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Electric current generated by ultrasonically induced Lorentz force in biological media

  • A. MontalibetEmail author
  • J. Jossinet
  • A. Matias
  • D. Cathignol
Article

Abstract

The ions of solutions exposed to the propagation of ultrasound in the presence of a magnetic field experience Lorentz force. Their movement gives rise to a local electric current density, which is proportional to the electric conductivity of the medium. In vitro assessment of this current is performed using simple models of biological media. A constant magnetic field of 0.35T and 500kHz pulsed ultrasound are used. The sensing electrodes are exposed to neither the pressure wave nor the magnetic field, thus ensuring that the signal is not due to any undesirable electrode effect. The experimental results confirm that the current is proportional to the electrical conductivity of the medium. The changes in the measured current against the width of the measurement chamber show that the electrodes only collect fraction of the current created within the medium. The magnitude of the measured current is 50nA in a saline solution of 0.5S/m conductivity. The technique enabled the determination of the conductivity of a porcine blood sample against haematocrit. It is concluded that this type of measurement has the potential to allow the electrical conductivity of a medium to be determined using ultrasound.

Keywords

Ultrasound Magnetic field Electric conductivity Current density Electrolyte 

List of symbols

a

distance of a fluid element from its equilibrium position (m)

B

magnetic induction (T)

c

celerity of ultrasound (m.s−1)

C

molar concentration (mol.m−3)

Cm

membrane capacity (F.m−2)

dQ

elementary charge (C)

dS

surface element (m2)

dt

time intervals (s)

dτ

volume element (m3)

f

ultrasound frequency (Hz)

F

molar charge, 1 faraday (96487 C.mol−1)

i(t)

electric current (A)

I

magnitude of the instantaneous current (A)

j

base of imaginary numbers

jy

current density along axis Oy (A.m−2)

J

magnitude of the instantaneous current density (A.m−2)

m

ionic mass (kg)

M

molar mass of a solvated ion (kg.mol−1)

n

ionic charge

q

electric charge (C)

qe

electron charge (1.602 10–19 C)

r

radius of a cell (m)

t

time (s)

p

instantaneous acoustic pressure (Pa)

P

magnitude of the acoustic pressure (Pa)

uy,uz

instantaneous ionic speed along axes Oy, Oz, respectively (m.s−1)

Uy,Uz

magnitude of ionic speed along axes Oy, Oz, respectively (m.s−1)

vz

instantaneous speed of a fluid element along axis Oz (m.s−1)

Vz

magnitude of the speed of a fluid element (m.s−1)

x, y, z

Cartesian co-ordinates

μ

ion mobility (m2.s−1. V−1)

σ

mass density (kg.m−3)

σ

electric conductivity (S.m−1)

σ1

electric conductivity of the interior of erythrocytes (S.m−1)

σp

electric conductivity of plasma (S.m−1)

ϕ

volume concentration of the particles in a suspension

Ψ

phase angle (rd)

ω

angular frequency (rd.s−1)

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Copyright information

© IFMBE 2001

Authors and Affiliations

  • A. Montalibet
    • 1
    Email author
  • J. Jossinet
    • 1
  • A. Matias
    • 1
  • D. Cathignol
    • 1
  1. 1.National Institute for Health and Medical ResearchLyonFrance

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