Flexible Piezoelectric Sensors Based on Ionic Liquid‐doped Poly(L‐Lactic Acid) for Human Coughing Recognition

Abstract

Cough is a common symptom of various respiratory diseases. However, recognizing a subject's cough using acoustic imaging can be challenging due to the complexity of coughing and the vulnerability of acoustic acquisition to external interference. This research aims to address these issues by utilizing a flexible piezoelectric ionic liquid‐doped poly(L‐lactic acid) (PLLA) sensor to gather the pressure signals from the human surface. 1‐butyl‐3‐methylimidazolium bis (trifluoromethylsulfonyl)imide ([BMIm]TFSI) ionic liquid (IL) can enhance the piezoelectric performance of PLLA thin film, the corresponding output voltage, and impact sensitivity are improved to three times and 105.1% for the PLLA/IL thin film with 1 wt% IL, 140 °C annealing 2 h and four times drawing ratio. The effect of IL on the crystallization behavior and piezoelectric properties of thin films during their preparation is investigated. The flexible PLLA/IL sensor is integrated into a wearable electronic system which collects and transmits piezoelectric signals from cough‐induced vibrations to the filter for denoising, then the acquired cough data are decomposed using the Empirical Mode Decomposition method and trained in a multi‐layer perception model to detect human coughing. It's evident that the flexible piezoelectric PLLA/IL sensors can be applied to human coughing recognition and show great potential applications in intelligent healthcare.

A poly(L-lactic Acid)-based flexible piezoelectric energy harvester with micro-zigzag structures

“…The crystal structures of the PLLA film were analyzed in two states: as-prepared and after being stretched four times and then immediately annealed at 140 • C for four hours. XRD analysis was conducted (see figure 2 All other identified bands are in line with the inherent variations in PLLA and show good agreement with the [18,31,32]. The SEM images in figure 2(e) depict the morphologies of PLLA films with DR4 and DR1.…”

“…This highlights the immense application possibilities of additive manufacturing technology [30]. In this scenario, the utilization of UV-curable elastic polymer as a substrate or encapsulation layer for flexible electronics is considered a practical approach [31,32]. Compared to conventional polymers like polyethylene terephthalate, polyimide, and polymethyl methacrylate [33], it becomes crucial to employ material with excellent flexibility to enhance the vibration properties of energy harvests.…”

Flexible strain sensors based on silver nanowires and UV-curable acrylate elastomers for wrist movement monitoring

“…Elastic polymer is one of the effective materials utilized as a substrate 20 or capsulation layer 3,21 of flexible sensors. Compared to traditional polymers, including polyethylene terephthalate, polyethylene naphthalate, polyimide, polymethyl methacrylate, etc.…”