tdehaeze/digital-brain
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

Update Content - 2020-10-09

Browse Source
This commit is contained in:
Thomas Dehaeze 2020-10-09 16:00:04 +02:00
parent 5216efabad
commit 2376d7255d
4 changed files with 56 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
content/zettels/force_sensors.md
View File

@ -7,9 +7,9 @@ draft = false
Backlinks: Backlinks:
- [Sensors]({{< relref "sensors" >}}) - [Sensors]({{< relref "sensors" >}})
- [Nanopositioning system with force feedback for high-performance tracking and vibration control]({{< relref "fleming10_nanop_system_with_force_feedb" >}})
- [Collocated Control]({{< relref "collocated_control" >}}) - [Collocated Control]({{< relref "collocated_control" >}})
- [Position Sensors]({{< relref "position_sensors" >}}) - [Position Sensors]({{< relref "position_sensors" >}})
- [Nanopositioning system with force feedback for high-performance tracking and vibration control]({{< relref "fleming10_nanop_system_with_force_feedb" >}})
- [Signal Conditioner]({{< relref "signal_conditioner" >}}) - [Signal Conditioner]({{< relref "signal_conditioner" >}})
Tags Tags
@ -21,7 +21,7 @@ Tags
### Dynamics and Noise of a piezoelectric force sensor {#dynamics-and-noise-of-a-piezoelectric-force-sensor} ### Dynamics and Noise of a piezoelectric force sensor {#dynamics-and-noise-of-a-piezoelectric-force-sensor}
An analysis the dynamics and noise of a piezoelectric force sensor is done in ([Fleming 2010](#org25f6243)) ([Notes]({{< relref "fleming10_nanop_system_with_force_feedb" >}})). An analysis the dynamics and noise of a piezoelectric force sensor is done in ([Fleming 2010](#org69854d3)) ([Notes]({{< relref "fleming10_nanop_system_with_force_feedb" >}})).
### Manufacturers {#manufacturers} ### Manufacturers {#manufacturers}
@ -32,6 +32,7 @@ An analysis the dynamics and noise of a piezoelectric force sensor is done in ([
| HBM | [link](https://www.hbm.com/en/6107/force-sensors-with-flange-mounting/) | Germany | | HBM | [link](https://www.hbm.com/en/6107/force-sensors-with-flange-mounting/) | Germany |
| Kistler | [link](https://www.kistler.com/fr/produits/composants/capteurs-de-force/?pfv%5Fmetrics=metric) | Swiss | | Kistler | [link](https://www.kistler.com/fr/produits/composants/capteurs-de-force/?pfv%5Fmetrics=metric) | Swiss |
| MMF | [link](https://www.mmf.de/force%5Ftransducers.htm) | Germany | | MMF | [link](https://www.mmf.de/force%5Ftransducers.htm) | Germany |
| Sinocera | [link](http://www.china-yec.net/sensors/) | China |
### Signal Conditioner {#signal-conditioner} ### Signal Conditioner {#signal-conditioner}
@ -53,4 +54,4 @@ However, if a charge conditioner is used, the signal will be doubled.
## Bibliography {#bibliography} ## Bibliography {#bibliography}
<a id="org25f6243"></a>Fleming, A.J. 2010. “Nanopositioning System with Force Feedback for High-Performance Tracking and Vibration Control.” _IEEE/ASME Transactions on Mechatronics_ 15 (3):433–47. <https://doi.org/10.1109/tmech.2009.2028422>. <a id="org69854d3"></a>Fleming, A.J. 2010. “Nanopositioning System with Force Feedback for High-Performance Tracking and Vibration Control.” _IEEE/ASME Transactions on Mechatronics_ 15 (3):433–47. <https://doi.org/10.1109/tmech.2009.2028422>.

15
content/zettels/inertial_sensors.md
View File

@ -17,10 +17,10 @@ Tags
## Review of Absolute (inertial) Position Sensors {#review-of-absolute--inertial--position-sensors} ## Review of Absolute (inertial) Position Sensors {#review-of-absolute--inertial--position-sensors}
- Collette, C. et al., Review: inertial sensors for low-frequency seismic vibration measurement ([Collette, Janssens, Fernandez-Carmona, et al. 2012](#orgd9207bb)) - Collette, C. et al., Review: inertial sensors for low-frequency seismic vibration measurement ([Collette, Janssens, Fernandez-Carmona, et al. 2012](#orgc31d4ec))
- Collette, C. et al., Comparison of new absolute displacement sensors ([Collette, Janssens, Mokrani, et al. 2012](#org08a3c9d)) - Collette, C. et al., Comparison of new absolute displacement sensors ([Collette, Janssens, Mokrani, et al. 2012](#org79555eb))
<a id="org4f07187"></a> <a id="orgf5b5084"></a>
{{< figure src="/ox-hugo/collette12_absolute_disp_sensors.png" caption="Figure 1: Dynamic range of several types of inertial sensors; Price versus resolution for several types of inertial sensors" >}} {{< figure src="/ox-hugo/collette12_absolute_disp_sensors.png" caption="Figure 1: Dynamic range of several types of inertial sensors; Price versus resolution for several types of inertial sensors" >}}
@ -35,12 +35,13 @@ Tags
| Guralp | [link](https://www.guralp.com/products/surface) | UK | | Guralp | [link](https://www.guralp.com/products/surface) | UK |
| Nanometric | [link](https://www.nanometrics.ca/products/accelerometers) | Canada | | Nanometric | [link](https://www.nanometrics.ca/products/accelerometers) | Canada |
| Kistler | [link](https://www.kistler.com/fr/produits/composants/accelerometres/?pfv%5Fmetrics=metric) | Swiss | | Kistler | [link](https://www.kistler.com/fr/produits/composants/accelerometres/?pfv%5Fmetrics=metric) | Swiss |
| Beran | [link](https://www.beraninstruments.com/Products/Vibration-Transducers-and-Cabling) | UK |
Wireless Accelerometers Wireless Accelerometers
- <https://micromega-dynamics.com/products/recovib/miniature-vibration-recorder/> - <https://micromega-dynamics.com/products/recovib/miniature-vibration-recorder/>
<a id="orgf6bb056"></a> <a id="orgaedbdbc"></a>
{{< figure src="/ox-hugo/inertial_sensors_characteristics_accelerometers.png" caption="Figure 2: Characteristics of commercially available accelerometers <sup id=\"642a18d86de4e062c6afb0f5f20501c4\"><a href=\"#collette11_review\" title=\"Collette, Artoos, Guinchard, Janssens, , Carmona Fernandez \&amp; Hauviller, Review of sensors for low frequency seismic vibration measurement, CERN, (2011).\">collette11_review</a></sup>" >}} {{< figure src="/ox-hugo/inertial_sensors_characteristics_accelerometers.png" caption="Figure 2: Characteristics of commercially available accelerometers <sup id=\"642a18d86de4e062c6afb0f5f20501c4\"><a href=\"#collette11_review\" title=\"Collette, Artoos, Guinchard, Janssens, , Carmona Fernandez \&amp; Hauviller, Review of sensors for low frequency seismic vibration measurement, CERN, (2011).\">collette11_review</a></sup>" >}}
@ -57,13 +58,13 @@ Wireless Accelerometers
| Guralp | [link](https://www.guralp.com/products/surface) | UK | | Guralp | [link](https://www.guralp.com/products/surface) | UK |
| Nanometric | [link](https://www.nanometrics.ca/products/seismometers) | Canada | | Nanometric | [link](https://www.nanometrics.ca/products/seismometers) | Canada |
<a id="org618d271"></a> <a id="orgcf4f484"></a>
{{< figure src="/ox-hugo/inertial_sensors_characteristics_geophone.png" caption="Figure 3: Characteristics of commercially available geophones <sup id=\"642a18d86de4e062c6afb0f5f20501c4\"><a href=\"#collette11_review\" title=\"Collette, Artoos, Guinchard, Janssens, , Carmona Fernandez \&amp; Hauviller, Review of sensors for low frequency seismic vibration measurement, CERN, (2011).\">collette11_review</a></sup>" >}} {{< figure src="/ox-hugo/inertial_sensors_characteristics_geophone.png" caption="Figure 3: Characteristics of commercially available geophones <sup id=\"642a18d86de4e062c6afb0f5f20501c4\"><a href=\"#collette11_review\" title=\"Collette, Artoos, Guinchard, Janssens, , Carmona Fernandez \&amp; Hauviller, Review of sensors for low frequency seismic vibration measurement, CERN, (2011).\">collette11_review</a></sup>" >}}
## Bibliography {#bibliography} ## Bibliography {#bibliography}
<a id="orgd9207bb"></a>Collette, C., S. Janssens, P. Fernandez-Carmona, K. Artoos, M. Guinchard, C. Hauviller, and A. Preumont. 2012. “Review: Inertial Sensors for Low-Frequency Seismic Vibration Measurement.” _Bulletin of the Seismological Society of America_ 102 (4):1289–1300. <https://doi.org/10.1785/0120110223>. <a id="orgc31d4ec"></a>Collette, C., S. Janssens, P. Fernandez-Carmona, K. Artoos, M. Guinchard, C. Hauviller, and A. Preumont. 2012. “Review: Inertial Sensors for Low-Frequency Seismic Vibration Measurement.” _Bulletin of the Seismological Society of America_ 102 (4):1289–1300. <https://doi.org/10.1785/0120110223>.
<a id="org08a3c9d"></a>Collette, C, S Janssens, B Mokrani, L Fueyo-Roza, K Artoos, M Esposito, P Fernandez-Carmona, M Guinchard, and R Leuxe. 2012. “Comparison of New Absolute Displacement Sensors.” In _International Conference on Noise and Vibration Engineering (ISMA)_. <a id="org79555eb"></a>Collette, C, S Janssens, B Mokrani, L Fueyo-Roza, K Artoos, M Esposito, P Fernandez-Carmona, M Guinchard, and R Leuxe. 2012. “Comparison of New Absolute Displacement Sensors.” In _International Conference on Noise and Vibration Engineering (ISMA)_.

31
content/zettels/piezoelectric_actuators.md
View File

@ -31,11 +31,12 @@ Tags
| PiezoData | [link](https://www.piezodata.com/piezo-stack-actuator-2/) | China | | PiezoData | [link](https://www.piezodata.com/piezo-stack-actuator-2/) | China |
| Queensgate | [link](https://www.nanopositioning.com/product-category/nanopositioning/nanopositioning-actuators-translators) | UK | | Queensgate | [link](https://www.nanopositioning.com/product-category/nanopositioning/nanopositioning-actuators-translators) | UK |
| Matsusada Precision | [link](https://www.matsusada.com/product/pz/) | Japan | | Matsusada Precision | [link](https://www.matsusada.com/product/pz/) | Japan |
| Sinocera | [link](http://www.china-yec.net/piezoelectric-ceramics/) | China |
### Model {#model} ### Model {#model}
A model of a multi-layer monolithic piezoelectric stack actuator is described in ([Fleming 2010](#org2c80449)) ([Notes]({{< relref "fleming10_nanop_system_with_force_feedb" >}})). A model of a multi-layer monolithic piezoelectric stack actuator is described in ([Fleming 2010](#orgb44e3bc)) ([Notes]({{< relref "fleming10_nanop_system_with_force_feedb" >}})).
Basically, it can be represented by a spring \\(k\_a\\) with the force source \\(F\_a\\) in parallel. Basically, it can be represented by a spring \\(k\_a\\) with the force source \\(F\_a\\) in parallel.
@ -59,14 +60,14 @@ Some manufacturers propose "raw" plate actuators that can be used as actuator /
## Mechanically Amplified Piezoelectric actuators {#mechanically-amplified-piezoelectric-actuators} ## Mechanically Amplified Piezoelectric actuators {#mechanically-amplified-piezoelectric-actuators}
The Amplified Piezo Actuators principle is presented in ([Claeyssen et al. 2007](#org95701f0)): The Amplified Piezo Actuators principle is presented in ([Claeyssen et al. 2007](#orgf81e0e2)):
> The displacement amplification effect is related in a first approximation to the ratio of the shell long axis length to the short axis height. > The displacement amplification effect is related in a first approximation to the ratio of the shell long axis length to the short axis height.
> The flatter is the actuator, the higher is the amplification. > The flatter is the actuator, the higher is the amplification.
A model of an amplified piezoelectric actuator is described in ([Lucinskis and Mangeot 2016](#orgb10ad87)). A model of an amplified piezoelectric actuator is described in ([Lucinskis and Mangeot 2016](#orgda19a07)).
<a id="org98b8df0"></a> <a id="orgbce0bed"></a>
{{< figure src="/ox-hugo/ling16_topology_piezo_mechanism_types.png" caption="Figure 1: Topology of several types of compliant mechanisms <sup id=\"d9e8b33774f1e65d16bd79114db8ac64\"><a href=\"#ling16_enhan_mathem_model_displ_amplif\" title=\"Mingxiang Ling, Junyi Cao, Minghua Zeng, Jing Lin, \&amp; Daniel J Inman, Enhanced Mathematical Modeling of the Displacement Amplification Ratio for Piezoelectric Compliant Mechanisms, {Smart Materials and Structures}, v(7), 075022 (2016).\">ling16_enhan_mathem_model_displ_amplif</a></sup>" >}} {{< figure src="/ox-hugo/ling16_topology_piezo_mechanism_types.png" caption="Figure 1: Topology of several types of compliant mechanisms <sup id=\"d9e8b33774f1e65d16bd79114db8ac64\"><a href=\"#ling16_enhan_mathem_model_displ_amplif\" title=\"Mingxiang Ling, Junyi Cao, Minghua Zeng, Jing Lin, \&amp; Daniel J Inman, Enhanced Mathematical Modeling of the Displacement Amplification Ratio for Piezoelectric Compliant Mechanisms, {Smart Materials and Structures}, v(7), 075022 (2016).\">ling16_enhan_mathem_model_displ_amplif</a></sup>" >}}
@ -158,51 +159,51 @@ For a piezoelectric stack with a displacement of \\(100\,[\mu m]\\), the resolut
### Electrical Capacitance {#electrical-capacitance} ### Electrical Capacitance {#electrical-capacitance}
The electrical capacitance may limit the maximum voltage that can be used to drive the piezoelectric actuator as a function of frequency (Figure [2](#org6712594)). The electrical capacitance may limit the maximum voltage that can be used to drive the piezoelectric actuator as a function of frequency (Figure [2](#orgda04c00)).
This is due to the fact that voltage amplifier has a limitation on the deliverable current. This is due to the fact that voltage amplifier has a limitation on the deliverable current.
[Voltage Amplifier]({{< relref "voltage_amplifier" >}}) with high maximum output current should be used if either high bandwidth is wanted or piezoelectric stacks with high capacitance are to be used. [Voltage Amplifier]({{< relref "voltage_amplifier" >}}) with high maximum output current should be used if either high bandwidth is wanted or piezoelectric stacks with high capacitance are to be used.
<a id="org6712594"></a> <a id="orgda04c00"></a>
{{< figure src="/ox-hugo/piezoelectric_capacitance_voltage_max.png" caption="Figure 2: Maximum sin-wave amplitude as a function of frequency for several piezoelectric capacitance" >}} {{< figure src="/ox-hugo/piezoelectric_capacitance_voltage_max.png" caption="Figure 2: Maximum sin-wave amplitude as a function of frequency for several piezoelectric capacitance" >}}
## Piezoelectric actuator experiencing a mass load {#piezoelectric-actuator-experiencing-a-mass-load} ## Piezoelectric actuator experiencing a mass load {#piezoelectric-actuator-experiencing-a-mass-load}
When the piezoelectric actuator is supporting a payload, it will experience a static deflection due to its finite stiffness \\(\Delta l\_n = \frac{mg}{k\_p}\\), but its stroke will remain unchanged (Figure [3](#orgaf653d1)). When the piezoelectric actuator is supporting a payload, it will experience a static deflection due to its finite stiffness \\(\Delta l\_n = \frac{mg}{k\_p}\\), but its stroke will remain unchanged (Figure [3](#org6b0f065)).
<a id="orgaf653d1"></a> <a id="org6b0f065"></a>
{{< figure src="/ox-hugo/piezoelectric_mass_load.png" caption="Figure 3: Motion of a piezoelectric stack actuator under external constant force" >}} {{< figure src="/ox-hugo/piezoelectric_mass_load.png" caption="Figure 3: Motion of a piezoelectric stack actuator under external constant force" >}}
## Piezoelectric actuator in contact with a spring load {#piezoelectric-actuator-in-contact-with-a-spring-load} ## Piezoelectric actuator in contact with a spring load {#piezoelectric-actuator-in-contact-with-a-spring-load}
Then the piezoelectric actuator is in contact with a spring load \\(k\_e\\), its maximum stroke \\(\Delta L\\) is less than its free stroke \\(\Delta L\_f\\) (Figure [4](#org796d9a3)): Then the piezoelectric actuator is in contact with a spring load \\(k\_e\\), its maximum stroke \\(\Delta L\\) is less than its free stroke \\(\Delta L\_f\\) (Figure [4](#org440990f)):
\begin{equation} \begin{equation}
\Delta L = \Delta L\_f \frac{k\_p}{k\_p + k\_e} \Delta L = \Delta L\_f \frac{k\_p}{k\_p + k\_e}
\end{equation} \end{equation}
<a id="org796d9a3"></a> <a id="org440990f"></a>
{{< figure src="/ox-hugo/piezoelectric_spring_load.png" caption="Figure 4: Motion of a piezoelectric stack actuator in contact with a stiff environment" >}} {{< figure src="/ox-hugo/piezoelectric_spring_load.png" caption="Figure 4: Motion of a piezoelectric stack actuator in contact with a stiff environment" >}}
For piezo actuators, force and displacement are inversely related (Figure [5](#org05901df)). For piezo actuators, force and displacement are inversely related (Figure [5](#orgf610cbd)).
Maximum, or blocked, force (\\(F\_b\\)) occurs when there is no displacement. Maximum, or blocked, force (\\(F\_b\\)) occurs when there is no displacement.
Likewise, at maximum displacement, or free stroke, (\\(\Delta L\_f\\)) no force is generated. Likewise, at maximum displacement, or free stroke, (\\(\Delta L\_f\\)) no force is generated.
When an external load is applied, the stiffness of the load (\\(k\_e\\)) determines the displacement (\\(\Delta L\_A\\)) and force (\\(\Delta F\_A\\)) that can be produced. When an external load is applied, the stiffness of the load (\\(k\_e\\)) determines the displacement (\\(\Delta L\_A\\)) and force (\\(\Delta F\_A\\)) that can be produced.
<a id="org05901df"></a> <a id="orgf610cbd"></a>
{{< figure src="/ox-hugo/piezoelectric_force_displ_relation.png" caption="Figure 5: Relation between the maximum force and displacement" >}} {{< figure src="/ox-hugo/piezoelectric_force_displ_relation.png" caption="Figure 5: Relation between the maximum force and displacement" >}}
## Bibliography {#bibliography} ## Bibliography {#bibliography}
<a id="org95701f0"></a>Claeyssen, Frank, R. Le Letty, F. Barillot, and O. Sosnicki. 2007. “Amplified Piezoelectric Actuators: Static & Dynamic Applications.” _Ferroelectrics_ 351 (1):3–14. <https://doi.org/10.1080/00150190701351865>. <a id="orgf81e0e2"></a>Claeyssen, Frank, R. Le Letty, F. Barillot, and O. Sosnicki. 2007. “Amplified Piezoelectric Actuators: Static & Dynamic Applications.” _Ferroelectrics_ 351 (1):3–14. <https://doi.org/10.1080/00150190701351865>.
<a id="org2c80449"></a>Fleming, A.J. 2010. “Nanopositioning System with Force Feedback for High-Performance Tracking and Vibration Control.” _IEEE/ASME Transactions on Mechatronics_ 15 (3):433–47. <https://doi.org/10.1109/tmech.2009.2028422>. <a id="orgb44e3bc"></a>Fleming, A.J. 2010. “Nanopositioning System with Force Feedback for High-Performance Tracking and Vibration Control.” _IEEE/ASME Transactions on Mechatronics_ 15 (3):433–47. <https://doi.org/10.1109/tmech.2009.2028422>.
<a id="orgb10ad87"></a>Lucinskis, R., and C. Mangeot. 2016. “Dynamic Characterization of an Amplified Piezoelectric Actuator.” <a id="orgda19a07"></a>Lucinskis, R., and C. Mangeot. 2016. “Dynamic Characterization of an Amplified Piezoelectric Actuator.”

21
content/zettels/signal_conditioner.md
View File

@ -7,6 +7,7 @@ draft = false
Backlinks: Backlinks:
- [Position Sensors]({{< relref "position_sensors" >}}) - [Position Sensors]({{< relref "position_sensors" >}})
- [Force Sensors]({{< relref "force_sensors" >}})
Tags Tags
: [Force Sensors]({{< relref "force_sensors" >}}), [Sensors]({{< relref "sensors" >}}), [Electronics]({{< relref "electronics" >}}) : [Force Sensors]({{< relref "force_sensors" >}}), [Sensors]({{< relref "sensors" >}}), [Electronics]({{< relref "electronics" >}})
@ -29,28 +30,40 @@ The signal conditioning electronics can have different functions:
## Charge Amplifier {#charge-amplifier} ## Charge Amplifier {#charge-amplifier}
This can be used to interface with:
- piezoelectric sensors
| Manufacturers | Links | Country | | Manufacturers | Links | Country |
|---------------|---------------------------------------------------------------------------------------------------------------------|---------| |-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------|---------|
| PCB | [link](https://www.pcb.com/sensors-for-test-measurement/electronics/line-powered-multi-channel-signal-conditioners) | USA | | PCB | [link](https://www.pcb.com/sensors-for-test-measurement/electronics/line-powered-multi-channel-signal-conditioners) | USA |
| HBM | [link](https://www.hbm.com/en/2660/paceline-cma-charge-amplifier-analogamplifier/) | Germany | | HBM | [link](https://www.hbm.com/en/2660/paceline-cma-charge-amplifier-analogamplifier/) | Germany |
| Kistler | [link](https://www.kistler.com/fr/produits/composants/conditionnement-de-signal/) | Swiss | | Kistler | [link](https://www.kistler.com/fr/produits/composants/conditionnement-de-signal/) | Swiss |
| MMF | [link](https://www.mmf.de/signal%5Fconditioners.htm) | Germany | | MMF | [link](https://www.mmf.de/signal%5Fconditioners.htm) | Germany |
| DJB | [link](https://www.djbinstruments.com/products/instrumentation/view/9-Channel-Charge-Voltage-Amplifier-IEPE-Signal-Conditioning-Rack-Mounted) | UK |
| MTI Instruments | [link](https://www.mtiinstruments.com/products/turbine-balancing-vibration-analysis/charge-amplifiers/ca1800/) | USA |
| Sinocera | [link](http://www.china-yec.net/instruments/signal-conditioner/multi-channels-charge-amplifier.html) | China |
| L-Card | [link](https://en.lcard.ru/products/accesories/le-41) | Rusia |
## Voltage Amplifier {#voltage-amplifier} ## Voltage Amplifier {#voltage-amplifier}
| Manufacturers | Links | Country | | Manufacturers | Links | Country |
|---------------|------------------------------------------------------------------------------------|---------| |---------------|-----------------------------------------------------------------------------------|---------|
| Femto | [link](https://www.femto.de/en/products/voltage-amplifiers.html) | Germany | | Femto | [link](https://www.femto.de/en/products/voltage-amplifiers.html) | Germany |
| HBM | [link](https://www.hbm.com/en/2660/paceline-cma-charge-amplifier-analogamplifier/) | Germany |
| Kistler | [link](https://www.kistler.com/fr/produits/composants/conditionnement-de-signal/) | Swiss | | Kistler | [link](https://www.kistler.com/fr/produits/composants/conditionnement-de-signal/) | Swiss |
| MMF | [link](https://www.mmf.de/signal%5Fconditioners.htm) | Germany | | MMF | [link](https://www.mmf.de/signal%5Fconditioners.htm) | Germany |
## Current Amplifier {#current-amplifier} ## Current Amplifier {#current-amplifier}
This can be used to interface with:
- photodiodes
| Manufacturers | Links | Country | | Manufacturers | Links | Country |
|---------------|------------------------------------------------------------------|---------| |---------------|------------------------------------------------------------------------------------------------------|---------|
| Femto | [link](https://www.femto.de/en/products/current-amplifiers.html) | Germany | | Femto | [link](https://www.femto.de/en/products/current-amplifiers.html) | Germany |
| FMB Oxford | [link](https://www.fmb-oxford.com/products/controls-2/control-modules/i404-quad-current-integrator/) | UK |
<./biblio/references.bib> <./biblio/references.bib>