A thermally buckled piezoelectric energy harvester is designed to power biomedical devices inside the body. The energy harvester (EN) uses the vibrations inside the body to generate the electricity needed for powering biomedical sensors and devices. The piezoelectric beam consists of a brass substrate and two piezoelectric patches attached to the top and the bottom of the substrate. The bimorph beam is inside a rigid frame. The bimorph beam is buckled due to the difference in the coefficient of the thermal expansion of the beam and the frame.
Inside the body, most of the energy content come from the low-frequency vibrations (less than 50 Hz). Having high natural frequency is a major problem in Microelectromechanical systems (MEMS) energy harvesters. Considering the small size of the EN, 1 ܿ݉cm3, the natural frequency is expected to be high. In our design, the natural frequency is lowered significantly by using a buckled beam. A mass is also used in the middle of the beam to decrease the natural frequency even more. Since the beam is buckled, the design is bistable and nonlinear which increases the output power.
In this paper, the natural frequencies and mode shapes of the EN are analytically derived. The geometric nonlinearities are included in the electromechanical coupled governing equations. The governing equations are solved and it is shown that the device generates sufficient electricity to power biomedical sensors and devices inside the human body.
In this manuscript, we envision deployable structures (such as solar arrays) and origami-inspired foldable structures as metamaterials capable of tunable wave manipulation. Specifically, we present a metamaterial whose bandgaps can be modulated by changing the fold angle of adjacent panels. The repeating unit cell of the structure consists of a beam (representing a panel) and a torsional spring (representing the folding mechanism). Two important cases are considered. Firstly, the fold angle (angle between adjacent beams), Ψ, is zero and only flexural waves propagate. In the second case, the fold angle is greater than zero (Ψ > 0). This causes longitudinal and transverse vibration to be coupled. FEM models are used to validate both these analyses.
Increasing the fold angle was found to inflict profound changes to the wave transmission characteristics of the structure. In general, increasing the fold angles caused the bandwidth of bandgaps to increase significantly. For the lowest four bandgaps we found bandwidth increases of 252 %, 177 %, 230 % and 163 % respectively at Ψ = 90 deg (relative to the bandwidths at Ψ = 0). In addition, significant increase in bandwidth of the odd-numbered bandgaps occurs even at small fold angles- the bandwidth for the first and third bandgaps effectively double in size (increase by 100%) at Ψ = 20 deg relative to those at Ψ = 0. This has important ramifications in the context of tunable wave manipulation and adaptive filtering.
In addition, by expanding out the characteristic equation of transfer matrix for the straight structure, we prove that the upper band edge of the nth bandgap will always equal the nth simply supported natural frequency of the constituent beam. Further, we found that the ratio (EI/kt) is an important parameter affecting the bandwidth of bandgaps. For low values of the ratio, effectively, no bandgap exists. For higher values of the ratio (EI/kt), we obtain a relatively large bandgap over which no waves propagate. This can have important ramifications for the design of foldable structures. As an alternative to impedance-based structural health monitoring, these insights can aid in health monitoring of deployable structures by tracking the bandwidth of bandgaps which can provide important clues about the mechanical parameters of the structure.
The design and modeling of a bar made of functionally graded materials are studied in this paper. The material properties of the bar are harmonically varied along the bar. The bar is mathematically modeled and its governing equation is derived. The mode shapes and the natural frequencies of the system are calculated analytically using the boundary conditions at the two ends of the bar. The wave propagation in the bar is studied and the frequency band gap of the system is found. It is shown that by varying the material properties of the bar, we can design a system with a desired frequency band gap.
This paper investigates energy harvesting from arterial blood pressure via the piezoelectric effect by using a novel
streaked cylinder geometry for the purpose of powering embedded micro-sensors in the brain. Initially, we look
at the energy harvested by a piezoelectric cylinder placed inside an artery acted upon by blood pressure. Such
an arrangement would be tantamount to constructing a stent out of piezoelectric materials. A stent is a cylinder
placed in veins and arteries to prevent obstruction in blood flow. The governing equations of a conductor coated
piezoelectric cylinder are obtained using Hamilton’s principle. Pressure acting in arteries is radially directed and
this is used to simplify the modal analysis and obtain the transfer function relating pressure to the induced voltage
across the surface of the harvester. The power harvested by the cylindrical harvester is obtained for different
Radially directed pressure occurs elsewhere and we also look at harvesting energy from oil flow in pipelines.
Although the energy harvested by the cylindrical energy harvester is significant at resonance, the natural frequency
of the system is found to be very high. To decrease the natural frequency, we propose a novel streaked stent
design by cutting it along the length, transforming it to a curved plate and decreasing the natural frequency.
The governing equations corresponding to the new geometry are derived using Hamilton’s principle and modal
analysis is used to obtain the transfer function.
The batteries of the current pacing devices are relatively large and occupy over 60 percent of the size of pulse
generators. Therefore, they cannot be placed in the subtle areas of human body. In this paper, the mastication force and
the resulting tooth pressure are converted to electricity. The pressure energy can be converted to electricity by using the
piezoelectric effect. The tooth crown is used as a power autonomous pulse generator. We refer to this envisioned pulse
generator as the smart tooth. The smart tooth is in the form of a dental implant. A piezoelectric vibration energy
harvester is designed and modeled for this purpose. The Piezoelectric based energy harvesters investigated and analyzed
in this paper initially includes a single degree of freedom piezoelectric based stack energy harvester which utilizes a
harvesting circuit employing the case of a purely resistive circuit. The next step is utilizing and investigating a bimorph
piezoelectric beam which is integrated/embedded in the smart tooth implant. Mastication process causes the bimorph
beam to buckle or return to unbuckled condition. The transitions results in vibration of the piezoelectric beam and thus
generate energy. The power estimated by the two mechanisms is in the order of hundreds of microwatts. Both scenarios
of the energy harvesters are analytically modeled. The exact analytical solution of the piezoelectric beam energy
harvester with Euler–Bernoulli beam assumptions is presented. The electro-mechanical coupling and the geometric
nonlinearities have been included in the model for the piezoelectric beam.
A nonlinear piezoelectric wind energy harvester is proposed which has a low startup wind speed and is not restricted to a
specific wind speed. By using the piezoelectric transduction mechanism, the gearbox is eliminated from the system and
the start up speed is improved. Permanent magnets are placed in the blade part of the windmill. The interactions
between the rotating magnets, positioned on the blades, and the tip magnets mounted on the piezoelectric beams directly
and parametrically excite the beams. The nonlinear magnetic force makes the vibrations of the beams nonlinear and can
make the beams bi-stable. This phenomenon is utilized to enhance the power output and to improve the robustness of the
power production. Two designs are presented which incorporate parametric and ordinary excitations to generate electric
power. The performance of each design is examined through experimental investigations. An analytic model is
developed which is verified by the experimental results and explains the nonlinear phenomena captured by the
Linear and nonlinear piezoelectric devices are introduced to continuously recharge the batteries of the pacemakers by
converting the vibrations from the heartbeats to electrical energy. The power requirement of the pacemakers is very low.
At the same time, after about 10 years from the original implantation of the pacemakers, patients have to go through
another surgical operation just to replace the batteries of their pacemakers. We investigate using vibration energy
harvesters to significantly increase the battery life of the pace makers. The major source of vibrations in chest area is due
to heartbeats. Linear low frequency and nonlinear mono-stable and bi-stable energy harvesters are designed according to
especial signature of heart vibrations. The proposed energy harvesters are robust to variations of heart beat frequency
and can meet the power requirement of the pacemakers.
A novel hybrid energy harvester has been proposed which utilizes the presence of nonlinearity and multiple harvesting
mechanisms to maximize the power output and the frequency bandwidth. The linear energy harvesters are frequency
selective meaning they only generate power if they are excited accurately at their natural frequency. Nonlinear effects
can make the harvester more broadband i.e. increase the efficient range of excitations frequency. We incorporate two
magnets into the design, to have a nonlinear repulsive force acting on the beam. The piezoelectric patches and the
electromagnetic coils convert the mechanical energy of the vibrations of the beam to electrical energy. The proposed
energy harvester is therefore a hybrid energy harvester. The method of multiple scales is used to solve the nonlinear
energy harvesting system. The electromechanical couplings have been considered in the nonlinear analysis. As a test the
special case of linear piezoelectric harvesting has been revisited and the proposed solution precisely matches the exact solution in the literature. The paper concludes by predicting the performance of a fabricated harvester which shows the effectiveness of both nonlinear and hybrid harvesting.
An analytical method is developed to calculate the natural frequencies and the corresponding mode shapes of a zigzag
structure proposed for MEMS energy harvesting from ambient vibrations. The high natural frequencies of the existing
designs of MEMS vibrational energy harvesters are serious drawbacks. A zigzag design is proposed to overcome this
deficit. The governing partial differential equations are solved using separation of variables for each of the lateral beams
in the structure. The vibration of each beam is related to the vibration of its neighbor beams by continuity and
equilibrium conditions. Finally enforcing the boundary conditions results the corresponding eigenvalue problem
revealing the natural frequencies and mode shapes. The usefulness of the design is proved by the relation between the
natural frequencies and number of elements, providing a method of designing a MEMS harvester with low natural