Abstract: In accordance with the present disclosure, a system and a method are disclosed for measuring a time varying magnetic field. In one aspect, a system comprises a plurality of induction coils arranged to measure the time varying magnetic field using at least one voltage induced in at least one of the induction coils in the plurality of induction coils, a plurality of snubber circuits connected to the plurality of induction coils, each of the snubber circuits of the plurality of snubber circuits arranged to suppress a resonance of a respective one of the induction coils of the plurality of induction coils, and a summing circuit connected to each of the snubber circuits of the plurality of snubber circuits, the summing circuit arranged to sum voltages induced in each of the induction coils in the plurality of induction coils.

Abstract: A human-portable utility locator system for locating and tracing a buried utility line characterized by an electromagnetic field emission. The locator may include a horizontal spaced sensor pair for detecting the horizontal field asymmetry of the emitted field in one or more independent frequency bands, which is employed to assist in determining an accurate “virtual depth” measurement for producing detection events. An event detector may be disposed to detect events corresponding to extremum in the B-field gradient with respect to time and a user interface (UI) coupled to the event detector signals the detected event to a user. In a preferred embodiment, one pair of spaced-apart 3D magnetic sensor arrays is disposed substantially orthogonal to another intermediate spaced-apart pair of sensors.

Abstract: An apparatus for detecting tampering with an integrated circuit (IC), the apparatus comprising a second circuit comprising at least one conductor for conducting electrical current, the electrical current comprising, during at least one period of time, current of known strength, the electrical current generating a magnetic field, at least one magnetic field sensing device operatively associated with the IC, the sensing device having at least one electrical characteristic responsive to changes in a sensed magnetic field, the magnetic field sensing device being positioned so as to sense the magnetic field generated by current in the at least one conductor, and an analyzer operatively associated with the at least one magnetic field sensing device and the IC, the analyzer determining that the IC is being tampered with based, at least in part, on changes in the at least one electrical characteristic of the at least one magnetic field sensing device in response to changes in the sensed magnetic field generated by th

Abstract: A magnetic tracking system is particularly adapted for a combination with an imaging system, for example with a rotational X ray device. The magnetic tracking system includes pairs of first and second field generators that are disposed on opposite sides of a measuring volume. The first field generators may particularly be attached to a radiation source and the second field generators to a detector of the X ray device. Moreover, the first and second field generators may be constituted by coils with opposite magnetic polarity. Due to the attachment of the field generators to the X ray device, motions of the X ray device do not disturb the magnetic field in a frame of reference fixed to the imaging system.

Abstract: A sensor having a power management mechanism controlled by an external trigger signal is presented. The sensor includes a magnetic field signal generating circuit and a control circuit coupled to the magnetic field signal generating circuit. The control circuit, responsive to an externally generated trigger signal, initiates a supply current pulse that activates the magnetic field signal generating circuit for a predetermined time interval.

Abstract: An inspection apparatus is provided that can include at least one probe receiving unit. The at least one probe receiving unit can be capable of processing data corresponding to one or more of image information of the type that can be generated by a visual inspection probe, eddy current information of the type that can be generated by a eddy current probe, and ultrasound information of the type that can be generated by a ultrasound probe.

Abstract: A quantitative evaluation method, a method for manufacturing a silicon wafer, and a silicon wafer manufactured by the method, enabling more efficient evaluation of the concentration of atomic vacancies existing in a silicon wafer. The quantitative evaluation method includes steps of: oscillating, in a state in which an external magnetic field is applied to a silicon wafer (26) while keeping the silicon wafer (26) at a constant temperature, an ultrasonic wave pulse and receiving a measurement wave pulse obtained after the ultrasonic wave pulse is propagated through the silicon wafer (26) for detecting a phase difference between the ultrasonic wave pulse and the measurement wave pulse; and calculating an elastic constant from the phase difference. The external magnetic field is changed to calculate the elastic constant corresponding to a change in the external magnetic field for evaluating a concentration of atomic vacancies in the silicon wafer (26).

Abstract: A stent and a magnetoelastic resonant sensor are provided for sensor a physical characteristic in a bodily vessel or cavity. External coils interact with the sensor to induce a resonance that is responsive to the physical characteristic, such that the device may wirelessly measure physical characteristics such as mass loading effects and viscosity changes due to progression of pathology in implanted stents and stent grafts. The sensor may be fashioned from a magnetoelastic material and may be integrated near the inner sidewall of the stent. The sensor may take on a complex patterned shape to enhance the sensitivity and flexibility of the sensor structure. When the sensor is interrogated with a time-varying magnetic field, the sensor will mechanically vibrate and generate a magnetic flux which is maximum at a resonant characteristic determined by the mass load on the sensor and the viscosity of the fluid surrounding the sensor.

Abstract: An integrated magnetic-field sensor designed to detect an external magnetic field, comprising a first magnetoresistive structure for detecting the external magnetic field, the first magnetoresistive structure including first magnetoresistive means having a main axis of magnetization and a secondary axis of magnetization set orthogonal to one another. The magnetic-field sensor further comprises a magnetic-field generator, including a first portion configured for generating a first magnetic field having field lines in a first field direction, and a second portion, which is coplanar and is connected to the first portion, configured for generating a second magnetic field having field lines in a second field direction, the first magnetoresistive means being configured so that the main axis of magnetization extends parallel to the first field direction, and the secondary axis of magnetization extends parallel to the second field direction.

Abstract: Methods and systems are provided for determining a state of charge of a battery. The battery is subjected to a predetermined magnetic field such that the battery and the predetermined magnetic field jointly create a resultant magnetic field. The resultant magnetic field is sensed. The state of charge of the battery is determined based on the resultant magnetic field.

Abstract: An eddy current probe uses magnetic gap. The probe has a small size; and coil number in the probe is reduced. Hence, the probe can move easily inside and outside a tube and detect an end of the tube as close as possible.

Abstract: An object detecting apparatus that detects an object including a magnetic body including: a detection signal acquiring unit that acquires a detection signal based on a magnetic signal; a disturbance source detection signal storage unit that stores a detection signal of a disturbance source that generates a disturbance component with respect to the detection signal; a determining unit that determines whether the detection signal acquired by the detection signal acquiring unit contains the disturbance component; an amplitude correction unit that corrects an amplitude of the disturbance source detection signal and generates an amplitude-corrected disturbance source detection signal; a disturbance component suppression unit that generates a determination signal by suppressing the disturbance component contained in the detection signal; and an object determination unit that determines whether the object is the object to be detected based on the determination signal.

Abstract: An arrangement and a method for influencing and/or detecting and/or locating magnetic particles in a region of action include a driver generating a magnetic drive field so that magnetization of the magnetic particles changes. The magnetic particles include first and second magnetic particles. The arrangement further include a receiver having a first receiving probe providing a first signal and a second receiving probe providing a second signal. A detector determines signal features arising from the first particle in the first signal and in the second signal.

Abstract: A method for classifying electrical sheet is produced. The electrical sheet is used to produce an electrical machine and is available in the form of a strip roll wherein a magnetic flux that changes over time and that causes a shape change of the strip roll and magnetic losses is produced in the strip roll by means of an excitation winding fed by a feeding device, the shape change and/or the magnetic losses are measured by means of a measuring device and the measurement signal obtained is fed to an evaluation device, and the evaluation device categorizes the electrical sheet in regard to noise emission and/or magnetic losses using the measurement signal.

Abstract: A system includes a first circuit configured to convert a first analog signal to a first digital signal. The system includes a second circuit configured to determine an area of the first digital signal above a set value and an area of the first digital signal below the set value to provide a second digital signal indicating an offset of the first analog signal.

Abstract: A measuring arrangement where a magnet moves or is positioned because of the movement or position of an object, and this movement or positioning of the magnet is collected by a sensor, an in particular a non-magnetic dividing wall being provided between the magnet and the sensor. A mechanical converter, in particular a gear, being arranged between the object and the magnet.

Abstract: An arrangement and a method for influencing and/or detecting magnetic particles in a region of action includes a generator for generating a magnetic selection field having a pattern in space of its magnetic field strength such that a first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the region of action. A driver is configured to change the position in space of the two sub-zones in the region of action by means of a magnetic drive field so that the magnetization of the magnetic particles changes locally. The generator includes at least one permanent magnet which is at least partially shielded by an electrically high conductive shielding.

Abstract: An apparatus for calibrating a metal detecting device of a materials processing line. A placement arm is provided to control the path of a calibrating sample in order to simulate movement of tramp metal moving on a processing line along with materials being processed. Upper and lower arms of the placement arm are joined by an adjustable elbow which can be set to a maximum angle of extension in order to accurately place the calibrating sample at a preferred location in a detecting field of the metal detecting device.

Abstract: An arrangement for influencing and/or detecting magnetic particles includes a selector for generating a magnetic selection field having a pattern in space of its magnetic field strength such that a first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the region of action. A driver changes the position in space of the two sub-zones in the region of action by a magnetic drive field so that the magnetization of the magnetic particles changes locally, and a receiver acquires signals. The signals depend on the magnetization in the region of action, and the magnetization is influenced by the change in the position in space of the first and second sub-zone. The receiver has first and second compensators, each including a compensation coil.

Abstract: A sensor device for detecting one or more magnetic particles (102) in a sample fluid is described. The sensor device (100) uses at least one rotating magnetic field generator (108) for applying a rotating magnetic field to the sample and more particularly the one or more magnetic particles (102) incorporated therein. The sensor device also comprises a controller for controlling the magnetic field generator such that the rotating frequency of the applied magnetic field is substantially larger than the critical slipping frequency for the magnetic particle. The effect of the induced rotation is sensed using a sensor element (112). Presence, amount and binding properties of the magnetic particles (102) may be derived from the measured effect. Alternatively or additionally the viscosity of the sample fluid may be determined.

Abstract: A method for influencing and/or detecting magnetic particles in a region of action includes generating a magnetic selection field having a pattern in space of its magnetic field strength such that a first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the region of action. The method further includes changing the position in space of the two sub-zones in the region of action by means of a magnetic drive field so that the magnetization of the magnetic particles change locally, and acquiring signals that depend on the magnetization in the region of action. The magnetization is influenced by the change in the position in space of the first and second sub-zone. The magnetic drive vector of the magnetic drive field is rotated in at least one rotation plane.

Abstract: A magnetic field is generated by at least one coil in magnetic communication with at least a portion of a vehicle responsive to a first time-varying signal operatively coupled to the at least one coil in series with a sense resistor. A second signal is generated responsive to a voltage across the sense resistor and is response to a magnetic condition of the at least one coil, which is response to the magnetic communication of the at least one coil with the portion of the vehicle.

Abstract: A metal detection device, system and method are provided. The device includes a receiver that receives a signal pattern representing electromagnetic field disturbances over time caused by movement of metal doors in a detection region. The device further includes a memory in communication with the receiver. The memory stores a recorded signal pattern of a previously received signal pattern and at least one quality criterion. The device further includes a processor in communication with the memory. The processor determines pattern vitals indicating a quality of the received signal pattern. The processor further determines whether the at least one quality criterion is met based at least in part on the pattern vitals. The processor further updates the recorded signal pattern based at least in part on determining whether the at least one quality criterion is met.

Abstract: A system and method for measurement of parameters of a conductive material, include generating an oscillating electromagnetic field (EMF) interacting with a sample portion from a remotely positioned source; measuring values of components of impedance of the electromagnetic; populating a system of equations including a theory of electromagnetism-based mathematical model of the electromagnetic system; solving the system of equations to calculate values of a distance between the sample portion and the source, thickness of the sample portion in proximity to a point of projection of the source onto the sample portion and electromagnetic properties of the sample portion; outputting the calculated values as the measured values; and repeating the steps of generating, populating, solving, outputting and repeating using the calculated values for the step of populating in place of the measured component values.

Abstract: A non-contact sensor system is provided that comprises a first sensor element disposed within a first member having an axis Y, and a second member configured to rotate about the axis Y at a value X. The second member is configured to interface with the first member. The non-contact sensor system further comprises a second sensor element disposed on the second member proximate the first sensor element without physically contacting the first sensor element, and the first sensor element and the second sensor element are operatively coupled to facilitate sensing the value X. The non-contact sensor system may be configured to sense velocity, acceleration, and other values.

Abstract: A method and an arrangement for influencing and/or detecting and/or locating magnetic markers in a region of action is disclosed, which method comprises the steps of: generating a magnetic drive field so that the magnetization of the magnetic marker changes, generating a magnetic selection field having a pattern in space of its magnetic field strength providing a magnetic field gradient in the region of action, acquiring a first signal by means of a first receiving probe and acquiring a second signal by means of a second receiving probe, the first receiving probe and the second receiving probe being located at different locations relative to the region of action, the first signal and the second signal depending on the magnetization of the magnetic marker in the drive field and in the selection field and further depending on the location of the magnetic marker, the magnetic selection field having a first magnetic field strength configuration, repeating at least once the acquisition of the first signal and of t

Abstract: A sensor measures the interaction of an applied magnetic field to an iron sample surface to determine whether the sample surface has been graphitized. The sensor measures the magnetic force resulting from the interaction or the magnetic flux density to determine the content of magnetic material in localized regions of the sample surface. The sensor includes a cantilever beam with a strain gauge for measuring magnetic force. Alternatively, the sensor includes a magnetic flux density sensor to measure magnetic flux density.

Abstract: The invention relates to a method and arrangement for the contactless determination of conductivity-influencing properties and their spatial distribution over the entire cross section of an electrically conductive substance moving in a primary magnetic field (B). The substance may be a liquid or a solid. A simultaneous measurement of a number of mechanical state parameters of the magnetic system is performed (three-dimensional components of the force and the torque), said parameters being variable by the effect of a secondary field on the magnetic system, the secondary field being produced on the basis of eddy currents induced in the substance by the primary field (B). To determine the spatial distribution of the property that is sought, the primary field is changed in intensity or form a number of times and a measurement of the state parameters is carried out for each change.

Abstract: A method of securely deploying information to a device includes placing a device into a shielded structure and exchanging timing messages between a keying device located inside the shielded structure and a beacon located outside of the shielded structure. The shielded structure is closed. The exchange of timing messages is terminated, and upon termination, the keying device transfers the information via one or more shielded messages to the device, and the beacon jams the frequency at which the shielded messages are transferred. The shielded structure is opened, and the keying device and beacon exchange messages to verify the secure deployment of the information.

Abstract: An enhanced wireless eddy current probe is disclosed which has means to wirelessly couple to a non-destructive inspection (NDI) system situated some distance away from an inspection point on a material under inspection. The disclosed enhanced wireless eddy current probe provides means for executing advanced functions necessary for a complex eddy current inspection operation. These functions include, but are not limited to, storing, loading, and executing a predetermined firing sequence on an array of coil elements, probe balancing, probe calibration, and providing bibliographic information specific to said probe to a wirelessly coupled NDI system.

Abstract: The invention relates to a method and a sensor device (100) for the detection of magnetic particles (M) in a sample. The magnetic particles (M) can bind to binding sites (Z) at a binding surface (12), where they can be detected by a detection unit (13, 14). A controller (15) is provided for controlling magnetic attraction (B) of the magnetic particles (M) towards the binding surface (12) in dependence on the detection signal (S) of the detection unit (14) in such a way that rotational relaxation conditions for the magnetic particles (M) are changed. In particular, this change can be controlled to maximize the binding of magnetic particles (M) to the binding surface (12) within a given measurement time. The change can for example be achieved by repeatedly switching the magnetic attraction off for prolonged periods, giving the magnetic particles (M) better chances to orient properly with respect to the binding surface (12).

Abstract: An electromagnetic detection system comprising: a transmitter loop for generating a primary magnetic field, and a first pair of spaced apart receiver coils and second pair of spaced apart receiver coils for measuring a secondary magnetic field generated in response to the primary magnetic field. The transmitter loop drives the transmitter to generate the primary magnetic field.

Abstract: A magnetic induction tomography system and method for studying the electromagnetic properties of an object includes generator coils adapted for generating a primary magnetic field, and sensor coils adapted for sensing a secondary magnetic field. Actuators provide relative movement between the generator coils and/or the sensor coils on the one hand and the object to be studied on the other hand.

Abstract: A self-calibrating magnetic field monitor is disclosed. In one embodiment, a magnetic field sensor repeatedly generates an electronic signal related to the magnetic field. In addition, a calibration module generates a relative baseline signal based on an average value of the electronic signals for a given time period. A comparator compares the electronic signal with the relative baseline signal and generating an output signal if a difference in the comparing is greater than or equal to a threshold.

Abstract: The invention relates to a device for measuring the mass of a magnetic material (6) present in an analysis medium, that comprises: a modulator (24) of the phase of a high-frequency and/or low-frequency component of a magnetic field for exciting the analysis medium with a modulation signal having a value that is modified by a frequency fmod; and a demodulator (36) capable of demodulating the amplitude of an amplitude signal, measured in response to the excitation field, from the modulation signal, wherein said demodulator is connected to the output of a filter (34) and to the input of an estimation unit (44).

Abstract: Testing an electrical component, the component including a printed circuit board (‘PCB’) with a number of traces, the traces organized in pairs with each trace of a pair carrying current in opposite directions and separated from one another by a substrate layer of the PCB, where testing of the electrical component includes: dynamically and iteratively until a present impedance for a pair of traces of the component is greater than a predetermined threshold impedance: increasing, by an impedance varying device at the behest of a testing device, magnetic field strength of a magnetic field applied to the pair of traces by the impedance varying device, including increasing the present impedance of the pair of traces; measuring, by the testing device, one or more operating parameters; and recording, by the testing device, the measurements of the operating parameters.

Abstract: A metal detector (40) used for identifying contaminants in products (23) introduced into the metal detector by a conveyor. The detector (40) includes coils (1), a search head (2) and an analog to digital converter (3) that generates a reactive signal (13) in response to the presence of a contaminant in the region of the coils. A calculation processor (32) receives the reactive signal (13) along with the value of the conveyor speed (9) to determine a calibration ratio R that is unique to each individual metal detector (40). The optimum frequency F for metal detector operation is equal to the conveyor speed (9) divided by the ratio R. The ratio R simplifies the selection of filter parameters (4, 8) for a speed filter (30) which correlates the conveyor speed (9) with the frequency F so as to deliver an optimized signal to the detection algorithm (10) used to determine the presence of a contaminant based on the signal (13) derived from the coils (1).

Abstract: Autonomous fitness for continuing service assessment equipment interacts with the operator through natural speech, voice and sound and provides active failure prevention through automatic and/or continuous fitness for service assessment of a material under evaluation. The equipment comprises at least one computer and a material features acquisition system operable to detect a plurality of material features. The features are then evaluated according to rules that capture the multidiscipline knowledge of experts and are already inputted into the computer. The computer iterations are processed until an acceptable conclusion is made regarding the condition of the material under evaluation.

Abstract: A write head is tested by measuring the effect that magnetic fields have on the inductance of the write head. For example, a perpendicular write head may be placed in a magnetic field with a first angle, e.g., non-parallel and non-perpendicular, to the air bearing surface and the inductance is measured. After altering the angle of the magnetic field the inductance is again tested. In another embodiment, the angles may be parallel and perpendicular to the air bearing surface. The difference in the inductance value can be used to determine a characteristic of the write head, such as the presence of a recording pole. In some embodiments, the inductance may be measured while applying a bias current to the write head while the write head is in an external magnetic field.

Abstract: A method for detecting an anomaly in an assembly of a first and a second object of electrically conductive material forming an intermediate space between them, comprising providing a device (5) comprising a transmitter/receiver arrangement (7) for generating an electromagnetic field, and for measuring a signal indicative of an eddy current which is generated in the assembly by the electromagnetic field; arranging the device in a measurement position within the intermediate space; activating the device so as to receive a signal indicative of an eddy current in the assembly; and comparing the signal with a norm so as to detect if an anomaly is present at the measurement position, and a device for detecting an anomaly in an assembly of a first and a second object forming an intermediate space between them, the device comprising a transmitter/receiver arrangement a fixation means which. is arranged to fix the transmitter/receiver arrangement at a measurement position with respect to the inspection object.

Abstract: A positioning, communication, and detection system designed to provide a three dimensional location of an object, navigation tools, and bidirectional surface-to-subsurface communications, and methods of using the system. The system can include one or multiple transmitters comprising electromagnetic beacons, software defined radio receivers with an associated processing unit and data acquisition system, and magnetic antennas. The system may use theoretical calculations, scale model testing, signal processing, and sensor data.

Abstract: A measuring device to measure a magnetic field having at least one measuring coil and at least one sensor to measure low-frequency magnetic fields, which measuring coil and which sensor have their planes of extension each positioned or positionable transverse to the flux direction of the magnetic field. The measuring coil and the sensor are connected to a signal processing device with which, depending on a first measurement signal provided by the measuring coil and a second measurement signal provided by the sensor, an output signal that essentially corresponds to the magnetic field can be generated. The measuring coil, the sensor, and the signal processing device are monolithically integrated into a semiconductor chip. The measuring coil may also be formed by means of traces of a printed circuit board on which the semiconductor chip that has the sensor and the signal processing device is located.

Abstract: An interior space of the at least one housing of a force-measuring device is filled with a gas composition that is distinguishable in at least one parameter from the ambient atmosphere. A sensor that is arranged in the interior space, or on the housing, measures this distinguishable parameter. A processing unit of the force-measuring device compares signals obtained from the sensor to monitor and determine the condition of the force-measuring device.

Abstract: A biosensor is described. The biosensor includes a fixed multilayer stack providing a magnetization oscillation, a voltage source electrically coupled to the fixed multilayer stack, and a binding molecule covalently bonded to the biosensor. The voltage source provides a direct current through the fixed multilayer stack to generate the magnetization oscillation and a target molecule including a magnetic nanoparticle forms a complex with the binding molecule and alters the magnetization oscillation.

Abstract: A flexible array probe is disclosed suitable for use in the non-destructive testing and inspection of test pieces with varying cross-sectional geometries. Array elements—such as, but not limited to, eddy current sensors, piezoelectric sensor elements, and magnetic flux leakage sensors—are mounted on thin alignment fins and coupled together with pairs of pivot mechanisms along the axis of desired rotation. The pivot mechanisms allow rotation in exactly one dimension and force the flexible array probe to align its elements orthogonally to the surface of the structure under test. Alignment and coupling fixtures are also disclosed.

Abstract: A probe for a magnetic remanence measurement method, in particular for detecting foreign material deposits and inclusions in hollow spaces, the hollow spaces being formed in a non-ferromagnetic material and the foreign material deposits and inclusions being made of a ferromagnetic material, wherein the probe includes at least one magnetic field sensor, at least one first and one second magnet, the magnets being configured before the at least one magnetic field sensor in a direction of introduction into the hollow space, and being situated relative to one another in such a way that their pole axes run non-parallel to one another.

Abstract: In a position detecting device including a movable member provided in a displaceable manner on a base member, and a proximity sensor which detects the position of the movable member, the proximity sensor includes a magnetic field generating portion, a detecting portion which detects a change in magnetic field according to the displacement of the movable member, and a protruding portion made of a nonmagnetic material, which protrudes toward an object to be detected. A seat position detecting device of a vehicle including the configuration of the position detecting device mentioned above is provided. The base member is comprised of a lower rail which is fixedly installed on a floor of a vehicle body, and the movable member is comprised of an upper rail which is attached to a seat for a vehicle and slidably engaged with the lower rail and which is allowed to be fixed in arbitrary sliding positions on the lower rail.

Abstract: An arrangement for influencing and/or detecting magnetic particles, and/or calibrating such an arrangement includes generating a magnetic selection field having a magnetic field strength pattern such that a first sub-zone having a low magnetic field strength and a second sub-zone having a higher magnetic field strength are formed in the region of action. A driver changes the position in space of the two sub-zones in the region of action by magnetic drive field so that the magnetization of the magnetic particles changes locally. The arrangement includes a drive signal chain, a detection signal chain, and a receiver for acquiring detection signals that depend on the magnetization in the region of action. The magnetization is influenced by the change in the position in space of the first and second sub-zones. A compensation controller provides a compensation signal to the drive signal chain and/or to the detection signal chain by a coupler.

Abstract: A detection unit 4 with detection means 3 and fluid inflow/outflow guide means 2 is connected to a passage 1 for fluid with conductive material or to a pool section 5 for pooling of the fluid. The detection unit 4 guides inflow and outflow of the fluid through the fluid inflow/outflow guide means 2 and detects a concentration of conductive material through the detection means 4. A concentration of conductive material in the fluid is continuously measured with high accuracy.

Abstract: A wall stud detector comprises a housing having a surface for moving over a substrate and a recess in the surface extending into the housing. A target associated with the housing comprises an outer casing and a magnet located in the outer casing. The outer casing comprises a central enclosure for the magnet and an outer peripheral portion. The outer peripheral portion of the target is spaced from the outer peripheral portion of an adjacent target when the target and the adjacent target are stacked with respect to each other.