1

I am currently studying Ultrasonic transducers – Materials and design for sensors, actuators and medical applications by Kentaro Nakamura. Chapter 1.2.2 Piezoelectricity says the following:

Piezoelectricity means electricity derived from pressure (Moulson and Herbert, 2003: 339-410). Thus, the direct piezoelectric effect, defined by the Curie brothers and illustrated in Fig. 1.4(a), is the generation of electricity from pressure, and the converse piezoelectric effect is the generation of pressure from electricity, shown in Fig. 1.4(b). enter image description here

I'm a novice to electronics, so I'm not totally sure what's being depicted in these circuit diagrams of figure 1.4. I know that the circles with the positive and negative ends are voltage sources, and I know that \$P\$ is the polarisation. So what is being depicted in these circuit diagrams of figure 1.4

The Pointer
  • 1,241
  • 1
  • 11
  • 24
  • There's an arrow missing from the diagram. Bottom Left should have 2 arrows squeezing the piezo (like bottom R).This shows the sample getting thinner, longer as you squeeze it, producing +V. Above it, what happens as you stretch it (producing -V); above that, the sample at rest. RHS shows how it behaves when you apply voltage. –  Dec 14 '20 at 20:00
  • Piezoelectric crystals develop a voltage when compressed. They also will compress or expand when a voltage is applied to them. Works both ways. They are used often when you want to precisely move something very small distances, like the head of an electron microscope for example. – Kyle B Dec 14 '20 at 20:11
  • The circles with -0+ are meant to show *voltmeters* (analog ones) and the arrow is meant to show the needle on the meter! That's not a standard symbol, but the standard symbol doesn't have a needle, so – user253751 Dec 14 '20 at 20:32
  • OTOH, in the right hand column, the pairs of dots (light gray dot, above text, above darker gray dot) _are_ supposed to represent voltage sources. The symbols in the diagrams are unconventional. – Solomon Slow Dec 14 '20 at 21:08
  • @BrianDrummond Why, for instance, in the case of the bottom left example, does the arrow point to the positive, whereas on the right-hand side it says "V \$-\$ve"? So they're opposites (except for the 0 voltage case). It's very confusing. – The Pointer Dec 14 '20 at 23:45
  • @SolomonSlow So the dots on the right-hand side represent voltage sources, and the circles on the left-hand side represent voltmeters? And, if so, then can you please elaborate on what this is meant to be showing in totality? – The Pointer Dec 14 '20 at 23:47
  • Also, can someone please clarify what the arrow for the polarisation \$P\$ means? Is this meant to denote the *direction* of polarisation? And, if so, then what does the "direction of polarisation" mean in this case? – The Pointer Dec 14 '20 at 23:49
  • Now it's not just about interpreting a diagram but about understanding the piezoelectric effect. Should be numerous online sources for that. –  Dec 15 '20 at 01:25
  • @BrianDrummond Which part? I'm asking about the diagram. I understand what polarisation means, in terms of the piezoelectric material, but the arrow is unclear in this context. Do you have any sources that directly address this? – The Pointer Dec 15 '20 at 01:29
  • Re, "can you please elaborate." The textbook is telling you about _piezoelectricity._ https://en.wikipedia.org/wiki/Piezoelectricity In certain solid crystals (also, in some ceramics) there is a correlation between stress in the material and an electric field in the material: An externally imposed electric field gradient causes stress, and externally imposed stress causes an electric field gradient. – Solomon Slow Dec 15 '20 at 14:50
  • @SolomonSlow I understood that part. The part that I'm having difficulty understanding, in context of what you just wrote, is the circle on one side and the dots on the other side, and how precisely they play into the description you just gave. – The Pointer Dec 15 '20 at 14:59
  • 1
    I don't have expert knowledge, but my understanding is that most practical piezoelectric devices look and work somewhat like a capacitor—two conductive "plates" (i.e., thin metal foils) with a slice of piezoelectric material between them, acting as the dielectric. The difference between that and a regular capacitor being that the physical dimensions of the device vary slightly in accordance with the voltage between the plates, and vice versa. I think that the "wires" in the book's diagrams are supposed to connect to "plates" that cover the tops and bottoms of each of the piezo crystals. – Solomon Slow Dec 15 '20 at 19:49
  • @SolomonSlow Ok, thanks for the clarification. – The Pointer Dec 16 '20 at 03:20

0 Answers0