The smart healthcare devices connected with the internet of things (IoT) for medical services can obtain physiological data of risk patients and communicate these data in real-time to doctors and hospitals. These devices require power sources with a sufficient lifetime to supply them energy, limiting the conventional electrochemical batteries. Additionally, these batteries may contain toxic materials that damage the health of patients and environment. An alternative solution to gradually substitute these electrochemical batteries is the development of triboelectric energy harvesters (TEHs), which can convert the kinetic energy of ambient into electrical energy. Here, we present the fabrication of a TEH formed by a stainless steel substrate (25 mm × 15 mm) coated with a molybdenum disulfide (MoS2) film as top element and a polydimethylsiloxane (PDMS) film deposited on indium tin oxide coated polyethylene terephthalate substrate (PET/ITO). This TEH has a generated maximum voltage of 2.3 V and maximum output power of 112.55 μW using a load resistance of 47 kΩ and a mechanical vibration to 59.7 Hz. The proposed TEH could be used to power potential smart healthcare devices.
Piezoelectric vibration energy harvesting (pVEH) microdevices can convert the mechanical vibrations to electrical voltages. In the future, these microdevices can provide an alternative to replace the electrochemical batteries, which cause contamination due to their toxic materials. We present the electromechanical modeling of a pVEH microdevice with a novel resonant structure for air conditioning vents at office buildings. This electromechanical modeling includes different multilayers and cross-sections of the microdevice resonator as well as the air damping. This microdevice uses a flexible substrate and it does not include toxics materials. The microdevice has a resonant structure formed by multilayer beams and U-shape proof mass of UV-resin (730 μm thickness). The multilayer beams contain flexible substrates (160 μm thickness) of polyethylene terephthalate (PET), two aluminum electrodes (100 nm thickness), and a ZnO layer (2 μm thickness). An analytical model is developed to predict the first bending resonant frequency and deflections of the microdevice. This model considers the Rayleigh and Macaulay methods, and the Euler-Bernoulli beam theory. In addition, the electromechanical behavior of the microdevice is determined through the finite element method (FEM) models. In these FEM models, the output power of the microdevice is obtained using different sinusoidal accelerations. The microdevice has a resonant frequency of 60.3 Hz, a maximum deflection of 2.485 mm considering an acceleration of 1.5 m/s2, an output voltage of 2.854 V and generated power of 37.45 μW with a load resistance of 217.5 kΩ. An array of pVEH microdevices connected in series could be used to convert the displacements of air conditioning vents at office buildings into voltages for electronic devices and sensors.
Industry 4.0 and the Internet of Things have significantly increased the use of sensors and electronic products based on flexible substrates, which require electrical energy for their performance. This electrical energy can be supplied by piezoelectric vibrational energy harvesting (pVEH) devices. These devices can convert energy from ambient mechanical excitations into electrical energy. In order to develop, these devices require piezoelectric films fabricated with a simple and low-cost process. In this work, we synthesize ZnO nanorod film by a solvothermal method and deposit by spraying on ITO (indium-tin-oxide)/PET (polyethylene terephthalate) flexible substrate for a pVEH microdevice. The results of the characterization of the ZnO nanorod film using X-ray diffraction (XRD) confirm the typical reflections for this type of nanomaterial (JCPDS 36-145). Based on transmission electron microscopy (TEM) images, the size of the nanorod film is close to 1380 nm, and the average diameter is 221 ± 67 nm. In addition, the morphological characteristics of the ZnO nanorod film are obtained using atomic force microscopy (AFM) tapping images. The pVEH microdevice has a resonant frequency of 37 Hz, a generated voltage and electrical power of 9.12 V and 6.67 μW, respectively, considering a load resistance of 107.7 kΩ and acceleration of 1.5 g. The ZnO nanorod film may be applied to pVEH microdevices with flexible substrates using a low-cost and easy fabrication process.
Hollow ZnO microspheres were successfully synthesized by a hydrothermal method and then functionalized with graphene oxide (GO) flakes, previously obtained through electrochemical oxidation.
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