Mark A. Reed

Coil Optimization Method for Electromagnetic Induction Systems

Electromagnetic induction systems have proven to be very effective in detecting subsurface metallic and magnetic objects. Such systems often employ separate transmit and receive coils, and thus it is desirable for the transmit and receive coils in these systems to have minimal mutual coupling. It is also desirable for the product of the fields generated by the transmit and receive coils to be as large as possible to maximize the detection depth. We demonstrate that a pair of spiral coils can be optimized to achieve these desired properties. A mathematical representation is chosen for the coils, which allows the coil pair to be optimized using an iterative convex method, which, due to its convexity, is very fast. We then present results showing a pair of nonuniformly wound spiral coils created with this optimization.

Optimized coils for electromagnetic induction systems

Electromagnetic induction (EMI) systems often use separate transmit and receive coils. In these systems, it is desirable for the transmit and receive coils to have minimal mutual coupling and a maximum eld product, thus maximizing the detection depth. We demonstrate that a pair of spiral coils can be optimized to achieve these desired properties. A mathematical representation is chosen for the coils that allows the coil pair to be optimized using an iterative convex method, which, due to its convexity, is very fast. We then present results showing both a pair of nonuniformly-wound, single-sided spiral coils and a pair of nonuniformly-wound, double-sided, spiral coils created with this optimization.

Improved method for the optimization of coils in the presence of magnetic soil

Continuous-wave (CW) electromagnetic induction (EMI) systems operating in the presence of magnetic soil often encounter issues with the voltage that the soil induces in the receive coil. Previously, an optimization procedure that represents the coils as stream functions and attempts to create coils to mitigate the effects of the soil was presented. In this paper, the optimization convergence is improved, and a new soil constraint that improves the coils created by the optimization is developed. New coil metrics are introduced, and new coils are designed using the new soil constraint, which allows more freedom for the optimization to adjust the soil response. The new coils indicate the possibility of improvement over current coil designs.

Formulation of a method for the optimization of coils for electromagnetic induction systems in the presence of magnetic soil

Continuous-wave (CW) electromagnetic induction (EMI) systems operating in the presence of magnetic soil often encounter issues with the voltage that the soil induces in the receive coil. A formulation is developed to allow the calculation of the soil response of a CW EMI coil head that is represented by stream functions. This formulation is then included in an optimization procedure for stream-function coils that is designed to optimize a coil head for improved sensitivity while nulling the coil heads soil response at a specific height above the soil. Example coils are created using the optimization method, and the new coils are compared to other common coil types.

Optimization of planar coils for electromagnetic induction systems

Continuous-wave electromagnetic induction systems used for subsurface sensing often employ separate transmit and receive coils. In these systems, it is desirable to have zero mutual coupling between the transmit and receive coils and for the coils to have maximum sensitivity at a specific location. A representation of a pair of coils as stream functions on planar surfaces is created, and then a method of optimizing these stream functions for minimum mutual coupling and maximum sensitivity using a convex solver is developed. A pair of coils is optimized for varying amounts of dissipated power and stored energy, and the solutions are categorized. The sensitivity of the optimized coils is then compared to other common coil types.

Formulation for a practical implementation of electromagnetic induction coils optimized using stream functions

Continuous-wave (CW) electromagnetic induction (EMI) systems used for subsurface sensing typically employ separate transmit and receive coils placed in close proximity. The closeness of the coils is desirable for both packaging and object pinpointing; however, the coils must have as little mutual coupling as possible. Otherwise, the signal from the transmit coil will couple into the receive coil, making target detection difficult or impossible. Additionally, mineralized soil can be a significant problem when attempting to detect small amounts of metal because the soil effectively couples the transmit and receive coils. Optimization of wire coils to improve their performance is difficult but can be made possible through a stream-function representation and the use of partially convex forms. Examples of such methods have been presented previously, but these methods did not account for certain practical issues with coil implementation. In this paper, the power constraint introduced into the optimization routine is modified so that it does not penalize areas of high current. It does this by representing the coils as plates carrying surface currents and adjusting the sheet resistance to be inversely proportional to the current, which is a good approximation for a wire-wound coil. Example coils are then optimized for minimum mutual coupling, maximum sensitivity, and minimum soil response at a given height with both the earlier, constant sheet resistance and the new representation. The two sets of coils are compared both to each other and other common coil types to show the method’s viability.

Optimal coils with zero mutual inductance for electromagnetic induction systems

Electromagnetic induction (EMI) systems often use separate transmit and receive coils. In these systems, it is desirable for the transmit and receive coils to have both minimal mutual coupling and a maximum field product, thus maximizing the detection depth. A mathematical representation is chosen for a pair of spiral coils that allows the coils to be optimized using an iterative convex method. This method, which is very fast, allows the coils to be optimized for the desired properties of minimum mutual coupling and a maximum field product. We then present results showing a pair of nonuniformly-wound, double-sided spiral coils.

Optimization, analysis, and comparison of coils for EMI systems

Many different coil head configurations are used in electromagnetic induction (EMI) systems for sensing buried targets. The design of these types of coils is not well described in current literature, and it is difficult to compare the performance of different coil head designs to one another. Comparing two particular implementations is not particularly challenging, but fairly comparing general coil head designs is nontrivial. This work details normalized target sensitivity and soil sensitivity metrics that account for differences such as overall coil size, length, and wire diameter and for variations in sensitivity patterns. The metrics are used to optimize double-D, dipole/quadrupole, and concentric coil head designs, which are then analayzed and compared to one another.

Metrics for the comparison of coils used in electromagnetic induction systems

Many different coil head configurations are currently used in electromagnetic induction (EMI) systems for sensing buried targets. It is difficult to compare the performance of different coil head designs to one another. Comparing two particular implementations is not particularly challenging, but fairly comparing general coil head designs is nontrivial. This work details both a target sensitivity metric and soil sensitivity metric that account for differences such as overall coil size, length, and wire diameter. The metrics are then used to compare the performance of a range of concentric EMI coil head designs.

Implementation of optimized electromagnetic induction coils

Electromagnetic induction (EMI) systems often employ separate transmit and receive coils that are placed in close proximity to one another. This placement is desirable for packaging reasons, but it makes achieving minimal mutual coupling between the two coils difficult. An iterative-convex optimization procedure that allows coils to be designed for both minimum mutual coupling and maximum on-axis sensitivity is demonstrated, and then this procedure is used to create a pair of double-sided, non-uniformly wound spiral coils, which improve upon previous coils by making the transmit coil resistance uniform. The effects of capacitive loading within the coils are explored, and results showing that the coils perform as expected at low frequency are presented.