Abstract:
This invention relates to a method for using electromagnetic radiation to destroy data stored on a device that includes a data storage region and a conductive region. For example, common Compact Disks (often called a CD) and Digital Versatile Disks (often called a DVD) both have regions of the disk constructed to have at least one data storage layer and at least one conductive layer. The method disclosed in this invention relies on electromagnetic radiation, such as microwave radiation, to set up an electric field in the conductive layer of the data storage disk, where the electrical field is strong enough to alter the physical proprieties of a fraction of the data storage region of the disk. The data stored in and near these physically altered regions is destroyed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable  
         FEDERALLY SPONSORED RESEARCH  
         [0002]    Not Applicable  
         SEQUENCE LISTING OR PROGRAM  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of Invention  
           [0005]    This invention relates to a method for destroying data stored on a device that includes a data storage region and a conductive region. For example common Compact Disks (often called a CD) and Digital Versatile Disks (often called a DVD) both have at least one layer that stores data and at least one conductive layer. In this sense a conductive layer is one fabricated from a material that interacts with electromagnetic radiation to produce an electric field.  
           [0006]    The essence of this invention then is a method that exposes the data storing disk to sufficient electromagnetic radiation so that an electrical field is formed on (or within) the data storage device that is strong enough to break down sections of the material forming the layer (or layers) used to store data.  
           [0007]    2. Prior Art  
           [0008]    Various methods to destroy data-holding-media have been in use for as long as people have been storing data on some type of storage media. In recent years this would means that as people have created various documents there has been a need to destroy some of these copies. An example would be a lawyer working on revisions of a legal brief. In this example, once the final draft is complete, the lawyer may wish to destroy the intermediate copies. The intermediate drafts of the lawyer&#39;s brief could have been:  
           [0009]    1. Printed on paper.  
           [0010]    2. Stored on magnetic based media, such as those commonly called “floppy disks”.  
           [0011]    3. Stored on recordable disks that use laser light (either visible or invisible) to read the data, such as a Compact Disk (commonly called a CD).  
           [0012]    In order to destroy the intermediate copies the lawyer could:  
           [0013]    1. In the case of paper based documents; the lawyer could use a paper shredder.  
           [0014]    2. In the case of magnetic media, the lawyer would have two options. The lawyer could use one of the commercially available software utilities that are used to rewrite every byte on the disk. However, this is a time consuming process. The other option would be to use one of the commercially available magnetic devices. These devices expose the entire disk to a large magnetic field, thus disrupting the orderly magnetic patterns used to store the data. In many situations this is the most convenient option.  
           [0015]    3. In the case of a recordable disk there are some issues. One is that most of these disks can be written but a single time, eliminating the option of over-writing every byte on the disk. The other problem is that even with the more expensive read/write disks, the rewriting of every byte is a very time consuming operation. Therefore currently the only practical option is to physically destroy the disk.  
           [0016]    Of particular interest as background for this invention is how CDs are currently destroyed. Since the disks are physically harder than paper, the use of a shredder would require one more powerful (and thus more costly) than typical paper shredders. It is important to note that currently most large business operations use some type of machine in order to destroy data on CDs and DVDs. For example “Whitaker Brothers Business Machines” located at 12410 Washington Ave Rockville Md. 20852 makes an industrial grade CD destroyer. This unit called the “Whitaker Bros. 101-CD Datastroyer” sells, in December 2002, for $2,549.00. The manufacture claims this unit can be used to destroy up to 600 CDs per hour. As a point of comparison personal paper shredders that cut the paper into strips can be bought for well under $100.00 and sophisticated units that can handle stapled multi-page documents, and that can cut the paper into “confetti”, can be bought at most office supply stores for well under $200.00.  
           [0017]    As a side note, it should mentioned that one feature of the Whitaker CD destroyer is that it cuts up the disks, but preserves that center ring. This is important since there are times that software vendors use the center ring to print ID numbers. By preserving the center ring, a company can show that a licensed copy of software has been destroyed. (This is sometimes required as part of the auditing requirements set out in the software licensing agreement.)  
           [0018]    More important for this invention is to note that in smaller organizations, or for personal use, a CD destroyer can&#39;t be justified based on the high cost of the device. In some cases, such as small software companies (where the entire efforts of the R&amp;D group can be stored on a single CD) the intermediate builds of the software written to CDs are sometimes being destroyed manually. In at least one case, a software engineer has been given a hammer and told to use it to destroy each week&#39;s CDs.  
           [0019]    In addition to cutting a data disk into parts, several inventors have used other mechanical means to disrupt the data storage layer of CDs. This is done while leaving the CD mostly intact (so as to preserve the disk for auditing purposes). Most often these are specialized devices that have been optimized for use in declassifying CD type disks. By declassifying is meant that the National Security Agency (NSA) has set very rigorous standards that must be followed when a data disk with classified information is no longer needed. The process of removing the classified information, while preserving the disk for auditing purposes, is called declassification. An example of one of these system, called the CD/Optical data eraser model 1200 is made by “Proton Engineering Inc.” (Proton Engineering can be contacted at P.O. Box 1852, Palm City, Fla. 34990 or on the web at w.proton-eng.com.) This system retails in December 2002 for $4995.00. Other examples of systems that disrupt the data layer on a CD by mechanical means include systems described in the following U.S. patents:  
           [0020]    U.S. Pat. No. 5,520,865 by George Sargent disclosed a “Method for defacing compact discs”. In Sargent&#39;s invention a set of knurling wheels is used to cut grooves into a CD.  
           [0021]    U.S. Pat. No. 6,189,466 by William Olliges discusses a “System for the secure destruction of compact disc data”. Olliges&#39; invention uses a system of high pressure rollers to emboss a disk.  
           [0022]    U.S. Pat. No. 6,334,582 by Charles Castronovo described a “High-security CD disk erasure process, and portable machine for accomplishing high-speed, high-security CD disk erasure”. In this system a rotating cutter is used along with a collection system that collects the flakes cut from the disk and then grinds the flakes into dust.  
           [0023]    All these previously listed systems rely on relatively complex mechanical mechanisms to accomplish the job. While several of these systems meet the demanding requirements of the NSA declassification standard, they are relatively expensive. However, most home and office users don&#39;t deal with classified data. As such a lower cost system that destroys large sections of the data storing surfaces, and renders the disk unreadable in conventional computers, is adequate.  
           [0024]    Also it should be noted that recently the vast majority of PCs that are being built have been shipping with a CD (or DVD) writer. With this development, it should be obvious that a low cost, yet simple to use device is needed that typical home and office users can use to destroy the data on unneeded CDs and DVDs.  
         OBJECTS AND ADVANTAGES OF THE PRESENT INVENTION  
         [0025]    The objective of the current invention is to provide a low cost simple to operate device that can be used to destroy the data stored on certain types of data disks. In particular the types of data disks would contain one or more data layers and at least one conductive layer, as is typical in the construction of compact disks (commonly called a CD) and digital versatile disks (sometimes called digital video disks but most commonly called a DVD).  
         BRIEF SUMMARY OF THE INVENTION  
         [0026]    In accordance with the present invention a method for using electromagnetic radiation for destroying data stored on a data storage device that includes a data storage region and a conductive region is disclosed. The types of data disks would include common compact disks (often called a CD) and Digital Versatile Disks (often called a DVD). Note that both of these types of disks have regions that are constructed with at least one layer that stores data and at least one conductive layer.  
           [0027]    For this invention the electromagnetic radiation may be from a microwave source, such as a source with a power and frequency output as found in common household microwave ovens. [Note that a typical magnetron used in a household microwave oven emits microwave radiation at about 2.45 GHz and has an output power of approximately 650 watts.] 
       
    
    
     DRAWING  
       [0028]    In the Drawing, FIG. 1, a schematic view of the mechanical modifications made to convert a common microwave oven into the preferred embodiment of this invention is shown. 
     
    
     THEORY OF OPERATION  
       [0029]    For over 50 years the interaction of conductive surfaces with microwaves has been well known. This was first exploited at the beginning of World War II. At the time electromagnetic waves that were emitted in the 2 to 3 GHz range (microwaves) were found to reflect off of metal, but not to be absorbed by the air. This was exploited in the design of radar systems. It was soon realized that these same wavelengths could be used to excite water molecules causing them to heat up. Appling this discovery to the cooking of food was done, and commercial microwave ovens were offered for sale starting in about 1947. Over the past half of century the wide spread acceptance of these types of ovens has driven down the cost of manufacturing such that complete ovens can be bought at retail stores in December 2002 for less than $50.00.  
         [0030]    Another track of inventions followed where lasers are used for writing data to a data storage disk. Interestingly the read back of the data requires a light be reflected back towards a sensor. For this invention the mechanism of how this reading is done isn&#39;t important. Instead the fact that the reflective surface is made of conductive material is important. What is important is that in CDs and DVDs that the thin metal layer has some interesting proprieties when exposed to sufficient electromagnetic radiation. In particular microwave radiation sets up an electric field that is strong enough to vaporize paths through the conductive material. As the conductive layer is being vaporized it is altering the physical proprieties of the disk. In particular some of the material of the disk is being burnt. The effect is that some parts of the data disk that are destroyed include sections of the material that are used to store data.  
         [0031]    Within seconds of exposing a CD or DVD type disk to microwave radiation there are thousands of pathways burned through the data layer by the electrical arcing. In other words, the electrical field is strong enough to alter the physical proprieties of some fraction of the data storage region. The data within these burned out regions is destroyed and based on the large number of these burns the data that was originally on the disk can no longer be read.  
         [0032]    One interesting aspect of this destruction is that the center ring isn&#39;t destroyed. This means that this invention can be used on a disk that includes an ID numbers, where the altered disk with ID numbers can be preserved for auditing purposes.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    For demonstration purposes a conventional microwave oven (one that produces microwave radiation at 2.45 GHz and 650 watts of output power) can be used. In this case one, or a few, disks can be placed in the oven and full power applied for about 4 seconds. During the time power is applied arcing will be visible as patterns of light dancing around the disk. It is while this arcing is occurring that portions of the data layer are being destroyed. However, there are three problems with this approach.  
         [0034]    1. When the oven door is opened there will be a smell of burnt plastic.  
         [0035]    2. If the oven is left on too long the microwaves will be reflected back into the magnetron, causing it to overheat.  
         [0036]    3. It is inconvenient to use.  
       DESCRIPTION—FIG.  1 —THE PREFERRED EMBODIMENT  
       [0037]    To address the problems of using a conventional microwave oven several modifications need to be made. However, before discussing these modifications it is important to note that using a conventional microwave oven as the basis of the design is done for illustrative purposes. However, using the core of a typical microwave oven would make sense for practical economic reasons. For example modifying the magnetron design used in a typical microwave oven would be expensive and the volume of these data destroyer machines wouldn&#39;t justify the cost of modifying the magnetron. [However, if the volume of these data destroyer machines were to be higher than expected, then investigating a modified magnetron might make sense.] However, based on the expected volume of units the preferred embodiment is based on modifying an existing microwave oven  110 . By modified microwave oven it is meant that the magnetron and its support logic (such as its power supply) would be used while the mechanical assembly, including the oven housing and magnetron control circuits, would be modified. In particular a new casing could be used, as opposed to actually slicing apart the casing of an off-the-shelf microwave oven.  
         [0038]    The first modification is that that the door  120  is sealed (such as with screws) so that in normal operation the door isn&#39;t opened. (It could be opened for cleaning, but in typical operation the disk will enter and leave the enclosure without opening the front door.) For this modification the door window could be left in place. Leaving the window makes sense since the visible arcing seen when the data layer on the disk is being destroyed can be mildly entertaining.  
         [0039]    Instead of using the door  120  the disks are inserted into the enclosure using a conveyor belt  170  that moves through the modified ovne  110 . It is very important to note that the openings for the conveyor belt  170  that are cut in to the side of the enclosure for microwave oven  110  be kept narrow (shorter than half a wavelength, where at 2.45 GHz the wavelength is approximately 4 inches). In addition a metal brush can be added that runs the length of the opening to guarantee that no microwave radiation escapes the enclosure.  
         [0040]    The conveyor belt  170  is turned on two sprocket wheels  180  and  190 . [These three parts form the conveyor belt assembly.] The data disks that are to be destroyed are then placed in a mechanism designed to load the individual data disks into the modified microwave oven  110 . The mechanism for loading the disks is shown in FIG. 1 as a hopper  140 . This hopper is where data disks waiting to be destroyed are placed. The data disks are lowered on to the conveyor belt  170  from the hopper  140  using gravity. The belt in turn has cut-outs so that a single disk falls in at a time. Note that care must be taken in the selection of the material to use for the conveyor belt  170 . This is because the arcing that is destroying the data layers, and the microwave radiation itself, could melt parts of a plastic belt. Note that in principle this conveyor belt mechanism is similar to that used in the “Microwave Conveyor Bacon System” sold by “Microwave Research and Applications Inc.” located at 8685 Cherry Lane, Laurel, Md. 20707. (More information on the Bacon Conveyor can be seen on the web at http://www.microwaveresearch.com/conveyorbaconsystem/index.html)  
         [0041]    The disks exiting the enclosure would be dropped, using gravity, into a disk collection bin  150 . The modified microwave oven  110  and the conveyor belt assembly  170 ,  180  and  190  would sit on stand  160 . Note that in FIG. 1 the stand  160  and disk collection bin  150  are shown as two parts that don&#39;t protect the mechanical parts needed for the conveyor belt assembly  170 ,  180  and  190 . In practice the stand  160  and/or the disk collection bin  150  would be designed to enclose the conveyor belt assembly  170 ,  180  and  190  such as to protect it, and to protect the user from coming into contact with any moving parts.  
         [0042]    Alternatively a “loading mechanism” that is similar to that used in loading CDs from a mass storage devices could be used. These are the types of mechanism used by several providers of so called jukebox devices. [These are often used to store many CDs and then under program control the “loading mechanism” is used to insert a single CD into the reader.] The design of this type of mechanism is well know to those skilled in the art of mechanical design and so it is mentioned here simply to point out that the conveyor belt is but one of several methods that could be used to construct the machine.  
         [0043]    The above mentioned methods for inserting disks into the enclosure help to make the machine simple to use and eliminate some to the burnt smell. In order to completely remove the smell of burnt plastic, a filter and fan assembly  130  needs to be installed into the machine. There is nothing unique about the filter or fan and as such the selection of these elements could be performed by a skilled engineer.  
         [0044]    The next modifications would be to the control circuits. These would be modifications to the basic control circuits that are supplied with typical microwave ovens. In essence the circuit would be modified such that short (approximately 4 second) burst of power would be applied to the magnetron when a disk is in the enclosure.  
         [0045]    Ideally when a user turned the machine on the fan would start running and the conveyor belt would turn. These would happen whether or not any disks were in the hopper  140 . (Alternatively these could be programmed to automatically turn on when a disk is placed in the hopper and to turn off some period of time after the last disk has left the hopper.) Then synchronized to the position of conveyor belt  170 , power would be applied to the magnetron (internal to modified microwave oven  110 ). Note that in the simplest of cases power would be applied to the magnetron at regular intervals. For example is the conveyor belt takes 12 seconds to pass through the enclosure the magnetron could be cycled on for 2 seconds and then off for 4 seconds. This would subject any disk to 4 seconds of radiation. Note that while a cycle of 4 seconds on and 8 seconds off would also work, the 2 second on and 4 second off cycle may be preferred. This is because the period of time when the disk is entering and exiting the enclosure not all of the disk will be exposed to the radiation. This will result in an un-even burn pattern. While technically not a problem, it might make some users nervous if large parts of the data storage area on the disk aren&#39;t thoroughly burned. (Of course you could fix this by turning on the power for a greater fraction of each 12 second cycle.)  
         [0046]    More sophisticated control could be designed, such as adding sensors to the conveyor belt so that power is applied to the magnetron when the disk is centered in the cavity. Another alternative is to add sensors so that power is applied to the magnetron when two disks are centered in the cavity. In this second alternative, the conveyor belt  170  would be designed such that the spacing of the holes needed to hold the disks would be such as to allow two disks to be in the oven at the same time.  
         [0047]    It should be clear that the purpose of the controller is to synchronize when power is applied to the magnetron with the position of the conveyor belt assembly  170 ,  180  and  190 . Ideally power is applied to the magnetron only when a data disk is within the enclosure of the modified microwave oven  110 . In addition the controller should regulate the power to the magnetron such that it is cycled on and off. This is because by using the same magnetron that was designed for microwave oven use, the design needs to account for the fact that microwave reflection from the conductive layer of the data disk could heat up the magnetron and, if left uncheck, the heat could cause the magnetron to fail.  
         [0048]    Whichever method is selected for controlling the magnetron, it is important to recognize this is a very basic control problem that any engineer trained in embedded systems would have the skills to complete. In the simplest case an on/off switch would control the fan  130  and conveyor belt  170 . This same switch would start a free running timing circuit that would turn the magnetron on for 2 seconds and then off for 4 seconds (assuming our example 12 second rate for moving the disk through the enclosure). More complex control could be obtained with an embedded processor (such the ARM core that is commercially available from several vendors of embedded systems). The processor could then have sensors attached to it that indicate where the conveyor belt  170  is at any time (and with that information the position of the disk would be known). In addition another sensor could be used to indicate if there is a disk on the conveyor belt  170  as it passes through the microwave oven  110 .  
         [0049]    Note that “Buildmet Technologies Pvt Ltd” of Bangalore India (on the web at www.buildmet.com and their microwave controller page at www.buildmet.com/uwave.html ) specializes in the design and modification of microwave oven controls. They sell basic microwave oven control circuits. For a fee they will sell the design plans complete with the controller software code in source form, so that the buyer may modify the circuit to fit their needs. Besides selling the design, the company, “Buildmet” will, for a fee, perform the modifications needed for custom applications. In addition to “Buildmet” there are many other engineering consulting firms that could be contracted.  
         [0050]    It was previously stated that “microwave reflection from the conductive layer of the data disk could heat up the magnetron”. Thus with any method used to control power to the magnetron it is important to note that the magnetron should not be powered 100% of the time. This is because the assumption for the preferred embodiment is that the magnetron from a microwave oven is being used. Part of the reason that mass produced microwave oven magnetrons are so inexpensive is that it is assumed metal won&#39;t be placed in the oven. If metal were placed in the oven then microwaves would be reflected back at the magnetron causing it to heat up. Note that mass produced magnetrons aren&#39;t designed to handle this addition heat. Since this invention assumes that metal will be subjected to microwave radiation then if the embodiment of this invention uses a magnetron from a commercially available microwave oven then applying power approximately 33% to 50% of the time is reasonable. (The alternative is to redesign the common microwave oven magnetron so that it can handle the extra heat caused by the reflections of the microwave energy from the disk, but for the previously stated cost reasons, this may not be desirable.)  
         [0051]    While this embodiment has primarily discussed destroying a single disk at a time, there is no reason that this is a limitation. In fact the enclosure of a typical microwave oven can hold several disks at once. Thus if we assume that the conveyor belt  170  is moving two disks through the enclosure every 12 seconds, then the magnetron would be powered only 33% of the time (4 seconds within each 12 second period). At this rate the data disks would be destroyed at 10 disks per minute, or 600 per hour.  
       CONCLUSION  
       [0052]    From the description above a number of advantages of the present invention become obvious:  
         [0053]    A. Using the principles disclosed in this invention a low cost device can be constructed that can be used to destroy data on various types of common data storage devices, such as CDs and DVDs.  
         [0054]    A skilled engineer would recognize that the modifications described herein would approximately double the cost of a base microwave oven. Since the base oven can be obtain in December 2002 for less than $50.00 the complete system could be constructed at a cost of approximately $100.00.  
         [0055]    B. The device can be constructed so as to be simple to use.  
         [0056]    Although the descriptions above contain many specificities, these should not be constructed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example CDs and DVDs are used as examples of data disks that would work with this invention. However, other formats, such as old style laser disks, that is those used to store movies before the DVD format was invented, could also be used with this invention in order to destroy the data on those disks. In addition other, yet to be defined data formats, could be specified where the data is stored on a disk with one or more data layers and one or more conductive layers. It should be appreciated that the data on these disks could also be destroyed using this invention. It should also be noted that the shape of the data storage device does not need to be a round disk, but any shape would work. Also this application has been assuming a data storage layer that is near the reflective surface. However, it should be clear that the data storage layer and the reflective layer could be one and the same. The important attribute is that the data disk has a conductive layer such that exposing the disk to electromagnetic radiation sets up an electric field that destroys the data layer. In the case where the conductive surface is the same as the data storage layer, the only requirement is that the electric fields created in the conductive layer be sufficient to destroy the data. For example, when using this invention with a CD the destruction of the data storage layer is for the most part a byproduct of the vaporization of the conductive layer. Thus if data could be stored on or in the conductive layer, it would be destroyed using this invention.  
         [0057]    In addition the source of electromagnetic energy could be modified in either (or both) power output or frequency. Thus it will be appreciated that various modifications and alterations might be made by those skilled in the art without departing from the spirit and scope of the invention. The invention should therefore be measured in terms of the claims which follow.