Mechanism study on electromagnetic acoustic transducer for ultrasonic generation in ferromagnetic material

Based on the proper assumptions and approximations, the coupling mechanism of the electromagnetic acoustic transducer (EMAT) for ultrasonic generation within ferromagnetic material was studied by analyzing the eddy current distribution, Lorentz force, magnetostriction force and magnetization force. Some useful numerical calculations are presented to explain the EMAT behavior with general geometric arrangements. It is indicated that for the ferromagnetic material the magnetostriction effect dominates the EMAT phenomenon for ultrasonic wave generation in low magnetic field intensity, while the material does not reach its magnetizing saturation. But, with the increase of the bias magnetic field and saturation, the magnetostrictive terms will make no contributions to the ultrasonic generation and the Lorentz force becomes the only exciting mechanism. It is important to determine both the Lorentz and magnetostriction forces and select the appropriate working manner for achieving an optimized design.

纳米微孔高性能塑料WPX的性能和应用

目前，国内电声行业扬声器的音盆的制作材料主要是聚丙烯(PP)及纸浆成型，少量的高档产品采用价格昂贵的碳纤、玻纤编织、蜂巢等复合材料。这几年，国外出现了结构微发泡材料，注塑成型的音盆，低音效果十分理想。但这些国家对我们实行技术封锁，不肯提供这方面的设备与技术。鉴于上述情况，我们研制了纳米级分子立体排列微孔结构、高刚性、高耐温、热塑性塑料材料，填补了电声发声材料领域的空白。