Zhile Han

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.

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 Modified 2D Multiresolution Hybrid Algorithm for Ultrasound Strain Imaging

Ultrasound elastography is an imaging modality to evaluate elastic properties of soft tissue. Recently, 1D quasi-static elastography method has been commercialized by some companies. However, its performance is still limited on high strain level. In order to improve the precision of estimation during high compression, some algorithms have been proposed to expand the 1D window to a 2D window for avoiding the side-slipping. But they are usually more computationally expensive. In this paper, we proposed a modified 2D multiresolution hybrid method for displacement estimation, which can offer an efficient strain imaging with stable and accurate results. A FEM phantom with a stiffer circular inclusion is simulated for testing the algorithm. The elastographic contrast-to-noise rate (CNRe) is calculated for quantitatively comparing the performance of the proposed algorithm with conventional 1D elastography using phase zero estimation and the 1D elastography using downsampled (d-s) baseband signals. Results show that the proposed method is robust and performs similarly as other algorithms in low strain but is superior when high level strain is applied. Particularly, the CNRe of our algorithm is 15 times higher than original method under 4% strain level. Furthermore, the execution time of our algorithm is five times faster than other algorithms.

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.

Fabrication and performance of a micro 50-MHz IVUS Transducer based on a 1-3 composite with geometric focusing

In this paper a micro 50-MHz IVUS Transducer based on a 1-3 piezo-composite with geometric focusing was presented. The using 1-3 PZT composite material was developed in our laboratory with 12 um kerfs and 18 um pillars. The transducer was focused in the elevation direction by geometrically shaping the composite material using a PTEF ball with a 5 mm radius. After the silver conductive backing layer was cured, the transducer was divided into the size of 1.0 × 1.0 mm. The final fabricated transducer was fixed in a needle tip, and its diameter is 9F. According to the testing results with our homemade IVUS system, its lateral resolution is about 120 um, which effectively improved the lateral resolution of current IVUS system.

A graphic processing unit based intravascular ultrasound (IVUS)

A practical intravascular ultrasound system prototype is presented. The system is designed to work in compliance with high frequency interventional ultrasound imaging catheter, which has a center frequency as high as 60MHz. Differ from former architecture, a graphic processing unit is utilized as a primary processing component to accomplish most of the crucial computations in this machine, based on which, real time algorithm verification becomes much easier. This paper explains the motivation to start the project, introduces the hardware architecture that have been adopted and specifies the processing flow cooperate with this architecture. The time budget of experimental algorithm running on this prototype is analyzed and few images obtained with it are illustrated.

Effect of temperature and wavelength on photoacoustic signal

In this paper, the effect of temperature and wavelength on photoacoustic signals was qualitatively studied.

Design of micromachined self-focusing piezoelectric composite ultrasound transducer

Based on the Fresnel half-wave band interference, a micromachined self-focusing piezoelectric composite ultrasound transducer was proposed in this paper. The theoretical analysis was deduced based on the concept of constructive interference of acoustic waves and electromechanical response of piezoelectric composites. The calculated and simulation results showed that it combined the advantages of composite transducer and plate self-focusing transducer, and can achieve high electromechanical coupling coefficient, low acoustic impedance, high intensity, short focal length and micro size. Because it was based on the micro-electromechanical systems, the fabrication process was accurate and controllable, which made it have good potential for interventional ultrasound imaging, cellular microstructure imaging, skin cancer detection and industrial nondestructive testing applications.