Shunt-diode rectifier: a new scheme for efficient piezoelectric energy harvesting

Brenes, Alexis,Lefeuvre, Elie,Badel, Adrien,Seok, Seonho,Yoo, Chan-Sei Institute of Physics Publishing 2019 Smart materials & structures Vol.28 No.1

<P>This paper highlights the interest of shunt-diode rectifiers to optimize the performances of piezoelectric vibration energy harvesters based on linear load adaptation. It provides, for the first time, a full analytical study of the input power and frequency bandwidth of such a system. We show that this architecture is well-suited for piezoelectric energy harvesting. In the presented approach, a so-called shunt diode is connected across the electrodes of the piezoelectric transducer, which makes the piezoelectric voltage unidirectional instead of alternating. Thus, DC–DC converters usually used for power optimization can be directly connected to the transducer. We show that weakly-coupled linear inertial piezoelectric energy harvesters generate higher power when connected to a shunt-diode rectifier than to a bridge rectifier. Moreover, the frequency bandwidth is enlarged by the use of the single-diode shunt rectifier, especially for strongly-coupled piezoelectric generators. The proposed architecture is also interesting for low piezoelectric voltages, at which voltage drops across the diodes used for AC–DC conversion critically degrade the power efficiency. Experimental results validate the presented analytical study and highlight the higher efficiency of the shunt-diode rectifier circuit. Compared to a standard bridge rectifier architecture, we demonstrate an increase of +43% output power on a weakly-coupled generator and an increase of +5% bandwidth on a strongly-coupled generator.</P>

Unipolar synchronized electric charge extraction for piezoelectric energy harvesting

Brenes, Alexis,Lefeuvre, Elie,Badel, Adrien,Seok, Seonho,Yoo, Chan-Sei Institute of Physics Publishing 2018 Smart materials & structures Vol.27 No.7

<P>This paper highlights the interest of a shunt rectifier to improve the efficiency of the synchronized electric charge extraction (SECE) circuit formerly developed for piezoelectric energy harvesters. Compared to the classical SECE circuit, which requires a full-bridge rectifier, the proposed architecture is especially interesting for low-amplitude vibrations generating a low piezoelectric voltage, typically lower than 2 V RMS. We provide a full analytical study validated by experimental measurements to illustrate the high performance of the so-called unipolar SECE (USECE) as well as the impact of the resonator characteristics on the overall performance of the harvester. We also propose a model including the main causes of power dissipation, which is validated experimentally, showing that the power efficiency of the circuit is much less dependent on the vibration frequency and magnitude than classical SECE. The proposed architecture combines the high input power of SECE with the high power efficiency resulting from unipolar operation, reaching more than 75% power efficiency in situations where classical SECE is limited to an efficiency lower than 35%. Our experimental results show an increase of +200% output power obtained with USECE compared to classical SECE, which is due to the combination of a higher input power and a higher power efficiency of the proposed circuit.</P>

Analysis of piezoelectric energy harvesting system with tunable SECE interface

Lefeuvre, E,Badel, A,Brenes, A,Seok, S,Woytasik, M,Yoo, C-S Institute of Physics Publishing 2017 Smart materials & structures Vol.26 No.3

<P>Numerous interface circuits have been proposed over the past years to improve the performances of piezoelectric energy harvesting devices. The so-called synchronous electric charge extraction interface (SECE) brought the advantage of harvesting power independently of the load voltage. In counterpart, its performances exhibited sensitivity to the electromechanical coupling. It was shown, in particular, that harvested power was significantly decreased at high coupling. To overcome this drawback, the so-called tunable SECE interface has recently been proposed. Instead of the total charge extraction performed by the original SECE, the tuning method consists in extracting only a portion of the electric charge. This paper presents the analytical modeling of an energy harvesting system composed of a linear piezoelectric resonator associated to the tunable SECE interface. Contrary to previous model limited to describe the system behavior at resonance, this model enables to extend the analysis off-resonance. The presented theoretical analysis and experimental results clearly show the possibility to increase both the power and the frequency bandwidth by adequate control of the tunable SECE interface.</P>

Power and frequency bandwidth improvement of piezoelectric energy harvesting devices using phase-shifted synchronous electric charge extraction interface circuit

Lefeuvre, Elie,Badel, Adrien,Brenes, Alexis,Seok, Seonho,Yoo, Chan-Sei Sage Science Press (UK) 2017 Journal of intelligent material systems and struct Vol. No.

Robotically assisted transcranial Doppler with artificial intelligence for assessment of cerebral vasospasm after subarachnoid hemorrhage

Shooka Esmaeeli,Courtney M. Hrdlicka,Andres Brenes Bastos,Jeffrey Wang,Santiago Gomez-Paz,Khalid A. Hanafy,Vasileios-Arsenios Lioutas,Christopher S. Ogilvy,Ajith J. Thomas,Shahzad Shaefi,Corey R. Fehn 대한신경집중치료학회 2020 대한신경집중치료학회지 Vol.13 No.1

Background: Transcranial Doppler (TCD) ultrasound is an essential tool for the detection of cerebral vasospasm after subarachnoid hemorrhage (SAH) but is limited by the availability of skilled operators. We examined the clinical feasibility and concordance of a robotically assisted TCD system with artificial intelligence with routine handheld TCD after SAH. Methods: We evaluated TCD velocities in the anterior cerebral artery (ACA) and middle cerebral artery (MCA) of two patients with high-grade SAH and angiographic evidence of vasospasm. A single channel TCD device with a handheld diagnostic probe as well as a robotically assisted TCD device was used, the relationship of the two tests was evaluated using the bootstrap method of resampling for the concordance correlation coefficient (CCC) paired with a Pearson’s correlation analysis, followed by a Bland-Altman plot. Results: Patient 1 developed angiographic and TCD evidence of vasospasm in the proximal right MCA, but except for periods of disorientation remained neurologically intact. Angiographic, TCD and clinical evidence of ACA spasm occurred 6 days after ictus in patient 2. Robotically measured mean flow velocities were comparable to manual TCDs in the MCAs (CCC=0.83; 95% confidence interval [CI], 0.42 to 0.96; P=0.001) but not in the ACAs (CCC=0.26; 95% CI, –0.01 to 0.71; P=0.26). Conclusion: Robotically assisted TCD system with artificial intelligence provides an alternative to manual TCD for assessment of MCA velocities in patients with SAH, expanding the availability of TCD to settings in which specialized clinicians are not available. Further studies for validation of this technology are warranted.

Major histocompatibility complex selection dynamics in pathogen-infected túngara frog ( <i>Physalaemus pustulosus</i> ) populations

Kosch, Tiffany A.,Bataille, Arnaud,Didinger, Chelsea,Eimes, John A.,Rodrí,guez-Brenes, Sofia,Ryan, Michael J.,Waldman, Bruce The Royal Society 2016 Biology letters Vol.12 No.8

<P> Pathogen-driven selection can favour major histocompatibility complex (MHC) alleles that confer immunological resistance to specific diseases. However, strong directional selection should deplete genetic variation necessary for robust immune function in the absence of balancing selection or challenges presented by other pathogens. We examined selection dynamics at one MHC class II (MHC-II) locus across Panamanian populations of the túngara frog, <I>Physalaemus pustulosus</I> , infected by the amphibian chytrid fungus <I>Batrachochytrium dendrobatidis</I> (Bd). We compared MHC-II diversity in highland túngara frog populations, where amphibian communities have experienced declines owing to Bd, with those in the lowland region that have shown no evidence of decline. Highland region frogs had MHC variants that confer resistance to Bd. Variant fixation appeared to occur by directional selection rather than inbreeding, as overall genetic variation persisted in populations. In Bd-infected lowland sites, however, selective advantage may accrue to individuals with only one Bd-resistance allele, which were more frequent. Environmental conditions in lowlands should be less favourable for Bd infection, which may reduce selection for specific Bd resistance in hosts. Our results suggest that MHC selection dynamics fluctuate in túngara frog populations as a function of the favourability of habitat to pathogen spread and the vulnerability of hosts to infection. </P>