Low-frequency detection and ranging

An apparatus comprising:

• an antenna configured for use with transmission or reception of radio frequency signals or low-frequency detection and ranging (LFDAR);
• a radio frequency (RF) transmitter coupled to the antenna and configured to transmit or receive RF signals;
• a proximity sensor coupled to the antenna and configured to capture an output voltage of the antenna in response to the antenna being in proximity to an object,
• wherein the proximity sensor includes a non-inverting amplifier having an inverting input terminal, a non-inverting input terminal and an output terminal;
• a feedback resistor coupled between the non-inverting input terminal and the output terminal;
• an excitation signal coupled to the inverting input terminal;
• a series resonant circuit coupled to the non-inverting input terminal, and wherein the series resonant circuit includes a resistor, an inductor and a capacitor, wherein the inductor is sized to allow the series resonant circuit to self-resonate with a quality factor that provides a resolution that allows different object materials to be distinguished from one another, and wherein input voltage source is coupled to the inverting input of the non-inverting amplifier, and a load resistor is coupled between the output terminal and ground;
• a digital signal processor configured to:
• compute a difference between an amplitude and phase of the captured output voltage and a stored amplitude and phase associated with the object;
• and
• estimate a distance of the antenna from the object based on the amplitude difference and phase difference.