# US 2013/0154649 A1 · Transmit signal of a metal detector > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0154649 A1 - Document ID: US20130154649A1 - Status: Published application - Kind: A1 - Application number: 13/720,828 - Filed: 2012-12-19 - Published: 2013-06-20 - Earliest claimed: 2011-12-19 - Assignees: Minelab Electronics Pty Limited - Inventors: Bruce Halcro CANDY - Web page: https://patentgrep.com/patent/US20130154649A1 ## CPC - G01V 3/107: {using compensating coil or loop arrangements} - G01V 3/15: specially adapted for use during transport, e.g. by a person, vehicle or boat - G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02) ## Abstract A metal detector for detecting a metallic target in a soil including: transmit electronics for generating a repeating transmit signal cycle, the repeating transmit signal cycle including at least one receive period and at least one non-zero transmit coil reactive voltage period; a transmit coil connected to the transmit electronics for receiving the repeating transmit signal cycle and generating a transmit magnetic field; a receive coil for receiving a receive magnetic field during the at least one receive period and providing a receive signal induced by the receive magnetic field; and receive electronics connected to the receive coil for processing the receive signal during the at least one receive period to produce an indicator output signal, the indicator output signal including a signal indicative of a presence of the metallic target when under an influence of the transmit magnetic field; wherein the repeating transmit signal cycle is generated such that a waveform of the repeating transmit signal cycle includes a substantially half-sine during the at least one non-zero transmit coil reactive voltage period, and that a current through the transmit coil is substantially constant and non-zero during the at least one receive period. ## Claims ### Claim 1 A metal detector for detecting a metallic target in a soil including: transmit electronics for generating a repeating transmit signal cycle, the repeating transmit signal cycle including at least one receive period and at least one non-zero transmit coil reactive voltage period; a transmit coil connected to the transmit electronics for receiving the repeating transmit signal cycle and generating a transmit magnetic field; a receive coil for receiving a receive magnetic field during the at least one receive period and providing a receive signal induced by the receive magnetic field; and receive electronics connected to the receive coil for processing the receive signal during the at least one receive period to produce an indicator output signal, the indicator output signal including a signal indicative of a presence of the metallic target when under an influence of the transmit magnetic field; wherein the repeating transmit signal cycle is generated such that a waveform of the repeating transmit signal cycle includes a substantially half-sine during the at least one non-zero transmit coil reactive voltage period, and that a current through the transmit coil is substantially constant and non-zero during the at least one receive period. ### Claim 2 (depends on 1) The metal detector of claim 1, wherein the repeating transmit signal cycle includes a high-voltage period, the high-voltage period followed by a very-low-voltage period; wherein the high-voltage period includes one of the at least one non-zero transmit coil reactive voltage period, and the very-low-voltage period includes one of the at least one receive period. ### Claim 3 (depends on 2) The metal detector of claim 2, wherein the repeating transmit signal cycle further includes a low-voltage period following the very-low-voltage period. ### Claim 4 (depends on 1) The metal detector of claim 1, wherein the repeating transmit signal cycle includes at least two different sequences, a first sequence and a second sequence, the first sequence including a first non-zero transmit coil reactive voltage period and a first receive period, and the second sequence including a second non-zero transmit coil reactive voltage period and a second receive period, and the second sequence is an inversion of the first sequence. ### Claim 5 (depends on 1, 2, 3, 4) A metal detector according to any one of claims 1 to 4, further including: at least one negative feedback loop for controlling at least one characteristic of the repeating transmit signal cycle based on the same or at least one other characteristic of the repeating transmit signal cycle. ### Claim 6 A repeating transmit signal cycle for generating a transmit magnetic field through a transmit coil in an operation to detect a metallic target in a soil, including: at least one receive period during which a current through the transmit coil is substantially constant and non-zero; and at least one non-zero transmit coil reactive voltage period during which a waveform of the repeating transmit signal cycle includes a substantially half-sine. ### Claim 7 (depends on 6) The repeating transmit signal cycle of claim 6, including a high-voltage period, the high-voltage period followed by a very-low-voltage period; wherein the high-voltage period includes one of the at least one non-zero transmit coil reactive voltage period, and the very-low-voltage period includes one of the at least one receive period. ### Claim 8 (depends on 7) The repeating transmit signal cycle of claim 7, further including a low-voltage period following the very-low-voltage period. ### Claim 9 (depends on 6) The repeating transmit signal cycle of claim 6, including at least two different sequences, a first sequence and a second sequence, the first sequence including a first non-zero transmit coil reactive voltage period and a first receive period, and the second sequence including a second non-zero transmit coil reactive voltage period and a second receive period, the second sequence being an inversion of the first sequence. ### Claim 10 (depends on 6, 7, 8, 9) A metal detector configurable to transmit the repeating transmit signal cycle of any one of claims 6 to 9. ### Claim 11 A method for detecting a metallic target in a soil including: generating a repeating transmit signal cycle, the repeating transmit signal cycle including at least one receive period and at least one non-zero transmit coil reactive voltage period; generating a transmit magnetic field for transmission through a transmit coil based on the repeating transmit signal cycle; receiving a receive magnetic field during the at least one receive period and providing a receive signal induced by the receive magnetic field; and producing an indicator output signal, the indicator output signal including a signal indicative of a presence of the metallic target when under an influence of the transmit magnetic field; wherein the repeating transmit signal cycle is generated such that a waveform of the repeating transmit signal cycle includes a substantially half-sine during the at least one non-zero transmit coil reactive voltage period, and that a current through the transmit coil is substantially constant and non-zero during the at least one receive period. ### Claim 12 A coil arrangement for reducing non-linear motion signals from a receive signal of a metal detector transmitting a transmit signal, the transmit signal including a period of zero reactive voltage with non-zero transmit coil current. ### Claim 13 (depends on 12) The coil arrangement of claim 12, including: a transmit coil for transmitting a transmit magnetic field; and two receive coils positioned at opposite sides of the transmit coil for receiving magnetic fields. ### Claim 14 (depends on 12) The coil arrangement of claim 12, including: a transmit coil for transmitting a transmit magnetic field; and a receive coil with three loops for receiving magnetic fields, wherein a first loop is positioned entirely within horizontal limits of the transmit coil, and the remaining loops of the three loops have parts overlapping turns of the transmit coil. ### Claim 15 (depends on 12) The coil arrangement of claim 12, including: a transmit coil for transmitting a transmit magnetic field; and a receive coil with two loops, each loop positioned at opposite sides of the transmit coil for receiving magnetic fields. ### Claim 16 (depends on 12) The coil arrangement of claim 12, including: a transmit coil with two loops for transmitting a transmit magnetic field; and a receive coil with one loop for receiving magnetic fields; wherein the two loops of the transmit coil and the one loop of the receive coil form a concentric arrangement. ### Claim 17 (depends on 13, 14, 15, 16) A metal detector for transmitting a transmit signal, the transmit signal including a period of zero reactive voltage with non-zero transmit coil current, the metal detector including a coil arrangement, according to any one of claims 13 to 16, adapted to reduce non-linear motion signals in a receive signal of the metal detector.