Vishwas Bedekar

Laser-machined piezoelectric cantilevers for mechanical energy harvesting

In this study, we report results on a piezoelectric- material-based mechanical energy-harvesting device that was fabricated by combining laser machining with microelectronics packaging technology. It was found that the laser-machining process did not have significant effect on the electrical properties of piezoelectric material. The fabricated device was tested in the low-frequency regime of 50 to 1000 Hz at constant force of 8 g (where g = 9.8 m/s2). The device was found to generate continuous power of 1.13 muW at 870 Hz across a 288.5 kOmega load with a power density of 301.3 muW/cm3.

Magnetoelectric Interactions in Lead-Based and Lead-Free Composites

Magnetoelectric (ME) composites that simultaneously exhibit ferroelectricity and ferromagnetism have recently gained significant attention as evident by the increasing number of publications. These research activities are direct results of the fact that multiferroic magnetoelectrics offer significant technological promise for multiple devices. Appropriate choice of phases with co-firing capability, magnetostriction and piezoelectric coefficient, such as Ni-PZT and NZFO-PZT, has resulted in fabrication of prototype components that promise transition. In this manuscript, we report the properties of Ni-PZT and NZFO-PZT composites in terms of ME voltage coefficients as a function of frequency and magnetic DC bias. In order to overcome the problem of toxicity of lead, we have conducted experiments with Pb-free piezoelectric compositions. Results are presented on the magnetoelectric performance of Ni-NKN, Ni-NBTBT and NZFO-NKN, NZFO-NBTBT systems illustrating their importance as an environmentally friendly alternative.

Design and fabrication of bimorph transducer for optimal vibration energy harvesting

High energy density piezoelectric composition corresponding to 0.9Pb(Zr_0.56Ti_0.44)O₃-0.1Pb[(Zn_0.8/3Ni_0.2/3) Nb_2/3]O₃ + 2 mol% MnO₂ (PZTZNN) and 0.8[Pb(Zr_0.52Ti_0.48) O₃]-0.2[Pb(Zn_1/3Nb_2/3)O₃] (PZTPZN) were synthesized by conventional ceramic processing technique using three different sintering profiles. Plates of the sintered samples were used to fabricate the piezoelectric bimorphs with optimized dimensions to exhibit resonance in the loaded condition in the range of ~200 Hz. An analytical model for energy harvesting from bimorph transducer was developed which was confirmed by experimental measurements. The results of this study clearly show that power density of bimorph transducer can be enhanced by increasing the magnitude of product (d · g), where d is the piezoelectric strain constant and g is the piezoelectric voltage constant.

Magnetoelectric properties of core-shell particulate nanocomposites

In this study, we report results on magnetoelectric (ME) core-shell Pb(Zr,Ti)O3 (PZT)-NiFe2O4 (NF) particulate nanocomposites. NF particles forming the shell had size in range of 20–30 nm. The grain size of sintered nanocomposites was found to be in the range of 500–800 nm. The sintered nanocomposite exhibited piezoelectric coefficient (d33) of 60 pC/N, dielectric constant of 865, and ME coefficient of 195 mV/cm Oe. High ME coefficient was observed for wide range of dc bias magnetic field. This approach of fabricating layered composite has a promise to provide large ME coefficients in particulate sintered structures.

Pen harvester for powering a pulse rate sensor

Rapid developments in the area of micro-sensors for various applications such as structural health monitoring, bio-chemical sensors and pressure sensors have increased the demand for portable, low cost, high efficiency energy harvesting devices. In this paper, we describe the scheme for powering a pulse rate sensor with a vibration energy harvester integrated inside a pen commonly carried by humans in the pocket close to the heart. Electromagnetic energy harvesting was selected in order to achieve high power at lower frequencies. The prototype pen harvester was found to generate 3 mW at 5 Hz and 1 mW at 3.5 Hz operating under displacement amplitude of 16 mm (corresponding to an acceleration of approximately 1.14 grms at 5 Hz and 0.56 grms at 3.5 Hz, respectively). A comprehensive mathematical modelling and simulations were performed in order to optimize the performance of the vibration energy harvester. The integrated pen harvester prototype was found to generate continuous power of 0.46–0.66 mW under normal human actions such as jogging and jumping which is enough for a small scale pulse rate sensor.

Comparative Study of Energy Harvesting from High Temperature Piezoelectric Single Crystals

This experimental study reports the mechanical energy harvesting from piezoelectric single crystal materials with operating range higher than 500 °C and compares their performance with state-of-the-art soft Pb(Zr,Ti)O3 (PZT) material. Yttrium calcium oxyborate YCa4O(BO3)3 (YCOB) and lanthanum gallium silicate La3Ga5SiO14 (LGS) crystals were found to exhibit stable piezoelectric and dielectric properties up to 1000 °C. Single and three-crystal stacks of YCOB, LGS, lithium niobate LiNbO3 (LN), and soft PZT were tested in longitudinal mode configuration (33-mode). The power density of soft PZT was found to be about three orders of magnitude higher than that of high temperature crystals at room temperature however its operating range was limited to 150 °C. On the other hand, YCOB and LGS crystals annealed at 600 °C exhibited similar magnitude of power as that at room temperature.

Synthesis and microstructural characterization of barium titanate nanoparticles decorated SiCN-MWCNT nanotubes "nanonecklace"

In this paper, we report synthesis and characterization of flexible polymer-derived ceramic silicon carbon nitride nanotubes decorated with barium titanate (BTO) nanoparticles where multi-walled carbon nanotubes act as a template. The synthesis was achieved by controlled pyrolysis of polyurea (methylvinyl) silazane and BTO metal-organic precursor. Structural characterization by advanced microscopy techniques revealed 10–50 nm BTO nanoparticles uniformally covering the nanotubes. X-ray photoelectron spectroscopy was used to confirm the BTO perovksite phase. Possible application of this novel structure—nanoNecklace—is in nanocapacitors (NCs) where high dielectric material BTO is arranged on SiCN layer.

Metal-ceramic laminate composite magnetoelectric gradiometer

Gradiometer resembles in functionality a magnetic field sensor where it measures the magnetic field gradient and its sensitivity is determined by the ability to quantify differential voltage change with respect to a reference value. Magnetoelectric (ME) gradiometer designed in this study is based upon the nickel (Ni)-Pb(Zr,Ti)O(3) (PZT) composites and utilizes the ring-dot piezoelectric transformer structure working near the resonance as the basis. The samples had the ring-dot electrode pattern printed on the top surface of PZT, where ring acts as the input while dot acts as the output. There is an insulation gap between the input and output section of 1.2 mm. The generated magnetic field due to converse ME effect interacts with the external applied magnetic field producing flux gradient, which is detected through the frequency shift and output voltage change in gradiometer structure. The measurements of output voltage dependence on applied magnetic field clearly illustrate that the proposed design can provide high sensitivity and bandwidth.

Detection of Corrosion using Impedance Spectroscopy

In this study we investigate the effect of corrosion damage of Aluminum (Al) on the impedance response of piezoelectric sensor attached to the Al. The piezoelectric sensor had a square geometry with fundamental planar mode. A basic environment (NaOH) was used to induce corrosion damage on the Al 6061 grade. A systematic variation in the real part of the electromechanical impedance was found as the specimen corrosion proceeded. The results also indicate that there is an optimal distance between the piezoelectric sensor and the location where damage is occurring that provides highest damage index.

Design of impedance spectroscopy based structural health monitoring sensors for fatigue damage detection in aluminum beams

Piezoelectric sensors have been previously used for continuous structural health monitoring using impedance spectroscopy. However, three important issues still remain to be investigated for efficient design of such sensors, namely (i) the effect of sensor geometry on sensitivity of impedance based damage detection, (ii) the selection of frequency band for continuous health monitoring, and (iii) identification of damage quantification metric. In this study, we address these issues and report the results on aluminum beam subjected to mechanical fatigue. A commercially available Materials Testing Machine was used in order to perform a load controlled fatigue test (250–1350 lbs @ 20 cycles/sec) on a notched aluminum beam. Sensor geometry was optimized with the help of damage index metric based health monitoring. Next, optimized geometry was selected to further study the selection of frequency band with a new approach based on number of peaks in the impedance signature under identical testing conditions. The results of this study provide a benchmark for designing the sensors for structural health monitoring.