Together with the evolution of digital health care, the wearable electronics field has evolved rapidly during the past few years and is expected to be expanded even further within the first few years of the next decade. As the next stage of wearables is predicted to move toward integrated wearables, nanomaterials and nanocomposites are in the spotlight of the search for novel concepts for integration. In addition, the conversion of current devices and attachment-based wearables into integrated technology may involve a significant size reduction while retaining their functional capabilities. Nanomaterialbased wearable sensors have already marked their presence with a significant distinction while nanomaterial-based wearable actuators are still at their embryonic stage. This review looks into the contribution of nanomaterials and nanocomposites to wearable technology with a focus on wearable sensors and actuators.

Researcher/Author: Wanasinghe Arachchige Dumith Madushanka Jayathilaka, Kun Qi, Yanli Qin, Amutha Chinnappan, William Serrano‐García, Chinnappan Baskar, Hongbo Wang, Jianxin He, Shizhong Cui, Sylvia W Thomas, Seeram Ramakrishna

Advanced Materials, Wiley Online Library, 2019/ 31/ 7, 1805921 (1 to 21), 10.1002/adma.201805921; https://onlinelibrary.wiley.com/doi/10.1002/adma.201805921

An ultra-broadband terahertz (THz) emitter covering a wide range of frequencies from 0.1 to 10 THz is highly desired for spectroscopy applications. So far, spintronic THz emitters have been proven as one class of efficient THz sources with a broadband spectrum while the performance in the lower THz frequency range (0.1–0.5 THz) limits its applications. In this work, a novel concept of a current-enhanced broad spectrum from spintronic THz emitters combined with semiconductor materials is demonstrated. A 2–3 order enhancement of the THz signals in a lower THz frequency range (0.1–0.5 THz) is observed, in addition to a comparable performance at higher frequencies from this hybrid emitter. With a bias current, there is a photoconduction contribution from semiconductor materials, which can be constructively interfered with the THz signals generated from the magnetic heterostructures driven by the inverse spin Hall effect (ISHE). These findings push forward the utilization of metallic heterostructure-based THz emitters on the ultra-broadband THz emission spectroscopy.

Researcher/Author: Mengji Chen, Yang Wu, Yang Liu, Kyusup Lee, Xuepeng Qiu, Pan He, Jiawei Yu and Hyunsoo Yang  

Adv. Optical Mater. 2019, 7, 1801608; https://doi.org/10.1002/adom.201801608

A stretchable electrocardiogram (ECG) patch (SEP) that monolithically integrates ECG monitoring chip-on-board (COB) with polydimethylsiloxane (PDMS) and liquid-metal interconnects is presented. The 4.8 x 4.8 cm2 SEP is conformal and robust to mechanical deformation. The use of Silicon On-Insulator rigid complementary-metal-oxide-semiconductor chip allows sophisticated power management and signal processing. The chip’s dense inputs/output pads are interfaced with coarser liquid-metal interconnects using dual-sided COB design. Robust ECG signal response (=100 mVP–P up to 1 kHz), subjected to mechanical deformation and moisture is demonstrated. The SEP allows up to 10% stretch, providing sufficient pliability to enable conformal contact to the human chest. Low profile soft carbon black-PDMS nanocomposite electrodes, robust to deformation, enable good skin contact and allow for low-noise signal acquisition that is comparable to larger commercial wet electrodes.

Researcher / Author: Yida Li, Alireza Alian, Li Huang, Kah Wee Ang, Dennis Lin, Dan Mocuta, Nadine Collaert, and Aaron V-Y Thean
ADV. Electron, Master,  2018, 1800463; https://doi.org/10.1002/aelm.201800463.

For full publication paper, email: hifes@nus.edu.sg

Triboelectric nanogenerators and sensors can be applied as human− machine interfaces to the next generation of intelligent and interactive products, where flexible tactile sensors exhibit great advantages for diversified applications such as robotic control. In this paper, we present a self-powered, flexible, triboelectric sensor (SFTS) patch for finger trajectory sensing and further apply the collected information for robotic control. This innovative sensor consists of flexible and environmentally friendly materials, i.e., starch-based hydrogel, polydimethylsiloxane (PDMS), and silicone rubber. The sensor patch can be divided into a two-dimensional (2D) SFTS for in-plane robotic movement control and a one-dimensional (1D) SFTS for out-of-plane robotic movement control. The 2D-SFTS is designed with a grid structure on top of the sensing surface to track the continuous sliding information on the fingertip, e.g., trajectory, velocity, and acceleration, with four circumjacent starchbased hydrogel PDMS elastomer electrodes. Combining the 2D-SFTS with the 1D-SFTS, three-dimensional (3D) spatial information can be generated and applied to control the 3D motion of a robotic manipulator, and the real-time demonstration is successfully realized. With the facile design and very low-cost materials, the proposed SFTS shows great potential for applications in robotics control, touch screens, and electronic skins.

Researcher / Author: Tao Chen, Qiongfeng Shi, Minglu Zhu, Tianyiyi He, Tianyiyi He,  Lining Sun, Lei Yang, and Chengkuo Lee.

ACS Nano,2018,12 (11),DOI:10.1021/acsnano.8b06747;

 https://doi.org/10.1002/aelm.201800463.

For full publication paper, email: hifes@nus.edu.sg

Utilization of ubiquitous low-grade waste heat constitutes a possible avenue towards soft
matter actuation and energy recovery opportunities. While most soft materials are not all
that smart relying on power input of some kind for continuous response, we conceptualize a
self-locked thermo-mechano feedback for autonomous motility and energy generation
functions. Here, the low-grade heat usually dismissed as ‘not useful’ is used to fuel a soft
thermo-mechano-electrical system to perform perpetual and untethered multimodal locomotions.
The innately resilient locomotion synchronizes self-governed and auto-sustained
temperature fluctuations and mechanical mobility without external stimulus change, enabling
simultaneous harvesting of thermo-mechanical energy at the pyro/piezoelectric mechanistic
intersection. The untethered soft material showcases deterministic motions (translational
oscillation, directional rolling, and clockwise/anticlockwise rotation), rapid transitions and
dynamic responses without needing power input, on the contrary extracting power from
ambient. This work may open opportunities for thermo-mechano-electrical transduction,
multigait soft energy robotics and waste heat harvesting technologies.

Researcher / Author: Xiao-Qiao Wang, Chuan Fu Tan, Kwok Hoe Chan, Xin Lu, Liangliang Zhu, Sang-Woo Kim and Ghim Wei Ho

NATURE COMMUNICATIONS | (2018) 9:3438; https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201805921

Triboelectric nanogenerator (TENG) is a promising technology because it can harvest energy from the environment to enable self-sustainable mobile and wearable electronic devices.

In this work, we present a flexible touch pad capable of detecting the contact location of an object and generating substantial energy simultaneously based on the coupling of triboelectric effects and electrostatic induction. The touch pad consists of Polytetrafluoroethylene (PTFE) thin film, multiple Aluminum (Al) electrodes and Polyethylene terephthalate (PET) layers, which can be achieved through low cost, simplified and scalable fabrication process. Different from the conventional
multi-pixel-based positioning sensor (i.e., large array of sensing elements and electrodes), the analogue method proposed here is used to implement the positioning function with only four electrodes. Position location can achieve a detecting resolution of as small as 1.3 mm (the size of locating layer is 7.5 cm x 7.5 cm). For the energy harvesting part, a multilayer structure is designed to provide higher current output. The open circuit voltage of the device is around 420 V and the short circuit current can reach up to 6.26 uA with current density of 0.25 uA/cm2. The maximum output power obtained is approximately 10 mW, which is 0.4 mW/cm2. The flexibility and significantly reduced number of electrodes enable the proposed touch pad to be readily integrated into portable electronic devices, such as intelligent robots, laptops, healthcare devices, and environmental surveys, etc.

Researcher / Author:  Tao Chen, Qiongfeng Shi, Kunpu Li, Zhan Yang, Huicong Liu, Lining Sun, Jan A Dziuban and Chengkuo Lee .
Nanomaterials 2018, 8(7), 503; https://doi.org/10.3390/nano8070503

For full publication paper, email: hifes@nus.edu.sg

A hybrid energy harvester is presented in this paper to harvest energy from water flow motion and temperature difference in an irrigating pipe at the same time. The harvester is based on the integration of thermoelectric and electromagnetic
mechanisms. To harvest the water flow motion, a turbine fan with magnets that are attached on the blades is placed inside of the water pipe. Multiple coils turn the water flow energy into electricity with the rotation of the turbine. The thermoelectric generators (TEGs) are attached around the pipe, so as to harvest energy due to temperature difference. For a maximum temperature difference of 55 ◦C (hot side 80 ◦C and room temperature 25 ◦C), twelve serial-connected TEGs can generate voltage up to 0.346 V. Under a load resistance of 20 ´Ω, the power output of 1.264 mW can be achieved. 

For a maximum water flow rate of 49.9 L/min, the electromagnetic generator (EMG) can produce an open circuit voltage of 0.911 V. The EMG can be potentially used as a water flow meter due to the linear relationship between water flow rate and output voltage. Under the joint action of TEG and EMG, the maximum terminal voltage for TEG is 66 mV and for EMG is 241 mV at load resistances of 10 and 100 ´Ω, respectively, resulting in a corresponding power output of 0.435 and 0.584 mW.

Researcher / Author:  Huicong Liu, Jiankang Zhang, Qiongfeng Shi, Tianyiyi He, Tao Chen, Lining Sun, Jan A Dziuban and Chengkuo Lee.

The research paper is published in Micromachines on 09/08/2018, 395.
doi/abs/10.1002/smtd.201800078

For full publication paper, email: hifes@nus.edu.sg

Researcher / Author:  Tao Chen, Qiongfeng Shi, Zhan Yang, Jinchang Liu, Huicong Liu, Lining Sun, and Chengkuo Lee.

Nanomaterials, vol. 8, no.7, 503, 2018; https://doi.org/10.3390/nano8070503

For full publication paper, email: hifes@nus.edu.sg

Adaptive tendril coiling of climbing plants has long inspired the artificial soft microsystem for actuation and
morphing. The current bionic research efforts on tendril coiling focus on either the preparation of materials with the
coiling geometry or the design of self-shaping materials. However, the realization of two key functional features of the
tendril, the spring-like buffering connection and the axial contraction, remains elusive. Herein, we devise a conductive
tendril by fusing conductive yarns into tendril configuration, bypassing the prevailing conductivity constraints and
mechanical limitations. The conductive tendril not only inherits an electrophysiology buffering mechanics with exceptional
conductance retention ability against extreme stretching but also exhibits excellent contractive actuation performance. The
integrative design of the ultraelastic conductive tendril shows a combination of compliant mobility, actuation, and sensory
capabilities. Such smart biomimetic material holds great prospects in the fields of ultrastretchable electronics, artificial
muscles, and wearable bioelectronic therapeutics.

Researcher / Author: Yin Cheng, Ranran Wang, Kwok Hoe Chan, Xin Lu, Jing Sun and Ghim Wei Ho

ACS Nano 2018, 12, 3898−3907; https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201805921