# US 2022/0045720 A1 · 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 2022/0045720 A1 - Document ID: US20220045720A1 - Status: Published application - Kind: A1 - Application number: 17/394,336 - Filed: 2021-08-04 - Published: 2022-02-10 - Earliest claimed: 2020-08-05 - Assignees: Apple Inc. - Applicants: Apple Inc. - Inventors: Jouya Jadidian; Sujeet Milind Patole - Web page: https://patentgrep.com/patent/US20220045720A1 ## 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: 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. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the resonant circuit is a series resistor-inductor-capacitor (RLC) resonance circuit. ### Claim 3 (depends on 2) The apparatus of claim 2, further comprising: 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; the series resonant circuit coupled to the non-inverting input terminal; the input voltage source coupled to the inverting input of the non-inverting amplifier; and a load resistor coupled between the output terminal and ground. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the resonant circuit includes a resistor, an inductor and a capacitor, and the inductor is sized to allow the series resonant circuit to self-resonate with a quality factor that provides sufficient resolution to distinguish between different object materials. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the resonant circuit is a parallel resistor-inductor-capacitor (RLC) resonance circuit. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the one or more processors are further configured to determine a range of the object from the open electrode. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the object is a human body part. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the LFDAR is configured for differential input and output. ### Claim 9 (depends on 1) The apparatus of claim 1, wherein the minimum detection range of the LFDAR is less than about 1 centimeter. ### Claim 10 A method comprising: applying an excitation voltage to an open electrode of a low-frequency detecting and ranging (LFDAR) sensor embedded in an electronic device; obtaining, using the LFDAR sensor, time domain samples of an output voltage of a resonant circuit of the LFDAR coupled to the open electrode; converting, using one or more processors of the electronic device, the time domain samples into frequency domain samples; for each frequency domain sample, determining, using the one or more processors, an amplitude difference and a phase difference as compared to an amplitude and phase of the excitation voltage; and determining, using the one or more processors, a material class of an object within a detection distance of the open electrode based on the amplitude difference and the phase difference. ### Claim 11 (depends on 10) The method of claim 10, further comprising: reducing electromagnetic radiation emission of the electronic device based on the material class and estimated range. ### Claim 12 A method comprising: applying an excitation voltage at a particular excitation frequency to an open electrode of a low-frequency detecting and ranging (LFDAR) sensor; (a) obtaining, using the LFDAR sensor, time domain samples of an output voltage of a resonant circuit of the LFDAR coupled to the open electrode; (b) converting, using one or more processors, the time domain samples into frequency domains samples; (c) for each frequency domain sample, determining, using the one or more processors, an amplitude difference and a phase difference as compared to an amplitude and phase of the excitation voltage; (d) forming, using the one or more processors, a cluster of the amplitude differences and phase differences; (e) classifying and estimating, using the one or more processors, a range for the cluster; (f) storing, using the one or more processors, the classification and estimated range; (g) adjusting, using the one or more processors, the excitation frequency; and (h) repeating steps (a)-(g) until a specified number of excitation frequencies is exhausted. ### Claim 13 An apparatus comprising: one or more motion sensors; one or more radio frequency (RF) transmitters; a low-frequency detection and ranging (LFDAR) sensor comprising: 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; one or more processors configured to: obtain time domain samples of an output voltage of the resonant circuit; convert the time domain samples into a 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; determine a material class for the object by comparing the amplitude differences and phase differences of the frequency domain samples to a plurality of previously generated material classes; and reduce electromagnetic radiation emitted by the one or more RF transmitters based on the material type and estimated range. ### Claim 14 (depends on 13) The apparatus of claim 13, wherein the one or more processors are configured to stabilize the output voltage of the resonant circuit based on motion data output by the one or more motion sensors. ### Claim 15 (depends on 13) The apparatus of claim 13, wherein the open electrode is an antenna coupled to the one or more RF transmitters. ### Claim 16 (depends on 13) The apparatus of claim 13, wherein the excitation frequency is randomized to prevent interference with other LFDARs. ### Claim 17 (depends on 13) The apparatus of claim 13, wherein the maximum or minimum detection range of the LFDAR is determined by a size of the open electrode and a ground, and their relative placement with respect to each other. ### Claim 18 (depends on 13) The apparatus of claim 13, wherein the object is a human body part. ### Claim 19 (depends on 13) The apparatus of claim 13, wherein the resonant circuit includes a resistor, an inductor and a capacitor, and the inductor is sized to allow the resonant circuit to self-resonate with a quality factor that provides sufficient resolution to distinguish between different object materials. ### Claim 20 (depends on 13) The apparatus of claim 13, wherein the one or more processors are further configured to estimate a range of the object from the open electrode by comparing the amplitude differences and phase differences of the frequency domain samples to a plurality of previously generated range estimations.