Nowadays, thermal-energy-harvesting is an important research topic for powering wireless sensors. Among numerous thermal-energy-harvesting approaches, some researchers demonstrated novel thermomagnetic-energy harvesters to convert a thermal-energy from an ambient temperature-difference to an electrical-output to power the sensors. However, the harvesters are too bulky to be integrated with the sensors embedded in tiny mechanical-structures for some structuralhealth- monitoring applications. Therefore, miniaturized harvesters are needed. Hence, we demonstrate a miniature thermomagnetic-energy harvester. The harvester consists of CuBe-beams, PZT-piezoelectric-sheet, Gd-soft-magnet, NdFeB-hard-magnet, and mechanical-frame. The piezoelectric-sheet and soft-magnet is bounded at fixed-end and freeend of the beams, respectively. The mechanical-frame assembles the beams and hard-magnet. The length×width×thickness of the harvester is 2.5cm×1.7cm×1.5cm. According to this, our harvester is 20-times smaller than the other harvesters. In the initial-state of the energy-harvesting, the beams’ free-end is near the cold-side. Thus, the soft-magnet is cooled lower than its curie temperature (Tc) and consequently changed from paramagnetic to ferromagnetic. Therefore, a magnetic-attractive force is produced between the soft-magnet and hard-magnet. Consequently, the beams/soft-magnet are down-pulled toward the hard-magnet fixed on the hot-side. The soft-magnet closing to the hot-side is heated higher than its Tc and subsequently changed to paramagnetic. Consequently, the magnetic-force is eliminated thus the beams are rebounded to the initial-state. Hence, when the harvester is under a temperature-difference, the beams’ pulling-down/back process is cyclic. Due to the piezoelectric effect, the piezoelectric-sheet fixed on the beams continuously produces voltage-response. Under the temperature-difference of 29°C, the voltage-response of the harvester is 30.4 mV with an oscillating-frequency of 0.098 Hz.
In this paper, we demonstrate a self-powered AC-current sensor using a piezoelectric connected-in-series approach to increase the sensitivity. The sensor consists of a CuBe-beam, piezoelectric-PZT-sheet, NdFeB hard-magnet, and mechanical-frame. When the sensor is placed in an alternative magnetic-field induced by an alternative current-carrying wire, the magnet fixed on the beam is subjected to an alternative magnetic-force produced by the magnetic-field. Therefore, the beam is oscillated. Consequently, the piezoelectric-sheet fixed on the beam is periodically deformed and continuously produces voltage-response. When beams are connected in-series, the total voltage-response is significantly enlarged while the background-noise remains the same. The experimental result shows the sensitivity of the sensor consisting 8 beams connected in-series under the magnetic-field generated by a wire of 8-Ampere from a breaker is enlarged from 130 mV/A to 640 mV/A.
In this paper, we demonstrate an attachable energy-harvester-powered wireless vibration-sensing module for milling-process monitoring. The system consists of an electromagnetic energy harvester, MEMS accelerometer, and wireless module. The harvester consisting of an inductance and magnets utilizes the electromagnetic-induction approach to harvest the mechanical energy from the milling process and subsequently convert the mechanical energy to an electrical energy. Furthermore, through an energy-storage/rectification circuit, the harvested energy is capable of steadily powering both the accelerometer and wireless module. Through integrating the harvester, accelerometer, and wireless module, a self-powered wireless vibration-sensing system is achieved. The test result of the system monitoring the milling process shows the system successfully senses the vibration produced from the milling and subsequently transmits the vibration signals to the terminal computer. Through analyzing the vibration data received by the terminal computer, we establish a criterion for reconstructing the status, condition, and operating-sequence of the milling process. The reconstructed status precisely matches the real status of the milling process. That is, the system is capable of demonstrating a real-time monitoring of the milling process.
We report an electromagnetic inductance/coil-based non-destructive method to target distal screw-holes in an intramedullary interlocking-nail surgical operation for fixing a long-bone fracture. The method is a radiation-free approach addressing the over-exposure issue of radioactivity caused by the typical X-ray-imaging approach. According to the method, we fabricate a targeting-system consisting of an internal inductance, external coil, guiding-mechanism, and driving/measurement electronics. When a voltage is applied to the internal inductance embedded in one of the distal screw-holes of a nail inserted in a bone, a directional magnetic flux is generated by the internal inductance due to the electromagnetic induction. Subsequently, the directional magnetic flux penetrates the nail and bone. When the external coil outside the bone scans along the axial and angular directions of the nail/bone, different amount of the generated magnetic flux is detected by the coil and consequently corresponding voltage response is induced in the coil due to the electromagnetic induction. In contrast to the magnetic flux generated and detected by the inductance and coil, respectively, we also investigate the reverse physics-behavior of the flux transmission (i.e., flux generated and detected by the coil and inductance) in order to improve the approach. Finally, by correlating the induced-voltage responses with the scanned axial-locations along the nail/bone, correlation curves are plotted. Through analyzing the curves, a criterion for predicting the location of the screw-holes of the nail is established. When compared the predicted location with the actual location of the screw-hole, the maximum targeting error is 2 mm for locating a screw-hole with a diameter of 5 mm. The result shows the targeting-method is accurate, fast, and easy for the surgeons and significantly simplifies the existed interlocking-nail surgical procedures.
In this paper, we demonstrate a non-contact magnetic/piezoelectric-based thermal energy harvester utilizing an optimized thermal-convection mechanism to enhance the heat transfer in the energy harvesting/converting process in order to increase the power output. The harvester consists of a CuBe spring, Gadolinium soft magnet, NdFeB hard magnets, frame, and piezoelectric PZT cantilever beams. According to the configuration, the energy harvesting/converting process under a temperature-difference is cyclic. Thus, the piezoelectric beams continuously oscillate and subsequently produce voltage responses due to the piezoelectric effect. The maximum voltage response of the harvester under a temperaturedifference of 25°C is 16.6 mV with a cycling frequency of 0.58 Hz. In addition, we compare the testing result of the harvester utilizing the new thermal-convection mechanism reported in this paper and using previous thermal-convection mechanism reported elsewhere. According to the comparison, the results show the harvester utilizing the new thermal-convection mechanism has a higher cycling frequency resulting in a higher power output than the previous mechanism.
We report electric field control of nanoscale magnetic domain pattern transformation processes due to the converse
magnetoelectric effect in a magnetoelectric device. The magnetoelectric device is a Ni-microdot/PZT-film bi-layer
heterostructure. Due to the converse magnetoelectric effect, nanoscale magnetic domain (i.e. dot-domain/pseudo-single-domain/
short-stripe-domain/vortex-core) in the central region of a Ni microdot is controlled under an electric field (1.6
MV/m). The electric field induced domain-pattern transformation process (i.e. deformation and rotation of the nanoscale
domain in the central region of the Ni microdot) is observed with the magnetic force microscopy. Upon removal of the
electric field, the deformed/rotated nanoscale magnetic domain-pattern/vortex-core returns to its original state, i.e.