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Adding threat-detection measures, such as heavy, power-hungry radar antennae, or spinning lidar units,
增加威胁探测措施，如重型耗电的雷达天线或旋转激光雷达装置
radar's optical equivalent, would either reduce range or prevent lift-off in the first place.
（雷达的光学等效装置）可以在一开始就减少投掷射程或防止投掷。
Dr Roy and Mr Garg think, however, that they have hit on a low-power, lightweight self-defence system suitable for small drones.
但Roy博士和Garg博士认为他们发现了一种适用于小型无人机的低功率、轻型自卫系统。
Instead of employing light or radio waves to detect incoming threats, it harnesses sound waves and the Doppler effect.
无需光波和无线电波，它可以利用声波和多普勒效应来探测威胁来袭。
The Doppler effect is the frequency shift heard as a source of sound approaches or recedes.
多普勒效应是当声源靠近或后退时听到的频率偏移。
It is, for example, the reason the pitch of a police siren changes as a patrol car passes in the street.
例如，这就是警车在街上经过时警笛声改变的原因。
To take advantage of it Dr Roy and Mr Garg plan to fit drones with diminutive loudspeakers, like those found in smartphones.
Roy博士和Garg博士计划利用这一点给无人机装上小型扬声器，就像智能手机上的那样。
These would broadcast an ultrasonic tone outward from the drone.
它们会从无人机向外发射超声波。
Similarly tiny microphones would then listen for reflections from incoming objects.
类似的，小型麦克风会听取来自临近物体的反射。
The Doppler shift of these reflections, run through a bit of on-board processing
这些反射的多普勒频移，经过一些机载处理
(but far less than that needed for radar or lidar) would give the bearing of the threat, and thus permit the drone to take evasive action.
（但远远少于雷达或激光雷达所需的处理），就能确定威胁的方位，从而使无人机采取规避行动。
To test the principle of what they call their DopplerDodge drone defence system,
为了测试他们的DopplerDodge无人机防御系统，
Dr Roy and Mr Garg have constructed a static version in their laboratory,
Roy博士和Garg博士在他们的实验室里构建了一个静态版本，
and have been throwing objects of various sizes and shapes at it, as if it were a hovering drone.
并向它投掷各种大小和形状的物体，就好像它是一个在空中盘旋的无人机。
At the moment, it can detect these objects from distances of up to four metres away.
目前，它可以探测到4米以外的物体。
That is pretty close, but would still give a drone a tenth of a second's notice of an incoming missile.
这个距离很近，但是仍然可以给无人机十分之一秒的时间来注意临近的投掷。
This would be sufficient for it to move itself out of the way.
这足以让无人机避开。
Tests on actual drones will take place shortly, and then, if all goes as planned,
不久将进行无人机的实际测试，如果一切按计划进行，
the two researchers will attempt to extend the system's range to 30 metres—a reasonable approximation of a stone's throw.
两位研究人员将尝试将系统的射程扩大到30米——一个接近扔石头的合理距离。
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