|转至：电工之家
电容器是一种可以灌装电荷的容器，它与我们经常看到的电阻、电感一样都是常见的三种元件之一，因此它在电路中的作用是非常重要的，比如我们家里的家电产品电风扇、洗衣机、电冰箱等都需要电容器来启动；在电子产品中更是用到各种各样的电容，比如电解电容器、涤纶电容器、云母电容器、瓷片电容器等等；在我们的电力部门也常常会用到电容器进行功率因数的补偿，便于提升 用电效率，以上电容都是我们专门制作的，其实在我们电路中还有一些“隐形” 的电容，比如两根电线之间会存在电容；晶体管各个电极之间会存在电容；甚至在印制电路板这间也会存在电容，这些所存在的电容我们称为分布式电容。
电容器的介电常数
我们从电容的结构来看，电容容量的大小受三个方面的影响，一个是电容器的极板面积S、一个是电容器极板间的距离 d、另一个就是电容器两个极板之间所填充的绝缘物质，这种填充的绝缘物质要与真空这种绝缘介质相比较，我们知道真空中绝缘介质是固定不变的，大约是ε0= 8. 86 × 10-12 F/ m（法每米），比较的结果会得出一个每种绝缘物质的相对介电常数εr，那么电容器定义式中C=εS/d，这个ε是真空介电常数ε0与不同绝缘物质的相对介电常数εr相乘得到的，也就是ε=ε0εr。因此我们要讲电容的介电常数，常常说的是每种绝缘物质的相对介电常数εr。
在电容器制作好之后，要想提升电容器的容量，常常会在电容的绝缘介质上想方法，最常见的几种电介质有有机电介质、无机电介质、电解液电介质、气体电介质以及纸电介质等几种。在平时使用的电容中，电介质比较高的除了陶瓷电容器的电介常数在5.8这样一个高数值外，比它还高的有云母电容器，它的电介质可高达6至7.5之间，另外还有玻璃这种绝缘电介质，可高达5.5至8之间。
介电常数的意义
我们知道这个叫介电常数的ε，在制作电容时希望它的数值大些好，这样可以减小电容器的体积，增大电容器的容量值，这是我们希望看到的一面。但是在电子电路中一些常见的分布式电容对电路是有害的，比如当电源线距离很长时或者电路的频率很高时，都会给线路或者仪器正常工作造成一定的干扰。另外我们也会看到在收音机、电视机的电路板上所焊接的电子元器件，它们的引脚安装的都非常短，也是为了避免分布电容的存在 ，这时使用一些介电常数非常小的材料就很有必要了。同时它的存在也会对所制造的集成电路造成不利影响，我们在制作集成电路时也会想方设法用低介电常数的材料。
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