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Soft strain sensors have attracted significant attention in wearable human motion monitoring applications. However, there is still a huge challenge for decoupled measurement of multidirectional strains. In this study, we have developed a biaxial and stretchable strain sensor based on a carbon nanotube (CNT) film and a microdome array (MA)-patterned elastomeric substrate. The MA structures lead to generating localized and directional microcracks of CNT films within the intended regions under tensile strain. This mechanism allows a single sensing layer to act as a strain sensor capable of decoupling the biaxial strains into axial and transverse terms. The ratio of resistance change between two perpendicular axes is about 960% under an x-directional strain of 30%, demonstrating the biaxial decoupling capability. Also, the proposed strain sensor shows high stretchability and excellent long-term reliability under a cyclic loading test. Finally, wearable devices integrated with the strain sensor have been successfully utilized to monitor various human motions of the wrist, elbow, knee, and fingers by measuring joint bending and skin elongation.

Probing micro-bumps for pre-bond testing is an essential process to check for a known good die. In recent technologies, micro-bumps such those used in 3-D-IC are too small and dense, which gives the probing a new challenge. Moreover, developers are concerned that the tip ends of the micro-bumps are mechanically damaged during the pre-bond testing, which is detrimental for the post-process IC assembly. Thus, many low damage probing solutions have been developed, but they still inevitably damage the tip end of the micro-bumps when the conventional probing method, vertical contact, is used. In this paper, for the first time, we demonstrate lateral contact probing on 55- $\mu \text{m}$ pitch micro-bumps without any damage to the tip ends. We successfully realized the testing with monolithically fabricated probes by nickel electroplating with a high aspect ratio photoresist mold. The measured fatigue life of the fabricated probes was at least100 000 cycles. Furthermore, the measured current carrying capacity was more than 180 mA. Proving our concept, the contact test results on the micro-bumps showed no damage to the tip end, and the contact resistance was below 1.13 $ {\Omega }$ . Finally, the10 000 probes achieved a uniform 55- $\mu \text{m}$ pitch, which ensured the possibility in real testing. [2018-0041]

A number of flexible and stretchable strain sensors based on piezoresistive and capacitive principles have been recently developed. However, piezoresistive sensors suffer from poor long-term stability and considerable hysteresis of signals. On the other hand, capacitive sensors exhibit limited sensitivity and strong electromagnetic interference from the neighboring environment. In order to resolve these problems, a novel stretchable strain sensor based on the modulation of optical transmittance of carbon nanotube (CNT)-embedded Ecoflex is introduced in this paper. Within the film of multiwalled CNTs embedded in the Ecoflex substrate, the microcracks are propagated under tensile strain, changing the optical transmittance of the film. The proposed sensor exhibits good stretchability (ε ≈ 400%), high linearity (

Wearable pressure sensors have been attracting great attention for a variety of practical applications, including electronic skin, smart textiles, and healthcare devices. However, it is still challenging to realize wearable pressure sensors with sufficient sensitivity and low hysteresis under small mechanical stimuli. Herein, we introduce simple, cost-effective, and sensitive capacitive pressure sensor based on porous Ecoflex-multiwalled carbon nanotube composite (PEMC) structures, which leads to enhancing the sensitivity (6.42 and 1.72 kPa

Flexible and wearable pressure sensors have attracted a tremendous amount of attention due to their wider applications in human interfaces and healthcare monitoring. However, achieving accurate pressure detection and stability against external stimuli (in particular, bending deformation) over a wide range of pressures from tactile to body weight levels is a great challenge. Here, we introduce an ultrawide-range, bending-insensitive, and flexible pressure sensor based on a carbon nanotube (CNT) network-coated thin porous elastomer sponge for use in human interface devices. The integration of the CNT networks into three-dimensional microporous elastomers provides high deformability and a large change in contact between the conductive CNT networks due to the presence of micropores, thereby improving the sensitivity compared with that obtained using CNT-embedded solid elastomers. As electrical pathways are continuously generated up to high compressive strain (∼80%), the pressure sensor shows an ultrawide pressure sensing range (10 Pa to 1.2 MPa) while maintaining favorable sensitivity (0.01-0.02 kPa

In this research, the 3D printed package for optical transmittance change base strain sensor was developed. Optical transmittance based strain sensor is consisted by light source, light detector and functional film which transmittance changed by the external strain. Functional film is carbon nanotube embedded elastomer and it changes its visible light transmittance by the strain. To adjust the optical strain sensor on the human motion detection, we positioned light source and detector in the sensor package. To achieve this problem, we adopted the 3D printed polylactic acid (PLA) package for fabricating ring type strain sensor for finger bending detection.

In this work, we report a novel optical type flexible and stretchable strain sensor based on a carbon nanotube(CNT)-elastomer nanocomposite thin film. At the initial state, the percolated CNTs embedded on the surface of the elastomer film block most of the light illuminated on the film. As an external tensile strain is applied to the CNT-elastomer film, cracks on the film are generated and propagated, leading to an increase of optical transmittance of the CNT-elastomer film, which can be detected by a photodetector. The sensor shows a great strain sensing performances with high sensitivity, quick dynamic response, small hysteresis, high stability, and independence on light intensities.

This paper reports a novel flexible optical pressure sensor based on a porous elastomer film as a light transmission medium with ultra-high sensitivity and simplicity. The pore-closing behavior under external pressure and corresponding change of light transmittance of porous elastomer film were investigated. The porous elastomer film based optical pressure sensor showed highly sensitive and stable performance with the sensitivity of 2.177 kPa−1 over the pressure range of 0–10 kPa. Finally, the optical pressure sensor was integrated with thin film solar cell to modulate the generated electrical current towards self-powered sensing platform.

We have developed a self-powered gas sensor operating without external power under a light source, unlike a sensor that requires an external power source, such as a chemiresistive gas sensor or an electrochemical gas sensor. The sensor consists of a colorimetric film and an organic solar cell. The sensor uses a color change caused by the reaction of the N, N,N',N'-tetramethyl-p-phenylenediamine (TMPD) with NO 2 gas. The color change caused by the redox reaction of the colorimetric material does not require a separate light source and photodetector, unlike the conventional colorimetric sensor, because it directly changes the output of the solar cell by changing the transmittance of the film. Using this sensor, 1, 5, 10, 20ppm NO 2 gas was detected without external power source, and the performance of the gas sensor could be improved by using microstructure. This work is the first demonstration of self-powered gas sensor based on the combination of photovoltaic cell and microstructured colorimetric film.

In this work, we developed micro-crack based stretchable strain sensors consist of polydimethylsiloxane (PDMS) with micro-dome structure arrays and carbon nanotube (CNT) film coated on its surface. Due to a stress concentration caused by micro-dome structure under a certain strain, micro-cracks of CNT film are generated and propagated more easily as compared with the case of a CNT film on the plane surface. In addition, because the micro-cracks are only positioned at designed region which is between micro-domes, electrical resistances in elongated and perpendicular directions are clearly different thanks to the novel mechanism. As results of these phenomena, strain decoupling is achieved and a sensitivity of the sensor can be modulated by adjusting the dimension of micro-dome arrays. We also conducted the numerical simulation based on finite element method (FEM) to verify the designed sensing mechanism and predict the performance of the sensor. This kind of work is important for the motion detecting sensor for acquiring decoupled information from complex signal. Finally, we fabricated a smart glove that could detect a biaxial strain applied on the back of a hand skin to demonstrate that this sensor could be used as wearable device.

In this work, we proposed a novel method for facile hydrodynamic trapping and anchoring of bacterial cells using nanowire array with fishnet-like structure in microfluidic channel. Vertically well-aligned ZnO nanowires were directly synthesized onto side walls of microslit structures by hydrothermal method to form mesh-like cage structures. We found that the mesh-like cages were effective in trapping and anchoring of Escherichia coli cells as model bacteria. In addition, we observed two anchoring modes; impaling and wedging, by electron microscopy and they resulted in irreversible and reversible damage to the anchored cells, respectively. We expected that the suggested bacterial cell trapping method can be used as a simple cell-manipulating platform for advanced microfluidic system.