Ni usb 6353

A 16 bits DAQ board is connected to the circuit (National Instruments NI-USB 6353); the DAQ has been set to acquire, at rate 1 MSa/s, a number of 3000 samples (corresponding to 300 periods of the driving voltage) of each differential voltage $u_i=V_i-V_0$ , where $V_i$ is the potential of each electrode surface $S_i$ and $V_0$ is the potential of the lower electrode, chosen as reference, Figure 2a. The current signal I flowing through the outer electrodes is acquired as a single ended trace referred to ground. A dedicated control panel, shown in Figure 3, developed in LabView, acquires the data of the driving current and of $u_i$ . During a measurement cycle, the DAQ reads the nine differential voltages ( $u_i$ ) and the current signal (I). The measurement time for each channel is 3 ms, thus the acquisition time is 30 ms. After acquisition, the control panel calculates the AC-coupled RMS value of each quantity and saves the results into a text file. The volume of the defects is then computed with a Matlab script which calculates the quantity $\Delta R\left(D\right)$ as described in the next subsection.

The voltage transient measurements using a charge-balanced biphasic current-controlled waveform were performed with an analog stimulus isolator (AM 2200, AM Systems, Sequim, WA, USA). A bespoke MATLAB program (R2016a, Mathworks, Natick, MA, USA) was used to generate stimulating waveform with specific pulse width, amplitude, and frequency. The pulses were injected into the electrode-electrolyte test cell, and a data acquisition board (NI USB-6353, National Instruments, Austin, TX, USA) was used to record the voltage transient responses. The charge-balanced biphasic pulse used in the experiments were cathodic-first current pulse with 100 μs duration followed by 100 μs inter-phase delay. The stimulating frequency was set at 50 Hz. The maximum negative potential excursion (E_mc) was esteimated to be the potential immediately after the end of the cathodic pulse (Fig. 5A). The time delay at which the current becomes zero was measured to be approxmiately 12 μs, and E_mc was recorded at 12 μs following the end of the cathodic current pulse. V_dr is the negative driving voltage which is maximum voltage to deliver the cathodic current pulse.