| 摘要 |
<p>A sensor element comprises first and second channel devices and at least one reflector. Each of the first and second channel devices is directed towards the reflector(s) and is able to transmit radiation along its length towards the reflector, and to transmit reflected radiation away from the reflector. At least one of the channel devices is separated from the reflector. The first and second channel devices are arranged so that radiation may not be transmitted between the channel devices without reflection from the reflector.</p> |
