IEEE Circuits and Systems Magazine - Q3 2018 - 39

For low values of k2QM, all of the resonant electronic
interfaces outperform the standard approach.

H. Discussion of Performance
Considering the Normalized Harvested
Power Versus the k 2QM Product
In Fig. 19, the resonant harvesting techniques are compared showing the normalized harvested power as a function of the k 2 Q M product. To perform the analysis, the
resonant rectifiers were compared considering a constant
input force and, the matching resistive load of the DET
technique as output impedance.
ESSH and ASSH techniques were not considered in the
comparison because the maximum energy harvested using both the approaches depends on the pre-set lower
threshold voltage V L, as shown in [85].
For low values of k 2 Q M , all of the resonant electronic
interfaces outperform the standard approach.
The energy injection technique in this case also presents the highest peak performance. The main drawback
in using both the energy injection and SECE techniques
is due to the damping effects. After attaining an optimal
value for the k 2 Q M product, the damping effect leads to
a significant energy loss, so both the SECE and energy
injection techniques are mainly effective in weakly
coupled energy harvesting systems or, equivalently,
for low values of the coupling coefficient k.

Conversely, the PS-SECE technique attains a constant
normalized harvested power also in the case of strongly
coupled systems. This is due to the control of the tradeoff between energy extraction and damping effect,
which is achieved by shifting the phase of the switching
control signal.
In the case of weakly coupled systems, DSSH performs similarly to the energy injection technique, outperforming all of the SSHI approaches. Furthermore,
ESSH-like techniques allow control of the trade-off between energy extraction and damping effect by tuning
the value of the intermediate capacitor.
I. Autonomous Switch Control
in Resonant PEH Rectifiers
To implement a self-powered resonant harvesting interface, an autonomous control of all of the switches is
needed. Figure 20 shows the most common techniques
used to detect the peak output voltage generated by the
piezoelectric transducer.
The first approach, Fig. 20(a), consists of applying the
derivative operator to the voltage generated by the piezoelectric transducer. The comparator, connected at the output of the derivative operator, is used as zero-crossing

1.2
Normalized Output Power

Normalized Output Power

0.8

0.4

0.0
0.001

1
Normalized Load

Standard
S-SSHI
ESSH
DSSH

1,000

SECE
SSDCI
Hybrid SSHI
Energy Injection

Figure 18. Resonant rectifier performance comparison
considering the normalized output power vs the normalized
load [69].

THIRD quaRTeR 2018

k2QM

Energy Injection
PS-SECE
SECE
Standard
Hybrid SSHI

3
SSDCI
DSSH
P-SSHI
S-SSHI

Figure 19. Resonant rectifier performance comparison
considering the normalized harvested power vs the k 2 Q M
product [69].

Ieee cIRcuITs anD sysTems magazIne

Table of Contents for the Digital Edition of IEEE Circuits and Systems Magazine - Q3 2018