In reed relays, the reed switch is driven using a solenoid coil, see the figure below. Reed relays work with relatively little power and are usually controlled using transistors, TTL, or CMOS inputs. If the reed relay contacts are dry-switched (less than 5V at 10mA), then the reed relay contacts can be pulled several billion times. In applications such as automatic test equipment, reed relays may switch millions of times each year.
The reed relay consists of a copper insulated coil and a dry reed
With the proper design and materials, the reed switch is placed on the magnetic shield and placed in the coil. This allows extremely low signal levels to pass through the reed relays with little or no interference. See below. This is almost impossible to achieve in other technologies unless it is costly.
With coaxial shielding, reed relays look like a high-frequency signal transmission line. As the reed pipe becomes smaller and smaller, the length of the reed relay is also reduced to less than 8 mm, and the distributed capacitance (between the reed switch and the magnetic screen) is reduced to less than 0.8 pF. See the figure below. This allows reed relays to transmit frequencies up to 6 GHz without severe loss of signal strength (by 3 dB). A typical insertion loss of 0.2 dB and voltage standing wave ratio (VSWR) 2:1.1 is now achievable. The RF characteristics of reed relays are comparable to gallium arsenide metal-oxide-semiconductor field-effect transistors and can transmit frequencies of 1 GHz and above. Reed sensors have excellent RF characteristics, and are therefore widely used today in semiconductor test equipment and cellular communications. equipment.