电话是人们所熟悉的,它是把声信号调制成电信号,经导线把被调制的电信号传送到接收端,然后再把电信号解调成昔频信号——声音。这种有线电的通信方式目前在社会上得到广泛的应用,但它存在着保密性差,金属材料、尤其铜的来源少,价格贵,电缆线的重量重,抗腐性差等缺点。再者随之通信事业的发 The telephone is familiar, it is the acoustic signal modulated into electrical signals, the modulated electrical signals through the wire to the receiving end, and then the electrical signal is demodulated to the former signal - sound. However, it has some shortcomings such as poor confidentiality, little metal source, especially copper, expensive price, weight of cable, poor corrosion resistance and so on. Furthermore, the development of communications