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

Abstract

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.

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

“…When the pressure was below 4 kPa, the sensitivity of the sensor reached −14.25 MHz/kPa. Even when the applied pressure increased into the high-pressure range, the sensitivity of the sensor (−0.6 MHz/kPa) was still higher than the maximum sensitivity achieved in the most recent studies [12,15,16,20,[28][29][30]. In contrast, the sensor with a 5 × 5 bilayer pyramid dielectric structure possessed superior sensitivity as well as a considerable working range.…”

“…Flexible pressure sensors have been developing rapidly in many fields of application, including biomedical applications and wearable devices [ 1 , 2 , 3 , 4 ], and can efficiently realize the regulation of physiological state, allowing timely intervention for the protection of human health, and resulting in great improvement to the quality of human life [ 5 , 6 , 7 , 8 ]. However, most present flexible pressure sensors require redundant wires and batteries, which presents a considerable challenge in miniaturized scenarios, as well as those requiring movement [ 9 , 10 ], such as implant devices, limb motion [ 8 , 11 , 12 ], rotating environments [ 13 , 14 ], and the inside of pipes [ 15 , 16 ]. Meanwhile, systems that do not require large power sources make sensors more convenient for continuous detection and processes necessitating a longer endurance.…”

Wireless and Flexible Tactile Sensing Array Based on an Adjustable Resonator with Machine‐Learning Perception

“…In this design, the relationship between the resonant frequency and the permittivity of the dielectric can be described as follows. According to the equivalent circuit as shown in Figure 1a, the resonant frequency ( f ) and the quality factor (Q) of the RF resonant sensor is expressed as [31] 1 2…”

“…[25,26] Although wireless RF sensing technology has demonstrated considerable application potential, the array construction of RF tactile sensors still faces several challenges. In typical sensor array based on split-ring resonator (SRR) arrays [27][28][29] or compact inductor-capacitor (LC) arrays, [30][31][32] sensor units are required to operate at various frequencies. According to the existing methods, different inductance geometries need to be constructed for this purpose, which requires a complex micromachining process owing to the limited device area.…”

Full Soft Capacitive Omnidirectional Tactile Sensor Based on Micro-Spines Electrode and Hemispheric Dielectric Structure

“…Compared with silicon-based devices with high hardness, the sensors manufactured with soft materials are more suitable for biomimetic tactile perception due to their good stretchability and conformality [ 12 , 13 ]. Various flexible materials such as polyethylene (PE) [ 14 ], polydimethylsiloxane (PDMS) [ 15 , 16 ], and polyurethane (PU) [ 17 , 18 ] have been widely applied to tactile sensors. Generally, these soft and flexible tactile sensors are based on sensing mechanisms including capacitive [ 19 , 20 ], piezoelectric [ 12 ], and piezoresistive [ 21 , 22 ].…”