A Multichannel FRA-Based Impedance Spectrometry Analyzer Based on a Low-Cost Multicore Microcontroller

Abstract

Impedance spectrometry (IS) is a characterization technique in which a voltage or current signal is applied to a sample under test to measure its electrical behavior over a determined frequency range, obtaining its complex characteristic impedance. Frequency Response Analyzer (FRA) is an IS technique based on Phase Sensitive Detection (PSD) to extract the real and imaginary response of the sample at each input signal, which presents advantages compared to FFT-based (Fast Fourier Transform) algorithms in terms of complexity and speed. Parallelization of this technique has proven pivotal in multi-sample characterization, reducing the instrumentation size and speeding up analysis processes in, e.g., biotechnological or chemical applications. This work presents a multichannel FRA-based IS system developed on a low-cost multicore microcontroller platform which both generates the required excitation signals and acquires and processes the output sensor data with a minimum number of external passive components, providing accurate impedance measurements. With a suitable configuration, the use of this multicore solution allows characterizing several impedance samples in parallel, reducing the measurement time. In addition, the proposed architecture is easily scalable.

Bioimpedance Sensors: A Tutorial

“…Digital implementations of synchronous detection can be implemented, using e.g. microcontrollers [219], but most commonly, the Fourier transform is used, e.g. using undersampling [220].…”

1.0 V-0.18 µm CMOS Tunable Low Pass Filters with 73 dB DR for On-Chip Sensing Acquisition Systems

“…The Frequency Response Analyzer (FRA-EIS) technique is based on dual (0, 90 • ) synchronous demodulation, that is, it uses a technique known as phase-sensitive detection (PSD) to extract at an excitation frequency f 0 the real and imaginary response. As shown in Figure 1b, the signal is typically amplified by an instrumentation amplifier (IA), then a mixer working at the same frequency f 0 (0, 90 • ) demodulates the signal, and a low pass filter (LPF) extracts the DC components X-Y, proportional to the real and imaginary response, while noisy signals at other frequencies filtered [5][6][7][8][9][10][11]. In this case, the LPF is going to be used as a DC magnitude extractor at th last stage of the FRA-EIS read-out system to recover the signal, and it is required to hav an adjustable value in the order of sub-Hz to Hz (Table 1) to adjust the accuracy-spee trade-off.…”

Development of a Portable Impedance Spectrometer

“…However, this approach is computationally expensive, highly sensitive to noise and its complicated signal processing hardware implies large costs. [23][24] As a result, the commercial spectrometers deal with one frequency at a time. 25 In most of the work using spectroscopy, static impedance is used since the response is not expected to vary with time or voltage.…”