Mems Micro-antennas for Wireless Biomedical Systems

Invasive and implantable biomedical devices used for diagnostic and therapy, ranging from neural prosthesis to video-capsule endoscopy (VCE) systems, are emerging innovative technologies and they are expected to originate significant business activity in the near future. The success of such systems is in part due to the advent of microtechnologies, which made possible the miniaturization of several sensors and actuators, as well their integration with readout and communication electronics. The new biomedical devices offer the possibility of improved quality of life, as well cost savings associated with health care services. However, one open challenging is to communicate to and from a biomedical device placed inside the human body with devices outside the human body. The lack of antennas, small enough to be integrated with the sensing microsystem, is a difficult task to overcome because such communications must be made at relatively low frequencies, due to live tissue signal attenuation. The straightforward solution is to increase the devices size to dimensions where it becomes possible to integrate an antenna. Up to now solutions, use conventional antennas together with miniaturization techniques to achieve the smallest antennas possible. However, the size of such devices is usually limited by the antenna and, is some cases, also by the batteries size. Micro-Electro-Mechanical Systems (MEMS) are becoming an available option for RF communication systems since they can offer, simultaneously, devices with improved performance and they use IC-compatible materials, allowing their integration in a silicon chip, side by side with semiconductor circuits. Up to now, MEMS have been used for antenna applications to obtain non-conventional front-ends with improved, or new characteristics. However, some preliminary tests have shown that some MEMS structures could have the ability to operate as an antenna itself and this solution would have the potential to be smaller than the conventional antennas. In this chapter, it is first discussed the need for small wireless biomedical devices. This requires the use of a microsystem completely integrated, from sensors to communications, thus requiring the use of integrated antennas. The electrical properties of substrates available P.M. Mendes and J.H. Correia 230 in integrated circuit technology are very important for antenna design and one method used to characterize wafer materials is presented. Moreover, the antenna integration requires the availability of an electrically small antenna fabricated on materials compatible with the fabrication of integrated circuits. This integration requires the use MEMS techniques, like micromachining and wafer level packaging. Finally, MEMS structures previously used for non-conventional front-ends will be introduced and investigated, having in mind a new application, the MEMS structure itself will be operating as an antenna. The development of new integrated antennas using MEMS solutions has the potential to make the devices smaller and more reliable, which will make them cheaper and adequate for mass production, resulting in a key advantage for competitors in the RF market. Also, the availability of smaller biomedical wireless devices can lead to new applications not yet fully envisioned. The new solutions envisions power saving, smaller volume, lower cost, and increased system lifetime, which are very important features in biomedical microsystems for diagnosis and therapy. Wireless Biomedical Devices