信息科学与电子工程专业英语 Lecture03_new.ppt

2. “电子战”的核心－国防应用 ② 电子对抗技术 电子对抗就是敌对双方为削弱、破坏对方电子设备的使用效能，保障己方电子设备发挥效能而采取的各种电子措施和行动，又称电子战。电子对抗分3个方面：电子对抗侦察、电子干扰和电子防御。 4. 在生物医学方面的应用 诊断：（磁共振） 热效应：微波理疗、组织固定。 治疗 非热效应：免疫组织化学和免疫细胞化学研究。 * These devices work in the density modulated mode, rather than the current modulated mode. This means that they work on the basis of clumps of electrons flying ballistically through them, rather than using a continuous stream.3 这些器件工作在密度调制模式而不是电流调制方式。这意味着它们是基于真空管发出的电子簇工作的，而不是用连续的电子流。 Unit 3-3 微波 ——器件 * A microwave oven works by passing microwave radiation, usually at a frequency of 2450?MHz (a wavelength of 12.24?cm), through the food. Water, fat, and sugar molecules in the food absorb energy from the microwave beam in a process called dielectric heating. 微波炉是通过穿过食物的微波辐射工作的，通常频率是在2450 MHz（波长12.24厘米）。食物中的水、脂肪和糖分子在称为电介电加热的过程吸收微波波束的能量。 Unit 3-3 微波 ——用途 * Many molecules (such as those of water) are electric dipoles, meaning that they have a positive charge at one end and a negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field induced by the microwave beam. 许多分子（如那些水）是电偶极子，这意味着它们一端带正电，另一端带负电，因此它们力图与微波波束所引起的交变电场保持一致而发生旋转。 Unit 3-3 微波 ——用途 * This molecular movement creates heat as the rotating molecules hit other molecules and put them into motion. Microwave heating is most efficient on liquid water, and much less so on fats and sugars (which have less molecular dipole moment), and frozen water (where the molecules are not free to rotate). 旋转分子撞击其它分子使他们运动，这种分子运动产生热量。微波加热对液态水是最有效的，其次为脂肪和糖类（分子偶极矩较少）以及冷冻水（分子不能自由转动）。 Unit 3-3 微波 ——用途 * Microwave heating is sometimes incorrectly explained as a rotational resonance of water molecules: such resonance only occurs at much higher frequencies, in the tens of gigahertz. Moreover, large industrial/commercial microwave ovens operating in the 900?MHz range also heat water and food perfectly well. 微波加热有时被错误地解释为水分子的旋转共振，而这种共振只能发生在数十千兆赫的高频。此外，大型工业/商业微波炉在900兆赫的范围内工作，也能很好地加热水和食物。 Unit