Piezoelectric sensing and actuation CEE575

Transcription

1 Piezoelectric sensing and actuation CEE575

2 Sensor: Mechanical energy to electrical energy Actuator: Electrical energy converted to mechanical energy (motion)

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5 Materials For many years, natural crystals (such as quartz and tourmaline) were used exclusively for piezoelectric sensors Neural Polarized Recently, man-made Piezoelectric ceramics have replaced natural materials Ceramics typically have crystal structure, in the center of which is a small tetravalent ion (e.g. Barium) Most recently, it was discovered that lead zirconate titrate (PZT) materials exhibited the better operating temperatures PZT = Pb[Zr (x) Ti (1-x) ] Ceramics can be hundreds of times more sensitive than natural crystals

6 Behavior of piezoelectric ceramics Due to charge dissipation, a voltage will only be measurable if the applied force is dynamic. If the force stops pushing on the element, the voltage will drop to zero.

7 Voltage vs. mechanical stress

8 Manufacturing piezoelectric sensors

9 HOW PZT Ceramics are made 1. Mix ingredients(powder) in specific proportions (manufacturer specific). 2. Heat and mix with binder material 3. Form into a shape (disk, rod, etc.) and let cool. 4. Heat to slightly below the Currie Temperature ( and expose to electric field (DC current). This will cause the internal lattice s field to align. The direction of the applied electrical field is know as the direction of polarization. 5. Once the applied field is removed, the dipoles will stay aligned in this induced orientation.

10 Piezoelectric ceramics

11 Piezoelectric constants (see notes )

12 Piezoelectric Sensors Compressive Flexural

13 Accelerometers and stacks

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20 Example application Uses the analysis of transient stress waves to study material behavior such as friction, impact, and fracture. In order to use radiated stress waves to study physical phenomena, we must have a good understanding of the way waves propagate, the way seismic and Nano-seismic sources can be represented, the way waves can be measured, and how to manipulate recordings of waves (signals) for enhanced understanding. Source: McLaskey, Glaser

21 Made possible by high fidelity sensors (shown below), developed in the Glaser lab, which are sensitive to surface normal displacements down to 1 pm in amplitude (1 x 10^-12 m) in the frequency range of ~8 khz to ~3 MHz.

22 Ball drop experiment

23 Drying Shrinkage

24 Gregory C. McLaskey: Drying Shrinkage Cracking in Concrete Project Cast a number of small concrete specimens, such as the one shown below, allowed them to cure for only 24 hours and then took them partially out of the mold and allowed one surface to dry. I instrumented the mold with an array of Glaser-type high fidelity conical peizoelectric sensors and monitored the concrete specimen for vibrations produced from cracking. The specimen shown below was instrumented with 14 sensor and was continuously monitored for 17 days.

25 Assembled sensors Pickup Accelerometer

26 Advanced guitar pickup design

27 Optimal sensor placement on guitars

28 Commercial version Intuitivepickups.com

29 Macro composite fiber Latest advances in Piezoelectric sensing:

30 System Architecture Connector Micro Controller Haptic Driver MFC Pipe Transmitter Micro Controller Haptic Driver Magnetic Base MFC MFC Pipe Receiver Macro Fiber Composite (MFC)

31 Initial laboratory experiment Successfully transmitted 10-bit data packet across 1.2m PVC pipe

32 Field experiment: characterizing the channel Near construction site Central transmitter Two receivers (40m, 70m) 1m below ground Source: Joseph, Kerkez 2014

33 Measuring sound

34 Ultrasonic depth sensors Calculate the distance to an object by measuring the return time of an acoustic signal Piezo

35 Ultrasonic actuators Adapted from: Ultrasonic sensors are devices that use electrical mechanical energy transformation to measure distance from the sensor to the target object. Ultrasonic waves are longitudinal mechanical waves which travel as a sequence of compressions and rarefactions along the direction of wave propagation through the medium.

36 Bottom and internal structure

37 Resonator As shown in the above images, a disc and the metal cone which is the heart of the ultrasonic sensor is glued to the base. The top most metallic conical cup also known as the resonator is used to efficiently radiate the ultrasonic wave generated (also concentrate the waves in case of ultrasonic receiver). The round shaped sheet is a disc and also called vibrator generates the ultrasonic waves. The resonator is soldered on the vibrator.

38 Wiring The unimorgh disc is electrically connected with the external leads through two wires. It is backed by a block of damping material that suppresses the piezoceramic material after it generates the ultrasonic waves. As shown in the above image, there is a small difference in construction of ultrasonic transmitter and receiver respectively.

39 Piezo elements Distance Calculation The ultrasonic sound travels in the atmosphere and by striking with the target object, a fraction is reverting back. Once the ultrasonic waves are transmitted through the transmitter and echo is sensed by the receiver the distance can be calculated using this equation: Distance = elapsed time x speed of sound/2

40 See notes Measuring wind speed: Sonic anemometers

41 3d Sonic anemometer examples ds

42 2D Sonic anemometers With some simplifications, we can assume that the wind direction is negligible in certain directions (e.g. vertical) to obtain relations for 2D or 1D sonic anemometers