The following are patents on metal detector coils.

Download Patent # Title Description
PDF 301K US3549985 Metal Detector Device Having a Disk-ShapedHead for Housing a Coil System Seems to mostly cover plastics & fillers
PDF 462K US3753185 Metal Detector Search Coil Bill Mahan, D-Tex
PDF 276K US3882374 Transmitting-Receiving Coil Configuration IB
PDF 1162K US4255711 Coil Arrangement for Search Head of a Metal Detector Compass, concentric IB
PDF 624K US4276484 Method and Apparatus for Controlling Current in Inductive Loads Such as Large Diameter Coils Pulse method
PDF 613K US4293816 Balanced Search Loop for Metal Detector White's concentric loop
PDF 405K US4345208 Anti-falsing and Zero Nulling Search Head for a Metal Detector Daytona search coil
PDF 405K US4552134 Equipment for Determining the Position of a Metal Body in a Medium With Low Electric Conductivity Particular IB coil arrangement
PDF 735K US4862316 Static Charge Dissipating Housing for Metal Detector Search Loop Assembly White's concentric loop
PDF 439K US4890064 Metal Detector Sensing Head with Reduced Eddy Current Coils Minelab
PDF 1142K US5038106 Detector of Metalliferous Objects Having Two Pairs of Receiving Loops Symmetrical and Orthogonal to a Driving Loop see US5039946
PDF 877K US5039946 Metalliferous Objects Detector Having a Pair of Angularly Positioned Driving Loops and a Pair of Parallel, Coaxial Receiving Loops see US5038106
PDF 614K US5245307 Search Coil Assembly for Electrically Conductive Object Detection
PDF 411K US5498959 Metal Detector With Multipolar Windings Shaped So As To Eliminate the Neutralizing Effects When Several Metal Masses Are Passing Through Simulataneously Walk-through type coil arrangement
PDF 392K US5557206 Apparatus & Method for Detecting a Weak Induced Magnetic Field by Means of Two Concentric Transmitter Loops Geophex, concentric IB coil
PDF 429K US5859532 Method of and Measuring Arrangement for Metal Detection With a Coil Device Having Several Separately Controllable Regions Coil arrangements for walk-through type
PDF 1216K US5863445 Etched Coil Unibody Digital Detector Handheld wand.
PDF 465K EP0249110 Sensors for Metal Detectors Some various coil arrangements
PDF 56K US6690169 Interference Cancelling Metal Detector Including Electronic Selection of Effective Sensing Coil Arrangement Minelab
PDF 779K US6791329 Portable Metal Detection and Classification System Coil methods for a powered rover
PDF 154K US6822429 Inductive Sensor Arrangement Comprising Three Sense Coil Cooperating with Said Three Field Coils to Perform Three Field/Sense Coil Pairs and Method for Detecting of Ferrous Metal Objects Say that 3 times fast.
PDF 96K US7075304 Variable Damping Induction Coil Metal Detection Uses a MOSFET for the damping resistor
PDF 98K US7157913 Re-Configurable Induction Coil for Metal Detector Carl V. Nelson, PI flip-coil
PDF 147K US7176691 Switched Coil Receiver Antenna for Metal Detector Carl V. Nelson, PI flip-coil
PDF 61K US7656153 Metal Detector with Improved Receiver Coil Allan Westersten, PI flip-coil
PDF 88K US7994789 Dual-Field Search Coil for Pulse Induction Metal Detectors White's TDI
PDF 189K US11454736 Metal Detector Minelab, Coil compensation
PDF 256K US11474274 Metal Detector Minelab, Coil compensation
PDF 465K EP0249110 Sensors for Metal Detectors Some various coil arrangements
PDF 80K EP0764856 Sensor for a Metal Detector Several IB coil arrangements
PDF 552K WO08703380 Metal Detector Sensing Head with Reduced Eddy Current Coils Minelab, same as US4890064