A new approach to wireless tech for implants and sensors

Posted by Emory Kale
In the near future, people affected by health issues as varied as Alzheimer, diabetes, hearing loss, heart failure or even missing limbs could all have something in common: a smart, efficient, in-body or on-body device that makes their daily life easier and more enjoyable. 
 
Body implants such as pacemakers and hearing aids have been used to counter organ dysfunction for decades. The WISERBAN project is making a giant leap in their development: aiming to provide smarter communications among such devices, with reduced size and lower energy consumption. 
 
 
To this end, the development of tiny and ultra-low-power wireless communications is key. It allows these devices to communicate changes in conditions and adjust treatments accordingly. Only limited autonomy and wireless connectivity can be achieved using today's wireless solutions because of their size and power consumption. Conscious of the fact that this limitation is currently holding back 'wireless body-area network' (WBAN) capability for use in lifestyle and bio-medical applications, the WISERBAN project brings together major medical-device manufacturers, research institutes and chip makers to overcome this obstacle. 
 
WISERBAN is focusing on the extreme miniaturization of 'body-area network' (BAN) devices. It touches on the areas of radio-frequency (RF) communications, 'Microelectromechanical systems' (MEMS) and miniature components, miniature reconfigurable antennas, miniaturised and cost-effective system-in-package (SiP), ultra-lowpower MEMS-based radio system-on-chip (SoC), sensor signal processing and flexible communication protocols. 
 
The two major innovations brought by the WISERBAN device are its unique low-power radio architecture and its size: 4 x 4 x 1mm3. At the radio level, we created a unique combination of ultra-deep-submicron 'complementary metaloxide-semiconductor' (CMOS) circuits with a heterogeneous set of MEMS devices - such as 'bulk acoustic wave' (BAW) RF resonators, 'surface acoustic wave' (SAW) RF filters and lowfrequency 'silicon resonators' (SiRes)-whereas today's approach relies on CMOS-only chips which require several external and bulky passive components such as crystals and RF filters. 
 
The joint usage of MEMS with CMOS enables much smaller SiP integration when compared to modules using CMOS chips, as well as the engineering of disruptive radio architectures which use the advantages of MEMS devices to compensate for limitations in the CMOS circuits - and vice versa. This allows for a highly efficient start-up time for the transceiver section, thereby enabling rapid wake-up of the radio. This is crucial for low power operation as it eliminates the unnecessary current consumption that normally arises from the slow start-up of classical radio architectures. 
 
WISERBAN is pushing innovation into many wireless technologies, such as miniature antennas, radio chips, digital-processing circuits and MEMS devices, but also software for system control and for wireless sensor networking. System integration - which is about getting them to work together in a unique demonstrator or a product - is thus a very complex task and a major project challenge. It has required the development of rigorous top-down specification and architecture breakdown, making sure that each block takes into account its environing conditions and interfaces with other components. 
 
A concrete example of the success of the project is the realization -at the first attempt-of the WISERBAN SoC, which is the system integration of several technology 'bricks' like MEMS and radio circuits with a 'digital signal processor' (DSP) on a single silicon die in 65nm CMOS. 
 
Another very interesting result is the availability of the first miniature antenna prototypes which have been developed taking into consideration the stringent environment and propagation conditions related to end-user housings (e.g. hearing-aid housing, cochlear implant housing). Both passive and active antennas - active meaning that the device incorporates tuning mechanisms to cover the entire 2.4GHz frequency band - have been developed and characterized successfully at laboratory level. 
 
On the software side, the industrial end-user partners have elaborated a common framework for building the control software pieces. On the wireless networking side, a dedicated protocol stack was developed and optimized with respect to low-power communication for body-sensor networks. The potential of this protocol has already been demonstrated on a benchmark sensor network constructed with off-the-shelf radio circuits, in anticipation of implementing a WISERBAN network. 
 
The project was coordinated by the Centre Suisse d'Electronique et de Microtechnique (CSEM) in Switzerland. There is a wealth of information at WISERBAN's site, and the European Commission' Community Research and Development Information Service (CORDIS).