Electric current generated by ultrasonically induced Lorentz force in biological media

The ions of solutions exposed to the propagation of ultrasound in the prese nce 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 perform ed using simple models of biological media. A constant magnetic field of 0. 35 T and 500kHz pulsed ultrasound are used. The sensing electrodes are expo sed to neither the pressure wave nor the magnetic field, thus ensuring that the signal is not due to any undesirable electrode effect. The experimenta l results confirm that the current is proportional to the electrical conduc tivity of the medium. The changes in the measured current against the width of the measurement chamber show that the electrodes only collect a fractio n of the current created within the medium. The magnitude of the measured c urrent is 50 nA in a saline solution of 0.5 S/m conductivity. The technique enabled the determination of the conductivity of a porcine blood sample ag ainst haematocrit. It is concluded that this type of measurement has the po tential to allow the electrical conductivity of a medium to be determined u sing ultrasound.