Metallic Object

Abstract: An assumption is made that the Time Domain Electromagnetic (TEM) response of a buried axisymmetric metallic object can be modelled as the sum of two dipoles centered at the midpoint of the body. The strength of the dipoles depends upon the relative orientation between the object and the source field, and also upon the shape and physical properties of the body. Upon termination of the source field, each dipole is assumed to decay as k(t+α)−βe−t∕γ. The parameters k, α, β and γ depend upon the conductivity, permeability, size and shape of the object, and these can be extracted from the measurements by using a nonlinear parametric inversion algorithm. Investigations carried out using an analytic solution for a sphere and laboratory measurements of steel and aluminum rectangular prisms, suggest the following two-step methodology: (1) The value of β is first used as a diagnostic to assess whether the metallic object is non-magnetic or magnetic, (2) the ratios of k1∕k2 and β1∕β2 are then diagnostic indicators as...

Abstract: A treatment delivery apparatus comprises a metallic object and a treatment carrier device which is connected by a heat-sensitive biodegradable connector link to the magnetic object. This carrier device contains the treatment, i.e. the drug, to be transported. An electromagnet is positioned outside of the body part for producing a magnetic field which captures the magnetic object. This electromagnet may be either a simple coil system attached to a robotic arm which moves the electromagnet adjacent the body part, or a multicoil electromagnet system surrounding the body part. In either case, the robotically moved electromagnet or multicoil electromagnet system moves the magnetic object within the body part to a desired location. A computer controls either the robotic arm or multicoil current magnitudes and directions. This computer also provides visualization for observing the location and movement of the magnetic object and carrier device. Upon reaching the desired location, the magnetic object is heated, which causes the heat-sensitive biodegradable connector link to melt, which separates the drug-containing carrier device from the magnetic object. The electromagnet means then moves the magnetic object back out of the body part. The treatment-containing carrier device remains in the desired location and the drug is delivered to the specific location.

Abstract: A total of 305 magnetic resonance (MR) examinations were performed in 236 patients with metallic implants. Most examinations were performed at 0.3 T. The metallic implants included central nervous system shunting devices, tantalum mesh, surgical wire, skin staples, surgical clips, metallic orthopedic devices, and a few miscellaneous metallic objects. Patients with cardiac pacemakers, electrical implants, prosthetic cardiac valves, and aneurysm clips were excluded from MR examinations. The images were reviewed for evidence of metallic artifact. The conspicuity of artifact was related to the composition, mass, orientation, and position of the metallic object in the body. In most instances, the metallic artifact did not interfere with the interpretation of the image. The patients' records were also reviewed for adverse effects noted by each patient during the MR examination. Only two patients reported discomfort that could possibly have been related to their metallic implants, but in both cases it seemed unl...

Abstract: Every structure scatters an impulse plane wave in a unique fashion. The structural information of an object can be extracted by analyzing the late-time scattered field as the impulse-response of the structure. The late-time scattered field, which represents the source-free response of the structure, contains a summation of damped sinusoids. The frequency and damping factor of these damped sinusoids are uniquely associated with the structural information, and can be used to identify an unknown object. We propose to create uniquely identifiable scattered fields from an object by incorporating “notches” in the structure giving rise to specific damped sinusoids in the source-free scattered field of the structure. In this manner, data can be embedded into the structure of an object which is detectable using electromagnetic waves, allowing a metallic object to serve as a chipless radio-frequency identification tag (RFID). Data is encoded as complex natural resonant frequencies (referred to as poles) in the structure and is retrieved from the scattered field. Data retrieval is based on Singularity Expansion Method (SEM) analysis using target identification techniques. Each complex-frequency pole provides two-dimensional data (real and imaginary) which can be extracted from the late-time impulse response of the structure using a numerical technique such as the Matrix Pencil Method. We have designed and prototyped a 6-bit (3-pole) tag. The tag is analyzed using simulations and measurements. The tag is successfully read remotely via its scattered fields. The measured data are compared with simulation, and are in close agreement.