Weiwei Shao

Piezoelectric Filter Module Used in Harmonics Elimination for High-Efficiency Piezoelectric Transformer Driving

Switching driving, such as pulse width modulation, has been used in many power circuits because of its high efficiency. However, given the capacitance of a piezoelectric transformer (PT) for high harmonics in a square waveform, using switching technology directly in a driver circuit is difficult without an inductance linked with the PT. This paper proposes a design of a piezoelectric filter module for eliminating harmonic frequencies in the driving of a PT. Compared with a traditional inductor filter, the performance, cost, and space advantages make the module a wiser choice. The particular design of several PFs fabricated on one piece of piezoelectric plate has future integration potential with the transformer. The third harmonic filtering experiment shows that the module exhibits excellent performance on the elimination of harmonics and improvement of the whole converters efficiency, making the large inductor for wide-range damping of harmonics unnecessary. Efficiency analyses for a simplified push-pull power amplifier model prove the existence of an optimum output waveform for a tradeoff consideration on the circuit efficiency and driving complexity of a PT. This study offers detailed guidance for the future development of novel converter circuits.

Temperature distribution of piezoelectric transformer with heat couple component using finite element method

The temperature field of a piezoelectric transformer with heat couple component are analyzed at steady state conditions in this paper. The contour extensional vibration mode of the transformer is determined by impedance simulation analysis and experiment result. Mechanical vibration losses, piezoelectric losses, dielectric losses are considered for a piezoelectric transformer. In order to verify the calculated temperature results, the piezoelectric transformer s temperature distributions were measured by the infrared thermometry. The experiment results show a good uniformity with the calculation results. For the piezoelectric transformer with heat couple component, friction heat were considered as another heat source of temperature distribution. The temperature distribution results show the heat couple component depresses temperature gradient of the piezoelectric transformer and improves piezoelectric material utilization rate effectively.

A muliple outputs of piezoelectric transformer based on the stress distribution

A new type of piezoelectric transformer which is based on the stress distribution of the piezoelectric transformer to change the output voltage is presented. In this paper, we verified the feasibility of the principle of the new piezoelectric transformer from the simulation and experiment. The experiment results show a good consistent with the theoretical analysis. The designed piezoelectric transformer is very capable of multiple output and the structure is simple. The proposed piezoelectric transformers can provide applications in multiple output of piezoelectric transformers of all the vibration mode.

A micro dual-frequency transducer based on contour-extensional vibration and thickness mode

This paper presents a single piezoelectric transducer with dual-frequency characters by utilizing contour-extensional mode and thickness mode. A 2.5 MHz and 8.5 MHz frequency transducer prototype is designed by Finite element method (FEM) analyses and verified by experiment. Performance of the transducer is then evaluated through the measurement of admittance curves and pulse-echo responses. It’s demonstrated experimentally that the proposed transducer has -6dB bandwidth of 39.4% @1.0 Vpp at 2.4 MHz and 34.6% @1.1 Vpp at 8.9 MHz, respectively. The proposed dual-frequency transducer has potential applications in vivo thrombolytic therapy and ultrasound-guide of pedicle screws.This paper presents a single piezoelectric transducer with dual-frequency characters by utilizing contour-extensional mode and thickness mode. A 2.5 MHz and 8.5 MHz frequency transducer prototype is designed by Finite element method (FEM) analyses and verified by experiment. Performance of the transducer is then evaluated through the measurement of admittance curves and pulse-echo responses. It’s demonstrated experimentally that the proposed transducer has -6dB bandwidth of 39.4% @1.0 Vpp at 2.4 MHz and 34.6% @1.1 Vpp at 8.9 MHz, respectively. The proposed dual-frequency transducer has potential applications in vivo thrombolytic therapy and ultrasound-guide of pedicle screws.

Acoustic particle sorting by integrated micromachined ultrasound transducers on polymer-based microchips

Ultrasonic standing waves (USWs) particle sorting has shown great potential to develop diverse applications in biotechnology and medical research due to its ability to offer non-contact, label-free particle manipulation. Currently, most reported on-chip acoustic particle sorters rely on high Q-value materials and elaborate geometry designs, which make these devices not easy to build and unsuited for mass fabrication. In this work, we propose a novel two-stage acoustic particle sorting strategy with the advantages of operating on low-cost polymer-based microchips and using integrated micro-machined piezoelectric transducers (PZTs).

High frequency Self-focusing transducer fabricated by a laser engraving technique

High frequency transducers (>15 MHz) have been widely used in small animal ultrasound, ophthalmic ultrasound, skin ultrasound and intravascular ultrasound et. al. The images obtained by a plane transducer have lower resolution and sensitivity compared with a focusing one. It is usually hard to make the focusing transducer with micro size, short focal length and high frequency. For solving these problems, self-focusing transducers were developed, which pattern a Fresnel half-wave bands on the piezoelectric materials surface as the electrode. Using this method can achieve transducers with micro size (∼1–2 mm in diameter), short focal length (∼350 μm) and high frequency (>100 MHz). But this method need wire lead to contact each ring separately, so it is hard to keep every annular ring complete. And the instrument accuracy requirements are quite strict. Therefore, based on recent progress on laser cutting, a high frequency self-focusing piezoelectric transducer using laser cutting technique is developed, which engraved the piezoelectric ceramic into annular rings to form Fresnel half-wave-band sources.

An intracranial implantable ultrasound device for seizure mapping

Epilepsy is the third most commonly diagnosed neurological disorder. For drug-resistant patients, epilepsy surgery is the only option. The outcome of epilepsy surgery largely depends on an accurate mapping of epileptogenic zone. In clinic, this is done with subdural electrode array to monitor the Electrocorticography (ECoG) with a disappointing low spatial resolution of ∼ 1cm. As a result, the cure rate of neocortical epilepsy can barely reach ∼ 30%. Recent study showed that the neurovascular based CBV(Cerebral Blood Volume) increases spatially overlapped with seizure focus and functional ultrasound imaging can provide high resolution 3D maps of seizure focus in animal models. To apply ultrasound imaging techniques in clinic, we propose to develop implanted ultrasound transducers 3mm∗1.5mm∗0.8mm which can be incorporated with the electrode array to record the CBV changes during seizure onset. This device can provide high resolution 3D seizure maps to guide the epilepsy surgery.

A Topology for Inductorless Actuation of Piezoelectric Transformer With Special Driving Waveform

The presence of an inductor during actuation of a piezoelectric transformer (PT) is a problem that has been investigated for many years. An inductorless driving topology to solve the inductor problem is proposed in this paper. This topology consists of a driver circuit and a pure piezoelectric matching network between the circuit and PT. The driver circuit is constructed to provide a specially designed waveform. The Fourier spectrum of the waveform presents dominant fundamental and third harmonics, with higher harmonics controlled to negligible levels. The third harmonic component is eliminated by a piezoelectric filter (PF), which is a component of the piezoelectric matching network. Another component is a piezoelectric inductor used to compensate for the capacitances of the PT and PF. An experimental setup is constructed to verify the performance of the driving topology. A total efficiency of 76.3% with an input power of 14.5 W is achieved when the whole driving system is considered. Although its performance is not exactly ideal, this topology is a highlight of investigations of the inductorless actuation of PTs. The proposed circuit and pure piezoelectric matching network indicate potential improvements in the performance and miniaturization of PT-based converters.

A High Frequency Geometric Focusing Transducer Based on 1-3 Piezocomposite for Intravascular Ultrasound Imaging

Due to the small aperture of blood vessel, a considerable disadvantage to current intravascular ultrasound (IVUS) imaging transducers is that their lateral imaging resolution is much lower than their axial resolution. To solve this problem, a single-element, 50 MHz, 0.6 mm diameter IVUS transducer with a geometric focus at 3 mm was proposed in this paper. The focusing transducer was based on a geometric-shaped 1-3 piezocomposite. The impedance/phase, pulse echo, acoustic intensity field, and imaging resolution of the focusing transducer were tested. For comparison, a flat IVUS transducer with the same diameter and 1-3 piezocomposite was made and tested too. Compared with their results, the fabricated focusing transducer exhibits broad bandwidth (107.21%), high sensitivity (404 mV), high axial imaging resolution (80 μm), and lateral imaging resolution (100 μm). The experimental results demonstrated that the high frequency geometric focusing piezocomposite transducer is capable of visualizing high axial and lateral resolution structure and improving the imaging quality of related interventional ultrasound imaging.

A study on the equivalent circuit of longitudinal vibration piezoelectric transformers with contacted heat transfer device

In this paper, the electrical equivalent circuits of the piezoelectric transformer (PT) with heat transfer system (HTS) had been studied. A heat transfer model of the longitudinal vibration PT had been built and an experiment study on the equivalent circuit model of the PT with HTS was proposed. this work provides a useful information for the application of piezoelectric transformer in high-power condition.