Piezoelectric Transformer Research Articles

Hot Pressed K0.5Na0.5NbO3 Material for Piezoelectric Transformer for Energy Harvesting

Hot Pressed K0.5Na0.5NbO3 Material for Piezoelectric Transformer for Energy Harvesting

Ceramic Piezoelectric Transformer in Vacuum for Acceleration of Electrons and Production of X-Rays.

Experiments on acceleration of electrons and production of X-ray radiation with use of ceramic piezoelectric transformers installed in vacuum are described and analyzed. The piezoelectric transformer operates at resonance frequency. Electrons are accelerated from the high-voltage electrode of the ceramic piezoelectric transformer toward the grounded target, where they emit bremsstrahlung and characteristic X-ray radiation in the target material. The returning of the charge to the high-voltage electrode is provided due to electrons emitted from a filament installed in the vicinity of the target. It was found that the X-ray yield increases linearly at increasing of the pressure of the residual gas in the chamber within two orders of magnitude up to about 10 mTorr, when the gas discharge around of the piezoelectric transformer arises. Possibilities for application of piezoelectric transformers for production of accelerating voltage in small-size accelerators are discussed.

Study and Modeling of a Traveling Wave Piezoelectric Transformer

This paper reports the study and the modelling of a new topology of traveling wave piezoelectric transformer (TWPT). Unlike conventional piezoelectric transformers, the proposed transformer uses progressive waves to carry out the electromechanical conversion. Moreover, associated with an appropriate converter, it enables any kind of AC-DC or AC-AC power conversion. An analytical modelling of the system is carried allowing defining numerically the voltages, currents, displacements and stresses in the piezoelectric transformer over time as a function of the geometrical and physical parameters of the materials.

Energy Harvesting from a Piezoelectric Transformer

Energy Harvesting from a Piezoelectric Transformer

Vertically aligned carbon nanotube arrays as thermal interface material for vibrational structure of piezoelectric transformer

The application and characterization of thermal interface material (TIM) for vibrational structures is investigated in this paper. The vibrating feature during the operation requires unique solution for its thermal management, since the connection between the device and heat dissipater should be able to conduct heat efficiently and impose minimum constraint onto the vibration simultaneously. As a typical vibrational device, piezoelectric transformers (PTs) are discussed in this paper. The PTs have urgent demands for thermal dissipation since their power conversion efficiency decrease rapidly with the rising temperature. A novel method by applying vertically aligned carbon nanotube (VACNT) arrays to the interface between PT and heat dissipater is presented to enhance the performance of piezoelectric transformers. VACNT arrays are one of the excellent TIMs. It can directly establish thermal contact between two surfaces by van der Waals’ forces. In addition, the unique anisotropic character of CNT arrays provides enough flexibility to accommodate the vibration during the operation. Different configurations of TIMs are compared with each other in this work, including CNT arrays, tape of polypropylene (PP) membrane and without heat transfer structure (HTS). The results indicate that the temperature rise is lowest and the efficiency is highest at the same power density while CNT arrays served as the TIM. Almost no significant fretting and wearing damage occurred on PT electrode surface with CNT arrays TIM even after working continuously for 120 days. Meanwhile, the thermo-physical properties of CNT arrays at contact interface are measured by optical transient thermo-reflectance technique.

Design and construction of a multifunction piezoelectric transformer

In recent years, piezoelectric materials have particularly found advantageous field of application in electrical energy’s conversion. Especially, the piezoelectric transformers are becoming more and more usable in electrical devices owing to several advantages such as small size, high efficiency, no electromagnetic noise, and non-flammability. The purpose of this study was to investigate a transformer design that allows having multi-functionality with different efficiency and wider range of voltage gain at resonance frequency. The piezoelectric transformer construction utilizes radial mode both at the input and output port and has the unidirectional polarization in the ceramics. An electromechanical equivalent circuit model based on Mason’s equivalent circuit was developed so as to describe the characteristics of the piezoelectric transformer. Excellent matching was found between the simulation data and experimental results. Finally, the results of this study will allow to deterministically designing multifunction piezoelectric transformers with specified performance.

Stable operation of a high-power piezoelectric transformer comprising two identical bolt-clamped Langevin-type transducers and a stepped horn

We previously developed a 100 W piezoelectric transformer comprising two identical bolt-clamped Langevin-type transducers (BLTs) and a stepped horn whose cross-sectional area ratio determines the specified step-up voltage transformation ratio. Unlike conventional piezoelectric transformers, this transformer is driven at a frequency quite near its mechanical resonance, and thus can be mechanically held firmly at its clearly identified vibratory node without mechanical energy loss. However, it has been revealed that the high-power operation of the transformer often becomes very unstable owing to the “jumping and dropping” phenomena first found by Takahashi and Hirose [Jpn. J. Appl. Phys. 31, 3055 (1992)]. To avoid this instability, we have investigated the peculiar phenomena, and found that they can be attributed to a heavily distorted electric field inside the piezoelectric ceramic disks of the BLT on the primary side of the transformer being driven by a low-impedance voltage source near the mechanical resonance. The resultant concentration of the electric field leads to the local reversal of piezoelectric polarization in every half period of the vibration, viz., the instability. Consequently, we have developed a scheme for the steady high-power operation of this type of piezoelectric transformer and examined its validity experimentally. The method has eventually improved the linearity and power transfer efficiency of the transformer significantly.

A −8 mV/+15 mV Double Polarity Piezoelectric Transformer-Based Step-Up Oscillator for Energy Harvesting Applications

This paper presents two circuit topologies of battery-less integrated boost oscillators suitable for kick-starting electronic systems in fully discharged states with ultra-low input voltages, in the context of energy harvesting applications based on thermoelectric generators, by coupling a piezoelectric transformer in a feedback loop. With respect to the prior work, the first presented solution is a double polarity circuit designed in a $0.18~\mu \text{m}$ CMOS technology able to boost ultra-low positive and negative voltages without using switching matrixes. The circuit exploits a CMOS inverter made up of low threshold transistors, and also includes a hysteretic voltage monitor consuming only ~15 nW to enable an external circuit. The minimum achieved positive and negative oscillation voltages are +15 and −8 mV, which to the best of the authors’ knowledge, are among the lowest start-up voltages achieved in literature up to now without using magnetic components. Moreover, the input impedance in the range of several $\text{k}\Omega $ makes the presented solution suitable also for high impedances sources, such as rectennas. The second presented circuit, designed in a $0.32~\mu \text{m}$ CMOS technology, exploits an input stage based on depletion-mode MOSFETs in a common source stage configuration and achieves a maximum step ratio of ~60.

Low-Temperature Co-Fired Unipoled Multilayer Piezoelectric Transformers.

The reliability of piezoelectric transformers (PTs) is dependent upon the quality of fabrication technique as any heterogeneity, prestress, or misalignment can lead to spurious response. In this paper, unipoled multilayer PTs were investigated focusing on high-power composition and co-firing profile in order to provide low-temperature synthesized high-quality device measured in terms of efficiency and power density. The addition of 0.2 wt% CuO into Pb0.98Sr0.02(Mg1/3Nb2/3)0.06(Mn1/3Nb2/3)0.06(Zr0.48Ti0.52)0.88O3 (PMMnN-PZT) reduces the co-firing temperature from 1240 °C to 930 °C, which allows the use of Ag/Pd inner electrode instead of noble Pt inner electrode. Low-temperature synthesized material was found to exhibit excellent piezoelectric properties ( , , %, pC/N, and °C). The performance of the PT co-fired with Ag/Pd electrode at 930 °C was similar to that co-fired at 1240 °C with Pt electrode (25% reduction in sintering temperature). Both high- and low-temperature synthesized PTs demonstrated 5-W output power with >90% efficiency and 11.5 W/cm3 power density.

Piezoelectric Transformer Aided X-Ray Generation in Vacuum

The results of an experimental study of x-ray generation aided by a ceramic piezoelectric transformer placed in vacuum are presented. X-rays were emitted with the piezoelectric transformer tuned to resonance at about 20 kHz. A characteristic emission peak of a titanium target at energy of 4.5 keV against the Bremsstrahlung background was observed in the measured x-ray spectra. The maximum energy of the x-ray Bremsstrahlung reaches 12 keV. This means that the electrons are accelerated in vacuum in the field of the piezoelectric transformer to at least 12 keV.

A 15-mV Inductor-Less Start-up Converter Using a Piezoelectric Transformer for Energy Harvesting Applications

This paper presents an inductor-less start-up converter for a sub-100-mV energy harvester based on an Armstrong oscillator topology using a piezoelectric transformer and a normally ON MOSFET. Two models of the converter have been detailed and validated experimentally for the start-up phase and steady-state operation to, respectively, determine the minimum start-up input voltage and the voltage gain. The models have been validated experimentally in a setup associating the converter and a thermoelectric generator. Based on a Rosen-type piezoelectric transformer and off-the-shelf components, the proposed start-up topology begins to oscillate at 15 mV and achieves a 1-V output voltage at only 43 mV. Compared to the literature, the topology needs no inductive component and achieves self-starting operation with a smaller input voltage.

A Study on the Driving of High Frequency DC–DC Converter Using Piezoelectric Transformer

A Study on the Driving of High Frequency DC–DC Converter Using Piezoelectric Transformer

Boosting MEMS Piezoelectric Transformer Figures of Merit via Architecture Optimization

This letter documents the design and demonstration of microelectromechanical systems (MEMS) piezoelectric transformers with a measured boost in effective figure of merit as high as 4.2X. This boost is enabled by an architecture approach, which takes transformers with figures of merit limited by the inherent effective electromechanical coupling factor, ${k}_{\textsf {eff}}^{\textsf {2}}$ , and device quality factor, and provides enhanced effective transformer figures of merit through architecture optimization. This is enabled by a parallel input series out transducer architecture inspired by prior approaches with multi-layer bulk piezoelectric transformers but first demonstrated here in MEMS with discrete transformers fabricated with ~45-MHz lead-zirconate-titanate (PZT)-on-silicon electromechanical resonators.

Packaged angle-sensing device with magnetoelectric laminate composite and magnetic circuit

A packaged angle sensor consisting of four PZT/FeGa/PZT magnetoelectric (ME) laminate composites, four magnetic accumulation arcs, a magnetic accumulation (MA) ring, a multi-polar magnetic ring (MPMR), a shaft, and necessary shells is fabricated and characterized. The ME laminate composite with a slim shape is placed between the MA arc and the MA ring. The MPMR fixed on the shaft is used to apply a magnetic field associated with angle information to the ME laminate composites. Under the role the MA parts, the magnetic field applied to the ME laminate composites can be enhanced about 7 times. With the increasing of the rotational speed, the frequency of the sensor’s output signal is increased linearity, which can be used to measure the rotational speed. The amplitude of the output signal is increased as well and finally reached a stable value of 45.3 Vpp. In order to realize static test without the participation of an excitation coil, one of the ME laminate composites has been used as a piezoelectric transformer. In experimental, a resolution of 0.2° and a favorable stability with a standard deviation in population of ∼40 μVpp are achieved from this sensor. These characteristics show that the packaged sensor can be successfully used in rotational parameters testing and has the potential to establish self-powered wireless angle-sensing devices.

Effect of subgrade on piezoelectric energy harvesting under traffic loads

Piezoelectric energy harvesting in roads generated by traffic loads was theoretically and experimentally investigated, and an indoor model of a layered road for piezoelectric transformation was developed using the traffic load model groove. Elastic double-layer beams resting on the subgrade soil were used to consider piezoelectric energy harvesting under traffic loads. Based on the vibration differential equations of elastic double-layer beams, the electromechanical equation was obtained using the Fourier transform. The experimental results of the piezoelectric energy harvesting were close to the theoretical ones, which indicated that the proposed method was useful in predicting piezoelectric energy harvesting from roads under traffic loads. The results also show that the influence of the transducer position on the output voltage and power should be considered, and that the thickness of the concrete panel and the condition of the subgrade soil can affect the output voltage and output power of the piezoelectric transducer. Moreover, the electrical energy was proportional to the vibration frequency and the excitation load.

New Tunable Piezoelectric Transformers and Their Application in DC–DC Converters

This paper introduces a new tunable piezoelectric transformer (TPT) and demonstrates its operation in a dc–dc converter application. Piezoelectric transformers (PTs) have been conventionally used in high-voltage, low-power applications such as electronic ballasts. Recently, radial type PTs have been developed for higher power ac–dc and dc–dc step down applications. Based on the latter, a new TPT has been developed featuring an auxiliary secondary terminal to control the voltage gain of the transformer. This results in some exciting characteristics from a dc–dc converter standpoint, like an adjustable frequency response of the TPT, and fixed frequency control of the converter with no-cross talk between the primary and secondary in the control circuit. This paper introduces the design concept behind TPT-based dc–dc converters, and proposes a control scheme for their implementation. Experimental results with a 30 W, 220:55 V converter unit are shown to validate these concepts.

Fabrication and Electromechanical Modeling of a Flexural-Mode MEMS Piezoelectric Transformer in AlN

This paper presents the fabrication and electromechanical characterization of a novel AlN-based microelectromechanical systems (MEMS) flexural-mode piezoelectric transformer (PT) realized in a silicon-on-insulator bulk-micromachining process with segmented electrodes at the secondary side, which are series-connected in order to increase the output voltage. The goal of this work is to propose a MEMS-based alternative to inductors and magnetic transformers for power management in micro-power mm-scale electronic systems. The fabricated device is fully modeled by means of the Butterworth-Van Dyke (BVD) two-port network. The device is modeled analytically with the classic equations of a fully clamped-edge membrane and through finite-element method simulations. Characterization is performed through impedance measurements and an alternative empirical method suitable for MEMS devices is proposed for directly extracting its lumped parameters electromechanical circuit. Finally, the effect of the feed-through capacitance is fully analytically modeled, and this paper presents a variant of the BVD network of the PT with an inner BVD circuit, allowing an easier estimation of the effects of the complex zeros introduced by the feed-forward capacitance. The presented device achieves a measured maximum voltage gain of 58mV/V at ~36.3 kHz and maximum efficiency of ~75%.

Highly efficient solid state magnetoelectric gyrators

An enhancement in the power-conversion-efficiency (η) of a magneto-electric (ME) gyrator has been found by the use of Mn-substituted nickel zinc ferrite. A trilayer gyrator of Mn-doped Ni0.8Zn0.2Fe2O3 and Pb(Zr,Ti)O3 has η = 85% at low power conditions (∼20 mW/in3) and η ≥ 80% at high power conditions (∼5 W/in3). It works close to fundamental electromechanical resonance in both direct and converse modes. The value of η is by far the highest reported so far, which is due to the high mechanical quality factor (Qm) of the magnetostrictive ferrite. Such highly efficient ME gyrators with a significant power density could become important elements in power electronics, potentially replacing electromagnetic and piezoelectric transformers.

Piezoelectric energy harvester impedance matching using a piezoelectric transformer

To harvest maximum power from a piezoelectric energy harvester requires conjugate impedance matching, consisting of both resistive and inductive load. In practical circuits, dc-dc converters working in discontinuous conduction mode are used for emulated resistive impedance matching. These converters contain a large and expensive electromagnetic component to reduce the wire conduction losses. A new approach toward piezoelectric energy harvester resistive impedance matching is presented by using a step-down piezoelectric transformer with a bi-directional inductor-less half-bridge circuit working under zero voltage switching conditions. The large and expensive magnetic transformer and inductor in previous works are replaced with a ceramic component with no electromagnetic interference. The presented technique can reduce the circuit size and the ceramic transformer can be manufactured on the harvester cantilever.

Low temperature co-fired multilayer piezoelectric transformers for high power applications

Piezoelectric transformers (PT's) offer high efficiency in compact volumes compared to their electromagnetic counterparts. In particular, multilayer PT's can deliver both efficiency and higher power when they are made of hard-piezoceramics. However, hard-piezoceramics usually have high sintering temperatures (~1200°C), which limit the inner electrode of the multilayer structure to precious metals such as silver‑palladium (Ag/Pd) with high Pd content or platinum (Pt). High Pd content or Pt increases device price dramatically and their electrical/thermal performances are not satisfactory for high power multilayer applications. Therefore, two compositions were developed by utilizing a commercially available hard-piezoelectric ceramic (APC 841) and sintering temperature was brought down to 1000°C or below by keeping essential high power properties at satisfactory levels (mechanical quality factor ~1000, planar coupling coefficient>0.5, and dielectric loss<0.02). Then, ring-dot step-down multilayer PT's were prototyped and co-fired with Ag/Pd:90/10 electrodes accordingly. PT's were able to reach an output power density level of 30Wcm−3 (Poutput/Volume) with >96% efficiency (Poutput/Pinput) and a 20°C temperature rise. In addition, PT's were tested at higher output power levels and were able to generate 45Wcm−3 and 60Wcm−3 with a temperature rise of 40°C and 80°C, respectively.