The goal of this paper is twofold: first to add together all different causes that can alter the offset of a differential temperature sensor and, second, to present a new differential temperature sensor architecture that can digitally compensate for this behavior and therefore extends the sensor dynamic range. Measurements performed on a 65 nm CMOS differential temperature sensor are presented to illustrate the discussion. As evolution of the state of the art, an automatic calibration procedure and the new sensor topology is presented. With this new topology, not only the thermal offset can be digitally calibrated, but the application field of differential temperature sensors is widened, being now suitable for use in measurements where both wide input range and high differential sensitivity are required.
Reverter, F.; Perpiñà, X.; Barajas, E.; León, J.; Vellvehi, M.; Jordà, X.; Altet, J. Sensors and actuators A. Physical Vol. 242, p. 195-202 DOI: 10.1016/j.sna.2016.03.016 Data de publicació: 2016-05-01 Article en revista
This paper analyses how a single metal-oxide-semiconductor field-effect transistor (MOSFET) can be employed as a thermal sensor to measure on-chip dynamic thermal signals caused by a power-dissipating circuit under test (CUT). The measurement is subjected to two low-pass filters (LPF). The first LPF depends on the thermal properties of the heat-conduction medium (i.e. silicon) and the CUT-sensor distance, whereas the second depends on the electrical properties of the sensing circuit such as the bias current and the dimensions of the MOSFET sensor. This is evaluated along the paper through theoretical models, simulations, and experimental data resulting from a chip fabricated in 0.35 mu m CMOS technology. Finally, the proposed thermal sensor and the knowledge extracted from this paper are applied to estimate the linearity of a radio-frequency (RF) amplifier. (C) 2016 Elsevier B.V. All rights reserved.
In this work, we have developed a thermal sensor based on poly(3,4 ethylenedioxythiophene) (PEDOT) nanofilms
as thermoelectric material. The PEDOT nanofilms have been synthesized by the electrochemical polymerization
method. The thicknesses of the films were around 120 nm. The doping level of PEDOT was controlled by chemical
reduction using hydrazine. The achieved Seebeck coeficient is 40 uV/K. A PEDOT nanofilm was integrated into an
electronic circuit that amplifies the voltage originated from the Seebeck effect. The temperature increment produced
by a fingerprint touching the film is enough to switch on a light emitting diode.
In a recent paper on a displacement current sensor for contactless detection of bio-activity
related signals , it was stated that “A potential means for human presence detection…is via
sensing…human biopotentials” [because] “physiological events associated with the biological
functions of many human organs produce electric fields,” and that “the ECG is relatively easier
to measure compared to other biopotentials and, hence, can potentially provide an important
[underscore added] means of detection of human presence.”
Contactless biopotential measurement using off-body electrodes has attracted many authors that
have proposed various solutions, some of which are far more expensive than that devised in .
Usually, one or two aluminium discs at a few centimetres from the chest are connected to a
high-impedance voltage amplifier and the large impedance between these electrodes and ground
makes the circuit very susceptible to capacitive (electric-field) interference hence it requires
electric shields or driven guards. Measuring displacement current instead of electrode voltage in
contactless biopotential measurements, as proposed in , avoids high impedance nodes hence
measurements should be far less susceptible to electric field interference. Consequently, it is
stated in  that “[Contactless] capacitive sensors therefore can be used to sense the
displacement current induced by the time-varying electric fields associated with various human
biopotentials.” This is in principle an interesting approach worth being considered and the
authors deserve praise for that.
A detailed study about magnetic sensing techniques based on anisotropic magnetoresistive sensors shows that the technology is suitable for low-frequency space applications like the eLISA mission. Low noise magnetic measurements at the sub-millihertz frequencies were taken by using different electronic noise reduction techniques in the signal conditioning circuit. We found that conventional modulation techniques reversing the sensor bridge excitation do not reduce the potential 1/f noise of the magnetoresistors, so alternative methods such as flipping and electro-magnetic feedback are necessary. In addition, a low-frequency noise analysis of the signal conditioning circuits has been performed in order to identify and minimize the different main contributions from the overall noise. The results for chip-scale magnetoresistances exhibit similar noise along the eLISA bandwidth (0.1 mHz - 1 Hz) to the noise measured by means of the voluminous fluxgate magnetometers used in its precursor mission, known as LISA Pathfinder.
Kokolanski, Z.; Jordana, J.; Gasulla, M.; Dimcev, V.; Reverter, F. Sensors and actuators A. Physical Vol. 224, p. 185-191 DOI: 10.1016/j.sna.2015.01.017 Data de publicació: 2015-04-01 Article en revista
This paper proposes and analyses a microcontroller-based interface circuit for inductive sensors with a variable self-inductance. Besides the microcontroller (mu C) and the sensor, the circuit just requires an external resistor and a reference inductor so that two RL circuits are formed. The mu C appropriately excites such RL circuits in order to measure the discharging time of the voltage across each inductor (i.e. sensing and reference) and then it uses such discharging times to estimate the sensor inductance. Experimental tests using different commercial mu Cs at different clock frequencies show the limitations (especially, due to parasitic resistances and quantisation) and the performance of the proposed circuit when measuring inductances in the millihenry range. A non-linearity error lower than 0.3% full-scale span (FSS) and a resolution of 10 bits are achieved, which are remarkable values considering the simplicity of the circuit. (C) 2015 Elsevier B.V. All rights reserved.
Mateos, I.; Patton, B.; Zhivun, E.; Budker, D.; Wurm, D.; Ramos, J. Sensors and actuators A. Physical Vol. 224, num. April, p. 147-155 DOI: 10.1016/j.sna.2015.01.029 Data de publicació: 2015-04-01 Article en revista
Noise measurements have been carried out in the LISA bandwidth (0.1-100 mHz) to characterize an all-optical atomic magnetometer based on nonlinear magneto-optical rotation. This was done in order to assess if the technology can be used for space missions with demanding low-frequency requirements like the LISA concept. Magnetometry for low-frequency applications is usually limited by 1/f noise and thermal drifts, which become the dominant contributions at sub-millihertz frequencies. Magnetic field measurements with atomic magnetometers are not immune to low-frequency fluctuations and significant excess noise may arise due to external elements, such as temperature fluctuations or intrinsic noise in the electronics. In addition, low-frequency drifts in the applied magnetic field have been identified in order to distinguish their noise contribution from that of the sensor. We have found the technology suitable for LISA in terms of sensitivity, although further work must be done to characterize the low-frequency noise in a miniaturized setup suitable for space missions. (C) 2015 Elsevier B.V. All rights reserved.
An adaptive autofocus technique for the control of speckle effect in optical feedback interferometry (OFI) is discussed. The beam spot size effect over the OFI signal is presented, justifying the proposed approach. An automated setup for the control of speckle effect using a liquid lens with electro-optical focusing is demonstrated. The spot size is modified according to the signal to noise ratio (SNR) bounds selected for the captured OFI signal, therefore avoiding signal fading caused by speckle effect and possible chaotic behavior because of strong feedback. The quality and shape of the acquired OFI signal when the spot size change takes place shows a transient oscillation without any additional effects over the OFI SNR and the OFI shape. Experimental examples are provided proving the effectiveness of the approach for speckle control in displacement and velocity measurements within a movement range of 20 mm. (C) 2014 Elsevier B.V. All rights reserved.
ToF cameras are now a mature technology that is widely being adopted to provide sensory input to robotic applications. Depending on the nature of the objects to be perceived and the viewing distance, we distinguish two groups of applications: those requiring to capture the whole scene and those centered on an object. It will be demonstrated that it is in this last group of applications, in which the robot has to locate and possibly manipulate an object, where the distinctive characteristics of ToF cameras can be better exploited.
After presenting the physical sensor features and the calibration requirements of such cameras, we review some representative works highlighting for each one which of the distinctive ToF characteristics have been more essential. Even if at low resolution, the acquisition of 3D images at frame-rate is one of the most important features, as it enables quick background/foreground segmentation. A common use is in combination with classical color cameras. We present three developed applications, using a mobile robot and a robotic arm, to exemplify with real images some of the stated advantages.
Altet, J.; Gómez, D.; Perpinyà, X.; Mateo, D.; Gonzalez, J.; Vellvehi, M.; Jordà, X. Sensors and actuators A. Physical Vol. 192, p. 49-57 DOI: 10.1016/j.sna.2012.12.010 Data de publicació: 2013-04 Article en revista
This work aims at showing a new approach for determining the efficiency of linear class A RF power amplifiers by means of non-invasive, steady-state thermal monitoring. The theoretical basis of the technique is indicated and its suitability in a real case application scenario is presented. More in detail, silicon surface thermal monitoring is performed with built-in sensors and infrared measurements on an RF power amplifier. The first monitoring circuit consists of differential sensors, which can be used for contact-less on-line efficiency monitoring or to easy production testing. The obtained results are corroborated by means of Infrared measurements. Off-chip temperature sensors have applications in failure analysis or circuit debugging scenarios. As a result, we observe a good agreement between the efficiency predicted with the thermal measurements (less than 5% of error) when compared to values measured with standard electrical equipment.
Casals-Terré, J.; Duch, M.; Plaza, J.; Esteve, J.; Perez Castillejos, Raquel; Vallés, E.; Gómez, E. Sensors and actuators A. Physical Vol. 162, num. 1, p. 107-115 DOI: 10.1016/j.sna.2010.04.025 Data de publicació: 2010-07-01 Article en revista
Design, fabrication and testing of a novel micromachined “quasi-digital” microflow regulator for integrated microfluidic systems. Operation relies on the use of a permanent magnet which interacts with
an electrodeposited layer of Co–Ni on an array of V-shaped cantilever beams under a constant pressure.
Each valve actuates as an on–off fluidic switch, opening or closing its corresponding microchannel. The flow can be adjusted to a set of different values (digital) by changing the position of the magnet. The
microflow regulator has been designed, fabricated and experimentally tested showing a flow variation of 211% at a pressure of 160 mbar.
Pyroelectric cells based on fabricated screen-printed PZT and commercial PVDF films are proposed as
thermal energy harvesting sources in order to supply low-power autonomous sensors. The cells are electrically
modelled as a current source in parallel with output impedance. Heating and cooling temperature
fluctuations generated by air currents were applied to the pyroelectric converters. The generated currents
and charges were respectively in the order of 10−7 A and 10−5 C for temperature fluctuations from
300K to 360K in a time period of the order of 100 s, which agrees with the theoretical model. Parallel
association of cells increased the generated current. The dependence of the generated current on relevant
technological parameters has been also characterized. Finally, current from cyclic temperature fluctuations
was rectified and stored in a 1 F load capacitor. Energies up to 0.5 mJ have been achieved, enough
to power typical autonomous sensor nodes during a measurement and transmission cycle.
Fonollosa, J.; Carmona, M.; Santander, J.; Fonseca, L.; Moreno-Sereno, M.; Marco, S. Sensors and actuators A. Physical Vol. 149, num. 1, p. 65-73 DOI: 10.1016/j.sna.2008.10.008 Data de publicació: 2009 Article en revista
Casals-Terré, J.; Duch, M.; Plaza, J.; Esteve, J.; Perez-Castillejos, R.; Valles, E.; Gómez, E. Sensors and actuators A. Physical Vol. 147, num. 2, p. 600-606 Data de publicació: 2008-09 Article en revista
Trifonov, T.; Rodriguez, A.; Marsal, L.; Pallares, J.; Alcubilla, R. Sensors and actuators A. Physical Vol. 141, num. 2, p. 662-669 DOI: 10.1016/j.sna.2007.09.001 Data de publicació: 2008-02 Article en revista
This work focuses on the fabrication of three-dimensional (3D) microstructures by electrochemical etching of n-type silicon. We exploit the possibility of modulating the pore diameter along the growing direction to produce quasi-3D structures which exhibit periodicity also in third dimension. The fabricated structures are further processed to convert them into truly 3D networks consisting of interconnected silicon veins embedded in air. In particular, we show how a variety of complex 3D networks can be obtained starting from a simple initial pore arrangement, e.g. square or hexagonal. These 3D structures can be easily fabricated with very high precision and uniformity on a large scale. They constitute ideal hosts for sensing applications as well as perfect molds for casting 3D structures of unusual materials.
This paper describes new theoretical and experimental results showing that the pulsed digital oscillator, a set of sigma–delta-based oscillator structures for MEMS recently introduced by the authors, can maintain a good oscillation behaviour even for sampling frequencies below the Nyquist limit. Specifically, the theory is extended to the undersampling region and the complete set of ‘perfect’ frequencies (sampling frequencies at which the oscillation frequency is the natural frequency of the resonator) is analyzed. Therefore, an extension of the use of this kind of oscillators to high frequency applications becomes straightforward.
Mechanical energy generated by human activity may be converted to electrical energy using piezoelectric film inserts inside a shoe. This electrical energy can be collected in the form of charge accumulated in a storage capacitor. Under this scheme, the storage capacitor needs only to be connected to the load when it has enough energy for the requested operation. This time interval depends on several parameters: piezoelectric type and magnitude of excitation, required energy and voltage, and magnitude of the capacitor. This work analyzes these parameters to find an appropriate choice of storage capacitor and voltage intervals.
This paper proposes a novel method to measure the electrical conductivity of solutions in the time domain by using a single square-wave current and two titanium electrodes. This method allows us to determine both the conductivity (σ) of the solution and the two parameters of the constant-phase element (CPE) due to the electrodes. Experimental results show that the proposed method achieves conductivity measurement ranges close to those obtained with platinum probes or tetrapolar measurements, which are more expensive, and provides information about electrode condition.
Jimenez, V.; Pons, J.; Dominguez, M.; Bermejo, S.; Castañer, L.; Nieminen, H.; Ermolov, V. Sensors and actuators A. Physical Vol. 128, num. 1, p. 89-97 DOI: 10.1016/j.sna.2006.01.032 Data de publicació: 2006-03 Article en revista
In the actuation of electrostatically controlled capacitive MEMS devices, drive voltages over the supply voltage are commonly required. In order to obtain such voltages, charge pumps are often used. This paper presents and discusses two methods to drive capacitive MEMS devices using IC-compatible Dickson charge pumps designed to minimize power consumption. Drive circuits include voltage shaping to minimize charge injection in order to provide better reliability. The main design constraints to integrate them in state of the art IC technologies are identified and quantified. The required charge pumps are also optimized to provide an efficient use of its total capacitance. The transient dynamics of charge pumps connected to a RF MEMS variable capacitor are also analysed and discussed. Finally, the proposed methods are tested and validated through experimental results.
Dominguez, M.; Ricart, J.; Moreno, A.; Contestí, X.; Garriga, S. Sensors and actuators A. Physical Vol. 121, num. 2, p. 388-394 DOI: 10.1016/j.sna.2005.03.046 Data de publicació: 2005-06 Article en revista
A new low cost PCB solution for airflow metering is presented. The structure has been designed to increase the sensor bandwidth while keeping a total low cost of the sensor and its electronics. Two silicon dice are used: one in the cold point (a temperature sensor) and another in the hot point (a heater and a temperature sensor). The dice are directly placed on top of small Pyrex structures, which provide the necessary thermal isolation between the hot and cold points of the sensor, as well as with the outer environment. The time constant of the sensor is approximately 1 s. The sensor works in the closed loop mode, controlled by a thermal sigma–delta modulator. Airflow velocities down to 0.1 m/s can be measured.
A new driving mode of electrostatic actuators has been examined. It is based on charge drive rather than on voltage drive. Charge drive is accomplished by a pulsed current source delivering a given amount of charge to the actuator. It is theoretically shown that if the drive is ideal, any position across the gap is stable. The main reason underlying this result is that the electrostatic force does not depend on the remaining gap of the actuator and hence, the pull-in instability is avoided. These findings are supported on simulations using an analog high level description language allowing to represent the actuator by its differential equations. The effect of parasitic capacitances has also been examined and the stability conditions analyzed. A simple analytical stability condition can be written relating the value of the parasitic capacitance to the maximum deflection allowed for a stable equilibrium point. These results are also supported by simulation. Finally, the current leakage effects on the stability and drift of the equilibrium position have been analyzed. A trade-off between the relative loss of charge and the minimum refresh frequency required has been formulated.
Perez Castillejos, Raquel; Plaza, J.A.; Esteve, J.; Losantos, P.; Acero, M.C.; Cané, C.; Serra-Mestres, F. Sensors and actuators A. Physical Vol. 84, num. 1, p. 176-180 DOI: 10.1016/S0924-4247(99)00318-0 Data de publicació: 2000-08-01 Article en revista
An introduction to ferrofluids in MEMS applications is presented. Ferrofluids are fluids with magnetic properties. By applying a magnetic field, the balance of forces within the ferrofluid is varied so that the magnetic fluid can move or apply pressure. These capabilities can be used in the field of the microsystems. In this work, we have obtained the typical values of pressure which can be expected from a ferrofluid. Using a piezoresistive pressure sensor, a pressure of 0.04 bar has been obtained.
Measurements of voltage and current transients of a scaled model of an electrostatic microactuator have been performed. Experiments were made at a variety of values of the actuation source resistance, and the effects on the pull-in time and on the energy consumed in a switching event were analysed. It is concluded that the pull-in time remains sensibly constant until source resistance values are reached corresponding more closely to current-controlled than to voltage-controlled actuation. Furthermore, the energy consumed per switching event monotonically decreases with increasing source resistance. There is an optimum source resistance at which a minimum can be found for the product of pull-in time and energy in agreement with earlier theoretical predictions. The experimental results are quantitatively compared with Saber simulations incorporating an analog hardware description language model for the actuator.
Castañer, L.; Jimenez, V.; Dominguez, M.; Masana, F.; Rodriguez, A. Sensors and actuators A. Physical Vol. 66, num. 1-3, p. 131-137 DOI: 10.1016/S0924-4247(97)01760-3 Data de publicació: 1998-04 Article en revista
A modified hot-wire fluid-flow sensor design is described in which the convection of heat takes place at a distant point from the temperature sensor itself. The distant arrangement is also applied to the cold point of the flow meter. Thermal contact between the sensors themselves and the distant points is ensured by metal leads. This novel approach is implemented by using a low-cost packaging solution consisting of a lead frame and low-thermal-conductivity plastic epoxy encapsulation. The sensors are bipolar junction common-collector transistor arrays, the hot-point sensor being surrounded by an NiCr resistor. The system is completed by a sigma-delta thermoelectric converter which ensures the feedback loop and provides a digital readout. This device has been fabricated and tested and shows a sensing range of 0.2–91 min-1 water flow.
This paper presents a magnetic sensor on thin-film SOI-SIMOX that takes advantage of a previous bipolar structure, the VCBM (voltage-controlled bipolar MOS transistor) to improve magnetic response with low power consumption. The buried oxide avoids substrate currents, while keeping a high relative sensitivity, up to 50% T-1, of the sensor. The paper introduces the structure and theoretical operation regions for both electric and magnetic features. Experimental results on two devices validate the previous analysis, presenting the main figures of merit. Finally, the total device efficiency parameter is introduced.
This paper presents a magnetic sensor on thin-film SOI-SIMOX that takes advantage of a previous bipolar structure, the VCBM (voltage-controlled bipolar MOS transistor) to improve magnetic response with low power consumption. The buried oxide avoids substrate currents, while keeping a high relative sensitivity, up to 50% T−1, of the sensor. The paper introduces the structure and theoretical operation regions for both electric and magnetic features. Experimental results on two devices validate the previous analysis, presenting the main figures of merit. Finally, the total device efficiency parameter is introduced.