scispace - formally typeset
Search or ask a question

Showing papers on "Inductive sensor published in 2009"


Proceedings Article
06 Oct 2009
TL;DR: In this article, the authors derived the matching conditions for optimal power efficiency for inductive power transmission structures with varying distance and size ratios and investigated the achievable power efficiency of a given structure with respect to resonant matching and load impedance.
Abstract: Inductive power transmission is proposed more and more also for consumer applications. In this work, limitations with respect to efficiency of the whole magnetic system are investigated. The power efficiency of a given structure is dependent on resonant matching and on the load impedance. First, the matching conditions for optimal power efficiency are derived. Then the achievable efficiency for inductive transmission structures with varying distance and size ratios are investigated. Recent publications on inductive power transmission are evaluated and discussed based on these results. As a conclusion, inductive power transmission in a larger space (e.g. a whole room) is very inefficient. On the other hand, inductive power transmission at a surface can be efficient as conventional power supplies. Based on this insight, an inductive power transmission pad has been designed and built, with the purpose to charge mobile devices like mobile phones. It can charge an arbitrary number of devices and allows free positioning of the devices on the pad. It consists of an array of planar transmitter coils and has a size of 20 cm x 26 cm. It can detect the position of a receiver and activates only the coils underneath a receiver.

298 citations


Journal ArticleDOI
TL;DR: The feasibility of the proximity sensing capability and the dual-mode operation of the proposed sensor in real-time are demonstrated and the capacitance change caused by an approaching object has been estimated through simulation of multiple two-dimensional models as an initial study.
Abstract: In this paper, we report a flexible dual-mode capacitive sensor for robot applications which has two sensing capabilities in a single platform; tactile and proximity sensing capability. The sensor consists of a mechanical structure based on PDMS (Polydimethylsiloxane) and a mesh of multiple copper electrode strips. The mesh is composed of 16 top and 16 bottom copper strips crossed each other to form a 16 times 16 capacitor array. The proposed sensor is able to switch its function from tactile sensing to proximity sensing or vice versa by reconfiguring the connection of electrodes. The tactile sensing capability has been demonstrated already and reported in our previous paper (Lee et al.,, 2006); therefore, in this paper, we will demonstrate the feasibility of the proximity sensing capability and the dual-mode operation of the proposed sensor in detail. The capacitance change caused by an approaching object has been estimated through simulation of multiple two-dimensional models as an initial study. The measured data have shown similar trends with the simulation results. We tested various materials from conducting metals to a human hand for proximity measurement. The fabricated sensor could detect a human hand at a distance up to 17 cm away from the sensor. We also have successfully demonstrated the feasibility of dual-mode operation of the proposed sensor in real-time exploiting a custom designed PCB, a data acquisition pad, and Labview software.

178 citations


Patent
20 Feb 2009
TL;DR: A magnetic positioning system for use in inductive couplings as mentioned in this paper is a magnet that provides sufficient magnetic force, but does not have enough electrical conductivity to overheat in the presence of the anticipated electromagnetic field.
Abstract: A magnetic positioning system for use in inductive couplings. The magnetic positioning system having a magnet that provides sufficient magnetic force, but does not have enough electrical conductivity to overheat in the presence of the anticipated electromagnetic field. The magnet may be a bonded magnet or a shielded magnet. In another aspect a plurality of magnets are used to provide magnetic attraction forces and said magnetic repulsion forces that cooperate to align the inductive power supply and the remote device. In another aspect, a sensor allows differentiation between different positions of the remote device or inductive power supply. In another aspect, multiple magnets in the inductive power supply interact with multiple magnets in the remote device to position the remote device in different positions.

164 citations


Proceedings ArticleDOI
19 Jun 2009
TL;DR: Wire Spy as discussed by the authors is a wirelessly-networked event detector with an inductive sensor which clamps to the cable of an appliance, which matches human-labeled events to the time-series of features.
Abstract: Individual appliances’ electricity consumption is automatically disaggregated from a single custom metering system on the main feed to an occupied residential building. A data acquisition system samples voltage and current at 100 kHz, then calculates real and reactive power, harmonics, and other features at 20Hz. A probabilistic eventdetector using the generalized likelihood ratio (GLR) matches human-labeled events to the time-series of features. Machine-learning classification was most successful with the 1-nearest-neighbor algorithm, correctly identifying 90% of the laboratorygenerated training events and 79% of validation examples. The challenge of obtaining adequate training data for the real-world home leads to the development of the Wire Spy, a wirelessly-networked event detector with an inductive sensor which clamps to the cable of an appliance.

116 citations


Patent
03 Dec 2009
TL;DR: In this paper, a method of a portable electronic device for self-calibration of a proximity sensor is presented, where a background measurement is obtained by the proximity sensor and a detection threshold is adjusted based on the background measurement.
Abstract: A method of a portable electronic device for self-calibration of a proximity sensor. A background measurement is obtained by the proximity sensor and a detection threshold of the proximity sensor is adjusted based on the background measurement. The background measurement is a measure of a received signal when no signal is transmitted by the proximity sensor, and the detection threshold is associated with a sensitivity of the proximity sensor to environmental conditions. A source signal is emitted by the proximity sensor based on the adjusted detection threshold of the proximity sensor, and a return signal is received by the proximity sensor corresponding to the source signal. A function of the portable electronic device may be performed base don the received return signal.

104 citations


Patent
01 Jun 2009
TL;DR: In this paper, a contact switch and a touch sensor are integrated so that they share a common sensor line, achieving space, cost and manufacturing savings over input devices that utilize distinct sensor lines for each of its sensor elements.
Abstract: An input device providing integrated contact switch and touch sensor elements is disclosed. A contact switch and touch sensor can be integrated so that they share a common sensor line, achieving space, cost and manufacturing savings over input devices that utilize distinct sensor lines for each of its sensor elements. By configuring a contact switch and touch sensor to share a common sensor line, a controller can use a single pin to scan both the contact switch and touch sensor elements, rather than using distinct pins to scan distinct sensor lines associated with each sensor element. By using fewer pins to scan the same number of sensor elements, a smaller controller can be used which can reduce the size and cost of the input device, and increase manufacturing throughput time associated with the input device.

74 citations


Patent
11 Mar 2009
TL;DR: In this article, an input device with switchable sensor configurations can switch between a sensor configuration in which each sensor element is enabled to sense input and another sensor configuration where only a subset of its sensor elements are enabled.
Abstract: An input device with switchable sensor configurations. In one embodiment, the input device can switch between a sensor configuration in which each of its sensor elements is enabled to sense input and a sensor configuration in which only a subset of its sensor elements are enabled to sense input. In another embodiment, the input device can switch between a sensor configuration in which each of its sensor elements is enabled to sense input and a sensor configuration in which one or more groupings of its sensor elements are enabled to collectively sense input. In a further embodiment, the input device can operate in a detection mode that switches between sensor configurations to determine a position of an input.

69 citations


Patent
02 Jul 2009
TL;DR: In this article, the driving voltage across a primary inductor oscillates at a frequency significantly different from the resonant frequency of the inductive coupling system, which is called non-resonant inductive power transmission.
Abstract: Non-resonant inductive power transmission wherein the driving voltage across a primary inductor oscillates at a frequency significantly different from the resonant frequency of the inductive coupling system. Embodiments of the invention include systems and methods for: power regulation using frequency control, fault detection using voltage peak detectors and inductive communication channels.

64 citations


Proceedings ArticleDOI
13 Nov 2009
TL;DR: A novel fully integrated inductive tongue computer interface for disabled people that consists of an oral unit placed in the mouth, including inductive sensors, related electronics, a system for wireless transmission and a rechargeable battery.
Abstract: This work describes a novel fully integrated inductive tongue computer interface for disabled people. The interface consists of an oral unit placed in the mouth, including inductive sensors, related electronics, a system for wireless transmission and a rechargeable battery. The system is activated using an activation unit placed on the tongue, and incorporates 18 inductive sensors, arranged in both a key area and a mouse-pad area. The system's functionality was demonstrated in a pilot experiment, where a typing rate of up to 70 characters/minute was obtained with an error rate of 3%. Future work will include tests with disabled subjects.

51 citations


Journal ArticleDOI
TL;DR: In this article, the evolution of wear during a tapered roller bearing test, using a suite of condition monitoring techniques, that incorporated electrostatic wear-site sensors to identify charge during surface wear and oil-line sensors to detect debris in oil scavenge lines.

49 citations


Proceedings ArticleDOI
04 Oct 2009
TL;DR: Methods are suggested and tested to measure and optimize the wireless energy transfer efficiency for mid-range inductive coils with relatively low profile using magnetic resonance, showing that by tuning to the optimum resonant frequency and designing proper matching circuitry, an efficiency of about 25% for moderate profiles can be achieved.
Abstract: Methods are suggested and tested to measure and optimize the wireless energy transfer efficiency for mid-range (10–100cm) inductive coils with relatively low profile using magnetic resonance. These coils can be used to provide energy for wireless sensors and battery-operated devices. It is shown that for every system, a resonance frequency can be identified where the wireless energy transfer efficiency is optimal. Several prototypes are developed and tested as a proof of validity of the proposed technique. It is also shown that by tuning to the optimum resonant frequency and designing proper matching circuitry, an efficiency of about 25% for moderate profiles can be achieved.

Journal ArticleDOI
TL;DR: The sensor model and its frequency and geometry-dependent behavior are studied to increase the probe sensitivity as much as possible and its measuring capability in real insulation systems that were subjected to high partial discharge activity will be tested.
Abstract: Partial discharges are not only a consequence but a symptom of insulation degradation in electrical equipment. Partial discharges are revealed outside the insulation as very narrow high-frequency pulses that were superimposed to the grid frequency high-level voltages or currents and thus are fairly hard to detect. This paper presents an application of a new inductively coupled sensor that allows these signals to be measured in an accurate inexpensive manner. The sensor model and its frequency and geometry-dependent behavior are studied to increase the probe sensitivity as much as possible. Its measuring capability in real insulation systems that were subjected to high partial discharge activity will be tested.

Patent
27 Feb 2009
TL;DR: A capacitance sensing circuit may include a switching circuit configured to generate a sensor current by charging and discharging a capacitive sensor electrode, and a current mirror that generates a mirror current based on the sensor current as mentioned in this paper.
Abstract: A capacitance sensing circuit may include a switching circuit configured to generate a sensor current by charging and discharging a capacitive sensor electrode, and a current mirror that generates a mirror current based on the sensor current. Based on the mirror current, a measurement circuit generates an output signal representative of a capacitance of the capacitive sensor electrode.

Patent
28 Sep 2009
TL;DR: In this paper, an inspection system positions a balancing shim to asymmetrically balance a magnetic field generated by an inductive sensor, which forms part of the inspection system, while relays and capacitors used to tune the inductive sensors to a desired resonance frequency are geometrically arranged to minimize electrical interference generated by operation of the relays.
Abstract: An inspection system positions a balancing shim to asymmetrically balance a magnetic field generated by an inductive sensor, which forms part of the inspection system. Additionally, relays and capacitors used to tune the inductive sensor to a desired resonance frequency are geometrically arranged to minimize electrical interference generated by operation of the relays and capacitors. A shielding device, which may be formed on a printed circuit board, protects a magnetic field generated by the inductive sensor from external electromagnetic interference. A slot positioned in the inductive sensor may be used to tune a resonant mode of the inductive sensor to accurately and particularly detect metallic shanks and/or other metallic objects in shoes, socks, and/or clothing.

Proceedings ArticleDOI
05 May 2009
TL;DR: In this paper, a simple yet efficient proximity sensor obtained by combining inductive and capacitive sensing principles is presented, which uses a signal conditioning unit based on a carrier frequency principle.
Abstract: This paper presents a simple yet efficient proximity sensor obtained by combining inductive and capacitive sensing principles. Capacitive proximity sensors based on shielding of electric field are known for detecting presence of humans in its vicinity. Such systems may fail to distinguish the proximity of a human from grounded conductive objects. A novel, cost effective, sensing scheme that uses a single sensor, which performs both the inductive and capacitive proximity mode of operation is proposed in this paper. The measurement system uses a signal conditioning unit based on a carrier frequency principle. A prototype sensing system has been built and its application as a seat occupancy sensing system in a vehicle has been verified. The developed system successfully senses human proximity and distinguishes it from other conductive objects.

Journal ArticleDOI
TL;DR: An application-specific integrated circuit (ASIC) front end for readout and control of planar high-frequency contactless inductive position sensors that contain transmitter and receiver coils on a fixed printed circuit board and a moving passive resonant target is described.
Abstract: We describe an application-specific integrated circuit (ASIC) front end for readout and control of planar high-frequency contactless inductive position sensors that contain transmitter and receiver coils on a fixed printed circuit board and a moving passive resonant target. Such an inductive position sensor suffers from transmitter-to-receiver signal coupling, which can result in a phase-sensitive offset; hence, an error in the position measurement occurs. For the receiver front end, we consider two analog synchronous mixer demodulators, which we call mixer-1 and mixer-2, and analyze their ability to reject phase-sensitive offsets due to transmitter signal breakthrough. The mathematical analysis is validated with measured results from the fabricated ASIC in a 0.35-mum CMOS process technology. The ASIC front end contains the transmitter driver, the two receiver mixer variants, a frequency divider/shifter, and an amplifier low-pass filter. Measurements from five ASIC samples connected to the sensor show that, with a system gain of 320, the average output offset variation with phase difference from -99 to +117deg is more than 237 mV with mixer-1 compared to less than 7 mV with mixer-2.

Proceedings ArticleDOI
18 Jun 2009
TL;DR: The goal of this paper is to show that the variation of the input inductance is invariant to angular displacement of a moving coil, which is important for implementation of the sensor in humanoid robot’s foot.
Abstract: — A planar displacement inductive sensor, usable in robotics, is presented in the paper. The sensor is composed of two sensor elements. The first sensor element detects vertical displacement while the second sensor element detects horizontal displacement. Combining information from these two sensor elements, it is possible to determine displacement in a plane. Sensor element is a pair of meander coils. One coil is a fixed coil and has the input while the other coil is short-circuited and moves in x-z plane. The variation of input inductance between coils serves as a measure of displacement. The goal of this paper is to show that the variation of the input inductance is invariant to angular displacement of a moving coil, which is important for implementation of the sensor in humanoid robot’s foot. Calculated results were obtained using a new simulation tool developed in MATLAB.

Patent
04 Sep 2009
TL;DR: In this paper, an inductive proximity sensor that includes an oscillator having first and second inductor-capacitor circuits arranged such that an inductance of one of the inductors has substantially greater sensitivity to an external target than an induction of the other inductors, is presented.
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.

Patent
20 Feb 2009
TL;DR: In this article, the authors present a sensor, a sensing method thereof, and a filter therefor, consisting of a sensed-data output unit and a determination unit, which outputs an output signal that represents whether or not the object touches or approaches the sensor.
Abstract: The present invention discloses a sensor, a sensing method thereof, and a filter therefor. The sensor comprises a sensed-data output unit and a determination unit. The sensed-data output unit outputs sensed data that varies depending on whether or not an object touches or approaches the sensor. The determination unit: compares a threshold value with the sensed data to recognize whether or not the object touches or approaches the sensor; varies first and second strength values using the sensed data; varies the threshold value using the first and second strength values; and outputs an output signal that represents whether or not the object touches or approaches the sensor. The first strength value shows a sensed data value when the object does not touch or approach the sensor, and the second strength value shows the sensed data value when the object touches or approaches the sensor.

Patent
26 Mar 2009
TL;DR: In this paper, a portable device with a proximity sensor is described, which includes a shielding plate for shielding impedance applied in a direction opposite to the direction that the proximity sensor detects the proximity such that the sensor is not affected by a change in the surrounding environment and can detect the proximity at the same sensitivity at all times.
Abstract: A portable device with a proximity sensor is provided. The portable device with a proximity sensor of the present invention includes a shielding plate for shielding impedance applied in a direction opposite to the direction that the proximity sensor detects the proximity such that the proximity sensor is not affected by a change in the surrounding environment and can detect the proximity at the same sensitivity at all times. Moreover, when the portable device is placed upside down on a conductive surface that causes low impedance, a proximity sensor placed adjacent to the conductive surface is deactivated to prevent malfunction.

Patent
02 Apr 2009
TL;DR: A magnetic proximity sensor is attached to a ferrous object such that the sensor alerts a practitioner if a threshold of magnetic strength has been exceeded by bringing the object within a certain proximity to the magnet of an MRI scanner as discussed by the authors.
Abstract: A magnetic proximity sensor is attached to a ferrous object such that the sensor alerts a practitioner if a threshold of magnetic strength has been exceeded by bringing the ferrous object within a certain proximity to the magnet of an MRI scanner The magnetic proximity sensor includes at least one magnetic field sensor for sensing a magnetic field strength An alarm in communication with the field sensor alerts a practitioner that a threshold of magnetic strength has been exceeded A battery powers the field sensor and the alarm The field sensor may produce an output voltage corresponding to the sensed magnetic field strength, and a potentiometer may provide a reference voltage corresponding to a threshold magnetic field strength A comparator compares the reference voltage to the output voltage, and triggers an alarm if the output voltage exceeds the reference voltage

Journal ArticleDOI
TL;DR: E Easily integrated high-precision position sensor systems manufactured by means of MEMS technologies, inductive and capacitive, have been brought in operation successfully and are presented.

Proceedings ArticleDOI
09 Oct 2009
TL;DR: An inductive coupling based proximity communication system is proposed for data readout of remote powered sensor systems with ultra small form factor in ñmm3 range for implantable applications.
Abstract: An inductive coupling based proximity communication system is proposed for data readout of remote powered sensor systems with ultra small form factor in nmm3 range for implantable applications. The passive transponder is powered with a 1×1mm on-chip inductor, which also enables readout signaling using pulse signaling. The required resonance frequency for pulse signaling is obtained using a transponder PLL that locks to the incoming frequency transmitted by the reader system. Communication with a passive 1mm2 sensor node implemented in 0.13µm technology is demonstrated.

Patent
02 Oct 2009
TL;DR: In this article, an inductive proximity sensor and related method for sensing a presence/position of a target, with mounting effect compensation, is presented, which includes providing a proximity sensor having first and second coils that are both at least indirectly in communication with control circuitry.
Abstract: An inductive proximity sensor and related method for sensing a presence/position of a target, with mounting effect compensation, are disclosed. In at least one embodiment, the method includes providing a proximity sensor having first and second coils that are both at least indirectly in communication with control circuitry. The method also includes receiving respective first and second signals at least indirectly indicative of respective first and second electromagnetic field components respectively experienced by the first coil as influenced both by a target and a structure supporting the sensor and the second coil as influenced by the supporting structure. The method further includes determining by way of the circuitry a third signal based at least in part upon the first signal, as modified based at least in part upon the second signal, whereby the third signal is indicative of the presence or position of the target relative to the sensor.

Proceedings ArticleDOI
02 Oct 2009
TL;DR: In this paper, a liquid level sensor has been developed that is suitable to determine the oil-water interface level and oil level in a single tank using two coils wound on a plastic pipe.
Abstract: A novel approach for monitoring oil-water interface level and oil level in a single tank is presented. A liquid level sensor has been developed that is suitable to determine the oil-water interface level and oil level. This sensor can realize two sensing functions, namely, inductive and capacitive sensing functions. For achieving this multi-sensing function, the designed sensor employed two coils wound on a plastic pipe. According to the relationships between oil-water interface level and inductance produced by a coil connected using the two coils, oil level and capacitance measured from two coils, the oil-water interface level and the oil level can be estimated at same time.

Proceedings ArticleDOI
02 Oct 2009
TL;DR: Based on the inductive balance principle and the detection requirement of wear debris, the off-line wear debris sensor and the on-line debris sensor are designed in this article, and some measures of low noise design are used in the signal detection circuit of sensors.
Abstract: Wear debris concentration and granularity in the lubricant oil contains the information about wear condition of machine. Based on the inductive balance principle and the detection requirement of wear debris, the off-line wear debris sensor and the on-line debris sensor are designed. And some measures of low noise design are used in the signal detection circuit of sensors. The experiments prove that the off-line sensor has satisfying accuracy and consistency for the concentration of the ferromagnetic wear debris, and the online sensor has effective detection capability for the granularity of the ferromagnetic wear debris and large unferromagnetic wear debris.

Patent
20 Apr 2009
TL;DR: In this article, a wearable low-load sleep recording device, which can record the multi-physiological parameters of the chests and the abdomens of experimenters in sleeping such as a breathe signal, an electrocardio-signal and a body position/body move signal, is presented.
Abstract: The invention relates to a wearable low-load sleep recording device, which can record the multi-physiological parameters of the chests and the abdomens of experimenters in sleeping such as a breathe signal, an electrocardio-signal and a body position/body move signal. The sensors of the chest breathe signal and the abdomen breathe signal all adopt inductive sensors; the sensor of the electrocardio-signal adopts a common electrode; the sensor of the body position/body move signal adopts an acceleration sensor; the inductive sensors, the common electrode, the acceleration sensor and a correlative electronics circuit are attached on a conveniently wearable vest; physiological signals which are obtained by the sensors are transformed into digital signals so as to be memorized in a medium, such as SD/MMC card, or wirelessly transmitted to the outer place, and used for analyzing and processing after the event; and the sleep recording device also can realize real-time alarm in the case of breathe suffocation/breathlessness.

Patent
23 Jun 2009
TL;DR: In this paper, a flexible metal domed spring structure is mounted over the inductive sensor area and a stem portion extends from a actuator area of the housing structure and having a distal end disposed adjacent to or in contact with the spring structure.
Abstract: An exemplary embodiment of an inductive electrical sensor assembly includes a hollow housing structure defining an open space within the housing structure and a circuit board mounted in the open space. The circuit board includes an inductive sense area. A flexible metal domed spring structure is mounted over the inductive sensor area. A stem portion extends from a actuator area of the housing structure and having a distal end disposed adjacent to or in contact with the spring structure. The domed spring structure is adapted to be flexed toward the inductive sensor area by force exerted by the stem portion when a user exerts force on the actuator area, the flexing of the domed spring structure resulting in a change of inductance of the inductive sensor area which may be sensed to indicate an actuator push. An exemplary embodiment of the sensor assembly may include a resiliently deformable potting material substantially filling open spaces in the hollow housing structure between the top surface and the circuit board, and an open space below the circuit board, enabling flexure of the domed spring structure while providing environmental protection.

Patent
06 Apr 2009
TL;DR: In this article, a system for use in association with a mechanical transmission, including a gear selector lever movable between a plurality of shift positions corresponding to respective transmission settings, an inductive position sensor, and a visual indicator that provides a visual indication of the selected transmission setting.
Abstract: A system for use in association with a mechanical transmission, including a gear selector lever movable between a plurality of shift positions corresponding to respective transmission settings, an inductive position sensor that senses a shift position of the gear selector lever, and a visual indicator that provides a visual indication of the selected transmission setting. The position sensor includes inductive sensor elements electromagnetically coupled together and sensor circuitry integrated onto a circuit board which generates a sensor output signal corresponding to the shift position of the gear selector lever. The visual indicator includes an indicator panel having alphanumeric characters that designate respective transmission settings, a plurality of LEDs integrated onto the circuit board, and control circuitry that provides a control signal in response to the sensor output signal which illuminates or brightens an LED positioned adjacent a respective one of the alphanumeric characters corresponding to the selected transmission setting.

Journal ArticleDOI
TL;DR: In this article, the authors proposed the use of magnetoplated wire (MPW) as a sensing coil, which is a copper wire whose circumference is plated with a magnetic thin film.
Abstract: Inductive proximity sensors are noncontact sensing devices used to detect the approach of a target by an increase in coil resistance due to eddy current loss. Extending the operating distance of these sensors is demanded. In this paper, we propose the use of a magnetoplated wire (MPW) as a sensing coil. The MPW is a copper wire, whose circumference is plated with a magnetic thin film. We analyze the impedance of a proximity sensor using a copper wire (COW) and MPW coils by a finite element method. The use of the MPW results in a decrease in AC resistance due to the proximity effect, an increase in inductance, and the generation of a higher flux than when the COW is used. Therefore, it is possible to increase the quality factor Q of the MPW coil. As a result, the operating distances of the MPW and COW coils are 5.0 and 3.8 mm, respectively. The operating distance of the MPW coil is 1.3-fold that of the COW coil.