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Wireless power transfer

Belongs to:
Vehicles and transportation
Synonyms:
Inductive charging, Wireless charging, Wireless power
Description:

Electrical energy is transferred through magnetic alternating fields from a charging station to the device to be charged without any wire (thus wireless). This technology is commonly used for electric toothbrushes and is now rising in the areas of smartphones and electric vehicles.
Currently, there are two methods:
The Inductive Power Transfer (IPT) uses a primary coil to generate a magnetic oscillating field at the charging station. This field runs through a secondary coil at the device to be charged and induces an alternating current which can be used with a rectifier to recharge a battery.
The Magnetic Resonance Coupling (MRC) is an extension of the inductive power transfer with additional resonant oscillation circuits in between the coils. The effect results in a higher efficiency factor and a higher operating range but in cost of a lower power limit.
Known technologies and standards are Qi, Powermat, Rezence and WiTricity.

Frequency ranges:
  • 1 kHz–100 MHz
Type of field:
electric, magnetic, and electromagnetic

Measurements (acc. to literature)

car
Measurand Value Feature Remarks
electric field strength 0.39 V/m (simulated) 85 kHz phatom is standing perpendicularly behind the vehicle on level with the reception coil; measures of the phantom: 117 cm, 20 kg; sending and receiving coils are aligned [1]
electric field strength 0.4 V/m (simulated) - phatom is standing perpendicularly behind the vehicle on level with the reception coil; measures of the phantom: 173 cm, 65 kg; sending and receiving coils are aligned [1]
electric field strength 0.5 V/m (simulated) 85 kHz phatom is standing perpendicularly behind the vehicle on level with the reception coil; measures of the phantom: 176 cm, 73 kg; sending and receiving coils are aligned [1]
electric field strength 0.6 V/m (simulated) 85 kHz phatom is standing perpendicularly behind the vehicle on level with the reception coil; measures of the phantom: 173 cm, 65 kg; sending and receiving coils are misaligned [1]
electric field strength 0.65 V/m (simulated) 85 kHz phatom is standing perpendicularly behind the vehicle on level with the reception coil; measures of the phantom: 117 cm, 20 kg; sending and receiving coils are misaligned [1]
electric field strength 0.8 V/m (simulated) 85 kHz phatom is standing perpendicularly behind the vehicle on level with the reception coil; measures of the phantom: 176 cm, 73 kg; sending and receiving coils are misaligned [1]
electric field strength 0.9 V/m (simulated) 85 kHz phatom is standing parallely behind the vehicle on level with the reception coil; measures of the phantom: 117 cm, 20 kg; sending and receiving coils are aligned [1]
electric field strength 0.95 V/m (simulated) 85 kHz phatom is standing parallely behind the vehicle on level with the reception coil; measures of the phantom: 173 cm, 65 kg; sending and receiving coils are aligned [1]
electric field strength 1.05 V/m (simulated) 85 kHz phatom is standing parallely behind the vehicle on level with the reception coil; measures of the phantom: 176 cm, 73 kg; sending and receiving coil are aligned [1]
electric field strength 1.25 V/m (simulated) 85 kHz phatom is standing parallely behind the vehicle on level with the reception coil; measures of the phantom: 117 cm, 20 kg; sending and receiving coils are misaligned [1]
electric field strength 1.3 V/m (measured) 85 kHz phatom is standing parallely behind the vehicle on level with the reception coil; measures of the phantom: 173 cm, 65 kg; sending and receiving coils are misaligned [1]
electric field strength 1.6 V/m (simulated) 85 kHz phatom is standing parallely behind the vehicle on level with the reception coil; measures of the phantom: 176 cm, 73 kg; sending and receiving coils are misaligned [1]
electric field strength 2.4 V/m (mean, simulated) 85 kHz peak value from three different body models, standing at the rear side, directly next to the bumper and looking to the car. Power: 7 kW. [2]
electric field strength 2.81 V/m (maximum, simulated) 85 kHz Charging system with 3.3 kW power of an electric vehicle with a battery voltage of 400 V. The value is simulated on the skin of an adult male who is lying on his side next to the car (worst case position). [3]
electric field strength 2.83 V/m (maximum, simulated) 85 kHz This peak value was simulated when the adult male model was lying besides the car model and has contact between his shoulder and the chassis of the car. Power: 7 kW. [4]
electric field strength 5.95 V/m (maximum, simulated) 85 kHz This peak value was simulated when the adult male model was lying besides the car model and holding his arm between the charging coils. Power: 7 kW. [4]
magnetic flux density 1.98–0.03 µT (maximum, measured) 20 kHz Measured in 20 cm distance to the coachwork of a golf car which is charged with 1.14 kW. Measurement bandwidth: 9 kHz - 30 MHz. [5]
magnetic flux density 2.48 µT (maximum, simulated) 85 kHz Charging system with 3.3 kW power of an electric vehicle with a battery voltage of 400 V. The value is simulated on the skin of an adult male who is lying on his side next to the car (worst case position). [3]
magnetic flux density 4.84 µT (maximum, measured) 30 kHz charging system of a Renault Kangoo under a steel chassis. Measurement on the height of the secondary coil under the chassis. Power: 2 kW. [6]
bus
Measurand Value Feature Remarks
electric field strength 0.021 V/m (maximum, measured) 90 kHz measures at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
electric field strength 0.026 V/m (maximum, measured) 70 kHz at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
electric field strength 0.1 V/m (maximum, measured) 30 kHz at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44; measures of the coil: 95.5 x 82.6 cm [7]
electric field strength 0.109 V/m (maximum, measured) 50 kHz at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
electric field strength 0.1892 V/m (measured) 20 kHz measured at the back of the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coils: 95.9 x 82.6 cm [7]
electric field strength 0.1905 V/m (calculated) 20 kHz measured in front of the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coils: 95.5 cm x 82.6 cm [7]
electric field strength 0.196 V/m (measured) 20 kHz measured at the left side of the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
electric field strength 0.1985 V/m (measured) 20 kHz measured on the right side of the bus at level of the coils; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
electric field strength 0.2119 V/m (measured) 20 kHz measured inside the bus above the coils; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coils: 95.5 x 82.6 cm [7]
electric field strength 0.545 V/m (maximum, measured) 10 kHz at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 xm [7]
magnetic flux density 0.0053 µT (maximum, measured) 70 kHz at the location of the greatest maximum inside the bus: measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
magnetic flux density 0.0081 µT (maximum, measured) 30 kHz at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44; measures of the coil: 95.9 x 82.6 cm [7]
magnetic flux density 0.0191 µT (measured) 20 kHz measured at the left side of the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
magnetic flux density 0.0193 µT (measured) 20 kHz measured in front of the bus; bus measures: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
magnetic flux density 0.0194 µT (measured) 20 kHz measured inside the bus above the coils; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.9 x 82.6 cm [7]
magnetic flux density 0.0195 µT (measured) 20 kHz measured at the right side of the bus at level of the coils; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x .82.6 cm [7]
magnetic flux density 0.0196 µT (measured) 20 kHz measured behind the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.9 x 82.6 cm [7]
magnetic flux density 0.03 µT (maximum, measured) 90 kHz at the location of the greatest maximum inside the bus: measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coil: 95.5 x 82.6 cm [7]
magnetic flux density 0.23 µT (maximum, measured) 50 kHz at the location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44 m [7]
magnetic flux density 7.98 µT (maximum, measured) 10 kHz at location of the greatest maximum inside the bus; measures of the bus: 6.71 x 2.44 x 2.44 m; measures of the coils: 95.5 x 82.6 cm [7]
mobile phone
Measurand Value Feature Remarks
magnetic field strength 0.4 A/m (simulated) 6.78 MHz at a distance of 15 cm centrally over the mobile phone charging station; size of the station: 14.4 x 8 x 0.2 cm³; simulated for 1 W input power [8]
magnetic field strength 1.2 A/m (simulated) 6.78 MHz at a distance of 5 cm centrally over the mobile phone charging station; size of the station: 14.4 x 8 x 0.2 cm³; simulated for 1 W input power [8]
magnetic field strength 3.75 A/m (simulated) 6.78 MHz at a distance of 5 cm centrally over the mobile phone charging station; size of the station: 14.4 x 8 x 0.2 cm³; simulated for 1 W input power [8]
SAR 30 mW/kg (maximum, simulated) 6.78 MHz a standing adult male backwards to a desk with a charging system. Averaged over 10 g tissue. Scaled to 1.34 A of operating current in the transmitter coils. [9]
SAR 42 mW/kg (maximum, simulated) 6.78 MHz a sitting adult male in front of a desk with charging systems. Averaged over 10 g tissue. Scaled to 1.34 A of operating current in the transmitter coils. [9]
not specified, IPT
Measurand Value Feature Remarks
electric field strength 4.5 mV/m 140kHz in situ field while charging at the hand; coils positioned at the chest of a body phanthom [10]
electric field strength 5.8 mV/m (simulated) 140kHz in situ field while charging at the forearm; coils positioned at the chest of a body phanthom [10]
electric field strength 9.9 mV/m (simulated) 140kHz in situ field while charging in the middle of the chest; coils positioned in front of the chest of a body phanthom [10]
electric field strength 25.2 mV/m (simulated) 140kHz in situ field between two charging cycles at the forearm; coils positioned at the chest of a body phanthom [10]
electric field strength 29.2 mV/m (simulated) 140kHz in situ field between two charging cycles at the hand; coils positioned at the chest of a body phanthom [10]
electric field strength 57.8 mV/m (simulated) 140kHz in situ field between two charging cycles in the middle of the chest; coils positioned in front of the chest of a body phanthom [10]
magnetic flux density 4.1 µT (measured) 5 - 50 kHz at a horizontal distance of 160 mm to the circular charger pad (diameter: 4.2 m) [11]
magnetic flux density 5.6 µT (simulated) 5 - 50 kHz at a horizontal distance of 140 mm to the ciruclar charger pad (diameter: 4.2 m) [11]
magnetic flux density 7.5 µT (simulated) 5 - 50 kHz at a horizontal distance of 120 mm to the circular charger pad (diameter: 4.2 m) [11]
magnetic flux density 11.3 µT (simulated) 5 - 50 kHz at a horizontal distance of 100 m to the ciruclar charger pad (diameter: 4.2 m) [11]
magnetic flux density 17.8 µT (measured) 5 - 50 kHz at a horizontal distance of 80 mm to the circular charger pad (diameter: 4.2 m) [11]
magnetic flux density 30.2 µT (simulated) 5 - 50 kHz at a horizontal distance of 60 mm to the circular charger pad (diamter: 4.2 m) [11]
magnetic flux density 57 µT (simulated) 5 - 50 kHz at a horizontal distance of 40 mm to the ciruclar charger pad (diameter: 4.2 m) [11]
magnetic flux density 131.3 µT (simulated) 5 - 50 kHz at a horizontal distance of 20 mm to the circular charger pad (diameter: 4.2 m) [11]
magnetic flux density 317.5 µT (simulated) 5 - 50 kHz at the circular charger pad (diameter: 4.2 m) [11]
SAR 0.35 nW/kg (simulated) 140kHz while charging at the hand, averaged over 10 g of tissue; coils positioned at the chest of a body phanthom [10]
SAR 0.62 nW/kg (simulated) 140kHz while charging at the forearm, averaged over 10 g of tissue; coils positioned in front of the chest of a body phanthom [10]
SAR 1.1 nW/kg (maximum, simulated) 140kHz while charging in the middle of the chest, averaged over 10 g of tissue; coils arranged in front of the the chest of the body phanthom [10]
SAR 13.7 nW/kg (simulated) 140kHz between to charging cacles at the hand, averaged over 10 g of tissue; coils positioned at the chest of a body phanthom [10]
SAR 24.9 nW/kg (simulated) 140kHz between to charging cycles at the forearm, averaged over 10 g of tissue; coils positioned in front of the chest of a body phanthom [10]
SAR 41.5 nW/kg (simulated) 140kHz between two charging cycles in the middle of the chest, averaged over 10 g of tissue; coils arranged in front of the the chest of the body phanthom [10]
not specified, MRC
Measurand Value Feature Remarks
electric field strength 18 mV/m (maximum, calculated) 100kHz analytical and numerical value for center-to-center alignment of the coil; coil diameter: 2.5 m; normalized to 1 A [12]
electric field strength 46 mV/m (maximum, calculated) 100kHz analytical and numerical value for Center-to-Center alignment of the coils; coil diameter: 1 m; normalized to 1 A [12]
electric field strength 95–96 mV/m (maximum, calculated) 100kHz numerical and analytical value for center-to-center alignment of the coils; coil diamter: 0.25 m; normalized to 1 A [12]
electric field strength 96–97 mV/m (maximum, calculated) 100kHz analytical and numerical value for center-to-center alignment of the coils, coil diameter: 0.5 m; normalized to 1 A [12]
electric field strength 180 mV/m (mean, simulated) 100kHz vector-averaged value in a body phantom for a coil diameter of 0.25 m; normalized to 1 A [12]
electric field strength 180 mV/m (mean, simulated) 100kHz vector-averaged value in a body phantom for a coil diameter of 2 m; normalized to 1 A [12]
electric field strength 190 mV/m (mean, simulated) 100kHz vector-averaged value in a body phantom for a coil diameter of 1 m; normalized to 1 A [12]
electric field strength 300 mV/m (mean, simulated) 100kHz vector-averaged value in a body phantom for a coil diameter of 0.5 m; normalized to 1 A [12]
electric field strength 380 mV/m (maximum, simulated) 100kHz maximum, vector-averaged value in a body phanthom for a coil diameter of 1 m; normalized to 1 A [12]
electric field strength 420 mV/m (maximum, simulated) 100kHz maximum, vector-averaged value in a body phanthom for a coil diameter of 2.5 m; normalized to 1 A [12]
electric field strength 500 mV/m (maximum, simulated) 100kHz maximum, vector-averaged value in a body phanthom for a coil diameter of 0.25 m; normalized to 1 A [12]
electric field strength 510 mV/m (maximum, simulated) 100KHz maximum, vector-averaged value in a body phanthom for a coil diameter of 0.5 m; normalized to 1 A [12]
SAR 23 nW/kg (mean, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 0.25 m; normalized to 1 A [12]
SAR 32 nW/kg (mean, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 2.5 m; normalized to 1 A [12]
SAR 38 nW/kg (mean, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 1 m; normalized to 1 A [12]
SAR 71 nW/kg (mean, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 0.5 m; normalized to 1 A [12]
SAR 73 nW/kg (maximum, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 1 m; normalized to 1 A [12]
SAR 77 nW/kg (maximum, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 2.5 m; normalized to 1 A [12]
SAR 85 nW/kg (maximum, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 0.25 m; normalized to 1 A [12]
SAR 120 nW/kg (maximum, simulated) 100kHz whole body SAR for a body phantom for a coil diameter of 0.5 m; normalized to 1 A [12]
SAR 0.3 mW/kg (simulated) 11.36 MHz the model (height approc. 170 cm) is located centrally at a distance of 10 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 115 cm (thorax middle) [13]
SAR 0.4 mW/kg (measured) 11.92 MHz the model (height approc. 170 cm) is located centrally at a distance of 10 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 115 cm (thorax middle) [13]
SAR 0.7 mW/kg (simulated) 11.36 MHz the model (height approc. 170 cm) is located centrally at a distance of 5 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 115 cm (thorax middle) [13]
SAR 0.75 mW/kg (simulated) 11.36 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 155 cm (at the height of the armpits) [13]
SAR 1 mW/kg (simulated) 11.92 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 155 cm (at the height of the armpits) [13]
SAR 1 mW/kg (simulated) 11.92 MHz the model (height approc. 170 cm) is located centrally at a distance of 5 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 115 cm (thorax middle) [13]
SAR 1.15 mW/kg (simulated) 11.36 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 155 cm (at the height of the nose) [13]
SAR 1.55 mW/kg (simulated) 11.36 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 95 cm (at the height of the pelvis) [13]
SAR 1.6 mW/kg (simulated) 11.36 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 115 cm (thorax middle) [13]
SAR 1.75 mW/kg (simulated) 11.92 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 155 cm (at the height of the nose) [13]
SAR 1.85 mW/kg (simulated) 11.92 MHz the model (height approx. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 95 cm (at the height of the pelvis) [13]
SAR 2.4 mW/kg (simulated) 11.92 MHz the model (height approc. 170 cm) is located centrally at a distance of 1 cm in front of the transmitting coils; the receiving coils are positioned at a distance of 13.5 cm to the left side; size of the coils: radius: 30.0 cm, width after winding: 20.0 mm, height of coil center (from ground): approx. 115 cm (thorax middle) [13]

References

  1. Laakso I et al. (2014): Computational dosimetry for wireless charging of an electrical vehicle.
  2. Laakso I et al. (2013): Evaluation of the induced electric field and compliance procedure for a wireless power transfer system in an electrical vehicle.
  3. Zhang W et al. (2015): Loosely Coupled Transformer Structure and Interoperability Study for EV Wireless Charging Systems.
  4. Shimamoto T et al. (2015): In-situ electric field in human body model in different postures for wireless power transfer system in an electrical vehicle.
  5. Hongseok K et al. (2015): Coil design for high efficiency and low magnetic field leakage of wireless charging system for electric vehicle.
  6. Ibrahim M et al. (2015): Advanced Modeling of a 2-kW Series- Series Resonating Inductive Charger for Real Electric Vehicle.
  7. Tell RA et al. (2014): Very-low-frequency and low-frequency electric and magnetic fields associated with electric shuttle bus wireless charging.
  8. Kang WG et al. (2013): Investigation of the assessment method for human exposure from a wireless power transfer system.
  9. Nadakuduti J et al. (2015): Compliance Testing Methodology for Wireless Power Transfer Systems.
  10. Sunohara T et al. (2014): Analysis of in situ electric field and specific absorption rate in human models for wireless power transfer system with induction coupling.
  11. Huang CY et al. (2009): Practical considerations for designing IPT system for EV battery charging.
  12. Chen XL et al. (2014): Theoretical assessment of the maximum obtainable power in wireless power transfer constrained by human body exposure limits in a typical room scenario.
  13. Laakso I et al. (2012): Evaluation of SAR in a human body model due to wireless power transmission in the 10 MHz band.