NL1039730C2

NL1039730C2 - Method and device for measuring dielectric properties of individual fluid samples present in an array of cavities in a stack of printed circuit boards.

Info

Publication number: NL1039730C2
Application number: NL1039730A
Authority: NL
Inventors: Natalia Hoog; Mateo Jozef Jacques Mayer
Original assignee: Stichting Wetsus Ct Excellence Sustainable Water Technology; Smart Frequencies B V
Priority date: 2012-07-15
Filing date: 2012-07-15
Publication date: 2014-01-16

Description

Method and device for measuring dielectric properties of individual fluid samples present in an array of cavities in a stack of printed circuit boards

The present invention relates to a method and device for measuring the dielectric properties of individual fluid samples present in an array of wave guide cavity resonators 5 characterized by the wireless coupling of electromagnetic energy into the array of cavities, by placing said wave guide cavity resonators in the dielectric of a stripline, connected to a function generator, switching means to electrically connect each wave guide cavity resonator individually to a spectrum analyzer or rectifier and at least a microcontroller, connected to the function generator and / or the spectrum analyzer and / or the rectifier, for 10 automated measurement of the dielectric properties of the fluïdum in each individual wave guide cavity resonator.

Introduction

The present invention relates to a method and device for inline measurement of the 15 properties of a fluïdum, without the use of chemicals, using the physical principles of transmission line technology. More specifically, the present invention relates to a method and device to measure the dielectric properties of fluids, fluid - solid suspensions, fluid -gas suspensions and solid - gas suspensions. Even more specifically, the present invention relates to a method and device to assess the properties of water, such as drinking 20 water, waste water and industrial process water.

Many prior art methods to determine the quality of drinking water, process water and industrial water are labor intensive, require the use of chemicals for chemical and / or biological analysis and are offline. As a result, many prior art water analysis techniques are expensive and introduce a time delay before measurement information is available.

25 A promising technique to track changes in the quality of a water stream is to asses its dielectric properties. Existing prior art methods to measure the dielectric properties of a solution are based on classic capacitance measurements in discrete elements such as a plate capacitor. These methods are offline and suffer from relatively large parasitic capacitance and / or parasitic inductance, thereby limiting the sensitivity of the 30 measurements, and / or require a relatively complex measurement set-up, involving relatively high investment cost. A recently developed technique for inline measurement of the dielectric properties of fluids is based on transmission line technologie. A fluid sample is applied as dielectric in a transmission line resonator, such as a coaxial stub resonator or a stripline resonator. Subsequently, the electric properties of the transmission line resonator, 35 further on referred to as stub resonator, are characterized by an amplitude versus frequency plot, further on referred to as A-f plot. The shape of the A-f plot is determined by the dielectric properties of the fluid under investigation. By the use of transmission line 1039730 2 theory i.e., by solving the telegrapher's equations, the dielectric properties of a fluid i.e, its complex dielectric permittivity and loss tangent as a function of frequency, can be derived directly from the A-f plot. More qualitatively, an A-f plot provides a fingerprint of the fluid and can be used to track changes of the fluid composition and to use these changes in an early 5 warning system.

The technology according to the present invention deals with a unique combination of stripline resonator design and design of resonator cavities in the dielectric of the stripline that are electromagnetically coupled with the stripline, resulting in a very sensitive and specific sensor system. The sensor technology according to the present invention is based 10 on printed circuit board (PCB) technology so that the sensor according to the present invention can be produced in a reliable, reproducible and cost effective way.

Additionally, the technology according to the present invention deals with a unique combination of dipole antenna technology and wave guide technology, resulting in a very sensitive and specific sensor system operating in a broad frequency range. The sensor 15 technology according to the present invention is feasible for application on large scale i.e., for inline measurement of dielectric properties of a fluïdum in piping systems in process industry as well as for application on very small scale i.e., for inline analysis of small fluid samples using printed circuit board (PCB) technology.

Additionally, the technology according to the present invention deals with a unique 20 combination of stub resonator design and electrical interface connections from the stub resonator to the transmission lines of the measurement set-up, further on referred to as "matched sensor system". The matched sensor system according to the present invention provides a very sensitive and reliable device to assess the dielectric properties of a fluïdum. Additionally, the matched sensor system can be produced in a reproducible and cost 25 effective way.

Additionally, the technology according to the present invention deals with a method and device for measuring the dielectric properties of individual fluid samples present in an array of wave guide cavity resonators characterized by the wireless coupling of electromagnetic energy into the array of cavities, by placing said wave guide cavity resonators in the 30 dielectric of a stripline, connected to a function generator, switching means to electrically connect each wave guide cavity resonator individually to a spectrum analyzer or rectifier and at least a microcontroller, connected to the function generator and / or the spectrum analyzer and / or the rectifier, for automated measurement of the dielectric properties of the fluïdum in each individual wave guide cavity resonator.

Description of the technology according to the present invention part 1

According to a first aspect, the present invention relates to a function generator FG. This 35 3 function generator preferably produces a sinus or square wave electrical signal with a frequency that can be adjusted in the range between 1 Hz and 50 GHz.

According to a second aspect, the present invention relates to a spectrum analyzer or a hf (high frequency) rectifier SA, preferably able to measure the amplitude of a sinus or square 5 wave electrical signal with a frequency in the range between 1 Hz and 50 GHz.

According to a third aspect, the present invention relates to a first PCB with a first stripline resonator on it. The definition of a stripline resonator in this document is any geometric shape on the PCB, that behaves as a transmission line, including a wire according the definition in this document or a ground plane according to the definition in this document.

10 According to a fourth aspect, the present invention relates to at least a first metal plated cavity or an array of metal plated cavities present in the dielectric of the first stripline. According to a fifth aspect, the present invention relates to at least a first metal connection point that is galvanically connected to the first metal plated cavity and that is located on the PCB surface and around the first metal plated cavity.

15 According to a fifth aspect, the present invention relates to at least a second PCB, said second PCB having at least a second metal plated cavity or an array of metal plated cavities at exactly the same PCB lay-out coordinates as the first PCB.

According to a sixth aspect, the present invention relates to at least a second metal plated cavity or an array of metal plated cavities at exactly the same PCB lay-out coordinates as 20 the cavities in the first PCB.

According to a seventh aspect, the present invention relates to means to stack and attach the second PCB onto the first PCB, whereby at least a first metal plated cavity in the first PCB is galvanically connected to at least a second metal plated cavity in the second PCB so that at least the connected individual first and second cavities merge into a third metal 25 plated cavity with a larger volume than the first metal plated cavity or the second metal plated cavity. The means to stack and attach the second PCB onto the first PCB may consist of, but are not limited to, glue, screws in accurately designed screw cavities in the PCBs, a resin like polyurethane resin and a hotmelt polymer like Pattex hotglue.

According to an eighth aspect, the present invention relates to at least the third metal 30 plated cavity being filled with the fluïdum under investigation.

According to a nineth aspect, the present invention relates to at least a microcontroller that is connected to the function generator or to the spectrum analyzer and equipped with software to automatically determine amplitude versus frequency plot (A-f) plots. The shape of the A-f plots reflect the dielectric properties of the fluidum under investigation.

35 Figure 1 gives a schematic overview of the technology according to the present invention. The numbers in figure 1 have relate to the following elements that were previously described in aspects one to nine: 4

1. First PCB

2. Second PCB, feasible for stacking onto the first PCB

3. Third PCB feasible for stacking onto the first PCB

4. First transmission line connector 5 5. First metal plated cavity, galvanically connected to a first metal connection point on the PCB surface, shown in figure 1 as the surface area between the 2 concentric circles of element 5.

6. First stripline resonator on the first PCB. It is noted that the first PCB may be plated and grounded on the backside. In that case, the PCB consists of a wire placed at a 10 fixed distance from a ground plane. Note that, in case a ground plane is applied, the cavities are NOT connected to the ground plane. It is also noted that the ground plane may be located on a second or third PCB.

The main aspects of the present invention have now been described. In the following, the aspects of the present invention will be further detailed. Also a number of preferred IS embodiments of the present invention will be explained.

Preferably the function generator FG and the spectrum analyzer SA have an internal resistance of 50 Ohm. The characteristic impedance of the stripline resonator preferably amounts 50 Ohm. All metal connections on the PCB are preferably gold plated. The length over diameter ratio of the cavities is preferably large than 1. The base resonant frequency 20 of the stripline resonator is preferably lower than that of the cavity or array of cavities. Preferably, the base resonant frequency of the stripline is a factor of 10 lower than the base resonant frequency of the metal plated cavities. More preferably, the base resonant frequency of the stripline is more than a factor 50 lower than that of the metal plated cavities. Preferably, the base resonant frequency of the stripline is in the range of 1 MHz to 25 200 MHz. Preferably, the base resonant frequency of the cavities is in the range of 100 MHz to 10 GHz.

In order to explain a number of preferred embodiments, a definition of a wire, a ground plane and a stub resonator is given.

In this document, a wire is defined as a metal containing conductor shaped as a cilinder, a 30 rectangular cuboid, a cuboid or any other 3D shape that may act as an electrical conductor. In this document, a ground plane is defined as any metal containing plane that may act as a conductor and / or shield for electromagnetic waves. In this document, the characteristic dimensions of a cilindrical wire are defined as the diameter of the wire and the length of the wire. In this document, the characteristic dimensions of a rectangular cuboid as defined as 35 the length of the cuboid, the width of the cuboid and the height of the cuboid. In this document, the characteristic dimensions of any other wire are defined as the value of the minimum number of mathematic parameters that are required to exactly define the 5 dimensions of that wire. In this document, a ground plane is defined as any metal containing plane that may act as a conductor and / or shield for electromagnetic waves. In this document, the characteristic dimensions of the ground plane are defined as the length of the ground plane and the width of the ground plane in case the ground plane is a 5 rectangle. The characteristic dimensions of any other ground plane than a rectangular ground plane are defined as the value of the minimum amount of mathematical parameters that are required to define the exact shape of the ground plane. In this document, a stub resonator is defined as a resonator based on any type of transmission line such as, but not limited to, a coaxial transmission line resonator, a stripline or any combination of striplines 10 and / or coaxial transmission line resonators.

In a first preferred embodiment, the ground connection of the first stripline resonator on the first PCB is limited to the ground of the first transmission line connector that is mounted on the PCB.

In a second preferred embodiment, the ground connection of the first stripline resonator on 15 the first PCB is a ground plane. It is noted that the cavitities in the dielectric of the first stripline resonator are not galvanically connected to this ground plane.

In a third preferred embodiment, the first stripline resonator consists of a first discrete wire, placed at a fixed distance from 2 parallel wires, such that the first discrete wire is present between the other 2 wires. Preferably, the 3 wires are present in the same plane. It is noted 20 that also so called "off center" transmission lines in which the first discrete wire is not placed exactly in the center between the other 2 discrete wires make part of the present invention.

In a fourth preferred embodiment of the present invention, the first stripline resonator on the first PCB consists of 2 discrete parallel wires. Preferably, the 2 parallel wires are present in 25 the same plane.

After explaining the preferred embodiments, the working principle of the new sensor system according to the present invention will now be further detailed. A function generator and a spectrum analyzer or rectifier are connected to the first stripline resonator on the first PCB. Subsequently, the function generator is programmed to produce a number of sinus or 30 square wave signals, with a known amplitude, and different frequencies. At each frequency, the attentuation of the signal is measured by the use of the spectrum analyzer or rectifier so that an amplitude versus frequency plot (A-f plot) is produced. From transmission line theory, it is known for a person skilled in the art, that the first stripline resonator has a base resonant frequency and higher harmonics. The third metal plated cavity of the array of 35 metal plated cavities, formed by stacking at least the first PCB and the second PCB, behaves like a half wavelength resonator. Since the third metal plated cavity is at least partly filled with the fluïdum under investigation, the resonant frequency of the third metal 6 plated cavity or the array of metal plated cavities will change with changes in composition of the fluidum under investigation. The amount of electromagnetic energy that is coupled from the first stripline resonator into the third metal plated cavity or the array of metal plated cavities, where it is dissipated for the greater part, is high at the resonant frequency of the 5 third metal plated cavity or the array of metal plated cavities. The amount of electromagnetic energy that is coupled from the first stripline resonator into the third metal plated cavity or the array of metal plated cavities, where it is dissipated for the greater part, is maximum in case a higher harmonic resonant frequency coincidences with the resonant frequency of the third metal plated cavity or the array of metal plated cavities.

10 From the reasoning above, it can be concluded that the system according to the present invention can be designed such that it is very sensitive to small changes in dielectric properties of the fluidum under investigation. Additionally, the reasoning above provides design criteria for the first stripline and for the third metal plated cavity or the array of metal plated cavities: 15 «the first stripline resonator should have a high quality factor, especially at higher harmonics, in order to efficiently couple electromagnetic energy into the cavities.

• the length of the cavities should be sufficiently long in order to ensure that the base resonant frequency of the cavities is in the frequency range at which higher harmonics of the first stripline resonator are still stable.

20 · by the use of a Maxwell equation solver, the geometry of the first stripline resonator and the cavities can be designed iteratively and such that their (higher harmonic) resonant frequencies will coincidence at, at least one, frequency. Around this frequency, the sensor is very sensitive to small changes in the dielectric properties of the fluidum under investigation.

25 · by designing cavities of different length, simply by the use of additional PCBs in the stack that have partially unplated cavities or no cavities at all, a sensor is obtained with high sensitivity in a broad frequency range.

It is noted that the technology according to the present invention is very feasible to detect bacterial growth in the cavities. By filling the cavities with a gel or medium for bacterial 30 growh and by placing the sensor into a fluid under investigation, the bacterial growth potential of a fluid under investigation can be determined, see also figure 2 in which object #7 stands for a bacterium. By filling the cavities with a polymer that selectively adsorbs or absorbs components present in a fluid under investigation, the technology according to the present invention can be applied to detect very low concentrations of those components in 35 a fluid. A commercially available polymer that is very feasible to be applied as polymer dielectric in the metal plated cavities according to the present inventions is a propylene macroporous polymer of the type Accurel.

7

Non limiting examples of a fluidum feasible to be investigated with the technology according to the present invention are drinking water, waste water, food.

Description of the technology according to the present invention part 2 5 According to a first aspect, the present invention relates to a function generator FG. This function generator preferably produces a sinus or square wave electrical signal with a frequency that can be adjusted in the range between 1 Hz and 50 GHz.

According to a second aspect, the present invention relates to a spectrum analyzer or a hf (high frequency) rectifier SA, preferably able to measure the amplitude of a sinus or square 10 wave electrical signal with a frequency in the range between 1 Hz and 50 GHz.

According to a third aspect, the present invention relates to a first dipole element connected to the first electrical connection point of both the function generator and the spectrum analyzer or rectifier.

According to a fourth aspect, the present invention relates to a second dipole element 15 connected to the second electrical connection point of both the function generator and the spectrum analyzer or rectifier.

According to a fifth aspect, the present invention relates to a volume, at least partly filled with the dielectric under investigation, that is placed between the first dipole element and the second dipole element.

20 According to a sixth aspect, the present invention relates to at least a microcontroller that is connected to the function generator and / or the spectrum analyzer or rectifier and that is equipped with software for automatic measurement of an amplitude versus frequency plot. Now that the main aspects of the technology according to the present invention have been explained, a number of embodiments of the technology according to the present invention 25 will be explained.

In a first preferred embodiment, the technology according to the present invention relates to a first conductive metal or metal coated cilinder, that can be filled with a fluidum and that is used as a first dipole element. The first conductive cilinder is on one end connected to a second non conductive cilinder. The other end of the second non conductive cilinder is 30 connected to a third conductive cilinder which has preferably the same length as the first conductive cilinder. Subsequently, the fluidum under investigation is pumped through the series of the first conductive cilinder, the second non conductive cilinder and the third conductive cilinder. Figure 3 gives a schematic overview of the construction according to this first preferred embodiment. For the first preferred embodiment, the numbers 1 and 2 in 35 figure 3 should be ignored. Number 3 relates to the fluidum under investigation that is pumped through the series of cilinders. Number 4 stands for one of the connection points that are to be connected with the function generator and the spectrum analyzer. For the 8 sake of completeness it is mentioned that the function generator, the spectrum analyzer or rectifier and the dipole construction according to figure 3 are preferably electrically connected in parallel. By the use of at least a microcontroller and software, an A-f plot is automatically produced. Since the properties of the dipole antenna depend on the dielectric 5 between the first conductive cilinder and the second conductive cilinder, the shape of the A- f plot reflects the dielectric properties of the fluid under investigation. It is noted that below at critical length of the second non conductive cilinder, the series of the first, second and third cilinder not only perform as a dipole antenna but also as a wave guide cavity whereby the cavity is supplied with energy through the function generator. Since the resonant 10 frequency of the wave guide cavity is different from that of the dipole antenna, the system will have a large number of resonant frequencies. This results in a sensor that is very feasible for impedance spectroscopy and determination of the dielectric properties of the fluïdum under investigation, resulting in a much more detailed fingerprint of the fluidum under investigation than a separate dipole or a separate cavity. Finally, it is noted that the 15 wave guide cavity, as a resonator according to the first preferred embodiment, has very interesting properties towards conductive or slightly conductive media. On one hand, the conductivity of the fluidum under investigation will result in an improved performance of the cavity resonator, since the second non conductive cilinder (the middle section in figure 3) will behave more like a wave guide since it has "conductive walls due to the conductivity". 20 On the other hand, the quality factor of the cavity resonator will decrease as a result of dielectric losses in the resonator. This at first sight unexpected behavior, appears to make the system, according to the first preferred embodiment, very reponsive to different conductive dielectrics in a broad conductivity range. A second effect is that the response of the dipole antenna to conductivity is different from that of the cavity resonator and, that the 25 differences in response between dipole antenna and cavity resonator, are also frequency dependent. As a result, the A-f plots obtained with the system according to the present invention provide very specific fingerprints of a dielectric. Finally, it is noted that the efficiency of the cavity resonator is determined by wave reflections at the end of the cilindrical ends of the cavity. Placing a conductive wall at both ends of the cilindrical cavity, 30 such that its ends are at least partly covered with a conductive surface, will drastically increase the quality factor of the cavity resonator. Placing any kind of conductive wall at one end of the cavity resonator or at both ends of the cavity resonator such that its surface is perpendicular to the axial length coordinate of the cavity cilinder, expressly is part of the technology according to the present invention. A practical way to realize a conductive wall 35 for recfection of electromagnetic waves in the cavity, is to mount a perforated metal plate at either one end or both ends of the cavity resonator. In this case, the fluidum can flow through the perforated holes so that the sensor can still be used as an inline flow through 9 sensor. Also, bending or narrowing of the cilinder near its ends may result in the desired reflections. It is noted that both the design with reflection layer and the design without reclection layer are part of the technology according to the present invention.

In a second preferred embodiment, the cilinders in the system according to the first 5 embodiment are filled with particles, see also figure 4 in which number 5 stands for particles. These particles preferably consist of glass beads, activated carbon, polymer particles or ion exchange resin or quartz sand due to its sorption and monosize properties.

It is expressly noted that, by the system according the present invention, it is possible to measure dielectric properties of heterogeneous mixtures using either homogenious 10 distribution or chaotic distribution or semichaotic distribution or layer structure dielectric mixtures laws. In case of glass beads, the sensor can be used as a biofilm monitor for fluid flowing through the sensor. In case a biofilm is formed on the glass beads, the sensor will detect a change in dielectric properties of the dielectric in the cilinders. Since the biofilm contains organic components, a capacitive cell membrane and since it adds frequency 15 dependent conductivity to the fluidum in the cilinders, the sensor system according to the present invention will produce a detailed and unique fingerprint (A-f plot) of the system with biofilm. An additional advantage of using glass beads is that samples of the glass beads can be taken. The glass beads can be analyzed on the presence of biomass on the surface using a light microscope or by analyzing the concentration of ATP on the glass surface. By 20 relating different ATP concentrations to the corresponding A-f plots, the biofilm mass on the glass beads can be determined quantitatively as a function of time from automatically measured A-f plots. Analogously, the cilinders in the system according to the first embodiment can be filled with ion exchange resin, so that the load degree of ion exchange resin can be determined quantitatively as a function of time from automatically measured A-25 f plots. In case the cilinders in the system according to first embodiment are filled with polymer particles, such as macroporous polypropylene polymers, chemical compounds can be absorbed by the particles or can adsorp onto the particle surface. As a result, it is possible to detect traces of pollutants in water and to measure the concentration of these pollutants in water as a function of time. It is noted that also a coaxial stub resonator can be 30 filled with glass beads or polymer particles or ion exchange resin. In case a coaxial stub resonator is filled with glass beads, it can be used as a biofilm monitor as well. By taking samples of the glass beads as described above, a quantitative relation can be determined between the biofilm mass in the coaxial stub resonator and the shape of the A-f plot obtained when the coaxial stub resonator is connected to a function generator and a 35 spectrum analyzer or rectifier. Application of a coaxial stub resonator filled with glass particles as a biofilm monitor with sampling possibilities, expressly makes part of the technology of the present invention.

10

In a third preferred embodiment of the present invention, the fluïdum under investigation is not pumped through the series of the first conductive cilinder, the second non conductive cilinder and the third conductive cilinder. Instead, the second non conductive cilinder is left out of the system, see also figure 5. The dielectric under investigation is pumped between 5 the first conductive cilinder and the second conductive cilinder, see fluid flow number 3 in figure 5. Both cilinders in figure 5 refer to the dipole conductors. Number 5 in figure 5 stands for the connection points of both dipole conductors.

In a fourth preferred embodiment of the present invention, a suspension of particles is pumped between both dipole conductors, see also figure 6. Number 6 in figure 6 stands for 10 a particle.

In a fifth preferred embodiment of the present invention, the system in figure 5 is immobilized in a cube by adding a resin, such as a polyurethane resin to it. Subsequently, a hole indicated as number 4 in figure 5 is drilled into the cube, such that fluid flow number 3 becomes possible.

15 In a sixth preferred embodiment of the present invention, the system in figure 3 is realized by stacking printed circuit boards. For this purpose metal plated cavities are made in a series of PCBs. Each PCB has the metal plated cavities at exactly the same PCB coordinates. Around each metal plated cavity, a first metal connection point is present, whereby said first metal connection point is galvanically connected to the first metal plated 20 cavity, and located on the PCB surface and around the metal plated cavity. By stacking the PCBs, a cilinder such as indicated with number 2 in figure 3 is obtained. Subsequently, a number of PCBs with cavities, that are not metal plated and that are positioned on the PCB at exactly the same coordinates as the metal plated cavities, are added to the stack. After this, a number of PCBs with metal plated cavities is added to the stack. The result is a 25 series of a first metal plated dipole cilinder, a second non metal plated dipole cilinder and a third metal plated dipole cilinder as shown in figure 3. It is noted that also this system can be used as a dipole antenna system and as a cavity at the same time, resulting in a very sensitive sensor system. The wire connections such as indicated by number 4 in figure 3, can, for example, be a wire in the last PCB of the stack PCBs forming the first metal plated 30 dipole cilinder and a wire in the last PCB of the stack of PCBs forming the third metal plated dipole cilinder. An important advantage of applying PCB technology to realize a sensor with the technology according to the present invention is the high reproducibility and cost effectiveness at which a sensor can be produced. The high reproducibility at which the sensor can be produced opens possibilities for miniaturization of the system. Since smaller 35 sensor dimensions result in higher resonant frequencies, the measurements can be performed at relatively high frequencies providing extra information on the dielectric properties of the fluïdum under investigation.

11

Now the technology according to the present invention has been explained in detail, a number of preferred application conditions is mentioned.

Preferably, the dipole is operated at a frequencies between 1 MHz and 10 GHz. Preferably, the wave guide cavity resonators are operated at a frequency between 10 MHz and 100 5 GHz. Preferably, all PCB connections are gold plated.

Non limiting examples of a fluïdum feasible to be investigated with the technology according to the present invention are drinking water, waste water, food.

Description of the technology according to the present invention part 3 10 According to a first aspect, the present invention relates to a function generator FG. This function generator preferably produces a sinus or square wave electrical signal with a frequency that can be adjusted in the range between 1 Hz and 50 GHz.

According to a second aspect, the present invention relates to a spectrum analyzer or a hf (high frequency) rectifier SA, preferably able to measure the amplitude of a sinus or square 15 wave electrical signal with a frequency in the range between 1 Hz and 50 GHz.

According to a third aspect, the present invention relates to a first transmission line that is connected to the function generator FG.

According to a fourth aspect, the present invention relates to a second transmission line that is connected to the spectrum analyzer SA.

20 According to a fifth aspect, the present invention relates to a printed circuit board (PCB). According to a sixth aspect, the present invention relates to a first transmission line connector, connecting the first transmission line to the PCB.

According to a seventh aspect, the present invention relates to a second transmission line connector, connecting the second transmission line to the PCB.

25 According to an eighth aspect, the present invention relates to a stub resonator according to definition in this document, that is printed on the PCB.

According to a nineth aspect, the present invention relates to a first electrical interface connection E1, connecting the stub resonator to the first transmission line interface on the PCB. Interface E1 is a transmission line printed on the PCB with a characteristic 30 impedance that preferably varies with the length coordinate of the transmission line, thereby matching the characteristic impedance of the transmission line from the function generator FG to the characteristic impedance of the stub resonator.

According to a tenth aspect, the present invention relates to a second electrical interface connection E2, connecting the stub resonator to the second transmission line interface on 35 the PCB. Interface E2 is a transmission line printed on the PCB with a characteristic impedance that preferably varies with the length coordinate of the transmission line, thereby matching the characteristic impedance of the transmission line from the spectrum 12 analyzer SA to the characteristic impedance of the stub resonator.

According to an eleventh aspect, the present invention relates to at least one hole and preferably more holes in the PCB. The holes are unplated (no metal coating on the "walls of the holes") and positioned in the active part of the stub resonator i.e., such that at least part 5 of the holes make part of the dielectric determining the electrical properties of the stub resonator. Preferably, the dielectric under investigation is at least partly present in the holes and consists for more than 10 percent by volume of a fluid.

Figure 7 gives a schematic overview of the technology according to the present invention. The numbers in figure 7 relate to the following elements that were previously described in 10 aspects one to eleven: 1. Function generator F1 2. First transmission line 3. First transmission line connector 4. First electrical interface connector E1 15 5. Stub resonator 6. Second electrical interface connector E2 7. Second transmission line connector 8. Second transmission line

9. Spectrum analyzer SA

20 10. Hole in the PCB dielectric

The main aspects of the present invention have now been described. In the following, the aspects of the present invention will be further detailed. Also a number of preferred embodiments of the present invention will be explained.

Preferably, the function generator FG (#1 in figure 7) and the spectrum analyzer SA (#9 in 25 figure 7) have an internal resistance of 50 Ohm. The characteristic impedance of the first transmission line (#2 in figure 7) and the second transmission line (#8 in figure 7) preferably amounts 50 Ohm. Connectors E1 (#3 in figure 7) and E2 (#7 in figure 7) preferably have a characteristic impedance of 50 Ohm. The stub resonator (#5 in figure 7) preferably has a characteristic impedance of 50 Ohm. However, it is noted that the characteristic impedance 30 of the stub resonator depends on the dielectric present in the holes in the active part of the PCB (#10 in figure 7). Therefor, it will depend on the dielectric present in the holes, whether or not the stub resonator is matched to the rest of the measuring set-up. Additionally, it is noted that, from a construction point of view, it may be feasible to design a stub resonator with a characteristic impedance that is considerably different from that of the function 35 generator FG, spectrum analyzer SA, transmission lines and connectors.

Now the technology according to the present invention has been explained, a number of additional remarks with respect to figure 7 are made. The hole (#10) in figure 7 is can be 13 placed at different positions in the dielectric of the stripline, for example at position 5. Preferably, multiple holes are made in the resonator. The solid line (wire) cut in 2 pieces by hole 10, preferably has exactly the same length as both parallel wires in figure 7. Hole 10 is preferably placed between the solid line and one of both parallel wires without damaging 5 any wire. Hole 10 can be plated as shown in figure 8. Also a ground plane can be applied on the backside of the PCB as shown in figure 9, whereby the hole in the PCB is not metal plated. Finally a ground plane can be applied on the backside of the PCB as shown in figure 10, whereby also the hole in the PCB is metal plated. Plating of the holes can be interesting in case the sensor is applied as a corrosion sensor. In case the plated holes 10 corrode, the A-f plot will change.

Example 1

Consider a measurement system with a function generator FG and spectrum analyzer SA, both with an internal resistance of 50 Ohm. The first and second transmission lines as well as the first and second transmission line connectors have a characteristic impedance of 50 15 Ohm. The stub resonator has, from a construction point of view, a characteristic impedance of 20 Ohm. In case the first electrical interface connection E1 and the second electrical interface connection E2 would be transmission lines with a characteristic impedance of 50 Ohm as well, radio waves would be reflected at the connection points of E1 and E2 with the stub resonator. This would result in a considerable decrease of the sensitivity of the 20 measurement system. Additionally, it would be very difficult to predict the behavior of the measurement system as a function of frequency so that interpretation of A-f plots becomes difficult. To overcome reflections at the connection point of the stub resonator, electrical interface connections E1 and E2 are designed such that their characteristic impedance is a function of their length coordinate. In this example, interface connection E1 has a 25 characteristic impedance of 50 Ohm at the first transmission line connector. Going from the first transmission line connector to the stub resonator, the characteristic impedance of the interface connection E1 gradually decreases from 50 Ohm to 20 Ohm at the stub resonator. Analogously, the characteristic impedance of E2 gradually increases from 20 Ohm to 50 Ohm going from the stub resonator to the second transmission line connector.

30 The gradual change of characteristic impedance of E1 and E2 as a function of its length coordinate is realized by changing the geometrical shape of the striplines as a function of their length coordinate using transmission line theory.

Surprisingly, it was found that a measuring system according to the present invention is very stable and insensitive to reflection even if the characteristic impedance of E1 and E2 35 near the stub resonator is NOT exactly matched to the characteristic impedance of the stub resonator. This is further explained in example 2.

14

Example 2.

Consider the same measurement system as in example 1. However, in example 2, the characteristic impedance of E1, going from the first transmission line connector to the stub resonator, gradually decreases from 50 Ohm to 30 Ohm at the stub resonator (and not to 5 20 Ohm as in example 1). Analogously, the characteristic impedance of E2 gradually increases from 30 Ohm to 50 Ohm going from the stub resonator to the second transmission line connector. Since the stub resonator has a characteristic impedance of 20 Ohm, there is an impedance mismatch of 10 Ohm at the connection point of E1 and E2 to the stub resonator. In spite of this impedance mismatch, the effect of wave reflections on 10 the accuracy and reliability of the measurement set-up appears to be very limited. Although E1 and E2 only provide limited impedance matching, the presence of E1 and E2 appears to be a very effective measure to avoid undesired wave reflections. In fact, limited impedance matching through E1 and E2 has a surprisingly stabilizing effect on the performance of the measurement set-up at different conditions. It is noted that, possibly also the direct 15 connection of the stub resonator to E1 and E2 i.e., through PCB wires instead of connectors with a finite length, contributes considerably to the reduction of wave reflections.

After the explanation in examples 1 and 2, a number of preferred embodiments will now be elucidated.

20 In a first preferred embodiment of the present invention, the function generator is software configurable by the use of a first microcontroller such as a PIC16F88. The spectrum analyzer preferably consists of a rectifier using a germanium type diode. The rectified signal is connected to an analog to digital converter of the first microcontroller. Since the frequency of the signal is already known (because it is software configurable), the A-f plot 25 can be generated automatically and communicated and stored onto an external device. Also an alarm can be generated automatically if the A-f plot deviates from a pre-defined reference plot.

In a second preferred embodiment of the present invention, the transmission lines on the PCB, including the stub resonator, consist of a discrete wire placed at a fixed distance over 30 a ground plane. In this document, a wire is defined as a metal containing conductor shaped as a cilinder, a rectangular cuboid, a cuboid or any other 3D shape that may act as an electrical conductor. In this document, a ground plane is defined as any metal containing plane that may act as a conductor and / or shield for electromagnetic waves. In this document, the characteristic dimensions of a cilindrical wire are defined as the diameter of 35 the wire and the length of the wire. In this document, the characteristic dimensions of a rectangular cuboid as defined as the length of the cuboid, the width of the cuboid and the height of the cuboid. In this document, the characteristic dimensions of any other wire are 15 defined as the value of the minimum number of mathematic parameters that are required to exactly define the dimensions of that wire. In this document, the characteristic dimensions of the ground plane are defined as the length of the ground plane and the width of the ground plane in case the ground plane is a rectangle. The characteristic dimensions of any 5 other ground plane than a rectangular ground plane are defined as the value of the minimum amount of mathematical parameters that are required to define the exact shape of the ground plane.

In a third preferred embodiment of the present invention, the transmission lines on the PCB, including the stub resonator, consist of a first discrete wire placed at a fixed distance 10 from 2 parallel wires such that the first discrete wire is present between the other 2 wires.

Preferably, the 3 wires are present in the same plane. It is noted that also so called "off center" transmission lines in which the first discrete wire is not placed exactly in the center between the other 2 discrete wires make part of the present invention.

In a fourth preferred embodiment of the present invention, the transmission lines on the 15 PCB, including the stub resonator, consist of 2 discrete parallel wires. Preferably, the 2 parallel wires are present in the same plane.

In a fifth preferred embodiment of the present invention, the transmission lines on the PCB are not all based on the same geometrical design principles but each of them on any (combinations) of the designs described in the second, third and fourth preferred 20 embodiment.

In a sixth preferred embodiment of the present invention a multilayer PCB is applied in which all transmission lines are positioned inside the dielectric of the PCB. In the dielectric that is determining the properties of the stub resonator, holes are made. These holes are filled with the dielectric under investigation, for example by placing the PCB in the fluid 25 under investigation. The holes are positioned in the PCB such that they do not damage any of the stripline conductors. As a result, the E1, E2 and the stub resonator are completely isolated from the fluid under investigation even though the PCB is placed in this fluid. As a result, a very stable and reliable measuring system is obtained.

In a seventh preferred embodiment of the present invention, the configuration described in 30 the sixth embodiment is combined with any of the preferred embodiments one to six.

In an eighth preferred embodiment of the present invention, the holes in the PCB are filled with a growth medium for bacteria such as a polymer or a gel. In case bacterial growth occurs, the dielectric properties of the polymer of gel will change which will result in a change in the A-f plot. Hence a sensor for detection of bacterial growth is obtained. It is 35 noted that this principle is also applicable for detection of chemical compounds in case an adsorbent for these compounds is immobilized in the holes.

In a nineth preferred embodiment of the present invention, any of the preferred 16 embodiments one to eight is combined with a selection of any other of the preferred embodiments one to eight.

Now the features of the technology according to the present invention have been explained, the unique features of the invention are summarized: 5 1. The measuring system is very stable and sensitive because of • Impedance matching through E1, E2, and the absence of additional connectors between E1 and the stub resonator and E2 and the stub resonator.

• The absence of contact between the stripline and stub resonator conductors 10 and the fluid under investigation • The presence of well defined unplated holes in the active part of the stub resonator in which the dielectric under investigation is placed.

2. The measuring system is based on PCB technology and can be produced in a very reliable and cost effective way.

15 Non limiting examples of a fluïdum feasible to be investigated with the technology according to the present invention are drinking water, waste water, food.

Description of the technology according to the present invention part 4 According to a first aspect, the present invention relates to a function generator FG. This 20 function generator preferably produces a sinus or square wave electrical signal with a frequency that can be adjusted in the range between 1 MHz and 100 GHz.

According to a second aspect, the present invention relates to a spectrum analyzer or a hf (high frequency) rectifier SA, preferably able to measure the amplitude of a sinus or square wave electrical signal with a frequency in the range between 1 MHz and 100 GHz.

25 According to a third aspect, the present invention relates to a first transmission line resonator on a PCB that is connected to the function generator FG.

According to a fourth aspect, the present invention relates to an array of waveguide cavities made in the dielectic of the first transmission line resonator according to the description in one of the technology descriptions of the invention in parts 1 to 4, see also figures 1 to 10. 30 According to a fifth aspect, the present invention relates to striplines on the PCB, connected to each individual cavity resonator on the PCB and to the first contact point of at least one individual switch per cavity. The switch can be a microswitch, microrelay, solid state relay, a transistor, a FET.

According to a sixth aspect, the present invention relates to a stripline going from at least 35 the second contact point of the switch to a first transmission line connector that is mounted on the PCB.

According to a seventh aspect, the present invention relates to means, consisting at least 17 of a microcontroller and software, to switch on and off, each individual switch. By switching on an individual switch, a cavity resonator is electrically connected to the first transmission line connector that is mounted on the PCB.

According to a eighth aspect of the present invention, the spectrum analyzer SA or the 5 rectifier is connected to the first transmission line connector.

According to a nineth aspect, the present invention relates to a microcontroller connected to the function generator and / or the spectrum analyzer and / or the rectifier, for automated measurement of the dielectric properties of the fluïdum, in each individual wave guide cavity resonator, that is connected to the first transmission line connector, by switching on 10 an individual switch.

According to a tenth aspect, each individual wave guide cavity resonator is filled with a dielectric under investigation.

Now the aspects of the technology according to the present invention have been explained, a more general explanation of the technological concept is given. The function generator is IS connected to the strip line resonator. In the dielectic of the stripline resonator, wave guide cavity resonators are placed. The wave guide cavity resonators are supplied with energy through the electromagnetic field generated by the stripline resonator. Each wave guide cavity resonator is connected individually to the transmission line connector by the use of its individual switch. After connecting an individual wave guide cavity resonator via its 20 individual switch to the transmission line connector, an A-f plot is made by the use of the function generator and the spectrum analyzer or rectifier. After the A-f plot of the individual cavity resonator is successfully determined, the switch of the cavity resonator is switched off and the individual switch of the next cavity resonator is switched on. Subsequently, the A-f plot of the next wave guide cavity resonator is measured. It is noted that the A-f plot 25 measurements and the switching on and off of the switches are automated by the use of at least a microcontroller.

The technology according to the present invention is feasible for testing of the quality of drinking water, waste water, food. The technology according to the present invention can also be applied for the detection and / or screening and / or selection of microorganisms. 30 For this purpose, the individual wave guide cavity resonators are preferably filled with a gel, plate count agar or another medium for growing bacteria. Subsequently, the medium is wetted by a fluid to be investigated. Preferably, this wetting is automated by the use of a robot system. Subsequently, it is measured automatically by determination of A-f plots whether or not bacterial growth occurs in each individual wave guide cavity resonator. It is 35 mentioned that the technology according to the present invention is very feasible for application in the pharmaceutical, veterinary and agricultural sectors.

It is also noted that the system according to the present invention is feasible for classical 18 impedance measurements at low frequencies i.e., starting from DC measurements (0 Hz) until 1 MHz. In that case 2 conductive cilinders, with a non conductive cilinder in between, are applied and the function generator is connected through switches with every individual cavity. Also, each individual cilinder is connected to the spectrum analyzer or rectifier by the 5 use of switches. The result is that DC or low frequency impedance spectroscopy can be executed with every individual cilinder. The cilinders and electric connections are realized by the use of stacking technology as described in this document. Also all switches and required electronic part are mounted on the same PCB. The PCB can be produced in an environmentally friendly (RoHS compliant) and cost effective way and may be reused of 10 disposed after a screening test. This DC and low frequency impedance spectroscopy makes expressly part of the present invention. Also the combination of the DC and low frequency impedance spectroscopy combined with any other concept described in this document makes expressly part of the current invention.

15 20 25 30 35 19

Clauses 1. Sensor for measuring the dielectric properties of individual fluidum samples characterized by • a function generator connected to 5 «a first stripline resonator • a first printed circuit board (PCB) • an array of wave guide cavity resonators, placed in at least the dielectric of the first striplineline resonator on the first printed circuit board, and / or in a stack of the first printed circuit board and additional printed circuit boards 10 whereby • each individual wave guide cavity resonator is supplied wirelessly with electromagnetic energy supplied by the function generator via the first stripline resonator and • each individual wave guide cavity resonator is connected to a switch 15 whereby • the switch is connected to a first transmission line connector • a first spectrum analyzer or rectifier that is connected to the first transmission line connector • at least a first microcontroller equipped with software to switch on and off the 20 individual switches of the individual wave guide resonators • at least software in the first microcontroller, or at least a second microcontroller with software, connected to the function generator and / or spectrum analyzer, for automatic determination of A-f plots of every individual wave guide cavity resonator 25 · one fluidum and / or different fluidums under investigation placed in more than one individual wave guide cavity resonator 2. Sensor according to clause 1 whereby the individual wave guide cavity resonators are filled with drinking water samples to determine the quality of drinking water.

3. Sensor acccording to clause 1 whereby the individual wave guide cavity resonators 30 are filled with waste water samples to determine the quality of waste water.

4. Sensor according to clause 1 whereby the individual wave guide cavity resonators are filled with food to determine the quality of food.

5. Sensor according to clause 1 whereby the individual wave guide cavity resonators are filled with a sterilized growth medium for bacteria, such as plate count agar, and 35 where a small fluid sample is added to more than one resonator to analyze the presence of bacteria in the small fluid sample.

6. Sensor according to any of the previous claims 1 to 5 equipped with a robot adding 20 samples to be analyzed at the desired wave guide cavity resonator for automated sample analysis 7. Method for measuring the dielectric properties of individual fluïdum samples characterized by a sensor according to any of the previous claims 1 to 6.

5 10 15 20 25 30 1039730 35

Claims

A sensor for measuring the dielectric properties of individual fluid samples characterized by • a function generator operatively connected to 5. a first stripline resonator operatively connected to a • first printed circuit board (PCB), • an array of wave guide cavity resonators, which are placed at least in the dielectric of the first stripline resonator on the first PCB, and / or in a stack of the first PCB and additional PCBs, wherein • each individual wave guide cavity resonator is wirelessly supplied with electromagnetic energy by the function generator, via the first stripline resonator and • each individual wave guide cavity resonator is operatively connected to a switch wherein: the switch is operatively connected to a transmission line connector, • a first spectrum analyzer or rectifier which is operatively connected to the first transmission line connector • at least a first microcontroller equipped with software to enable or disable the individual switches of the individual wave guide cavity resonators • minimum software in the first microcontroller, or at least a second microcontroller with software, with which the function generator and / or the spectrum analyzer or rectifier can be controlled or read out 25 for the automatic determination of Af plots of each individual wave guide cavity resonator. • a test fluid and / or different test fluid mounted in at least a portion of 2 or more individual wave guide cavity resonators.

The sensor of claim 1 wherein the individual wave guide cavity resonators are filled with drinking water samples to determine the quality of drinking water.

The sensor of claim 1 wherein the individual wave guide cavity resonators are filled with waste water samples to determine the quality of waste water.

The sensor of claim 1 wherein the individual wave guide cavity resonators 35 are filled with food to determine the quality of food.

The sensor of claim 1 wherein the individual wave guide cavity resonators are filled with sterilized growth medium for bacteria to analyze the presence of 1039730 bacteria in a fluid sample.

Sensor according to one of the preceding claims 1 to 5 plus a robot that automatically places samples of a fluid or different fluids in the desired wave guide cavity resonator for automated analysis of 5 samples by means of an A-f plot.

Method for measuring the dielectric properties of individual fluid samples characterized by a sensor according to one of the preceding claims 1 to 6. 10 15 20 25 30 1039730 35