阅读理解：
When a person sees an object，his or her eye senses many different waves of visiblelight as they bounce off the object.The eye and brain then work together to organize thesesensations and reconstruct the objects original shape. So，to make an object invisible，scientists have to keep waves from bouncing off it.And they have to make sure the objectcasts no shadow.Otherwise，the absence of reflected light on one side would give the obiectaway.
The scientists new invisibility device is the size of a drink coaster and shaped like aring.The ring is made of a special material with unusual ability.When microwaves strike thering，very few bounce off it.Instead，they pass through the ring，which bends the waves allthe way around until they reach the opposite side.The waves then return to their originalpaths.
When the researchers put a small cdpper loop inside the ring，it，too，is nearly invisible. However，the cloaking device and anything inside it do cast a pale shadow.And the deviceworks only for microwaves，not for visible light or any kind of electromagnetic radiation.So，Harry Potters invisibility cloak doesnt have any real competition yet.
invisibilityn.看不见，无形 spectrumn.光谱
microwaven.微波 ultraviolet ray 紫外线
radiantadj.辐射的 wavelengthn.波长
练习：
Acan now make an invisible cloak of the same kind as he uses.
Ctry to invent a device Similar in idea to the invisible cloak he uses.
2.What is true of microwaves?
BTheir wavelengths are longer than those of visible light.
DThey are visible to the human eye.