FYS 3231/ 4231 Sensors and measurement technology 6 Principles of Sensing (1/2) Autumn 2022 Anja Kohfeldt Administrative • Deadline for chosing presentation topic of Friday! 43 44 45 date name topic Tue 25-10 Movement, Position and Speed Ralv Glasø Sverdrup Holmsen Radar, GPR, Ultra sonic, micro wave Diana Rohollahi Opto-electric motion sensors Yoon Jung Oh Inductive & magnetic sensors Gyroscopes Mustafa Najjar Accelerometers Tue 01-11 Force, pressure, flow Daniel Beckhaug Force sensors Dennis Edward Kalinowski Optical strain gauges Yilmaz Turkyilmaz Classical pressure sensors Rein Åsmund Torsvik Vacuum sensors Flow basics & thermal transport sensors Mohammed Zain Farooqi MEMS and other flow sensors (pick 4 ) Tue 08-11 acoustics and humidity Standard mics Optical, piezoelectric and dynamic mics Humidity 1 Humidity 2 Sigrid Videm Gravitational wave detection (LIGO, VIRGO, KAGRA) Tue 15-11 light and radiation Jan Harald Aasen Photo diodes, -transistos - resistors (quantum detectors) Even Tobias Eriksen Imaging detectors (CCD, CMOS) Georg Scheurecker Thermal radiation detecors (bolometers, MCT) Silje Vik Scintillators & Gamma spectroscopy Lisa Leonhartsberger Ionizing detecors Tue 22-11 temperature and chemical/bio sensors Øyvind Ringen Ceramic and resistive temperature sensors Youssef Abdulqader Aldabak Semiconductor and thermo-electric sensors Samson Fekade Badishe Other thermo sensors (optical, acousitcal, piezo) KeithFYS Finlayson 3231/4231, høst 2022Chemical sensors Kristiane Holm Biological sensors, bioimpedance • Presenting is mandatory for final exam! 46 47 chapter 7, 8, 9 7.1-4 7.8, 8.5 8.4 9.2 9.3 10, 11, 12 10 10+ 11.1-11.6 11.10 12.1-12.3 12.4-12.10 13, 14 13.1-13.4 13.5-13.7 14.1-14.4 14.5-14.8 15, 16 15.1-15.5 15.6 15.8 16.1 16.2 17, 18 17.3-17.5 17.6-17.8 17.9-17.11 18.1.1 18.3-18.42 18.1.2, other Overview • Recap • Physical Principles of Sensing – – – – – – Electric Charges, Fields, Potentials Capacitance Magnetism Hall Effect Induction Resistance FYS 3231/4231, høst 2022 3 Recap In your lab groups: • Test Plan: – Is your test plan for the lab task sufficient to let someone else conduct the measurement? – What is missing or need to be improved? • Lab Journal: – Monday groups: can you reproduce your last measurement? – Friday groups: what do you need to record for a calibration measurement? FYS 3231/4231, høst 2022 4 Direct Sensor vs. Hybrid Sensor Recap! Direct sensor Hybrid sensor • Direct energy conversion into generation or modulation of electrical signal, one step • E.g. thermopile, photo diode • Needs one or more transducers in addition to direct sensor • E.g. chemical sensors, microphone FYS 3231/4231, høst 2022 5 Recap! Direct sensors • Having a look into the black box x[n] stimulus S(x[n]) sensor FYS 3231/4231, høst 2022 y[n] electrical signal 6 Electric charge • Q in [C] (1C= 1 As) – Q for quantum, elementary charge – π = π = 1,602 β 10−19 πΆ • Positive and negative • Forming a field between different charge points FYS 3231/4231, høst 2022 7 Electric field • Defined as force on a charge: Coulomp law πΉΤ¦ππππ = 1 π1 π2 4ππ0 π 2 • Electrical field strengh πΈ = πΉΤ¦ππππ π0 = π 4ππ0 π 2 π π • Permittivity π = π0 π , – electrical field constant π0 = 8,854 ⋅ 10−12 π΄π ππ – measure of the electric polarizability of a dielectric FYS 3231/4231, høst 2022 8 πΉΤ¦ππππ π πΈ= = π0 4ππ0 π 2 π = π0 π Electric field • Electric displacement field π· = ππΈ πΆ ′ π2 – Bond charge separation in dielectric materials • Electric flux ΦπΈ = β«π΄ ππ· Χ¬β¬Τ¦ [C] – Description of fields – “number of field lines” passing a given area A FYS 3231/4231, høst 2022 9 Dipole in electric field πΉΤ¦ππππ 2π π πΈ= = π0 4ππ0 π 3 r FYS 3231/4231, høst 2022 10 Charge in solids FYS 3231/4231, høst 2022 11 Triboelectric effect • Electric charge separation due to object movement • Contact electrification of certain materials • Cause of static electricity FYS 3231/4231, høst 2022 12 + Triboelectric effect Hair, oily skin Nylon, dry skin Glass Acrylic, Lucite Leather Rabbit's fur Quartz Lead Cat's fur Silk Aluminium Paper (Small positive charge) Cotton Wool (No charge) 0 Steel (No charge) Wood (Small negative charge) Amber Sealing wax Polystyrene Rubber balloon Hard rubber Nickel, Copper Brass, Silver Gold, Platinum Polyester Plastic wrap Polyethylene (like Scotch tape) Polypropylene Vinyl (PVC) Silicon Teflon (PTFE) Silicone rubber FYS 3231/4231, høst 2022 13 Capacitance • the ratio of the change in electric charge q of a system to the corresponding change in its electric potential V • πΆ= π π • Flat capacitor: • πΆ= π΄ π0 π π • dielectric FYS 3231/4231, høst 2022 14 Capacitive sensors • One of parameters defining C is modulated • πΆ= π΄ π0 π π →V= π πΆ • Different geometries to modulate, e.g. cylindrical capacitor • Dielectric constant π negative temperature and frequency dependent – → used in integrated sensors FYS 3231/4231, høst 2022 15 Temp. dependency κ for water Capacitive sensors FYS 3231/4231, høst 2022 Material Κ @ troom Air/vacuum 1 Rubber 7 Ti ceramics 14-110 Diamond 5,5 Glass 4-4,5 Compound TFC 300-5000 Water 78,5 16 Electric vs. Magnetic field Electric Magnetic Created around electric charge Nature Proportional to the electric charge πΉππππ = ππΈ Force β΄ to magnetic field Movement Created around …? Field effect Inductive Poles Dipole Field strength π»= πΉΤ¦πππ π0 πΌ π [1 π΄ ] π Displacement field Flux FYS 3231/4231, høst 2022 17 Electric vs. Magnetic field Electric Magnetic Created around electric charge Nature Created around moving electric charge and magnets Proportional to the electric charge πΉππππ = ππΈ Force Proportional to charge and speed of electric charge β΄ to magnetic field Movement Capacitive Field effect β΄ to the electric field Inductive Monopole or Dipole Poles Dipole πΈ= πΉΤ¦ππππ π0 [1 π· = π0 ππ πΈ Ψ = β«π΄π π· Χβ¬Τ¦ π π π πΆ = 1 ] πΉπππ = π π£ π΅ π ππ(Θ) Field strength πΆ ] π2 Displacement field [1πΆ] Flux [1 FYS 3231/4231, høst 2022 π»= πΉΤ¦πππ [1 π0 πΌ π π΅ = π0 ππ π» Φ = β«π΄π π΅ Χβ¬Τ¦ π΄ ] π [1π] [1ππ = 1ππ2 ] 18 Magnetism • Force field between pair of magnetic poles (N,S) based on atoms and arrangement – permanent magnets: spinning e- around nucleus – or caused by electric current in conductor FYS 3231/4231, høst 2022 19 Magnetism Permanent • Ferromagnetics and special alloys with rare earth materials, Alnico, RE-Cobalt Coils • Conductor in cylindrical coil form result in uniform magnetic field in center • π΅ = π0 ππ FYS 3231/4231, høst 2022 20 Magnetism Paramagnetism Diamagnetism • • • • • Due to unpaired electron movement Induced magnetic field in direction of applied field No memory effect w/o mag. field Example: H • • • Repulsive force by induced mag. Field in opposite direction Paired electrones Example: Bismut Superconductor! FYS 3231/4231, høst 2022 Ferromagnetism • Magnetic dipoles pointing in same direction 21 Magnetoresistive effect • Sideways force FB on charge q0 traveling with velocity in magnetic field B → Spiral movement of charge → «longer way» = change in resistace πΉΤ¦π΅ = π0 ππ΅ sin π FYS 3231/4231, høst 2022 22 Hall Effect d • Voltage difference in a current leading conductor in stationary magnetic field due to force πΉΤ¦π΅ = π0 ππ΅ sin π • Hall voltage: πΌπ΅ ππ» = πππ Charge density, Hall constant, material dependent FYS 3231/4231, høst 2022 23 Faraday’s law • Prediction of how magnetic fields will interact with an electric circiut to produce an electromotive force • → electromagnetic induction FYS 3231/4231, høst 2022 24 Faradays induction experiment I FYS 3231/4231, høst 2022 25 Induction • Induced voltage, or electromotive force equals rateat which magnetic flux through circuit changes • π= πΦπ΅ −π ππ‘ = π π΅π΄ −π ππ‘ = ππ −πΏ ππ‘ • Changing magnetic field B or area of circuit A – Misplacing B source with respect to receiving circuit (moving or changing orientation) – Varying current in coil producing B – Changing geometry of pick-up circuit FYS 3231/4231, høst 2022 26 Induction Inductance πΦπ΅ πΏ= = π0 ππ π2 ππΊ π FYS 3231/4231, høst 2022 27 Induction: Lenz Law • “The induced current will appear in such a direction that it opposes the current that produced it.“ • Broad applications: – Electromagnetic breaking – Metal detectors – Induction cooktops FYS 3231/4231, høst 2022 28 Resistance • Electrones moving in materials along electric field • Material property: ability to pass charges • π = π πΌ π [1 π΄ = 1Ω] π π π΄ • π = ρ specific resitivity FYS 3231/4231, høst 2022 29 Temperature sensitivity of a Resistor • Specific resistivity is temperature dependent π‘ − π‘0 π = π0 1 + πΌ π‘0 • Linear approximation, valid for defined temperature ranges. • In reality often non-linear, higher-order polynominals • Metals: PTC • Semicondu. & oxides: NTC • Conventional resistor with πΌ = 10−5 or lower FYS 3231/4231, høst 2022 30 Strain Sensitivity • Measure of mechanical deformation • Effects geometry and specific resistivity • → piezoresistivity • Stress: π = • • πΉ π = ππ πΈ π = πΈπ E Young modulus of material E strain • π = π π π΄ = π2 π volume π FYS 3231/4231, høst 2022 31 Strain Sensitivity • Applications: pressure weight FYS 3231/4231, høst 2022 acceperometers 32 Moisture Sensitivity of R • Some materials with π sensitive for moisture • Conductors covered in hygroscopic material = hygristors FYS 3231/4231, høst 2022 33 summary • Electric and magnetic fields with vector force on charges • Materials characteristics may change with temperature, moisture, external stress, that influences capacitance and/or inductance • Test setup designs allowing for modulation (geometry) as sensors FYS 3231/4231, høst 2022 34 Next time: – More sensing effects • Piezoelectric effect • Pyroelectric effect • Thermoelectric effects – Material behaviour in environments • Sound waves • Thermal material properties • Heat transfer FYS 3231/4231, høst 2022 35
