Timothy A. Fofonoff

Three-legged wireless miniature robots for mass-scale operations at the sub-atomic scale

We propose to bring the instruments to the samples in the form of miniature wireless instrumented robots called the NanoWalkers. With the NanoWalker robot approach, instrumentations and throughput requirements can be adjusted extremely fast by simply adding, replacing, or removing robots at will. It is the aim of this project to develop a powerful and flexible environment that we believe may revolutionize the way drug, biological, material discovery, and characterization will be performed in the future.

Microelectrode array fabrication by electrical discharge machining and chemical etching

Wire electrical discharge machining (EDM), with a complementary chemical etching process, is explored and assessed as a method for developing microelectrode array assemblies for intracortically recording brain activity. Assembly processes based on these methods are highlighted, and results showing neural activity successfully recorded from the brain of a mouse using an EDM-based device are presented. Several structures relevant to the fabrication of microelectrode arrays are also offered in order to demonstrate the capabilities of EDM.

The application of conducting polymers to a biorobotic fin propulsor

Conducting polymer actuators based on polypyrrole are being developed for use in biorobotic fins that are designed to create and control forces like the pectoral fin of the bluegill sunfish (Lepomis macrochirus). It is envisioned that trilayer bending actuators will be used within, and as, the fins webbing to create a highly controllable, shape morphing, flexible fin surface, and that linear conducting polymer actuators will be used to actuate the bases of the fins fin-rays, like an agonist-antagonist muscle pair, and control the fins stiffness. For this application, trilayer bending actuators were used successfully to reproduce the cupping motion of the sunfish pectoral fin by controlling the curvature of the fins surface and the motion of its dorsal and ventral edges. However, the speed of these large polymer films was slow, and must be increased if the fins shape is to be modulated synchronously with the fins flapping motion. Free standing linear conducting polymer films can generate large stresses and strains, but there are many engineering obstacles that must be resolved in order to create linear polymer actuators that generate simultaneously the forces, displacements and actuation rates required by the fin. We present two approaches that are being used to solve the engineering challenges involved in utilizing conducting polymer linear actuators: the manufacture of long, uniform ribbons of polymer and gold film, and the parallel actuation of multiple conducting polymer films.

A highly flexible manufacturing technique for microelectrode array fabrication

A new technique for manufacturing microelectrode arrays is described and assessed. This technique uses wire Electrical Discharge Machining (wire EDM) to form detailed array structures from a single sample of solid metal. Chemical etching can then be used to increase the electrode aspect ratios. Electrode lengths of 5 mm, widths of 40 /spl mu/m, and spacings of 250 /spl mu/m have been fabricated using this technique. Arrays of electrodes of varying lengths can also be fabricated. For intracortical recording applications, the signal paths are isolated from one another by securing an insulating substrate.

Mechanical assembly of a microelectrode array for use in a wireless intracortical recording device

Fabrication of a microelectrode array assembly for neural activity recording is described. The assembly forms the mechanical front-end of the telemetric electrode array system, a wireless intracortical recording device designed for motor cortex studies in nonhuman primates. The electrodes are manufactured by wire electrical discharge machining solid titanium. They are then secured in a polyimide substrate. A flexible printed circuit board connector cable connects the array structure to the electrical frontend. Parylene and platinum are used as the encapsulation materials. Results from the implantation of a prototype microelectrode array assembly are discussed.

General description of the wireless miniature NanoWalker robot designed for atomic-scale operations

The NanoWalker is a miniature wireless instrumented robot designed for high-speed autonomous operations down to the atomic scale. As such, it requires very advanced electro-mechanical specifications and complex embedded sub-systems. The locomotion is based on three piezo-ceramic legs that are modulated at high frequencies to achieve several thousand steps per second with computer-controlled step sizes ranging from a few tenths of nanometers to a few micrometers. Each robot has an onboard 48 MIPS computer based on a digital signal processor (DSP) and 4 Mb/s half-duplex infrared communication system. A special instrument interface has been embedded in order to allow positioning capability at the atomic scale and sub-atomic operations within a 200 nanometer surface area using a scanning tunneling microscope (STM) tip. The design allows 200,000 STM-based measurements per second. In this paper, we describe the many sub-systems and the approaches used to successfully integrate them onto such a miniature robot.

NanoRunner: a very small wireless robot with three piezoactuated legs suited for design experimentations and validations through preprogrammed behaviors

The NanoRunner is designed to be primarily used as an experimental wireless robot in order ot quickly test and validate several hardware/software issues and ideas prior to being implemented on the more expensive and complex wireless instrumented NanoWalker robot. As such, the NanoRunner, Like the NanoWalker is based on three piezo- actuated legs forming a pyramid with the apex pointing upward. Unlike the NanoWlaker, the NanoRunner has much simpler embedded electronics and is not capable of an accuracy and computational throughput comparable to the NanoWalker. Because of its lighter weight, it can move or run much faster. Furthermore, the NanoRunner does not have a fast infrared communication infrastructure for downloading executable code. Instead the NanoRunner is first pre-programmed with a specific behavior suitable for the tasks to be performed. Nonetheless, the NanoRunner has all the required electronics to be fully autonomous while performing its experimentation tasks. Although not as sophisticated as the NanoWalker, the NanoRunner offers a smaller and simpler robot implementation for less demanding tasks. Another major motivation for the NanoRunner is to validate various ideas in order to decrease the overall size of the robot. The size is critical since our goal is to allow more robots to work within the same area. In this paper, the NanoRunner is described. Aspects such as construction, assembly, and the method used for downloading executable code in order to pre-program the robots behavior are also covered.

Embedded electronics for a 64-channel wireless brain implant

The Telemetric Electrode Array System (TEAS) is a surgically implantable device for the study of neural activity in the brain. An 8x8 array of electrodes collects intra-cortical neural signals and connects them to an analog front end. The front end amplifies and digitizes these microvolt-level signals with 12 bits of resolution and at 31KHz per channel. Peak detection is used to extract the information carrying features of these signals, which are transmitted over a Bluetooth-based radio link at 725 Kbit/sec. The electrode array is made up of 1mm tall, 60-micron square electrodes spaced 500 microns tip-to-tip. A flex circuit connector provides mechanical isolation between the brain and the electronics, which are mounted to the cranium. Power consumption and management is a critical aspect of the design. The entire system must operate off a surgically implantable battery. With this power source, the system must provide the functionality of a wireless, 64-channel oscilloscope for several hours. The system also provides a low-power sleep mode during which the battery can be inductively charged. Power dissipation and biocompatibility issues also affect the design of the electronics for the probe. The electronics system must fit between the skull and the skin of the test subject. Thus, circuit miniaturization and microassembly techniques are essential to construct the probes electronics.

Assembly-ready brain microelectrode arrays

The capabilities of wire electrical discharge machining as a method of constructing microelectrode arrays are highlighted, and new assembly procedures based on this technique are presented. Particular attention is paid to the design of the connection between the mechanical array and the front-end electronics, a problem that is common to the construction of all microelectrode array assemblies.

Implementing frequency-modulated piezo-based locomotion for achieving further miniaturization for wireless robots

Amplitude modulated piezo-based locomotion requires one power amplifier for each quadrant electrode on the piezo-legs of miniature robots. Since each amplifier has a significant amount of quiescent current, several DC/DC converters must be embedded to source at least the total amount of quiescent current. In order to achieve a significant reduction in the overall size of the piezo-actuated robots, the number of DC/DC converters is reduced through frequency modulation. Using frequency modulation, the amplitudes of deflection or the step sizes are reduced by modulating the piezo-legs above the resonant frequency. Although the frequency modulated approach can result in much smaller robots than what can be achieved using the amplitude modulated technique, it has some drawbacks that the amplitude modulated approach does not have. First, the magnitudes of deflection of the piezo-legs using frequency modulation are typically more difficult to control. Secondly, for much smaller amplitudes of deflection, the onboard electronics must operate faster, yielding an increase in power consumption and an increase in temperature of the miniature robot, which in turn may affect sensitive embedded instruments. Furthermore, modulating the piezo-legs above the resonant frequency yields a reduction in efficiency, which translates into additional heat. When very small deflections are required, the risk of the temperature to rise beyond the Curie temperature of the piezo-material may also become an issue. All these factors must be considered carefully when frequency modulated piezo-based locomotion is used.