Modeling and Control of MEMS-based Multi-layered Prestressed Piezoelectric Cantilever Beam

Piezoelectric materials are the preferred smart materials for sensing and actuation in the form of micro and nano-engineering structures like beams and plates. Cantilever beams play a significant role as key components in atomic force microscopy and bio and chemical sensors. Adding an active layer such as lead zirconate titanate (PZT) thin-film to form smart cantilever beams with sensing and actuation capabilities is highly desirable to facilitate miniaturization, enhance performance and functionali- ties such as enabling on-chip high-speed parallel AFM. During the micro-fabrication process, residual stresses develop in the different layers of the cantilever beam, causes initial deflection. The residual stress in the different layers of the cantilever beam and the application of voltage to the PZT thin-film affects their dynamics. This the- sis investigates the dynamic behaviour and develops a control technique and a novel charge readout circuit to improve the performance of a micro-fabricated multi-layer prestressed piezoelectric cantilever beam as an actuator and a deflection sensor. Firstly, the fabrication process of a unimorph PZT cantilever beam is explained. A low thermal budget Ultra-high vacuum e-beam evaporated polysilicon thin-film (UHVEEpoly) process is used for the fabrication of multi-layered PZT cantilever beam in d31 mode. The sharp peaks at resonant frequencies in the frequency response of the PZT cantilever beam show very little damping and a large settling time of the cantilever beam. Secondly, the dynamic behaviour of the prestressed PZT cantilever beam is in- vestigated subjected to change in driving voltage. Experimental investigations show a shift in resonant frequencies of a PZT cantilever beam. However, there is no reported mathematical model that predicts the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam subjected to a change in driving voltage. This work developed a mathematical model with experimental val- idation to estimate the shift in resonance frequencies of such cantilever beams with the change in the driving voltage. A very good agreement between the model predic- tions and experimental measurements for the frequency response of the cantilever beam at different driving voltages has been obtained. A novel linear formulation has been developed to predict the shift in resonance frequencies of the PZT can- i tilever beam for a wide range of driving voltages. The formulation shows that the shift in resonance frequencies of a multi-layered prestressed piezoelectric cantilever beam per unit of applied voltage is dependent on geometric parameters and material properties. Thirdly, a robust resonant controller has been designed and implemented to re- duce the settling time of a highly vibrating PZT cantilever beam. The controller design is based on a mixed negative-imaginary, passivity, and a small-gain approach. The motivation to design a resonant controller using the above-mentioned analyti- cal framework is its bandpass nature and the use of velocity feedback, as the charge collected from a vibrating PZT cantilever beam gives the velocity information of the beam. The proposed controller design results in finite gain stability for a pos- itive feedback interconnection between two stable linear systems with a large gain and phase margin. Experimental results demonstrate that the designed resonant controller is able to effectively damp the first resonant mode of a cantilever, signifi- cantly reducing settling time from 528 ms to 32 ms. The robustness of the designed resonant controller is tested against changes in the cantilever beam dynamics due to residual stress variation and or stress variation due to driving voltage. Finally, to facilitate the miniaturization of on-chip sensors and parallel high- speed AFM, a single layer of a PZT thin-film in a cantilever beam is used as a deflection sensor and an actuator instead of bulky optical deflection sensors. A novel charge readout circuit is designed for deflection sensing by capturing the electrical charge generated due to the vibration of the PZT beam. The signal-to-noise ratio and sensitivity analysis of the readout circuit shows similar results compared to the commercially available optical deflection sensors. Our work highlights very important aspects in the dynamic behaviour and perfor- mance of a multi-layered prestressed piezoelectric cantilever beam. The agreement between the proposed theoretical formulation and experimental investigations in modeling, control design, and a novel readout circuit will provide the platform for further the development and miniaturization of microcantilever-based technologies, including on-chip parallel HS-AFM

Phytochemical Composition, Antioxidant Potential, and Medicinal Significance of <em>Ficus</em>

Ficus, a genus of plant family Moraceae, includes about 850 species. Most of the species of Ficus are used as a source of nutrition for humans. The roots, aerial roots, stem, bark, leaves, latex, fruit, and pulp of the Ficus plants are medicinally important due to the presence of a variety of bioactive phytochemical compounds, such as polyphenols, phenolic acids, triterpenoids, flavonoids, flavonols, anthocyanins, carotenoids, glycosides, polysaccharides, reducing compounds, and vitamins K, E, and C. Most of these phytochemical compounds possess strong antioxidant potential in terms of metal chelating, metal reducing, lipid reducing, and free radical scavenging capacities, which may be helpful in reducing the oxidative stress in the biological systems. On account of their high phytochemical content and strong antioxidant potential, these plants show several biological activities including antimicrobial, antidiabetic, anti-obesity, hepatoprotective, cardioprotective, and renal-protective, and anticancer activities. These plants have been found to be effective in the treatment of diabetes, stomachache, piles, skin diseases, inflammation, and cancer

Re-use of agricultural wastes for the removal and recovery of Zr(IV) from aqueous solutions

This study assesses the feasibility of Zr(IV) removal and recovery from aqueous solutions by novel biosorbents prepared from selected agricultural wastes. Sugarcane bagasse was selected for further investigation after showing increased biosorption capacity during the initial screening experiment. The biosorption efficiency of native (untreated), SDS-treated and immobilised bagasse for Zr(IV) removal was studied and optimization of the experimental conditions carried out including pH, biosorbent weight, contact time, initial metal ion concentration and temperature to maximise adsorption. Sorbent–sorbate reaction behaviour was estimated by fitting equilibrium data by non-linear and transformed linear forms of the Langmuir, Freundlich and Redlich–Peterson isotherms as well as pseudo-first and second-order kinetic models. The best fitting isothermal or kinetic model was optimized by comparing linear and non-linear R2 value and non-linear regression error functions. H2SO4 proved to be the most effective desorbing agent in recovery of the sorbed Zr(IV) ions from all forms of bagasse. Biosorbent characterisation and effectiveness of the process was confirmed by Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX). The data illustrate that native (untreated), SDS-treated and immobilised bagasse have great potential to remove and recover Zr from wastewater

Physical and Chemical Modifications in Starch Structure and Reactivity

Starch is a naturally occurring glucose homo-polysaccharide of nutritional, pharmaceutical, and industrial importance. The complex polymeric structure and poor solubility of native starch in water limits their importance at pharmaceutical and industrial level. The structure, reactivity, and functionality of the native starch can be modified by physical, chemical, enzymatic, and biotechnological methods. Various physical modifications techniques, including the thermal, radio-thermal, freezing and thawing, annealing, high-pressure, ultrasonic, and pulsed electric field treatment, and chemical modifications, including oxidation, etherification, esterification, cationization, cross-linking, and graft polymerization, have been found to change the surface properties, polarity and linearity of the molecular chains, the degree of substitution, the polymeric, granular, and crystalline structure, amylose to amylopectin ratio, solubility, viscosity, pasting, gelatinization, swelling, water absorption, and emulsifying properties of starch. The structural changes have resulted in the improvement of thermal and freeze-thaw stability, viscosity, solubility, water binding capacity, swelling power, gelling ability, and enzymatic digestibility of starch. The exposure of reactive functional groups after physical or chemical modification modifies the reactivity of starch toward water, oil, acids, enzymes, and other chemical species. These modification techniques have led to some revolutionary changes in reactivity, functionality, and application of starch in various fields

Biodecolorization of Reactive Black 5 by laccasemediator system

Reactive azo dyes are widely used as textile colorants, typically for cotton dyeing, due to their variety of color shades, and minimal energy consumption. In the present study, commercial laccase from Trametes versicolor was used for the biodecolorization of Reactive Black 5 (RB-5) dye using different redox mediators viz, N-hydroxybenzotriazole (HBT), 2,2′-azino-bis-(3-ethylbenzthiazoline- 6-sulfonic acid (ABTS), 2,6-dimethoxy phenol (DMP), syringaldehyde, vanillin, aceto-vanillone, p-coumaric acid and catechol. Commercial laccase alone did not show any considerable decolorization of RB-5. However, the laccase in the presence of syringaldehyde showed the strongest decolorization rate (98%), followed by vanillin (55.21%), aceto-vanillone (53.25%), ABTS (42.78%), p-coumaric acid (41.9%), DMP (39%), and catechol (36.33%); while least decolorization was observed with HBT at dye/mediator ratio of only 1:5 after 30 min. Therefore, syringaldehyde performance was evaluated at different mediator/dye ratios (1:1, 1:5 and 1:10) using commercial laccase and it was compared with that of synthetic mediator like HBT. It was found that the presence of syringaldehyde was essential for biodecolorization of RB-5. Moreover, it was observed that syringaldehyde was an effective natural redox mediator as compared to synthetic HBT. Enhanced decolorization (98%) of RB-5 by laccase was observed with 1:5 syringaldehyde and dye ratio for 30 min but maximum removal (22%) of RB-5 was recorded with HBT at 1:1 after 40 min. Thus, the study reveals that the phenolic compounds could be used as potential redox mediators for enhanced laccase-mediated decolorization of azo dyes.Keywords: Reactive Black 5 (RB-5), redox mediators, laccase, biodegradation, azo dyesAfrican Journal of Biotechnology Vol. 11(29), pp. 7464-7471, 10 April, 201

Dual port microstrip patch antennas and circuits with high interport isolation for in-band full duplex (IBFD) wireless applications

In-Band Full Duplex (IBFD) is one effective way to increase the spectral efficiency and the throughput of wireless communication systems by transmitting and receiving simultaneously on the same frequency band but the coupling (called Self Interference or SI) of transmit signal to its receiver is one major problem. IBFD operation can be realized successfully by suppressing this coupling or Self Interference (SI). The required amount of SI cancellation depends on the power and bandwidth of transmitted signal. Generally, the SI should be suppressed to RF transceiver noise floor. To achieve this amount of SI suppression, SI suppression mechanism is normally implemented at three stages across the IBFD transceiver and they are known as antenna cancellation, RF/analog cancellation and digital base-band cancellation. Most of the SI suppression is achieved at antenna stage to relax the required amount of SI cancellation at the rest of two stages .Thus, a dual port microstrip patch antenna with very high port to port RF isolation is required in addition to digital self interference cancellation techniques to enable simultaneous transmit and receive wireless operation at same carrier frequency using single antenna for full duplex radio transceivers. The objective of my research work presented in this dissertation is to design, implement and measure dual port microstrip patch antennas which deploy different feeding techniques along with Self Interference Cancellation (SIC) circuits to get high interport isolation to enable such antennas for realization of IBFD wireless operation using single/shared antenna architecture. The goal is to achieve high interport isolation for dual port antenna with minimum effect on radiation performance of antennas

High isolation slot coupled antenna with integrated tunable self-interference cancellation (SIC) circuitry

This letter presents a high interport isolation, compact dual polarized slot coupled monostatic patch antenna with integrated tunable analog/RF self interference cancellation (SIC) circuitry for 2.4/2.5 GHz In Band Full Duplex (IBFD) wireless applications. The presented antenna deploys hybrid feeding for improved interport isolation through polarization diversity and integrated single-tap RF SIC circuitry provides additional isolation on top of antenna isolation. Brief mathematical description for deployed single-tap RF SIC is also presented. The implemented prototype of proposed antenna module provides around 80 dB interport isolation for 20 MHz bandwidth and better than 97 dB peak isolation when measured in lab in the presence of environmental reflections. Moreover, 20 MHz SIC bandwidth with 80 dB interport isolation can be tuned within antenna’s 10 dB return loss impedance bandwidth of 60 MHz