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Ferrofluids

Research Activity

Ferrofluids are synthetic compounds, in either aqueous or non aqueous solutions, composed by colloidal suspensions of ultra-fine (5-10 nm) single domain magnetic particles. The ferrofluidic nanoparticles are covered with a thin polymeric layer (surfactant) to prevent their agglomeration caused by Van der Waals forces.
The use of ferrofluids gives the opportunity to control the device specifications by electrically manipulating the ferrofluidic core properties (such as viscosity, volume, etc.).

Motivation
As compared with conventional solutions, the advantages of the development of ferrofluidic transducers are:

  • The use of ferrofluidic masses as the inertial mass of transducers improves the robustness against external shocks;
  • The absence of mechanical moving parts avoids mechanical stress and increases the lifetime of the devices;
  • The proposed architectures are suitable to implement sensing and actuating strategies in existing structures without any invasive or destructive action;
  • the possibility to manage low amount of fluid;
  • the decoupling between mechanics (housing the ferrofluid and the target fluid) and electrical parts;
  • the electric tunability of the transducer specifications;
  • low cost.


The Resonant Inclinometer

The device consists of:

  • a pipe filled with de-ionized water with a drop of ferrofluid;
  • a primary coil to produce the restoring force;
  • two secondary coils implementing a differential inductive readout;
  • two resonant coils to move the drop around his equilibrium position thus reducing the static friction;
  • a step-motor to impress the angular movement;


The use of a resonant configuration allows:

  • Decrease of static friction;
  • High resolution (0.02).
  • Sensitivity = 0.2 V/
  • Operating range = +/- 16


Gyroscope

The device consists of:

  • a glass plate with de-ionized water and a drop of ferrofluid;
  • two electromagnets to impose the harmonic motion at the ferrofluidic volume;
  • a differential inductive readout;
  • two permanent magnets to implement a retaining mechanism against the Coriolis force;


The characterization set-up consists of:

  • a step-motor;
  • an encoder.


resolution:
0.12 rad/sec
sensitivity:
186.8 mV/rad/sec

Vibration Sensor
...to sense the pysical movement of a media connected to the sensor via a beam...

The device consists of:

  • a pipe filled with de-ionized water with a a drop of ferrofluid in;
  • a primary coil to induce the restoring force;
  • two secondary coils to realize a differential inductive readout;
  • a membrane to transfer vibrations to the ferrofluidic drop;


The characterization system consists of:

  • a shaker to produce vibrations through a rigid beam;
  • a laser to measure independently the imposed movement.



The device exhibits a selective
behaviour around 42 Hz and a
useful band up to 50Hz.


Sensor based on Rosensweig Effect

The device consists of:

  • a glass plate filled with deionized water surrounding a small volume of ferrofluid;
  • a permanent magnet placed on the bottom of the glass support to fix the position of the ferrofluid mass;
  • a differential inductive sensing system;


The characterization set-up consists of:

  • a shacker;
  • a sliding system;
  • an OADM-12U6430/S35A laser sensor device.






Uncertainty:
40 mV

Sensitivity:
0.285 V/m



FP3 Pump


The device consists of:

  • a pipe filled with de-ionized water with three drops of ferrofluid;
  • two ferrofluidic valves;
  • a plunger ;
  • an electromagnetic driving system.


Volume for cicle:
0.08 ml 0.01 ml
Flow rate for the minimum cicle (4 s):
1.2 ml/min 0.1 ml/min.

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