EP1103078A1 - Offset arrangement of electrodes on a piezoelectric transducer - Google Patents
Offset arrangement of electrodes on a piezoelectric transducerInfo
- Publication number
- EP1103078A1 EP1103078A1 EP99931636A EP99931636A EP1103078A1 EP 1103078 A1 EP1103078 A1 EP 1103078A1 EP 99931636 A EP99931636 A EP 99931636A EP 99931636 A EP99931636 A EP 99931636A EP 1103078 A1 EP1103078 A1 EP 1103078A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- electrodes
- transducer
- piezoelectric member
- sheet
- subject
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
- A61B5/0205—Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/30—Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
- H10N30/302—Sensors
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/87—Electrodes or interconnections, e.g. leads or terminals
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
- A61B5/107—Measuring physical dimensions, e.g. size of the entire body or parts thereof
- A61B5/1071—Measuring physical dimensions, e.g. size of the entire body or parts thereof measuring angles, e.g. using goniometers
Definitions
- the present invention relates to a novel transducer, a method of monitoring a human or animal subject, and a method of shaping a transducer. More particularly, but not exclusively, the present invention relates to a motion detecting transducer suitable for detecting the state of wakefulness of the driver of an automobile or for detecting the motion of a human (particularly an infant) during sleep.
- a passive transducer i.e. a transducer to which no power is supplied.
- Piezoelectric phenomena provide such an avenue in that the physical motion of the constituent material creates its own voltage.
- a piezoelectric transducer is described in US-A-4359726.
- a polarised piezoelectric foil is contiguously enveloped by a pair of electrodes which are formed on the foil by a process of surface metalisation.
- US-A-4359726 suffers from two problems. Firstly, due to the large area of the contiguous electrodes the capacitance between them is high. This high capacitance is a hindrance to the frequency response control of the transducer.
- a second problem with the contiguous electrodes is that, if an end user needs to cut the transducer sheet to size to fit the transducer into a desired location (such as a vehicle seat or a baby's bassinet), a short circuit can be created between the electrodes since the piezoelectric film is very thin.
- a transducer comprising a piezoelectric member which deforms in use to provide an electrical output; and first and second electrodes arranged on opposed sides of the piezoelectric member to pick up the electrical output, wherein the electrodes are offset so as to provide one or more regions in which the electrodes do not overlap.
- the capacitance between the electrodes is reduced.
- the capacitance can also be conveniently controlled by selecting a suitable amount of offset between the electrodes.
- an end user can cut the transducer in the non-overlapping region(s) without creating a short circuit between the electrodes.
- the total area of overlap is less than 50% of the total combined area of the electrodes.
- One or both electrodes may be formed in a variety of patterns which are discontinuous when viewed along a planar cross-section taken through the electrode(s) .
- the electrodes may comprise rectangular grids which are diagonally offset from each other.
- the electrodes may be formed in offset serpentine patterns. This has the advantage that overlap can be completely avoided if required.
- the first electrode comprises a plurality of fingers; and the second electrode comprises one or more fingers arranged between the fingers of the first electrode.
- the capacitance between the electrodes can be controlled by varying the width of the interlocking fingers and their degree of overlap.
- the fingers may have different widths, or the fingers of the first electrode may have a width substantially equal to the width of the finger(s) of the second electrode.
- the electrodes may have unequal areas. In this case the electrode with the larger area can act as an EMI shield.
- the piezoelectric member may have a variety of shapes but in a preferred embodiment the piezoelectric member comprises a sheet and the electrodes are arranged on opposed major faces of the sheet. This enables the transducer to cover a wide area and the patterned electrodes cover a wider area per unit capacitance than conventional continuous electrodes.
- the sheet is thin, with a distance of less than 0.3 mm (and typically less than 0.1 5 mm) between the electrodes.
- a method of shaping a transducer comprising a piezoelectric member which deforms in use to provide an electrical output; the method comprising manually cutting the transducer to a desired shape and size.
- the second aspect of the present invention provides an end user with a convenient method of adapting the size and shape of a transducer (for instance using a knife or a pair of scissors) to enable the transducer to be accurately positioned in a desired location adjacent to a subject.
- the transducer may be adhered to the subject's skin but in a preferable embodiment the transducer is positioned by placing it in or on a subject support (such as a seat or bed) whereby when the subject occupies the support the transducer is able to pick up movement signals from the subject.
- a subject support such as a seat or bed
- the piezoelectric member comprises a sheet, enabling the transducer to cover a wide area.
- the transducer comprises one or more electrodes which pick up the electrical output.
- the end user may need to avoid cutting through the electrodes in order to prevent a short circuit.
- a transducer according to the first aspect of the invention may be used, enabling the user to cut through the non-overlapping region(s) without risking a short circuit.
- transducer connections are permanently connected via rivets or other means to external electronics. This makes it difficult to install the transducer.
- a transducer comprising a piezoelectric member which deforms in use to provide an electrical output; first and second electrodes arranged on opposed sides of the piezoelectric member to pick up the electrical output; and a clamp for releasably securing the electrodes on each side of the piezoelectric member.
- the transducer can be installed more easily by positioning it in a desired location with the electrodes detached, then securing the electrodes with the clamp.
- the clamp can be designed such that if, for example, the transducer is treated roughly by a child, the clamp will release the electrodes without causing any damage to the transducer.
- the clamp is sprung so as to resiliently secure the electrodes.
- the piezoelectric member comprises a sheet and the electrodes are releasably secured on opposed major faces of the sheet.
- the electrodes may connect ohmically with the piezoelectric member, either directly or via third and fourth electrodes (eg. layers of conductive ink adhered to the opposed sides of the piezoelectric member) .
- the first and second electrodes couple capacitively with the piezoelectric member (either directly or via the third and fourth electrodes) .
- the first and second electrodes may be integral with the clamp (ie. the clamp may be electrically conducting) .
- the clamp is made of an insulating material.
- a method of monitoring a subject comprising: a) acquiring a movement signal from the subject; b) extracting vital sign information from the movement signal, eg. cardiac or respiratory signals; c) analyzing the vital sign information to determine the complexity of the vital sign information; and d) generating an alarm signal when the complexity falls below a predetermined threshold.
- the present invention recognises that a certain level of complexity is desirable in a healthy subject. Therefore if the complexity falls below a predetermined threshold (indicating that the subject is entering into an unhealthy, anomalous pattern) an alarm signal is generated.
- the complexity is determined by determining the fractal dimension of the vital sign information.
- suitable analysis algorithms are wavelet filter banks (ie. measuring how much energy is dispersed over different wavelet generations); Lempel-Ziv complexity measurements; and Lyapunov exponents.
- a predetermined threshold ie. indicating that the complexity of the movement signal is decreasing
- an alarm signal is generated.
- short-time Fourier transforms or Gabor expansion may be utilised - measuring how much energy is present in each bin and using standard deviation, peak measurements etc. Examples of suitable complexity measurements are described in Zhang et al, "Detecting Ventricular Tachycardia and Fibrillation by Complexity Measure", IEEE Transactions on
- the piezoelectric member employed in each aspect of the invention is positioned adjacent to a flexible member (eg. a foam sheet), or the piezoelectric material may comprise a foamed mixture of a piezoelectric polymer and an elastomer.
- the piezoelectric material comprises a polymer such as polyvinylidene fluoride (PVDF) or one of its copolymers.
- PVDF polyvinylidene fluoride
- the transducers and methods of the present invention may be employed in a variety of applications.
- One application is monitoring of one or more vital signs (e.g. heartbeat, respiration) .
- the transducer may be employed in infant sleep monitoring (in which an alarm is generated if the infant's sleep pattern becomes anomalous).
- the transducer may be used to detect the state of wakefulness of the driver of a vehicle (in which an alarm is generated when the driver becomes drowsy).
- the transducer can be put on top of or into the driver's seat, and connected ohmically to the vehicle's power system and the alarm/monitor electronics.
- the transducer may be consciously manipulated by the user to provide active control of a device.
- Figure 1 shows a transducer and detector according to a first embodiment
- Figure 2 shows a transducer and detector according to a second embodiment
- Figure 3 shows the transducer of figure 1 in use
- Figure 4 shows a capacitive clamp connector
- Figure 5 is a plan view showing an electrode arrangement
- Figure 6 is a planar cross-section taken along line AA in figure 4;
- Figure 7 is a planar cross-section taken along line BB in figure 4.
- Figure 8 is a block diagram of a set of processing electronics
- Figure 9 shows a differential transducer
- Figure 10 shows an alternative set of processing electronics for the differential transducer
- Figure 1 1 is a flow diagram of a method of generating an alarm signal.
- Figure 1 shows a transducer in the form of a piezoelectric polymer sheet 1 sandwiched between flexible layers 3.
- Piezoelectric polymer sheet 1 may be formed of materials and by techniques known in the art.
- Layer 3 may be an elastomer foam having a density chosen to provide the required deformation of polymer sheet 1 when a desired force is applied to piezoelectric polymer sheet 1 .
- Wires 4 are connected from electrodes 2, which are either printed or deposited on the polymer sheet 1 , to detector electronics, 5.
- the layer 3 is adhered to the sheet 1 by a suitable glue. When sheet 1 is deformed a voltage develops across the sheet 2 related to the force applied to, and hence deformation of, the sheet.
- the voltage from electrodes 2 is applied to detector electronics 5 which may generate an alarm signal when prescribed conditions exist.
- the transducer is in the form of a piezoelectric polymer foam block.
- a piezoelectric polymer is mixed with an elastomer and foamed to produce a resilient piezoelectric polymer foam block 6.
- Wires 8 are connected to electrodes 7, such as wire or conductive plastic mesh, which are embedded in the foam during the manufacturing process of the piezoelectric polymer foam block 6, and detect voltages produced when forces are applied to piezoelectric polymer foam block 6, which deform it. The voltage across line 8 is monitored by detector 9 which again produces an alarm when prescribed motion conditions exist.
- the electrodes 7 are coated with non-conductive dielectric layers 1 7
- the transducer 1 , 2, 3 is placed on a baby's bassinet 1 0, and the baby 1 1 placed on top of the transducer 1 , 2, 3.
- the deformation of piezoelectric polymer sheet 1 will cause the voltage between electrodes 2 to vary in relation to the changing forces applied to piezoelectric polymer sheet 1 .
- the sheet is stretched along its length to pre-align the polymer molecules.
- the piezoelectric effect is then also enhanced, in all axes, by applying an electric field across the thickness of the sheet as it is cooling down.
- the charge generation of the molecules is as much as three orders of magnitude more effective along the length of the sheet (ie. by stretching/releasing along the alignment direction of the molecules) than across the thickness of the sheet.
- the density and thickness of the foam can be selected so as to result in the desired deformation of the transducer to produce the desired range of output voltages.
- One suitable piezoelectric polymer is PVDF (polyvinylidene fluoride) and its copolymers.
- Figure 4 is a representation of a capacitive clamp engaged on the foamed version of the transducer shown in figure 2.
- the permanent electrodes 7 do not make an ohmic connection, but rely on a capacitive connection to releasable electrode plates 14 which are held in place by a non-conductive sprung clamp 1 5.
- the plates 14 are then ohmically connected via wires 1 6 to the signal processing electronics 9.
- the clamp 1 5 can also logically hold any first level current amplifier circuitry required to reduce the susceptibility of the signal to electromagnetic noise during transport to the signal processing electronics.
- the clamp 1 5 can be released by gripping the sheet, and sliding the clamp to the right as shown in Figure 4.
- the transducer can be easily installed and the clamp will release without ripping the sheet if the transducer is treated roughly.
- the electrodes 2,7 need not be contiguous conductive layers, but may be a pattern which does not occupy 1 00% of the surface of the polymer, or several isolated conductive patterns, such as used in keyboard applications or printed circuit applications.
- FIG. 5-7 An example of a suitable electrode pattern is shown in figures 5-7.
- An upper electrode and a lower electrode (shown in dashed lines in figure 5) are printed on opposite faces of a piezoelectric polymer sheet 29 which is sandwiched between protective layers 20.
- the upper electrode comprises five parallel fingers 22 connected to a strip 23 which is connected in turn to the cylindrical outer conductor 24 of a coaxial output cable 25.
- the lower electrode comprises five parallel fingers 26 connected to a strip 27 which is connected in turn to the central conductor 28 of the coaxial output cable 25.
- the strips 23,27 may be connected to a capacitive clamp of the type shown in Figure 4.
- the piezoelectric layer 29 is quite thin - typically 28-1 1 0 micrometers thick. As a result, if continuous electrodes are used, an electrical short may be created between the electrodes when a user cuts the transducer to size.
- the electrodes are discontinuous and the fingers 22,26 are offset from each other (ie. out of register which each other) when viewed along a line of sight perpendicular to the sheet. This minimises overlap between the electrodes and enables the transducer to be cut across the fingers without creating an electrical short. Similar advantages can be achieved with other patterns, such as diagonally offset grid patterns or serpentine patterns.
- the fingers are shown with equal width in figure 6 but in an alternative configuration the lower fingers 26 are wider than the upper fingers 22.
- the increased area of the lower electrode gives an EMI shielding effect.
- the area of the lower electrode is greater than 95 % of the total combined area of the two electrodes.
- the user can be directed not to cut across the overlapping strips 23,27, for instance by putting a coloured stripe in the corresponding parts of the protective layers 20.
- overlap can be entirely avoided by positioning the strips 23,27 on opposite sides of the sheet.
- the arrangement of figures 5-7 has a lower capacitance than an arrangement with continuous and/or non-offset electrodes. This results in an improved frequency response.
- the signal from the transducer 30 via the releasable clamp 31 may be either differential from a two element transducer, or single ended, in which case one side of the transducer is grounded.
- the releasable damp may have buffer amplifier circuitry incorporated in it, or all of the signal conditioning may be addressed in the signal conditioning electronics 32 of the main alarm assembly, which provides overvoltage protection, and analogue domain filtering suitable to the environment in which the device is used, eg. low pass filtering, notch and/or comb filtering.
- the conditioned signal is compared in Comparator 33 to a reference signal generated from a combination of a Pulse Width Modulator in the microcontroller device 34 and the following low pass filter 35.
- the reference threshold level for the comparator is controlled by the stored program or internal logic of the microcontroller device, which calibrates this threshold by a combination of averaging and minimum signal sampling, to set a stable, reliable threshold strongly correlated to the ambient electrical noise in the local environment.
- the most simple example of a calibration routine is to have the end-user indicate via an input switch, when the transducer is not being activated (eg. a baby is not lying on it) . While this switch is being held down, the microcontroller adjusts the duty cycle of the Pulse Width Modulator's digital output, so that the reference level produced by the low pass filter is just high enough to turn off the comparator output when the input is considered to be this transducer with no activity signal.
- a more intelligent automatic calibration scheme based on a long term averaging algorithm can be used to adjust the duty cycle of the Pulse Width Modulator during normal operation to arrive at a more flexible method of determining the ambient noise threshold, without the intervention of the end-user.
- the low pass filter's 35 corner frequency is determined by the frequency of the Pulse Width Modulator's output.
- the motion conditions which trigger an alarm may vary from case to case.
- the alarm may be triggered by detection of motion.
- the absence of motion at prescribed times may actuate the alarm.
- certain patterns, regular or irregular may cause an alarm to be actuated.
- Figure 9 illustrates a differential transducer.
- a pair of piezoelectric sheets 60,61 , coated with electrodes 62-65 (which may be patterned and offset) are mounted between foam blocks 66-68. Electrodes 62, 65 are tied to local ground. Electrodes 63, 64 are applied to a differential amplifier configuration 69 such as an instrumentation amplifier.
- the transducer is placed with the upper sheet 60 adjacent to a subject. The upper sheet 60 deforms in response to movement from the subject. The lower sheet 61 does not deform as much as the upper sheet 60 in response to movement from the subject but is in substantially the same noise environment as the upper sheet. Therefore the differential signal 70 is a movement signal with the reference noise signal from the sheet 61 removed.
- Figure 1 0 illustrates an alternative implementation of the signal processing required to isolate cardiac and respiratory signals from the differential transducer input.
- the target signal input 71 and the reference input 72 are processed through analog signal conditioning 73 to meet signal input limits.
- the processed versions are subtracted 75 from one another to remove ambient common mode noise signals, and then converted to digital signals 76. It can be appreciated that the analog - digital conversion may also be done before subtraction, allowing subtraction to take place in the digital domain. There are well known advantages and disadvantages to both approaches. Thereafter, the required digital processing 77, can be done.
- the extracted signal output is then either put directly onto a bus connecting to signal processing electronics 78 (eg. an automotive electronics interface), or else drives a display interface directly, or both.
- signal processing electronics 78 eg. an automotive electronics interface
- the digital signal processor 77 implements the process illustrated in figure 1 1 .
- the processor extracts vital sign information from the movement signal, eg. by a suitable filter algorithm which extracts cardiac, respiratory signals etc.
- the processor analyses the complexity of the vital sign information over a predetermined period.
- wavelet filter banks how much energy is dispersed over different wavelet generations
- short-time Fourier transforms/Gabor expansion similar to above - how much energy in each bin, eg. standard deviation, peaks etc
- Lempel-Ziv complexity measure L
- Lyapunov exponents e.g., a variety of algorithms may be employed, including: wavelet filter banks (how much energy is dispersed over different wavelet generations); short-time Fourier transforms/Gabor expansion - similar to above - how much energy in each bin, eg. standard deviation, peaks etc; Lempel-Ziv complexity measure; and Lyapunov exponents.
- the level of complexity is compared to a predetermined threshold in step 41 . If the complexity drops below the threshold, an alarm is generated at step 41 .
Abstract
Description
Claims
Applications Claiming Priority (7)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
NZ33109698 | 1998-07-24 | ||
NZ33109698 | 1998-07-24 | ||
NZ33169898 | 1998-09-02 | ||
NZ33169798 | 1998-09-02 | ||
NZ33169798 | 1998-09-02 | ||
NZ33169898 | 1998-09-02 | ||
PCT/NZ1999/000112 WO2000005771A1 (en) | 1998-07-24 | 1999-07-23 | Offset arrangement of electrodes on a piezoelectric transducer |
Publications (1)
Publication Number | Publication Date |
---|---|
EP1103078A1 true EP1103078A1 (en) | 2001-05-30 |
Family
ID=27353860
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP99931636A Withdrawn EP1103078A1 (en) | 1998-07-24 | 1999-07-23 | Offset arrangement of electrodes on a piezoelectric transducer |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP1103078A1 (en) |
AU (1) | AU4808099A (en) |
BR (1) | BR9912365A (en) |
CA (1) | CA2338254A1 (en) |
WO (1) | WO2000005771A1 (en) |
Families Citing this family (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6801803B2 (en) * | 2000-10-16 | 2004-10-05 | Instrumentarium Corp. | Method and apparatus for determining the cerebral state of a patient with fast response |
US6731975B1 (en) | 2000-10-16 | 2004-05-04 | Instrumentarium Corp. | Method and apparatus for determining the cerebral state of a patient with fast response |
DE50203457D1 (en) * | 2001-04-30 | 2005-07-28 | Siemens Ag | CONTINUOUS CONTACT FOR AN ELECTRICAL COMPONENT AND PIEZOELECTRIC COMPONENT IN MULTILAYER CONSTRUCTION |
DE102008031641B4 (en) * | 2008-07-04 | 2017-11-09 | Epcos Ag | Piezo actuator in multilayer construction |
CZ308222B6 (en) | 2013-10-08 | 2020-03-11 | Linet Spol. S. R. O. | Device for contactless monitoring of vital patient signs |
WO2015189476A1 (en) * | 2014-06-12 | 2015-12-17 | Mega Elektroniikka Oy | Electrode band for sensing bio-electrical signal |
US11284808B2 (en) | 2014-10-11 | 2022-03-29 | Linet Spol. S.R.O. | Device and method for measurement of vital functions, including intracranial pressure, and system and method for collecting data |
AT524289A1 (en) * | 2020-10-12 | 2022-04-15 | Pacemaker Tech Gmbh | Method for force or pressure measurement, in particular for a gait analysis, with a piezoelectric sensor and piezoelectric sensor for this purpose |
Family Cites Families (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4376302A (en) * | 1978-04-13 | 1983-03-08 | The United States Of America As Represented By The Secretary Of The Navy | Piezoelectric polymer hydrophone |
FR2475804A1 (en) * | 1980-02-12 | 1981-08-14 | Lewiner Jacques | IMPROVEMENTS ON COMPOSITE SHEETS CONSTITUTING ELECTROMECHANICAL TRANSDUCERS AND TRANSDUCERS EQUIPPED WITH SUCH SHEETS |
US4509527A (en) * | 1983-04-08 | 1985-04-09 | Timex Medical Products Corporation | Cardio-respiration transducer |
JPS612376A (en) * | 1984-06-14 | 1986-01-08 | Ngk Spark Plug Co Ltd | Sheet-shaped piezoelectric body |
US5448996A (en) * | 1990-02-02 | 1995-09-12 | Lifesigns, Inc. | Patient monitor sheets |
JPH08222777A (en) * | 1995-02-14 | 1996-08-30 | Star Micronics Co Ltd | Piezoelectric element and its manufacture |
JPH09331685A (en) * | 1996-06-10 | 1997-12-22 | Sera Tec:Kk | Laminated piezoelectric actuator |
-
1999
- 1999-07-23 BR BR9912365-7A patent/BR9912365A/en not_active IP Right Cessation
- 1999-07-23 WO PCT/NZ1999/000112 patent/WO2000005771A1/en not_active Application Discontinuation
- 1999-07-23 CA CA002338254A patent/CA2338254A1/en not_active Abandoned
- 1999-07-23 EP EP99931636A patent/EP1103078A1/en not_active Withdrawn
- 1999-07-23 AU AU48080/99A patent/AU4808099A/en not_active Abandoned
Non-Patent Citations (1)
Title |
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See references of WO0005771A1 * |
Also Published As
Publication number | Publication date |
---|---|
WO2000005771A1 (en) | 2000-02-03 |
BR9912365A (en) | 2001-04-17 |
CA2338254A1 (en) | 2000-02-03 |
AU4808099A (en) | 2000-02-14 |
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