When a square wave pulsed signal is adopted as excitation to obtain electrical impedance information for a conductive medium, the amplitude decay of the higher harmonics in square wave spectrum can have a significant effect. Adding an inductor or capacitor to a first-order resistant-capacitive-type sensing system creates a second-order resonant element that creates a freely damped oscillating signal at both the rising and falling edges of the excitation. The excitation amplitude near the resonant frequency is, therefore, enhanced. The equivalent resistance in the resonant element can be obtained by measuring the first positive peak voltage of the freely damped signal at the falling edge of the pulse. Tests indicate that resistance measurements for frequencies from 30 kHz to 1 MHz can be implemented only by a fixed frequency square wave excitation signal generated by a digital circuit. This method can be used for conductivity measurements of conductive media, such as electrolyte solutions, water and human skin, using both wired and wireless transmitters.