Capacitive sensor including resonant network

• US 20130277351A1
• Filed: 12/30/2011
• Published: 10/24/2013
• Est. Priority Date: 01/07/2011
• Status: Active Grant

• Current Assignee: IEE International Electronics & Engineering SA (Aerospace Hi-Tech Holding Group Company Limited)
• Original Assignee: IEE International Electronics & Engineering SA (Aerospace Hi-Tech Holding Group Company Limited)
• Inventors: Lamesch, Laurent
• Granted Patent: US 9,061,641 B2
• Time in Patent Office: Days
• US Class Current: 219/202
• CPC Class Codes: B60N 2/002 Seats provided with an occupancy detection means mounted therein or thereon detection means responsive to presence or absence of children B60N2/266
• CPC Class Codes: B60N 2/5685 Resistance
• CPC Class Codes: B60R 21/015 including means for detecting the presence or position of passengers, passenger seats or child seats , and the related safety parameters therefor, e.g. speed or timing of airbag inflation in relation to occupant position or seat belt use
• CPC Class Codes: B60R 21/01532 using electric or capacitive field sensors
• CPC Class Codes: B60R 21/0154 in combination with seat heating
• CPC Class Codes: H05B 1/0252 Domestic applications

Abstract

A capacitive sensor comprises a sensing antenna electrode (10) for capacitively coupling to a counterelectrode to form a capacitance (40, 42), this capacitance being responsive to an electric-field-influencing property of an object or person proximate to the antenna electrode. The counterelectrode may be or may not be part of the capacitive sensor. The capacitive sensor further comprises a capacitive sensing network connected to the antenna electrode to apply an oscillating signal thereto and to and to determine the capacitance based upon characteristics of the oscillating signal. The capacitive sensing network includes at least one inductor (16) and a plurality of reactive components (36) arranged to form a resonant network together with the capacitance (40, 42), the plurality of reactive components being activatable and deactivatable in such a way as to modify a resonance frequency of the resonant network.

Claims

1. A capacitive sensor, comprising

an antenna electrode for capacitively coupling to a counterelectrode to form a capacitance, said capacitance being responsive to an electric-field-influencing property of an object or person proximate to said antenna electrode;

a capacitive sensing network connected to said antenna electrode to apply an oscillating signal thereto and to determine said capacitance based upon characteristics of said oscillating signal;

wherein said capacitive sensing network includes at least one inductor and a plurality of reactive components arranged to form a resonant network with said capacitance, said plurality of reactive components being activatable or deactivatable in such a way as to modify a resonance frequency of said resonant network.

3. The capacitive sensor as claimed in claim 1, wherein said reactive components comprise capacitors.

4. The capacitive sensor as claimed in claim 1, wherein said reactive components comprise further inductors.

5. The capacitive sensor as claimed in claim 1, comprising an electronically controlled switching arrangement configured to individually activate and deactivate said reactive components.

6. The capacitive sensor as claimed in claim 1, wherein said capacitive sensing network includes a controller operatively connected with said electronically controlled switching arrangement to control said resonance frequency.

7. The capacitive sensor as claimed in of claim 1, wherein said capacitive sensing network comprises

means to sustain said oscillating signal in or to drive said oscillating signal into said antenna electrode or said heating element;

as well as a high-impedance amplifier having an input node operatively connected to said antenna electrode or said heating element to probe said oscillating signal, and an output node to provide an output signal indicative of said oscillating signal.

8. The capacitive sensor as claimed in claim 7, wherein said means to sustain said oscillating signal in or to drive said oscillating signal into said antenna electrode or said heating element comprises a negative resistance device to sustain said oscillating signal in said resonant network and to compensate for resistive losses and power extracted from said resonant network.

9. The capacitive sensor as claimed in claim 8, wherein said capacitive sensing network comprises a feedback branch from the output node of said high-impedance amplifier to said negative resistance device to regulate an amplitude of said oscillating signal to a reference amplitude.

10. The capacitive sensor as claimed in claim 7, wherein said means to sustain said oscillating signal in or to drive said oscillating signal into said antenna electrode or said heating element comprises an AC source operatively connected to said antenna electrode or said heating element to drive as said oscillating signal an alternative current into said resonant network and a frequency control unit for controlling the frequency of said alternative current.

11. The capacitive sensor as claimed in claim 1, wherein said capacitive sensing network comprises a driven shield electrode.

12. The capacitive sensor as claimed in claim 11, comprising a voltage follower connected between said antenna electrode or said heating element and said driven shield electrode to keep said driven shield electrode at the same AC potential as said antenna electrode or said heating element.

13. A vehicle seat, comprising a capacitive sensor as claimed in claim 1.

2. A combined seat heater and capacitive occupancy sensor, comprising:

a heater network including a heating element connected between a first node and a second node to dissipate heat when a heating current is caused to flow between said first and second nodes, across said heating element,

a capacitive sensing network connected to said heating element to use said heating element as an antenna electrode, said heating element being arranged for forming a capacitance with a counterelectrode, said capacitance being responsive to an electric-field-influencing property of an object or person proximate to said heating element, said capacitive sensing network being configured to apply an oscillating signal to said heating element and to determine said capacitance based upon characteristics of said oscillating signal;

wherein said heater network comprises a common mode choke with at least two windings, said heating element being connected in series between a first and a second winding of said at least two windings so as to be operatively connectable to a power source via said common mode choke;

and wherein said capacitive sensing network includes a plurality of reactive components, arranged to form a resonant network with at least one of said first and second winding and with said capacitance, said plurality of reactive components being activatable or deactivatable in such a way as to modify a resonance frequency of said resonant network.

15. The combined seat heater and capacitive occupancy sensor as claimed in claim 2, wherein said reactive components comprise at least one of capacitors and further inductors.

16. The combined seat heater and capacitive occupancy sensor as claimed in claim 2, comprising an electronically controlled switching arrangement configured to individually activate and deactivate said reactive components.

17. The combined seat heater and capacitive occupancy sensor as claimed in claim 16, wherein said capacitive sensing network includes a controller operatively connected with said electronically controlled switching arrangement to control said resonance frequency.

18. The combined seat heater and capacitive occupancy sensor as claimed in claim 2, wherein said capacitive sensing network comprises means to sustain said oscillating signal in or to drive said oscillating signal into said antenna electrode or said heating element;

as well as a high-impedance amplifier having an input node operatively connected to said antenna electrode or said heating element to probe said oscillating signal, and an output node to provide an output signal indicative of said oscillating signal.

19. The combined seat heater and capacitive occupancy sensor as claimed in claim 18, wherein said means to sustain said oscillating signal in or to drive said oscillating signal into said antenna electrode or said heating element comprises a negative resistance device to sustain said oscillating signal in said resonant network and to compensate for resistive losses and power extracted from said resonant network.

20. The combined seat heater and capacitive occupancy sensor as claimed in claim 19, wherein said capacitive sensing network comprises a feedback branch from the output node of said high-impedance amplifier to said negative resistance device to regulate an amplitude of said oscillating signal to a reference amplitude.

21. The combined seat heater and capacitive occupancy sensor as claimed in claim 18, wherein said means to sustain said oscillating signal in or to drive said oscillating signal into said antenna electrode or said heating element comprises an AC source operatively connected to said antenna electrode or said heating element to drive as said oscillating signal an alternative current into said resonant network and a frequency control unit for controlling the frequency of said alternative current.

22. The combined seat heater and capacitive occupancy sensor as claimed in claim 2, wherein said capacitive sensing network comprises a driven shield electrode.

23. The combined seat heater and capacitive occupancy sensor as claimed in claim 22, comprising a voltage follower connected between said antenna electrode or said heating element and said driven shield electrode to keep said driven shield electrode at the same AC potential as said antenna electrode or said heating element.

24. A vehicle seat, comprising a combined seat heater and capacitive occupancy sensor as claimed in claim 2.

14. A capacitive sensing network configured to apply an oscillating signal to an antenna electrode forming a capacitance with a counterelectrode, said capacitance being responsive to an electric-field-influencing property of an object or person proximate to said antenna electrode, and to determine said capacitance based upon characteristics of said oscillating signal;

said capacitive sensing network comprising an interface for connecting said capacitive sensing network to a seat heater including a heating element for dissipating heat when a heating current is caused to flow across said heating element, said interface being configured for operating said heating element as said antenna electrode,

wherein said interface comprises a common mode choke including a first winding for connecting a first node of said heating element to a first terminal of a power supply, a second winding for connecting a second node of said heating element to a second terminal of said power supply,

and wherein said capacitive sensing network includes a plurality of reactive components, arranged to form a resonant network with said first and second windings and said capacitance when said heating element is connected between said first and second windings, said plurality of reactive components being activatable or deactivatable in such a way as to modify a resonance frequency of said resonant network.