Advanced Mechanical Stress Sensors for Automotive and Structural Health Monitoring

Transcription

1 Advanced Mechanical Stress Sensors for Automotive and Structural Health Monitoring Daniele Caltabiano Anna omarico Giuditta Roselli Mohammad Abbasi Matteo Cesana Feb 22 nd, 2018 olimi

2 AST - UL&Sensors 2 The team is working on Advanced Sensors (stress, pressure, force,...) Ultra low power processing I (u & DS) RF for IoT connectivity Smart ower (energy conversion and actuators)

3 Outline 3 Automotive sensors iezoresistivity ressure/force sensors Structural health monitoring

4 Outline 4 Automotive sensors iezoresistivity ressure/force sensors Structural health monitoring

5 Electrical conductor Strain gauges 5 Strain gauge Used to measure strain of an object Stretching => narrower and longer => increase resistance Compressing => broader and shorter => decrease resistance 2 (*) From Wikipedia

6 In conducting and semi-conducting materials, changes in inter-atomic spacing resulting from strain affect the bandgaps, making it easier (or harder depending on the material and strain) for electrons to be raised into the conduction band. This results in a change in resistivity of the material. iezoresistivity 6 Silicon crystallographic structure iezoresistivity in Silicon depends on Dopant (p-type vs n-type) Doping concentration Crystallographic orientation Temperature L L T T GF up to type silicon piezoresistivity diagram [010] GF_max [100]

7 ressure sensors 7 Stress ressure Voltage Membrane iezoresistors iezoresistive ressure Sensors Membrane 4x piezoresistors Wheatstone bridge Optional thermal bridge

8 ressure sensors - ackaging Full moulded vs ceramic cavity and gel 8 MEMS LS35HW ASIC CB ackage: Mechanical/Chemical protection (e.g. Wire bonding) Electrical interface

9 Braking System 4 calipers pedal -Sensors in Automotive 9 Engine Control Oil pressure Fuel pressure Barometric air pressure Manifold air pressure Exaust gas Airbag System ressure satellite Occupant detection edestrian detection Others Tire pressure Heating, Ventilation, A/C...

10 Hydraulic pressure sensors 10 Based on ST MEMS technology 16 Bit ADC Embedded cavity Specification example 250 bar full scale Hydraulic (dot4) compatibility -40 / +120 C working temperature Example automotive applications Braking systems Hydraulic connection (tractor-attachment)

11 Chemical Compatibility 11 Dot4 brake fluid is very corrosive Our sensor successfully performed 500 thermal cycles (-55 C C)

12 reliminary pressure tests 12 ST-MEMS pressure sensors in CERDI16 assembly, 2 dices per package with protection gel Functional characterization Characterization pneum with different temperatures - OK

13 ressure sensors - FEM simulations 13 Geometry optimization Membrane diameter or thickness iezoresistors position Verify robustness and reliability

14 Working principle A force is applied on a deformable substrate iezoresistors on the Si chip sense the deformation High load Force sensors External force (50kN/4) 14 Specifications example 50 kn full scale -40, +120 C working temperature Example applications E-bike torque sensor Vehicle transmission torque sensor Dry braking systems

15 Outline 15 Automotive sensors iezoresistivity ressure/force sensors Structural health monitoring

16 Structural Health Monitoring - Objective 16 redictive maintenance Structural Health Monitoring (SHM) by means of sensors embedded in the concrete

17 Application scenarios 17 New structures (pillars and beams) Bridges Buildings Tunnels Tubes Old structures illars

18 Monitor deformation SHM - Tunnels 18

19 SHM - Tunnels 19

20 Tunnel Boring Machine 20

21 Tunnel beams 21 Beam production Weight is 16 T

22 Sensors configuration 22 ATENTED

23 Smart axial sensor 23 Two different sensor are integrated in one package Vertical: Capable of measuring axial stress lanar: Capable of measuring planar stress ATENTED

24 Simulations 24 Concrete creep is well described in Model Code 2010 and generally approximated by exploiting a Kelvin chain Sensor Simulated sensor response to a force step applied to the concrete cube Flat compensated output

25 We faced lots of other problems: Chemical Sensor damage due to high ph during concrete shrinkage Mechanical Concrete voids close to the sensors Other non modeled phenomena Shrinkage and cracking Reality 2 Concrete voids Lab chemical tests Acid solution: HCL, ph=1 Basic solution: NH4OH, ph=12

26 Concrete cube testing 26 May 17 th, olito load test Concrete casting May 4 th Load test: May 17 th Axial out: 650uV/V/Ma

27 Beam test UniRM2 27 Concrete casting: Oct 28 th, /02/2018

28 Tunnel beam UniRM2 28 Concrete casting: July /02/2018

29 Tunnel beam UniRM2 Concrete casting: July /02/2018

30 Sensors for Structural health monitoring Sensor A Ma Time Sensor comp-shrink output [Mpa] 3D-1.08*l Sigma inf

31 Conclusions 31 Basic concept of piezoresistivity Stress sensors example for automotive and structural health monitoring Multidisciplinary approach for sensor design Mechanical analysis for reliability Electrical sensitivity for digital conversion Chemical compatibility to final application scenario Contact us for internship in those fields