A Wireless and Passive Flexible Pressure Sensor with High Sensitivity and Wide Range for Rehabilitation Monitoring

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.

This paper presents a kind of passive wireless pressure sensor comprised of a planar spiral inductor and a cavity parallel plate capacitor fabricated through low-temperature co-fired ceramic (LTCC) technology. The LTCC material with a low Young’s modulus of ~65 GPa prepared by our laboratory was used to obtain high sensitivity. A three-step lamination process was applied to construct a high quality cavity structure without using any sacrificial materials. The effects of the thickness of the sensing membranes on the sensitivity and detection range of the pressure sensors were investigated. The sensor with a 148 μm sensing membrane showed the highest sensitivity of 3.76 kHz/kPa, and the sensor with a 432 μm sensing membrane presented a high detection limit of 2660 kPa. The tunable sensitivity and detection limit of the wireless pressure sensors can meet the requirements of different scenes.

Internet of Things (IoT) technology has recently been widely utilized into a variety of industrial applications. Wireless Passive Surface Acoustic Wave (SAW) sensors have attracted great attention in numerous IoT enabled applications. The sensor nodes are not directly supplied by the power supply as it absorbs the energy from the interrogating Radio Frequency (RF) pulses to excite the SAW. Temperature and pressure are two imperative parameters to monitor whether the pipelines in water distribution system are properly functioning. In this study, the wired and wireless response signals of the passive SAW delay line temperature and pressure sensor is compared. There is a 1/5 attenuation on the response signal when wireless interrogation and response signal receiving process is applied. A wireless passive SAW delay line temperature and pressure sensor was planted in a framework simulating the environment of the water pipelines, and the response signals of the sensor node in different ambient environments are analysed and compared. Compared to the air environment, there is only a sight attenuation of the response signal when the sensor node is planted in the simulating water pipeline environment framework.

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.

SAW-MEMS microphone which operation principle is based on electrical field distortion of SAW is proposed. Simulation results of microphone sensitivity performed using COMSOL software are presented. Proposed SAW - MEMS microphone also can be used as a wireless passive accelerometer and pressure sensor. Realization of this device look challenging for MEMs technology.

Self-rollable Polymer Stent Integrated with Wireless Pressure Sensor for Real-time Monitoring of Cardiovascular Pressure

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.

Enhanced-performance flexible pressure sensors enabled by synergistic effect of hierarchical porous structures for motion sensing and deep learning-assisted speech recognition.

The development of smart stents, capable of monitoring cardiovascular diseases and communicating vascular abnormalities to medical doctors, has garnered significant attention in the field of biomedical engineering. Various ex-situ fabrication strategies have been proposed to concurrently manufacture the smart stent and pressure sensor, thereby reducing the risk of sensor detachment caused by blood flow. However, the practical utility of these devices is still limited due to the rigidity of the wireless pressure sensor. In this study, we propose a flexible and stretchable smart self-reporting stent that incorporates a wireless pressure sensor. The fabrication process has been optimized to create a serpentine-shaped wireless pressure sensor that matches the shape and flexibility of the polymer stent struts. We thoroughly investigated the structural integrity, resonance frequency, stretchability, flexibility, and radial force of the manufactured smart self-reporting stent under different conditions. The wireless pressure sensor demonstrated a sensitivity of 0.15 MHz mmHg−1, as determined through experimental analysis. To demonstrate the feasibility of the proposed smart stent, we implanted it into the arteries of a three-dimensional phantom system. The obtained results, combined with the flexible and stretchable nature of the proposed smart self-reporting stent, highlight its potential for effective monitoring of the heart’s functional dynamics and detection of in-stent restenosis.

With the rapid emergence of flexible electronics, flexible pressure sensors are of importance in various fields. In this study, a dopamine-modified melamine sponge (MS) was used to prepare a honeycomb structure of carbon black (CB)/MXene-silicone rubber (SR)@MS flexible pressure sensor (CMSM) through layer-by-layer self-assembly technology. Using SR as a binder to construct the honeycomb structure not only improves the mechanical properties of the sensor but also provides more attachment sites for CB/MXene, enhancing the stability of the conductive network. The honeycomb structure CMSM flexible pressure sensor exhibits high sensitivity (7.44 kPa-1), a wide detection range (0-240 kPa), short response/recovery times (150 ms/180 ms), and exhibits excellent stability. In addition, a flexible smart insole has been developed based on a 6-unit CMSM sensor array, achieving plantar pressure detection. By combination of the ResNet-50 neural network algorithm with plantar pressure data under different postures, the recognition of 16 types of human motion postures has been achieved, with an accuracy rate of 90.63%. This study proposes a flexible sponge pressure sensor with excellent mechanical performance and sensing capabilities, providing new ideas and references for the design of flexible wearable sensor devices.

This paper mainly presents the design and fabrication of a TDMA (time division multiple access) passive wireless pressure sensor using 2.45 GHz surface acoustic wave (SAW) delay lines. The SAW pressure sensor consists of two LiNbO3 substrates. The first layer is a pressure-detective thin substrate, on which an interdigital transducer (IDT) and reflectors are fabricated. The second layer is a support substrate, in which a reference pressure cavity is etched. These two substrates are directly bonded. The pressure measurement was successfully demonstrated in a pressure range of 20∼280 kPa with good repeatability. In addition, the influence of a tire on the wireless interrogation of the sensor was investigated. Automobile tires have little negative influence on wireless communication, at least if they do not rotate.

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.

Innovations in soft materials have advanced the development of implantable devices for pressure monitoring, but fabrication and integration challenges remain, such as limited patterning resolution and poor scalability, hindering their miniaturization and wireless sensing capabilities. This study introduces methods and advantageous features of incorporating liquid metal into microfabriated, wireless soft implantable pressure sensors and wearable readout systems for large-area pressure mapping and adaptive implantation with autonomous folding and self-healing capabilities. Eutectic gallium-indium, a type of liquid metal, serves as both the deformable electrode for capacitive sensors and a low-resistance conductor for inductors. It is integrated into a thin-film, battery-free, inductive-capacitive wireless sensing platform. Scalable wireless sensor arrays are created through microfabrication for large-area pressure mapping. The wireless pressure sensor is also integrated with soft ferromagnetic and self-healing layers in cuff-type sensors to allow for autonomous folding in response to external magnets, eliminating the need for suturing. In addition, a miniaturized wearable readout system integrated into medical gloves enables wireless and real-time pressure monitoring. The presented wireless soft pressure-sensing method with large-area mapping and secure implantation capabilities offers alternatives to conventional medical tools for intraoperative monitoring and examinations.

Flexible pressure sensor with high sensitivity and fast response for electronic skin using near-field electrohydrodynamic direct writing

Flexible pressure sensors are crucial for E-skins to enable tactile sensing capabilities. However, flexible pressure sensors often exhibit high hysteretic response caused by internal and external mechanical dissipations in flexible materials. The hysteresis gives rise to reliability issues, especially in the presence of dynamic stress. In this letter, we report a flexible capacitive pressure sensor design with hierarchically microstructured electrodes to obtain both high sensitivity and low hysteresis. The sparsely spaced large pyramid microstructure improves the sensitivity, whereas the small pyramid reduces the hysteresis caused by interfacial adhesion. The optimized sensor shows excellent performances in terms of high sensitivity (~3.73 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ), ultralow detection limits (0.1 Pa), significantly reduced hysteresis (~4.42%), and enhanced sensing capability for pluses, which demonstrates its potential for advanced electronic skins.