Structural Health Monitoring, Damage Detection & Mechatronics, Volume 7 by Alfred Wicks & Christopher Niezrecki

Author:Alfred Wicks & Christopher Niezrecki
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

8.3 Structure of the Electric Impedance

As stated in Sect. 8.1, this paper proposes a new shunt impedance Z with the aim of improving the performances of the traditional broadband controller made up of the series of a NC and a resistance (R-NC, Fig. 8.2a). This new impedance considers the addition of an inductance in series to the R-NC shunt (RL-NC, Fig. 8.2b).

Fig. 8.2Shunt impedance layout: R-NC (a) and RL-NC (b)

In order to better understand the working principle of this new circuit, it is worth analysing at first the behaviour of the simple R-NC impedance (Fig. 8.2a). This impedance consists of a resistance (R) in series to a negative capacitance (NC). The effect of adding a NC in a generic shunt impedance is to enhance the control performances of the piezoelectric actuator with respect to the traditional shunts (e.g. R, RL) [5, 10]. The use of a NC can be interpreted as a way to improve the characteristics of the piezoelectric actuator, making it more performing in terms of control action given to the structure [10, 11]. This effect depends on the value taken by the negative capacitance compared to the one of the piezo-actuator: the closer C n is to C p,i , the higher the attenuation provided by the shunt is [5].

If we look at the FRF of the EMS, the effect of the NC, connected in series to the piezo-actuator, is to move each short circuit natural frequency of the EMS to lower values [3], and the closer C n is to C p,i the higher the shift is. The new value of each short circuit eigenfrequency can be expressed as:

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