James E. Lenz

A review of magnetic sensors

Eleven of the most common technologies used for magnetic field sensing are described and compared. These are the search coil, flux-gate, optically pumped, nuclear precession, SQUID, Hall-effect, magnetoresistive, magnetodiode, magnetotransistor, fiber optic, and magnetooptic technologies. The use of these sensors in relation to working with or around the Earths magnetic field is addressed. Three classes of applications and a specific application from each are examined: low-sensitivity (noncontact switching), medium-sensitivity (magnetic anomaly detection and magnetic compassing), and high-sensitivity (brain-function mapping). >

Magnetic materials characterization using a fiber optic magnetometer

The fiber optic magnetometer is a relatively new sensor concept which shows promise for high sensitivity measurements. It employs glass fibers which are configured in a Mach–Zehnder interferometer where the fringe pattern output is extremely sensitive to path length changes. The sensing leg is sensitized to magnetic fields by electroplating the fiber with magnetostrictive Ni‐Fe‐Co alloys. The magnetic M properties of the metal‐coated fiber are measured using an M‐H looper and its magnetostriction λ using the fiber magnetometer setup. Data for Ni‐Fe alloys are presented which compare the measurements of M and λ versus tension. From this data physical relationships between λ and M for the metal‐coated fibers are identified.

Optically Powered Sensors: A Systems Approach To Fiber Optic Sensors

For more than 10 years fiber optic sensors have been projected as a dominant sensor technology for the future. This projection has yet to be realized. There continues to be a substantial level of research and development in various fiber sensors concepts yet only a few products are available commercially. The six major factors limiting the success of the fiber sensors in the marketplace are identified. An alternate approach to fiber sensors is described which take a systems approach to producing fiber sensors. It combines the advantages of optical fibers with the low power electronic sensor technology currently available. A single multimode fiber is connected between the readout and the transducer. Optical energy transmitted from the readout is converted to electricity at the transducer. Digital data from the transducer is synchronously transmitted over the fiber to the readout. Prototypes of magnetic (i.e., current), temperature, position, and proximity sensors have been built and will be described. A discussion comparing optical and electrical sensors is also included.

A multi-sensor approach to airport surface traffic tracking

A dual sensor system using a large number of inexpensive short range sensors can act as a valuable adjunct to surface surveillance radars, as well as provide a low cost tracking system for non-radar equipped airports. A measurement program was conducted to collect data on magnetic and infrared signatures of aircraft and other vehicles on airport surfaces. The data indicates that short range sensors can provide detection and tracking of vehicles, and may be able to perform some classification function.<<ETX>>

Fiber optic data bus for solid state sensors

A sensor system is described which is immune to EMI (electromagnetic interference) by combining a fiber-optic data bus with existing solid-state sensors. By optimizing the electrical design, through the wide variety of standardized circuits, this system allows for using a relatively inexpensive optical design based on standard optical components. Also power consumption can be traded off with added functions at the transducer end. With low-power electronics the options to address individual sensors, multiplex between sensors, change the sensor sample rate, and set threshold alarms are relatively simple compared to performing these functions with an optical scheme.<<ETX>>

Fiber Optic Magnetometer Design

Magnetic sensors have been used in applications ranging from keyboard switches to submarine detection. Recently developed fiber optic magnetometers promise to provide high performance/moderate cost alternative to existing sensors. The special properties of fiber magnetometers such as directional response, high sensitivity, room temperature operation are discussed in the context of other magnetometers. Fiber magnetometer design considerations, fabrication procedures, and performance measurements using magnetostrictive alloy coatings are presented. Optimum performance is obtained with a 36% - 64% nickel-iron alloy electroplated over the polymer jacket on a single mode fiber. Sensor designs for fiber optic magnetometers are shown.

Electronic rumble strip

Single vehicle run-off-road accidents are responsible for significant numbers of injuries and fatalities, and significant property damage. This fact spurs interest in warning systems to alert drivers that vehicles are drifting towards the edge of the road, and that a run-off road accident is imminent. An early attempt at such a warning system is the use of machined grooves on the shoulder to create a rumble strip. Such a system only provides warning, however, as the vehicle actually leaves the traffic lane. More desirable is a system that warns in anticipation of such departure. Honeywell has under development a magnetic lateral guidance system that couples a sensitive magnetoresistive transducer with a magnetic traffic marking tape being developed by 3M. While this development was initially undertaken for use in automated highways, or for special tasks such as guiding snowplow owners, the system can provide an effective, all-weather warning system to provide alert of impending departure from the roadway. This electronic rumble strip is actually a simpler system than the baseline guidance system, and can monitor both distance from the traffic lane edge and the speed of approach to the edge with a low cost sensor.

Hybrid fiber optic sensors

For more than 10 years, fiber optic sensors have been projected as a dominant sensor technology for the future. This projection has yet to be realized. There continues to be a substantial level of research and development in various fiber sensors concepts, yet only a few products are available commercially. The major factors limiting the success of the fiber sensors in the marketplace will be identified. An alternate approach to fiber sensors is described which takes a systems approach to producing fiber sensors. It combines the advantages of optical fibers with the low‐power electronic sensor technology currently available. A single multimode fiber connected between the readout is converted to electricity at the transducer. Optical energy transmitted from the readout is converted to electricity at the transducer. Digital data from the transducer are synchronously transmitted over the fiber to the readout. Magnetic (i.e., current), temperature, position, and proximity sensors have been built and will be d...