Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Sustainable yarn type-piezoelectric energy harvester as an eco-friendly, cost- effective battery-free breath sensor Nirmal Prashanth Maria Joseph Raj, Nagamalleswara Rao Alluri, Venkateswaran Vivekananthan, Arunkumar Chandrasekhar, Gaurav Khandelwal, Sang-Jae Kim ⁎ Nanomaterials & System Lab, Department of Mechatronics Engineering, Jeju National University, Jeju 690-756, South Korea HIGHLIGHTS • Cost-effective brush coating technique employed to coat all layers of nano- generator. • Flexible Yarn-piezoelectric nanogen- erator has dual functionality-har- vesting/sensing. • Self-powered breath sensor has good repeatability/stability with test sub- jects. • Proposed nanogenerator is suitable to harness linear/nonlinear surface mo- tions. • Fabrication process is eco-friendly, less time consuming, and high re- producibility. GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Bi 4 Ti 3 O 12 nanoparticles Piezoelectric nanogenerator Self-powered breath monitoring sensor Sol-gel technique Polyvinylidene fluoride Synergistic effect ABSTRACT A cost-effective layer-by-layer brush-coating technique was developed to fabricate a flexible yarn-based piezoelectric nanogenerator (FY-PNG) to harness abundant waste mechanical energy. A simple sol-gel method was used to syn- thesize the orthorhombic crystalline phase of bismuth titanate perovskite, i.e., Bi 4 Ti 3 O 12 (BiTO). A single FY-PNG device generated a maximum peak-to-peak open-circuit voltage (V OC(P–P) ), short-circuit current (I SC(P–P) ), and in- stantaneous area power density of 60 V, 400 nA, and 18.5 mW/m 2 , respectively, upon application of a 1 N periodic mechanical load. The switching polarity of the FY-PNG demonstrated good phase shifting between the output signals and confirmed that the output derived from the device and not from any external sources. The working mechanism, electrical poling effect, force analysis, repeatability, stability, charging, energy storage analysis, and sensitivity to biomechanical force of the FY-PNG was thoroughly investigated. The FY-PNG device output was used to power five commercial green light-emitting diodes (LEDs) and a display system. Additionally, a non-invasive self-powered breathing sensor (SPBS) was developed to monitor human inhalation/exhalation. The repeatability and reproduci- bility of SPBS evaluated using different devices and test subjects demonstrated a good variation in output (i.e., 0.2–0.4 V) for inhalation/exhalation; the SPBS was also evaluated under slow/fast and constant breathing conditions. The proposed brush-coating technique for FY-PNGs is an efficient, cost-effective, eco-friendly, and easily scalable technique that can pave the way to the design of novel-shaped PNG devices for applications such as implantable self- powered biosensors and automotive electronic systems. https://doi.org/10.1016/j.apenergy.2018.07.016 Received 21 April 2018; Received in revised form 16 June 2018; Accepted 4 July 2018 ⁎ Corresponding author. E-mail addresses: nirmalpm@jejunu.ac.kr (N.P. Maria Joseph Raj), alluri@jejunu.ac.kr (N.R. Alluri), arunecebe@jejunu.ac.kr (A. Chandrasekhar), gaurav@jejunu.ac.kr (G. Khandelwal), kimsangj@jejunu.ac.kr (S.-J. Kim). Applied Energy 228 (2018) 1767–1776 0306-2619/ © 2018 Elsevier Ltd. All rights reserved. T