With the coming of the hot summer, various kinds of mosquito repelling devices are also being sold like hot cakes. Recently, a new kind of sound-wave mosquito repelling device was launched to the market and was warmly welcomed by the young parents.

According to the producer, the most venomous mosquitoes in summer are the pregnant ones. However, they tend to fly away from the eyes of the male mosquito. The producers say they just make use of this phenomenon to design the electric frequency conversion circuit. The mosquito repelling device can inject an ultrasound whose sound frequency is similar to that of male mosquito's. In this way could we dispel the male mosquitoes. On the direction sheet, there is a note saying "It can be worn on the Children's collar and will do no harm to the children."

But what's the real practical effect of the little machine? Does it really do no harm to the children?

Some professor say this kind of mosquito repelling device is almost useless. "Until now, there is no enough evidence that sound or sound frequency can eject mosquito". Some foreigners also pointed out that sound wave mosquito repelling device didn't achieve the expected goals.

Cheng Yang, the research engineer of CAS Institute of Acoustics says, theoretically speaking, ultrasound has the ability to dispel mosquito, but the practice application shows that the effect is little. Different kinds of mosquitoes have different acceptance frequencies. So the special repelling device is effective only to one certain kind of mosquitoes.