Electrophysiological devices are connected to the body through electrodes. In some applications, such as nerve stimulation, it is needed to minimally pierce the skin and reach the underneath layers to bypass the impedance of the first layer called stratum corneum. In this study, we have designed and fabricated surface microneedle electrodes for applications such as electrical peripheral nerve stimulation. We used molybdenum for microneedle fabrication, which is a biocompatible metal; it was used for the conductive layer of the needle array. To evaluate the performance of the fabricated electrodes, they were compared with the conventional surface electrodes in nerve conduction velocity experiment. The recorded signals showed a much lower contact resistance and higher bandwidth in low frequencies for the fabricated microneedle electrodes compared to those of the conventional electrodes. These results indicate the electrode-tissue interface capacitance and charge transfer resistance have been increased in our designed electrodes, while the contact resistance decreased. These changes will lead to less harmful Faradaic current passing through the tissue during stimulation in different frequencies. We also compared the designed microneedle electrodes with conventional ones by a 3-dimensional finite element simulation. The results demonstrated that the current density in the deep layers of the skin and the directivity toward a target nerve for microneedle electrodes were much more than those for the conventional ones. Therefore, the designed electrodes are much more efficient than the conventional electrodes for superficial transcutaneous nerve stimulation purposes.

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This paper presents a large displacement out-of-plane Lorentz actuator array for surface manipulation. Actuators are formed from single crystal silicon flexible serpentine springs on either side of a rigid crossbar containing a narrow contact pillar. A rigid mounting rail system was employed to enable a 5 × 5 array, which offers scalability of the array size. Analytical and finite element models were used to optimize actuator design. Individual actuators were tested to show linear deflection response of ±150 µm motion, using a ±14.7 mA current in the presence of a 0.48 T magnetic field. This actuator array is suitable for various 2D surface modification applications due to its large deformation with low current and temperature of operation, and narrow contact area to a target surface.

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This paper presents the results of studying the shielding effect of a vertical moving shutter micromachined electric field mill. In this design, a set of interdigital sensing electrodes are located in the same plane as the moving shutter, with the shutter's vertical motion enabling modulation of the sensed electric field. The effects of various geometrical parameters of the shutter, including the spacing between the fingers and their width, were simulated to study the collected charge as a function of shutter displacement. For the cases with shutter finger spacings 1.5 to 2 times finger-widths, when the shutter lifted up to a height equal to the comb finger-width, the electrode signal dropped by approximately 22-26%. When the shutter lowered for a height equal to finger-width, the charge increased by approximately 24%. To verify the results of the simulations, one shutter design was selected and fabricated. Thermal actuators were employed to move the shutter vertically, in order to study the shutter shielding effect as a function of displacement. The sensor's mechanical performance test demonstrated 25 µm of displacement when heated to 100 • C. The electric field sensing functionality of the sensor was also tested under an electric field of 9.4 kV m −1 . The vertical motion of the shutter successfully demonstrated its ability to vary the field on the sensing electrodes. An output voltage of 7 ± 0.5 µV was measured per oscillation of the 1.3 × 2 mm shutter for a 25 µm movement. The sensor demonstrated a sensitivity of 0.74 mV kV −1 m −1 .