Mechanical Impedance Matching Research Articles

Introduction to Piezoelectric Actuators: Research Misconceptions and Rectifications - Part II

<p>Piezoelectric actuator developments require interdisciplinary knowledge on materials physics, electrical designing and mechanical engineering. Because of the limited knowledge of newly-involved researchers, they occasionally publish misleading information, some sort of misconceptions, reflected in the delay of innovative developments of the next generation. This paper is Part II of a series of my tutorial course, and reviews the popular 10 among the researchers’ misconceptions primarily related with the misunderstanding of ‘voltage and electric field’, ‘ionic displacement and strain’, ‘thin film fabrication’, ‘energy transmission coefficient’, ‘thin film device designing’, ‘piezoelectric vibration damping’, ‘mechanical impedance matching’, ‘piezoelectric energy harvesting”, ‘resonance & anti-resonance’, ‘best-selling devices’, and provides rectifications, aiming at their future progress.</p>

Potential reduction of the inertial mass of tuned vibration absorbers by means of mechanical impedance matching

In this paper, a new technology for vibration isolation based on impedance matching using a linear magnetic gear is presented. Using that operational principle, a prototype of an Impedance Matching Tuned Vibration Absorber (Z-TVA) is designed, manufactured and tested. An inertial mass is coupled to the fast-moving stage of the linear magnetic gear, increasing its motion proportionally to the square of the gear ratio, and therefore its effectiveness as a vibration absorber.A theoretical model is postulated and validated with tests at a component level, demonstrating a promising solution for drastically reducing the required mass and installation and maintenance cost. A potential reduction of the required mass of a vibration absorber of more than an order of magnitude is predicted.

Piezoelectric Energy Harvesting Systems

Energy harvesting from wasted or unused power has been the topic of discussion for a long time. This paper focuses on harvesting energy from mechanical vibrations using piezoelectric transducers. We will consider comprehensively three major phases/steps associated with piezoelectric energy harvesting: (i) mechanical-mechanical energy transfer, including mechanical stability of the piezoelectric transducer under large stresses, and mechanical impedance matching, (ii) mechanical-electrical energy transduction, relating with the electromechanical coupling factor in the composite transducer structure, and (iii) electrical-electrical energy transfer, including electrical impedance matching, such as a DC/DC converter to accumulate the energy into a rechargeable battery. The problem found in the current research teams is on a narrow research area of each above phase. In order to provide comprehensive strategies on how to improve the efficiency of the harvesting system, I provide a general guideline for piezoelectric energy harvesting systems.We dealt with detailed energy flow analysis in piezoelectric energy harvesting systems with stiff “Cymbals” (∼100 mW) and flexible piezoelectric transducers (∼1 mW) under cyclic mechanical load, in order to provide comprehensive strategies on how to improve the efficiency of the harvesting system. Energy transfer rates are practically evaluated for all three steps above. For your information, the former “Cymbal” is to be applied to the automobile engine vibration, while the latter flexible transducer is to the human-wearable energy-harvesting system.We should also point out here that there is another research school of piezo-energy harvesting; that is, small energy harvesting (mW or lower) for signal transfer applications, where the efficiency is not a primary objective. This school usually treats a burst/pulse load to generate instantaneous electric energy for transmitting signals for a short period (100 ms ∼ 10 s) without accumulating the electricity in a rechargeable battery. Successful piezoelectric products in the commercial market belong mostly to this category at present, including “LightningSwitch” [remote switch for room lights, with using a piezoelectric unimorph component], and the 25 mm caliber “Programmable Ammunition” [electricity generation with a multilayer piezo-actuator under shot impact], both of which were originally designed in our group (spin-off company, Micromechatronics Inc., State College, PA).

Piezoelectric Energy Harvesting Systems—Essentials to Successful Developments

AbstractIn recent years, industrial and academic research units have focused on harvesting energy from mechanical vibrations using piezoelectric transducers. These efforts have provided research guidelines and have brought to light the problems and limitations of piezoelectric systems. There are three major phases associated with piezoelectric energy harvesting: (i) mechanical–mechanical energy transfer, including mechanical stability of the piezoelectric transducer under large stresses, and mechanical impedance matching, (ii) mechanical–electrical energy transduction, relating to the electromechanical coupling factor in the composite transducer structure, and (iii) electrical–electrical energy transfer, including electrical impedance matching, such as a direct current (DC/DC) conversion to transfer the energy to a rechargeable battery. This Review starts from the historical background of piezoelectric energy harvesting, followed by several misconceptions by current researchers. The main part deals with step‐by‐step detailed energy flow analysis energy harvesting systems with lead zirconate titanate (PZT)‐based devices to provide comprehensive strategies on how to improve the efficiency of the harvesting system.

A method for comparing wave energy converter conceptual designs based on potential power capture

The design space for ocean wave energy converters is notable for its divergence. To facilitate convergence, and thereby support commercialization, we present a new simple method for analysis and comparison of alternative device architectures at an early stage of the design process. Using Thévenin's theorem, Falnes crafted an ingenious solution for the monochromatic optimal power capture of heaving point absorber devices by forming a mechanical impedance matching problem between the device and the power take-off. However, his solutions are limited by device architecture complexity. In this paper, we use the mechanical circuit framework to extend Falnes' method to form and solve the impedance matching problem and calculate the optimal power capture for converter architectures of arbitrary complexity. The new technique is first applied to reprove Falnes' findings and then to assess a complex converter architecture, proposed by Korde. This work also provides insight into a master-slave relationship between the geometry and power take-off force control problems that are inherent to converter design, and it reveals a hierarchy of distinct design objectives unbeknownst to Korde for his device. Finally, we show how application of the master-slave principle leads to the reduction in the dimensionality of the associated design space.

Mechanical and electrical impedance matching in a piezoelectric beam for Energy Harvesting

A piezoelectric beam is one of transducers for energy harvesting. It provides easy implementation and good performance in changing mechanical stress into electric voltage. In order to maximize output power, it is important to provide mechanical and electrical impedance matching. In the paper the authors proposed a methodology which allows to find values of lumped elements in an electromechanical model after completing appropriate measurements. Due to linear equations, it is possible to model a beam in both mechanical and electrical ways, and match the best load depending of frequency. The proposed model of a piezoelectric cantilever shows a potential use of these devices in micro scale as a cantilever which is a part of a silicon structure. Moreover, in the paper, the authors discuss mechanical aspects of using a weight as the way to tune the piezoelectric beam to a specific frequency. The electrical aspect of matching the source impedance with load, which is based on an electrical model of a piezoelectric transducer, is also presented. In the paper a mathematical model was verified by an experiment in which a laboratory stand equipped with a vibration generator, a piezoelectric energy harvester and acceleration sensors was used.

Enhancing efficiency of piezoelectric element attached to beam using extended spacers

This paper describes a new method that enhances the efficiency of a piezoelectric element attached to a beam, based on mechanical impedance matching. The attached piezoelectric element is often used to suppress bending vibration passively or actively. This element can also be used as a sensor or an energy-harvesting source and placement optimization is often used for enhancing its efficiency. When the efficiency is insufficient despite using placement optimization, the size or number of piezoelectric elements is increased. Although these two methods improve the efficiency of the piezoelectric element qualitatively and quantitatively, respectively, the improvements are still insufficient for practical applications. We have proposed a method based on mechanical impedance matching for enhancing the efficiency of the attached piezoelectric element and found that the width and thickness of the element were independent of the maximum value of the modal equivalent stiffness ratio, the parameter that determines the performance of passive vibration suppression under the ideal condition. However, the maximum value of the modal equivalent stiffness ratio depends on the length of the piezoelectric element. In this paper, we propose yet another new method that does not require a piezoelectric element of large length. In this method, the modal equivalent stiffness ratio is independent of the length of the piezoelectric element under the ideal condition. As this new method involves extending the region of the beam with respect to mechanical impedance matching using spacers extended in the longitudinal direction, the efficiency of the piezoelectric element is improved. Although the only difference between the new method and our previous methods is the extended parts of the spacers, the proposed method was theoretically investigated because of the need to additionally consider the effect of the extended parts. The optimum condition for the proposed method was theoretically formulated, and the effectiveness of the new method and the theoretical analysis was verified through simulations and experiments.

Improvement of efficiency of piezoelectric element attached to beam based on mechanical impedance matching

Abstract This paper describes new methods that improve the efficiency of a piezoelectric element attached to a beam based on mechanical impedance matching. Piezoelectric elements are often used to suppress bending vibration. They are also used as sensors or energy-harvesting sources. In such cases, the piezoelectric element is usually bonded onto the host structure by an adhesive bond. The efficiency of the piezoelectric element depends on the bonding location. When the efficiency is insufficient despite a good location, the size or number of piezoelectric elements is increased. However, the efficiency of the piezoelectric element is usually insufficient even if these methods are applied. In order to enhance the efficiency of the piezoelectric elements without using active methods, this paper proposes a mechanical impedance matching method that uses spacers or tuning for the size of the piezoelectric element. Because the attached piezoelectric element and host structure in this region behave as springs in parallel to the bending deformation, the stored strain energy in the piezoelectric element is maximized under the condition that their spring constants match. The proposed methods were theoretically investigated with consideration for the effects of the bonding layer, spacers, and host structure. The optimum conditions for the proposed methods were theoretically formulated, and the effectiveness of the proposed methods and theoretical analysis was verified through simulations and experiments.

Surface acoustic waves (SAW) accelerated microfluidic mixing for improved microcalorimetry in biochips

By measuring very small local temperature changes, microcalorimetry is used to determine the rates of energy released or absorbed during biochemical reactions. The measurement signal-to-noise ratio can be significantly increased by accelerating the reaction kinetics by active microfluidic mixing. We present a biochip incorporating a self-referencing droplet-based microreactor consisting of a thermopile-based microcalorimeter (50 Ni/Au thermocouples in series) on a glass substrate with a surface acoustic wave (SAW)-based microfluidic mixing system on a LiNbO3 piezoelectric substrate. In our design, the SAW mechanical energy is transmitted from the piezoelectric substrate through the glass substrate to the droplets via a water film which acts as a pseudo mechanical impedance matching layer. The cumulative energy released by a standard calorimetric test reaction (sucrose dilution) is measured with the system. Results show that, by overcoming the diffusion-limited reaction rate, SAW-accelerated mixing in the droplets increases the thermal power released during the experiment by a factor 2, increasing the measurement SNR by the same factor. This enthalpy measurement accuracy improvement makes the system well-suited to sensitive thermodynamic measurements on biochip devices.

High Frequency Ultrasound, a Tool for Elastic Properties Measurement of Thin Films Fabricated on Silicon

The main goal of this work is to develop an ultrasonic high frequency method for characterization of thin layers. The development of high frequency acoustic transducers for longitudinal waves and shear waves on silicon has enabeled the characterization of thin films deposited on this substrate. Three types of transducers have been achieved : (i) single crystal LiNbOSubscript text3 Y+163° for shear waves generation, and (ii) Y+36° for longitudinal waves, bonded and thinned on silicon substrate to achieve ultrasonic transducers in the frequency range 300-600 MHz ; (iii) thin films ZnO transducers were realized due to sputtering technologies working in the frequency range 1 GHz- 2.5 GHz. Using an inversion method and a network analyser which provide the scattering S11 parameter of the transducer versus the frequency we deduce the elastic properties of films deposited on the wafer surface. Thanks to these transducers the acoustic properties of thin films such as SU-8 based nanocomposites (doped with TiO2 , SrTiO3 or W nanoparticles) will be presented. In order to achieve mechanical impedance matching between silicon and water we control the mass of the embedded particles which provide a way to adjust the elastic properties of the characterized material. In another application an Indium metallic layer have been characterized in the high frequency range. We also use this method to characterize dielectric permittivity of the ZnO transducers.

Exceptional versatility of solvated block copolymer/ionomer networks as electroactive polymers

Responsive materials possess properties that change abruptly when exposed to an external stimulus, and electroactive polymers constitute examples of robust, lightweight materials that change shape upon electrical actuation. We demonstrate that solvated block copolymer networks afford tremendous versatility in designing electronic and ionic electroactive polymers. As dielectric elastomers, styrenic block copolymer systems attain extraordinary actuation strains approaching 300%, along with high electromechanical coupling efficiencies. Changing the solvent improves the blocking stress and yields remarkably high energy densities, while providing a unique opportunity for mechanical impedance matching and control of shape recovery kinetics, as well as mode of deformation. Dielectric elastomers composed of acrylic copolymers actuate beyond 100% in-plane strain without any prestrain, whereas block ionomer networks swollen with ionic solutions yield ionic polymer–metal composites, which actuate by bending. Selective solvation of block copolymer networks represents an effective and largely unexplored means by which to tune the function and properties of electroactive polymers through systematic manipulation of copolymer and solvent attributes.

Energy Flow Analysis in Piezoelectric Energy Harvesting Systems

Energy recovery from wasted or unused power has been the topic of discussion for a long time. In recent years, industrial and academic research units have focused on harvesting energy from mechanical vibrations using piezoelectric transducers. These efforts have provided the initial research guidelines and have brought in light the problems and limitations of implementing the piezoelectric transducer. There are three major phases/steps associated with piezoelectric energy harvesting: (i) mechanical-mechanical energy transfer, including mechanical stability of the piezoelectric transducer under large stresses, and mechanical impedance matching, (ii) mechanical-electrical energy transduction, relating with the electromechanical coupling factor in the composite transducer structure, and (iii) electrical-electrical energy transfer, including electrical impedance matching, such as a DC/DC converter to accumulate the energy into a rechargeable battery. This paper deals with detailed energy flow analysis in piezoelectric energy harvesting systems with typical stiff “Cymbals” and flexible piezoelectric transducers, in order to provide comprehensive strategies on how to improve the efficiency of the harvesting system. Energy transfer rates are practically evaluated in the above all steps.

Stretch-activated ion channels: what are they?

Mechanosensitive ion channels (MSCs) exist in all cells, but mechanosensitivity is a phenotype not a genotype. Specialized mechanoreceptors such as the hair cells of the cochlea require elaborate mechanical impedance matching to couple the channels to the external stress. In contrast, MSCs in nonspecialized cells appear activated by stress in the bilayer local to the channel--within about three lipids. Local mechanical stress can be produced by far-field tension, amphipaths, phase separations, the cytoskeleton, the extracellular matrix, and the adhesion energy between the membrane and a patch pipette. Understanding MSC function requires under standing the stimulus.

SU-8 photoresist and SU-8 based nanocomposites for broadband acoustical matching at 1 GHz

So as to integrate acoustic functions in BioMEMS using 1 GHz ZnO transducers deposited on silicon substrates, acoustic waves propagation through the silicon substrate and its transmission in water needs to be maximized (the insertion losses at the Si / water interface are about 6dB).In the context of integration, it is interesting for mechanical impedance matching to use photosensitive materials such as SU-8 so that patterns may be obtained. Nanocomposite materials based on SU-8 mixed with nanoparticles having adequate impedances were fabricated. These new materials are characterized in terms of their acoustic velocity, impedance and attenuation. For this, the nanocomposite layers are deposited on the substrate by spin coating to obtain a thickness of about 10 μm, in order to separate acoustic echoes from the material (even if λ/4 layer thickness is lower than 1 μm).The insertion losses of the device immersed in water can be simulated as a function of frequency for a given reflection coefficient between the silicon substrate and the photoresist. The characteristics of some nanocomposites made with SU-8 and various concentrations of nanoparticles like Ti02, SrTiO3 or W have been determined.

A low-power wireless sensing device for remote inspection of bolted joints

A new bolted-joint monitoring system is presented. This system consists of structural joint members equipped with piezoelectric (PZT) sensing elements and a wireless impedance device for data acquisition and communication. PZT enhanced washers are used to continuously monitor the condition of the joint by monitoring its dynamic characteristics. The mechanical impedance matching between the PZT enhanced devices and the joint connections is used as a key feature to monitor the preload changes and to prevent further failure. The dynamic response is readily measured using the electromechanical coupling property of the PZT patch, in which its electrical impedance is directly coupled with the mechanical impedance of the structure. A new miniaturized and portable impedance measuring device is implemented for the practical implementation of the proposed method. The proposed system can be used for the remote and rapid inspection of bolt tension and connection damage. Both theoretical modelling and experimental verification are presented to demonstrate the effectiveness of the proposed concept.

On the sensing and tuning of progressive structural vibration waves

Progressive flexural waves can be generated only in finite structures by fine tuning the excitation and the boundary conditions. The tuning process eliminates the reflected waves arising from discontinuities and edge effects. This work presents and expands two new methods for the identification and tuning of traveling waves. One is a parametric method based on fitting an ellipse to the complex spatial amplitude distribution. The other is a nonparametric method based on the Hilbert transform providing a space-localized estimate. With these methods, an optimization-based tuning of transverse flexural waves in a one-dimensional structure, a vibrating beam, is developed. Existing methods are designed for a single frequency and are based on either combining two vibration modes or mechanical impedance matching. Such methods are limited to a designated excitation frequency determined by a specific configuration of the system. With the proposed methods, structural progressive waves can be generated for a wide range of frequencies under the same given system configuration and can be tuned in real time to accommodate changes in boundary conditions. An analytical study on the nature of the optimal excitation conditions has been carried out, revealing singular configurations. The experimental verification of the sensing and tuning methods is demonstrated on a dedicated laboratory prototype. The proposed methods are not confined to mechanical waves and present a comprehensive approach applicable for other physical wave phenomena.

Modeling of distributed piezoelectric actuators integrated with thin cylindrical shells

The dynamic interaction between induced strain piezoelectric (PZT) actuators and their host structures is often ignored in the modeling of intelligent structures. A more realistic investigation of intelligent material systems must account for the dynamic behaviors of integrated actuator/substrate systems. In this paper, a generic method for the dynamic modeling of distributed PZT actuator-driven thin cylindrical shells has been developed using a mechanical impedance approach. The impedance characteristics of a cylinder corresponding to the excitation of a pair of pure bending moments have been developed, from which the dynamic output moments (or forces) of PZT actuators can be accurately predicted. Direct comparisons have been made between a conventional static modeling approach and the impedance method in order to identify the critical differences between these modeling methods for thin cylindrical structures. The case studies demonstrate that the mechanical impedance matching between PZT actuators and host structures has an impact on the output performance of the actuators. The dynamic essence of integrated PZT/substrate systems has thus been revealed.

Impedance matching element for a gravitational radiation detector

A novel broad-band mechanical impedance matching transformer, with applications to gravitational radiation detectors is described. The transformer utilises transverse modes in a tapered beam, or 'whip'. The whip is analysed by the WKB method, and the calculated wavefunction and amplitude gain are shown to be in reasonable agreement with experiment.