Wassim Borchani

A concept for energy harvesting from quasi-static structural deformations through axially loaded bilaterally constrained columns with multiple bifurcation points

A major obstacle limiting the development of deployable sensing and actuation solutions is the scarcity of power. Converted energy from ambient loading using piezoelectric scavengers is a possible solution. Most of the previously developed research focused on vibration-based piezoelectric harvesters which are typically characterized by a response with a narrow natural frequency range. Several techniques were used to improve their effectiveness. These methods focus only on the transducer?s properties and configurations, but do little to improve the stimuli from the source. In contrast, this work proposes to focus on the input deformations generated within the structure, and the induction of an amplified amplitude and up-converted frequency toward the harvesters? natural spectrum. This paper introduces the concept of using mechanically-equivalent energy converters and frequency modulators that can transform low-amplitude and low-rate service deformations into an amplified vibration input to the piezoelectric transducer. The introduced concept allows energy conversion within the unexplored quasi-static frequency range (?1?Hz). The post-buckling behavior of bilaterally constrained columns is used as the mechanism for frequency up-conversion. A bimorph cantilever polyvinylidene fluoride (PVDF) piezoelectric beam is used for energy conversion. Experimental prototypes were built and tested to validate the introduced concept and the levels of extractable power were evaluated for different cases under varying input frequencies. Finally, finite element simulations are reported to provide insight into the scalability and performance of the developed concept.

Self-powered piezo-floating-gate smart-gauges based on quasi-static mechanical energy concentrators and triggers

Changes in physical processes like ambient temperature or pressure variations occur at frequencies that are significantly lower than 1 Hz. This poses a challenge for designing self-powered sensors that monitor these quasi-static physical processes and at the same time scavenge operational energy for sensing, computation, and storage from the signal being monitored. In this paper, we present a novel paradigm for designing a self-powered sensor/data logger that exploits the physics of negative-stiffness mechanical energy concentrators with the physics of our previously reported piezoelectricity driven impact ionized hot-electron injection (p-IHEI)-based sensors. The operational principle is based on the sudden transitions from unstable mode branch switching during the elastic postbuckling response of slender columns, which are used to generate high-frequency deformations as an input to the p-IHEI-based sensor. The experimental results demonstrate that the proposed self-powered sensor based on an integrated circuit fabricated in a 0.5-μm CMOS technology can count and record the number of quasi-static input events with frequencies spanning less than 1 Hz.

Characterization of Mechanically-Equivalent Amplifiers and Frequency Modulating Concepts for Energy Harvesting Devices

One of the major obstacles that are limiting the development of deployable integrated sensing and actuation solutions is the scarcity of power. Converted energy from ambient loading in civil and mechanical structures is typically used as an alternative solution. Although, piezoelectric vibration harvesters have been widely used, these elements exhibit a narrow natural frequency response range, thus considerably limiting the levels of harvestable power. Most of the previously used methods focus only on modifying the transducer’s properties and configurations. These techniques do little to modify the stimuli from the source. In contrast, this work proposes to focus on the input signal generated within the structure by inducing amplified response amplitude and a frequency up-conversion toward the harvesters’ natural response spectrum. This paper introduces the concept of using mechanically-equivalent frequency modulators that can transform the low-amplitude and low-rate service and ambient deformations into an amplified input to the piezoelectric transducer. The introduced methods will allow energy generation and conversion for loads within the unexplored quasi-static frequency range (<< 1 Hz). The post-buckling behavior of bilaterally restrained columns and bistable plates is used for frequency up-conversion. A bimorph cantilever PVDF piezoelectric beam, attached to the columns and plates, are used for energy conversion. Experimental prototypes were built and tested to validate the introduced concept. The levels of extractable power are evaluated for different cases under varying input frequencies. Finally, numerical simulations provide insight into the scalability and performance of the developed concepts.Copyright

Monitoring of Postoperative Bone Healing Using Smart Trauma-Fixation Device With Integrated Self-Powered Piezo-Floating-Gate Sensors

Objective: Achieving better surgical outcomes in cases of traumatic bone fractures requires postoperative monitoring of changes in the growth and mechanical properties of the tissue and bones during the healing process. While current in-vivo imaging techniques can provide a snapshot of the extent of bone growth, it is unable to provide a history of the healing process, which is important if any corrective surgery is required. Monitoring the time evolution of in-vivo mechanical loads using existing technology is a challenge due to the need for continuous power while maintaining patient mobility and comfort. Methods: This paper investigates the feasibility of self-powered monitoring of the bone-healing process using our previously reported piezo-floating-gate (PFG) sensors. The sensors are directly integrated with a fixation device and operate by harvesting energy from microscale strain variations in the fixation structure. Results: We show that the sensors can record and store the statistics of the strain evolution during the healing process for offline retrieval and analysis. Additionally, we present measurement results using a biomechanical phantom comprising of a femur fracture fixation plate; bone healing is emulated by inserting different materials, with gradually increasing elastic moduli, inside a fracture gap. Conclusion: The PFG sensor can effectively sense, compute, and record continuously evolving statistics of mechanical loading over a typical healing period of a bone, and the statistics could be used to differentiate between different bone-healing conditions. Significance: The proposed sensor presents a reliable objective technique to assess bone-healing progress and help decide on the removal time of the fixation device.

Model Development for Dynamic Energy Conversion in Post-Buckled Multi-Stable Slender Columns

Broadband piezoelectric energy harvesting solutions from ambient loading have been extensively studied with the purpose of increasing the efficiency of vibration-based harvesters. Most of the previously developed methods focus on the transducer’s properties and configurations, and require vibration input excitations. In contrast, we have previously experimentally shown a mechanical energy concentrator system that exploits the quasi-static input deformations (strains) generated within the structure and induces an amplified amplitude and frequency up-converted response. The tested energy converting devices transform low-amplitude and low-rate service strains into an amplified vibration input to the piezoelectric transducer. The snap-through behavior of bilaterally constrained columns was used as the mechanism for energy concentration. This paper presents a theoretical model, based on energy method, for the post-buckling behavior of a bilaterally constrained slender column under quasi-static axial loadings. The total potential energy of the buckled elastic element is the sum of the potential energies due to bending, compression and external applied force. The transverse deflection is limited by the lateral constraints. Therefore a constrained minimization problem of the total potential energy is solved to determine the equilibrium configurations. Equilibrium transitions are correlated to the changes in the magnitude of the weight coefficients that define the contribution of buckling modes to the deflected shape. Transition states are defined in terms of the axial displacements, axial forces, column shape, and energies stored in the system.Copyright

Control of postbuckling mode transitions using assemblies of axially loaded bilaterally constrained beams

AbstractMultistable structural members are extensively used in various fields, including microelectromechanical systems (MEMS) actuation, sensing, and energy harvesting. The multistable configurati...

Control of Snap-Through Transitions in the Response of Mechanically-Equivalent Frequency Modulators

Converted energy from ambient loading in civil and mechanical structures is typically used as a viable alternative. Although, piezoelectric vibration harvesters have been widely used given their energy conversion ability, these elements exhibit a narrow natural frequency response range, thus considerably limiting the levels of harvestable power.Recently our group has introduced the concept of using mechanically-equivalent frequency modulators that can transform the low-amplitude and low-rate service and ambient deformations into an amplified input to the piezoelectric transducer. The introduced methods allow energy generation and conversion within the unexplored quasi-static frequency range (≪ 1 Hz). The post-buckling behavior of bilaterally constrained columns was used for frequency up-conversion, and piezoelectric cantilever beams, attached to the columns, were used for energy conversion.The introduced concept was experimentally validated and finite element simulations were developed to evaluate the effect of system parameters (stiffness, thickness, and walls gap) on the position of the snap-through transition events and the levels of force-displacement at the multiple-equilibrium configurations. It was shown that the considered system parameters can determine the absolute levels of force and displacement, but they offer limited control on the number and the relative spacing between the energy-drop events. This paper shows that the combination of multiple slender elastic columns modulators, in parallel configurations, allows for the tailoring of the number and magnitude of the mode branch switching during the postbuckling response of the complete system. Experimental and numerical results are presented to validate the proposed concept.Copyright

An energy harvesting solution based on the post-buckling response of non-prismatic slender beams

Systems based on post-buckled structural elements have been extensively used in many applications such as actuation, remote sensing and energy harvesting thanks to their efficiency enhancement. The post-buckling snap- through behavior of bilaterally constrained beams has been used to create an efficient energy harvesting mechanism under quasi-static excitations. The conversion mechanism has been used to transform low-rate and low-frequency excitations into high-rate motions. Electric energy can be generated from such high-rate motions using piezoelectric transducers. However, lack of control over the post-buckling behavior severely limits the mechanism’s efficiency. This study aims to maximize the levels of the harvestable power by controlling the location of the snapping point along the beam at different buckling transitions. Since the snap-through location cannot be controlled by tuning the geometry properties of a uniform cross-section beam, non-uniform cross sections are examined. An energy-based theoretical model is herein developed to predict the post-buckling response of non-uniform cross-section beams. The total potential energy is minimized under constraints that represent the physical confinement of the beam between the lateral boundaries. Experimentally validated results show that changing the shape and geometry dimensions of non- uniform cross-section beams allows for the accurate control of the snap-through location at different buckling transitions. A 78.59% increase in harvested energy levels is achieved by optimizing the beam’s shape.

Small and large deformation models of post-buckled beams under lateral constraints

This study aims at theoretically and experimentally investigating the buckling behavior of bilaterally constrained beams with respect to different geometric parameters and conditions. The theoretical models are developed based on small and large deformation theories, respectively. The nonlinear Euler–Bernoulli beam theory is used to form the governing equations. An energy method is introduced to solve the equilibrium beams by minimizing the total potential energy with respect to the weight coefficients of the buckling modes. The theoretical models are compared with experiments. Good agreements are obtained with respect to the force–displacement relationship and deformed beam shape configuration. This study indicates that the small deformation model is insufficient in predicting beam end shortening since the longitudinal displacement is negligible in the model. The large deformation model effectively predicts severe deflection of beams in terms of end shortening and rotation. Parametric studies are carried out to indicate the applicability of the presented models. In particular, the small deformation model is defined as “more applicable” when the difference of the post-buckling response between the small and large deformation models is less than 5% (Diff < 5%), given that its computational cost is generally smaller than the large model. In contrast, when the difference is greater than 5%, the large deformation model is suggested. In the end, a polynomial function is fitted to define the relationship between the ratio of net gap-to-beam length η and highest achievable buckling mode Φ. The presented small and large deformation models are effective in understanding and predicting the post-buckling responses of laterally confined beams under different conditions.

Sub-Hz self-powered sensing based on mechanical-buckling driven hot-electron injection

Physical processes like changes in ambient temperature, pressure, material accumulation or growth induce stress/strain responses in structures (civil or biomechanical) that occur at frequencies ranging from Hz down to micro-Hertz (μHz). The quasi-static nature of this process poses a challenge for designing self-powered sensors that not only monitor these physical processes but at the same time scavenge operational energy for sensing, computation and storage from the signal being monitored. In this paper we propose a novel sub-Hz self-powered sensing approach which exploits the combination of the physics of post-buckling response in slender elastic columns and the physics of hot-electron injection in floating-gate transistors. Experimental results using a fabricated prototype demonstrate that the sensor can self-power, compute and record the statistics of quasi-static input signals operating at frequencies down to 1mHz.