Passive wireless SAW - MEMS pressure sensor/microphone

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.

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.

Recent radio-frequency resonance-based hightemperature sensors have enable the next generation of passive wireless sensing for harsh environments, such as inside of jet engines. A novel manufacturing technique for an evanescentmode-resonator-based and antenna-integrated wireless passive pressure sensor is proposed therein. This technique employs a planar PCB manufacturing tool to laser etch a 3-D structure on an alumina substrate. A laser machining study is conducted to find etch consistency and fine-tune laser etching parameters. The wireless passive pressure sensor is tested through various mechanical and thermal loads to measure its performance. The sensor is proven to work in the range of $25^{\circ}\mathrm{C} -1700^{\circ}\mathrm{C}$, sensing pressures of 0 psi to 163 psi with resonances within the frequency range of 6.33 GHz--6.7 GHz.

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.

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 a novel monolithic pressure sensor tag for passive wireless applications. The proposed pressure sensor tag is based on an ultra-high frequency RFID system. The pressure sensor element is implemented in the 0.18 µm CMOS process and the membrane gap is formed by sacrificial layer release, resulting in a sensitivity of 1.2 fF/kPa within the range from 0 to 600 kPa. A three-stage rectifier adopts a chain of auxiliary floating rectifier cells to boost the gate voltage of the switching transistors, resulting in a power conversion efficiency of 53% at the low input power of −20 dBm. The capacitive sensor interface, using phase-locked loop archietcture, employs fully-digital blocks, which results in a 7.4 bits resolution and 0.8 µW power dissipation at 0.8 V supply voltage. The proposed passive wireless pressure sensor tag costs a total 3.2 µW power dissipation.

This work introduces a wireless, passive, and flexible pressure sensor by combining a radio frequency (RF) sensor with a porous polymer. The porous Ecoflex with tunable porosity and interconnectivity is fabricated by the sacrificial template method, which exhibits superior mechanical compressibility and highly reversible deformation behavior. Then, this porous Ecoflex was sandwiched by flexible electrodes and leveraged electromagnetic coupling for wireless signal transmission to construct a passive pressure sensor. A remarkable sensitivity of 3.04 kPa/MHz across an ultrawide pressure range from 0 to 700 kPa was achieved when the mass ratio of Ecoflex to NaCl was 1:2. It also demonstrates a fast response, excellent cycling stability, and the ability to detect subtle pressure change. Practical applications demonstrate that the sensor can accurately capture motion characteristics during upper limb rehabilitation training, allowing real-time monitoring of multidimensional movements such as wrist flexion and extension and forearm rotation. Moreover, an intelligent recognition system based on this sensor is developed, which achieves 99% accuracy in handwritten digit recognition by integrating neural network models. This research presents a viable strategy for developing next-generation wearable medical devices and intelligent human–machine interfaces.

A wireless pressure sensor based on a microwave cavity resonator is proposed herein. A metallic post is located at the center of the cavity to form an evanescent-mode tunable resonator and the resonant frequency depends on the air gap between the cavity cap and the post. When the cavity has a deformation resulted from external pressure, the resonant frequency is shifted. A slot antenna is integrated with this pressure sensor for wireless detection without occupying any additional volume. Simulation results show that the pressure sensor operates from 12.55 to 10.50 GHz corresponding to applied pressure from 0 to 100 psi. This proposed wireless passive pressure sensor is suitable for applications where physical contact or active elements are hard to be implemented.

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.

Silicon MEMS as electrostatically levitated rotational gyroscopes and 2D optical scanners, and wafer level packaged devices as integrated capacitive pressure sensors and MEMS switches are described. MEMS which use non-silicon materials as LTCC with electrical feedthrough, SiC and LiNbO3 for probe cards for wafer-level burn-in test, molds for glass press molding and SAW wireless passive sensors respectively are also described.

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.

Evanescent-mode-resonator-based and antenna-integrated wireless passive pressure sensors for harsh-environment applications

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.

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