Agnès Bonvilain

Microfabricated thermally actuated microrobot

The work presented in this paper concerns the study, the design, the fabrication and the experimentation of a legged microrobot. Legs were developed by integrating in each two thermal bimorph actuators, which give two degrees of freedom. After their fabrication and their experimentation, the legs were integrated on a body to realize the complete structure of the microrobot in a monolithic way. This microrobot was totally made by microfabrication in a clean room. The microrobot has a total volume of 6 mm/spl times/3.5 mm/spl times/0.5 mm and possesses six legs. Its experimentation allowed to determine its potential performances. This microrobot can find numerous applications in microrobotics, such as the inspection of stuffy environments, the micro-escorting or as a plug and play function in a system.

Development of a Novel Artificial Urinary Sphincter: A Versatile Automated Device

Management of male severe stress urinary incontinence is currently achieved by the treatment of choice: an artificial urinary sphincter (AUS). This implantable system is designed to exert a constant circumferential force around the urethra. Although continence is totally or partially recovered in most of the patients, this method has some significant drawbacks. Besides the difficulty and discomfort of using the device, the revision rate caused by constant urethral compression, leading to urethral injuries, remains high. We present in this study a new AUS concept, with an ergonomic control, providing a lower exerted pressure on the urethral tissues and improving the continence efficiency. In fact, the implant includes a system which automatically detects circumstances involving high-intravesical pressure and adapts the occlusive pressure accordingly. The device was evaluated using isolated goat urethra, and then, in vivo. Recorded data of 16 human subjects performing different daily exercises were used to assess the detection algorithms. It is shown that occlusive pressure can be controlled by the implant with an accuracy of 1 cm H2O (98 Pa). Acceptable detection performance of seven of the eight targeted activities was observed.

Modelling and characterization of an instrumented medical needle in sight of new microsensor design for its insertion guidance

A needle used in in-vivo medical percutaneous procedures is subject to auto-deflection coming from its interactions with inhomogeneous and anisotropic tissues and organs in human body. In this paper we present the modelling and the characterization of microsensors glued on a medical needle in order to detect its real-time deflection by measuring strain variations on the needle. A first prototype has been developed by gluing metal foil strain gauges to the surface of a biopsy needle. The characterization of this prototype is carried out in comparison with theoretical analysis and finite element method (FEM) modelling. Results acquired through these different methods show an excellent conformity and confirm the feasibility of an instrumented medical device.

Designing ultra-low power systems with non-uniform sampling and event-driven logic

Circuit power consumption is closely related to data processing. This observation is the foundation of a new low-power approach based on a non-uniform sampling scheme combined with asynchronous event-driven logic. This will be useful for handheld computing systems and mobile applications such as wireless solutions for telemetry and metering, or medical implants. These last applications required a very low level of consumption because they remain active during several years. Here, an alternative to the classical design techniques for ultra-low power consumption is presented. Our case study is applied to physiological signals used in a medical implant and shows a drastic reduction of the power consumption compared to the classical approach.

Rectus Abdominis ElectroMyoGraphy and MechanoMyoGraphy comparison for the detection of cough

We recently developed a novel active implant for the treatment of severe stress urinary incontinence. This innovative medical device has been developed with the main purpose of reducing the mean urethral occlusive pressure of the current prosthesis. This goal is achieved by detecting circumstances implying either high or low intra-abdominal pressures by a single 3-axis accelerometer. In fact, posture and activity of the patient are monitored in real time. We investigated in this study the possibility of detecting cough events (one of the main causes of urine loss in incontinent patient) by MechanoMyoGraphy (MMG) of the Rectus Abdominis (RA) using the same accelerometer. We compared MMG signal detection characteristics (burst onset times and RMS values) to the method of reference, the ElectroMyoGraphy (EMG). It is shown that detection of cough effort by MMG presents lower performances, mostly in terms of cough anticipation, than EMG detection. However, MMG still remains a good option for an implantable system comparing to implantable EMG disadvantages.

First experimentations of microsensors microfabricated on a long and thin medical needle

Further to the first fabrication of strain microgauges on cylindrical metal substrates [1], that we cannot experiment because of problems of wire bonding, we have reviewed the bonding process. These microgauges enable the real-time measurement of the medical needle strain distribution from which its deflection status can be deduced. So this paper deals with the new bonding process of the microgauges and the detailed experimentations. These experimentations consist in constrain the needle and verify that we can measure the strain. They allow also the calculations and the comparison of the theoretical and experimental gauge factor. Finally we discuss about the improvement of the prototype in terms of optimization of the process. And some material questions must find solution.

Micromachined thermal actuated microlegs for an insectlike microrobot

This paper deals with a work in progress concerning the fabrication of an insect-like microrobot. Thermal actuation has been chosen to move this microrobot, because of their large motions and their interesting density of energy. An integrated structure was chosen. Compliant thermal micro- actuators have been studied, fabricated and experimented. The characterization and modeling of these actuators have been done. Then, microlegs were modelized and designed with two degrees of freedom for each leg. The design of the microlegs and the operating cycle are given in this paper. Then the various stages of the microfabrication process are precisely described the microlegs are constituted of two thermal bimorphs connected together with a microbeam. Several microlegs are fabricated on one silicone wafer and bonded on a printed board to allow their activation. Their experimentation allows to give the results of each of the two degrees of freedom concerning the motions of these microlegs. Based on the results of these first experiments, the second generation of microlegs was conceived, made and tested, with the aim of decreasing the energy consumption. Then the next step will be the microfabrication of a new type of microlegs, before the whole structure of the microrobot including their legs in a monolithic way on one single silicon wafer.

Study and development of a station for manipulation tasks in the microworld

This paper deals with a work in progress concerning the development of a station for micromanipulation tasks in the air (at present not in a liquid environment). A microgripper is developed, based on piezoelectric unimorphs and bimorphs. This microgripper allows to manipulate micro-objects from several microns to several hundreds of microns in diameter. In the future the microgripper will be controlled in position and force. The first results in position control of our piezoelectric unimorph actuators show an accuracy better than 10 nm at the tip of the actuator. A low cost XY-table is also developed using SMA wires to create relative motions between the microgripper and the manipulated object. For the manipulation of smaller objects, from several hundreds of nanometers to some micrometers, a work is also in progress to develop a micromanipulation station based on an AFM microscope head connected to a simple force-feedback haptic. Moreover, based on some studied microactuators for micromanipulation, an insect-like microrobot with legs is under development. The design of legs is realized using the microactuators previously described. We are now in order to test these legs and consider the whole mechanical structure of the microrobot.