Abstract: A system includes: a radar scanner disposed to scan the interior of a container; an interrogator in communication with the scanner; and a processing system in communication with the interrogator, in which the processing system displays information about the interior of the container. A method includes: mounting a radar scanner antenna to a container so as to scan the interior of the container; connecting a coupler to the scanner so that the scanner communicates scanning data via the coupler to the exterior of the container. Another method includes: coupling an interrogator and radar processing system to a scanner mounted on a container; and processing radar scan data from the interior of the container. Another method includes: linking a radar processing system via a communications link to an interrogator that is coupled to a scanner mounted on a container; and processing radar scan data from the interior of the container.

Abstract: A system for measuring the range to an RFID tag including situations containing high clutter and multi-path signals is disclosed. The system includes an RFID reader; an RFID tag; and a coordinated pulse radar system. In the system the RFID reader causes the tag to respond to received signals in a first backscatter state at a first time and a second backscatter state at a second time. The pulsed radar system transmits short pulses coordinated by the backscatter state of the RFID tag and the system creates a differential signal comprised of the differences between radar signals obtained during the first and second states of the tag to obtain an uncorrupted measure of a round trip time of flight of said radar pulses between the pulse radar system and the RFID tag.

Abstract: A system for measuring range to an RFID tag including situations containing high clutter and multi-path signals is disclosed. The system includes an RFID reader; an RFID tag; and a coordinated signal compression radar system. The reader causes the tag to respond to received signals in a first backscatter state at a first time and a second backscatter state at a second time. The signal compression radar system transmits signals coordinated by the backscatter state of the tag and creates a differential signal comprised of the differences between radar signals obtained during the first and second states of the tag to obtain an uncorrupted measure of a round trip time of flight of said radar signals between the radar system and the RFID tag. The radar may use signals typical of pulse compression radar systems such as chirp modulation or Orthogonal Frequency Domain Modulation (OFDM), either pulsed or semi-continuous.

Abstract: The wireless detection beacon is for use with a Radio Frequency (RF) interrogator transmitting at a first frequency and receiving at a second frequency. The wireless detection beacon includes a substrate, a power supply carried by the substrate, an antenna assembly carried by the substrate, and a local oscillator (LO) carried by the substrate and configured to be powered by the power supply to provide an LO signal at a third frequency. A mixer is carried by the substrate and coupled to the antenna assembly and the LO. The mixer is configured to generate an outgoing beacon signal to the antenna assembly at the second frequency based upon mixing an incoming signal from the RF interrogator at the first frequency with the LO signal at the third frequency.

Abstract: A communication processing apparatus alternately transmits a carrier wave carrying a command and receives a response from a tag while transmitting an unmodulated carrier wave. A transmission control unit changes the phase of the unmodulated carrier wave transmitted from a transmission/reception circuit in response to start of reception of the reflected wave from the tag. The transmission/reception circuit includes a circuit for separating and detecting an I signal and a Q signal included in the reflected wave from the tag. A phase detection unit uses the I signal and the Q signal to detect change of the phase of the reflected wave. A distance calculation unit measures a time from a change of the phase of the unmodulated carrier wave to a detection of a corresponding change in the phase of the reflected wave, and uses the time to calculate the distance from the antenna to the tag.

Abstract: The present invention relates to a transponder comprising an antenna structure (31) configured to receive an incoming signal with RF power of a first frequency f1 and to retransmit the incoming signal as a transparent output signal with RF power of a second frequency f2 when hit by the incoming signal. The transponder further comprises: an amplifier (39) configured to provide an amplified transparent output signal based on the incoming signal; a frequency converter (35) configured to frequency convert the incoming signal into the transparent output signal; and a first frequency filter (33) connected to the antenna structure. The first frequency filter is tuned to the first frequency f1 to avoid amplifying incoming signals with RF power of frequencies other than the first frequency f1.

Abstract: The present invention is a method for aiding pilots in resolving flight identifier (flight ID) confusion. The method includes receiving a first flight ID in a processing system. The method further includes comparing the first flight ID to a second flight ID. The method further includes providing an alert when the compared first flight ID and second flight ID are at least substantially similar. The first flight ID is associated with a first aircraft, the second flight ID is associated with a second aircraft, the first aircraft and second aircraft being located in substantially proximal airspace.

Abstract: A system for preventing light pollution includes one or more radar units that monitor for vehicles in a volume surrounding or containing one or more obstructions having one or more obstruction lights. A master radar detection processing unit receives sensed radar detection information from the one or more radar units with associated radar signal processing units and determines whether a vehicle is present within the monitored volume. A plurality of obstruction light controller units are interconnected in a network, such as a wireless network. Each obstruction light controller unit turns on an obstruction light when a vehicle enters the monitored volume or a failure condition exists, and turns off the obstruction light when the vehicle has vacated the monitored volume and no failure condition exists. The one or more radar units can transmit sensed radar detection information to a master radar detection processing unit via the network.

Abstract: A radio frequency signal acquistion and source location system, including a first signal acquisition and source location module comprising an RF transceiver coupled to an antenna, the antenna provided with a electronic steering circuit. The antenna operative to launch an interrogation signal, the interrogation signal steerable by an electronic steering circuit. A processor operatively coupled to the RF transceiver and the electronic steering circuit, the processor provided with a data storage for storing a signal data record for each of at least one response signal(s) received by the RF transceiver(s). The signal data record including a signal identification, a received signal strength indicator and an RF signal direction along which respective signal(s) are received by the antenna, the RF signal direction derived from the electronic steering circuit. A postion logic operative upon the data record(s) derives a three dimensional signal origin location of each response signal.

Abstract: System and method making it possible to operate in an interrogator mode and/or in a passive listening mode wherein it comprises in combination at least the following elements: an antenna (6) having a given aperture sector, a control means (31) making it possible to toggle the system into a first interrogator operating mode using a first given angle sector or into a second passive listening operating mode using a second angle sector of greater value than the first, means (23) making it possible to add together the signals received on the sum pathway and on the difference pathway of the antenna in the case of the passive listening operating mode.

Abstract: A reader device (110) for reading information transmitted from a transponder (130) via a backscatter signal (132) generated by the transponder (130) in response to a stimulus signal (112) generated by the reader device (110), the reader device (110) comprising a first power estimation unit (114) adapted for estimating a first power value indicative of the power of the stimulus signal (112) at a position of the transponder (130) by evaluating a power information included in the backscatter signal (132), a second power estimation unit (116) adapted for estimating a second power value indicative of the power of the backscatter signal (132) at a position of the reader device (110), and a distance estimation unit (118) adapted for estimating a distance (d1) between the reader device (110) and the transponder (130) based on the first power value and the second power value.

Abstract: The invention concerns a method and system of locating objects by means of UWB signals, the system including a search device (D1), incorporated in a portable apparatus (11) and provided with a pair of antennae (A1, A2), and at least one target device (D2) attached to an object sought (12). The target device (D2) includes, in addition to the transceiver (34, 35), a very low power consumption wake up receiver (46) which, when the target device is in a standby state, can receive a UWB wake up signal to switch on said device. This target device is arranged for measuring a time difference (tdiff) between the respective receptions of two locating signals respectively emitted by the two antennae (A1, A2) of the search device and for transmitting said time difference in a return signal that further contains, in a preferred variant, a signal processing time (trproc). Thus, it is not necessary for the two devices to be synchronized.

Abstract: A charging station for mobile devices that acts as an intermediary device to facilitate communication between mobile devices and other proximate devices. The charging station may receive data with a mobile device via a first communication protocol (e.g., Bluetooth) or in a first data format and may transmit the received data to a proximate device via a second communication protocol (e.g., WiFi) or in a second data format. The charging station may then receive responsive data from the proximate device via the second communication protocol (e.g., WiFi) or second data format and transmit the responsive data the mobile device via the first communication protocol (e.g., Bluetooth) or first data format. In some embodiments, the charging station may communicate status data about a mobile device to other proximate devices.

Abstract: The present invention includes a method for identifying a facility on the ground or at sea, the method being implemented on an airborne responder linked to at least two antennas, the method including a step of choosing a first transmission antenna and a step of transmitting an interrogation message from the chosen antenna. The method further includes testing whether a response has been received by the responder, and, if at least one response signal is received by at least one of the antennas, choosing a transmission antenna as a function of the response signal or signals received. If no response message is received, a different transmission antenna is chosen from the antenna that transmitted the last interrogation message. The method is repeated from the step of transmitting the interrogation message.

Abstract: An apparatus and method to generate and detect virtual targets. Position information for one or more virtual targets is calculated onboard a vehicle from real position information obtained from GPS satellites or other external or internal sources. This virtual position information is coded, mixed with a carrier frequency, amplified, and radiated to a nearby test vehicle, such as an aircraft. The amplitude of the radiated signal is adjusted such that the signal containing the virtual position information is received by the test aircraft only. The radiated signal thus adjusted is below the detection threshold of any aircraft further away. The test aircraft decodes the signal and interprets the decoded virtual position information as real aircraft in its vicinity. The coded signals may be structured to comply with the requirements of the FAA's ADS-B system. The apparatus may be mounted on the test aircraft itself, or on a nearby aircraft.

Abstract: Example methods, apparatuses, and articles of manufacture are disclosed herein that may be utilized to facilitate or otherwise support RF ranging-assisted local motion sensing based, at least in part, on measuring one or more characteristics of a range between communicating devices in one or more established RF links.

Abstract: In a radio location system for vehicles moving along a guideway, a transmitter for energizes a transponder beside the guideway. A first detector for detects a response signal from the energized transponder to determine the transponder identification. A second detector detects a positional signal received from the transponder that is decoupled from the first signal and contains precise positional information. In one embodiment, the second detector picks up a crossover signal from a crossover antenna.

Abstract: A wireless power transmission method is provided. The method includes exchanging information for wireless power transmission between a wireless power transmission device and a terminal, in order to determine a communication protocol.

Abstract: A radar device is provided. The radar device is installed in a movable body, transmits electromagnetic waves at a predetermined frequency, and receives response waves transmitted from a transponder device in response to the electromagnetic waves, respectively. The radar device includes a representative distance calculating module for calculating a representative distance from the radar device to the transponder device based on the response waves that are continuous over a predetermined azimuth angle range, a representative relative azimuth calculating module for calculating a representative relative azimuth of the transponder device from the radar device based on the continuous response waves, and a positioning module for calculating a location of the radar device based on positional information of the transponder device that is contained in each of the response waves, the calculated representative distance, and the calculated representative relative azimuth.

Abstract: A system is disclosed for detection of whether a movable object, such as a sports object, e.g. a football or an ice hockey puck, has passed goal plane. It is known to encircle the goal plane with conductors (1, 2, 3, 4) to produce an electromagnetic field to excite signal emitter means in the movable object, alternatively detect the signal emitted by the emitter means. With the present invention these circuits are sectioned into a plurality of separate circuits, which provides an improved spatial resolution of the system in particularly when the movable object is close to the conductors.

Abstract: A method and system that prevents engagement with neutral aircraft utilizes secondary surveillance radar (SSR) in conjunction with traffic alert collision avoidance systems (TCAS) conventionally found on various commercial aircraft. The system and method provide for detecting interrogating signals sent out by a TCAS system of an interrogating aircraft searching for another aircraft that may pose a threat for collision. The system and method of the invention provide for a base system generating signals responsive to the interrogation signals such that there is a decreasing time difference between the interrogating signals and the responsive signals. The decreasing time difference indicates to the interrogating aircraft that another aircraft is approaching its airspace urging the neutral aircraft to change course and avoid entering a guarded tactical airspace thus avoiding unnecessary engagement of the aircraft.

Abstract: An electronic device for wirelessly tracking the position of a second electronic device is disclosed. The electronic device includes transceiver circuitry and processing circuitry. The transceiver circuitry includes a beacon generator to generate a beacon at a particular frequency and direction. An antenna array transmits the beacon, and receives at least one modulated reflected beacon from the second electronic device. The transceiver circuitry also includes a discriminator to discriminate between received modulated reflected beacons and received reflected interfering beacons. The processing circuitry couples to the transceiver circuitry and tracks the position of the second device based on the modulated reflected beacons.

Abstract: In accordance with a particular embodiment of the invention, a kinematic indicator generator may receive tracking data describing the position and velocity of a target. The tracking data may be used to identify an event describing an action of the target that may have occurred. The probability that the event occurred may be calculated and indicated by a confidence. The kinematic indicator generator may generate a kinematic indicator that includes the event and the confidence.

Abstract: A secure communication topology can be used for communications between a locator and one or more transponders to determine the location of the transponders. An example system may include a locator that is configured to transmit an interrogation signal that is encoded for receipt by one or more of the transponders. When a transponder receives and correlates the interrogation signal with an internally stored reference sequence, the transponder can transmit one or more reply transmissions at precisely determined time delay intervals. The time delay intervals are secretly known by both the locator and the transponder. The reply transmissions can each correspond to previously sampled noise signals that are also secretly known by both the transponder and the locator.

Abstract: Active RFID technologies are used to tag assets and people within buildings or open areas, such as parking lots or military bases; and to identify, preferably within a few meters, the real-time location (RTL) of the tag, i.e. to create a real-time location system, known as an RTLS. A novel and complex algorithm is provided that combines signal strength computations with factors that incorporate physical realities, such as walls and floors, to determine a tag's real-time location more accurately.

Abstract: A radio frequency signal acquisition and source location system, including a first signal acquisition and source location module comprising an RF transceiver coupled to an antenna, the antenna provided with a electronic steering circuit. The antenna operative to launch an interrogation signal, the interrogation signal steerable by an electronic steering circuit. A processor operatively coupled to the RF transceiver and the electronic steering circuit, the processor provided with a data storage for storing a signal data record for each of at least one response signal(s) received by the RF transceiver(s). The signal data record including a signal identification, a received signal strength indicator and an RF signal direction along which respective signal(s) are received by the antenna, the RF signal direction derived from the electronic steering circuit. A position logic operative upon the data record(s) deriving a three dimensional signal origin location of each response signal.

Abstract: A system and method for monitoring and tracking the position of a subject comprises, in an exemplary embodiment, a transponder configured for being co-located with the subject and a means for enabling communication between the transponder and a remote GPS-enabled receiver, such as a cell phone or the like, for selectively triangulating the position of the transponder. In the exemplary embodiment, the means for enabling such communication is software that is installed in and executed by the receiver. The software allows the receiver to triangulate the geographic position of the transponder by fixing a first reference point based on the location of the GPS-enabled receiver, fixing a second reference point based on the location of a network broadcast site through which the receiver and transponder communicate, and calculating the location of the transponder based on the angular position of the transponder relative to the network broadcast site.

Abstract: A circuit of a node of a radio network, and a method for distance measurement with a transceiver for receiving a first signal with a first frequency by downmixing to an intermediate frequency, with a phase measurement unit, which is set up to determine a first value of a first phase for a first frequency value of the first frequency. The transceiver is formed to transmit a second signal with a first frequency value of a second frequency for determining a first value of a second phase. The control circuit is set up to change the first frequency and the second frequency, in that a second frequency value of the first frequency and the first frequency value of the first frequency have a frequency difference, and whereby a second frequency value of the second frequency and the first frequency value of the second frequency have the frequency difference. The phase measurement unit is set up to determine a second value of the first phase for the second frequency value of the first frequency.

Abstract: In a synthetic aperture radar system monitoring an area containing at least one moving target for identification, the target is equipped with an identification device, which receives the radar signal transmitted by the radar system, and transmits a processed radar signal obtained by modulating the incoming radar signal with a modulating signal containing target information, such as identification and status information, and by amplifying the modulated radar signal; the radar echo signal reflected by the monitored area and containing the processed radar signal is received and processed by a control station of the radar system to locate the target on a map of the monitored area, and to extract the target information to identify the target.

Abstract: A wireless communication tag according to the present invention includes a first antenna 8 previously set with predetermined identification information, and for wirelessly communicating various types of data with a reader/writer 6; a controller (IC chip 14) for controlling the data communicated through the first antenna; a second antenna 10 for receiving an electromotive radio wave 4e for causing electric power by a radio wave; and a charging unit (rectifying circuit 16 and a capacitor 18) for causing electric power by the electromotive radio wave received from the second antenna as well as for storing the caused electric power. With use of the electric power stored in the charging unit, the first antenna supplies data relating to the identification information to the reader/writer. The second antenna also can provide the reader/writer with the identification information.

Abstract: A timing circuit that can function as an accurate persistent node in an RFID tag includes a power capture circuit for capturing power from a power source, and a counter circuit that provides a count representing a progression of time. The count can then be compared to a reference value representing a time constant of the circuit.

Abstract: The invention relates to a monitoring device and method allowing surveillance of an aircraft in relation to aircraft and/or craft on an airport displacement zone. The invention is a system comprising a dedicated transmitter and receiver to receive the information regarding the location and displacement of the cooperative aircraft and to monitor the location of the said aircraft in relation to the cooperative aircraft. The monitoring application is based on the detection of conflict zones by inter-correlation of constraint surfaces of the airport zone. The invention applies to aircraft carrying communication moans for ADS-B networks for an airport zone monitoring application.

Abstract: A process and a device for detecting aircrafts circulating in an air space surrounding an airplane is disclosed. The device (1A) comprises means (2, 3) for detecting an aircraft circulating in the air space surrounding the airplane and, in case of a detection, for determining a first position and a second position of the aircraft with respect to the airplane, and means (8A) for comparing said first and second positions so as to check whether they match.

Abstract: A health monitoring system is provided for a vehicle with an identity configured to travel on a surface. The system includes a body positioned on the surface and configured to stimulate a dynamic response from the vehicle as the vehicle travels over the body; a response sensor associated with the body and configured to measure the dynamic response from the vehicle; and an identification sensor associated with the body and configured to collect data corresponding to the identity of the vehicle.

Abstract: An adaptive inductive ballast is provided with the capability to communicate with a remote device powered by the ballast. To improve the operation of the ballast, the ballast changes its operating characteristics based upon information received from the remote device. Further, the ballast may provide a path for the remote device to communicate with device other than the adaptive inductive ballast.

Abstract: A locating system, includes at least one initiator configured to operate at a first clock frequency, and to transmit a measurement signal including a first preamble; and at least one transponder configured to operate at a second clock frequency, to receive the measurement signal, and to transmit a response signal to the initiator, the response signal including a second preamble. The initiator is further configured to calculate, based on the response signal, a distance between the initiator and the transponder for determining a location of the transponder.

Abstract: The object of the present invention is to provide an article management method by which detecting the location of an object is performed easily and introduction costs for detecting the location of an object are suppressed. The article management method includes a first RF chip attached to an article, a first reader/writer into which a shared memory portion and a second RF chip are incorporated, and a second reader/writer. The first reader/writer obtains information stored in the first RF chip, the shared memory portion retains the obtained information about the first RF chip, the second RF chip reads out that information about the first RF chip stored in the shared memory portion, the second reader/writer, by the second RF chip, obtains the information about the first RF chip and information stored in the second RF chip and information about the location of the second RF chip.

Abstract: Methods for estimating a distance between an originator and a transponder, methods for calculating a fine time adjustment in a radio, computer-readable storage media containing instructions to configure a processor to perform such methods, originators used in a system for estimating a distance to a transponder, and transponders used in a system for estimating a distance to an originator. The methods utilize fine time adjustments to achieve sub-clock cycle time resolution. The methods may utilize offset master clocks. The methods may utilize a round-trip full-duplex configuration or a round-trip half-duplex configuration. The method produces accurate estimates of the distance between two radios.

Abstract: An adaptive inductive ballast is provided with the capability to communicate with a remote device powered by the ballast. To improve the operation of the ballast, the ballast changes its operating characteristics based upon information received from the remote device. Further, the ballast may provide a path for the remote device to communicate with device other than the adaptive inductive ballast.

Abstract: An adaptive inductive ballast is provided with the capability to communicate with a remote device powered by the ballast. To improve the operation of the ballast, the ballast changes its operating characteristics based upon information received from the remote device. Further, the ballast may provide a path for the remote device to communicate with device other than the adaptive inductive ballast.

Abstract: Systems and methods to use radar systems for radio frequency identification (RFID) applications. In one embodiment, radar systems are adapted to use RFID communications protocols and methods to enhance the usefulness of radar systems beyond the determination of the presence, distance, direction and/or speed of a vehicle or object, to additionally include the transmission of data such as object identification and additional messages or data.

Abstract: Systems, apparatuses, and methods estimate the distance between a player and a ball by transmitting a chirp (sweep signal) to a radio tag located on the ball. During the chirp, the frequency of the transmitted signal is changed in a predetermined fashion. The radio tag doubles the transmitted frequency and returns the processed signal to a transceiver typically located on the player. The currently transmitted frequency is then compared with the received frequency to obtain a difference frequency from which an apparatus may estimate the distance. The apparatus may simultaneously receive the processed signal from the radio tag while transmitting the sweep signal.

Abstract: A high-precision distance measuring with a reduced error in a distance measuring system which calculates a distance from an arrival time of each pulse signal constituting a pulse sequence is provided. For an oscillator which generates pulse signals by counting the number of pulse signals constituting a received pulse sequence, a relative time difference between a transmitting device and a return device is acquired, a distance from the transmitting device to the return device is calculated, and the calculated distance is corrected based on the calculated relative time difference.

Abstract: A chipless microwave identification tag (200) comprising: a dielectric substrate (210); and a plurality of antenna elements (220) made from a conductive material and disposed on at least one surface (205, 255) of the dielectric substrate (210); wherein when the tag (200) is excited by an incident microwave signal (131), a reflected wave (141) to identify the tag (200) is generated with a number of specific frequencies altered by microwave resonation of the antenna elements (220).

Abstract: The invention relates to an automatic aircraft landing guidance system having an electromagnetic detecting and locating device, positioned on the ground and a first multifunction transmitting/receiving radiofrequency beacon, on board each guided aircraft and transmitting in particular a continuous wave. The detecting and locating device uses the continuous wave transmitted by the beacon to perform a passive locating intended to improve the accuracy of the measurement of the angular position of the aircraft. It also comprises means for generating and periodically transmitting to the aircraft, via the beacon, information enabling said aircraft to rejoin an optimum landing path from its position. The invention applies more particularly to the guidance of autonomous and automatic aircraft such as drones in the approach and landing phase.

Abstract: There is provided a method and system for positioning a transponder, the system comprising an antenna array of at least two spaced-apart antennas coupled to a common generating and switching unit. The generating and switching unit is configured for generating a periodic signal and switching the signal between said at least two antennas, constituting a positioning signal transmitted to the transponder. The system comprises a receiver for receiving a returned signal and a phase difference estimator coupled to the receiver and operable to measure phase differences between portions of the returned signal. The system further comprises a positioning utility coupled to said phase difference estimator and configured to determine the position of the transponder relative to the positioning system.

Abstract: The invention relates to a method of implementing operations involving the processing a radio-communication frame (CMF) in a system comprising at least three radio transmitter/receiver devices (1-5), consisting in transmitting the frame in response to a first request signal (REQ1) transmitted by a device belonging to the system (1). According to the invention, the frame is processed in the device (1) that transmitted the first request signal (REQ1) as well as in other devices belonging to the system (1, 3-5) which transmitted respective request signals (REQ2-REQ4) within a pre-determined time period.

Abstract: Distance to a modulated backscatter tag is measured with a RFID reader that measures changes in phase with frequency of modulated backscattered RF signals. Measured distances are linked to a specific tag. The effects of other sources of reflected and interfering signals are mitigated. The techniques eliminate the need for high RF bandwidth used in time-of-flight methods, and may be used with linear, limiting or other types of amplifiers in the reader receiver. Unambiguous distance to a tag may be found using the derivative of phase with RF frequency of the modulated signal backscattered by a tag. The distance to a tag can be measured with an accuracy on the order of a centimeter. The techniques utilize the characteristics of cooperative backscatter tags (transponders, labels, etc.). New readers implement the techniques which may use unmodified tags.

Abstract: An apparatus for transmitting and receiving radio-frequency signals. including a cylindrical antenna array which has an omnidirectional channel; an IFF interrogator and an IFF transponder connected to the cylindrical antenna array; and a means for sharing the omnidirectional channel between the IFF interrogator and the IFF transponder.

Abstract: The present invention comprises a radio frequency identification device that utilizes multiple operating frequencies. In one embodiment of the present invention, one frequency (e.g., an ultra-high frequency such as 915 MHz, 800 MHz, 915 MHz, or microwave frequency such as 2.45 GHz) is used for data transmission, and another frequency (e.g., a low or high frequency such as 13.56 MHz) is used for field penetration. In another embodiment, one frequency is used for reading information received from the multi-frequency identification device, and another frequency is used for writing to the multi-frequency identification device. In an additional embodiment, the multi-frequency identification device utilizes one antenna for all frequencies. In another embodiment, the multi-frequency identification device utilizes two or more antennas for different frequencies, and one common memory. In other embodiments, one or two digital parts, analog parts, antennas, and memories can be used.