The aim for designers of medical devices and systems is to improve the functionality of their devices for diagnostic and therapeutic use, keep costs down, and make their use more convenient for patients. Parallel to this demographical evolution run two technological developments: biotechnology, including mapping of the human genome, and the shift from microelectronics to nanoelectronics.
In the long term electronics will give people a personal body area network (BAN) (Fig. 1) that will be used to gather vital body information into a central intelligent node. This, in turn, will communicate wirelessly with a basestation. BANs will be built on a number of small low-power sensor/actuator nodes with sufficient computing power, wireless capabilities, and integrated antenna. Each node will have enough intelligence to carry out its task. These could range from storing and forwarding algorithms to complex, nonlinear data analysis. These nodes will be able to communicate with other sensor nodes or with a central node worn on the body. The central node will communicate using standard telecommunication infrastructure, such as a WiFi or mobile phone network.
The network will also be able to deliver services to the owner of the BAN, including the management of chronic disease, medical diagnostic, home monitoring, biometrics, and sports and fitness tracking.
The realisation of BANs largely depends on extending the capabilities of existing devices; a number of medical and technological obstacles need to be removed. For example, the lifetime of battery-powered devices is limited at present and must be extended if it is to power many of these applications. Likewise, the interaction between sensors and actuators needs to be enlarged to support new applications such as multi-parameter biometrics. Also, devices need intelligence built-in so they can store, process and transfer data.
Semiconductor technology scaling produces smaller electronic devices that need less power. It also|allows the development of therapeutic and diagnostic devices with better functionality.
Microsystem technology, in particular MEMS (micro-electromechanical system) technology, can support devices that combine electrical and mechanical properties. An early application of MEMS technology is the development of energy scavengers to power autonomous medical systems. An example is the energy scavengers that generate micropower from body-heat, based on the conversion of thermal energy into electrical energy. Because this energy source is continuous, the systems can be always-on and have an almost infinite lifetime. The challenge will be to prove that such devices can extract enough power from the human body, that is 100µW or more, to supply the systems in future.
Another potential use of MEMS technology involves sensor and actuator systems that provide the interface to the outside world, as well as to the mixed-signal circuitry that surrounds it. Finally, MEMS technology supports the creation of new components for ultra-low-power (ULP) radio-frequency transceivers. ULP radios are used, for example, to provide communication between sensor nodes and the body-worn central node, and will consume power of 50µW on average.
Packaging techniques make wearing mobile, wireless medical devices easy and comfortable through the integration of complex heterogeneous systems into small devices.Nanotechnologies allow the direct interaction of a body's biological system, such as cells, antibodies, or DNA, via miniature interconnecting devices.
Processor architectures developed for low-power consumption increase the intelligence of the sensor nodes. Consequently, the sensors themselves are able to perform more complex data processing. Although the ultimate BAN-carrying human being is some way off—realistically not appearing until 2010 at the earliest—several partial implementations are emerging. Best known are applications within the research field of bioelectronics, which holds tremendous opportunities. Combining the power of biological (or biochemical) reactions with electronic signal detection and amplification leads to new and exciting bioelectronic diagnostics.
Another incipient field is the wireless monitoring of human body information, such as the development of a wireless electroencephalogram (EEG) for the diagnosis of epileptic patients. A wireless wearable EEG will eventually allow for monitoring at home, via the Internet. Such wireless EEG systems exist today, but are unwieldy. The challenge of shrinking them to acceptably small dimensions remains.
In this context, IMEC recently made an important breakthrough by developing a miniature 1cm3 three-dimensional stacked system-in-a-cube. The first 3D-stack prototype comprises a commercial low-power 8 million instruction per second (MIPS) microcontroller and a 2.4GHz wireless transceiver, crystals, and other necessary passives, as well as a custom-designed matched dipole antenna.
The high level of integration is achieved through z-axis stacking of separate layers with different functionality, hence '3D stacking.' Each layer connects to its neighbouring layers through a dual row of fine-pitch solder balls. The low-power 3D SiC can be used in a variety of wireless products, ranging from monitors for human-body information (brain activity, muscle activity, heart activity, and so on) to environmental data. Eventually, it could be used as a BAN.
This generic technology will first be incorporated into a wearable, wireless EEG, developed by IMEC and the University Hospital Leuven in 2003. Once integrated into the 1cm3 cube (Fig. 2), the wireless EEG solution will allow patients to wear a device during the electroencephalogram. In short, these technological developments mean that not only will we live longer, but will have access to unmatched medical self-help that will ensure that quality of life accompanies longevity.
