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.
Highlights
We proposed a transfer-paste method to prepare the flexible LC pressure sensors with a sandwich structure based on different flexible substrates, which can meet the needs of a variety of different bonding surfaces, and they can be integrated as flexible LC sensing arrays to solve the problem of complex wired sensor arrays
Resonance fre-12 of 21 quency curves of sensors based on Ecoflex, PI, and PDMS are respectively illustrated in the sensor based on Ecoflex micro-column and substrate (b), Ecoflex micro-column and PI substrate (c), and PDMS micromicro-column and substrate (d), which were applied different pressures. (e) The comparison of the pressure sensitivity of column and substrate (d), which were applied different pressures. (e) The comparison of the pressure sensitivity of varvarious flexible pressure sensors
We proposed a sandwich-structured flexible LC pressure sensor based on Ecoflex micro-column as a dielectric, which is sandwiched between the two capacitor
Summary
As life expectancy and various health risks are simultaneously on the rise, people usually do physical exercises to maintain a healthy body. In order to reduce the risk of exercise injury, it is essential to continuously monitor limb motion magnitude for human health. Traditional rigid biomedical sensors have mechanical properties which are significantly different from those of the soft and curved surfaces of human tissues [1]. Flexible pressure sensors have been widely used in applications as wearable devices for monitoring human motion. Most sensors require wire connections for data transmission, which will greatly
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