Ultrasound remote sensing system

Abstract

A system to measure a physical parameter(s) of a structure with acoustic power and data transmission may have: a base module configured for radiating acoustic waves that couple into said structure, and for measuring acoustic waves propagating into said monitored structure. A harvester device is configured to produce electrical power when exposed to said radiated waves produced by said base module. An energy storage device is connected to the harvester device, and configured for storing the electrical power received from the harvester device. A sensor device is configured for being mounted to the structure and being powered by said energy storage device and / or the harvester device, the at least one sensor configured to measure a parameter of said monitored structure, and to produce signal acoustic waves for propagating into said monitored structure, characteristics of the signal acoustic waves being a function of the measure of the parameter; wherein the base module is configured to output a value that is a function of the measure of the parameter.

Description

ULTRASOUND REMOTE SENSING SYSTEMCROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of United States Patent Application no. 63 / 718,844, filed on November 11, 2024, and incorporated herein by reference.TECHNICAL FIELD

[0002] The application relates to sensors for measuring physical properties of a structure, such as temperature, displacement, acceleration, deformation and / or pressure, using acoustic waves.BACKGROUND

[0003] To ensure proper functioning of some apparatuses, the measurement and monitoring of physical properties of structures of the apparatuses may be necessary. Therefore, physical properties such as temperature, displacement, acceleration, deformation and / or pressure are commonly measured via sensors.

[0004] In some instances, it may not be possible to install wires for sensors. An example is the measuring of temperature inside a rotor of an electric vehicle motor. Monitoring the temperature of certain critical electric motor components may be difficult, notably because of constrained access and because of the electromagnetic noise, that may interfere with existing electromagnetic wave protocols (e.g., WiFi®, Radio, Bluetooth®, etc.). For example, integrating a sensor that precisely measures the temperature in a rotor turning at several thousand revolutions per minute, and communicating this information wirelessly and reliably, may be a challenge. Other fields of technology may have similar challenges, such as robotics, civil engineering, etc.SUMMARY

[0005] In one aspect, there is provided a system to measure at least one physical parameter of a structure with acoustic power and data transmission, the systemcomprising: a base module configured for radiating acoustic waves that couple into said structure, and for measuring acoustic waves propagating into said monitored structure; a harvester device configured to produce electrical power when exposed to said radiated waves produced by said base module; an energy storage device connected to the harvester device, and configured for storing the electrical power received from the harvester device; and a sensor device configured for being mounted to the structure and being powered by said energy storage device and / or the harvester device, the sensor device including at least one sensor configured to measure a parameter of said monitored structure, and to produce signal acoustic waves for propagating into said monitored structure, characteristics of the signal acoustic waves being a function of the measure of the parameter; wherein the base module is configured to output a value that is a function of the measure of the parameter.

[0006] Further in accordance with the aspect, for instance, the harvester device, the energy storage device and the sensor device are grouped together into a mote configured to be installed on the monitored structure.

[0007] Still further in accordance with the aspect, for instance, the system includes a plurality of the mote.

[0008] Still further in accordance with the aspect, for instance, the harvesting device includes a piezoelectric transducer.

[0009] Still further in accordance with the aspect, for instance, the harvesting device includes a resonant tank, and a rectifier circuit.

[0010] Still further in accordance with the aspect, for instance, the energy storage device includes a capacitor or a rechargeable battery.

[0011] Still further in accordance with the aspect, for instance, the sensor device includes a switch connecting the harvester device to at least two different electrical loads, said switch being activated by a controller for the harvester device to harvest energy or for the sensor device to produce the signal acoustic waves.

[0012] Still further in accordance with the aspect, for instance, said controller includes a voltage-controlled oscillator (VCO), a frequency of said VCO being set by a readout of the sensor device, the controller closing the switch only when the output of the VCO is within a set range.

[0013] Still further in accordance with the aspect, for instance, the sensor device includes an internal trigger, an output impedance matching circuit connected to a piezoelectric transducer, and a circuit sending a pulse to the impedance matching circuit after the trigger, a delay between the pulse and the trigger being set by a time constant being a function of sensor output.

[0014] Still further in accordance with the aspect, for instance, the piezoelectric transducer of the harvester device and of the sensor device are a single shared transducer.

[0015] Still further in accordance with the aspect, for instance, the trigger is generated when the base module stops radiating acoustic waves.

[0016] Still further in accordance with the aspect, for instance, a propagation time of an acoustic signature produced by the mote is used to identify / localize the mote in the structure.

[0017] Still further in accordance with the aspect, for instance, the sensor device includes at least one acoustic wave emission device configured to radiate the acoustic waves into the monitored structure.

[0018] Still further in accordance with the aspect, for instance, the sensor device monitors a voltage of an output of a transducer in the harvester device or of an output of the harvester device, and generates a trigger when said voltage is outside of a set range of values.

[0019] Still further in accordance with the aspect, for instance, said trigger is connected to a controller.

[0020] Still further in accordance with the aspect, for instance, the sensor device includes a controller being configured to send a signal to a transducer of the sensor device, one of the frequency, the amplitude and the shape of said signal being a function of a sensor device reading.

[0021] Still further in accordance with the aspect, for instance, said signal includes two pulses, a delay between said pulses being a function of the sensor device reading.

[0022] Still further in accordance with the aspect, for instance, said base module includes a controller, a voltage amplifier, a switch, a piezotransducer attached to the monitored structure, a signal amplifier and an analog-to-digital converter.

[0023] Still further in accordance with the aspect, for instance, the piezotransducers are positioned to maximize the amplitude of waves transmitted between the base module and the sensor device.

[0024] Still further in accordance with the aspect, for instance, said base module periodically sends short pulses of acoustic waves, and detects the amplitude of the echos from the sensor device, wherein the amplitude of the echoes or the main frequency component of the echoes or the shape of the echoes encodes a readout of the sensor device.

[0025] Still further in accordance with the aspect, for instance, said base module measures a delay between two pulses from the sensor device, wherein the delay encodes the sensor readout.

[0026] Still further in accordance with the aspect, for instance, the system is configured to measure a temperature inside an engine or an electrical motor, wherein the waves are transmitted through a ball bearing, through a liquid in contact with a monitored portion of the engine / motor, or through a sliding contact, and wherein the piezotransducers from the motes are glued or press-fitted to the engine / motor.

[0027] In accordance with another aspect of the present disclosure, there is provided a method for measuring a parameter of a monitored structure, comprising: radiating acoustic waves that couple into said monitored structure from a first location; at asecond location: producing electrical power harvested from the acoustic waves, measuring at least one parameter at the second location, and using the electrical power to produce and propagate signal acoustic waves back to the first location, the characteristics of the signal acoustic waves being a function of the measure of the parameter; and at the first location, measuring the signal acoustic waves and outputting a value that is a function of the measure of the parameter. Further in accordance with the other aspect, for instance, at the second location, storing the electrical power is stored.DESCRIPTION OF THE DRAWINGS

[0028] Reference is now made to the accompanying figures in which:

[0029] Fig. 1 is a block diagram of a system to measure at least one physical parameter of a structure with acoustic power and data transmission, in accordance with the present disclosure;

[0030] Fig. 2 is a schematic illustration of an arrangement of remote components on the structure to be monitored, as part of the system of Fig. 1, optionally grouped as a mote;

[0031] Fig. 3 is a circuit diagram of an exemplary configuration of the arrangement of the remote components of Fig. 2;

[0032] Fig. 4A is a graph showing a communication approach for the arrangement of remote components of Figs. 2 and 3;

[0033] Fig. 4B is a graph showing another communication approach for the arrangement of remote components of Figs. 2 and 3;

[0034] Fig. 5 is an exemplary topology of a resonant tank of the remote components of Figs. 2 and 3;

[0035] Fig. 6 is an exemplary topology of an energy storage device of the remote components of Figs. 2 and 3;

[0036] Fig. 7 is an exemplary topology of a voltage-controller oscillator (VCO) of the remote components of Figs. 2 and 3;

[0037] Fig. 8 is another exemplary topology of a voltage-controller oscillator (VCO) of the remote components of Figs. 2 and 3;

[0038] Fig. 9 is a perspective view of a mote in accordance with an embodiment of the present disclosure;

[0039] Fig. 10 is a series of assembly views of the mote of Fig. 9; and

[0040] Fig. 11 is a perspective view of an interior of a mote in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0041] Referring to the drawings, and more particularly to Fig. 1, a system to measure one or more physical parameters of a structure with acoustic power and data transmission is generally shown at 10, and is referred to herein as system 10, for simplicity. The system 10 may be used to measure one or more physical parameters, which may be temperature, displacement, acceleration, deformation and / or pressure, as examples among others. In a variant, the structure that is being monitored is a rotor A1 or like rotating component, such as in an electrical motor. The electrical motor may be part of an electrical vehicle. However, this is merely an example as the system 10 may be used in other apparatuses, and not necessarily for rotating components.

[0042] The system 10 may include one or more of the following components, units, subsystems, systems, assemblies, devices: a base module 20, a harvester device 30, an energy storage device 40, and / or a sensor device(s) 50. In a variant, the base module 20 is a powered device that is positioned remotely from the harvester device 30, the energy storage device 40, and / or the sensor device(s) 50. The harvester device 30, the energy storage device 40, and / or the sensor device(s) 50 will be referred to herein as the remote components of the system 10, as they are remotely positioned (i.e., separated) relative to the base module 20. For example, the harvesterdevice 30, the energy storage device 40, and / or the sensor device(s) 50 may be mounted onto the monitored structure (e.g., rotor A1), while the base module 20 is not - the base module 20 may be mounted to a stator or other structural part A2 relative to which the monitored structure, i.e., the rotor A1, rotates. However, this is only an example, and relative movement between the parts of the structure respectively supporting the base module 20, and the harvester device 30 / the energy storage device 40 / the sensor device(s) 50 is not necessary for the system 10 to be used. In another variant, the harvester device 30, the energy storage device 40, and / or the sensor device(s) 50 are grouped into one or more mote(s) 60 or like sensor unit(s). A mote 60 includes one or more sensor device(s) 50, and may also include its own harvester device 30 and / or energy storage device 40. However, two or more motes 60 may share a harvester device 30 and / or an energy storage device 40. In a variant, a single base module 20 may be used with two or more motes 60.

[0043] The base module 20 is powered, and is configured for radiating acoustic waves that couple into the monitored structure (e.g., rotor A1). The base module 20 may also be configured for measuring acoustic waves propagating into the monitored structure. As detailed herein, the measured acoustic waves may be indicative of a characteristic of a measured parameter of the monitored structure, such that the measuring by the base module 20 may be translated into a value of the parameter. The base module 20 may be referred to as communication module, transmitter / receiver, transducing unit. The base module 20 may include one or more processing unit(s) 21, and a non-transitory computer-readable memory 22 communicatively coupled to the processing unit and comprising computer-readable program instructions executable by the processing unit 21 for operating the system 10 in measuring physical parameter(s) and outputting a value(s) for the physical parameter(s).

[0044] The harvester device 30 is configured to produce electrical power when exposed to the radiated waves produced by the base module 20. The energy storage device 40 is connected to the harvester device 30. The energy storage device 40 is configured for storing the electrical power received from the harvester device 30. The sensor device 50 is configured for being mounted to the structure, e.g., the rotor A1. The sensor device 50 is powered by power from the energy storage device 40 and / or the harvester device 30. The sensor device 50 is configured to measure a parameterof the monitored structure, and to produce a signal, in the form of acoustic waves for example. By producing a signal, the sensor device 50 may emit signal acoustic waves, with the characteristic(s) of the acoustic waves will be as a function of the measured parameter. As another embodiment, when the sensor device 50 produces signal acoustic wave(s), the sensor device 50 may change the characteristics of the acoustic waves from the base module 20, for example by dephasing them, by modifying the amplitude of reflection, by changing the frequency content, as examples among others. The producing may therefore be achieved with or without energy consumption by the sensor device 50, as some of the changes in the characteristics of the acoustic waves from the base module 20 may be done passively, without energy consumption. Hence, it may be said that the signal acoustic waves represent a change of a characteristic(s) of the acoustic waves propagating into the monitored structure as a function of the measure of the parameter.

[0045] Thus, in a variant, the system 10 may have a single base module 20 and a multitude of remote motes 60, with the base module 20 interpreting the signal acoustic waves (a.k.a., acoustic wave signals) from the multitude of motes 60. The base module 20 and the motes 60 may not be wired to each other, but rather communicate via acoustic waves that propagate through the monitored structure. In a variant, the motes 60 do not require a wired power supply as the energy is harvested from the acoustic waves.

[0046] The base module 20 may be a self-enclosed module, e.g., operated by a battery, or may be powered by a power source, such as via a wire. A wire may be releasably connected to the base module 20, to power same and / or to recharge a battery in the base module 20. Since it may be stationary, the base module 20 may readily be connected in some embodiments to a control system. For example, the base module 20 may be connected to an EV (electric vehicle) control system (if the monitored structure is part of an EV). The base module 20 is responsible for the remote acoustic powering of the remote components of the system 10, such as the motes 60. The base module 20 is also configured for receiving signals sent back by the remote components of the system 10, such as the motes 60. The base module 20 may interpret the received signals (e.g., measured) and output values for the one or more physical properties measured by the remote components. The base module 20 may include as part of the processing unit 21 active electronics to enable the logicoperations and signal processing required to interpret the acoustic signals. For example, a high-voltage amplifier stage may be present to drive acoustic actuator elements (e.g., piezo elements) in the base module 20. The acoustic actuator elements may need to be in relatively close proximity with the monitored structure, while some part of the base module 20, e.g., the processing unit 21 and / or the non-transitory computer-readable memory 22 could be integrated into existing instruments in the control system (e.g., for the EV in an example), such as in a rotor end position sensor module.

[0047] In a variant, the base module 20 uses piezoelectric elements as acoustic actuators in contact with the monitored structure to inject acoustic waves therein. The piezoelectric elements may be piezoelectric ceramic elements. Moreover, the acoustic actuators of the base module 20 may optionally include transmission-enhancing passive elements such as acoustic lenses, that may be placed in contact with the monitored structure. This contact could be made via solid structures, such as driveshafts, bearing races or motor casings, or liquids such as the cooling oil circuit that runs through motor rotors (e.g., of a permanent synchronous magnet motor (PSM)). The base module 20 may include one or more of a controller, a voltage amplifier, a switch, one or more piezotransducers (or like piezo elements) attached to the monitored structure, a signal amplifier and an analog-to-digital converter. If present, the piezotransducers are positioned to maximize the amplitude of waves transmitted between the base module 20 and the sensor device 50 or from the sensor device 50 and the base module 20. As a mode of operation, the base module 20 may periodically send short pulses of acoustic waves in an emission mode. In a capture mode, the base module 20 may detect the amplitude of the echos from the sensor device 50, wherein the amplitude of the echoes or the main frequency component of the echoes or the shape of the echoes encodes a readout of the sensor device 50. This is one way to measure the acoustic wave signals from the sensor device 50, by which the base module 20 may output a value associated with the parameter measured by the sensor device 50.

[0048] Referring to Fig. 2, an exemplary arrangement of the remote components is provided. The acoustic waves propagate to the various remote components, such as to the motes 60 if the remote components are grouped into motes 60. The remote components themselves are integrated into the monitored structure at the point wherethe measurement is to be made. In the illustrated example, the motes 60 are integrated into the motor's rotor, which can rotate at speeds of 15-30 kRPM (depending on the embodiment) and may reach temperatures in excess of 150°C. The remote components, such as motes 60, receive acoustic waves and generate an electrical voltage via the harvester device 30 (e.g., via a piezoelectric component).

[0049] The harvester device 30 may include one or more piezo element 31 that is exposed to the acoustic waves propagating in the monitored structure (e.g., the rotor A1). The piezo element 31 may be referred to as a piezoelectric transducer or transducer. The piezo element 31 is an example of an electro-mechanical component that converts mechanical stimulation into an analog electrical signal. The piezo element 31 acts as a receptor that is excited by the acoustic vibrations sent by the acoustic actuator of the base module 20.

[0050] The harvester device 30 may also include a resonant tank 32, or like transformer that boosts the signal voltage. The resonant tank 32 uses the resonant properties of the piezo element 31 to amplify the acoustic signal received by the harvester device 30. In a variant, for optimization, impedance matching between the piezo element 31 and the resonant tank 32 may be achieved.

[0051] A rectifier 33 may optionally be present convert the signal, from AC to DC. In a variant, the rectifier 33 may be a diode rectifier bridge.

[0052] Still referring to Fig. 2, after rectification and amplification, the energy captured by the harvester device 30 may be recovered by the energy storage device 40. The energy storage device 40 may be include a capacitor(s), and the energy may be in the form of a charge in the capacitor. In an alternative embodiment, the energy storage device 40 is a rechargeable battery.

[0053] The sensor device(s) 50 may include an element sensitive to the physical parameter to be measured. For example, the sensor device 50 may be a thermistor 50A, as one possible type of sensor that may be used. Other types of sensors may be used to measure displacement, acceleration, deformation and / or pressure, to name a few examples. The element is connected to the energy storage device 40 so as to use the energy stored in the energy storage device 40 (e.g., capacitor). Thesensor device 50 may then activate the piezoelectric element 31 of the harvester device 30, which in turn produce signal acoustic waves toward the base module 20. The signal acoustic waves will be as a function of the measured parameter. Alternatively, the sensor device 50 may include its own piezoelectric element or like signal generator. Still referring to Fig. 2, the sensor device 50 may include a switch 51 (shown as state control) connecting the harvester device 30 to at least two different electrical loads, the switch 51 being activated by a controller 52 for the harvester device 30 to harvest energy or to change the acoustic impedance of the piezoelectric element and therefore change the amplitude or phase of the acoustic signal reflected from the mote 60. The switch 51 selectively activate the sensor 50A as well (though the sensor 50 could receive its power directly from the energy storage device 40. The controller 52 of the sensor device 50 may for example be a voltage-controlled oscillator (VCO). In a variant, while the sensor is shown at 50A, it is also possible for the controller 52 to include a sensor. For example, if a temperature sensor (e.g., thermistor) is integrated in the circuit of the controller 52, the output voltage of the VCO controller 52 may be function of the temperature. The output of the VCO may be connected to the piezoelectric element 31 by a switch. The frequency of the VCO may be set by a readout (a.k.a., read-out) of the sensor device 50, the controller 52 closing the switch 51 only when the output of the harvester device 30 is within a set range. The sensor device 50 may also include an internal trigger, an output impedance matching circuit (which may be resonant and include a transformer) connected to a piezo element, such as that of the harvester device 30, or another one. The sensor device 50 may include a circuit that sends a pulse to the piezo element after a trigger, the delay between that pulse and the trigger being set by the time constant that is a function of the sensor output (such as a thermistance). As another variant, the sensor device 50 monitors a voltage of an output of a transducer in the harvester device 30 or of an output of the harvester device 30, and generates a trigger when said voltage is outside of a set range of values.

[0054] The measurement data indicative of the physical parameter is encoded in the acoustic waves emitted by the piezo element (e.g., 31), and may then be decoded by the base module 20. In a variant, there are more than one set of remote components, such as more than one mote 60, whereby each mote 60 has a signature signal, for the base module 20 to discriminate between the various signals it receives from the various motes 60.

[0055] The various remote components shown in Fig. 2 may be grouped as a mote 60, with other motes 60 replicating the schematics of Fig. 2 being located elsewhere on the structure that is monitored. Referring to Fig. 3, a circuit schematic of the arrangement of Fig. 2 is shown.

[0056] Thus, in a variant, the remote components are grouped as a mote 60. The mote 60 can be described as being a small device that is readily implanted into the structure in which physical parameters are measured. The mote 60 may optionally be an entirely self-contained, hermetically packaged device that can be mechanically connected to the structure. For example, the mote 60 may connected to the structure by a number of means such as press-fitting, threading and / or glueing / cementing. The motes 60 could be designed to measure a variety of physical quantities and phenomena, depending on what sensing device 50 is chosen, e.g., a thermistor, a diode, a strain gauge, an inertial sensor, etc. An example of a temperature sensor is a platinum Resistance Temperature Detector (RTD) such as a PT100 temperature sensor.

[0057] In a variant, the mote 60 has its circuitry send back a signal containing the information about the physical parameter, to the base module 20 in the manner shown in Fig. 4A. According to the approach, the physical parameter measurement is coded in the delay between two pulses. The base module 20 senses these two pulses, computes the delay and translates it to a value for the physical parameter measurement. In another approach, the frequency of the signal emitted by the mote is measured by the base module 20.

[0058] These capacitors are used to generate two pulses that are sent to a piezo actuator (which can be the same device as the harvesting piezo). The first pulse is emitted when the harvesting circuit voltage gets below a certain value, indicating that the transducer unit has switched to the listening mode. A second pulse is emitted after a delay set by a temperature-sensitive element. The control unit receives both pulses, computes the delay and converts this delay to the mote temperature using a calibration table. To implement the concept for the work in this report, the delay between pulses was chosen to be regulated by the RC constant of a discharge circuit. The resistive component of this circuit was modulated by the variation of a RTD placed in a Wheatstone bridge configuration.

[0059] Another communication approach is shown in Fig. 4B, such as with the remote component arranged as in Fig. 2. According to the approach of Fig. 4B, the harvesting circuit 30 is used to charge capacitors 40 in a separate circuit. The capacitor(s) may be used to generate two pulses that are sent to an acoustic actuator, that may be the same piezo element as that of the harvesting device 30, or another acoustic actuator. The first pulse is emitted when the harvesting circuit voltage gets below a certain value, indicating that the base module 20 has switched to a listening mode. A second pulse is emitted after a delay set by the sensor unit 50. The delay between pulses may be regulated by the RC (resistor-capacitor) constant of a discharge circuit. In an embodiment for measuring temperature, the resistive component of the circuit may be modulated by the variation of a resistance temperature detector (RTD) placed in a Wheatstone bridge configuration. The base module 20 receives both pulses, computes the delay and converts this delay to a value of the physical parameter, for example using a look-up table, a.k.a., a calibration table.

[0060] The system 10 may therefore be operated according to a method for measuring a parameter of a monitored structure, and may be done using the processing unit 21 and the non-transitory computer-readable memory 22 communicatively coupled to the processing unit and comprising computer-readable program instructions executable by the processing unit 21 for: radiating acoustic waves that couple into said monitored structure from a first location; at a second location: producing electrical power harvested from the acoustic waves, measuring at least one parameter at the second location, and using the electrical power to produce and propagate signal acoustic waves back to the first location, the characteristics of the signal acoustic waves being a function of the measure of the parameter; and at the first location, measuring the signal acoustic waves and outputting a value that is a function of the measure of the parameter. The method may include, at the second location, storing the electrical power.

[0061] The system 10 may generally be described as being used to measure at least one physical parameter of a structure with acoustic power and data transmission. The system 10 may have: a base module configured for radiating acoustic waves that couple into said structure, and for measuring acoustic waves propagating into said monitored structure; a harvester device configured to produce electrical power when exposed to said radiated waves produced by said base module; an energy storagedevice connected to the harvester device, and configured for storing the electrical power received from the harvester device; and a sensor device configured for being mounted to the structure and being powered by said energy storage device and / or the harvester device, the at least one sensor configured to measure a parameter of said monitored structure, and to produce signal acoustic waves for propagating into said monitored structure, characteristics of the signal acoustic waves being a function of the measure of the parameter. The base module is configured to output a value that is a function of the measure of the parameter.

[0062] In an embodiment, the piezo elements used in the system 10 may be piezoelectric ceramic discs. Such ceramic discs may be connected via coaxial cables, with electrical leads soldered to their contact faces. In another variant, the disks may be connected by spring-like contacts. In a variant, the ceramic discs are glued to the surface of the structure. Larger diameter, thin discs (diameter for example 9.6mm, thickness for example 0.2mm may be chosen for transducer duties, i.e., in the base module 20. Thicker piezo elements may be favoured when a large acoustic amplitude is desired.

[0063] Small diameter, thin discs (e.g., diameter of 6mm, thickness of 0.2mm) may be easier to fit on the monitored structure (e.g., on the side of a bearing race). Large diameter, thicker discs (e.g., diameter of 10mm, thickness of 1mm) may be aligned with the frequency range used (1-1000 kHz), and may generate stronger acoustic signals in the structures.

[0064] Thus, the remote components may be arranged to form a circuit that uses acoustic waves of the base module 20 as a means for energy harvesting and for communicating.

[0065] Further details are now provided as examples, for some of the remote components, with reference to Fig. 2.

[0066] An exemplary resonant tank is shown in Fig. 5. The resonant tank is a series LC circuit. By matching the resonance frequency of the piezo element, it is possible to obtain a gain in voltage given a high enough quality factor. The piezo can beCp~ G c-modeled as a capacitance ( ), the parallel combination of through can be Crepresented by a single capacitance and the load is approximated as an open circuit |Z| » |ZC|( )

[0067] The resonant frequency and the quality factor can be derived as follows.However, as CP- » Cthe above equations can be reduced to equation 3 and 4.The damping resistance R is a combination of the parasitic resistance of the inductance, the capacitance, the piezo and the load.

[0068] Achieving a high-quality factor for a specific frequency might prove challenging as the components temperature coefficient, their aging rate and their tolerance widen the range of frequencies to account for over time. A potential solution for this problem would be to perform a frequency sweep on the transducer over a frequency range and to use the newly found resonant frequency as the harvesting frequency. Another solution would be to modulate the frequency of the transducer to create sidebands that cover a broader frequency range, to increase the amount of power transmitted at the harvesting frequency.

[0069] An exemplary topology of the energy storage device 40 is shown in Fig. 6. In Fig. 6, transistorsand Q2form a pair that controls the charge of the storage capacitor C5. When there is an input signal (during harvesting), the base of Q2is pulled high and therefore blocks the discharge of C5into the VCO. When transitioning into the sensing state, the base of Q2is pulled low byQ5blocks the voltage of thestorage capacitor from reaching the base of Q2and from partially discharging into the rest of the circuit. C6helps smooth the pulsating DC of the rectified signal.

[0070] There are three constants that impact the functioning of a mote 60.• TQ2: discharge time constant of C6and RLwhen transitioning into the sensing state.•τC5Rvco: discharge time constant of C5during the sensing period.•τRhC5: charge time constant of C5during the harvesting period

[0071] TQ2is an indicator of the delay between both states. The larger it is, the longer it will take for the oscillator to enter a meaningful regime. The duration of oscillation of the VCO is proportional to τC5Rvco. The VCO requires a supply voltage of at least 1.1V, but because of the available off the shelf Zener diodes this voltage can be increased to 2.2V. The stored energy is proportional to τRhC5. The harvesting resistance can be inferred from the rectified current and voltage, lrect and Vrect.

[0072] To enter the sensing state VQ2- VQ1> 0.7V and to stay in the sensing state, VC5> 2.2V. Equations 5 to 7 show the relationships between the passive components and the required operating voltages.C5, its charge time constant is small enough to consider

[0073] Given these equations, the desired frequency of operation (fs) and length of oscillation (Tc:c), it is possible to size the components appropriately.

[0074] With reference to Fig. 7, an exemplary topology of the voltage-controlled oscillator (VCO) is shown. In essence, the VCO transforms a temperature into a frequency. The frequency of the oscillator is controlled by changing the voltage at the cathodes of D7and D8. The circuit can be separated into three sections: a frequency control circuit, a DC block filter and an oscillator circuit.

[0075] The voltage divider formed by R3and R4controls the diodes junction voltage, which in turns changes their junction capacitance. R4is a temperature sensitive resistor. A thermistor typically has a larger resistance variation over the same temperature range compared to an RTD. A larger variation could widen the frequency range of the oscillator and therefore its margin for error (Af / C°). The Zener diode (De) ensures the voltage divider is driven by a known voltage. The frequency control circuit can also be implemented using a temperature-dependent capacitance. The circuit of Fig. 7 then becomes the circuit shown in Fig. 8.pF

[0076] The variable capacitance is modeled by the formula 13 (in )

[0077] A high-pass filter (R7and C7) act as a DC block to preventfrompropagating to the oscillator circuit. The value of C7» C8, it can therefore be omitted when calculating the oscillator frequency.

[0078] The remaining components form an oscillating circuit. The chosen topology is inspired by a Clapp oscillator. The oscillator frequency is given by equation 14.

[0079] Rb, C3, L3and C11also play a role in the resulting frequency, but their impact is negligible. Their role is to bias the transistor and adjust the feedback loop gain.

[0080] An alternative circuit to the VCO may use the same principle, but instead of using diodes and a voltage control circuit to adjust the frequency, it uses the variation in capacitance of the capacitor itself. This approach further reduces the number of components in the circuit.

[0081] The base module(s) 20 and mote(s) 60 could be fitted into various parts of a motor. A mechanical assembly that ensures a strong mechanical coupling between the two parts is preferred for optimal transmission of the ultrasonic signal. For example, in a PSM motor, one strategic location for base module(s) 20 is at the end of the rotor shaft and on a surface aligned with one of the main rotor bearings. These locations represent prime candidates for placement of the base modules 20. Sensor piezoelements may be located at different locations along the possible acoustic path from base module 20 to mote 60, such as on the rotor bearing race, on the rotor shaft and on the flange that retains the permanent magnet plate assembly. As another example, a sliding or a rolling element could be acoustically coupled to both the piezo transducer from the base module 20 and a portion of the rotor, such as the shaft or the flanges. As yet another embodiment, the piezo transducer from the base module 20 could be acoustically coupled to a cooling or lubricating liquid, such as oil, that is also acoustically coupled to the rotor. For example, oil might circulate in a hollow shaft, and the piezo transducer from the base module 20 could be coupled to an oil bath, such that an acoustic path is formed from the piezo transducer, to the oil bath, to the oil in the shaft, to a mote 60 on the rotor. All such elements may for example be glued with epoxy, as an option among others. Fig. 9 depicts an exemplary mechanical assembly for a mote 60.

[0082] The sleeve 61 is used both as the circuit housing and a ground connection between the circuit and the motor. A counterbore 62 houses the PCBs 63 (one of which features the harvester) and a through hole leaves enough space for a tab to go through and contact the piezo transducer. The sleeve 61 may optionally be filled with epoxy to keep the PCBs 63 (shown as 63A and 63B) in place while in operation. It is critical that the temperature sensing element of the circuit is completely submerged in epoxy. Therefore, a vent hole is added to the sleeve 61 where the sensing element lies, to prevent trapping air in the assembly when epoxy is poured.

[0083] As seen in Figs. 9 and 10, the piezoelectric transducer 64 is glued to one end of the sleeve 61, with the outer ring of the bullseye pattern in contact with the motor chassis, serving as the ground connection. The inner ring of the piezoelectric transducer 64 may be isolated from the sleeve 61 using a plastic ring 65. As an option, a tab or a spring 66 could make the connection between the piezoelectric transducer 64 and the circuits 63 to transmit the signal.

[0084] Referring to Fig. 11, the circuit is divided into the two PCBs 63: the harvester 63A and the oscillator 63B. The current version of these PCBs uses pogo pins to establish the necessary electrical connections between the PCBs. The harvester 63A houses the components for the resonant tank, the rectifier, the state control and energy storage circuit. The oscillator 63B contains the rest of the components as well as a tab 66 that serves as a connection point for the piezoelectric element 64 (Fig. 10). A connection between the circuit ground and the sleeve may also be necessary.

[0085] Th

[0086] The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

Claims

CLAIMS1. A system to measure at least one physical parameter of a structure with acoustic power and data transmission, the system comprising:a base module configured for radiating acoustic waves that couple into said structure, and for measuring acoustic waves propagating into said monitored structure;a harvester device configured to produce electrical power when exposed to said radiated waves produced by said base module;an energy storage device connected to the harvester device, and configured for storing the electrical power received from the harvester device; anda sensor device configured for being mounted to the structure and being powered by said energy storage device and / or the harvester device, the sensor device including at least one sensor configured to measure a parameter of said monitored structure, and to produce signal acoustic waves for propagating into said monitored structure, characteristics of the signal acoustic waves being a function of the measure of the parameter;wherein the base module is configured to output a value that is a function of the measure of the parameter.

2. The system according to claim 1, wherein the harvester device, the energy storage device and the sensor device are grouped together into a mote configured to be installed on the monitored structure.

3. The system according to claim 2, wherein the system includes a plurality of the mote.

4. The system of any one of claims 1 to 3, wherein the harvesting device includes a piezoelectric transducer.

5. The system according to claim 4, wherein the harvesting device includes a resonant tank, and a rectifier circuit.

6. The system according to any one of claims 1 to 5, wherein the energy storage device includes a capacitor or a rechargeable battery.

7. The system according to any one of claim 1 to 6, wherein the sensor device includes a switch connecting the harvester device to at least two different electrical loads, said switch being activated by a controller for the harvester device to harvest energy or for the sensor device to produce the signal acoustic waves.

8. The system according to claim 7, wherein said controller includes a voltage-controlled oscillator (VCO), a frequency of said VCO being set by a readout of the sensor device, the controller closing the switch only when the output of the VCO is within a set range.

9. The system according to any one of claims 1 to 8, wherein the sensor device includes an internal trigger, an output impedance matching circuit connected to a piezoelectric transducer, and a circuit sending a pulse to the impedance matching circuit after the trigger, a delay between the pulse and the trigger being set by a time constant being a function of sensor output.

10. The system according to claim 9 when dependent on claim 4, wherein the piezoelectric transducer of the harvester device and of the sensor device are a single shared transducer.

11. The system according to claim 9, wherein the trigger is generated when the base module stops radiating acoustic waves.

12. The system according to claim 3, wherein a propagation time of an acoustic signature produced by the mote is used to identify / localize the mote in the structure.

13. The system according to any one of claims 1 to 12, wherein the sensor device includes at least one acoustic wave emission device configured to radiate the acoustic waves into the monitored structure.

14. The system according to claim 1, wherein the sensor device monitors a voltage of an output of a transducer in the harvester device or of an output of the harvester device, and generates a trigger when said voltage is outside of a set range of values.

15. The system according to claim 14, wherein said trigger is connected to a controller.

16. The system according to claim 1, wherein the sensor device includes a controller being configured to send a signal to a transducer of the sensor device, one of the frequency, the amplitude and the shape of said signal being a function of a sensor device reading.

17. The system according to claim 16, wherein said signal includes two pulses, a delay between said pulses being a function of the sensor device reading.

18. The system according to any one of claims 1 to 17, wherein said base module includes a controller, a voltage amplifier, a switch, a piezotransducer attached to the monitored structure, a signal amplifier and an analog-to-digital converter.

19. The system according to claim 18, wherein the piezotransducers are positioned to maximize the amplitude of waves transmitted between the base module and the sensor device.

20. The system according to any one of claims 1 to 19, wherein said base module periodically sends short pulses of acoustic waves, and detects the amplitude of the echos from the sensor device, wherein the amplitude of the echoes or the main frequency component of the echoes or the shape of the echoes encodes a readout of the sensor device.

21. The system according to claim 20, wherein said base module measures a delay between two pulses from the sensor device, wherein the delay encodes the sensor readout.

22. The system according to any one of claims 1 to 21, wherein the system is configured to measure a temperature inside an engine or an electrical motor, wherein the waves are transmitted through a ball bearing, through a liquid in contact with a monitored portion of the engine / motor, or through a sliding contact, and wherein the piezotransducers from the motes are glued or press-fitted to the engine / motor.

23. A method for measuring a parameter of a monitored structure, comprising:radiating acoustic waves that couple into said monitored structure from a first location;at a second location:producing electrical power harvested from the acoustic waves, measuring at least one parameter at the second location, andusing the electrical power to produce and propagate signal acoustic waves back to the first location, the characteristics of the signal acoustic waves being a function of the measure of the parameter; andat the first location, measuring the signal acoustic waves and outputting a value that is a function of the measure of the parameter.

24. The method according to claim 23, further including, at the second location, storing the electrical power.

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