Instrumentation & Measurement Magazine 26-3 - 22

enables the detector to be
Fig. 2. (a) The autonomous wake-up detector presented in [8]. The detector converts the energy of the infrared radiation
into heat, which is used to generate cantilever motion that opens and closes the switches; (b) Plasmonically enhanced
MEMS photoswitch.
circuitry. To achieve the fastest transition between the open
and closed switch state, therefore avoiding the formation of
electric discharge arcs which would increase the power consumption,
the conductive element is a pre-stressed bi-stable
buckled plate whose two stable positions correspond to the
closed and opened switch state.
Another mechanically power-gating wake-up detector
is reported in [8]. The detector utilizes spectrally selective
plasmonically enhanced MEMS photoswitches that, upon exposure
to infra-red spectral signatures of the target of interest,
close the contacts and create conducting channels between
the power supply and processing circuitry, thus waking up
the processing circuitry. The switches consist of a pair of symmetric
cantilevers, composed of an inner and outer thermally
sensitive bi-material legs separated by a thermal isolation link
and an infrared (IR) absorbing or reflecting head (Fig. 2).
The IR absorber integrated on the head acts as an energy
converter, converting the radiation of specific incoming IR
spectral bands into heat. This heat increases the temperature
of the inner pair of legs, causing the cantilever to bend, which
brings the platinum tip into contact with the opposite electrical
contact, closing an electrically conductive path and generating
a wake-up signal. The switch is made insensitive to background
interference, such as ambient temperature change,
by its symmetrical cantilever design. The dynamically tunable
detection thresholds of the switches allow adjustments
of their sensitivity to different IR radiation patterns which
utilized in multiple applications
from plant water
content monitoring and
human presence sensing
to flame detection. Using
this energy autonomous
wake-up detector, an ultralow-power
sensor node was
developed, with a power
consumption of 2.6 nW.
The wake-up detector activates
a microcontroller that
initiates wireless data transmission
to a remote gateway.
Electronic Power-gating
In [9] an electronic power-gating wind force wake-up detector
is reported (Fig. 3). The detector utilizes a rotary triboelectric
nanogenerator (TENG) to convert wind energy into electric
energy, which is rectified by a half-wave rectifier and stored
into a storage capacitor C1
. The stored energy increases the capacitor's
voltage, and once it reaches the threshold voltage of
a transistor, the transistor turns on and starts the current flowing
through a relay coil, causing the relay switch to close and
wake up the system. A resistor (R1
) provides a discharge path
for the storage capacitor, to prevent false activation by wind
levels which are too weak.
Once active, the system estimates the wind force from the
electric energy on the capacitor and sends out a report signal
to a remote gateway. In standby mode, when there is no wind,
the system's power consumption is only 14 nW, due to leakage
current of the transistor.
A wake-up detector for detecting events generating a magnetic
field or acceleration is reported in [10] (Fig. 4). An event
of interest deflects a cantilever beam coated with a piezoelectric
material and featuring either a magnetic tip, or a proof
mass at its end, depending on the detector application. Once
the event passes, the deflected cantilever starts to oscillate
with its natural frequency (eigenfrequency) with decreasing
amplitude, until it settles back into its initial position. The cantilever's
oscillations stress the piezoelectric material which
Fig. 3. The autonomous wake-up detector presented in [9]. Wind energy is
converted into electric and stored in a capacitor, increasing its voltage. Once
the capacitor's voltage surpasses a predefined level the system's main stage is
woken up to estimate the wind force.
22
Fig. 4. The autonomous wake-up detector presented in [10]. The energy of a
transient magnetic field or acceleration is converted into electric and stored
in a capacitor, increasing its voltage. Once the capacitor's voltage reaches the
transistor's gate voltage, the transistor power-gates the processing circuitry
and wakes it up.
IEEE Instrumentation & Measurement Magazine
May 2023

Instrumentation & Measurement Magazine 26-3

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 26-3