The first steps to help blind people to see with sound are based on exactly double barrelled version of a normal electric torch.

• 帮助盲人利用声音来可见的最初作法的原理基于同样的原理。声音从一个形状像双筒电筒样的超声电筒发射出去。它的工作方式和军舰和潜水艇的声纳一样。