# US 12,184,354 B2 · Low-frequency detection and ranging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,184,354 B2 - Document ID: US12184354B2 - Status: Granted - Kind: B2 - Application number: 18/123,855 - Filed: 2023-03-20 - Published: 2023-11-23 - Granted: 2024-12-31 - Earliest claimed: 2020-08-05 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Jouya Jadidian; Sujeet Milind Patole - Web page: https://patentgrep.com/patent/US12184354B2 ## CPC - H03K 17/955: using a capacitive detector - H04B 5/73: for taking measurements, e.g. using sensing coils - H04B 5/26: using coils - H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M) - H04B: TRANSMISSION ## Abstract Embodiments are disclosed for a low-frequency detection and ranging. In an embodiment, an apparatus comprises: an open electrode; an alternating current (AC) voltage source configured to supply an excitation voltage to the open electrode at an excitation frequency; a resonant circuit coupled to the open electrode, the resonant circuit configured to oscillate when an object is within a detection distance of the open electrode; one or more processors configured to: obtain time domain samples of an output voltage of the resonant circuit when the resonant circuit is oscillating; convert the time domain samples into frequency domain samples; for each frequency domain sample, determine an amplitude difference and a phase difference as compared to an amplitude and phase of the excitation voltage; and determine a material class of the object based on the amplitude difference and the phase difference. ## Claims ### Claim 1 An apparatus comprising: a proximity sensor including: 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, 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; an input voltage source coupled to the inverting input of the non-inverting amplifier; a load resistor coupled between the output terminal and ground; circuitry coupled to the proximity sensor and configured to capture an output voltage of the proximity sensor in response to the proximity sensor being in proximity to an object; a digital signal processor coupled to the circuitry and 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 proximity sensor from the object based on the amplitude difference and phase difference. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein a minimum detection range of the proximity sensor is less than about 1 centimeter. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the inductor is about 1 mH or less. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the stored amplitude and phase are associated with an excitation frequency of the excitation signal. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the excitation signal is a single tone sine wave. ### Claim 6 (depends on 4) The apparatus of claim 4, wherein the excitation frequency is randomized. ### Claim 7 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. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein a minimum detection range of the proximity sensor is less than about 1 centimeter. ### Claim 9 (depends on 7) The apparatus of claim 7, wherein the inductor is about 1 mH or less. ### Claim 10 (depends on 7) The apparatus of claim 7, wherein the stored amplitude and phase are associated with an excitation frequency of the excitation signal. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the excitation signal is a single tone sine wave. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein the excitation frequency is randomized. ### Claim 13 (depends on 7) The apparatus of claim 7, wherein usage of the antenna is time multiplexed so that the antenna is not used for RF communication and LFDAR at the same time. ### Claim 14 (depends on 7) The apparatus of claim 7, wherein the RF transmitter performs RF communication at a first frequency and the proximity sensor performs LFDAR at a second frequency that is lower than the first frequency. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein the RF transmitter advertises the first frequency to other devices through a wireless broadcast.