Piezoelectric energy harvester with double cantilever beam undergoing coupled bending-torsion vibrations by width-splitting method

We propose piezoelectric energy harvester (PEH) with double-cantilever-beam (DCB) undergoing coupled bending-torsion vibrations by combining width-splitting method and asymmetric mass, in order that more ambient energy could be harvested from environmental vibration with multiple-frequency excitation. The geometrical dimensions are optimized for PEHDCB, when the maximum of output peak voltages Up-max and resonance frequency difference (Δf0) between the first and second modes are chosen as optimization objectives based on orthogonal test method. The energy harvesting efficiency is evaluated by the proportion of half-power bandwidth and quality factor, and the experimental and simulation results are compared to verify reliability. The Up-max1 and Pp-max1 are increased 25.2% and 57.3% for PEHDCB under the multi-frequency excitation, when the split-width method is applied into PEH with single-cantilever-beam (SCB) undergoing coupled bending-torsion vibrations. The deviations of Up-max1 and f0 are at the ranges of 4.9–14.2% and 2.2–2.5% for PEHDCB under the different mass ratios, and the measurement reliability is acceptable considering incomplete clamping, damping and inevitable assembly effects. The energy harvesting efficiency of PEHDCB presented is much higher than that of the conventional PEHSCB from environmental vibration with multiple-frequency excitation.

Analysis of the Influence of Ferromagnetic Material on the Output Characteristics of Halbach Array Energy-Harvesting Structure

Due to the particular arrangement of permanent magnets, a Halbach array has an significant effect of magnetism and magnetic self-shielding. It can stretch the magnetic lines on one side of the magnetic field to obtain an ideal sinusoidal unilateral magnetic field. It has a wide application range in the field of energy harvesting. In practical applications, magnetic induction intensity of each point in magnetic field is not only related to the induced current and conductor but also related to the permeability of the medium (also known as a magnetic medium) in the magnetic field. Permeability is the physical quantity that represents the magnetism of the magnetic medium, which indicates the resistance of magnetic flux or the ability of magnetic lines to be connected in the magnetic field after coil flows through current in space or in the core space. When the permeability is much greater than one, it is a ferromagnetic material. Adding a ferromagnetic material in a magnetic field can increase the magnetic induction intensity B. Iron sheet is a good magnetic material, and it is easy to magnetize to generate an additional magnetic field to strengthen the original magnetic field, and it is easy to obtain at low cost. In this paper, in order to explore the influence of ferromagnetic material on the magnetic field and energy harvesting efficiency of the Halbach array energy harvesting structure, iron sheets are installed on the periphery of the Halbach array rotor. Iron sheet has excellent magnetic permeability. Through simulation, angle between iron sheet and Halbach array, radian size of iron sheet itself and distance between iron sheet and Halbach array can all have different effects on the magnetic field of the Halbach array. It shows that adding iron sheets as a magnetic medium could indeed change the magnetic field distribution of the Halbach array and increase energy harvesting efficiency. In this paper, a Halbach array can be used to provide electrical power for passive wireless low-power devices.

An Experimental Study on Efficient Piezoelectric Coupled Beams and Corresponding Piezoelectric Bricks

In view of the low output power density of the existing footstep harvesters, two pairs of distinctive L-shaped beams and the corresponding piezoelectric brick models are developed to improve the utilization efficiency of the piezoelectric patches bonded on the beams. A theory model of the aforesaid L-shaped beam is established to analyze its dynamic performance. Two pairs of L-shaped beams and corresponding piezoelectric brick specimens are customized. The influences of some factors on the output voltage and average power from piezoelectric patches of aforesaid piezoelectric bricks are tested and analyzed. Numerical computation based on the theory model of L-shaped beam is conducted to extend the study on the electric output performances of the proposed piezoelectric bricks. Experiment and simulation results indicate that the peak-to-peak voltage and average power can reach up to 376 V (0.15 V/mm3) and 94.72 mW (37.89 μW/mm3) for a piezoelectric patch with a dimension of 50 mm × 50 mm × 1 mm of brick specimens. This research provides novel piezoelectric bricks to harvest footstep energy and obtains some instructive conclusions for the practical design of the piezoelectric brick with ideal energy harvesting efficiency and cost-effectiveness.

How Harvest More Ambient Energy from Environmental Vibration with a Multiple-Frequency Excitation

We propose piezoelectric energy harvester (PEH) with double-cantilever-beam (DCB) undergoing coupled bending-torsion vibrations by combining width-splitting method and asymmetric mass, in order that more ambient energy could be harvested from environmental vibration with multiple-frequency excitation. The geometrical dimensions are optimized for PEHDCB, when the maximum of output peak voltages Up−max and resonance frequency difference (Δf0) between the first and second modes are chosen as optimization objectives based on orthogonal test method. The energy harvesting efficiency is evaluated by the proportion of half-power bandwidth and quality factor, and the experimental and simulation results are compared to verify reliability. The Up−max1 and Pp−max1 are increased 25.2% and 57.3% for PEHDCB under the multi-frequency excitation, when the split-width method is applied into PEH with single-cantilever-beam (SCB) undergoing coupled bending-torsion vibrations. The deviations of Up−max1 and f0 are at the ranges of 4.9–14.2% and 2.2–2.5% for PEHDCB under the different mass ratios, and the measurement reliability is acceptable considering incomplete clamping, damping and inevitable assembly effects. The energy harvesting efficiency of PEHDCB presented is much higher than that of the conventional PEHSCB from environmental vibration with multiple-frequency excitation.

Implantable Wireless Systems: A Review of Potentials and Challenges

With the current advancement in micro-and nano-fabrication processes and the newly developed approaches, wireless implantable devices are now able to meet the demand for compact, self-powered, wireless, and long-lasting implantable devices for medical and health-care applications. The demonstrated fabrication advancement enabled the wireless implantable devices to overcome the previous limitations of electromagnetic-based wireless devices such as the high volume due to large antenna size and to overcome the tissue and bone losses related to the ultrasound implantable devices. Recent state-of-the-are wireless implantable devices can efficiently harvest electromagnetic energy and detect RF signals with minimum losses. Most of the current implanted devices are powered by batteries, which is not an ideal solution as these batteries need periodic charging and replacement. On the other hand, the implantable devices that are powered by energy harvesters are operating continuously, patient-friendly, and are easy to use. Future wireless implantable devices face a strong demand to be linked with IoT-based applications and devices with data visualization on mobile devices. This type of application requires additional units, which means more power consumption. Thus, the challenge here is to reduce the overall power consumption and increase the wireless power transfer efficiency. This chapter presents the state-of-the-art wireless power transfer techniques and approaches that are used to drive implantable devices. These techniques include inductive coupling, radiofrequency, ultrasonic, photovoltaic, and heat. The advantages and disadvantages of these approaches and techniques along with the challenges and limitations of each technique will be discussed. Furthermore, the performance parameters such as operating distance, energy harvesting efficiency, and size will be discussed and analyzed to introduce a comprehensive comparison. Finally, the recent advances in materials development and wireless communication strategies, are also discussed.