## General Mechanical

#### Complex Charge on Electrode Surface SAW Sensor

• FabSens
Subscriber

Hello,

I am currently working on a simulation of a SAW resonator (piezo = alpha quartz; electrode = aluminium) (see attached picture). For this, I did a modal analysis using Piezo & MEMS extention to determine the resonant frequencies of my system. Then I switched to Harmonic Response to create the admittance curve (from the complex charge of my electrodes). In the literature it is always referred to, that the complex charge distribution can simply determined.

Hence to my question:

How can I calculate the complex charge on the electrode-surface? I excite my system in the range of the resonance frequency with +/-0.1V on the left electrode (right electrode is set to 0 V).

I want to receive exactly the same results as it is described in:

"Kannan, Thirumalai. Finite element analysis of surface acoustic wave resonators. Diss. 2006."

on page 75, 76.

It would be great if someone can help me.

Thank you and kind regards

• Bill Bulat
Ansys Employee
Hi,I was unable to download the paper you referenced.nI thought that the Piezo and MEMS ACT enabled you to calculate impedance or admittance:nnWhat the ACT does can be done manually with APDL. Consider file wirebond3.dat associated with Technology Showcase #39 in our Help:nnI listed part of the file below. The complex frequency dependent charge reaction at the master node of a coupled set (CP,,VOLT) of nodes used to model an electrode is read into POST26 variable # 2. A complex factor (j*2*pi) is then specified as a coefficient used in an operation in which variable 1 (frequency) is multiplied by variable 2 (charge) to give variable 3 (current). The nodal voltage of the electrode is read into variable 4, which is divided by current (variable 3) to give impedance (variable 5). All variables are complex (the analysis was harmonic response). MAPDL's POST26 processor does complex math. The amplitude of the impedance is then plotted (PLVAR,5). Use the PLCPLX command before the PLVAR,5 command to plot the amplitude, real or imaginary part, or the phase of the impedance.nn/show,pngn/post26nfile,,rstpnnumvar,200nrforc,2,N_POSITIVE,chrgncfact,0,2*acos(-1)nprod,3,1,2,,currentnnsol,4,N_POSITIVE,voltnquot,5,4,3,,impedancen/title,Electrical impedancen/axlab,y,Impedancenprvar,2,3,4,5nplvar,5nnI hope this helps!nKind regards,nBillnn