Abstract
The main requirement for using the Fluctuation Enhanced Sensing technique is the ability to perform low-frequency noise measurements. The portability of the measurement system is also a quite desirable feature not limited to this specific application. In this paper, an approach for the realization of a dual channel spectrum analyzer that is capable of exploring frequencies down to DC, although based on a USB sound card, is proposed. The lower frequency range of the input signals, which is outside the frequency range of the sound board, is upconverted to higher frequencies by means of a very simple modulation board. Then, the entire spectrum is reconstructed numerically by proper elaboration. With the exception of the modulation board, the approach we propose does not rely on any specific hardware. Thanks to the efficiency of the spectra estimation and reconstruction software, which is based on a public domain library, the system can be built on a low-cost computer single board computer, such as the Raspberry PI3. Moreover, when equipped with an optical TCP/IP link, it behaves as a compact spectrum analyzer that along with the device under test can be placed into a shielded environment, thus being isolated from external electromagnetic interferences.
Highlights
The development of advanced sensing techniques requires the availability of dedicated instrumentation which, not being commercially available, must be custom developed
The power spectral density of the noise signal is often used as such a fingerprint; an in-depth experience in the field of Low-Frequency Noise Measurements (LFNM) can be useful for Fluctuation Enhanced Sensing (FES) application
The fact that we are mostly interested in the frequency range from a few tens of mHz up to a few tens of Hz in FES applications rules out the possibility of directly using PC sound boards because their input is AC coupled with a cut-in frequency in the order of a few Hz
Summary
The development of advanced sensing techniques requires the availability of dedicated instrumentation which, not being commercially available, must be custom developed. Overcoming the frequency limitations that prevent sound boards from being used as inexpensive and effective alternative to conventional benchtop and board-based spectral analyzers is the subject of this work As it will be shown in the few sections, by means of a very simple add-on board composed by a low pass filter and an analog multiplier for each channel and by resorting to proper digital signal processing, it is possible to reach the goal of realizing a two-channel spectrum analyzer with a low-frequency corner virtually extending to DC and with overall performances that are completely satisfactory for performing FES and LFNM, even when using cross-correlation approaches
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