Pulse magnetic flux density sensor designed for biomedical magnetic stimulation

Biomedical magnetic stimulations are widely used. However, proper stimulus intensity measurement has not been provided for clinical application. This paper proposes a Pulse Magnetic Flux density measuring Sensor (PMFS) that consists of 2an2 sensor coil and 2Oms time constant integrator. This PMFS works without the need of power supply which allows simple use for clinical magnetic stimulation. Introduction High magnetic flux density and frequent magnetic stimulations to rat heads produced microvacuolar changes on the neuropil portion of cortex [l]. It is an essential requirement for magnetic stimulation to measure the stimulus intensity before and after the practices. However, proper stimulus intensity index is not provided but using % of the maximum output or the capacitor bank charged voltage . As a solution to the raised problem, this paper proposes the PMFS that is able to measure magnetic flux density B and its time derivative dB/dt [2) as stimulus intensity indexes. Methods An optimal sensor coil size design is investigated. 1: Magnetic flux density distribution Bz by a donut shaped stimulation coil is calculated (inner radius 33.5mm,outer radius 54mm,N=9 turns, current I4600A). 2: Bz distortions by various sensor coil sizes are calculated. 3:Prototype PMFS is designed. Fig.lA. Polygon approximation for the stimulation coil. (K=32).Fig.lB. Magnetic flux density B calculation by Biot Savart’s law at the point d. 1:Magnetic flux density Bz is calculated by Eq.(l). A polygon approximation (Fig.l,K=32) and BiotSavart’s law are applied for the magnetic flux density calculations by each polygon segment. The magnetic flux density contributions from each polygon semnent are summed at an observation point. 2:Flux density distributions Bz measured by finite sensor coils are distorted as Bzs as Fig.2.