The first metal detector patent: 2066561 - Gerhard Fisher, 1937 (PDF-179K)
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Induction Balance (TR, VLF)
Pulse Induction
Magnetometer
Other Geophysical
Long Range Locator
Misc. (coils, etc.)
| Frequency Shift | ||
| 3355658 | Differentiating Metal Detector for Detecting Metal Objects and Distinguishing Between Detected Diamagnetic and Non-Diamagnetic Objects (PDF-515K) | Gardiner, VLF BFO |
| 3467855 | Object Detector and Method for Distinguishing Between Objects Detected Including a Pair of Radio Oscillators(PDF-635K) | Basic BFO |
| 3546628 | Oscillating Metal Object Detector (PDF-329K) | Simplest detector on earth |
| 3601691 | Metal Detector Responsive to Small Metallic Objects for Differentiating Between Ferrous and Non-Ferrous Objects (PDF-313K) | Gardiner, Z-response |
| 3662255 | Apparatus for Locating Concealed or Buried Metal Bodies and a Stable Inductor Usable in Such Detectors (PDF-801K) | Garrett Zero-Drift BFO |
| 3823365 | Metal Detecting Apparatus Having Improved Ground-Effect Immunity (PDF-1096K) | Uses induction balance |
| 3875498 | Metal Detector for Distinquishing Between Precious Metal Objects and Other Metals (PDF-529K) | D-Tex patent, your real basic BFO. |
| 3896371 | Metal Detector With a Resonating Circuit Being Driven by a Frequency Higher Than Its Natural Resonance Frequency (PDF-902K) | A.H. Pro, Z-response type |
| 3961238 | Selective Metal Detector Circuit Having Dual Tuned Resonant Circuits (PDF-345K) | Gardiner, very basic Z-response |
| 3986104 | Dual Frequency Metal Detector System (PDF-621K) | Gardiner |
| 4130792 | Metal Detector With Feedback Tuning (PDF-694K) | Z-response with feedback |
| 4196391 | Metal Locator with Stereotonic Indication of Translateral Position (PDF-1202K) | Stereo BFO. |
| 4204160 | Metal Detector With Automatic Optimum Sensitivity Adjustment (PDF-516K) | |
| 4255710 | Plural Search Frequency Directional Metal Detector Apparatus Having Enhanced Sensitivity (PDF-1276K) | Uses two gated oscillator frequencies (I think). |
| 4321539 | Digital BFO Metal Detecting Device with Improved Sensitivities at Near-Zero Beat Frequencies (PDF-1232K) | |
| 4439734 | Metal Object Locator Including Frequency Shift Detector (PDF-1134K) | Induction balance and ground balance. |
| 4678992 | Electronic Metal Detector (PDF-925K) | A.H. Super Pro, Z-response type |
| Induction Balance | ||
|---|---|---|
| 3471773 | Metal Detecting Device with Inductively Coupled Coaxial Transmitter and Receiver Coils (PDF-436K) | Basic TR with 4B-style coil (NOT coaxial!). |
| 3686564 | Multiple Frequency Magnetic Field Technique for Differentiating Between Classes of Metal Objects (PDF-1061K) | Multi-frequency detector from 1972. |
| 3826973 | Electronic Gradiometer (PDF-1282K) | Actually, a metal detector. |
| 3872380 | Metal Detector Distinguishing Between Different Metals by Using a Bias Circuit Actuated by the Phase Shifts Caused by the Metals (PDF-484K) | Gardiner, basic phase response IB. |
| 4016486 | Land Mine Detector with Pulse Slope, Width and Amplitude Determination Channels (PDF-664K) | |
| 4024468 | Induction Balance Metal Detector with Inverse Discrimination (PDF-1275K) | White's TR Discriminator (1975), includes good description with phase diagrams and circuitry with component values. |
| 4030026 | Sampling Metal Detector (PDF-1791K) | White's, the basis of most of their early-80's analog detectors. |
| 4053828 | Metal Detector with First and Second Nested Rectangular Coils (PDF-683K) | Not too practical for a handheld. |
| 4096432 | Metal Detector for Discriminatory Detection of Buried Metal Objects (PDF-319K) | Basic phase response IB. |
| 4099116 | Metal Detector With Phase Related Selective Discrimination Circuit (PDF-840K) | |
| 4110679 | Ferrous/Non-ferrous Metal Detector Using Sampling (PDF-1245K) | White's |
| 4128803 | Metal Detector System With Ground Effect Rejection (PDF-779K) | PNI (the old Bounty Hunter), probably the Red Baron series (RB3/5/7). |
| 4249128 | Wide Pulse Gated Metal Detector With Improved Noise Rejection (PDF-1021K) | White's |
| 4263553 | Discriminating Metal Detector With Compensation for Ground Minerals (PDF-779K) | |
| 4300097 | Induction Balance Metal Detector with Ferrous and Non-ferrous Metal Identification (PDF-882K) | |
| 4303879 | Metal Detector Circuit with Mode Selection and Automatic Tuning (PDF-1531K) | 1979 Garrett patent (ADS?) |
| 4325027 | Metal Detector for Locating Objects with Full Sensitivity in the Presence of Distributed Mineral Material (PDF-1352K) | Compass |
| 4334191 | Metal Detector Circuit Having Momentary Disabled Output (PDF-1150K) | Garrett |
| 4334192 | Metal Detector Circuit Having Automatic Tuning With Multiple Rates (PDF-1238K) | Garrett, probably their Master Hunter VLF. |
| 4344034 | Selective Ground Neutralizing Metal Detector (PDF-1218K) | Gardiner patent for phase discriminator. |
| 4348639 | Transmitter-Receiver Loop Buried Metal Object Locator with Switch Controlled Reference Vooltage (PDF-1008K) | Discovery Electronics' two-box detector. |
| 4423377 | Compact Metal Detector of the Balanced Induction Type (PDF-802K) | Garrett, handheld with integrated double-D coil. See also 4488115. |
| 4470015 | Metal Detector System With Undesirable Target and Mineralized Ground Discrimination (PDF-3127K) | Teknetics, lots of diagrams and waveforms. |
| 4486712 | Frequency Dependent Pulsed Gain Modulated Metallic Object Detector (PDF-941K) | |
| 4486713 | Metal Detector Apparatus Utilizing Controlled Phase Response to Reject Ground Effects and to Discriminate Between Different Types of Metals (PDF-1210K) | Lots of signal & phase diagrams |
| 4488115 | Low Battery Voltage Indicator Circuit for a Metal Detector (PDF-729K) | Garrett, see also 4423377 |
| 4507612 | Metal Detector Systems for Identifying Targets in Mineralized Ground (PDF-6034K) | Teknetics, tons of info. |
| 4514692 | Metal Detector and Discriminator Using Differentiation for Background Signal Suppression (PDF-734K) | |
| 4628265 | Metal Detector and Classifier with Automatic Compensation for Soil Magnetic Minerals and Sensor Misalignment (PDF-1126K) | |
| 4677384 | Target-Identifying Metal Detector (PDF-1728K) | Teknetics |
| 4700139 | Metal Detector Circuit Having Selectable Exclusion Range For Unwanted Objects (PDF-1208K) | Garrett patent with a pretty good explanation of I&Q signal processing. |
| 4709213 | Metal Detector Having Digital Signal Processing (PDF-2644K) | White's |
| 4783630 | Metal Detector With Circuits for Automatically Screening Out the Effects of Offset and Mineralized Ground (PDF-1073K) | White's |
| 4868504 | Apparatus and Method for Locating Metal Objects and Minerals in the Ground with Return of Energy from Transmitter Coil to Power Supply (PDF-1050K) | In other words, a metal detector. |
| 4868910 | Metal Detector with Microprocessor Control and Analysis (PDF-2815K) | White's, ton's of info on their target ID. |
| 4894618 | Metal Detector Using Cross-Correlation Between Components of Received Signals (PDF-1325K) | Minelab patent with good explanatory text. |
| 4912414 | Induction-Type Metal Detector with Increased Scanning Area Capability (PDF-1055K) | Describes a large array for use with a submersible, includes IB and PI methods. |
| 4942360 | A Method and Apparatus of Discrimination Detection Using Multiple Frequencies to Determine a Recognizable Profile of an Undesirable Substance (PDF-1275K) | Minelab multiple frequency. |
| 5148151 | Metal Detector Having Target Characterization and Search Classification (PDF-1251K) | Garrett patent on VDI, explanantion on phase response and VDI flowchart. |
| 5506506 | Metal Detector for Detecting and Discriminating Between Ferrous and Non-ferrous Targets in Ground (PDF-1669K) | |
| 5523690 | Metal Detector with Bivariate Display (PDF-1055K) | White's patent detailing VDI, includes 6805 assembly code. (see also 5596277) |
| 5596277 | Method and Apparatus for Displaying Signal Information from a Detector (PDF-959K) | White's patent detailing VDI, includes 6805 assembly code. (see also 5523690) |
| 5642050 | Plural Frequency Method and System for Identifying Metal Objects in a Background Environment Using a Target Model (PDF-2199K) | White's multi-frequency detector (see 5654638). |
| 5654638 | Plural Frequency Method and System for Identifying Metal Objects in a Background Environment (PDF-2306K) | White's multi-frequency detector (see 5642050). |
| 5691640 | Forced Balance Metal Detector (PDF-980K) | |
| 5721489 | Metal Detector Method for Identifying Target Size (PDF-1896K) | Garrett's target ID patent, lots of signal analysis and flow charts. See also 5786696. |
| 5786696 | Metal Detector for Identifying Target Electrical Characteristics, Depth and Size (PDF-1245K) | Garrett's target ID patent, lots of signal analysis and flow charts. See also 5721489. |
| 5969528 | Dual Field Metal Detector (PDF-559K) | Garrett's two-box add-on. |
| Pulse Induction | ||
| 4605898 | Pulse Field Metal Detector with Spaced, Dual Coil Transmitter and Receiver Systems (PDF-495K) | Walkthrough PI. |
| 4894619 | Impulse Induced Eddy Current Type Detector Using Plural Measuring Sequences in Detecting Metal Objects (PDF-495K) | |
| 5047718 | Improving the Discrimination of an Impulse Technique Metal Detector by Correlating Responses Inside and Outside of a Cut-Off Peak Area (PDF-481K) | |
| 5414411 | Pulse Induction Metal Detector (PDF-678K) | White's, block level. |
| 5537041 | Discriminating Time Domain Conducting Metal Detector Utilizing Multi-Period Rectangular Transmitted Pulses (PDF-2369K) | Minelab pulse. |
| 5576624 | Pulse Induction Time Domain Metal Detector (PDF-2032K) | |
| Magnetometers | ||
| 3919630 | Flux Detection Device Using a Parametrically Excited Second Harmonic Oscillator (PDF-546K) | |
| 4068164 | Harmonic Flux Gate Magnetometers and Gradiometers and Windings (PDF-1024K) | |
| 4277751 | Low-Power Magnetometer Circuit with Constant Current Drive (PDF-833K) | |
| 4293815 | Fluxgate Magnetometer Circuit with Earth's Field Elimination (PDF-1948K) | |
| 4439732 | Electrically Balanced Fluxgate Gradiometers (PDF-1260K) | |
| 4677381 | Flux-gate Electrical Drive Method and Circuit (PDF-873K) | |
| 4887033 | Magnetometer Having Coil Formed by Two Spiral Shaped Conductors (PDF-470K) | |
| 5168223 | High Sensitivity Saturable Core Magnetic Field Sensor with Symmetrical Structure (PDF-1082K) | |
| 5670882 | Ferrous Target Identification System with Magnetic Field Polarity and Gradient Indication (PDF-1099K) | |
| 5939881 | High Dynamic Range Digital Fluxgate Magnetometer (PDF-587K) | |
| Other Geophysical | ||
| 3500175 | Electromagnetic Prospecting Apparatus Utilizing VLF Radio Field (PDF-732K) | VLF Receiver. |
| 3614600 | Electromagnetic Prospecting Apparatus for Detecting Electrically or Magnetically Responsive Ore Bodies (PDF-1052K) | VLF Receiver. |
| 3617866 | Geophysical Surveying with Audio Frequency Electromagnetic Fields and Orthogonal Receiver Coils (PDF-1749K) | |
| 3636435 | Method of Electromagnetic Prospecting by Measuring Relative Gradient of a Resultant Electromagnetic Field (PDF-435K) | VLF Receiver. |
| 3763419 | Geophysical Using the Vertical Electric Component of a VLF Field as a Reference (PDF-670K) | |
| 3852659 | Geophysical Prospecting Method and Apparatus Utilizing Correlation of Received Waveforms with Stored Reference Waveforms (PDF-655K) | |
| 3950695 | Geophysical Prospecting Method Utilizing Correlation of Received Waveforms with Stored Reference Waveforms (PDF-793K) | |
| 3967190 | Method Using Induced Polarization for Ore Discrimination in Dissiminated Earth Deposits (PDF-1133K) | |
| 4070612 | Method and Apparatus for Measuring Terrain Resistivity (PDF-1042K) | |
| 4114086 | Inductive Source Method of Induced Polarization Prospecting (PDF-338K) | Prospecting method. |
| 4258321 | Radio Geophysical Surveying Method and Apparatus (PDF-1687K) | |
| Long Range Locator | ||
| 5748088 | Device and Method Using Dielectrokinesis to Locate Entities (PDF-999K) | Patent by Thomas Afilani (of Electroscope fame). Basically just a dowsing rod, proof that the USPTO will allow anything. |
| 5907280 | Static Electrification Assisted Dielectrokinetic Detection of Plastics and Other Materials (PDF-666K) | Patent by Thomas Afilani, more nonsense. |
| 6011476 | Metering Circuit to Detect Dielectrokinetic Response (PDF-603K) | Yet another patent by Thomas Afilani. |
| D245233 | Dowsing Rod (PDF-61K) | By Sam Wolfe - This is a Design Patent. |
| D248377 | Dowsing Rod (PDF-73K) | By Sam Wolfe - This is a Design Patent. |
| D306703 | Frequency Induction Locator to Find Gold and Silver (PDF-118K) | The Electroscope by Thomas Afilani - This is a Design Patent. |
| D406068 | Locator Device (PDF-96K) | DKL Lifeguard by Thomas Afilani - This is a Design Patent. |
| Misc. | ||
| 3882374 | Transmitting-Receiving Coil Configuration (PDF-276K) | IB |
| 3941690 | Portable Sluice Pan (PDF-499K) | |
| 4255711 | Coil Arrangement for Search Head of a Metal Detector (PDF-1128K) | Compass, concentric IB |
| 4293816 | Balanced Search Loop for Metal Detector (PDF-552K) | White's concentric loop |
| 4345208 | Anti-falsing and Zer Nulling Search Head for a Metal Detector (PDF-405K) | Daytona search coil |
| 4472269 | Sluice Box Classifier for Gold Mining Dredge (PDF-382K) | |
| 4862316 | Static Charge Dissipating Housing for Metal Detector Search Loop Assembly (PDF-703K) | White's concentric loop |
| 4890064 | Metal Detector Sensing Head with Reduced Eddy Current Coils (PDF-439K) | Minelab |
| 5247257 | Electronic Metal Detector Return Signal Phase Changer (PDF-680K) | A nail and two coils, weird. I don't know what to make of this one. |
| 5680048 | Mine Detecting Device Having a Housing Containing Metal Detector Coils and an Antenna (PDF-955K) | Appears to combine a metal detector and GPR in one search head. |
| 5696490 | FM (VHF) Infrared Wireless Digital Metal Detector (PDF-324K) | Places the control box near the coil and uses IR to transfer info to the meter, pretty useless. |
| 5863445 | Etched Coil Unibody Digital Detector (PDF-1216K) | Handheld wand. |
