SENSOR FOR CONTROLLING ACCESS TO A MOTOR VEHICLE, HAVING AN ELECTRODE SURROUNDED BY AN ANTENNA

1 . A device for a vehicle access control system, intended to be housed on board a motor vehicle for carrying out an approach detection of a user as well as recognition of said user, and comprising:

a so-called main electrode, intended to form a capacitor with a user for carrying out a capacitive-type approach detection; and

a transmitting and receiving antenna which is formed by a coil comprising a plurality of turns which all have a similar shape and is configured to transmit and receive a radiofrequency signal in order to identify a user;

wherein the main electrode is surrounded by one turn of the coil, referred to as the guard turn;

the guard turn comprising:

a first portion which delimits a region inside of which the main electrode is located,

a second portion which is offset relative to the main electrode, and

at least one notch which extends along an edge of the main electrode and connects the first portion and the second portion together, each notch comprising two sections which are parallel to one another and are connected together by a portion of the turn located at the bottom of the notch,

and the other turns of the coil each have a shape substantially similar to that of the guard turn, each with two portions separated in pairs by at least one notch.

2 . The device as claimed in claim 1 , wherein the notch extends along an edge of the main electrode, with sections of the notch which extend parallel to the edge of the main electrode.

3 . The device as claimed in claim 1 , wherein the guard turn comprises two notches which have their respective sections aligned in pairs, and which have their respective notch bottoms facing one another.

4 . The device as claimed in claim 3 , wherein the two notches (are symmetrical to one another, relative to a plane of symmetry passing between the two notch bottoms.

5 . The device as claimed in claim 3 , wherein the guard turn follows the shape of the main electrode along the entire circumference of said main electrode, except in a zone of said circumference located opposite the region between the two notch bottoms.

6 . The device as claimed in claim 3 , wherein a distance between the two notch bottoms is less than or equal to 20% of the smallest width of the main electrode.

7 . The device as claimed in claim 1 , wherein the main electrode has the shape of a square or solid rectangle.

8 . The device as claimed in claim 1 , wherein:

the transmitting and receiving antenna and the main electrode extend together on the same printed circuit;

the printed circuit is able to extend in a plane called the printed circuit plane; and

the turns of the transmitting and receiving antenna extend one above the other along an axis orthogonal to the plane of the printed circuit, with the guard turn and the main electrode lying together in the same plane.

9 . The device as claimed in claim 1 , further comprising a second electrode, intended to form a capacitor with a user for implementing capacitive-type distance detection, and located inside a surface delimited by the second portion of the guard turn.

10 . The device as claimed in claim 9 , further comprising:

a first assembly, comprising said main electrode, forming a first main electrode, and a first guard electrode-superimposed on the first main electrode along an axis orthogonal to the plane of the printed circuit;

a second assembly, comprising said second electrode, called the second main electrode, as well as a second guard electrode superimposed on the second main electrode along an axis orthogonal to the plane of the printed circuit;

and wherein:

first main electrode and the second guard electrode are arranged coplanar on the same top layer of the printed circuit;

the second main electrode and the first guard electrode are arranged coplanar on the same lower of the printed circuit, distinct from said upper layer of the printed circuit;

the guard turn surrounds the first main electrode and the second guard electrode, with the at least one notch which extends between the first main electrode and the second guard electrode; and

the transmitting and receiving antenna coil further comprises a second turn, called a second guard turn, surrounding the second main electrode and the first guard electrode, with at least one notch of said second guard turn which extends between the second main electrode and the first guard electrode.

11 . The device as claimed in claim 9 , further comprising:

a first assembly, comprising said main electrode, forming a first main electrode, and a first guard electrode superimposed on the first main electrode along an axis orthogonal to the plane of the printed circuit;

a second assembly, comprising said second electrode, called the second main electrode, as well as a second guard electrode superimposed on the second main electrode along an axis orthogonal to the plane of the printed circuit;

and wherein:

the first main electrode and the second main electrode are arranged coplanar on the same top layer of the printed circuit;

the first guard electrode and the second guard electrode are arranged coplanar on the same lower layer of the printed circuit, distinct from said upper layer of the printed circuit;

the guard turn surrounds the first main electrode and the second main electrode, with the at least one notch which extends between the first main electrode and the second main electrode; and

the transmitting and receiving antenna coil further comprises a second turn, called a second guard turn, surrounding the first guard electrode and the second guard electrode, with at least one notch of said second guard turn which extends between the first guard electrode and the second guard electrode.

12 . A system comprising:

a device as claimed in claim 1 ;

a control circuit, electrically connected to both ends of the coil of said device in order to control the transmission and reception of the radiofrequency signal; and

a capacitance-measuring circuit-, electrically connected to the first electrode and to the guard turn of said device, the connection to the guard turn being made at a connection point located halfway along the coil, considering the unwound length of said coil.

13 . The device as claimed in claim 2 , wherein the guard turn comprises two notches which have their respective sections aligned in pairs, and which have their respective notch bottoms facing one another.

14 . The device as claimed in claim 4 , wherein the guard turn follows the shape of the main electrode along the entire circumference of said main electrode, except in a zone of said circumference located opposite the region between the two notch bottoms.

15 . The device as claimed in claim 4 , wherein a distance between the two notch bottoms is less than or equal to 20% of the smallest width of the main electrode.

16 . The device as claimed in claim 5 , wherein a distance between the two notch bottoms is less than or equal to 20% of the smallest width of the main electrode.

17 . A system comprising:

a device as claimed in claim 2 ;

a control circuit, electrically connected to both ends of the coil of said device in order to control the transmission and reception of the radiofrequency signal; and

a capacitance-measuring circuit, electrically connected to the first electrode and to the guard turn of said device, the connection to the guard turn being made at a connection point located halfway along the coil, considering the unwound length of said coil.

18 . A system comprising:

a device as claimed in claim 3 ;

a control circuit, electrically connected to both ends of the coil of said device in order to control the transmission and reception of the radiofrequency signal; and

a capacitance-measuring circuit, electrically connected to the first electrode and to the guard turn of said device, the connection to the guard turn being made at a connection point located halfway along the coil, considering the unwound length of said coil.