Electromechanical transformation

As a receiver for mechanical action input, the sensitivity of the piezoelectric film is surprising. The simplest form of piezoelectric film can play a role of dynamic strain gauge, and it doesn't need external power supply, and the generated signal is even larger than the amplified signal after strain gauge. Therefore, the frequency response is not affected by any restriction to satisfy the high gain, and the upper limit is the wavelength of the given sensor.

This very high sensitivity is mainly determined by the size of the piezoelectric film material. The small thickness is the first to determine a very small cross section. Therefore, a fairly small longitudinal force can produce a large stress inside the material. It is easy to use this characteristic to increase the sensitivity parallel to the mechanical axis. If the flake shaped thin film element (such as LDT1~028K) is placed between two layers of flexible material, any pressure will change to a much larger longitudinal force. In fact, because most of the materials are flexible to some extent, this effect plays a major role in many cases. The ratio of effective sensitivity in 1 and 3 directions is generally 1000:1.

Piezoelectric film sensor compared with ordinary meter, often can cover a much larger area, so as to get meaningful results, should be in direct contrast to the condition of the same strain field. Although a very small area of capacitance also needs to be considered, the "point" type of sensor can be applied to what is needed. The maximum load resistive boundaries will be decided at the low frequency can be achieved, or depends on the signal can be detected maximum capacitive load. A simple high impedance field effect transistor buffer circuit can be satisfied by a conventional charge amplifier or a relatively high signal level.

Thermoelectric transformation

Kynar piezoelectric film, with 7~20 m in the interval of strong absorption performance, which is equivalent to exceed the working temperature of upper and lower membrane. Therefore, it can be a sensitive thermoelectric detector (for example, human thermal radiation). Because of its high thermal sensitivity, we should pay attention to the influence of the environmental signal on the output signal when it designs low frequency (<0.01~1Hz) mechanical sensors. If a very long time constant is used, the piezoelectric film will produce a voltage related to temperature change when it is connected. As the output signal has a few volts / centigrade, the significant drift may be observed.

Note: Kynar is a registered trademark of Elf Atochem NA

In general, most applications have a few over Hz cut-off frequencies unless a thermoelectric effect is particularly required. A 1nF capacitance element is connected to the input end of the oscilloscope, and even under the impedance of the 10M Omega, the attenuation below 16Hz will be produced. Only when the temperature of the membrane changes rapidly, the detectable signal can be produced.

A common mode suppression can be used to separate the mechanical strain of a very low frequency from the thermoelectric effect produced at the same time, and the opposite is true. For MSI's application engineers, this technology is quite familiar and can provide design support at any time.

Electrical design basis

In addition to ultrasonic applications, a useful mode of piezoelectric films in most application conditions is a series of voltage related voltage sources and capacitance. Any resistance load will form a partial voltage network with the characteristics of a simple RC high pass filter. The cut-off frequency is given by the lower form

F =1/2 RC time constant of 316LVM completely =RC. Working below the cut-off frequency will produce an output signal that is proportional to the change rate of the input parameter (differential ci