Simultaneous Inductive Sensing and Actuation of Magnetic Microrobots

The incorporation of magnetic materials into biomedical microrobots is widely appreciated as an advantageous way to enable their wireless control and actuation. These properties can additionally offer a basis for noninvasive magnetic sensing. In particular, magnetic particle imaging (MPI) and magnetic resonance imaging (MRI) have been considered for the localization and closed-loop control of magnetic microrobots. Nevertheless, these strategies typically require switching between distinct actuation and sensing modes, which limits the duty cycle of each and neglects an opportunity to obtain simultaneous inductive feedback during actuation.<br/><br/>Here, we use a low frequency rotating magnetic field (1 to 100 Hz), to show that it is possible to simultaneously apply and sense magnetic torques associated with model microrobots. To accomplish this, our prototype apparatuses finely adjust phase and amplitude to achieve cancellation between a sense and compensation coil. In one setup, the background signal from the rotating field was suppressed by 90 dB, enabling the detection of a stray field as low as 1 µT from a micromagnet. In another setup, we illustrated the possibility for detecting torque transfer to magnetotactic bacteria employed as living microrobots. By combining an inductive sensing apparatus with a selection field, we observe selective delivery of torque to multiple microrobots within a working volume. The sensitivity of inductive detection using these techniques can be shown to compare favorably to alternative methods for measuring stray fields originating from the magnetic materials in microrobots. These concepts build toward future closed-loop control schemes for magnetic microrobots based on simultaneous actuation and sensing.