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The
basic concept of "electronic cubes: e-CUBES",
within the frame of global ambient intelligence, is
shown in Figure 1. e-CUBES devices measure parameters
in their environment (through a sensor function) and
communicate this information, with rather low data rates,
within an ad-hoc wireless network of e-CUBES and towards
central nodes that connect the e-CUBES network to other
network services and systems and to the user.
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Figure
1: The concept of e-CUBES, within the
frame of global ambient intelligence.
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The
considerations undertaken on the various foreseeable
applications led the consortium to define a preliminary
architecture described in Figure 2:
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Figure
2: Prelimary architecture of e-CUBES
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The
reason for existence of these different functions are
as follows:
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The
sensors are
the basic components of the e-CUBES. The preferred
technology is MEMS, with a mandatory characteristics
of ultra-low power, for instance using capacitive
sensing. |
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The
low power analogue interface
is in charge of interfacing the analogue physical
world seen by the sensors to the digital world
of the microcontroller. The main constraints on
this function is the minimisation of the internal
components to reduce the power consumption, while
being compatible with:
-
noise levels adapted to the resolution of the
sensors
- the necessary bandwidth
- the dynamic range
The technological challenge here, for an optimal
version, is to identify a process compatible not
only with all these constraints, but also with
the digital and analogue components and basic
sub-functions.
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The
microcontroller is
in charge of interfacing with pretty all the functions
of the e-CUBES, particularly for sequencing all
the operations, while controlling the power dissipation
to reduce it at the lowest possible level. Its functionality
is extended in some applications to data compression
operations, self-organising procedure with other
e-CUBES for data transmissions and relay, calibration
operations, and other specific operations (such
as localisation procedures of the other e-CUBES). |
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The
wireless interface
is in charge of allowing the best link budget as
possible for the communications, using a combination
of techniques, from specific antenna schemes to
dynamic impedance matching. This interface is bi-directional:
uploading programs and commands from the base station,
and getting data back from the sensors. The main
challenge here is the optimal compromise between
the highest efficiency of the transmissions, the
lowest power dissipation during transmissions, and
the reduced dimensions acceptable in a given domain.
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The
events storage memory
is a generic memory with specific properties of
very low power consumed for a given amount of memory,
data/state remanence, possibly dynamic programmability
(re-programming), and dynamic sharing between data
and programs. In the simplest case, it can be a
standard flash memory. In the more complex case,
it can be a nanocells memory array (millipede type
for instance) |
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The
smart clock is a specific
function useful for different cases. It can be used
as:
- an "awakener"
of the microcontroller in the case of ultra low
power specific applications such as transient event
monitoring where, most of the time, there is nothing
(no event) to be noticed, but there are specific
short time events appearing from time to time, for
which a high resolution is necessary to identify
the problems to be monitored.
- or a self rate-switchable
clock (for power saving objectives).
- or a smart clock
for localisation purposes (different possible and
more or less complex procedures). |
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The
micropower source is
the basic local energy source of any basic e-CUBES.
In the simplest case, it can be a micro-battery
or a supercapacitor. It can also be a micro-fuel
cell in more elaborate versions. Its main characteristics
is that its lifetime is necessarily limited in time,
contrarily to the energy scavenger described hereunder. |
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The
energy scavenger is
a function designed to get energy from the environment:
- whether from the
real natural physical flows of energy (optical flux,
EM signals,
thermal flux, ...).
- or whether from
artificial sources, such as in the situation of
remote powering, where a source of power is directed
towards the e-CUBES from an external location.
Its intrinsic lifetime is not limited as a battery,
at least up to the reliability level of the technology
chosen to implement it. The complexity of this function
can be high, depending on the possibility of having
multiple sources of energy, as specific natural
sources can vary in time, depending on the exact
type of application (movements or not, day/night,
...). |
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The
power manager is a
smart circuit able to handle the power management
issues linked to the multiplicity of energy sources,
including the local ones, by analysing temporally
the available energy densities, deciding of a procedure
for maximising the collected energy for the e-CUBES,
by switching in time between the different energy
sources, while storing this energy in a specific
storage component (micro-battery as a buffer or
capacitor, or any other mechanism including micro-mechanical
energy storage devices). |
The
main common characteristics of all these functions is
the very low power level for operating reliably (without
interruption of the Service provided). It is also understood
that, in the present state of the technology, the underlying
technologies are heterogeneous, and that consequently,
one key challenge is the heterogeneous integration of
these functions, each realised optimally with its most
suited technology.
In order to achieve a cost effective
solution for the highly miniaturised e-CUBES
system, the Integrated Project proposes the use of 3D
interconnect technologies ("Cubic" interconnects
- hence the name e CUBES), the use of modularity
(reuse) and the use of wafer level fabrication technologies
(in order to reach the required economics of scale).
The e-CUBE is a 3D stack of functional sub-modules,
each of which is, in itself, composed of a 3D stack
of different (heterogeneous) functional layers (e.g.
e-CUBE application layers). This is illustrated in (Figure
3).
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Figure
3: Basic structure of an e-CUBES system:
3D stacking of functional sub-system layers
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The
minimal physical size of an e-CUBE is determined by
three main factors: the size of the constituent integrated
circuits, the minimum size of the antenna required for
power-efficient communication, and the power storage
and harvesting subsystem. The scaling roadmap of integrated
circuit technologies enables the realisation of complex
circuits in rather small sizes. The main size limitations
are therefore the antenna size and the power system.
Given the projected improvements in integrated circuit
technology, with respect to die size, power consumption
and frequency capabilities, the target size for e-CUBES
in this project is to be smaller than 1cm3 (see Figure
4), targeting e-CUBES with dimensions 1mm*1mm*0.5mm
in the future .
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Figure
4: Roadmap for reduction in size of the
e-CUBES
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