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High-density electrocortical (ECoG) microelectrode arrays are promising signal-acquisition platforms for brain-computer interfaces envisioned, e.g., as high-performance communication solutions for paralyzed persons. We propose a multi-channel microelectrode array capable of recording ECoG field potentials with high spatial resolution. The proposed array is of a 150 mm2 total recording area; it has 124 circular electrodes (100, 300 and 500 μm in diameter) situated on the edges of concentric hexagons (min. 0.8 mm interdistance) and a skull-facing reference electrode (2.5 mm2 surface area). The array is processed as a free-standing device to enable monolithic integration of a rigid interposer, designed for soldering of fine-pitch SMD-connectors on a minimal assembly area. Electrochemical characterization revealed distinct impedance spectral bands for the 100, 300 and 500 μm-type electrodes, and for the array's own reference. Epidural recordings from the primary visual cortex (V1) of an awake Rhesus macaque showed natural electrophysiological signals and clear responses to standard visual stimulation. The ECoG electrodes of larger surface area recorded signals with greater spectral power in the gamma band, while the skull-facing reference electrode provided higher average gamma power spectral density (γPSD) than the common average referencing technique.

This article addresses a novel fabrication process for an electrocorticogram (ECoG) electrode array. It consists of three regions: a flexible recording area, a flexible cable, and a rigid field for soldering the connectors. The flexible components can adapt to the curved shape of the cerebral cortex. Furthermore, the entire structure is a free-standing membrane, attached by removable polyimide straps to its carrier substrate. This configuration allows for a high level of control during soldering, electrode characterization and sterilization, as well as a soft release of the array off its carrier just before implantation. The array contains 128 gold electrodes, each 300 nm thick, sandwiched between two 5 μm thick polyimide films. The measuring area of the device is a regular hexagon with a side length of 7.2 mm, designed for implantation on the primary visual cortex of a Rhesus monkey. The flexible cable is 4 cm long. The rigid soldering area was designed for 4 × 32 OMNETICS connectors. The line resistance from an electrode site to the corresponding electrical connector pin is 540 Ω.

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We present an apparatus that permits quasisimultaneous measurements of several vibrating modes in a vibrating reed experiment. Position detection by laser beam deflection offers a simple setup and good sensitivity for higher modes of flexural as well as torsional vibrations. Frequency and damping from free decay data are determined by software which permits high accuracy, especially at low damping. This is particularly interesting for the measurement of the mechanical properties of thin films deposited on a low damping vibrating reed. As an example results on an Al film on a microstructurized silicon resonator are shown.