Abstract: A field device for determining and/or monitoring a chemical or physical, process variable in automation technology, which has at least a first electronic or electrical component and a second electronic or electrical component. The first component has an energy transmitting antenna and the second component has an energy receiving antenna. Between the two components a predetermined distance is provided, which sets the first component and the second component apart from one another. The predetermined distance is filled, at least partially, with a dielectric medium. The energy transmitting antenna is so embodied and/or arranged that it supplies the second component with energy continuously or at predetermined time intervals.

Abstract: Processes and apparatuses are provided for contactless measuring or monitoring in-situ and in real time composition or other electromagnetic impedance correlated properties of liquid or gaseous substances or bulk materials. One or more apparatus may include a resonance type impedance sensor having at least two coils, at least one coil of the at least two coils being at least one excitation coil connectable to at least one alternating current source with frequency sweep, at least one other coil of the at least two coils being at least one sensing coil connectable to at least one data processing system. The one or more methods may include calculating changes in amplitude and resonant frequency induced by electromagnetic interaction between said sensor and object to determine impedance of said object under test; and matching said impedance with predetermined calibration data to determine said chemical or physical properties of said object under test.

Abstract: An electromagnetic method for sensing the relative position of two items using coupled tuned resonant circuits. Two co-resonant tuned circuits are attached to two items 1 and 2 that move relative to one another. The coupling between the circuits is arranged to vary with their relative physical position. One of the tuned circuits is excited at or close to its resonant frequency. The degree of coupling between the tuned circuits is detected by its effect on the way the resultant oscillation changes with time, and this allows the relative position of the items to be established. The inductive elements of the tuned circuits can comprise anti-symmetrical regions 3, 4, 9 and 10 so that the magnetic fields generated by the oscillations are localised and sensitivity to externally applied magnetic fields is minimised. The inductive elements can be implemented directly as printed circuit board tracks.

Abstract: A position sensing head combines a sensing element and a simplified electronic module to enable operation with one wire, in addition to a circuit common, for providing power and transmitting a signal, while separating the sensing head from signal conditioning circuits by over 10 meters. The simplicity of the electronic module allows the use of basic electronic components that operate at more than 225° C. The signal is a variable frequency impressed onto the one wire, which can be read by a frequency meter. Another signal, such as a position or temperature, can be impressed onto the one wire at the same time as the first signal. The second signal is of a different frequency range so that it will not interfere with the first. A demodulator circuit can separate the two signals. The sensing element construction allows for locating up to three active elements measuring the same target.

Abstract: A wireless damage detector for ceramic armor plates includes an interrogator and a body armor ceramic plate. The interrogator includes an inductive primary coil having a resonant frequency. The plate includes a corresponding inductive secondary coil adapted to cooperate with the primary coil when the interrogator is positioned in an interrogation position wirelessly adjacent the plate. When in the interrogation position, the primary and secondary coils are inductively coupled, that is, form an inductive coupling, when the primary coil is energized at the resonant frequency. The plate includes at least one self-contained frangible continuity circuit electrically connected to the secondary coil. The inductive coupling induces an electrical current flow in the continuity circuit when the circuit is undamaged. A detector cooperates with the primary and secondary coils when the interrogator is in the interrogation position. The detector detects the inductive coupling. An indicator cooperates with the detector.

Abstract: A position sensor includes a detector, an oscillation circuit, a signal processing circuit, and a resonance circuit having a detection coil and a capacitor. The oscillation circuit forms a negative feedback loop from: an amplitude detection circuit that detects an amplitude of an oscillation signal outputted from the resonance circuit; an integrating circuit that outputs a signal corresponding to a difference between a predetermined reference voltage and the amplitude of the oscillation signal; a negative conductance control circuit that, based on the output of the integrating circuit, controls the negative conductance of the oscillation circuit such that the amplitude of the oscillation signal is equals to the predetermined reference voltage; and an operational amplifier that adjusts such that the oscillation voltage of the resonance circuit is equal to the applied voltage of the negative conductance control circuit.

Abstract: A toll violation enforcement system that contains a capture unit that receives a trigger signal and takes vehicle images of passing vehicles. A lighting unit configured to operate continuously is provided to establish a major lighting source incident on the vehicle. A processing unit is provided that processes the vehicle image and controls the settings employed by the capture unit. The processing unit preferably contains a plate location module for extracting an original resolution license plate area image from a first vehicle image; an exposure control module for controlling the exposure setting on the capture unit to provide consistent intensity of the license plate area; a resolution reset module for changing the image resolution for a second vehicle image; an image enhancement module for brightening pixels of the second vehicle image; and an image compression module for compressing the license plate area image and second vehicle image to a predetermined format.

Abstract: An apparatus for, and methods of use for, measuring film thickness on an underlying body are provided. The apparatus may include at least one Impedance Resonance (IR) sensor, which may include at least one sensing head. The at least one sensing head may include an inductor having at least one excitation coil and at least one sensing coil. The excitation coil may propagate energy to the sensing coil so that the sensing coil may generate a probing electromagnetic field. The apparatus may also include at least one power supply, at least one RF sweep generator electrically connected to the excitation coil; at least one data acquisition block electrically connected to the sensing coil; at least one calculation block; and at least one communication block. Methods of monitoring conductive, semiconductive or non-conductive film thickness, and various tools for Chemical Mechanical Polishing/Planarization (CMP), etching, deposition and stand-alone metrology are also provided.

Abstract: A substrate is electromagnetically coupled into an inductance-capacitance resonant circuit formed from (i) a member comprising a ferromagnetic material, (ii) an inductor and (iii) the substrate. The substrate is illuminated for a first time period X to cause photoconduction in the substrate. Decay in conductivity of the substrate is monitored for a second time period Y. The ratio of X to Y is greater than 1:10. Bulk lifetime of the substrate is determined from the decay.

Abstract: An electronic circuit is arranged in an external programming device and is used for contactless programming of a circuit to be programmed. The electronic circuit has a series resonant circuit that includes a transmitter coil and a capacitor. The transmitter coil of the series resonant circuit is used for inductive coupling to a receiver coil in the circuit to be programmed. For the purpose of evaluating the impedance that actually exists in the circuit to be programmed, there is provided a device for determining the value of the impedance from a phase difference between the control voltage of the series resonant circuit and the capacitor voltage of the series resonant circuit.

Abstract: An inductive detector arranged to measure position along a axis comprising: a transmit winding; a receive winding; a passive circuit comprising a winding in electrical series with a capacitor; wherein: the mutual inductance between the transmit winding and the receive winding is a function of the relative displacement of the passive circuit along the measurement axis; a first portion of one of the windings is wound on a first pitch and a second portion of the same winding is wound on a second pitch whose extent is greater than the first pitch.

Abstract: The present invention relates to an inductive proximity sensor that includes an oscillator having first and second inductor-capacitor circuits arranged such that an inductance of one of the inductor-capacitor circuits has substantially greater sensitivity to an external target than an inductance of the other inductor-capacitor circuit. The sensor also includes an alternating current drive to each of the inductor-capacitor circuits that is in-phase and depends on differences in voltage across the inductor-capacitor circuits. The sensor may be coupled to a calibration device that applies power and triggers a calibration routine within the sensor. In response to the trigger signal, a calibration processor within the sensor executes the calibration routine and adjusts the inductor-capacitor circuits and provides an indication of successful calibration.

Abstract: A test system for a radio frequency IC device includes a radio frequency IC chip and a radiation strip. The characteristics of the radio frequency IC device are measured by bringing the tip of a probe of a test apparatus in direct contact with a portion of the radiation strip and thereby providing a radio frequency signal. The tip of the probe is made to be a flat plate so as to obtain closer and more stable contact with the radiation strip.

Abstract: A monitoring device is for monitoring physical characteristics of a building material. The monitoring device is buried inside a block of the building material, and has a sensor to sense physical characteristics thereof. The sensor transmits a signal representative of the physical characteristics.

Abstract: A proximity and contact sensor (10) is provided with a sensor element (11) and a detection circuit (16). The sensor element is provided with a matrix (13) in which coil-shaped carbon fibers (12) are dispersed. A high-frequency oscillation circuit (19) of the detection circuit (16) supplies the sensor element with a high-frequency signal. A detector (22) in the detection circuit (16) receives an output signal from the sensor element (11) and detects proximity of an object (24). In one example, the coil-shaped carbon fibers (12) are contained in the matrix by 1 to 20% by weight. In another example, a high-frequency oscillation circuit generates a high-frequency signal of 100 to 800 kHz.

Abstract: An apparatus includes a member including a ferromagnetic material, an inductance-capacitance resonant circuit, a substrate disposed relative to the member, and a plurality of radiation sources. The member includes a post disposed at its center and a surface extending to an outer wall. The member defines a gap between the post and the outer wall. The inductance-capacitance resonant circuit is configured to resonate at a measurement frequency. The circuit includes an inductor disposed relative to the post. The substrate is disposed relative to the member. The substrate is electromagnetically coupled to the inductor. The plurality of radiation sources is disposed radially outward from and circumferentially around the post of the member. The apparatus can be used to simultaneously measure conductance (inverse sheet resistance), steady state photoconductance, true steady state minority carrier lifetime, photoconductance build-up and photoconductance decay lifetime.

Abstract: A coin detector includes an oscillator circuit using an oscillator for generating a magnetizing signal of a predetermined oscillation frequency and an eddy current sensor for producing an AC magnetic field for sensing the variation of the inductance of an eddy current produced upon passing of a coin, a FM demodulator and an AM demodulator respectively electrically coupled to the oscillator circuit by a respective buffer for demodulating the voltage frequency and voltage amplitude of the oscillation signal outputted by the oscillator circuit, and a recognition logic unit for computing the demodulated FM signal outputted by the FM demodulator and the demodulated AM signal outputted by the AM demodulator by means of using time as a parameter to recognize the authenticity and value of the sensed coin.

Abstract: Methods for making and systems employing pressure and temperature sensors are described. Embodiments include a capacitive element including a first conductor plate and a second conductor plate. Each plate includes a conductor layer formed on a substrate. In a pressure sensor embodiment, seal is positioned at or near the edges of the conductor plates, and a gas retained in a gap defined between the plates. In a temperature sensor embodiment, the gap defined between the plates is in fluid communication with the external environment.

Abstract: The invention relates to a method and a device for measuring pressure-based inductance of an electromagnetic tablet, which relates to the field of computer peripheral input device. The method comprises steps of: measuring a first parameter value when an electromagnetic pen is not operating; measuring a second parameter value when the electromagnetic pen is operating, and inductance value of inductor in a resonance circuit varies with pressure; and calculating the pressure-based inductance based on the first and second parameter values.

Abstract: Provided is a material for tactile sensor, which is easy to be formed, and in which the shape, size and orientation of coils dispersed in the medium are sufficiently controlled. The tactile-sensitive material includes a medium and a plurality of micro coils dispersed in the medium and constituting a LCR resonance circuit, and wherein each of the plurality of micro coils includes at least one spiral coil portion, and coil axes of the plurality of micro coils are aligned along at least one direction or directed in at least one plane. When a tactile stress is applied to the tactile-sensitive material, the C component is varied significantly, which contributes to the improvement in sensitivity of the tactile sensor. Further, by providing a core at the coil center, the sensitivity is more improved.

Abstract: A system and apparatus for providing an in-vivo assessment of relative movement of an implant that is positioned in a living being is provided that includes a first assembly and a second assembly that are positioned within the living being. The first assembly includes a passive electrical resonant circuit that is configured to be selectively electromagnetically coupled to an ex-vivo source of RF energy and, in response to the electromagnetic coupling, generates an output signal characterized by a frequency that is dependent upon a distance between the first assembly and the second assembly at the time of the electromagnetic coupling.

Abstract: The present invention related to devices and methods for using ferrite alignment keys in wireless remote sensor assemblies. In one aspect, the invention provides wireless resonant sensor assemblies comprising a pick-up coil, a ferrite alignment key positioned in and extending from the pick-up coil, and wireless resonant sensor having a receiving element wherein the pick-up coil and the wireless resonant sensor align upon insertion of the ferrite alignment key into the receiving element. The ferrite alignment key may also be part of a resonant sensor such that insertion of a pick-up coil into a receiving element of the alignment key results in a configuration where the alignment key is positioned in and extended from the pick-up coil. Methods of measuring one or more parameters of a monitoring system are also provided. The insertion of the ferrite alignment key aligns the pick-up coil and wireless resonant sensor thereby increasing sensing of the wireless resonant sensor by the pick-up coil.

Abstract: The present invention related to methods and systems for simultaneously sensing two or more environmental parameters of a sample. Included is an inductor-capacitor-resistor (LCR) resonator sensor and a pick up coil in operative association with the LCR resonator sensor wherein viscoelastic changes in the sensing film cause displacement of the antenna relative to the pick up coil.

Abstract: A coupling loop or antenna is provided that can be used with a system that determines the resonant frequency of a sensor by adjusting the phase and frequency of an energizing signal until the frequency of the energizing signal matches the resonant frequency of the sensor. In one embodiment multiple energizing loops energize an implanted sensor and a sensor coupling loop connected to an input impedance that is at least two times greater than the inductance of the sensor coupling loop receives the sensor signal.

Abstract: The present invention relates to an inductive proximity sensor that includes an oscillator having first and second inductor-capacitor circuits arranged such that an inductance of one of the inductor-capacitor circuits has substantially greater sensitivity to an external target than an inductance of the other inductor-capacitor circuit. The sensor also includes an alternating current drive to each of the inductor-capacitor circuits that is in-phase and depends on differences in voltage across the inductor-capacitor circuits. The sensor may be coupled to a calibration device that applies power and triggers a calibration routine within the sensor. In response to the trigger signal, a calibration processor within the sensor executes the calibration routine and adjusts the inductor-capacitor circuits and provides an indication of successful calibration.

Abstract: An inductive detector arranged to measure position along a axis comprising: a transmit winding; a receive winding; a passive circuit comprising a winding in electrical series with a capacitor; wherein: the mutual inductance between the transmit winding and the receive winding is a function of the relative displacement of the passive circuit along the measurement axis; a first portion of one of the windings is wound on a first pitch and a second portion of the same winding is wound on a second pitch whose extent is greater than the first pitch.

Abstract: Provided is a material for tactile sensor, which is easy to be formed, and in which the shape, size and orientation of coils dispersed in the medium are sufficiently controlled. The tactile-sensitive material comprises a medium and a plurality of micro coils dispersed in the medium and constituting a LCR resonance circuit, and wherein each of the plurality of micro coils comprises at least one spiral coil portion, and coil axes of the plurality of micro coils are aligned along at least one direction and/or directed in at least one plane. When a tactile stress is applied to the tactile-sensitive material, the C component is varied significantly, which contributes to the improvement in sensitivity of the tactile sensor. Further, by providing a core at the coil center, the sensitivity is more improved.

Abstract: A detector for a proximity sensor, includes: a sensing portion including a pair of sensing coils which has central axes along a direction intersecting with a moving direction of a sensed object moving in a predetermined moving path and is provided so as to interpose the moving path; a circuit block including a capacitor composing an LC resonant circuit with the sensing coils of the sensing portion and provided with an oscillator which oscillates the LC resonant circuit; and an electric connector composed of first connection terminals and a first conductor pattern that connect the sensing coils of the sensing portion in series, and second connection terminals and a second conductor pattern that connect the sensing coils to the oscillator.

Abstract: A conductivity sensor is disclosed. The conductivity sensor includes an oscillator for providing an input signal and a reactive circuit having an induction coil, a capacitive element, and a resistive element connected in parallel. The induction coil is adapted to be placed adjacent to a specimen. The conductivity sensor further includes a control circuit for driving the reactive circuit to resonance when the induction coil is placed adjacent to the specimen. The reactive coil is configured to provide an output signal having a parameter representative of the conductivity of the specimen when the reactive circuit is at resonance. The induction coil may include a first conductive element that spirals outward to an external perimeter and a second conductive element operably connected to the first conductive element. The second conductive element spirals inward from the external perimeter staggered relative to the first conductive element.

Abstract: An inductive sensor which uses two resonant LC circuits, one of reference and the other for measurement. The measurement inductor is arranged close to the active surface of the sensor. The reference inductor is shielded so that it is influenced less or not at all by the metallic body, but can follow the variations caused by the environmental temperature on the measurement inductor. The two LC circuits are excited by way of distinct pulses, so as to produce similar dampened oscillations, which are slightly different in terms of amplitude and phase. The reference oscillation can be elaborated to obtain a reference amplitude at a precise instant or during a reading time window to observe the oscillation of the measurement inductor.

Abstract: Apparatus and methods are disclosed for evaluating degradation of a transistor in a cross coupled pair of an RF oscillator independently. A MOS device can be coupled between a separated center-tap inductor. By appropriately sizing the MOS device and turning the MOS device on during operation of RF oscillator, a good contact can again be made that allows the oscillator to operate at design performance. By turning the MOS device off, the supplies can be separates such that I-V characteristics of both transistors of the cross-coupled pair may be obtained.

Abstract: A method for use in connection with installing a cable into a conduit having a first conduit end and a second conduit end, comprising the steps of—providing the cable with a metallic attribute,—providing within or proximate to the conduit, sensing means for sensing the metallic attribute,—introducing the cable into the first conduit end and driving it towards the second conduit end and—detecting that the sensing means has sensed the metallic attribute by sensing a change in inductance levels of the sensing means.

Abstract: An inductive programming switch for applications in special environments, comprising an inductive component and a container in which the inductive component is accommodated proximate to a wall of the container, the inductive component being connected to an electronic evaluation circuit, which is adapted to detect variations of parameters of the inductive component caused by the approach of a metallic object to the wall, the evaluation circuit being adapted to detect and identify a sequence of approach/spacing of the metallic object with respect to the wall and for modifying its functional parameters according to the sequence.

Abstract: The present invention related to devices and methods for using ferrite alignment keys in wireless remote sensor assemblies. In one aspect, the invention provides wireless resonant sensor assemblies comprising a pick-up coil, a ferrite alignment key positioned in and extending from the pick-up coil, and wireless resonant sensor having a receiving element wherein the pick-up coil and the wireless resonant sensor align upon insertion of the ferrite alignment key into the receiving element. The ferrite alignment key may also be part of a resonant sensor such that insertion of a pick-up coil into a receiving element of the alignment key results in a configuration where the alignment key is positioned in and extended from the pick-up coil. Methods of measuring one or more parameters of a monitoring system are also provided. The insertion of the ferrite alignment key aligns the pick-up coil and wireless resonant sensor thereby increasing sensing of the wireless resonant sensor by the pick-up coil.

Abstract: A substrate including a sensor unit, wherein the sensor unit includes a coil wound at least once arranged on the surface of the sensor or embedded within and near the surface thereof. With such an arrangement, an electric current that corresponds to information with respect to the substrate flows through the coil.

Abstract: A method and an arrangement for the detection of a coil in an electronic circuit, which is operated with a direct voltage lying within a prescribed voltage range, and in which the coil together with a condenser forms an electrical oscillating circuit.

Abstract: A capacitive ultrasonic transducer includes a flexible layer, a first conductive layer on the flexible layer, a support frame on the first conductive layer, the support frame including a flexible material, a membrane over the support frame being spaced apart from the first conductive layer by the support frame, the membrane including the flexible material, a cavity defined by the first conductive layer, the support frame and the membrane, and a second conductive layer on the membrane.

Abstract: According to some embodiments, motor-tuned nuclear magnetic resonance (NMR) probes may be tuned manually without overcoming the tuning motor holding force. An NMR probe includes a switchable manual-mode/motor-driven mode capacitance-adjustment assembly for adjusting the capacitance of a variable capacitor connected to an NMR RF coil. The capacitance-adjustment assembly includes a tuning shaft coupled to the variable capacitor through a gear assembly, and a mode-switching coupler coupled to the tuning shaft. The mode-switching coupler includes a first terminal coupled to a piezoelectric motor, and a second terminal coupled to the tuning shaft. In the manual mode, a user pushes up the tuning shaft, decoupling the two terminals of the mode-switching coupler and thus decoupling the motor from the tuning shaft. The user then manually rotates the tuning shaft. In the motor-driven mode, a spring tensioner presses the two terminals of the mode-switching coupler together, coupling the motor to the tuning shaft.

Abstract: A system and apparatus for providing an in-vivo assessment of relative movement of an implant that is positioned in a living being is provided that comprises a first assembly and a second assembly that are positioned within the living being. The first assembly comprises a passive electrical resonant circuit that is configured to be selectively electromagnetically coupled to an ex-vivo source of RF energy and, in response to the electromagnetic coupling, generates an output signal characterized by a frequency that is dependent upon a distance between the first assembly and the second assembly at the time of the electromagnetic coupling.

Abstract: This application relates to an apparatus and system for sensing strain on a portion of an implant positioned in a living being. In one aspect, the apparatus has at least one sensor assembly that can be mountable thereon a portion of the implant and that has a passive electrical resonant circuit that can be configured to be selectively electromagnetically coupled to an ex-vivo source of RF energy. Each sensor assembly, in response to the electromagnetic coupling, can be configured to generate an output signal characterized by a frequency that is dependent upon urged movement of a portion of the passive electrical resonant circuit and is indicative of strain applied thereon a portion of the respective sensor assembly.

Abstract: A salinity sensor for sensing or measuring salinity of a static or flowing fluid without contacting the fluid includes magnetic coil with a gapped core and a conduit for the fluid positioned in the gap in the core. The magnetic coil and the portion of the magnetic field produced by the coil that extends through the fluid in the gap are part of an LC or LCR circuit that can be driven to resonant frequency for a fluid of known salinity, which may include, but is not limited to, a fluid having zero salinity, as indicated by a peak output voltage on the circuit. Then, when the salinity of the fluid in the gap changes or a fluid with a different salinity is placed in the gap, the characteristics of the LC or LCR circuit, including inductance L and resonant frequency, change, and such changes can be detected and measured as an indication of the salinity of the fluid in the gap.

Abstract: A low cost, high performance method and apparatus for identifying electrical intermediate devices and measuring their position relative to an antenna is provided. The technique preferably uses electrical intermediate devices co-operating with AC energized antennae. The resulting electrical data can be used in a wide variety of user interfaces, identification systems and sensors to measure, for example, rotary position, linear position, weight, level, torque, vibration, turbidity and flow. The invention includes means for the contactless transmission of data and power to general instrumentation.

Abstract: Inconsistencies in a resin-based part are detected using a capacitive coupling probe having a tuned circuit and an impedance matching element. An alternating electric field produced by the probe penetrates the part. Inconsistencies in the resin part result in changes in the resonance of the circuit which are detected by a network analyzer.

Abstract: The exemplary embodiments of the invention provide techniques that assist in the absorption, reduction or elimination of the resonance of unwanted cavity modes in a cavity measurement system, such as a cylindrical TE0,n cavity measurement system used to measure various dielectric properties of a dielectric sample, for example. One non-limiting, exemplary system includes: sidewalls; a first endplate; a second endplate disposed opposite the first endplate so as to define a cavity bounded by the sidewalls, the first endplate and the second endplate; and first and second radio frequency (RF) coupling receptacles coupled to at least one of the sidewalls, the first endplate or the second endplate, wherein the first and second RF coupling receptacles are configured to pass a RF signal through the cavity. The first endplate has a plurality of conducting loops disposed on a surface facing the second endplate.

Abstract: The present invention relates to a method for the detection of a predamping state of an inductive sensor. The sensor has at least one oscillator with a resonant circuit and an oscillation amplifier. According to the method the oscillatory response of the oscillator is analyzed with an operating amplification or gain. According to the invention the method is further developed in that the oscillatory behaviour of the oscillator is additionally analyzed for an analysis amplification or gain, which is chosen lower than the operating amplification. The analysis amplification is also chosen in such a way that the oscillatory response of the oscillator reacts sensitively to objects or articles located in close proximity to the sensor. The invention also relates to an inductive sensor with predamping detection.

Abstract: A conductivity counter and method of determining conductivity of a fluid sample are disclosed. The counter is suitable for high-speed, accurate counting of discrete events or items, such as cancer cells, passing through a fluid sample cell. A variable frequency current source is used to supply an excitation current to a sample cell connected in parallel with an inductance or the electrical equivalence of an inductance. This configuration can be accurately modeled as a parallel RLC circuit when the system is operated at a stable frequency. The current source frequency is tuned to the resonance frequency of the equivalent RLC circuit, which effectively eliminates the capacitive and inductive components of the impedance, leaving only purely resistive components. The output of the equivalent RLC circuit is connected to a high input impedance buffer amplifier and then to a phase sensitive detector, which detects the phase shift resulting from the equivalent RLC circuit.

Abstract: An oscillator circuit for a sensor, with a tuned circuit and an operational amplifier, the electrical oscillation of the tuned circuit is capable of being tapped between a first terminal and a second terminal of the tuned circuit, and the first terminal of the tuned circuit being connected to the noninverting input of the operational amplifier and the output of the operational amplifier is fed back to the noninverting input of the operational amplifier. The oscillator circuit is designed to improve the dynamic behavior of the oscillator circuit by the second terminal of the tuned circuit —at least in terms of AC voltage —being directly connected to the inverting input of the operational amplifier.

Abstract: A proximity sensor system uses a sensor coil as the frequency determining element of an oscillator circuit. The frequency of the oscillator circuit is thus modulated based on the proximity of the sensor coil to a conductive element, thereby supplying a frequency modulated sensor signal. A frequency modulation (FM) detector circuit demodulates the sensor signal, and supplies a signal having an amplitude that varies with, and is representative of, the proximity of the sensor coil to the conductive element.

Abstract: The present invention discloses an automatic page detector, to determine which page of a book is open. The automatic page detector uses a sensor plate and an inductor as a sensor. In the invention, there is a sensor plate at each page of the book and the locations of the sensor plates for different pages are different. There is an array of inductors just beneath the sensor plates when the book is closed. The inductors are connected to the feedback loop of a LC oscillator through analog switches. The proximity of a sensor plate to an inductor will change the frequency of the LC oscillator. Scanning the analog switches by a microprocessor and detecting the variation of frequency of the LC oscillator during each scanning time period, the status of each sensor plate will be detected and we can determine which page of a book is opened.

Abstract: An untethered device is configured to inductively couple to a source device. The source device includes a driver circuit configured to generate a varying magnetic field and comprising a drive coil circuit. A phase detector is coupled to the driver circuit and configured to detect a phase of an input impedance of the driver circuit in response to the source device inductively coupling with the resonant circuit of the untethered device. A controller is coupled to the phase detector and the driver circuit, and is configured to adjust a frequency of a source voltage applied to the driver circuit in response to an output signal of the phase detector. The controller adjusts the source voltage frequency so that the phase of the input impedance as indicated by the output signal of the phase detector is substantially zero.