Source: http://www.google.com.ar/patents/WO2010061300A1?cl=en
Timestamp: 2018-01-23 13:18:59
Document Index: 202751372

Matched Legal Cases: ['arts 108', 'arts 108', 'arts 108', 'art 108', 'art 112', 'arts 110', 'arts 108', 'arts 308', 'arts 308', 'arts 308', 'art 308', 'art 312', 'arts 308']

Patent WO2010061300A1 - Device for measuring a fluid meniscus - Google Patents
The invention relates to a device (102) arranged for measuring a geometry of a fluid meniscus (132). The device comprises a fluid chamber (104) storing a first electrically conductive fluid (128) and a second electrically insulating fluid (324). The fluids are mutually immiscible and define a fluid meniscus...http://www.google.com.ar/patents/WO2010061300A1?cl=en&utm_source=gb-gplus-sharePatent WO2010061300A1 - Device for measuring a fluid meniscus
Publication number WO2010061300 A1
Application number PCT/IB2009/054758
Also published as CN102203546A, CN102203546B, EP2347214A1, EP2347214B1, US9109876, US20110204902
Publication number PCT/2009/54758, PCT/IB/2009/054758, PCT/IB/2009/54758, PCT/IB/9/054758, PCT/IB/9/54758, PCT/IB2009/054758, PCT/IB2009/54758, PCT/IB2009054758, PCT/IB200954758, PCT/IB9/054758, PCT/IB9/54758, PCT/IB9054758, PCT/IB954758, WO 2010/061300 A1, WO 2010061300 A1, WO 2010061300A1, WO-A1-2010061300, WO2010/061300A1, WO2010061300 A1, WO2010061300A1
Inventors Boer Bart M. De, Hoog Thomas J. De, Theodorus P. H. G. Jansen
Patent Citations (9), Classifications (7), Legal Events (6)
WO 2010061300 A1
The invention relates to a device (102) arranged for measuring a geometry of a fluid meniscus (132). The device comprises a fluid chamber (104) storing a first electrically conductive fluid (128) and a second electrically insulating fluid (324). The fluids are mutually immiscible and define a fluid meniscus (132) in between them. Furthermore a main electrowetting electrode (118) and auxiliary electrowetting electrodes (120, 122, 124, 126) are provided for controlling the geometry of the fluid meniscus. Hereto a voltage source (134) for providing a voltage between the main electrowetting electrode and the auxiliary electrowetting electrodes is comprised, as well as a measurement circuit (144) for separately measuring capacitances between the main electrowetting electrode and at least two of the auxiliary electrowetting electrodes. For this purpose the measurement circuit comprises a multiplexer for demodulating a signal indicative for said capacitances. The invention further relates to a method for measuring a fluid meniscus.
1. A device (102, 302) for measuring a geometry of a fluid meniscus (132, 328), comprising: a fluid chamber (104, 304) comprising a first fluid (128, 324) and a second fluid (130, 326), which first fluid is electrically conductive, which second fluid is electrically insulating, and which first and second fluids are mutually immiscible and in contact with each other over a fluid meniscus (132, 328), a main electro wetting electrode (118, 318) located in a main plane (319) and auxiliary electrowetting electrodes (120, 122, 124, 126) partially surrounding the fluid chamber and being located in respective auxiliary planes (121, 123, 125, 127), for controlling the geometry of the fluid meniscus, a voltage source (134, 33) for providing a voltage between the main electrowetting electrode and a plurality of auxiliary electrowetting electrodes, a measurement circuit (144, 342) for separately measuring capacitances between the main electrowetting electrode and at least two of the respective auxiliary electrowetting electrodes (320, 322), the measurement circuit comprising a multiplexer (212, 414) for demodulating a signal (210, 412) indicative for said respective capacitances.
2. The device according to claim 1, wherein the measurement circuit is arranged for measuring capacitances between the main electrowetting electrode and each of the auxiliary electrowetting electrodes (120, 122, 124, 12).
3. The device according to claim 1, comprising a voltage control circuit (154, 350) for controlling the voltage provided between the main electrowetting electrode and each of the auxiliary electrowetting electrodes based on a control signal (156, 343) provided by the measurement circuit.
4. The device according to claim 1, wherein the measurement circuit comprises an operational amplifier (204) for measuring capacitances between the main electrowetting electrode and at least two of the respective auxiliary electrowetting electrodes, wherein the operational amplifier is provided with a negative feedback loop (206), which negative feedback loop is provided with a measurement capacitor (208) having a predetermined measurement capacitance, wherein the operational amplifier is arranged for cooperation with an input (211) of the multiplexer.
5. The device according to claim 1, wherein the measurement circuit comprises a switching circuit (404) for measuring capacitances between the main electrowetting electrode and at least two of the respective auxiliary electrowetting electrodes, wherein the switching circuit comprises a first measurement capacitor (406) having a predetermined first measurement capacitance, and a second measurement capacitor (408) having a predetermined second measurement capacitance, wherein the first and second measurement capacitances are mutually different, the switching circuit further comprising a capacitance switch (410) for driving the first and second measurement capacitors in an alternating way, wherein the switching circuit is arranged for cooperation with an input (413) of the multiplexer.
6. The device according to claim 1, wherein the multiplexer is a time domain multiplexer (414), wherein the time domain multiplexer employs demodulation signals, each demodulation signal being a square wave signal having a low value and a high value, wherein the voltage source comprises voltage switches (331, 333, 407, 409) for alternatingly disconnecting the voltages corresponding to the high values of the respective demodulating values.
7. The device according to claims 1, wherein the multiplexer is a frequency domain multiplexer (212), wherein the voltage source is arranged for providing voltages at specific frequencies and wherein the frequency domain multiplexer employs demodulation signals each having a frequency component corresponding to the respective specific frequencies.
8. The device according to claim 1, wherein the first fluid has a first refractive index and the second fluid has a second refractive index, wherein the first and second refractive indices are mutually different.
9. The device according to claim 1, wherein the first fluid provides a first speed of sound and the and second fluid provides a second speed of sound, wherein the first and second speeds of sound are mutually different.
10. A catheter (140) comprising the device according to claim 1.
11. Use of the device according to claim 1, in a catheter for ultrasound applications.
12. Use of the device according to claim 1, in an optical storage drive.
13. Use of the device according to claim 1, in a photo camera.
14. A method for measuring a geometry of a fluid meniscus (132, 328) between an electrically conducting first fluid (128, 324) and an electrically insulating second fluid (130,
326) comprised in a fluid chamber (104, 304), the fluids being mutually immiscible, comprising steps (502, 504) of: providing a voltage between a main electrowetting electrode (118, 318) located in a main plane (119, 319) and auxiliary electrowetting electrodes (120, 122, 124, 126) partially surrounding the fluid chamber and being located in an auxiliary planes (121,
123, 125, 127), and separately measuring capacitances between the main electrowetting electrode and at least two of the auxiliary electrowetting electrodes (320, 322) by a measurement circuit (144, 342) comprising a multiplexer (212, 414).
15. The method according to claim 14, comprising a step (506) of controlling the voltage provided to the auxiliary electrowetting electrodes based on a signal provided by the measurement circuit.
The invention further relates to a catheter comprising such a device. The invention further relates to a method for measuring a geometry of a fluid.
In WO 2006/035407 Al, a controllable optical lens system is disclosed. Said system comprises a lens having a chamber housing first and second fluids, wherein the interface between the fluids define a lens surface. The system further comprises an electrode arrangement comprising a first electrode and a second electrode for electrically controlling the shape of the lens surface, a feedback control loop for controlling the electrode arrangement based on a signal provided by a capacitance sensing arrangement, which capacitance sensing arrangement serves for measuring a capacitance between the first and second electrodes.
The techniques disclosed in WO2006/035407 Al are less suitable for generating specific geometries for the fluid meniscus, e.g. an inclined flat meniscus or a symmetrical concave or convex shape.
It is an object of the invention to provide a device as described in the preamble for more accurately measuring the geometry of the fluid meniscus. This object is achieved by the device according to the invention, the device comprising a fluid chamber comprising a first fluid and a second fluid, which first fluid is electrically conductive, which second fluid is electrically insulating, and which first and second fluids are mutually immiscible and in contact with each other over a fluid meniscus, a main electrowetting electrode located in a main plane and auxiliary electrowetting electrodes partially surrounding the fluid chamber and being located in an auxiliary plane, for controlling the geometry of the fluid meniscus, a voltage source for providing a voltage between the main electrowetting electrode and a plurality of auxiliary electrowetting electrodes, and a measurement circuit for separately measuring capacitances between a main electrowetting electrode and at least two of the auxiliary electrowetting electrodes, the measurement circuit comprising a multiplexer for demodulating a signal indicative for said capacitances. Through providing a plurality of auxiliary electrowetting electrodes, and by measuring the capacitances between the main electrowetting electrode and at least two of the auxiliary electrowetting electrodes, the geometry of the fluid meniscus advantageously allows for more accurate determination. Said auxiliary electrowetting electrodes are mutually electrically connected via the electrically conductive first fluid comprised in the fluid chamber. Hence, depending on the first fluid's characteristics, there is significant interaction between the auxiliary electrowetting electrodes. The interaction between the auxiliary electrodes impedes the determination of a single capacitance. Namely, due to said interaction the signal representative for the capacitances between the main electrowetting electrode and the auxiliary electrowetting electrodes indicates an overall characteristic. To counteract the consequences of the interaction between the auxiliary electrowetting electrodes, the device according to the invention provides a multiplexer for demodulating the signal representative for the capacitances between the main electrowetting and each of the auxiliary electrowetting electrodes. More specifically, said signal is decomposed into components representative for the capacitances associated with separate auxiliary electrowetting electrodes. Consequently, the capacitances between the main electrowetting electrodes and at least two of the auxiliary electrodes are amenable for separate measuring. Namely, more information regarding an actual geometry of the fluid meniscus is available. As a result, the device according to the invention enables a more accurate measuring of a fluid meniscus' geometry.
A potential source of such a parasitic capacitance is a co-axial measuring cable. The involved embodiment of the device according to the invention may therefore be particularly beneficial for applications wherein an arrangement of the fluid chamber, the main electrowetting electrode and the auxiliary electrowetting electrodes is remotely located from the measuring circuit. Herein, said arrangement and said measurement circuit are preferably mutually connected via a co-axial cable. An example of such an application is given by a catheter, wherein said arrangement is mounted in a catheter's tip for redirecting an ultrasound and / or a laser beam during scanning. Given the relatively small dimensions of the catheter's tip, the measurement circuit cannot be integrated into said catheter's tip. Hence, a further advantage of this embodiment is in the fact that it enables the utilization of the device in a catheter.
In this particular example, each of the auxiliary electrowetting electrodes is accompanied by at least one parasitic capacitance. In addition to that, the parasitic capacitances are interconnected. Namely, the capacitances between the main electrowetting electrode and the auxiliary electrowetting electrodes mutually interact via the first and second fluids comprised in the fluid chamber. In addition to that, the parasitic capacitances are non- constant due to bending movements of the co-axial cable during use.
It is a further object of the invention to provide a method for measuring a geometry of a fluid meniscus between an electrically conducting first fluid and an electrically insulating second fluid comprised in a fluid chamber, the fluids being mutually immiscible, comprising the steps of providing a voltage between a main electro wetting electrode located in a main plane and auxiliary electrowetting electrodes partially surrounding the fluid chamber and being located in auxiliary planes, and separately measuring capacitances between the main electrowetting electrode and at least two of the auxiliary electrowetting electrodes by a measurement circuit comprising a multiplexer. In a preferred embodiment of the method according to the invention, a step is provided for controlling the voltage applied to the auxiliary electrowetting electrodes, wherein said voltage is based on a signal provided by the measurement circuit.
It is a further object of the invention to provide a catheter for real time control of the direction of sound and / or electromagnetic radiation. This object of the invention is achieved by the catheter according to the invention, which catheter is provided with the device according to the invention.
The invention further relates to the use of the device according to the invention in a catheter, an optical storage device and a photo camera, as defined in the claims 11 to 13.
Figure IA schematically depicts in cross section a device comprising a fluid chamber, a main electrowetting electrode and auxiliary electrowetting electrodes.
Figure IB schematically shows a bottom view of the device depicted in Figure IA. Figure 2 schematically displays a model for the electrical behavior of an electrowetting lens together with co-axial cables and a measurement circuit, the measurement circuit being applied into the device according to Figure IA and Figure IB.
Figure 3A schematically depicts in cross section a device comprising fluid chamber, a main electrowetting electrode and auxiliary electrowetting electrodes, the device further comprising a measurement circuit provided with a time domain multiplexer.
Figure 3B schematically displays a bottom view of the device depicted in Figure 3A.
Figure 4 schematically displays a model for the electrical behavior of an electrowetting lens together with co-axial cables and a measurement circuit, wherein the measurement circuit is applied into the device of Figure 3A and Figure 3B.
Figure 5 depicts a flowchart representing a method for measuring a geometry of a fluid meniscus.
A first embodiment of the device according to the invention is depicted in Figure IA, Figure IB and Figure 2. Figure IA depicts a cross section and a bottom view of a device 102 whereas a Figure IB shows a bottom view of said device. The device 102 comprises a fluid chamber 104, which fluid chamber 104 has a bottom 106 and a wall having wall parts 108, 110, 112 and 114, see also Figure IB. The wall parts 108, 110, 112 and 114 are provided with an insulating layer 116 for preventing shortcuts, see Figure IA. In alternative embodiments the fluid chamber may have a conical or a cylindrical wall, or any other suitable wall. The device 102 further comprises a main electrowetting electrode 118, which is attached to the bottom 106 in this particular embodiment, and auxiliary electrowetting electrodes 120, 122, 124 and 126, see Figure IB, which partially surround the fluid chamber 104 and are attached to the wall parts 108, 110, 112 and 114, respectively. In this particular example, the main plane 119 and the auxiliary planes 121, 123, 125 and 127 do not coincide.
Referring to Figure IA, the fluid chamber 104 comprises a first fluid 128 and a second fluid 130, which first and second fluids are mutually immiscible and define a fluid meniscus 132 being an interface between the fluids 128 and 130. The first fluid 128 is electrically conductive and the second fluid 130 is electrically insulating. That is, first fluid 128 has a first electrical conductivity and the second fluid 130 has a second electrical conductivity, wherein the second electrical conductivity is significantly small compared to first electrical conductivity. Ideally, the second electrical conductivity is nihil. Preferably, a first fluid's density and a second fluid's density have no significant mutual difference as to make the device 102 relatively insensitive to changes of its orientation with respect to the gravity field. During operation, voltages V1, V2, V3 and V4 are provided to the respective auxiliary electrowetting electrodes 120, 122, 124 and 126 by a voltage source 134 at frequencies ft, f2, f3 and ft, respectively. Herein, it holds that ft ≠ f2 ≠ f3 ≠ f4. Through providing said voltages to the auxiliary electrowetting electrodes 120, 122, 124 and 126, a geometry of the fluid meniscus 132 is controlled via controlling contact angles land .see Figure IA. The contact angle iis defined as the angle between the fluid meniscus 132 and the wall part 108, the contact angle is accordingly defined as being the angle between the fluid meniscus 132 and the wall part 112, see Figure IB. In this embodiment, the object is to generate an inclined straight fluid meniscus, as indicated in Figure IA. The contact angles are controlled through employing the electrowetting effect. The contact angles are estimated through measuring the capacitances between the main electrowetting electrode 116 and each of the auxiliary electrowetting electrodes 120, 122, 124 and 126. Namely, the aforementioned capacitances are determined by the dimensions of the areas 136 and 138 of the electrowetting electrodes covered with the electrically conductive first fluid 128, wherein the areas 136 and 138 covered with the electrically conductive first fluid 128 vary proportionally with said contact angles. Contact angles between the fluid meniscus 132 and the wall parts 110 and 114 are equally being controlled.
In this particular example, the device 102 is mounted in a catheter's tip 140 for the purpose of real time controlling the direction of an ultrasound beam 142 generated by an ultrasound transducer 144, as depicted in Figure IA. For that purpose, the first fluid provides a first speed of sound and the second fluid provides a second speed of sound, wherein the first speed of sound differs from the second speed of sound. The discontinuity in terms of speeds of sound occurring at the fluid meniscus 132 will redirect the ultrasound beam. Hence, through controlling the fluid meniscus' tilt angle, the ultrasound beam 142 is being steered towards a target location inside e.g. a human body. For more detailed information, the reader is referred to WO 2006/035407 Al. The device 102 is not limited to applications in catheters; other promising applications are in endoscopes, biopsy needles and scanning microscopes.
Because of the catheter tip's relatively small dimensions, a measurement circuit 144 and the voltage source 134 cannot be integrated with the catheter's tip 140. Consequently, the measurement circuit 144 and the voltage source 134 are remotely located from the catheter's tip 140. The measurement circuit 144 is arranged for separately measuring the capacitances between the main electrowetting electrode 118 and the auxiliary electrowetting electrodes 120, 122, 124 and 126 on the basis of a signal 153. The signal 153 is indicative for the capacitances between the main electrowetting electrode 118 and each of the auxiliary electrowetting electrodes 120, 122, 124 and 126, which capacitances are denoted by C1, C2, C3 and C4, respectively, see Figure IA and Figure IB. Hence in this particular example, each of the auxiliary electrowetting electrodes 120, 122, 124 and 126 are considered by the measurement circuit 144. The measurement circuit 144 and the voltage source 134 are physically connected to the electrowetting lens 102 by way of co-axial cables 146, 148, 150, 151 and 152. Although said co-axial cables are shielded such that no mutual coupling between the co-axial cables exists, the co-axial cables 146, 148, 150, 151 and 152 introduce significant parasitic capacitors having parasitic capacitances Cp1, Cp2, Cp3, Cp4 and Cp5. The parasitic capacitances are non-constant due to bending movements of the co-axial cables 146, 148, 150, 151 and 152 during use. It is noted that the cables 146, 148, 150 and 151 may be embodied by common electrically insulated cables, between which cables parasitic capacitances may come into being.
Figure 2 illustrates a model for the electrical behavior of the device 102. In addition, Figure 2 depicts the measurement circuit 144 applied in the device of Figures IA and IB in more detail. For the purpose of separately measuring the capacitances C1, C2, C3 and C4, a measurement circuit 202 comprises an operational amplifier 204 provided with a negative feedback loop 206, which feedback loop is provided with a measurement capacitor 208 having a measurement capacitance Cmeas. The operational amplifier's positive input V+ is grounded. Due to the negative feedback loop 206, the negative input V_ of the operational amplifier 204 is at virtual ground, i.e. it holds that V_ = V+. The latter implies that V_ = 0 [V]. Although currents will flow through the parasitic capacitances Cp1, Cp2, Cp3, Cp4, the voltages across the capacitances C1, C2, C3 and C4 are equal to V1, V2, V3 and V4, respectively. Currents flowing through C1, C2, C3 and C4 will not flow through CP5 since this capacitance is connected to the operational amplifier's negative input V_ which is at virtual ground. Therefore a voltage 14,^, characterizing a signal 210, which signal 210 is representative for the capacitances between the main electrowetting electrode 118 and the auxiliary electrowetting electrodes 120, 122, 124 and 126, follows from the following equation:
/tύC,K3asL;a - = ∑^~"* ;'i: = ;'i + Ϊ'2 -j- ^3. -f- J^ = JtIu C1 V1 + JL-JC2VI + iω ^3^' 3 ÷j^CΛ [I]? wherein ω corresponds to the imaginary part of the Laplace variable and / denotes the imaginary unit. Furthermore, Vmeas is the voltage measured across the capacitance Cmeas employing a Voltmeter known per se.
The measurement circuit 202 further comprises a multiplexer 212 which employs frequency domain multiplexing in this particular example. Alternatively, time domain multiplexing may be utilized. The operational amplifier 204 cooperates with an input 211 of the multiplexer 212. The multiplexer 212 duplicates the signal 210 which is representative for the capacitances C1, C2, C3 and C4, to a plurality of signals 214, 216, 218 and 220 which are each representative for said capacitances. The number of duplications corresponds to the number of auxiliary electrowetting electrodes. After duplication, the signals 214, 216, 218 and 220 are demodulated using demodulation signals having frequencies fϊ, f2, f3 and ft, respectively. The frequencies of the demodulation signals are identical to the frequencies at which the auxiliary electrowetting electrodes 120, 122, 124 and 126, see Figure IB, are being driven by the voltage source 134. The demodulation signals may be sinusoidal. Alternatively, the demodulation signals may be embodied by square waves or any other suitable waveform. The frequencies fϊ, f2, f3 and ft are such that after demodulation, merely one frequency component of the signals 214, 216, 218 and 220, see Figure 2, is demodulated to DC i.e. 0 [Hz], whereas possible other frequency components present in demodulated signals 222, 224, 226 and 228 are sufficiently far removed from 0 [Hz], e.g. at least 100 [Hz].
During operation the demodulated signals 222, 224, 226 and 228 are filtered through low-pass filters 230, 232, 234 and 236 respectively, having cut-off frequencies such that the demodulated signals' DC components are unaffected whereas higher frequency contents are effectively attenuated. Low-pass filtered signals 238, 240, 242 and 244 are characterized by voltages Vmeas, 1, Vmeas,2, Vmeas,3 and Vmeas,4, which voltages relate to the capacitances C1, C2, C3 and C4, respectively, according to the following relation:
with k G [i, 2. B, 4}. Therefore, each of the capacitances Ck between the main electrowetting electrode 118 and the auxiliary electrowetting electrodes 120, 122, 124 and 126 can be determined according to the following relation: c* = ''M"t;Ci"» [3],
with k E {1, 2. 3, ■+}. It is stressed that the first embodiment according to the invention is not necessarily restricted to a number of 4 auxiliary electrowetting electrodes, i.e. the index k is allowed to attain any positive integer, provided said integer is not less than 2.
Referring to Figures IA and IB, a voltage control circuit 154 is depicted. The voltage control circuit 154 is arranged for the purpose of controlling the voltages V1, V2, V3 and V4 provided to the auxiliary electrowetting electrodes 120, 122, 124 and 126 respectively, based on a control signal 156 provided by the measurement circuit 144, such that an actual geometry of the fluid meniscus 132 conforms to a desired geometry of the fluid meniscus 132. The desired geometry for the geometry of the fluid meniscus 132 is denoted by a contact angle setpoint φ^e t. In this particular embodiment, φSit is a four dimensional vector, comprising references for each of the contact angles φ1# φ2, φ3 (not shown) and φ4 (not shown) between the fluid meniscus 132 and the wall parts 108, 110, 112 and 114 respectively. The contact angle setpoint φ^ is translated into a capacitance setpoint C.st by way of a translation table 158. The capacitance setpoint C-g. is a four dimensional reference vector for the capacitances C1, C2, C3 and C4, i.e. the capacitances between the main electrowetting electrode and the auxiliary electrowetting electrodes 120, 122, 124 and 126. The translation table 158 may for example be experimentally obtained. At a four dimensional summation point 160, the capacitance setpoint C^έt is compared to a measured capacitance C^ ^^ , wherein C^,,^,^ is a vector comprising the capacitances C1, C2, C3 and C4 as determined by the measurement circuit 144. A controller 162 provides a four dimensional voltage control signal 164 to the voltage source 134, responsive to a difference Δ between C^ and C.^,eΛSU^ea , i.e. Δ = C^- ; - ^s,-^-,,-^,- . The voltage control signal 164 is also provided to the measurement circuit 144 in order to enable said measurement circuit to perform the calculation according to equation [3]. Subsequently the voltage source 134 provides the aforementioned voltages V1, V2, V3 and V4 to the auxiliary electrowetting electrodes 120, 122, 124 and 126, respectively. It is noted that merely for the purpose of this specific embodiment, the voltage control circuit 154 is dedicated to controlling a number of four voltages. That is there is no restriction on the number of voltages controlled the aforementioned voltage control circuit, provided said number is at least two.
A second embodiment of the invention is depicted in Figure 3 A, Figure 3B and Figure 4. Figure 3A depicts a cross section of a device 302 whereas Figure 3B displays a bottom view of said device 302. The device 302 comprises a fluid chamber 304, the fluid chamber 304 having a top 306 and a wall having wall parts 308, 310, 312 and 314, see Figure 3B. The wall parts 308, 310, 312 and 314 are provided with an insulating layer 316 for preventing shortcuts, see Figure 3A. In alternative embodiments the fluid chamber 304 may have a conical or a cylindrical wall, or any other suitable wall. The device 302 comprises a grounded main electro wetting electrode 318 attached to the top 306. In this particular example, the device 302 comprises two auxiliary electrowetting electrodes 320 and 322, which partially surround the fluid chamber 304 and which are attached to the wall parts 308 and 312, respectively. As indicated in Figure 3 A, the fluid chamber 304 comprises a first fluid 324 and a second fluid 326, which first and second fluids are mutually immiscible and are in contact with each other over a fluid meniscus 328. The first fluid 324 is electrically conductive and the second fluid 326 is electrically insulating. That is, first fluid 324 has a first electrical conductivity and the second fluid 326 has a second electrical conductivity, wherein the second electrical conductivity is significantly small compared to first electrical conductivity. Ideally, the second electrical conductivity is nihil.
During use voltages Vi and V2 are applied to the auxiliary electrowetting electrodes 320 and 322 by a voltage source 330. Through providing said voltages to the auxiliary electrowetting electrodes 320 and 322, a geometry of the fluid meniscus 328 is controlled via controlling contact angles land . The contact angle iis defined as the angle between the fluid meniscus 328 and the wall part 308, the contact angle is accordingly defined as being the angle between the fluid meniscus 328 and the wall part 312. In this example, it is the object to generate an upwardly facing geometry for the fluid meniscus 328, that is, seen from the bottom of the fluid chamber 304. Said contact angles are controlled through employing the electrowetting effect. The contact angles land are estimated through measuring the capacitances between the main electrowetting electrode 318 and each of the auxiliary electrowetting electrodes 320 and 322. Namely, the aforementioned capacitances are determined by the dimensions of the areas 332 and 334 of the electrowetting electrodes covered with the electrically conductive first fluid 324, wherein the areas 332 and 334 covered with the electrically conductive first fluid 324, proportionally change with the contact angles φi and φ2. The voltages Vi and V2 are alternatingly disconnected by way of a first voltage switch 331 and a second voltage switch 333, respectively. During a period of time ti, voltage Vi is connected whereas voltage V2 is disconnected. During a period of time t2, voltage V2 is connected whereas voltage Vi is not connected. Hence, one of the auxiliary electrowetting electrodes 320 and 322 is driven at a time, i.e. the periods ti and t2 are consecutively recurring.
In this embodiment, the device 302 is mounted in an optical storage drive for the purpose of real time controlling the direction of a laser beam 338 generated by the laser 340, see Figure 3A. For that purpose, the first fluid 324 has a first refractive index and the second fluid 326 has a second refractive index, wherein the first and second refractive are mutually different. The discontinuity in terms of refractive indices occurring at the fluid meniscus 328 will redirect the laser beam 338 provided by the laser 340. Hence, through controlling the contact angles Cp1 and φ2, the laser beam 338 is being focused towards a target location on e.g. an optical storage disc.
A measurement circuit 342 and the voltage source 330 are remotely located from the electro wetting lens 302, as depicted in Figures 3A and 3B. The measurement circuit 342 is arranged for separately measuring the capacitances between the main electrowetting electrode 318 and the auxiliary electrowetting electrodes 320 and 322, which capacitances are denoted by Ci and C2, respectively. The measurement circuit 342 and the voltage source 330 are physically connected to the device 302 preferably by way of co-axial cables 344, 346 and 348. Although the co-axial cables 344, 346 and 348 are shielded such that no mutual coupling between the co-axial cables comes into being, said co-axial cables introduce significant parasitic capacitors having capacitances Cp1, Cp2 and Cp3. Said parasitic capacitances are non-constant due bending movements of the co-axial cables 344, 346 and 348 during use.
Figure 4 depicts a model for the electrical behavior of the device 302. In addition, Figure 4 depicts the measurement circuit 342 applied in the device of Figures 3 A and 3B in more detail. For the purpose of separately measuring the capacitances Ci and C2, a measurement circuit 402 comprises a switching circuit 404. The switching circuit 404 comprises a first measuring capacitor 406 having a known capacitance Cmeas, and a second measurement capacitor 408 having a known capacitance x£V,s-_-, wherein % *= 1. The switching circuit 404 further comprises a capacitance switch 410 for driving the first and second measurement capacitors 406 and 408 in an alternating and mutually excluding way. By way of a first voltage switch 407 and a second voltage switch 409, the voltages Vi and V2 are alternatingly disconnected, respectively.
During period tls it holds that V2 is not connected. During a first part of period ti the capacitance switch 410 enables the first measurement capacitor 406, during a second part of period ti the capacitance switch 410 enables the second measurement capacitor 408. Therefore during the first part of period tl s a voltage r,,,SJ.sl, which voltage characterizes a signal 412 during the first part of period tl s the signal 412 being representative for the capacitances Ci and C2, is given by the following equation:
/LUC1 S V1 - !*„. ?ll4-1 ^ = _fω; Cp5 + Csz 'tlv3ai ÷ i^C^- ^l-'^.-i [4],
C^C-'-
C Rl = [5].
Likewise, in case the second measurement capacitor 408 is enabled, the following expression is obtained for a voltage IV^^ , which voltage is characterizing the signal 412 during the second part of period ti :
Considering equations [4] and [6], the resultant capacity CR2 is assumed to remain constant during period ti. Period ti is associated with a sample frequency of typically 1 kHz to 1 MHz, which is a frequency significantly larger than the bandwidth of the first and second fluids 324 and 326 comprised in the fluid chamber 304. Hence, the latter assumption is justified and consequently, it does not reduce an accuracy associated with the measuring of the capacitances Ci and C2. Combining equations [4] and [6], a system of two linear equations is obtained. The latter system incorporates two unknowns, i.e. the capacitance Ci and the parasitic capacitance CP3. Said system of linear equations can be solved for the unknown capacitance C1, which solution is given by the following equation:
C = ^' i£SzΞzh*≡^™≡ [7].
During a first part of period t2 the capacitance switch 410 enables the first measurement capacitor 406, during a second part of period t2 the capacitance switch 410 enables the second measurement capacitor 408. During period t2, it holds that Vi is disconnected. Therefore during the first part of period t2, a voltage IT«^ajS, which voltage characterizes the signal 412 during a first part of period t2, is given by the following equation:
c« = έ≡§: [9]-
Likewise, in case the second measurement capacitor 408 is enabled, the following expression is obtained for a voltage i ™?-r, , which voltage is characterizing the signal 412 during the second part of period t2:
^c2[V2 - 1 ;TO ; = :^ cF3 + Q1U^- +;- ^^^ [io].
Considering equations [8] and [10], the resultant capacity CR1 is assumed to remain constant during period t2. Like period t2, period ti is associated with a sample frequency of typically 1 kHz to 1 MHz, which is a frequency significantly larger than the bandwidth of the first and second fluids 324 and 326 comprised in the fluid chamber 304. Hence, the latter assumption is justified and consequently, it does not reduce an accuracy associated with the measuring of the capacitances Ci and C2. Combining equations [8] and [10], a system of two linear equations is obtained, the system incorporating two unknowns namely the capacitance C2 and the parasitic capacitance CP3. The latter system of linear equations can be solved for the unknown capacitance C2, which solution is given by the following equation:
^ (\ - i
The measurement circuit 402 further comprises a multiplexer 414 which employs time domain multiplexing. The switching circuit 404 cooperates with an input 413 of the multiplexer 414. The multiplexer 414 duplicates the signal 412 which is representative for the capacitances Ci and C2, to a plurality of signals 416 and 418 which are each indicative for the capacitances Ci and C2. The number of duplications corresponds to the number of auxiliary electro wetting electrodes. After duplication, the signals 416 and 418 are demodulated by demodulation signals by filters 420 and 422, respectively. The filters 420 and 422 are driven by demodulation signals, in this particular case the demodulation signals are square wave signals. Here a square wave signal is considered a signal that can attain two values; a low value and a high level. In this particular example, the low value is set equal to zero. A first square wave signal driving the filter 420 attains its high value during period ti whereas a second square wave signal driving the filter 422 attains its high value during period t2. Hence, the first square wave signal attains its high value when voltage Vi is connected whereas the second square wave signal attains its high value when V2 is connected. As a result, demodulated signals 424 and 426 can only be related to the capacitances Ci and C2, respectively.
Referring to Figures 3A and 3B, a voltage control circuit 350 is depicted. The voltage control circuit 350 is arranged for the purpose of controlling the voltages Vi and V2 provided to the auxiliary electrowetting electrodes 318 and 320 respectively, based on a control 343 signal provided by the measurement circuit 342, such that an actual geometry of the fluid meniscus 328 conforms to a desired geometry of the fluid meniscus 328, see Figure 3A.
The desired geometry for the geometry of the fluid meniscus 328 is denoted by a contact angle setpoint φS£ t, wherein φsst is a two dimensional vector in case of this specific embodiment, comprising references for each of the contact angles φi and φ2 between the fluid meniscus 328 and the wall parts 308 and 312 respectively. The contact angle setpoint φss t is translated into a capacitance setpoint £\_g ; by way of a translation table 352. In this specific example, the capacitance setpoint £.β, is a two dimensional vector comprising references for the capacitances Ci and C4, i.e. the capacitances between the main electrowetting electrode 318 and the auxiliary electrowetting electrodes 320 and 322. The translation table 352 may for example be experimentally obtained. At a two-dimensional summation point 354, the capacitance setpoint £_. is compared to a measured capacitance £--,«.-?„"«-■ , wherein C-,-*,-^ ^ is a two dimensional vector comprising the capacitances Ci and C2 as determined by the measurement circuit 342. A controller 356 provides a two dimensional voltage control signal 358 to the voltage source 330, responsive to a difference Δ between C-.g: and C^g^^gd , i.e. _1 = C^. - Cj^^^..^ • Subsequently the voltage source 330 provides the aforementioned voltages Vi and V2 to the auxiliary electrowetting electrodes 320 and 322 respectively. The voltage control signal 358 is also provided to the measurement circuit 342 in order to enable said measurement circuit to perform the calculation according to equations [7] and [H].
Figure 5 schematically depicts an embodiment of the method according to the invention by way of a flowchart. The method is arranged for measuring a geometry of a fluid meniscus between an electrically conducting first fluid and an electrically insulating second fluid comprised in a fluid chamber, wherein the fluids are mutually immiscible.
The method comprises a step 502 of providing a voltage between a main electrowetting electrode located in a main plane and auxiliary electrowetting electrodes partially surrounding the fluid chamber and being located in an auxiliary plane not being the main plane. The method further comprises a step 504 of separately measuring capacitances between the main electrowetting electrode and at least two of the auxiliary electrowetting electrodes by a measurement circuit comprising a multiplexer. The method comprises a step 506 of controlling the voltage provided between the auxiliary electrowetting electrodes based on a signal provided by the measurement circuit. While the invention has been illustrated and described in detail in the drawings and in the foregoing description, the illustrations and the description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. For instance, the device and the method according to the invention impose no restriction on the number of auxiliary electrowetting electrodes, provided this number is not less than 2. Furthermore, the first fluid's speed of sound as well as the first fluid's refractive index may be different from the second fluid's speed of sound and the second fluid's refractive index, respectively. In addition to that, a measurement comprising an operational amplifier provided with a negative feedback loop, which negative feedback loop is provided with a measurement capacitance, wherein the operational amplifier is arranged for cooperation with an input of the multiplexer, may be employed together with time domain multiplexing. It is noted that the device to the invention and all its components can be made by applying processes and materials known per se. In the set of claims and the description the word "comprising" does not exclude other elements and the indefinite article "a" or "an" does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope. It is further noted that all possible combinations of features as defined in the set of claims are part of the invention.
WO2006035407A1 28 Sep 2005 6 Apr 2006 Koninklijke Philips Electronics N.V. Controllable optical lens
WO2006048187A1 28 Oct 2005 11 May 2006 Eastman Kodak Company Lens with variable focal length and symmetry
EP0097570A2 * 9 Jun 1983 4 Jan 1984 Banque De France Device for checking the thickness of dielectric sheet material
US20070299625 * 30 Apr 2007 27 Dec 2007 Walter Englert Concept for determining the position of a movable object by means of magnetic fields
International Classification G02B3/14, G01B7/00
Cooperative Classification G01B7/28, G02B26/005, G01R27/2605
European Classification G02B26/00L1, G01B7/28
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