The optical image of the composite film shows the high transparency and flexibility of the film. a) The transmittance values and (b) output voltages and current densities of silk fibroin-based composite film at the different concentrations of KNN:Mn nanoparticles. The output voltage and current of the TENG fabricated with the stretchable film as a function of the concentrations of Ag NWs. The output voltages and (b) currents of the TENG with Al film, PDMS film with Ag NWs, and OH and DMAP-Au NPs supported Ag-PDMS film.
Output voltage and (b) current of TENGs with pure Al film and Au NP-decorated Al film covered with Citrate, OH and DMAP. Measured voltage of a commercial capacitor μF) loaded with the AC to DC signal conversion circuit, (c) Boosted voltage using the buck-boost circuit obtained using 1000 μF. d) Photograph of the wireless sensor system integrating the TENG with a signal processing circuit.
INTRODUCTION
Au NPs of citrate were synthesized by a modified process.[77] The Au NPs with a size of 5 nm were synthesized as a seed. It shows that the output power increases with the degree of dispersion, as shown in the inset. d) The generated output voltages with the combination of dispersants. The calculated piezoelectric potential difference between (a) aggregated and (b) well-distributed ferroelectric particles in the silk fibroin matrix. a) The output voltages and (b) current densities of the different ferroelectric particles when the concentrations of ferroelectric particles are 30 wt%.
The decrease of the output current in the TENG with the supporter was due to. And the single-scale mesoporous structured films showed a nonlinear sensitivity in contrast to multi-scale mesoporous structured film. a) The capacitive responses of the HMD pressure sensor with the porosity of 50 % and EMD pressure sensor with the porosity of against loading and unloading of a 2 kPa repeatedly.
THEORETICAL BACKGROUND
Representative transduction in motion sensor
- Piezoelectricity
- triboelectricity
A motion sensor that could detect external pressure, stretch, and motion strain has attracted attention for its greatest potential in wearable application technology. Representative transductions in a motion sensor, which convert mechanical deformation into an electronic signal, are an important component for accurate quantitative monitoring of external force. Mainly representative transductions such as piezo/triboelectricity [40], piezo-capacitance [39], piezo-resistivity [38], and are reported to quantitatively monitor the applied external force (pressure and bending/stretching) of motion sensors and details of representative motion sensor transduction is presented in this section.
Schematic images of three representative motion sensor transduction: (a) piezoelectricity/triboelectricity, (b) piezocapacitance, (c) piezoresistance. Motion sensor based on piezoelectricity mainly utilizes the charge generation in various nanostructured materials under applied external force due to the existence of electrical polarization in dielectrics.
EXPERIMENTAL PROCEDURE
- Silk fibroin based biodegradable piezoelectric composite sensor
- Highly stretchable self-powered 2D fabric motion sensor
- Ag NWs-embedded within PDMS film
- Self-powered triboelectric sensor based on Au NPs capped with DMAP, OH, citrate
- Wearable self-powered sensor based on triangular prism shaped supporter
- Hierarchically mesoporous structured dielectric based pressure sensor
- Measurement of electrical characteristics…
- Microstructural analysis
Cu wires were attached to both electrodes using Ag paste to measure the output voltage and current density. Polydimethylsiloxane (PDMS) (Sylgard 184, Dow Corning), aluminum wires and foils were used to fabricate a fiber-structured triboelectric nanogenerator. To make the PDMS tube, aluminum wires with different radii were dipped into the solution and pulled out very slowly for a uniform wall thickness (~400 μm) of the tube.
Acrylonitrile butadiene styrene (ABS) filament (Makerbot Industry, USA) was used to fabricate the mold for the support, by the FDM-based 3D printer at a steady rate for 20 minutes. The mass ratio between DI water and PDMS was about 2:3 to create 40% porosity in order to increase the compressibility of the support.
RESULTS AND DISCUSSION
Silk fibroin based biodegradable piezoelectric composite sensor
- Structural, electrical and optical characterization
- Output enhancement for high sensitivity in self-powered sensor
- Ag NWs-embedded within PDMS film for stable performance
- Output enhancement for high sensitivity in self-powered sensor
- Force-response output performance change
- Practical application in self-powered devices
Furthermore, the silk fibroin solution is so low viscous that the nanoparticles naturally and easily sink to the substrate surface, as shown in the left part of The cross-sectional image in the right part of Figure 6c confirms that the nanoparticles are well dispersed in the silk fibroin matrix. The output voltage and output current of the fiber-structured TENG of approximately 5 cm in length were measured under the cycled compressive force of about 50 N at an applied frequency of 10 Hz as shown in Figure 13a.
The output performance in the triboelectric nanogenerator is strongly dependent on the gap distance and the contact area between two materials, thus on the radius of the PDMS tube and the Al wire. The output current is the highest (~6 μA) in position III, almost 2 times improvement of the output current from flat fibers. We attribute this to the decrease in the radius of the PDMS tube caused by the stretching of the fiber.
A schematic diagram of the fabrication process of Au NPs-decorated stretchable film is shown in Figure 24, and detailed information is described in the experimental section. Compared to that (~0.045 mA) of the TENG made of Al film, the output currents are smaller. This will account for the increased potential difference with the Fermi level of PDMS (Fig. 29d).
Using the COMSOL multi-physics software, we calculated electrostatic potentials of the Au NPs-decorated TENGs with the above results, as shown in Figure 30d. The improvement in output power of the TENG with the stretchable film covered by DMAP-Au NPs can be explained by the improvement of the contact uniformity and the change of the surface potential. We systematically measured the output performance of the TENG with the stretchable film as a function of external force from 1 to 90 N, compared to that with Al foil, plotted in Figures 33a and 33b.
The output voltages (a) and currents (b) of the TENGs with Al film, Ag-PDMS film covered by DMAP-Au NPs as a function of pressure force. The measured voltage of the capacitor is also increased to a constant voltage of 2.6 V using a buck-boost circuit, as shown in Figure 34c.
Wearable self-powered sensor based on triangular prism shaped supporter
- Angle optimization of triangular prism shaped supporter
- Weight-response output performance change
- Self-powered pressure distribution sensor for monitoring local pressure action
To see the effect of the angle on the output power, we systematically measured the output voltage and current as a function of the angle from 0 to 35 o, which is shown in Fig. 40. The flat TENG without a support produced an output voltage and current of 8 V and 6 μA, respectively. When a 5 o angle bracket was used, the output voltage and current increased to 38 V and 30 μA, respectively.
The output current signal of flat TENG and with different angles from 0 o to 35 o of triangular prism shaped support. The change in the output power with the angle is explained via the uniformity of the contact between Al and PDMS. We measured the output current of the TENGs with the weight from 74 to 92 kg, plotted in Figure 42a.
The output voltages and currents increase with weight which can be attributed to the increase in effective contact area [94-96]. The output current as a function of walking speed from 1.2 m/s to 2.4 m/s was also measured and plotted in Figure 42b. It is also clearly visible that the output voltages and currents increase with speed.
The improvement in output signals at higher frequency is reported to be due to effective compensation effects of electrons lost by scattering with molecules in the air [97, 98]. To investigate the output power of the supported TENG, resistors were used as external loads from. TENG arrays (5 × 5) with an area of 1 × 1 cm2 were fabricated and the output power was measured during walking, as shown in Figures 44.
Hierarchically mesoporous structured dielectric based pressure sensor
- Mechanical test
- Hierarchically mesoporous design for linearly sensitive detection
- Ag NWs employment for highly sensitive detection
- Detection of bending direction in strain sensing application
- Artificial finger integrated multifunctional sensor
The capacitive pressure sensing mechanism of mesoporous film is based on the signal of capacitive change caused by the variation of the distance between two electrodes during compressive deformation. Using mechanical compression tests and COMSOL simulations, we investigated how the compressibility of mesoporous film affects the rate of variation of the thickness of mesoporous film, as shown in Figure 2a. It is noted that the flexibility (f) is determined by f=L/EA, where Li is the thickness of the mesoporous structured film, A is the effective area and E is the elastic modulus of the mesoporous structured film.
Therefore, the improvement of the compressibility of the mesoporous structured films with larger porosities can be expected to lead to highest sensitivity of the resulting pressure sensors. To first demonstrate the improvement in pressure sensitivity as induced by the high porosity in the identical mesoporous structured films, the capacitance variation of the mesoporous structured film with pressure applied to the surface was investigated under different porosities of the mesoporous structured film and 50% ) and multi-scale mesoporous structured film as shown in Figure 3a. Despite the increased sensitivity with the single-shell mesoporous structured film, as shown in Figure 3b, the sensitivity of this sensor suddenly decreased above a certain pressure value, due to the saturation of the deformation of the mesoporous structured dielectric.
As shown in Figure 4d, the capacitive signals of the sensor showed negligible degradation despite the intensively repeated loading cycle test, demonstrating that the sensor has high repeatability, durability and stability under mechanical loads. To investigate the detection of bending direction of the multiscale mesoporous structured sensors as a strain sensor, the identical capacitive measurement was done with the direction of the bending, convex and concave as shown in Figure 5a. Therefore, the position of the pores of different sizes plays an important role in enhancing the capacitance change. a).
The schematic mechanism that the difference in the thickness changes of HMD load sensors can be shown during convex and concave bending. To demonstrate the ability of multi-scale mesoporous structured multifunctional sensors as a motion detector, artificial fingers were developed by integrating the multifunctional sensors with artificial finger based on highly stretchable Ecoflex as shown in Figure 6a. In addition, the lifetime of the device can also be checked in water with glycerol concentration up to 48 hours.
By UPS measurement, it was clearly observed that the DMAP decreased the effective work function of the Au NPs. The strain sensitivity of the sensors varied according to the bending direction due to gradient porous structure.
CONCLUSION
