Sensitivity maps and system requirements for magnetic induction tomography using a planar gradiometer.
We evaluated analytically and experimentally the performance of a planar gradiometer as a sensing element in a system for magnetic induction tomography. A system using an excitation coil and a planar gradiometer was compared against a system with two coils. We constructed one excitation coil, two different sensing elements and a high-resolution phase detector. The first sensor was a PCB square spiral coil with seven turns. The second sensor was a PCB planar gradiometer with two opposite square spirals of seven turns, with a distance between centres of 8 cm. Theoretical sensitivity maps were derived from basic equations and compared with experimental data obtained at 150 kHz. The experimental sensitivity maps were obtained measuring the perturbation produced by a brass sphere of 12 mm in empty space. The advantage of using a gradiometer is that it can be adjusted to give a minimum signal for homogeneous objects, while increasing the sensitivity to local perturbations of the conductivity. Results show that a system using a planar gradiometer as detector has less demanding requirements for the electronic system than a system using simple coils.
Departament d'Enginyeria Electrònica, Universitat Politènica de Catalunya, Barcelona, Spain. jrosell@eel.upc.es
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Rosell
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Casañas
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Scharfetter
D017097:Electric Impedance; D004867:Equipment Design; D006801:Humans; D008280:Magnetics; D008962:Models, Theoretical; D012680:Sensitivity and Specificity; D014054:Tomography / Q000295:instrumentation* / Q000706:statistics & numerical data