Improving Performance and Versatility of Systems Based on Single-Frequency DFT Detectors Such as AD5933

Abstract

Abstract:Turning grand concepts such as the Internet of Things (IoT) and Smart Cities into reality requires the development and deployment of a wide variety of computing devices incorporated into the Internet infrastructure. Unsupervised sensing is the cornerstone capability that these devices must have to perform useful functions, while also having low cost of acquisition and ownership, little energy consumption and a small footprint. Impedimetric sensing systems based on the so-called single-frequency DFT detectors possess many of these desirable attributes and are often introduced in remote monitoring and wearable devices. This study presents new methods of improving performance of such detectors. It demonstrates that the main source of systematic errors is the discontinuous test phasor causing the crosstalk between the in-phase and quadrature outputs and the leakage of the input signal. The study derives expressions for these errors as a function of the number of samples and operating frequency, and provides methods for correction. The proposed methods are applied to the operation of a practical device-a network analyzer integrated circuit AD5933-and discussed in detail. These methods achieve complete elimination of leakage errors and expansion of the low limit of the operation frequency range by nearly two decades without additional hardware.

Electrochemical Impedance Sensors for Monitoring Trace Amounts of NO3 in Selected Growing Media

“…The AD5933 employs a trans-impedance amplifier for amplifying the current and then uses the 1024 point on-chip DFT algorithm for separating the real and imaginary parts of impedance. After digitalizing with the ADC [ 25 ], a discrete-time impedance wave, Z[n] ( n = 0, 1, 2, …N−1), is obtained by DFT: where Z i and Z q indicate respectively the real and imaginary parts of impedance returned by the DFT, both of which could be calibrated with respect to NO 3 concentration in the medium at a specific AC amplitude, with best calibration resolution usually obtained when using the impedance modulus. To our knowledge, this is the first time the AD5933 device was used along with a chemical sensor for environmental analysis; for sake of carefulness this warranted comparison with other known and well calibrated impedance meters.…”

A Wireless Multi-Sensor Dielectric Impedance Spectroscopy Platform

“…, sensor) to be excited with a known AC frequency. The impedance response signal is sampled by the ADC and a discrete Fourier transform (DFT) is then processed by the on-board engine [ 10 ]. The continuous-frequency sweep of the AD5933 device provides for much higher informational value than multi-frequency based sensing, to the extent that higher frequency resolution provides for better modeling and understanding of the DUT dielectric response .…”

Untitled

“…It is common to replace f p w 2 = and to skip N 1 , however these parameters are important for calculating the period [Matsiev, 2015] [Randles, 1947]. EIS allows analyzing various liquid and colloidal system and, as an example, we perform analysis of bottled water and milk.…”

“…If this condition is not met, so-called leakage errors occur. This problem is solved in three ways [L.Matsiev, 2015]. Firstly, it is proposed to select the sweep frequencies f in such a way that I V always contains an integer number of period k .…”

“…The AD5933 uses the Hanning function [L.Matsiev, 2015]: (14) The functions (13) allows keeping N at the same level for all frequencies, which is useful for digitizing the signal. However, this method distorts the original signal, instead of…”