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Piezoelectric Strain Rate Sensors

IP.com Disclosure Number: IPCOM000108007D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 4 page(s) / 129K

Publishing Venue

IBM

Related People

Lee, CK: AUTHOR [+2]

Abstract

Disclosed is a class of devices that directly measure the strain rate at a point of a structure. This class of sensors include a local strain rate sensor, a uniaxial strain rate sensor, a shear strain rate sensor and several types of strain rosettes, all of which can be created by interfacing piezoelectric laminates with current amplifiers.

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Piezoelectric Strain Rate Sensors

       Disclosed is a class of devices that directly measure the
strain rate at a point of a structure.  This class of sensors include
a local strain rate sensor, a uniaxial strain rate sensor, a shear
strain rate sensor and several types of strain rosettes, all of which
can be created by interfacing piezoelectric laminates with current
amplifiers.

      The current signal i(t) enclosed by the surface denoted by A of
the piezoelectric laminate can be shown to be (1)

                            (Image Omitted)

when a current amplifier is connected to the piezoelectric lamina
(Fig. 1).  Here e31(r), e32(r) and e31(r) are the piezoelectric
stress/charge constants of the piezoelectric material written with
respect to the coordinate axes of the testing structure and can be
changed by varying the skew angel r (1,2).  Furthermore MS1/Mt,
MS2/Mt are the extensional strain rates along the 1 and 2 axes,
MS6/Mt is the engineering shear strain rate (3).

      If the size of the piezoelectric lamina is small compared to
the test structure, the strain rate is almost constant within the
sensor area A and Eq. (1) can be simplified to be
In this case, a sensor which measures an average strain rate at a
point of the structure is generated.

      From Eq. (2), one can see that the simplest way of removing the
cross-axis sensitivity of a piezoelectric strain rate sensor is to
choose a material with e32 = e36 = 0.  However, this approach is
either not feasible or not the most cost-effective way for most of
the cases.  One of the main concepts disclosed in this article is
that a uniaxial strain rate sensor can be designed by matching the
anisotropic property of the piezoelectric material with the sensor
size and/or sensor gain.  Taking polyvinaylidene fluoride (PVF2) as
an example, one of the embodiments that can be used to create a
uniaxial strain rate sensor is shown in Fig. 2a, where
Combining Eqs.(2) and (3), the signal from the uniaxial strain...