Activity: A Peizoelectric Smart Sensor PVDF-A polymer with many uses

What is a Smart Sensor? We will use the term “Smart Sensor” to refer to systems that employs a sensor device mated to microelectronics. In this activity we will use metal coated PVDF films as our sensor system and a computer will take the place of the microelectronics. The system used in this activity is not engineered to minimize size and power consumption but clearly those would be goals in any widely deployed commercial device.

Preparation for Activity Items Needed: PVDF sensor films; electronic components for circuits A and C (to be described) ; computer with data acquisition hardware/software. An understanding of piezoelectric effect An understanding of the role of molecular structure in determining the peizoelectric properties of PVDF

Discussion Points What is the piezoelectric effect? Why is the  form of PVDF piezoelectric? How is the  form of PVDF produced?

Design Problems Design a PVDF based smart sensor system to give point in time information on the number of open spaces in a parking garage Design a sensor system to measure the velocity of a falling ball Design a sensor system to measure the vibrations in a factory building

Representations of the molecular structure of the vinylidene difluoride (VD) monomer and of the  and  forms of the PVDF polymer. PVDF-  form PVDF-  form VD-wire VD-space filling

Commercially available metal coated piezoelectric PVDF sensor elements

Electronic Circuits PVDF generates a measureable voltage Circuits with a very high Input impedance required Low power consumption, battery operated systems desirable for portability. (A) Impedance Adaptor, Voltage Follower (B) Electric Charge Measurement (C) Differential Amplifier, for measuring relative/combined signals

Deflection Sensor Two PVDF sensors- the sensors are mounted on both sides of a flexible material. The response of these films capable of quantifying the magnitude, speed and direction of the flexion movement. Circuit (A) used to follow voltage changes Circuit (C) is used to obtain a composite signal from the two sensors

Output PVDF sensors on flexed ruler- Note polarity (green/yellow). Blue represents output of circuit (C).

Output PVDF sensors on flexed ruler damped motion-Note polarity (green/yellow) and combined signal.

Plot of ln(Displacement) vs time showing that the motion of the solid material is described by the equation D=D 0 exp (- t/  ); this is the equation for an under damped oscillator.

PVDF sensors mounted on a solid substrate and connected to circuit (A). Circuit (A) output is directed to a USB data acquisition system interfaced to a laptop.

USB data port interfaced to laptop computer gives system properties of a “smart sensor”.

Discussion Points II How can we distinguish the piezoelectric and pyroelectric responses exhibited by a PVDF film? What is needed in terms of electronics to produce a peizoelectric PVDF smart sensor? Suggest new applications of PVDF piezoelectric sensors?