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The following are patents on Induction Balance type detectors including TR and VLF.
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Patent # |
Title |
Description |
 1710K |
US3405354 |
Apparatus for Limiting Phase-Angle Response Range, Particularly in Eddy Current Testing Apparatus |
Uses syncronous demodulation to determine target phase, see 3848182. |
| 874K |
US3471772 |
Instrument for Measuring the Range and Approximate Size of Buried or Hidden Metal Objects |
Synchronous detectors, lots of fundamental theory & equations. |
| 436K |
US3471773 |
Metal Detecting Device with Inductively Coupled Coaxial Transmitter and Receiver Coils |
Basic TR with 4B-style coil (NOT coaxial!). |
| 1282K |
US3826973 |
Electronic Gradiometer |
Actually, a metal detector. |
| 1330K |
US3835371 |
Apparatus for Detecting the Presence of Electrically Conductive Material Within a Given Sensing Area |
Focuses on submersible probe & cabling method |
| 728K |
US3848182 |
Apparatus for Limiting Phase-Angle Response Range, Particularly in Eddy Current Testing Apparatus |
See 3405354. |
| 484K |
US3872380 |
Metal Detector Distinguishing Between Different Metals by Using a Bias Circuit Actuated by the Phase Shifts Caused by the Metals |
Gardiner, basic phase response IB. |
| 664K |
US4016486 |
Land Mine Detector with Pulse Slope, Width and Amplitude Determination Channels |
| 1347K |
US4024468 |
Induction Balance Metal Detector with Inverse Discrimination |
White's TR Discriminator (1975), includes good description with phase diagrams and circuitry with component values. |
| 2003K |
US4030026 |
Sampling Metal Detector |
White's, the basis of most of their early-80's analog detectors. |
| 683K |
US4053828 |
Metal Detector with First and Second Nested Rectangular Coils |
Not too practical for a handheld. |
| 319K |
US4096432 |
Metal Detector for Discriminatory Detection of Buried Metal Objects |
Basic phase response IB. |
| 840K |
US4099116 |
Metal Detector With Phase Related Selective Discrimination Circuit |
Nautilus, feedback method for ground balance and discrimination. |
| 1271K |
US4110679 |
Ferrous/Non-ferrous Metal Detector Using Sampling |
White's |
| 779K |
US4128803 |
Metal Detector System With Ground Effect Rejection |
PNI (the old Bounty Hunter), probably the Red Baron series (RB3/5/7). |
| 1021K |
US4249128 |
Wide Pulse Gated Metal Detector With Improved Noise Rejection |
White's |
| 1277K |
US4263551 |
Method and Apparatus for Identifying Conductive Objects by Monitoring the True Resistive Component of Impedance Change in a coil System Caused by the Object |
Title says it all, looks at target response vs. frequency |
| 882K |
US4300097 |
Induction Balance Metal Detector with Ferrous and Non-ferrous Metal Identification |
Techna, now First Texas Mfg. (Bounty Hunter) |
| 1576K |
US4303879 |
Metal Detector Circuit with Mode Selection and Automatic Tuning |
1979 Garrett patent (ADS?) |
| 1352K |
US4325027 |
Metal Detector for Locating Objects with Full Sensitivity in the Presence of Distributed Mineral Material |
Compass |
| 1176K |
US4334191 |
Metal Detector Circuit Having Momentary Disabled Output |
Garrett |
| 1267K |
US4334192 |
Metal Detector Circuit Having Automatic Tuning With Multiple Rates |
Garrett, probably their Master Hunter VLF. |
| 1218K |
US4344034 |
Selective Ground Neutralizing Metal Detector |
Gardiner patent for phase discriminator. |
| 1008K |
US4348639 |
Transmitter-Receiver Loop Buried Metal Object Locator with Switch Controlled Reference Vooltage |
Discovery Electronics' two-box detector. |
| 876K |
US4423377 |
Compact Metal Detector of the Balanced Induction Type |
Garrett, handheld with integrated double-D coil. See also 4488115. |
| 3160K |
US4470015 |
Metal Detector System With Undesirable Target and Mineralized Ground Discrimination |
Teknetics, lots of diagrams and waveforms. |
| 941K |
US4486712 |
Frequency Dependent Pulsed Gain Modulated Metallic Object Detector |
| 1210K |
US4486713 |
Metal Detector Apparatus Utilizing Controlled Phase Response to Reject Ground Effects and to Discriminate Between Different Types of Metals |
Tesoro, lots of signal & phase diagrams |
| 758K |
US4488115 |
Low Battery Voltage Indicator Circuit for a Metal Detector |
Garrett, see also 4423377 |
| 6059K |
US4507612 |
Metal Detector Systems for Identifying Targets in Mineralized Ground |
Teknetics, tons of info. |
| 734K |
US4514692 |
Metal Detector and Discriminator Using Differentiation for Background Signal Suppression |
Fisher, basis for early X models. |
| 337K |
US4563645 |
Inductively Balanced Oscillatory Coil Current for Metal Detection |
| 1126K |
US4628265 |
Metal Detector and Classifier with Automatic Compensation for Soil Magnetic Minerals and Sensor Misalignment |
Fisher |
| 654K |
US4659989 |
Inductively Balanced Metal Detector Circuit with Orthogonal Balancing Signals and Including Phase and Polarity Detection |
| 1728K |
US4677384 |
Target-Identifying Metal Detector |
Teknetics |
| 1235K |
US4700139 |
Metal Detector Circuit Having Selectable Exclusion Range For Unwanted Objects |
Garrett patent with a pretty good explanation of I&Q signal processing. |
| 2644K |
US4709213 |
Metal Detector Having Digital Signal Processing |
Garrett |
| 1073K |
US4783630 |
Metal Detector With Circuits for Automatically Screening Out the Effects of Offset and Mineralized Ground |
White's |
| 2838K |
US4868910 |
Metal Detector with Microprocessor Control and Analysis |
White's, ton's of info on their target ID. |
| 352K |
US4881036 |
Phase Shift Compensation for Metal Detection Apparatus |
| 1325K |
US4894618 |
Metal Detector Using Cross-Correlation Between Components of Received Signals |
Minelab, good explanatory text. |
| 1055K |
US4912414 |
Induction-Type Metal Detector with Increased Scanning Area Capability |
Describes a large array for use with a submersible, includes IB and PI methods. |
| 1317K |
US5148151 |
Metal Detector Having Target Characterization and Search Classification |
Garrett patent on VDI, explanantion on phase response and VDI flowchart. |
| 1669K |
US5506506 |
Metal Detector for Detecting and Discriminating Between Ferrous and Non-ferrous Targets in Ground |
Minelab, combines synchronous demodulators with PI, calls it multi-frequency. Compare with US5576624 |
| 1055K |
US5523690 |
Metal Detector with Bivariate Display |
White's patent detailing VDI, includes 6805 assembly code. (see also 5596277) |
| 959K |
US5596277 |
Method and Apparatus for Displaying Signal Information from a Detector |
White's patent detailing VDI, includes 6805 assembly code. (see also 5523690) |
| 980K |
US5691640 |
Forced Balance Metal Detector |
| 690K |
US5721489 |
Metal Detector Method for Identifying Target Size |
Garrett's target ID patent, lots of signal analysis and flow charts. See also 5786696. |
| 502K |
US5729143 |
Metal Detector With Nulling of Imbalance |
Bucking signal calibrated for amplitude & phase |
| 656K |
US5786696 |
Metal Detector for Identifying Target Electrical Characteristics, Depth and Size |
Garrett's target ID patent, lots of signal analysis and flow charts. See also 5721489. |
| 559K |
US5969528 |
Dual Field Metal Detector |
Garrett's two-box add-on.
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| 922K |
US6172504 |
Metal Detector Target Identification Using Flash Phase Analysis |
White's, applies phase info to what's essentially a flash ADC ; see 6421621. |
| 716K |
US6421621 |
Metal Detector Target Identification Using Flash Phase Analysis |
White's, applies phase info to what's essentially a flash ADC ; see 6172504. |
| 723K |
US6583625 |
Metal Detector and Method in Which Mineralization Effects Are Eliminated |
| 105K |
US7078906 |
Simultaneous Time-Domain and Frequency-Domain Metal Detector |
Combo PI & phase sampling |
| 106K |
US7088103 |
Metal Detector Having a Plurality of Phase Discrimination Regions with Corresponding Selectable Exception Spaces Therein |
White's |
| 193K |
US7126323 |
Systems and Methods for Synchronous Detection of Signals |
| 227K |
US7432715 |
Method and Apparatus for Metal Detection Employing Digital Signal Processing |
Minelab |
| 1587K |
US9557390 |
Noise Reduction Circuitry for a Metal Detector |
Minelab, Go-Find TX? |
| 738K |
EP0580396 |
Metal Detector with Display |
White's VDI |