Microsensors. G.K. Ananthasuresh Professor, Mechanical Engineering Indian Institute of Science Bangalore, , India

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1 Microsensors G.K. Ananthasuresh Professor, Mechanical Engineering Indian Institute of Science Bangalore, , India

2 What are sensors? Sensors measure something, which we call a measurand. There are lots of sensors Based on the measurands Based on the way they measure

3 Sensors based on the measurand Accelerometer Measures acceleration Gyroscope Measures angular rate Pressure sensor Measures pressure of a fluid Viscosity meter Measures viscosity of a fluid Anemometer Measures wind speed Bolometer Measures radiation Blood analyser Measures the presence or quantity of a chemical species Virus detector Etc. Detects the presence of a virus

4 Based on the measurement technique (e.g., accelerometer) An apple and a string Capacitive Piezo resistive Fluid level Tunnelling current Laser interferometry Open loop or closed loop a mg ma a tan a mg g m ma g tan g

5 Based on the measurement technique (e.g., accelerometer) A mango and a string Capacitive Piezo resistive Fluid level Tunnelling current Laser interferometry Open loop or closed loop

6 Based on the measurement technique (e.g., accelerometer) A mango and a string Capacitive Piezo resistive Fluid level Tunnelling current Laser interferometry Open loop or closed loop

7 Based on the measurement technique (e.g., accelerometer) An apple and a string Capacitive Piezo resistive Fluid level Tunnelling current Laser interferometry Open loop or closed loop a

8 Based on the measurement technique (e.g., accelerometer) A mango and a string Capacitive Piezo resistive Fluid level Tunnelling current Laser interferometry Open loop or closed loop

9 Based on the measurement technique (e.g., accelerometer) An apple and a string Capacitive Piezo resistive Fluid level Tunnelling current Laser interferometry Open loop or closed loop

10 Sensors are transducers Transducers covert one form of energy to another form. Measurand Sensor Output Colour change Shape change State change Property change Change in response etc.

11 A Sensor s output is usually electrical. Sensors usually covert a measurand to an electrical quantity. Measurand Sensor Output Voltage Current Resistance Capacitance Inductance etc.

12 Quantitative vs. qualitative Presence or absence of the measurance Is it there or not? Qualitative High or low or medium? Quantitative How much is there precisely? We want a number

13 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth Magnitude of the output signal per unit measurand.

14 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth Smallest magnitude of the measurand that can be reliably and repetitively detected.

15 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The difference between the maximum and minimum values of the measurand that can be detected.

16 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The difference between the maximum and minimum values of the output signal.

17 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The extent over which the output signal is linear with respect to the measurand.

18 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The difference between the output signals for the same magnitude of the measurand while the measurand is increasing and decreasing.

19 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The time lag between the instance the measurand changes and the instance the output signal changes completely.

20 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The extent of change in the output even when the measurand is constant.

21 Characteristics of a sensor Sensitivity Resolution Range Full scale output (FSO) Linearity Hysteresis Response time Drift Bandwidth The range of frequencies of the time varying measurand over which the sensor responds reliably.

22 The same physical element may be able to sense multiple things Boustraw et al. 1990; flow rate sensor Can also measure Temperature, Vibration Sound Radiation Chemical species etc.

23 Some microsensors Capacitive accelerometer Piezo resistive pressure sensor Conductometric gas sensor Virus detecting micro cantilever Fibre optic crack sensor Portable blood analyser

24 Micromachined accelerometers: two examples ADXL202E by Analog Devices Sandia National Laboratories M. Lemkin, M. Ortiz, N. Wongkomet, B. Boser, and J. Smith, ʺA 3 axis surface micromachined sigma delta accelerometer,ʺ Proc. ISSCC ʹ97, pp , 1997.

25 Measurement of displacement k m b x() t There are several other ways of detection. Capacitve Piezoelectric Piezoresistive Magnetic Optical Single axis or multiple axes? Cross axis sensitivity? Over range protection? Direct mode Force feedback mode

26 A tradeoff in (micromachined) accelerometers k Seismi c mass m Over range protection b x() t mx bx kx ma At steady state kx f x ma a But, resonance k m m k Sensitivity Resonance frequency High sensitivity implies low resonance frequency; Low resonance frequency implies small operational range. Tradeoff is necessary

27 The effect of damping m k b 2 km under damping/resonating b 2 km over damping b 2 km Critical damping f Over damping reduces the useful frequency range. Under damping causes peaking that may lead to mechanical failure. Thus, damping is usually necessary but not too much or too little.

28 Getting linearity Good linearity 0A 0A 0A 0A xd x V d x d x d x d x out V V V V for x d A 2 0A d x d d d

29 Capacitance extraction circuit Chopper stabilization with boosted gain and correlated double sampling with crosscoupled switches. This helps reduce 1/f noise and offset. 1 part per million resolution 2.3 mv noise

30 System level simulation Mechanical Brownian noise + ε 0 A/(d+x) +V m C1 V s V 4 m a m k d V n Electronic noise and offsets Acceleration signal a+a n x Mass and suspension feedback ε 0 A/(d x) C2 V m A demodulator PID V out Low pass filter

31 A real accelerometer made in IISc The waveforms show the responses of the standard STM accelerometer and IISc s accelerometer under test when a 0.5 g is applied. Yellow : Standard accelerometer Pink : SOIMUMPs accelerometer Sambuddha Khan Thejas Annathasuresh Bhat ( )

32 Accelerometer: a summary Category Purpose Key words Principle of operation Application(s) Summary Sensor Measures the acceleration of the body on which this sensor is mounted. Proof-mass Suspension Converts the displacement caused by the inertial force on the proof-mass to a voltage signal via change in capacitance between movable and fixed parts. Automotive, aerospace, machine tools, bio-medical, etc.

33 A commercial high resolution accelerometer QA2000 Qflex accelerometer From Honeywell. ~3.2"

34 Piezoresitive pressure sensor Category Purpose Key words Principle of operation Application(s) Summary Sensor Measures the pressure, typically of gases or liquids. Piezoresistivity, diaphragm The external pressure loading causes the deflection, strain, and stress on the membrane. The strain causes change in the resistance of a material, which is measured using Wheatstone bridge configuration. Automotive industry, aerospace applications, appliance industry, bio-medical etc.

35 Motorola s pressure sensor

36 Conductometric gas sensor Category Purpose Key words Principle of operation Application(s) Summary Sensor It detects and quantifies the sources of a gas, i.e., its concentration Catalyst, combustible, adsorption, desorption The principle is that a suitable catalyst, when heated to an appropriate temperature, either promotes or reduces the oxidation of the combustible gases. The additional heat released by the oxidation reaction can be detected. The fundamental sensing mechanism of a gas sensor relies on a change in the electrical conductivity due to the interaction process between the surface complexes such as O -,O 2 -,H +,andoh - reactive chemical species and the gas molecules to be detected. Environmental monitoring, automotive application and air conditioning in air planes, spacecrafts and houses and sensor networks, ethanol for breath analyzers and food control application etc.

fabrication process: Gas sensors are fabricated using the single crystalline SNO 2

37 Conductometric gas sensors Nanomaterials Research Inc. gas sensors Typical materials used: Films of metal oxide like SnO 2 and Tio 2 Sample fabrication process: Gas sensors are fabricated using the single crystalline SNO 2 nanobelts. Nanobelts are synthesized by thermal evaporation of oxide powders under controlled condition without the presence of a catalyst.

38 A conductometric gas sensor: how doe it work? Pre adsorption of oxygen on semiconducting material surface. Adsorption of a specific gas that is to be detected. Reaction between oxygen and the adsorbed gas. Change in the conductivity of the resistor element. Desorption of reacted gas on the surface for re use. Conductivity: It is a property of material that quantifies the material s ability to conduct electric current when an electric potential (difference) is applied. It depends on the number of free electrons available. Adsorption: Adsoprtion is the process of collection and adherence of ions, atoms, or molecules on a surface. This is different from absorption, a much more familiar term. In absorption, the species enter into the bulk, i.e., the volume. On the other hand, in adsorption, they stay put on the surface. Desorption: This is the reverse of adsorption; species (ions, atoms, or molecules) or given out by the surface. Combustion: It is a technical term for burning. It is a heat-generating chemical reaction between a fuel (combustible substance) and an oxidizing agent. It can also result in light (e.g., a flame).

39 Hand held blood analyzer Abbott Point of Care With a few drops of blood, under a minute it gives blood analysis: gases, chemistry, cardiac markers, etc. The chip is small but the system is big.

40 Main points Sensors are transducers. Usually the output is electrical. Characteristics of sensors Miniaturization helps Because the cost, size, and power consumed are reduced while improving the performance. A lot of commercial microsensors are now available. The scope for further research and development is unlimited.

10 Measurement of Acceleration, Vibration and Shock Transducers

10 Measurement of Acceleration, Vibration and Shock Transducers Chapter 10: Acceleration, Vibration and Shock Measurement Dr. Lufti Al-Sharif (Revision 1.0, 25/5/2008) 1. Introduction This chapter examines the measurement of acceleration, vibration and shock. It starts