After testing various liquids, the researchers chose a metal alloy called Galinstan. Used in thermometers, it is similar to mercury but not poisonous.

在测试过不同的流体后，研究人员选择了一种名为Galinstan的合金。将其注射进温度计后，研究人员发现它与水银很相似，不过没有毒性。

Two small pouches, placed in the bottom of a shoe, are filled with the fluid and generate a current whenever they are compressed by the foot's up and down motion.

当他们将两个装有该流体的小袋子置于鞋内时，它们就会因人脚抬升和下落的动作而受到挤压，从而产生电流。

Transferring the energy from a device in a foot to a phone in the hand presents an obvious hurdle.

而如何将装置内的能量从脚部传输给手上的手机明显就成了难题。

Rather than plugging a cable into a shoe, the Wisconsin researchers suggest installing a wireless transmitter in the heel. This could make radio contact with mobile phone base stations.

威斯康星的研究人员用安装在脚后跟的无线发射机取代了需要塞进鞋子里的数据线。这样能量就可以与手机基站取得无线电联系。

Professor Krupenkin said: "Humans were 'very powerful energy-producing machines' that could produce as much as a kilowatt of power while sprinting."

克鲁本勤教授说：“人类是非常强大的‘能源生产器’，人在疾跑时可以产生上千瓦的电量。”