Abstract:
A metal detector that is to be attached to a human appendage and preferably the wrist and hand of a human. A metal detector includes a housing which is to be worn strictly by the human hand or the hand and the wrist. One version of the metal detector would be in the form of a glove. The second version would be in the form of a flexible base which is mounted between the hand and the wrist by a strap arrangement. Within both versions, there is a search coil located in the palm area of the hand. A metal detection circuit battery source is mounted on the portion of the housing that is located directly against the backside of the hand.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of this invention is directed to metal detection devices and more particularly to a metal detection device which is to be directly mounted on a human hand. 
     2. Description of the Prior Art 
     Metals have one important property possessed by no other elements that enables such to be readily distinguished with suitably sensitive apparatus. This property is their high electrical conductivity. By generating an alternating magnetic field in the vicinity of a metal object, electric currents are induced in the object which in turn set up a magnetic field around the object which distorts the original field. By detecting this distortion, the metal object can be located. 
     One common type of metal detector is deemed a pulse magnetization unit. Pulse magnetization units rely on the fact that a magnetic field takes a finite time to propagate through air or earth. The speed of propagation is the same as for electromagnetic radiation, that is, the speed of light. Such units operate as magnetic “radar” units. A short, high-powered pulse is generated in a search coil, and after the pulse is cut off, the unit goes from a transmit mode to receive mode. If there is a metallic object within the field, this object generates its own magnetic field by the process of induced magnetism, and this is detected a finite time after the transmitted pulse. Such metal detectors are used to detect coins, jewelry and any metallic object on beaches, parks and other places common to the usage by humans. Some people have made it a hobby to use such metal detectors to discover such lost metallic objects. 
     However, metal detectors are also used as stationary units within airports. The purpose of the stationary metal detector is to detect the presence of a dense metallic object on a person before that person enters an airplane either as a passenger or a crew member. Metal detectors are also used as portable units which can be readily carried by a person. These portable units are the detectors that are used to detect the presence of metal within areas, such as beaches and parks, that are frequently used as places of congregation by people. 
     Within the field of law enforcement, portable metal detectors are commonly used to detect the presence of metallic objects on a person that is subject to detainment. Normally, the metallic object that is being looked for is a knife or a gun. Typically, such metal detectors are in the shape of a “wand”. This wand comprises a hand graspable cylindrical object, usually about ten inches in length, that is intended to be moved in close proximity to the person that is being examined. Upon a metal object being detected, the metal detector will activate an annunciator which can be in the form of a vibrator, a light or a buzzer. The metal object can then be removed from the person that is being examined. 
     One problem with such a wand type of annunciator is that it requires that one hand of the operator be used to operate the metal detector. In law enforcement, it would be preferable to use a metal detector which did not require the entire usage of ones hand thereby leaving that hand free to perform other tasks such as permit the physical grasping of a discovered metallic object. It may also save a law enforcement officer&#39;s life to have available both hands to counter a physical accostation rather than having one hand occupied. 
     SUMMARY OF THE INVENTION 
     A metal detector circuit and power supply which is mounted in conjunction with a housing. The metal detector circuit includes a search coil, this search coil being included in the portion of the housing that is to be located directly adjacent the palm of a human hand. Typically, the housing could comprise a glove or could comprise a sheet material, flexible base upon which are mounted a pair of straps. One of the straps is to be located across the palm of the hand with the search coil being mounted in conjunction with this strap. The remaining strap is to include a disconnectable attachment such as a fastener arrangement that is commonly sold under the tradename of “Velcro”. This strap is to be generally wound around the wrist of the user. The battery for the detection circuit and the detection circuit are usually mounted on the portion of the base which is located directly adjacent the back of the hand. 
     A primary objective of the present invention is to construct a small size metal detector which is attached directly to the user&#39;s hand which leaves the user hand free to perform other tasks even while using the metal detection device. 
     Another objective of the metal detector of the present invention is to construct a metal detector which can be manufactured at a reasonable price and therefor sold to the ultimate consumer at a reasonable price. 
     Another advantage of one version of the metal detection apparatus of this invention is that it is constructed so as to be readily mountable on either the left hand or the right hand of the user. 
     Another objective of one version of the metal detector of the present invention is that the detector is not size dependent on the size of the hand on which it is mounted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exterior isometric backside view of the metal detector of the present invention showing such as it is mounted on a human appendage in the form of a hand and wrist; 
     FIG. 2 is a left end view of the metal detector of the present invention taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a right end view of the metal detector of the present invention taken along line  3 — 3  of FIG. 1; 
     FIG. 4 is a bottom view of the metal detector of the present invention showing more clearly the mounting arrangement of the metal detector in conjunction with the palm area of the hand; 
     FIG. 5 is an electrical schematic of the metal detector circuit that is utilized in conjunction with the metal detector of the present invention; 
     FIG. 6 is a side view of a glove version of metal detector of the present invention; and 
     FIG. 7 is a bottom view, or palm area view, of the metal detector glove of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring particularly to FIG. 1, there is shown in phantom lines a human wrist  10  which is connected to a human hand  12 . A housing in the form of a sheet material base  14  is mounted against the upper surface of the hand  12  and the upper surface of the wrist  10 . The sheet material base  15  is basically of a rectangular configuration. A typical material of construction for the base  15  would possibly be a semi-rigid plastic with this plastic covered by fabric  14  would be preferable. It is to be understood that the base  15  is to have a certain amount of flexibility to be capable of slightly changing shape so as to conform to the individual configurations of user&#39;s hands  12  and wrist  10 . 
     At the fore end of the base  15 , there is attached an elastic band  16 . The elastic band  16  is to be somewhat stretchable and is continuous. The user&#39;s fingers  18 ,  20 ,  22 , and  24  are to be slipped through the open area enclosed by the elastic band  16  with the elastic band  16  forming a tight fit across the palm section  26  of the hand  12 . Connected to the aft end of the base  15  is an attaching strap  28 . The outer end of the attaching strap  28  includes a fastener pad  30 . A similar fastener pad  32  is mounted on the exterior surface of a battery pouch  34 . When the attaching strap  28  is wrapped to the desired degree of tightness about the wrist  10 , the fastener pads  30  and  32  are engaged which retains the attaching strap  28  in an attached position relative to the base  15 . The battery pouch  34  is mounted on the sheet material base  15 . The battery pouch  34  is to provide a compartment  35  to retain a conventional battery  36 . Typically, the battery  36  will comprise a nine volt battery. The pouch  34  will generally be constructed of a fabric material. Within the pouch  34 , the battery  36  is connected by battery connector  37  to conductor  38  to an on/off switch  40  which is mounted on circuit housing  42 . Within the circuit housing  42  is located the circuit shown in FIG.  3 . The circuit housing  42  is mounted within pouch compartment  41  of pouch  39 . The circuit board  43  includes the electrical circuit of FIG.  5 . 
     It is to be noted that the base  15  can be mounted on either the user&#39;s left hand or right hand with the elastic band  16  extending across the palm section  26  of either hand. Therefore, the embodiment shown in FIG. 1 of the drawings is not size dependent and is not dependent upon being applied to a particular hand as it would be applicable to both. 
     Power for the circuit shown in FIG. 5 is supplied from the nine volt battery  36  through the on/off switch  40  which comprises a single pole, single throw, toggle switch. When the switch  40  is closed, voltage is applied to a three terminal, five volt regulator  44 . A part number LM78LO5 of National Semiconductor could be used for the five volt regulator  44 . A 0.1 microfarad (uf) decoupling capacitor  46  is used to reduce noise and transients on the five volt power line. 
     A microcontroller  48 , such as micro chip PIC16C54 of National Semiconductor, has eight bits. This microcontroller  48  develops and controls the timing signals required. Resistor  50  and capacitor  52 , twenty pico farads (pf), form a resistor/capacitor clock of approximately four megahertz (MhZ) which causes an instruction to be executed every one microsecond within the microcontroller  48 . 
     The process by which metal is detected starts with a thirty microsecond positive pulse generated by the microcontroller  48  on pin  17 . This pulse is coupled through a one kiloohm (Kohm) resistor  54  to the base of NPN transistor  56 . Transistor  56  saturates and pulls the voltage at biasing resistor  58  low which causes the PNP power Darlington transistor  60  to switch on. Capacitor  62 , which is charged through decoupling diode  64  and current limiting resistor  66  to approximately nine volts when transistor  60  is off, now discharges through transistor  60  into the search coil  68  causing a large current to flow. Part No. TIP115 of National Semiconductor would be satisfactory for the transistor  60 . The search coil  68  is mounted within the elastic band  16 . The conductor  70  connects with the search coil  68 . 
     The search coil  68  consists of five feet in length of number  30  magnet wire wound on a one inch diameter air core. The high current pulse through the search coil  68  causes a magnetic field to be produced. The end of the thirty microsecond pulse abruptly turns off transistor  60 . The collapsing magnetic field causes a large negative voltage to be induced across the search coil  68 . This negative voltage collapses producing a weak positive overshoot. Resistor  72  dampens the circuit to one positive over-shoot. These voltage fluctuations are coupled through resistor  74  and limited to 0.6 volts by diodes  76  and  78  at the input to amplifier  80 . The amplifier  80  consists of one-quarter of a quad operational amplifier, part number LM324, manufactured by National Semiconductor. Resistors  82  and  84  set the gain of the amplifier  80  at one thousand. The resulting highly amplified signal is applied to comparator  86  which consists of another one-quarter segment of the quad operational amplifier. Resistors  88  and  90  set the comparators  86  switch point at approximately 2.1 volts. 
     In the absence of metal near the search coil  68 , the output of the comparators  86  drops to zero volts for approximately 110 microseconds. As a metal object (not shown) is brought near the search coil  68 , the voltage across the search coil  68  stabilizes sooner. This reduces the time the comparator  86  is at zero volts. The time the comparator  86  is low is indicative of the size and proximity of the metal to the search coil  68 . Normal times range from 110 microseconds with no metal present to 70 microseconds for a piece of metal the size of a penny directly next to the search coil  68  or a pistol a short distance away from the search coil  68 . This negative pulse is presented to the microcontroller at  48  on pin  18 . The microcontroller  48  counts the number of instructions it can execute while pin  18  is low. The number thus produced is a quantification of metal near the search coil  68 . 
     It is desirable in the application to indicate to the operator not only the presence of metal near the search coil  68  but its relative size and location. This indication is provided by subtracting the current number (count of how long pin  18  is low) from the previous number measurement. A positive difference indicates that the search coil  68  is approaching a metal object. A negative difference indicates that the search coil  68  is farther from the metal object. The microcontroller  48  accumulates these positive and negative differences. Negative accumulations are ignored and set to zero. 
     A small DC motor  93  with an offset weight on its shaft (not shown), similar to those found in pocket pagers, is used to inform the operator of presence and location of metal near the search coil  68  by the vibrations produced while the motor  93  is on. This is controlled by pin number  1  of the microcontroller  48 . When pin number  1  is set high, current flows through resistor  92  saturating switch transistor  94 . When transistor  94  is on, current flows through the motor  93  and current limiting resistor  96 . The output of the motor  93  produces relatively strong vibrations which can be easily felt by the user. 
     Because of the dynamic nature of the circuit, the microcontroller  48  pulses the motor  93  one-fourth of a second on and one-fourth of a second off when indicating the presence of positive accumulations. This allows time to take a reading between pulses. The new difference value is computed and combined with previous accumulations. After each pulse, the accumulated value is decremented. A negative accumulation is set to zero. In this way, the process produces motor pulses when the search coil  68  is approaching metal and stops producing motor pulses within motor  93  when the search coil  68  is receding from metal. This technique produces a dynamic measurement which has two advantages over setting a value below which the circuit would indicate metal in the proximity. First, there is no need for adjustments to compensate for conditions, component differences and circuit drift. Circuit drift might be caused due to heat while an example of component differences would be slight changes in the output of the battery  36 . Any ambient condition is automatically adjusted for while the circuit remains at maximum sensitivity. Second, the circuit provides an indication while the search coil  68  is approaching a metal abject. This is significantly more information than just a metal object is nearby. These advantages allow the operator to quickly determine the amount of metal present and its precise location. 
     Usage of the metal detector shown. in FIG. 1, when activated, requires that the user&#39;s hand  12  be placed in close proximity to a metal object. A typical usage would be by a law enforcement officer when “padding a suspect down”. Upon the motor  93  being activated, the operator then knows to venture within the suspect&#39;s clothes in order to ascertain what type of metal has been detected. The purpose is to discover a dangerous piece of metal such as a gun or knife. It is to be noted that the structure shown in FIG. 1 can be mounted on either hand of the operator, not being required to be mounted on a single hand. 
     The same metal detector circuit shown in FIG. 5 could be mounted on a conventional glove  98 , which is shown in FIGS. 6 and 7. It is to be understood that the glove shown in FIGS. 6 and 7 is for a left hand, but the circuit of FIG. 5 could also be incorporated in conjunction with a right handed glove. The search coil  68  is mounted with the palm section  100  of the glove  98 . It is to be understood that the user&#39;s hand is to be located within the interior of the glove  98 . The battery  36  is mounted within a pouch  34  mounted on the backside of the glove  98 . Also, the circuit housing  42  is fixedly mounted in some conventional manner on the backside of the glove  98 . The fingers of the glove  98  may be cut off permitting the user&#39;s tips of the fingers to extend exteriorly of the glove  98 , if such is desired.