Abstract
Low-power A.C. generators of square-wave or sinusoidal signals can be used in combination with impedimetric sensors to detect stimuli on the basis of the voltage drop taking place at the sensor electrodes. When a.c. generators with a power of only a few µ-Watts are used, this approach becomes extremely sensitive. A very low-power generator is the LCD back panel driving signal, which has a flipping polarity with a voltage of 3-5Vpp, depending on the generator model. This type of square-wave generator is contained in many low-cost handheld digital multimeters, and it is used as signal tracer to test, for example, low-frequency amplifiers. As an example, this method has been used to acquire a human breath rate pattern, by using a zeolite-based water sensor. If the generator I-V characteristics has been measured, the achieved breath pattern can be converted from a voltage drop vs. time graph to an impedance or current intensity vs. time graph.
Highlights
Low-power A.C. generators of square-wave or sinusoidal signals can be used in combination with impedimetric sensors to detect stimuli on the basis of the voltage drop taking place at the sensor electrodes
The response to stimuli of an impedimetric sensor is detected as impedance (Z) variation, measured by a LCRmeter, or as variation of the intensity of current flowing in the device [6,7]
The I-V characteristics of the generator can be determined and the voltage response can be converted to current intensity or impedance variation by using this generator I-V characteristics
Summary
Low-power A.C. generators of square-wave or sinusoidal signals can be used in combination with impedimetric sensors to detect stimuli on the basis of the voltage drop taking place at the sensor electrodes. A breath rate sensor based on natural clinoptilolite has been proposed [8], the breath pattern was generated by measuring the current intensity flowing at sample surface after biasing this sensor with a 5kHz sinusoidal voltage signal (20Vpp).
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