D33 Mode Research Articles

A flexible ultrasound transducer array with micro-machined bulk PZT.

This paper proposes a novel flexible piezoelectric micro-machined ultrasound transducer, which is based on PZT and a polyimide substrate. The transducer is made on the polyimide substrate and packaged with medical polydimethylsiloxane. Instead of etching the PZT ceramic, this paper proposes a method of putting diced PZT blocks into holes on the polyimide which are pre-etched. The device works in d31 mode and the electromechanical coupling factor is 22.25%. Its flexibility, good conformal contacting with skin surfaces and proper resonant frequency make the device suitable for heart imaging. The flexible packaging ultrasound transducer also has a good waterproof performance after hundreds of ultrasonic electric tests in water. It is a promising ultrasound transducer and will be an effective supplementary ultrasound imaging method in the practical applications.

Screw-type actuator driven by piezoelectric transducers

The significant features of screw transmission are effort-saving and self-locking. Based on this, a screw-rod-type actuator is proposed, which is driven by a nut swung spirally together with piezoelectric transducers. The actuator consists of three parts: a nut fastened to a hollow cylinder, a precise screw rod, and two orthogonal piezoelectric vibrators worked on d33 mode. The screw rod is forced to rotate and translate by traveling wave within the helical surface of nut, which is generated by two vibrators. First, the actuator’s running mechanism is preliminarily illustrated. Second, modal analysis and optimal design of the stator are performed through finite element method. Finally, the prototype actuator is manufactured and tested. The experimental results have proven that this driving manner is feasible, and the main characteristics are as follows: the stable working frequency is about at 9.5 kHz, and the maximum no-load speed and output force are approximately 61 r/min and 2.1 N, respectively, under 300 Vpp.

Simulation and Experimental Studies on Tri-Phasic PZT Piezoelectric Transducer

This paper reports the simulation results of a tri-phase piezoelectric transducer composed of PZT-5H rods surrounded by hexagonal polymer walls in a vacuum ambient. The electrical and mechanical characteristics of these transducers are simulated and predicted. The measured piezoelectric properties of the fabricated transducer at 100 kHz are found to be very much in agreement with those of the predicted design. The simulation of the designed transducer was expected to have acoustic energy channeled in the d33 mode at resonance, with weak or no shear mode cross talk behavior from the other modes. The mechanical displacements measured were large and highly aligned along d33 mode. This implies that tri-phasic piezoelectric transducer performs as a single device with improved mechanical and electrical response. Such designed transducers can be highly useful for the noncontact non-destructive evaluation (NDE) and non-destructive testing (NDT) with high resolution and greater depth profile of various types of material studies. Thus using several design parameters variables new transducers with desirable features can be produced for wide range of applications.

Stacked macro fiber piezoelectric composite generator for a spinal fusion implant

A manufacturing method was developed to create a piezoelectric 3-layer stacked, macro fiber composite generator operating in d33 mode to promote bone growth in spinal fusion surgeries. A specimen of 9 × 17 × 9 mm thick was constructed from 800 μm diameter PZT fibers and medical grade epoxy. Electromechanical testing was performed at three stages of manufacturing to determine the influence of these processes on power generation. An average peak power of over 335 μW was generated in the heat-treated specimen during simulated human body loads. The work provides insights into manufacturing methods for lowered source impedance power generation for a variety of applications.

Effects of cyclic impacts on the performance of a piezo-composite electricity generating element in a d33 mode energy harvesting.

The increasing use of piezoelectric generators to harvest energy from various ambient sources requires the establishment of durability data for piezoelectric materials. In this paper, a d3 mode piezocomposite electricity generating element (PCGE) was tested for its durability under cyclic impact loading. For this purpose, a motor driven lever system was designed to apply constant impact force on PCGEs. To investigate the durability of PCGEs, the output voltage of the PCGEs was observed upon repeated application of an impact force until eventual loss of the generated voltage. The experimental results enabled to determine the number of cycles until which PCGEs can be used without loss of their electricity generation performance with respect to the stress level applied on the PCGEs. At low stress level (around 0.76 MPa or lower), the PCGE showed almost insignificant degradation even after 2 million cycles whereas degradation occurred sooner (after 8 x 10(5) cycles) at higher stress levels (around 0.92 MPa or higher). The effects of impact loading on the durability of the PCGEs were also examined by X-ray photographs of the specimens.

Design and Analysis of a Linear Ultrasonic Motor with Composite Bending and Torsional Vibration Modes

A new type linear ultrasonic motor using Second-order bending and First-order torsional modes (2B-1T) is proposed. The ultrasonic motor has two driving feet and the continuous linear motions of sliders are realized by the frictional force between stator and sliders. In this new design, bending vibration is excited by d33 mode, which controls the preload pressure, and torsional vibration is excited by d15 mode, which generates the driving force. The elliptical trajectories of both feet are achieved, when the phase difference of the two modes is 90° in time and space. The working principle of ultrasonic motor using 2B-1T is simulated. A parametric model of the stator is designed. The sensitive analyses of structural parameters are gained with modal analysis. The characteristics and trajectories of driver feet are studied by transient analysis. These results can provide theoretical basis for the development of this new type ultrasonic motor.

High performance PZT thick films based on bonding technique for d31 mode harvester with integrated proof mass

A high performance piezoelectric PZT thick film for energy harvester with integrated silicon proof mass is proposed for scavenging energy from ambient vibration. This PZT film is fabricated based on low temperature bulk PZT bonding and thinning techniques. A lumped-parameter model of energy harvester is created to optimize the structural parameters of the device. The dimension of PZT, oxide and silicon layer composite cantilever is about 4000μm×1000μm×28μm and the dimension of silicon mass is 2000μm×800μm×420μm. When the matched loading impedance is 100kΩ, the maximum output voltages of harvester at the acceleration of 0.5g and 1g are 3.4V and 6.08V, respectively. The maximum output powers at 0.5g and 1g are 20.2 and 57.6μW, respectively. The energy conversion efficiency of this device is calculated as 38.15% and 26.9% at 0.5g and 1g, respectively.

A flexible sensing device based on a PVDF/MWCNT composite nanofiber array with an interdigital electrode

This study reports the electrospinning of polyvinylidene fluoride (PVDF) piezoelectric nanofiber array on an interdigital (IDT) electrode to fabricate a flexible sensing device. This sensing device can convert the mechanical energies of low-frequency ambient vibrations and impacts into electrical signals. A mixed solution of PVDF and multi-wall carbon nanotube (MWCNT) was filled in a metallic needle injector that was connected with a high voltage of 1200V. When the PVDF droplet in the needle tip was subjected to a high electric field, an extremely fine PVDF fiber can be spun out. The electrospun fibers were collected orderly using an X–Y stage. In the electrospinning process, the fiber was polarized and transformed into the piezoelectric β-crystalline phase. PVDF/MWCNT crystallization as spherical composite structures can enhance the piezoelectric properties of PVDF fibers. Photolithography and etching processes were used to fabricate an IDT electrode with a gap of 100μm on a flexible polyimide (PI) substrate. The PVDF fiber array was packaged with epoxy/PI film. The packaged PVDF fiber array was repolarized in a high electric field of approximately 7V/μm to increase d33 mode conversion efficiency. The comparison of the analytical solution of the composite plate equation and the experimental results shows that the device can generate a peak voltage and current of 20.2mV and 39nA under 6Hz vibration. In addition, at an impact testing at 15Hz, the peak voltage of 24.4mV with a current of 130nA can be obtained.

Magnetic energy harvesting properties of piezofiber bimorph/NdFeB composites

The magnetic energy harvesting properties of piezoelectric bimorph/magnet composite are studied in this Letter. The devices are fabricated with NdFeB magnets and piezofiber (d33 mode), whose magnetoelectric (ME) coefficient reaches 526 V/cm·Oe (RMS) at the resonant frequency (27.3 Hz), and the maximum power density of which is 38.8 mW/cm3 at 9.78 Oe. Factors influencing the magnetoelectric property of the piezoelectric/magnet composite are discussed, which might guide further enhancement of its energy harvesting ability. This particular ME composite possesses far better energy harvesting abilities than magnetostrictive/piezoelectric composites, able to scavenge energy from power-frequency magnetic fields to support wireless sensor network.

Development of high performance piezoelectric d33 mode MEMS vibration energy harvester based on PMN-PT single crystal thick film

In this paper, we present the development of the d33 mode piezoelectric MEMS energy harvester, which is made of composite cantilever beams from single crystal PMN-PT thick film, and silicon layer. The PMN-PT piezoelectric thick film is deployed to improve the coupling coefficient and electromechanical coefficient. The d33 mode harvester based on interdigital electrodes contributes to improve its energy conversion efficiency. The hybrid processes composed of wafer bonding and mechanical lapping for thinning is successfully developed to prepare the PMN-PT thick film. The experimental results show that the fabricated prototype excited at 1.5g vibration level can generate a maximum output voltage of 5.36 VP–P and corresponding power of 7.182μW at the resonant frequency of 406.0Hz. The power density is calculated as 17,181.8μWcm−3, which is superior to the devices fabricated by other technologies in the reported literature.

Sintering and electrical properties of La-modified (Na0.52K0.45Li0.03)1−3xLax(Nb0.88Sb0.09Ta0.03)O3 lead-free ceramics

(Na0.52K0.45Li0.03)1−3xLax(Nb0.88Sb0.09Ta0.03)O3 (NKLLxNST) lead-free ceramics were prepared by normal sintering and their dielectric and piezoelectric properties were investigated. The X-ray methods indicate that the NKLLxNST ceramics with x≤0.003 present a pure perovskite phase at room temperature. The bulk density of NKLLxNST ceramics increases with proper amount of La2O3 contents, and reaches its highest value of 4.544g/cm3 with the addition of 0.3mol% La2O3. At x=0.003, remnant polarization Pr, piezoelectric constant d33 and planar mode electromechanical coupling factor kp of NKLLxNST ceramics reach the highest values of 37.80μC/cm2, 346pC/N and 40%, respectively, exhibiting excellent “soft” piezoelectric characteristics, demonstrating a tremendous potential of the compositions studied for device applications.

Finite element analysis of the piezoelectric stacked-HYBATS transducer

Finite element modeling (FEM) of a piezoelectric multilayer-stacked hybrid actuation/transduction system (stacked-HYBATS) is investigated in this paper using ANSYS software. This transducer consists of two positive strain components operating in d33 mode and one negative strain component operating in d31 mode to generate large displacements. FEM results are compared with experimental and analytical results to provide insight into the actuation mechanisms, verify the device’s three displacement components, and estimate its blocking force. FEM calculations found the effective piezoelectric coefficient to be exceptional, about 3.11 × 106 pm V−1 at resonance. Stacked-HYBATS was quantitatively compared to commercially available flextensional actuators using finite element analysis. It was found that under the same electric field the yielded displacement of a stacked-HYBATS is about 200% and 15% larger than that of a same-sized d31 and d33 flextensional actuator, respectively. These findings suggest that stacked-HYBATS is promising for precision positioning, vibration control, and acoustic applications.

Comparison of MEMS PZT Cantilevers Based on $d_{31}$ and $d_{33}$ Modes for Vibration Energy Harvesting

<i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> mode microelectromechanical systems piezoelectric energy harvesters (PEHs) were fabricated and compared to investigate their output powers converted from vibration. Both types of devices have the same dimensions in a cantilever structure and aim to effectively couple vibration from ambient conditions. The resonant frequencies of the cantilevers are 243 Hz. Two types of devices were compared using mathematical equations based on an equivalent circuit model. The output power of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> mode PEH was 2.15 μW and 2.33 μW in experiment and modeling, respectively. The <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> mode PEHs generated output power ranging between 0.62 and 1.71 μW when the width of the interdigital electrode (IDE) is ranging from 8 to 16 μm and finger spacing is varied from 4 to 16 μm. The output power of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> mode device strongly depends on the dimensions of IDE. The analysis of material constant and electrode design was conducted in conjunction with developing a mathematical equation. The result predicts that the output power of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33</sub> mode PEH can be higher than that of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sub> mode PEH when the finger width is reduced to 2 μm and finger spacing is between 8 and 20 μm.

A flexible piezoelectric micromachined ultrasound transducer

A novel flexible piezoelectric ultrasound transducer based on MEMS technology is studied, which can be used in medical imaging with the advantage of conformal contact with skin surfaces. The device was based on MEMS-technology and fabricated on a composite substrate of polyimide and biomedical-grade PDMS. DRIE was used to etch the polyimide film into an array pattern for placing the bulk PZT dices. The whole device was packaged by biomedical-grade PDMS for conformal contact with the body surface. A 4 × 4 array was fabricated with element size of 1 mm. The transducer worked in d31 mode at a resonant frequency of 2 MHz and an electromechanical coupling factor of 0.21. The variance of resonant frequency of the array elements was less than 3%. The resonant frequency was unchanged after bending for one hundred cycles or wrapping around a 1 cm diameter cylinder.

D33 mode piezoelectric diaphragm based acoustic transducer with high sensitivity

This paper presents the design, fabrication, and characterization of an acoustic transducer using a piezoelectric freestanding bulk diaphragm as the sensing element. The diaphragm bearing the spiral electrode operates in d33 mode, which allows the in-plane deformation of the diaphragm to be converted to the out-of-plane deformation and generates an acoustic wave in the same direction. A finite element code is developed to reorient the material polarization distribution according to the poling field calculated. The first four resonance modes have been simulated and verified by impedance and velocity spectra. The sensitivity and the sound pressure level of the transducer were characterized. The realized sensitivity of 126.21μV/Pa at 1kHz is nearly twenty times of the sensitivity of a sandwich d31 mode transducer.

Modeling and evaluation of d33 mode piezoelectric energy harvesters

A microfabricated d33 mode piezoelectric energy harvester (PEH) with unimorph cantilever structure patterned by interdigital electrodes was designed, fabricated and analyzed. New analytical expression for estimating output power was developed based on the modification of conformal mapping and Roundy's analytical modeling. The results using the new analytical equation can explain the effects of electrode design on the output power of d33 PEH. The output power increases with a longer finger width to a certain limit, and then decreases presumably due to depoling and polarization reversal by charge injection and charged defects in a piezoelectric layer.

Investigation of a d15 mode PZT-51 piezoelectric energy harvester with a series connection structure

A d15 mode piezoelectric energy harvester (PEH) with two PZT-51 elements in series connection (SC), in which the elements are arranged along the width direction, was fabricated, and it is compared with the traditional d15 mode PEH with a single PZT-51 element (SPEH) to discuss the output peak-to-peak voltage (Up−p). The energy harvesting performances of PEHSC are modeled by combining the single degree of freedom model and the electrical model with the piezoelectric constitutive equation of the d15 mode. The energy harvesting performances of PEHSC were systematically measured at various frequencies and load resistances, and Up−p and output power are 12.4 V and 8.7 μW at a load resistance of 2.2 MΩ and resonance frequency of 73 Hz. The experimental Up−p of PEHSC and SPEH are 25.4 and 15.6 V at the resonance frequencies under open circuit condition, and this indicates that the SC structure can improve the energy harvesting performance for d15 mode PEH. The experimental Up−p, output power and the transient voltage–time curve of PEHSC are in agreement with the results of finite element numerical solutions and theoretical modeling, so they are acceptable. The d15 mode and SC structure could potentially improve the energy harvesting performance of PEHs.

Fabrication of aluminium doped zinc oxide piezoelectric thin film on a silicon substrate for piezoelectric MEMS energy harvesters

Thin film piezoelectric materials play an essential role in micro electro mechanical system (MEMS) energy harvesting due to its low power requirement and high available energy densities. Non-ferroelectric piezoelectric materials such as ZnO and AlN are highly silicon compatible making it suitable for MEMS energy harvesters in self-powered microsystems. This work primarily describe the design, simulation and fabrication of aluminium doped zinc oxide (AZO) cantilever beam deposited on silicon substrate. AZO was chosen due its high piezoelectric coupling coefficient, ease of deposition and excellent bonding with silicon substrate. Doping of ZnO with Al has improved the electrical properties, conductivity and thermal stability. The proposed design operates in transversal mode (d31 mode) which was structured as a parallel plated capacitor using Si/Al/AZO/Al layers. The highlight of this work is the successful design and fabrication of Al/AZO/Al on silicon as the substrate to make the device CMOS compatible for electronic functionality integration. Design and finite element modeling was conducted using COMSOL™ software to estimate the resonance frequency. RF Magnetron sputtering was chosen as the deposition method for aluminium and AZO. Material characterization was performed using X-ray diffraction and field emission scanning electron microscopy to evaluate the piezoelectric qualities, surface morphology and the cross section. The fabricated energy harvester generated 1.61 V open circuit output voltage at 7.77 MHz resonance frequency. The experimental results agreed with the simulation results. The measured output voltage is sufficient for low power wireless sensor nodes as an alternative power sources to traditional chemical batteries.

Microfabrication of bulk PZT transducers by dry film photolithography and micro powder blasting

A facile fabrication process for bulk PZT microsystems using dry film photoresist and micro powder blasting is presented. Bulk PZT and dry film photoresist etching characteristics are evaluated as a function of process parameters and mask dimensions using 127 µm thick PZT substrates. The resulting process simplifies microscale patterning of bulk PZT compared with existing methods, with selection of suitable etching parameter providing excellent etch rate, selectivity and anisotropy. The technique is used to fabricate two different cantilever microactuator topologies based on piezoelectric d31 and d33 mode actuation, demonstrating the capabilities of the patterning method for applications in bulk PZT microelectromechanical systems (MEMS).

Micromachining of a Bimorph Pb(Zr,Ti)O3 (PZT) Cantilever Using a Micro-Electromechanical Systems (MEMS) Process for Energy Harvesting Application Moonkeun Kim, Beomseok Hwang, Jaehwa Jeong,

We designed and fabricated a bimorph Pb(Zr,Ti)O3 (PZT) cantilever with an integrated Si proof mass to obtain a low resonant frequency for an energy harvesting application. The cantilevers were fabricated on the micro-electromechanical systems (MEMS) scale. A mode of piezoelectric conversions were d31 and d33 mode in cantilever vibration Therefore, we designed and fabricated a single cantilever with d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes. Finally, we fabricated a device with beam dimensions of about 5,400 microm x 480 microm x 14 microm (< +/- 5%), and an integrated Si proof mass with dimensions of about 1,481 microm x 988 microm x 450 microm (< +/- 5%). In order to measure the d31 and d33 modes, we fabricated top and bottom electrodes. The distance between the top electrodes was 50 microm and the resonant frequency was 89.4 Hz. The average powers of the d31 unimorph, d31 bimorph, d33 unimorph, and d33 bimorph modes were 3.90, 9.60, 21.42, and 22.47 nW at 0.8 g (g = 9.8 m/s2) and optimal resistance, respectively.