Review—Energy Autonomous Wearable Sensors for Smart Healthcare: A Review

Abstract

Energy Autonomous Wearable Sensors (EAWS) have attracted a large interest due to their potential to provide reliable measurements and continuous bioelectric signals, which help to reduce health risk factors early on, ongoing assessment for disease prevention, and maintaining optimum, lifelong health quality. This review paper presents recent developments and state-of-the-art research related to three critical elements that enable an EAWS. The first element is wearable sensors, which monitor human body physiological signals and activities. Emphasis is given on explaining different types of transduction mechanisms presented, and emerging materials and fabrication techniques. The second element is the flexible and wearable energy storage device to drive low-power electronics and the software needed for automatic detection of unstable physiological parameters. The third is the flexible and stretchable energy harvesting module to recharge batteries for continuous operation of wearable sensors. We conclude by discussing some of the technical challenges in realizing energy-autonomous wearable sensing technologies and possible solutions for overcoming them.

1D Nanomaterial‐Based Highly Stretchable Strain Sensors for Human Movement Monitoring and Human–Robotic Interactive Systems

“…Ideally, the total resistance of an NC‐based strain sensor is the sum of four types of resistances in series namely: contact resistance between metallic interconnects and NC ( R C ); dimensional resistance ( R D ); internal resistance of the nanomaterial ( R I ); and tunneling resistance at the interconnection nodes of nanomaterial ( R T ). [ 8 ] The device sensitivity is dictated by the change in total resistance with the applied strain. Generally, for a CNT‐based NC with good robustness, there is negligible change in the first three resistances, that is, R C , R D , and R I with applied strain thus, they can be omitted to explain the device working mechanism.…”

“…Generally, for a CNT‐based NC with good robustness, there is negligible change in the first three resistances, that is, R C , R D , and R I with applied strain thus, they can be omitted to explain the device working mechanism. [ 8 ] Therefore, the sensitivity of the strain sensor is dictated by the number and quality of interconnection nodes between 1D nanomaterial, dynamic (time‐dependent) change of physical contact between them, and the tunneling current. When a uniaxial tensile strain is applied to the nanocomposite, 1D material filaments (i.e., MWCNTs) are separated apart, leading to loss of contact points and widening of their distances.…”

High-performance printed electronics based on inorganic semiconducting nano to chip scale structures

“…[ 82 , 148 , 182 , 184 , 208 , 209 ], stretchable interconnects [ 210 ] and many others [ 29 , 73 ]. These intrinsic stretchable inorganic materials have enabled many novel applications that were impossible for conventional electronics as well as for organic PE to achieve such as personal healthcare monitoring [ 17 , 207 , 211 ], human–machine interface (artificial intelligence) [ 59 , 212 , 213 ], neuromorphic computing [ 140 , 214 , 215 ], etc. where faster computing and mechanical flexibility is needed.…”

Recent Advances in Human Motion Excited Energy Harvesting Systems for Wearables

“…[ 133,135 ] Furthermore, with the development of low power sensors and electronics, more self‐powered applications can be realized by the embedded energy harvesters. [ 136,137 ]…”