This paper proposes a novel, tunable AC coupled capacitive feedback amplifier, exhibiting an ultra-low high pass corner frequency. This is accomplished by actively boosting the output resistive value of a MOS transistor in weak inversion. The circuit is based on a more general architecture, recently proposed by the authors, and is analyzed in terms of its capability to achieve ultra-low frequency operation, its DC performance, and noise. The proposed technique is demonstrated via measurement results from a fabricated test chip prototype using a standard 0.18 µm CMOS technology. The proposed amplifier provides a tunable high pass corner frequency from 20 mHz to 475 mHz, consuming 4.71 μW and a total area of 0.069 mm2., Grant PID2019-107258RB-C32 (AEI/FEDER), Ministry of Universities (grant BES-2017-080418) and Public University of Navarra. Open Access funding provided by Public University of Navarra

An improved class AB version of the super source follower is used to implement a compact and power-efficient second order analog low-pass filter. The proposed circuit achieves a 41% power reduction as well as an improvement in linearity and pass band gain with respect to its class A counterpart. Measurement results of a test chip prototype fabricated in a 180 nm CMOS technology show a power consumption ranging from 50.3 μW to 85.27 μW for cutoff frequencies from 600 kHz to 890 kHz, with a supply voltage of ±0.75 V. A third order intermodulation distortion of −35.34 dB (for an input signal of 0.4 mV pp and 350 kHz) and a THD of −69.7 dB (for an input signal of 0.4 mV pp and 100 kHz) are measured, which results in an improvement with respect to the conventional class A version of 13.98 dB and 43.6 dB, respectively. The silicon area is 0.0592 mm 2 (using external capacitors)., This work was supported by Grant PID2019-107258RB-C32 funded by MCIN/AEI/10.13039/501100011033. M. Martincorena-
Arraiza is funded by the Ministry of Universities under grant BES-2017-080418

The analysis, design and experimental characterization of a single-stage class-AB operational transconductance amplifier (OTA) with enhanced large- and small-signal performance is presented. The OTA is biased in weak inversion to save power and employs a non-linear current mirror as active load, leading a boosting current directly at the output branch. As a result, the amplifier's performance is improved without additional circuit elements and/or power consumption. A chip prototype has been fabricated in a 180-nm CMOS process, consuming a quiescent power of 2.5 µW from a supply voltage of ±0.5 V and a silicon area of 0.0013 mm 2 . For a load of 160 pF, it exhibits an average slew rate of 0.94 V/µs and a gain-bandwidth product of 22.1 kHz., This work has been supported by Grant PID2019-107258RB-C32 funded by MCIN/AEI/10.13039/501100011033.

In this paper, we describe a measurement procedure to fully characterise a novel vibration energy harvester operating in the ultra-low-frequency range. The procedure, which is more thorough than those usually found in the literature, comprises three main stages: modelling, experimental characterisation and parameter identification. Modelling is accomplished in two alternative ways, a physical model (white box) and a mixed one (black box), which model the magnetic interaction via Fourier series. The experimental measurements include not only the input (acceleration)–output (energy) response but also the (internal) dynamic behaviour of the system, making use of a synchronised image processing and signal acquisition system. The identification procedure, based on maximum likelihood, estimates all the relevant parameters to characterise the system to simulate its behaviour and helps to optimise its performance. While the method is custom-designed for a particular harvester, the comprehensive approach and most of its procedures can be applied to similar harvesters., This work has been supported by the Spanish Research Agency, and the EU/PTR Next Generation Funds under grants PID2019-107258RB-C32 and TED2021-131052B-C21, and also by the Government of Spain (Plan Estatal de Investigación Científica, Técnica y de Innovación 2021–2023) under grants PID2022-138491OB-C32 and PDC 2023-145876-C22.

An approach for the design of two-stage classAB OTAs with sub-1µA current consumption is proposed and
demonstrated. The approach employs MOS transistors operating
in subthreshold and allows maximum gain-bandwidth product (GBW) to be achieved for a given DC current budget, by
setting optimum distribution of DC currents in the two amplifier
stages. Following this strategy, a class AB OTA was designed in
a standard 0.5-µm CMOS technology supplied from 1.6-V and
experimentally tested. Measured GBW was 307 kHz with 980-nA
DC current consumption while driving an output capacitance of
40 pF with an average slew rate of 96 V/ms, This work was supported in part by Agenzia Estatal de Investigación (AEI), Ministerio de Ciencia e Innovación, Spanish Government under Grant PID2019-107258RB-C32

A frequency downscaling technique for enhancing the accuracy of analog lock-in amplifier
(LIA) architectures in giant magneto-impedance (GMI) sensor applications is presented in this
paper. As a proof of concept, the proposed method is applied to two different LIA topologies using,
respectively, analog and switching-based multiplication for phase-sensitive detection. Specifically, the
operation frequency of both the input and the reference signals of the phase-sensitive detector (PSD)
block of the LIA is reduced through a subsampling process using sample-and-hold (SH) circuits. A
frequency downscaling from 200 kHz, which is the optimal operating frequency of the employed
GMI sensor, to 1 kHz has been performed. In this way, the proposed technique exploits the inherent
advantages of analog signal multiplication at low frequencies, while the principle of operation of the
PSD remains unaltered. The circuits were assembled using discrete components, and the frequency
downscaling proposal was experimentally validated by comparing the measurement accuracy with
the equivalent conventional circuits. The experimental results revealed that the error in the signal
magnitude measurements was reduced by a factor of 8 in the case of the analog multipliers and by a
factor of 21 when a PSD based on switched multipliers was used. The error in-phase detection using
a two-phase LIA was also reduced by more than 25%., This work has been supported by Grant PID2019-107258RB-C32 funded by the Spanish
Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033), and by the project
PJUPNA2005 funded by the Public University of Navarre.

Esta tesis presenta técnicas innovadoras de baja tensión, baja potencia y baja frecuencia
utilizadas para diseñar nuevos bloques de circuitos (como amplificadores, filtros
y convertidores RMS-DC) adecuados para aplicaciones en el internet de las cosas
(IoT: Internet of Things) con restricciones de energía y área. La tesis esta estructurada
de la siguiente manera: primero, se presentan técnicas básicas de diseño de
dispositivos y circuitos para operación en bajo voltaje, baja potencia, baja frecuencia
y bajo ruido, que más tarde se utilizan para diseñar bloques circuitales adecuados
para aplicaciones IoT en entornos con energía y área restringida.
Los bloques circuitales presentados están adaptados para aplicaciones de baja
tensión y baja potencia, así como para operar en frecuencias ultrabajas, haciendo
uso de técnicas de eficiencia energética como transistores de puerta cuasi-flotante
(QFG: Quasy-Floating Gate), polarización adaptativa para obtener eficiencia en corriente
mediante sequidores de voltage volteado (FVF: Flipped Voltage Follower), o
la técnica de bootstrapping para obtener grandes constantes de tiempo RC con área
reducida, entre otros. Los circuitos propuestos son validados experimentalmente
y comparados con anteriores publicaciones relevantes de circuitos similares, para
demostrar su desempeño competitivo.
La tesis presenta filtros basados en SSF de clase AB simples y energéticamente
eficientes que aprovechan los beneficios de los transistores QFG; un convertidor
RMS-DC de dos cuadrantes compacto basado en una novedosa celda elevadora al
cuadrado/divisora (S/D: Squarer/Divider) con lazos translineales MOS (Metal Oxide
Semiconductor) electrónicamente simulados (ES-MTL: Electronically Simulated-
MOS Translinear) y polarización adaptativa basada en FVF, que logra una alta simetría
y rango dinámico; finalmente, se desarrolla una familia de amplificadores de corriente
alterna (AC: Alternate Current) de frecuencia ultra baja haciendo uso de la
transformación de red basada en nullores y la técnica de bootstrapping para reducir
la frecuencia de corte de paso alto basada en una constante de tiempo RC.
Aprovechando aún más la versatilidad de la representación de circuitos basada en
nullores, se desarrolla una versión simplificada de una nueva topología de amplificador
AC de frecuencia ultrabaja, eficiente en potencia área y ruido.
Los circuitos propuestos se han fabricado utilizando diferentes tecnologías CMOS
estándar (130 nm y 180 nm) y se proporcionan resultados de medidas experimentales,
así como análisis teóricos para caracterizar adecuadamente el rendimiento de
cada circuito propuesto y probar todo su potencial e idoneidad para entornos de
baja potencia, bajo ruido y baja frecuencia., This thesis presents innovative low-voltage, low-power and low-frequency techniques used to design novel circuit blocks (such as amplifiers, filters and RMS-to-DC converters) suitable for energy and area constrained IoT applications. The thesis is structured as follows: first, basic device and circuit level design techniques for lowvoltage, low-power, low-frequency and low-noise operation are presented, which are latter used to design circuit blocks suitable for IoT applications in power and area restricted environments.
The presented circuit blocks are adapted for low-voltage, low-power applications as well as ultra-low-frequency operation, making use of power efficient techniques such as Quasy-Floating Gate (QFG) transistors, adaptive biasing for current efficiency through Flipped Voltage Follower (FVF) or bootstrapping technique to obtain large RC time constants with reduced area, among others. The proposed circuits are experimentally validated and compared to previous relevant publications of similar circuits to prove their competitive performance. The thesis presents simple and power efficient class AB SSF-based filters exploiting the benefits of QFG transistors; a compact two-quadrant RMS-to-DC converter based on a novel Squarer/Divider cell with Electronically-Simulated MOS Translinear Loop (ES-MTL) and FVF-based adaptive biasing achieving high symmetry and dynamic range; finally, a family of ultra-low frequency AC Amplifiers is developed making use of nullor-based network transformation and bootstrapping technique to reduce RC time constant-based high-pass corner frequency. Further exploiting the versatility of nullor based circuit representation, a simplified power-, area- and noise-efficient version of a novel ultra-low frequency AC amplifier topology is developed.
The proposed circuits have been fabricated using different standard CMOS technologies (130 nm and 180 nm) and experimental measurement results are provided, as well as theoretical analyses to properly characterize the performance of each proposed circuit and test their full potential and suitability for low-power, low-noise and low-frequency environments., Proyectos TEC2016-80396-C2-1-R y PID2019-107258RB-C32 (Agencia Estatal de Investigación y el Ministerio de Ciencia e Innovación). Ministerio de Universidades, ayuda predoctoral BES-2017-080418, Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011), Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011)

In this paper, a bootstrapping technique is applied to a bulk-driven voltage buffer for canceling the gate-source transconductance in order to improve the cell gain, the linearity and reduce the input-referred noise. The bootstrapped circuitry is conveniently implemented by only using a capacitor and a pseudo resistor. The suitability of the technique is demonstrated by simulation results using a flipped voltage follower, even though it is general and can be applied to other structures. A 1-V buffer is designed in 0.18 µm CMOS technology, showing a 4.3 times improvement in the voltage gain (conventional 0.21 V/V, bootstrapped 0.90 V/V), increasing 5 times the input voltage range for a 1% THD (conventional 50 mV, bootstrapped 250 mV) and reducing the input equivalent noise around a 16% (conventional 180 nV/-√Hz, bootstrapped 155 nV/√Hz at 10 kHz)., This work has been funded by projects RTI2018-095994-B-I00 and PID2019-107258RB-C32 from MCIN/AEI/10.13039/501100011033, and by Fondo Europeo de Desarrollo Regional (FEDER).

A new method to process the vibration signal acquired by an accelerometer placed in a planetary gearbox housing is proposed, which is useful to detect potential faults. The method is based on the phenomenological model and consists of the projection of the healthy vibration signals onto an orthonormal basis. Low pass components representation and Gram–Schmidt’s method are conveniently used to obtain such a basis. Thus, the measured signals can be represented by a set of scalars that provide information on the gear state. If these scalars are within a predefined range, then the gear can be diagnosed as correct; in the opposite case, it will require further evaluation. The method is validated using measured vibration signals obtained from a laboratory test bench., Grant PID2019-107258RB-C32 funded by MCIN/AEI/10.13039/501100011033. M.M.-A. has a predoctoral grant BES-2017-080418 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future.

In this paper we propose, and demonstrate through a prototype, a completely novel device able to harvest mechanical energy from the multidirectional vibrations in a wind turbine, and convert it into electrical, to power autonomous sensors. The application is very challenging since vibrations are of ultra-low frequency, well below 1 Hz, with accelerations of tenths of cm/s2 (0.01 g), and the device must capture energy from the movement in any direction. According to our experiments, the device is capable to generate average powers around the milliwatt in the operation conditions of a wind turbine, which are enough for some very-low power sensor nodes, or at least to considerably extend the life-time of batteries. The device is based on the principle of moving (inertial) masses comprised of magnets in Hallbach arrays interacting with coils, and can work for movements on any direction of a plane. To the best of our knowledge, this is the first device specifically proposed for wind turbines and one of the few that work in such low frequencies, and capture energy from movements on any direction on a plane. Only three harvesters proposed in the literature, intended for distinct applications, can work at such low frequencies, and our device exhibits a better efficiency. Though comparisons with harvesters working in different contexts and, even using different conversion principles, is not completely fair, we make in this paper a comparison to the closest ones, resorting to two different figures of merit., This work has been supported by the Spanish Research Agency under grant AEI/FEDER, PID2019-107258RB-C32, and also by the Government of Navarre (Dpt. of Economic and Business Development) under grant 0011-1365-2021-000199. The open access of this paper has been funded by the Universidad Publica de Navarra.

A family of capacitively coupled alternating current (AC) amplifiers featuring ultra-low (below 1 Hz) corner frequency is presented. This is achieved by using high-gain devices which actively boost feedback resistance and thus reduce corner frequency. This procedure is often termed, though with a different purpose, as 'bootstrapping'. The proposed architectures are very general and admit several possible practical implementations. To demonstrate their usefulness, the circuits are implemented with two operational amplifiers (OA), but other active devices such as operational transconductance amplifiers (OTAs) can be alternatively used. All circuits have been theoretically analyzed, extensively simulated and measured, exhibiting high-pass cutoff frequencies as low as 30 mHz., This work was supported by AEI/FEDER (Grant PID2019‐107258RB‐C32), Ministry of Universities (grant BES‐2017‐080418), and Public University of Navarra.

A new approach to design super class AB operational transcon-ductance amplifiers (OTAs) with enhanced large-signal and small-signal performance is presented. It is based on employing two nested positive and negative feedback loops at the active load of an adaptively biased differential pair in weak inversion region. As a result, DC gain, gain-bandwidth product, settling time and noise are improved compared to conventional super class AB OTAs without extra circuit nodes or power consumption. Measurement results of a 180 nm CMOS test chip prototype show a current boosting factor higher than 5000 and a nearly ideal current efficiency. Due to the ultra-low quiescent currents and high driving capability, the circuit exhibits an excellent large-signal figure-of-merit (FOML) of 236 V-1. To illustrate the applicability of the proposed approach, a differential sample-and-hold (S/H) circuit was designed and fabricated on the same test chip. Measurement results of the S/H validate the advantages of the proposal., This work has been supported by the Spanish Ministerio de Ciencia e Innovación, grant PID2019-107258RB-C32.

In this work, the feasibility of a magnetic binary encoding system using 3D printing technology is analyzed. The
study has a double interest, that is, the possibility of printing a 3D piece that contains the codified information
and the development of a system for its decoding. For this purpose, magnetic nanoparticles (magnetite Fe3O4)
were embedded in a polymeric matrix of Polylactic Acid (PLA) and Poly-ε-caprolactone (PCL). Similar to a
conventional barcode, a rectangular piece with an alternating pattern of strips with absence (only polymer) and a
5 wt% of embedded magnetic nanoparticles was 3D printed employing the Fused Deposition Modelling tech-
nique (FDM). The information was decoded by means of a Giant Magnetoimpedance (GMI) sensor-based pro-
totype, by scanning the surface of the piece and measuring the changes in the magnetic field. As sensor nucleus,
an amorphous soft magnetic wire of nominal composition (Co0.94 Fe0.06)72.5 Si12.5 B15 was employed. The
decoding prototype incorporates a homemade electronic sensor interface that permits, at the time, the GMI
sensor excitation and the subsequent signal conditioning to optimize its response. The output signal enables the
detection of the magnetite nanoparticles and the magnetic decoding of the encoded information (“1” and “0”,
presence or absence of the magnetic nanoparticles, respectively)., This work has been funded by the Gobierno de Navarra - Departamento de Desarrollo Económico within the framework of the Project: “Advanced Manufacturing of Electronics, AMELEC”. It has also been partially funded by the Spanish Government - Ministerio Ciencia-Innovación (PID2019–107258RB-C32 of MCIN/AEI/10.13039/501100011033). Open access funding provided by Universidad Pública de Navarra. The authors also want to acknowledge the Technological Center specialized in mobility and mechatronics of Navarra (NAITEC), for supplying the 3D printed piece and Prof. M. Vázquez (ICMM, Madrid Spain) for kindly supplying the soft magnetic wires.

A novel approach to design low-power area-efficient
rail-to-rail output single-stage class-AB operational transconductance amplifiers (OTAs) with enhanced large- and small-signal
performance to drive large capacitive loads is presented. It is
based on a non-linear nested current mirror at the active load
of a splitted differential input pair biased in weak inversion that
boosts dynamic currents beyond their quiescent value directly
at the output branch. As a result, slew rate, DC gain, gainbandwidth product, settling time and noise performance are
improved without additional circuit elements or power consumption. An OTA prototype has been fabricated in a 180-nm CMOS
process, consuming a quiescent power of 2.9 µW from a supply
voltage of ±0.5 V and a silicon area of 0.001 mm2
. Measurement
results validate the advantages of the proposal, exhibiting positive
and negative slew rates of 110 V/ms and −58 V/ms, respectively,
and a gain-bandwidth product of 136 kHz with a phase margin
of 90◦
for a capacitive load of 160 pF., This work was supported by the Ministerio de Ciencia e Innovación (MCIN)/Agencia Estatal de Investigación (AEI)/10.13039/501100011033 under Grant PID2019-107258RBC32.

A detection platform based on non-linear Giant Magnetoimpedance Effect was analyzed for the design of a contactless and low-cost detector of magnetic nanoparticles. The sensor consists of two soft magnetic amorphous wires (Co66Fe2Si13B15Cr4, 1.5 cm in length) placed in parallel and connected electrically in series. Initially, a simple voltage divider was employed to characterize the variations of the first, V1fand second harmonic, V2f, voltages. Their response was analyzed under the effect of the remnant magnetic field generated by different amounts of Fe3O4 nanoparticles (mean diameter 140 nm) as a function of an external magnetic field, H. Due to the larger relative variations showed by V2f, the second harmonic was chosen for the final prototype development. An electronic interface was designed for both current excitation and V2f detection. The designed detection platform, characterized by high detection sensitivity, low-cost, portable, and reusable features, can be employed to efficiently detect magnetic nanoparticles., The work has been performed within the framework of the project MAT 2017-83631-C3-2R (Spanish Ministerio de Ciencia e Innovación) and AEI/FEDER (grant PID2019-107258RB-C32). The soft magnetic wire was kindly provided by Dr. A. Mitra, from NDE & Magnetic Materials Group, CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India. The authors would also like to acknowledge the use of 'Servicio General de Apoyo a la Investigación-SAI', Universidad de Zaragoza for the TEM microscopy service.

In this paper we describe and fully characterize a novel vibration harvester intended to harness energy from the vibration of a wind turbine (WT), to potentially supply power to sensing nodes oriented to structural health monitoring (SHM). The harvester is based on electromagnetic conversion (EM) and can work with vibrations of ultra-low frequencies in any direction of a plane. The harvester bases on a first prototype already disclosed by the authors, but in this paper, we develop an accurate model parameterized by a combination of physical parameters and others related to the geometry of the device. The model allows predicting not only the power generation capabilities, but also the kinematic behaviour of the harvester. Model parameters are estimated by an identification procedure and validated experimentally. Last, the harvester is tested in real conditions on a wind turbine., This paper has been supported by the Spanish Research Agency, and
the EU/PTR Next Generation Funds under grants PID2019-107258RBC32,
TED2021-131052B-C21, and PID2022-138491OB-C32. The Public
University of Navarre has also partially supported this project under
grant: PJUPNA2024-11690.

The nonlinear giant magnetoimpedance (GMI) effect was explored as a highly sensitive sensing technology in 3D-printed magnetic encoded systems. Magnetic nanoparticles with low (magnetite, Fe3O4) and high (Co ferrite, Co0.7Fe2.3O4) magnetic remanence were embedded (10 wt%) in a polymeric matrix of Polylactic Acid (PLA) and Poly-ε-caprolactone (PCL) and extruded in magnetic filaments to be 3D printed by the Fused Deposition Modelling technique (FDM). Two different geometries were constructed namely, individual magnetic strips and fixed barcoded pieces. The stray magnetic fields generated by the magnetic nanoparticles were detected through the non-linear (second harmonic) GMI voltage using a soft magnetic CoFeSiB wire as the nucleus sensor. The decoding response was analyzed as a function of the magnetization remanence of the nanoparticles, the distance between the individual magnetic strips, and the position (height) of the GMI decoding sensor. It has been shown that modification of the net magnetization direction of each individual fixed strip within the barcode geometry is possible through the application of local external magnetic fields. This possibility improves the versatility of the 3D binary encoding system by adding an additional state (0 without nanoparticles, 1 or −1 depending on the relative orientation of the net magnetization along the strips) during the codifying procedure., This work has been funded by the Gobierno de Navarra - Departamento de Desarrollo Económico within the framework of the Project: “Advanced Manufacturing of Electronics, AMELEC”. It has also been partially funded by the Spanish Government - Ministerio Ciencia - Innovación (PID2019-107258RB-C32 of MCIN/AEI/10.13039/501100011033) and from the grant PID2021–122613OB-I00 funded by MCIN/AEI/ 10.13039/501100011033. Open access funding is provided by Universidad Pública de Navarra.

In this paper, we propose the idea of using transimpedance amplifiers, in lieu of operational amplifiers (OAs) or transconductance amplifiers (OTAs) to design capacitively coupled AC amplifiers. The idea is demonstrated with a current feedback operational amplifier (CFOA) as an active element, which is actually an architecture consisting of voltage buffers and current copiers (mirrors). This last characteristic is further exploited to make the corner frequency of the AC amplifier tunable by means of bootstrapping low-valued resistors with the output buffer. It is particularly suited to achieve very-low corner frequencies as needed in applications such as bio- or seismic signals. The idea is demonstrated with simulations and experimental results with a discrete implementation., This work has been supported by theSpanish Research Agency, under grantAEI/FEDER PID2019-107258RB-C32, andby the Spanish Research Agency and theEU/PTR Next Generation Funds, undergrant TED2021-131052B-C21, AgenciaEstatal de Investigaci on, Ministerio deCiencia e Innovaci on, Open accessfunding provided by Universidad Públicade Navarra.

In this letter, a novel low-voltage junction field-effect transistor (JFET) oscillator with self-starting capability to implement an ac-dc boost converter is introduced. The circuit is transformer free and can operate with very low-voltage and low-frequency signals. In order to operate with positive and negative input signals, a coupled topology of JFETs has been used. The circuit has been built using off the shelf components, and can be used with electromagnetic harvesters, thermoelectric modules, and/or wearable devices. Experimental results with a practical harvester are provided in order to demonstrate the proposed ac-dc boost converter., This work was supported by Spanish Research Agency and the EU/PTR Next Generation Funds, under Grant TED2021-131052B-C21, Grant PID2019-107258RB-C32, and Grant PID2022-138491OB-C32.

We present a novel approach to estimating the instantaneous main shaft angular position in the context of wind turbine structural health monitoring. We show that only two IMU channels - gyroscope axial and accelerometer tangential - contain enough information to build an acceleration state-space model that properly captures the rotational dynamics of a wind turbine. The kernel of the model is an in-phase and quadrature time-varying sinusoid whose argument is driven by the integral of the gyroscope output. This approach clearly stands in contrast to most state-of-the-art methods, where the gyroscope output is explicitly modeled. The model equation describes the states dynamics, which simultaneously assesses the instantaneous amplitude and initial phase of the angular displacement through a first-order autoregressive process. Such a state-space model features only two states per time instant; furthermore, it is linear-in-states and therefore straightforwardly estimated by the linear Kalman filter. It is shown that the instantaneous azimuth estimates obtained from the state-space model, linearly combined with the gyroscope output, effectively cancel out the long-term drift in the estimate. The benchmark results suggest that the proposed method outperforms a state-of-the-art method, in terms of robustness against noise and adaptability to changing operating regimes in a wind turbine., This work has been supported by the Spanish Research Agency, under grant AEI/FEDER PID2019-107258RB-C32, the EU/PTR Next Generation Funds, under grant TED2021-131052B-C21, and the Government of Navarre under grant 0011-1365-2021-000199.

A novel architecture for an AC (i.e. high-pass) amplifier is proposed allowing a drastic reduction of the cutoff frequency to the sub-Hertz range. It builds upon the classic AC configuration with a high gain amplifier and a parallel RC circuit in the feedback loop, by increasing the feedback resistance through bootstrapping. Resistance multiplying factors higher than four orders of magnitude are easily achievable. The basic principle can be applied to several practical implementations, though in this letter it is demonstrate with measurement results of an op-amp based discrete implementation., This work was financially supported by the following grants from the Spanish Research Agency: TEC2016-80396-C2-1-R and PID2019-107258RB-C32 (AEI/FEDER). M.Martincorena Arraiza was funded by the Ministry of Universities under grant BES-2017-080418.

We present a novel approach to harmonic disturbance removal in single-channel wind turbine acceleration data by means of time-variant signal modeling. Harmonics are conceived as a set of quasi-stationary sinusoids whose instantaneous amplitude and phase vary slowly and continuously in a short-time analysis frame. These non-stationarities in the harmonics are modeled by low-degree time polynomials whose coefficients capture the instantaneous dynamics of the corresponding waveforms. The model is linear-in-parameters and is straightforwardly estimated by the linear least-squares algorithm. Estimates from contiguous analysis frames are further combined in the overlap-add fashion in order to yield overall harmonic disturbance waveform and its removal from the data. The algorithm performance analysis, in terms of input parameter sensitivity and comparison against three state-of-the-art methods, has been carried out with synthetic signals. Further model validation has been accomplished through real-world signals and stabilization diagrams, which are a standard tool for determining modal parameters in many time-domain modal identification algorithms. The results show that the proposed method exhibits a robust performance particularly when only the average rotational speed is known, as is often the case for stand-alone sensors which typically carry out data pre-processing for structural health monitoring. Moreover, for real-world analysis scenarios, we show that the proposed method delivers consistent vibration mode parameter estimates, which can straightforwardly be used for structural health monitoring., This work has been supported by the Spanish Research Agency under grant AEI/FEDER, PID2019-107258RB-C32, and also by the
Government of Navarre (Dpt. Of Economic and Business Development) under grant 0011-1365-2021-000159.