The instrument's micromolar sensitivity and resolution can only be exceeded in systems many times its price and size. The design features a compact electromagnet and power supply. The instrument's rugged design, low power consumption, and ability to operate in the absence of water lines allow its use in transportable applications. Its automated features will be appreciated by both novice and experienced users alike.

A reliable solid-state Gunn oscillator, operating at approximately 9.6 GHz, is the heart of the microwave bridge used in the CMS 8400. It provides extremely stable frequency and power output. A circulator provides good isolation and low signal loss, and the use of a reference arm allows for balanced detection, enhancing overall system sensitivity. The output frequency, phase, and bias are automatically adjusted whenever the sample is changed.

The uses a rectangular TE102 cavity with a center frequency of approximately 9.6 GHz and an unloaded 0 of 5,000. Its variable iris aperture matches a wide range of sample holders and dewars, with a maximum diameter of 9.5 mm. Critical coupling of the cavity is accomplished automatically by way of the motor driven iris. Magnetic field in the cavity may be modulated up to l0 Gauss peak-to-peak at l00 kHz.

A Lock-in Amplifier operates at 100 kHz and performs the signal processing function for the CMS 8400. The initial amplification and impedance matching between the microwave detector and the lock-in amplifier is provided by a fixed gain preamplifier in the microwave bridge. Gain, phase, and time constant are all controlled by means of the data acquisition software. Signal averaging can also be used to improve the signal to noise ratio for very weak signals.

The Field Controller sets and maintains the level of magnetic field applied to the sample. Field center point, scan width, and scan duration are all set from the external computer. A Hall-effect probe mounted between the pole pieces maintains the field at the required level.

The electromagnet supplied with the CMS 8400 system features three-inch diameter pole caps which provide a field of up to 7,000 Gauss. The pole caps are shimmed to provide a homogenous field over the entire sample area of the cavity. The reduced magnet gap of 15 mm results in homogeneity equal to a 4 inch or larger magnet.

The Magnet Power Supply is a well-regulated solid-state supply that can deliver up to 16 amperes. It is Hall regulated by the Field Controller and is temperature protected against cooling system failure.

Data acquisition for the CMS 8400 is based upon intuitive pull down menus. User selections are highlighted in the menu toolbox, and dialog boxes appear whenever keyboard entry is required. Careful consideration was given to the design of the user interface in order to provide an environment which is easy to learn, yet powerful enough for an experienced user.