建立无线运动检测系统

　　建立无线运动检测系统

　　无线技术是实现易于使用的运动检测系统的关键。有一系列广泛的无线技术用于将运动探测器连接到中心集线器，从ISM频段到ZigBee，到Wi-Fi和其他因特网连接的协议，但无线链路的可靠性非常重要。从制造商如Atmel、Silicon Labs和恩智浦半导体器件，可以用不同的方式来提供无线连接到中央集线器作为一个强大的运动检测和报警系统的一部分。

　　运动探测器变得越来越普遍，但结果是对各种恶意攻击变得更加开放。这对运动传感器系统的设计产生了影响，无线元素的关键是确保一个安全而灵活的实现，它适合于实际应用——实际上在有入侵时能够标志。

　　在这种系统中，无线技术以多种不同的方式被使用。许多运动传感器包括无线链路回到中央集线器，但这为开发人员提供了更多的技术和安全选择。无线电波本身甚至被用作运动传感器，比被动红外传感器提供更多的能力。

　　The problem is highlighted by recent examples where thieves have drilled through walls to avoid motion sensors. One way around this problem has been developed by a US startup called Xandem. It is using the fact that the presence of a body reduces the penetration of radio waves， and so can be used to detect motion. Its tomographic motion detection （TMD） technology can sense through walls and obstructions， and senses over areas that are otherwise extremely difficult to cover. It can remain completely hidden from view， enhancing both the security and the aesthetics of the installation.

　　A Xandem TMD system is built with two kinds of devices： nodes and a processing unit. Multiple nodes surround the area where motion is to be detected， using mesh networking technology that senses when objects move within the area of the mesh， even through walls and obstructions. Each node is not a sensor; the mesh network connecting the nodes is the sensor. The processing unit is a gateway with normally-closed relays that connect to any standard panel to act as the hub.