Electric field detector

Abstract

The electric field detector (20) comprises an electromechanical oscillator, a part of which consists of a piezoelectric element (1), a frequency measuring device (4) coupled to the oscillator to measure the oscillation frequency, and an electrical shielding assembly (5). The electrical shielding assembly is arranged close to the piezoelectric element (1) so that during use of the detector, the piezoelectric element moves by vibrating relative to the electrical shielding assembly. Thus, a variable part of the piezoelectric element is exposed to the electric field to be measured. The change in the oscillation frequency (f) then forms the electric field measurement result.

Description

Technical Field

[0001] The present specification relates to an electric field detector. Background Art

[0002] Electric field detectors comprising at least one electrode and a removable mask are known. The removable mask is made of a conductive material and is placed in front of one or more electrodes so as to partially shield the electrodes from the electric field to be measured. One or more variable parts of this (these) electrode(s) are therefore exposed to the electric field to be measured, thereby generating a current in one or more connections connecting the (each) electrode to the current detector. The detected current constitutes a measurement of the electric field. However, these detectors are bulky, expensive and energy-consuming, so they are not suitable for many applications, especially for applications for electrostatic field measurements on aircraft, drones or satellites.

[0003] To address these drawbacks, electric field detectors have recently been developed based on MEMS ("micro-electromechanical systems") devices made of silicon. However, vibrating the MEMS device with an electric field during each measurement can lead to deviations in the measurement results. In addition, the measurement is performed by evaluating the amount of charge, which requires the use of a high-resolution analog-to-digital converter. Such a converter itself is expensive and causes a large amount of energy consumption.

[0004] Technical issues

[0005] Based on this situation, the object of the present invention is to propose a new type of electric field detector which is small, cheap, low energy consumption and has accurate and reliable measurement results. Summary of the invention

[0006] In order to at least partially achieve this or other objectives, a first aspect of the present invention provides an electric field detector, the electric field detector comprising:

[0007] an electromechanical oscillator, at least a portion of which consists of a piezoelectric element intended to vibrate at an oscillation frequency during use of the detector;

[0008] - a frequency measuring device coupled to the oscillator in order to measure the oscillation frequency; and

[0009] - an electrical shielding assembly arranged close to the piezoelectric element without contacting this element, so that during use of the detector the piezoelectric element moves by vibrating relative to the electrical shielding assembly.

[0010] According to the invention, the electrical shielding assembly is further arranged so that during use of the detector, the portion of the piezoelectric element that is exposed to the electric field to be measured and that is restrained by this electrical shielding assembly varies during each oscillation of the oscillator. The electric field to be measured acting on the exposed and variable portion of the piezoelectric element during use of the detector produces a variation in the oscillation frequency that is measured by the frequency measuring device. Thus, the oscillation frequency forms the electric field strength measurement result.

[0011] The present invention therefore solves the disadvantages of the detectors of the prior art by using piezoelectric oscillators. Such oscillators are indeed cheap, light and small in size. Furthermore, their use does not require the generation of an electric field which could produce a bias in the measurement results.

[0012] In general, for the present invention, the material of the piezoelectric element can have various chemical compositions. Specifically, the piezoelectric element can be part of crystalline quartz, part of aluminum nitride (AlN), part of gallium phosphate (GaPO4), or a piezoelectric element generally represented by the acronym LGT and corresponding to the chemical formula La3Ga 5,5 Ta 0,5 O 14 Lanthanate crystals of , where La represents the element lanthanum, Ga represents the element gallium, Ta represents the element tantalum and O represents the element oxygen. Such crystalline material is available in the form of thin sheets or "wafers" which can be chemically etched to obtain a piezoelectric element having the desired shape of this element.

[0013] Likewise, in general, the piezoelectric element may have various shapes suitable for generating the vibrations required for the operation of the oscillator. Therefore, in various possible embodiments of the present invention, the piezoelectric element may include one of the following structures:

[0014] a beam intended to vibrate by bending during use of the detector, in particular a beam having a first fixed end and another free end opposite the first end;

[0015] - two parallel beams, each beam being intended to vibrate by bending during use of the detector, the two beams being connected to each other by a respective first end of each beam, the other end of each beam opposite to its first end being free; or

[0016] - Two parallel beams, each intended to vibrate by bending during use of the detector, the two beams being connected to one another on the one hand by two respective first ends of these beams and on the other hand by their other end opposite the first ends.

[0017] The electrical shielding assembly may comprise at least one metal portion, the edge of which is arranged in front of the piezoelectric element so as to partially shield the piezoelectric element with respect to the electric field to be measured at at least one moment during each oscillation. Preferably, however, the electrical shielding assembly may comprise two metal portions which produce the same partial shielding of the piezoelectric element symmetrically on two opposite sides of the piezoelectric element with respect to the electric field to be measured, when the detector is oriented so that the two metal portions are perpendicular to the electric field to be measured.

[0018] Generally, in addition to the piezoelectric element, the electromechanical oscillator may also include at least one electronic amplifier electrically connected to electrodes in contact with the piezoelectric element so as to form a loss-compensated oscillator loop structure. In this case, one of the electrodes may be electrically connected to the output of the amplifier so as to transmit the excitation voltage to the piezoelectric element during use of the detector, and another of the electrodes may be connected to the input of a current detection system so as to detect a response current originating from the piezoelectric element. The output of the current detection system is then connected to the input of the amplifier so as to form a loop structure.

[0019] Advantageously, during use of the detector, one and preferably each of the electrodes may be located on the piezoelectric element at a position masked by the electrical masking assembly relative to the electric field to be measured. Thus, measurement bias that may be introduced by each electrode may be reduced or eliminated.

[0020] Finally, a second aspect of the invention provides an electric field detection assembly, the electric field detection assembly comprising two detectors according to the first aspect, each of which has the same piezoelectric element and different corresponding electrical shielding assemblies. Therefore, the electric field to be measured produces a different oscillation frequency change between the two detectors when it is non-zero. The detection assembly further comprises a subtraction unit, which is arranged to characterize the difference between the oscillation frequencies measured by the corresponding frequency measuring devices of the two detectors. This difference then forms another electric field strength measurement result, which is less sensitive to changes in ambient temperature than the measurement results transmitted separately by each of the two detectors. In fact, since the piezoelectric elements of the two detectors are the same, changes in ambient temperature produce changes in the oscillation frequency, and in the absence of the electric field to be measured, the oscillation frequencies of the two detectors are the same. However, when the electric field to be measured is non-zero, due to the different corresponding electrical shielding assemblies of the two detectors, the electric field to be measured produces a modification of the oscillation frequency that is different between the two detectors. The subtraction unit can then eliminate the influence of the ambient temperature change from the electric field measurement result. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The features and advantages of the present invention will become more apparent in the following detailed description of some non-limiting exemplary embodiments, with reference to the accompanying drawings, which contain:

[0022] [ Figure 1 ] is a block diagram of an electric field detector according to the present invention;

[0023] [ Figure 2a ] can be used for [ Figure 1 ] a perspective view of a piezoelectric element in a detector;

[0024] [ Figure 2b ]yes[ Figure 2a ] is a front view of a piezoelectric element showing electrodes arranged on the element;

[0025] [ Figure 2c ] corresponds to [ Figure 2b ] a cross-sectional view;

[0026] [ Figure 2d ] corresponds to [ Figure 2b ];

[0027] [ Figure 2e ] corresponds to [ Figure 2d ] a cross-sectional view;

[0028] [ Figure 3 ] can be used instead of [ Figure 1 ] a perspective view of another piezoelectric element in a detector;

[0029] [ Figure 4 ] is a description of [ Figure 1 ] a cross-sectional view of the operating principle of the detector;

[0030] [ Figure 5 ] is a block diagram of an electric field detection assembly according to the present invention;

[0031] [ Figure 6a ] shows the use for [ Figure 5 ] a first possible variant of a detection assembly; and

[0032] [ Figure 6b ] shows the use for [ Figure 5 ]A second possible variant of the detection assembly. DETAILED DESCRIPTION

[0033] For the sake of clarity, the dimensions of the elements shown in these figures do not correspond to the actual dimensions nor to the ratio of the actual dimensions. Furthermore, some of these elements are only represented symbolically, and the same references indicated in different figures designate the same or functionally identical elements.

[0034] according to[ Figure 1], the detector 20 according to the present invention comprises an electromechanical oscillator, a frequency measuring device and an electrical shielding assembly. Figure 2a ]Described in [ Figure 1 ] The electromechanical oscillator comprises a piezoelectric element 1 having a pair of electrodes 61 and 62 for applying an excitation voltage V X applied to the element 1 and used to collect the response signal generated by this element 1, such as the response current I R In a known manner, the oscillator is formed by a loop structure which, in addition to the piezoelectric element 1, comprises a circuit for detecting a response current I indicated by reference numeral 2. R The current detection system 2 can be formed based on an operational amplifier 21 and an electrical resistor 22, wherein the operational amplifier has an inverting input, a non-inverting input and an output. The non-inverting input of the operational amplifier 21 is connected to the electrical ground of the detector 20, and the inverting input is connected to the output of the piezoelectric element 1. R The electrode 62 is connected to the operational amplifier 21, and the resistor 22 is connected between the inverting input and the output. Under these conditions, the output of the current detection system 2 is consistent with the response current I R Other electrical configurations for the current sensing system 2 are possible and known to those skilled in the art. The output of the current sensing system 2 is connected to the input of an amplifier 3, and the output of this amplifier 3 supplies the excitation voltage V applied to the electrode 61. X . This loop structure makes it possible to compensate for energy losses and to meet the phase conditions necessary for the presence of spontaneous oscillations. These oscillations cause vibrations of the piezoelectric element 1 and the frequency of the oscillations is the resonant frequency of the oscillator when it is used in an open loop circuit and in a sinusoidal drive mode. The frequency measuring device is indicated by reference numeral 4 and is denoted FREQ. The frequency measuring device can be connected in parallel with the electrode 61 to the output of the amplifier 3. It can be a standard electronic frequency meter available on the market.

[0035] The piezoelectric element 1 may be [ Figure 2a ] is a crystal quartz tuning fork shown in . The piezoelectric element thus consists of two beams 11 and 12 which are parallel to each other and spaced apart from each other, which are rigidly connected to each other by only one of their respective ends via a fixed base part 10. Such a beam model is said to have a free end and an embedded end. The dotted outline shows the bending deformation of the two beams 11 and 12. In principle, the end of each beam 11, 12 which is rigidly connected to the base part 10 corresponds to a vibration node of the element 1. The longitudinal direction of the beams 11 and 12 is parallel to the crystallization direction Y of the crystal quartz used to form the piezoelectric element 1, and the plane of the tuning fork is perpendicular to the crystallization direction X. [ Figure 2a] also shows an electrical shielding assembly 5 consisting of two metal plates 51 and 52. Reference letter E designates the electric field to be measured, which passes through each beam 11, 12 of the piezoelectric element 1 in the side portions of the beam protruding beyond the metal plates 51 and 52. For proper use of the detector 20, the detector is oriented so that the electric field E is substantially perpendicular to the metal plates 51 and 52.

[0036] [ Figure 2b ]and[ Figure 2c ] shows a first possible arrangement of electrodes 61 and 62 for use on the piezoelectric element 1. These electrodes are arranged longitudinally on each beam 11, 12, along the entire length or approximately the entire length of the beam, on coplanar beam faces and against the beam edge closest to the central axis of the tuning fork. Therefore, the electrode 61 has two electrode sections on the same side of the tuning fork, one arranged on the beam 11 and the other arranged on the beam 12. Similarly, the electrode 62 also has two electrode sections on the other side of the tuning fork from the electrode 61, one arranged on the beam 11 and the other arranged on the beam 12. The electrodes 61 and 62 arranged in this way extend or contract the inner edges of the two beams 11 and 12, which is the same at each vibration moment. All electrode sections thus arranged are shielded by the metal plates 51 and 52 with respect to the electric field E to be measured.

[0037] [ Figure 2d ]and[ Figure 2e ] shows a second possible arrangement for the electrodes 61 and 62. They are currently confined to a portion of each beam 11, 12 close to the base portion 10, and each electrode 61, 62 comprises two pairs of electrode segments arranged and connected to produce an opposing electric field between the inside and outside of each beam 11, 12 at the foot of each beam 11, 12, while the electric field remains symmetrical between the two beams 11 and 12. This piezoelectric excitation mode of the tuning fork causes each beam 11, 12 to "hinged" relative to the base portion 10, and each beam then vibrates by bending from this hinge.

[0038] [ Figure 3 ] shows another possible model of the piezoelectric element 1. The piezoelectric element is still composed of two identical and parallel beams 11 and 12, but these beams are connected to each other and to two fixed base parts 10' and 10". This model of the piezoelectric element is called a two-end hinge in the jargon of technicians in this field. Each of the beams 11, 12 still vibrates by bending parallel to the plane of the piezoelectric element 1, wherein the instantaneous directions of the bending of the two beams are opposite and the absolute values ​​of the instantaneous deflection values ​​of the two beams are the same. For other models of the piezoelectric element 1, the electrodes 61 and 62 can have similar [ Figure 2b ]and[ Figure 2c ] configuration, while being confined to the central portion along the length of the beam.

[0039] Other models are still possible for the piezoelectric element 1, in particular a model with a single vibrating beam, one end of which is free, while the other end, said to be "embedded", is rigidly connected to a fixed base part of the element. In a known manner, piezoelectric elements such as those just described can be manufactured from crystalline quartz wafers by chemical etching or reactive ion etching.

[0040] according to[ Figure 4 ], piezoelectric element 1, such as [ Figure 2a ]arrive[ Figure 2c ] is inserted between two electrical masks 51 and 52, which are arranged parallel to each other on two opposite sides of the element 1 but not in contact therewith. The two electrical masks 51 and 52 form an electrical shielding assembly 5. They are symmetrical so as to shield a portion of the piezoelectric element 1 from the external electric field E. The latter is perpendicular to the two masks 51 and 52 during optimal use of the detector 20. In other words, the two metal plates 51 and 52 are superimposed in a common projection plane parallel to the plates. In addition, the two metal plates 51 and 52 are sized so as to shield a limited portion of the piezoelectric element 1 that varies during each vibration. For [ Figure 2a ]and[ Figure 3 ], two metal plates 51 and 52 can mask the corresponding part of each beam 11, 12 positioned towards the center of the element, wherein the edges of these plates are parallel and superimposed on the central longitudinal area of ​​each beam, as shown in the figure. In this way, the longitudinal part of each beam 11, 12 is only exposed to the electric field E, and the longitudinal part is close to the outer edge of the beam, which means close to a face facing away from the other beams. In addition, this exposed part has a volume that varies according to the instantaneous vibration state of the beam. In some possible embodiments for each metal plate 51, 52, the plate can be composed of a metal layer portion, for example, made of silver (Ag) or gold (Au) that has been deposited on a flat substrate such as a glass plate. The two metal plates 51 and 52 are electrically connected to each other and can be maintained at a floating potential or can be connected to a potential reference terminal. In some simplified embodiments of the present invention, the electrical shielding assembly 5 can include only a single metal plate on only one side of the piezoelectric element 1.

[0041] We will now refer to [ Figure 4 ] describes the operating principle of the detector 20. The excitation voltage V XA stress distribution is generated in the piezoelectric element 1 which causes vibrations of the element 1. In the absence of an external electric field, the spontaneous oscillation of the electromechanical oscillator has a frequency value f0, which is the natural oscillation frequency of the electromechanical oscillator. This value f0 depends mainly on the dimensions of the piezoelectric element 1, the intrinsic parameters, the values ​​of the elastic parameters of the piezoelectric material and the electrical parameters of the entire oscillator. The operation of this oscillator at the value of its natural oscillation frequency f0 is known to those skilled in the art. Specifically, during oscillation at this natural frequency value f0, the excitation voltage V X The excitation voltage V is orthogonal to the deformation phase of the piezoelectric element 1. X Dissipative losses, such as those caused by viscous friction of the piezoelectric element 1 in the surrounding gas, are then accurately compensated. However, such losses are proportional to the instantaneous deformation speed of the piezoelectric element 1. More precisely, the excitation voltage V X A piezoelectric excitation force is generated in each beam 11, 12, and the piezoelectric excitation force is denoted as F exci And the vibration of the element 1 is maintained in a stable oscillation state. In the absence of any external electric field, the natural oscillation frequency value f0 can be experimentally measured by the frequency measurement device 4.

[0042] The external electric field, denoted E, is the electric field to be measured. When the electric field is non-zero, it passes through the piezoelectric element 1 in a portion thereof not shielded by the electrical shielding assembly 5. In this unshielded portion, which means the portion that is exposed to the electric field E and can be divided between the two beams 11 and 12 as shown in the example of the figure, the electric field E causes a piezo The additional piezoelectric force F is proportional to the instantaneous fraction of the piezoelectric element 1 that is traversed by the electric field E. Therefore, this additional force F piezo Proportional to the instantaneous deformation of the piezoelectric element 1 .

[0043] In the presence of an electric field E to be measured, the excitation voltage V in element 1 X The generated piezoelectric excitation force F exci Specific extra pressure force F piezo For this reason, the piezoelectric excitation force F is not significantly modified. exci The phase difference between the deformation of the piezoelectric element 1 and the deformation of the piezoelectric element 1. Therefore, the two forces F piezo and F exci Due to this phase quadrature relationship, when all other parameters of the oscillator remain unchanged, the additional piezoelectric force F on the oscillation frequency of the oscillator in the presence of an electric field E is piezo The value change caused is the largest. Then: Δf=(F piezo / F exci)f0 / (2Q), where Δf is the change in oscillation frequency caused by the electric field E and Q is the quality factor of the piezoelectric element 1 when used as an open-ring resonator and in sinusoidal drive mode. The change Δf is equal to the difference f-f0, where f is the oscillation frequency measured by the device 4 in the presence of the electric field E. The change in oscillation frequency is proportional to the electric field E: Δf=KE, the proportionality factor K depending in particular on the geometrical and electromechanical characteristics of the piezoelectric element 1 and on the geometrical characteristics of the masking assembly 5. This can be determined by digital modeling of the electromechanical oscillator or by calibration of the detector 20. For a piezoelectric element 1 of single crystal quartz and according to [ Figure 2a ], when the two beams 11 and 12 each have a length L equal to 3 mm (millimeters), a width e in the plane of the tuning fork equal to 200 μm (micrometers) and a thickness h measured perpendicular to the plane of the tuning fork equal to 30 μm, and when the two beams 11 and 12 are spaced apart by a distance d equal to 100 μm, K is equal to approximately 4 μHz / (V / m) (microhertz per volt per meter). Thus, the value of the oscillation frequency f as delivered by the device 4 measures the value of the trench electric field E: E=(f-f0) / K.

[0044] However, the natural oscillation frequency f0 measured by the device 4 when the electric field E is zero may vary depending on the temperature of the piezoelectric element 1, i.e. the temperature of the environment in which the detector 20 is used. The detector 20 as described above does not allow the contribution of the variation of the natural oscillation frequency f0 due to the variation of the ambient temperature to be separated from the contribution caused by the electric field E to be measured within the variation of the oscillation frequency f. Now referring to [ Figure 5 The detection assembly described allows the elimination of the thermal contribution affecting the natural oscillation frequency f0, so that the measurement result delivered by such a detection assembly only characterizes the electric field to be measured and makes this result the same or substantially the same regardless of the ambient temperature. This improvement may be particularly useful when the ambient temperature may vary significantly, such as is the case on satellites.

[0045] according to[ Figure 5 ], the electric field E detection assembly is generally indicated by reference numeral 30 and includes each according to [ Figure 1 ] of the detector 20. The two detectors 20a and 20b are identical to each other except for their electrical shielding assemblies. Specifically, the two detectors 20a and 20b have corresponding piezoelectric elements 1a and 1b, which are identical and oriented in the same manner, and may have the following features: Figure 2a] are single crystal quartz tuning fork type shown in . They therefore have the same natural oscillation frequency f0 and the latter varies with the ambient temperature in the same way for both detectors 20a and 20b. The two piezoelectric elements 1a and 1b are arranged in a fixed manner in the detection assembly 30, close enough to each other to be exposed to the same electric field E to be measured. On the other hand, the two detectors 20a and 20b have different corresponding electrical shielding assemblies so that the coefficient K defined above has two different values: Ka for detector 20a and Kb for detector 20b. Reference numerals 4a and 4b designate respective devices for measuring the oscillation frequencies of the detectors 20a and 20b. Thus, in the presence of the electric field E to be measured, the device 4a provides a first oscillation frequency value f a =f0+K a E, and the device 4b provides a second oscillation frequency value f b =f0+K b E. These two values ​​are transmitted to a subtraction unit 21 denoted DIFF. and the subtraction unit calculates the difference f a -f b =(K a -K b ) E. This difference, which constitutes the new measured value of the electric field E, is independent of the natural oscillation frequency f0 of the respective oscillators of the two detectors 20a and 20b. Therefore, through this natural oscillation frequency f0, it no longer depends on the ambient temperature. a -f b A residual dependence on the ambient temperature is still possible through the factor K a and K b appears, but it is less than the oscillation frequency f0, f as a function of temperature a and f b individual changes.

[0046] According to a first possibility, the electrical shielding assembly of the detector 20b, indicated by reference numeral 5b, can be selected by size and position so that it completely and continuously shields the piezoelectric element 1b of the detector 20b with respect to the electric field E during vibration. The detector 20b is thus insensitive to the electric field E: the coefficient K b is zero and the frequency f measured by the device 4b b The electrical shielding assembly of the detector 20a, indicated by reference numeral 5a, partially shields the corresponding piezoelectric element 1a, as shown in reference [ Figure 2a ]arrive[ Figure 4 ] described. Figure 6a ] illustrates this configuration of the electrical shielding assembly 5a (respectively 5b) relative to the piezoelectric element 1a (respectively 20b) within the detector 20a (respectively 1b). The measurement result delivered by the subtraction unit 21 for the electric field E is then fa -f0=K a E.

[0047] According to another possibility, the electrical shielding assembly 5b of the detector 20b can shield a limited portion of the piezoelectric element 1b of the detector 20b, which portion is complementary to the portion shielded by the electrical shielding assembly 5a of the detector 20a for the piezoelectric element 1a of the detector 20a. Figure 6b ] corresponds to [ Figure 6a ]. In this case: K b =-K a , and the measurement result delivered by the subtraction unit 21 for the electric field E is: f a -f b =2K a E.

[0048] It will be appreciated that the invention may be reproduced while modifying minor aspects of the embodiments described in detail above, while still retaining at least some of the advantages cited. In particular, it may be possible to use a device having a configuration different from [ Figure 2a ]and[ Figure 3 ] In addition, an electronic module different from the electronic module described but having the same functionality may be used instead of the electronic module described.

Claims

1. An electric field detector (20), comprising: - an electromechanical oscillator, at least a part of which consists of a piezoelectric element (1) which is intended to vibrate at an oscillation frequency during use of the electric field detector; - a frequency measuring device (4) coupled to the electromechanical oscillator in order to measure the oscillation frequency; as well as an electrical shielding assembly (5) arranged close to the piezoelectric element (1) without contacting the piezoelectric element, so that during use of the electric field detector the piezoelectric element moves by vibrating relative to the electrical shielding assembly, The electrical masking assembly (5) is arranged so that during use of the electric field detector (20), the portion of the piezoelectric element (1) which is exposed to the electric field (E) to be measured while being restrained by the electrical masking assembly varies during each oscillation of the electromechanical oscillator, The electric field (E) to be measured acts on the exposed and variable part of the piezoelectric element (1) during use of the electric field detector (20), thereby generating a change in the oscillation frequency (f) measured by the frequency measurement device (4), the oscillation frequency forming an electric field strength measurement result.

2. The electric field detector (20) according to claim 1, characterized in that The piezoelectric element (1) is a portion of crystalline quartz, a portion of aluminum nitride, a portion of gallium phosphate, or a portion having the chemical formula La3Ga 5,5 Ta 0,5 O 14 part of the crystal.

3. The electric field detector (20) according to claim 1 or 2, characterized in that: The piezoelectric element (1) comprises a beam which is intended to vibrate by bending during use of the electric field detector, the beam having a fixed first end and another free end opposite the first end, or the piezoelectric element (1) comprises two parallel beams (11, 12), each intended to vibrate by bending during use of the electric field detector (20), the two beams being connected to each other by a respective first end of each of the two beams, the other end of each beam opposite to the first end of the same beam being free, Alternatively, the piezoelectric element (1) comprises two parallel beams (11, 12), each beam being intended to vibrate by bending during use of the electric field detector (20), the two beams being connected to each other via two respective first ends of the beams on the one hand and two other respective ends of the beams opposite to the two first ends on the other hand.

4. The electric field detector (20) according to claim 1, characterized in that The electrical shielding assembly (5) comprises at least one metal portion, the edge of which is arranged in front of the piezoelectric element (1) so as to partially shield the piezoelectric element with respect to the electric field (E) to be measured at at least one moment of each oscillation.

5. The electric field detector (20) according to claim 4, characterized in that The electrical shielding assembly (5) comprises two metal parts (51, 52) which symmetrically produce the same partial shielding of the piezoelectric element (1) on two opposite sides of the piezoelectric element with respect to the electric field (E) to be measured when the electric field detector is oriented so that the two metal parts are perpendicular to the electric field to be measured.

6. The electric field detector (20) according to claim 1, characterized in that In addition to the piezoelectric element (1), the electromechanical oscillator comprises at least one electronic amplifier (3) which is electrically connected to electrodes (61, 62) in contact with the piezoelectric element so as to form a loss-compensated oscillator loop structure.

7. The electric field detector (20) according to claim 6, characterized in that One of the electrodes (61, 62) is electrically connected to the output of the at least one electronic amplifier (3) so as to apply an excitation voltage (V X ) is transmitted to the piezoelectric element (1), and another of the electrodes is connected to the input of a current detection system (2) so as to detect a response current (IR) originating from the piezoelectric element, and the output of the current detection system is connected to the input of the at least one electronic amplifier.

8. The electric field detector (20) according to claim 6 or 7, characterized in that During use of the electric field detector, one of the electrodes (61, 62) is located on the piezoelectric element (1) at a position of the piezoelectric element that is shielded by the electrical shielding assembly (5) relative to the electric field (E) to be measured.

9. An electric field detection assembly (30) comprising two electric field detectors (20a, 20b) each according to any one of the preceding claims, the two electric field detectors having identical respective piezoelectric elements (1a, 1b) and different respective electrical shielding assemblies (5a, 5b) so that when the electric field to be measured is non-zero, the electric field to be measured (E) produces different oscillation frequencies (f a 、f b ), The electric field detection assembly (30) further comprises a subtraction unit (21) arranged to characterize the oscillation frequency (f a 、f b ), the difference forming another electric field (E) strength measurement that is less sensitive to changes in ambient temperature than the measurement delivered by each of the two electric field detectors individually.

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