BS ISO 17859:2015 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Measurement method of piezoelectric strain at high electric field
4 Measuring environment
The measurement should be carried out in an environment free from acoustic noise and vibrations. It is desirable to control the measurement temperature 25 ± 5 °C and relative humidity less than 60 %.
The test specimen shall be of any ceramics that can be cut into desired shapes such as disks and quadrilateral plates. There is no limit in specimen size and shape, if the specimen is held horizontally with a small tilt.
5.2 Shape and size Specimens are made by cutting out from ceramics or single crystals. The shape of the specimen should be disk or quadrilateral plate, with smooth surfaces. Thickness distribution less than ± 1 % is desirable within the plate. The standard dimensions of the specimen are 0,3 mm – 1,0 mm in thickness, 5 mm – 15 mm in size, and 15 – 25 in the ratio of size to thickness. A desirable example of such disc is 0,5 mm in thickness and 10 mm in diameter.
5.3 Electrodes Electrodes should be deposited on both sides of the specimen plate, leaving the edge region free. This edge region should have an area of less than 10 % of the sample surface. The electrode is desirable with tough adhesion and without deterioration. An example of such electrode metal is Au, Ag and Pt.
5.4 Polarization The specimen should be treated by a poling procedure. Polarized direction should be shown on the specimen surface. Typically the positive side of the sample is marked with a dot or cross. 6 Principle The strain of the specimen is induced by the piezoelectric effect when an electric field is applied between the two electrodes of the specimen. The strain is detected as the thickness variation of the specimen using a displacement meter. The strain vs. E-field curve is drawn, and the piezoelectric constant is calculated from this curve.
7 Measurement equipment
7.1 Equipment Figure 1 shows an example of a system block diagram for piezoelectric strain measurement.
7.2 Components of equipment
7.2.1 Signal generator. A function generator is recommended to generate the triangular waveform with the frequency range of 0,1 Hz to 1 Hz. Figure 2 shows an example of an applied waveform.
7.2.2 Power source. A power source which can generate voltages as high as several kV should be used.
7.2.3 Displacement meter. A measuring accuracy of ± 10 nm is needed for the displacement sensor. Both contact and non-contact sensors can be used. Different kinds of measuring system which have the required measuring accuracy can be used, such as differential inductive displacement gauge, magneto- resistance type linear displacement sensor, laser interferometer, capacitive method, etc.
7.2.4 Monitor. Instruments such as analog-to-digital converters and oscilloscopes are used for monitoring the relation between applied E-field and displacement, and for data acquisition.
7.2.5 Specimen holder. The specimen can be held horizontally or vertically. The specimen is placed between a stationary contact and a moving contact. The tip of the moving contact is recommended to have a sphere shape with a radius less than 2 mm. The tip of the stationary contact should be flat with a diameter less than 30 % of specimen diameter. The mechanical stress to the specimen shall be kept as low as possible in the measurement. The specimen holder has a structure which stably holds the specimen under applied E-field between both electrodes of the specimen. Figure 3 shows an example of specimen holder structure. The bottom of the stationary contact is fixed in a metal base which is connected to the ground. The moving contact is supported by a linear bearing, which is fixed in a polymer block and is connected by a wire to the power source.
7.3 Environment of specimen holder
The specimen holder should be placed on an anti-vibration stage. A cover of the specimen holder is recommended to remove acoustic noise and to maintain a constant specimen temperature. It is effective to prevent discharge by immersing the specimen in isolation oil, although the use of isolation oil is not mandatory.