Sensors & Actuators Transduction principles 2014-2015 Sensors & Actuators - H.Sarmento
Outline Resistive transduction. Photoconductive transduction (resistive). Capacitive transduction. Inductive transduction. Piezoelectric transduction. Pyroelectric transduction. Photovoltaic transduction. Electromagnetic transduction. Thermoelectric transduction. 2014-2015 Sensors & Actuators - H.Sarmento 1
Modulating sensors Resistive Photoconductive Capacitive Inductive 2014-2015 Sensors & Actuators - H.Sarmento 2
Self generating sensors Piezoelectric Pyroelectric Photovoltaic Electromagnetic Thermoelectric 2014-2015 Sensors & Actuators - H.Sarmento 3
2014-2015 Sensors & Actuators - H.Sarmento 4 Resistive transduction Stimulus converted to a change in resistance. changes in the electrical resistivity r. changes in geometry: l, w and t. A l R r t t w w l l R R r r t w A
Changes in length Changes in the length of the wire by moving a sliding contact: position sensor. R sliding contact l r S l r S 1 R l r S R 2 Resistive transduction also called potentiometric transduction. 2014-2015 Sensors & Actuators - H.Sarmento 5
Changes in resistivity (1) Due to temperature: temperature sensors. 0 0 1 t t r r r 0 resistivity at reference temperature t 0 t0 Due to humidity: humidity sensors. [Source: Jyoti Shah, CSIR] 2014-2015 Sensors & Actuators - H.Sarmento 7
Change in resistivity (2) Due to a mechanical stress: strain gauges, pressure sensors, accelerometers. Piezoresistivity: in semiconductors resistivity highly depends on carriers (electrons and holes) mobility. when a semiconductor is stretched or compressed, the mobility of carriers changes. Resistive/piezoresistive transduction. 2014-2015 Sensors & Actuators - H.Sarmento 8
Photoconductive transduction Changes in resistivity due to incident electromagnetic radiation: photocell. r k E v E v light intensity (lux) k and depend on the material: 0.7 < < 0.9 for CdS (cadmium sulphide). 2014-2015 Sensors & Actuators - H.Sarmento 9
Capacitive transduction Stimulus converted to a change of capacitance. C r0 A d ε o is the absolute permittivity ε r is the relative permittivity changes in the permittivity of the dielectric changes in the area of the plates changes in the spacing between plates r 0 A d 2014-2015 Sensors & Actuators - H.Sarmento 10
Changes in permittivity (1) Due to displacement of the dielectric: position, displacement, and level sensors. C r0 A d Moveable dielectric 2014-2015 Sensors & Actuators - H.Sarmento 11
Changes in permittivity (2) Due to amount of water: humidity (air) and moisture sensors. C r0 A d pourous metallic membrane hygroscopic polymer pourous metallic membrane Due to polymer s polarization: glucose (bio) sensors. Due to biochemical reactions: DNA (bio) sensors. 2014-2015 Sensors & Actuators - H.Sarmento 12
Changes in the area of plates Due to displacement of a plate: position, displacement sensor. Moveable plate 2014-2015 Sensors & Actuators - H.Sarmento 13
Changes in the spacing between plates Due to displacement of a plate: position, pressure sensors. Moveable plate C r0 A d [Source: sensata] 2014-2015 Sensors & Actuators - H.Sarmento 14
Inductive transduction Stimulus converted to a change of self (or mutual) inductance. L n o r 2 Al changes in the number of turns changes in the permeability of the core 2014-2015 Sensors & Actuators - H.Sarmento 15
Changes in the number of turns Due to displacement of a wiper: position, displacement sensors. Self inductance displacement. L L n o r 2 Al linear rotary 2014-2015 Sensors & Actuators - H.Sarmento 16
Changes in permeability (1) Due to the displacement of the core: displacement sensor. Self inductance L n 2 o Al r r1 L 1 L 1 r 2 r1 L2 L 1 2014-2015 Sensors & Actuators - H.Sarmento 17
Changes in permeability (2) Due to the displacement of the core: displacement sensor. Self inductance L 1 r1 L 2 r1 r 2 r1 L2 L 1 2014-2015 Sensors & Actuators - H.Sarmento 18
Change of permeability(3) Due to the displacement o the core : displacement sensor. Mutual inductance [Source: Jacob Fraden, 2010] 2014-2015 Sensors & Actuators - H.Sarmento 19
Piezoelectric transduction (1) Due to mechanical stress: microphones, accelerometers, ultrasonic detectors. Stimulus converted to a change in electrostatic charge (or voltage). [Source: Jacob Fraden, 2010] Separation of electric charge across the crystal lattice. 2014-2015 Sensors & Actuators - H.Sarmento 20
Piezoelectric transduction (2) [Source: Jacob Fraden, 2010] The charge produced depends on the piezoelectric constant of the device. Q k f The capacitance is determined by the area, the width, and the dielectric constant of the material. V kf C k f o r x A 2014-2015 Sensors & Actuators - H.Sarmento 21
Piezoelectric model A charge source with a shunt capacitor or a voltage source with a series capacitor. [Source: Texas Instruments] The resistance accounts for the dissipation of static charge. 2014-2015 Sensors & Actuators - H.Sarmento 22
Pyroelectric transduction (1) Due to a temperature gradient in a pyroelectric material (PEM): motion, temperature, chemical and bio sensors. Stimulus converted to a change in electrostatic charge (or voltage). Change in temperature causes change in spontaneous polarization and results in change in electric charge. 2014-2015 Sensors & Actuators - H.Sarmento 23
Pyroelectric transduction (2) When the detector absorbs radiation, its temperature and hence its polarization changes, thus resulting in a surface charge on the capacitor plates. The charge produced depends on the piezoelectric constant of the device. L V P T C PL T o r A [Source: Jacob Fraden, 2010] Q PT P - pyroelectric coefficient 2014-2015 Sensors & Actuators - H.Sarmento 24
Pyroelectric model A charge source with a shunt capacitor. Q PT V P T C PL T o r A The resistance accounts for the dissipation of static charge. 2014-2015 Sensors & Actuators - H.Sarmento 25
Photovoltaic transduction Due to incident light radiation in a junction: photodiodes. Stimulus converted in a voltage induced by the absorbed photons. - - - - - - - - - - - + + + + + + + + + + + + - + - + - + n-type semiconductor p-type semiconductor 2014-2015 Sensors & Actuators - H.Sarmento 26
Photovoltaic transduction Due to incident light radiation in a junction: photodiodes. Stimulus converted in a voltage induced by the absorbed photons. - - - - - - - - - - - + + + + + + + + + + + + + - + - + - - - - n-type semiconductor p-type semiconductor 2014-2015 Sensors & Actuators - H.Sarmento 27
Photovoltaic transduction Due to incident light radiation in a junction: photodiodes. Stimulus converted in a voltage induced by the absorbed photons. - - - - - - - - - - - - - + + + + + + + + + + + + + + + - - - - n-type semiconductor p-type semiconductor 2014-2015 Sensors & Actuators - H.Sarmento 28
Electromagnetic transduction Due to magnetic flux: magnetic fields, position, and displacement sensors. Stimulus converted to a voltage (electromotive force) induced in a conductor by a change in the magnetic flux. 2014-2015 Sensors & Actuators - H.Sarmento 29
Thermoelectric transduction Due to a difference of temperature between the junction of two dissimilar materials (Seebeck effect): temperature sensors. Stimulus converted to a change in a voltage. Material A Material B [Source: Jacob Fraden, 2010] 2014-2015 Sensors & Actuators - H.Sarmento 30
Bibliography Jacob Fraden, Handbook of modern sensors: physics, designs, and applications, Springer, 4 th edition, 2010 JonWilson, Sensor Technology Handbook, 2005. Jeffrey Fortin, Chapter 2 - Transduction Principles, Springer, http://www.springer.com/cda/content/document/cda_downloaddocument/9780387362298- c1.pdf?sgwid=0-0-45-736504-p173666705 Winncy Y. Du, Resistive, Capacitive, Inductive, and Magnetic Sensor Technologies, CRC Press, 2015 Jeffrey Fortin, Chapter 2 transduction principles, Functional Thin Films and Nanostructures for Sensors Chapter 2: Sensor Characteristics and Physical Effects, http://www.seas.upenn.edu/sunfest/docs/papers/12- ohiri.pdf V. Tsoutia, C. Boutopoulosb, I. Zergioti b, S. Chatzandroulisa, Capacitive microsystems for biological sensing, Biosensors and Bioelectronics, 2011 Jacob Richter, Piezoresistivity in Microsystems, PhD Thesis, Technical University of Denmark, 2008 2014-2015 Sensors & Actuators - H.Sarmento 31