature sensitivity of PDC–SiCN‐based pressure sensor decreased from 220.5 to 50.8 kHz/°C by PIP process.

Wireless Passive Intracranial Pressure Sensor Based on Vacuum Packaging

This paper presents a wireless passive pressure sensor based on a pressure-sensitive capacitor specifically designed to monitor intracranial pressure (ICP) in patients with traumatic brain injuries. It is crucial that temperature will affect the accuracy of pressure detection. To improve temperature stability, the capacitor is composed of an SOI wafer as the sensing element and a glass cap for vacuum packaging. To realize reliable vacuum packaging, it is vital to transfer the electrical signal out of the vacuum cavity. The experimental results show that the proposed sensor demonstrated averaged pressure sensitivity and averaged temperature sensitivity of 0.5803 Hz/kPa and 0.024 Hz/°C. Additionally, the in-vivo test in the animal show that the proposed sensor has the similar detection effect with the commercial wired sensor, and naturally has the advantage of reducing the risk of infection, which further validated the feasibility and effectiveness of the wireless passive ICP monitoring system.

A Battery-Free, Chipless, Highly Sensitive LC Pressure Sensor Tag Using PEDOT: PSS and Melamine Foam

We have designed and developed a compact, contactless, chipless, high frequency wireless passive LC pressure sensor tag capable of measuring pressure from 0 Pa to 60 kPa. The LC pressure sensor tag design consists of a parallel combination of a planar inductor and a pressure sensitive interdigitated capacitor (IDC). The readout or signal detection and signal processing system combines a Colpitts oscillator, different electronic circuits, and a microcontroller-based signal processing unit. Operation of the sensor is based on mutual coupling of the inductor of the LC pressure sensor tag and the oscillation coil of the Colpitts oscillator. The pressure sensitive IDC consists of interdigitated electrodes and a melamine foam containing poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as an elastic pressure sensitive dielectric material. When pressure is applied to the LC pressure sensor tag, the capacitance of the IDC sensing element changes, which changes the resonance frequency. Because the LC pressure tag and the inductor of the oscillator are inductively coupled, the frequency of oscillation of the Colpitts oscillator changes. The LC pressure sensor has a highly sensitive sensing response of 762.65 Hz/kPa and a linear sensing performance over a wide measurement range, with a correlation coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}^{\sf 2}$ </tex-math></inline-formula> ) of 0.997. The LC pressure sensor tag is lightweight, highly sensitive, inexpensive to fabricate, and has good repeatability and stability values in the percentage of 2.8 and 1.1, respectively.

A large-pressure-range, large-sensing-distance wireless passive pressure sensor based on polymer infiltration pyrolysis-enhanced polymer-derived ceramic films

Large-pressure-range, large-sensing-distance evanescent-mode resonator wireless passive pressure sensors were fabricated from silicon carbonitride polymer-derived ceramic (PDC-SiCN) films enhanced by the polymer-infiltration-pyrolysis (PIP) process. The properties of PIP enhanced PDC films ensure a large pressure range for the sensor. To increase the sensing distance between the interrogation antenna and the sensor, the size or position of the resonator and slot antenna were optimized by High Frequency Structure Simulator simulations. The experimental results show that the resonant microwave signal can be wirelessly detected at distances up to 30 mm. The pressure sensor has a large pressure range (0–850 kPa) and high pressure sensitivity (211.8 kHz kPa−1) in pressure environments at room temperature.

A Capacitive Pressure Sensor Based on Cofirable Ceramic/Glass Materials with LTCC Technology

Abstract Because of good thermal, electrical, and mechanical properties, low-temperature cofired ceramic (LTCC) has shown great potential in microelectronic applications. One of the most promising directions of LTCC technology development are integrating and packing sensors. In this article, a wireless passive capacitive pressure sensor operating in the MHz range based on cofiring of heterogeneous materials with LTCC technology is proposed, and the design, simulation, and fabrication of the sensor are demonstrated and discussed. It consists of a circular spiral inductor and a capacitor of two electrodes separated by a glass medium. Furthermore, a unique process of cofiring of heterogeneous materials was introduced to avoid deformation of the capacitive embedded cavity during lamination or sintering. The results show that the inductance of the inductor and the capacitance of the capacitor embedded in the sensor are .28 μH and 16.80 pF, respectively. The novel sensor has a sensitivity of approximately 847 Hz/MPa within the pressure range from atmospheric pressure to 100 MPa.

Fabrication of a flexible wireless pressure sensor for intravascular blood pressure monitoring

This work presents the development of a wireless passive pressure sensor for cardiovascular pressure monitoring. The device is designed to be inserted into a stent that can be deployed within a blood vessel using a catheter-based delivery system. By utilizing micromachining techniques, a variable capacitor and an inductor were implemented in the sensor as an L-C resonator for wireless pressure sensing and signal retrieving. The sensor employs biocompatible polymeric material, parylene-C, as the substrate material. The pressure responses of the sensor, such as the sensitivity, linearity, and hysteresis, were measured and discussed. The sensitivity was approximately 6.19 × 10−2/kPa (8.25 × 10−3/mmHg), and the linearity over the ranges of 0–6 kPa (0–50 mmHg) and 6–33 kPa (50–250 mmHg) were approximately 91.5% and 87.6%, respectively. The wireless pressure sensing performance of the sensor was evaluated using the phase-dip technique. Additionally, the measured results indicate that the resonant frequency of the resonator shifted from 211 MHz to 182 MHz, as the pressure varied from 0 to 33 kPa (250 mmHg). The maximum standard error of the mean is 0.86 MHz. Finally, the influence of coil thickness on the wireless readout performance was investigated.

A Ceramic Diffusion Bonding Method for Passive LC High-Temperature Pressure Sensor.

Alumina ceramic is a highly promising material for fabricating high-temperature pressure sensors. In this paper, a direct bonding method for fabricating a sensitive cavity with alumina ceramic is presented. Alumina ceramic substrates were bonded together to form a sensitive cavity for high-temperature pressure environments. The device can sense pressure parameters at high temperatures. To verify the sensitivity performance of the fabrication method in high-temperature environments, an inductor and capacitor were integrated on the ceramic substrate with the fabricated sensitive cavity to form a wireless passive LC pressure sensor with thick-film integrated technology. Finally, the fabricated sensor was tested using a system test platform. The experimental results show that the sensor can realize pressure measurements above 900 °C, confirming that the fabricated sensitive cavity has excellent sealing properties. Therefore, the direct bonding method can potentially be used for developing all-ceramic high-temperature pressure sensors for application in harsh environments.

Wireless passive pressure sensor based on sapphire direct bonding for harsh environments

This study presents a wireless passive high-temperature pressure sensor based on sapphire direct bonding technology. The design, fabrication, and measurement of the sensor are demonstrated and discussed. Single-crystal sapphire is used to fabricate the sensor owing to its outstanding characteristics, and the prototype sensor consists of an inductance, a variable capacitance, and an embedded vacuum-sealed cavity formed by sapphire direct bonding. Compared with other manufacturing technologies, the sapphire direct bonding process is simple and can effectively avoid the deformation and collapse of the embedded cavity, thereby leading to a better sensor performance. A more compact sensor with greater sensitivity has been fabricated in this study. The copper interrogating antenna is employed to detect the variation in the sensor’s resonant frequency caused by the pressure applied. The characterization in high-temperature pressure environments successfully demonstrates the sensing capabilities for pressures from 20 kPa to 600 kPa up to 600 °C. At 600 °C, the sensor sensitivity reaches as high as 10 kHz/kPa. The proposed sensor can be applied for the monitoring of gas pressure in harsh environments, such as environments with high temperatures and chemical corrosion.