Wireless sensor reader with multiple fixed excitation frequencies

Abstract

A wireless sensor reader configured to determine a resonant frequency of a sensor may include a transmit circuit configured to transmit a wireless excitation pulse to the sensor at a transmit frequency to excite a resonant circuit within the sensor to resonate at a frequency proportional to a measured parameter, and a receiver circuit configured to receive the resonant circuit from the sensor. The receiver circuit is configured to receive a response signal from the sensor, the response signal being a continuous wave at a resonant frequency of the sensor. The wireless sensor reader may also include circuitry for determining a frequency of the sensor response signal, where the reader selects a transmission frequency of the excitation pulse from a plurality of discrete narrowband frequencies, the selection occurring prior to determining the frequency of the sensor response signal.

Description

Cross-references to related applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 468,354, filed May 23, 2023, entitled “WIRELESS SENSOR READER WITH MULTIPLE FIXED EXCITATION FREQUENCIES”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure generally relates to wireless sensor systems, and more specifically to wireless sensor systems in which a sensor is read by a reader, wherein the sensor is an LC resonant cavity circuit, and wherein the reader wirelessly excites the sensor to resonate, receives the reflected response signal, and determines its frequency, which has a known relationship with the measured physical parameter. Background Technology

[0003] Wireless sensor systems can employ resonant circuit technology, which utilizes passive wireless sensors to communicate remotely with excitation and reader circuitry. Typically, wireless sensors are implanted in specific locations, such as inside the human body, to detect and report sensed parameters. In some systems, the sensed parameters alter the resonant frequency of the wireless sensor. The reader can detect the resonant frequency of the wireless sensor to determine the sensed parameters.

[0004] In one application, a passive wireless sensor system can employ resonant circuit technology. The passive wireless sensor system can be a pressure monitoring device, for example, for its own use or integrated into other medical devices, including but not limited to pacemakers, defibrillators, drug elution devices, ventricular assist devices (VADs), etc. In one embodiment, the medical device may include one or more sensors configured to be positioned at a desired location within the human body. One or more sensors may be fabricated using microelectromechanical systems (MEMS) technology and may be configured to wirelessly transmit data to an external receiver or reader to facilitate the transmission of diagnostic health data to, for example, physicians, clinicians, nurses, caregivers, or patients.

[0005] Such a sensor, fabricated using MEMS technology, incorporates inductive and capacitive components. For example, the sensor includes an inductor (L) and a capacitor (C) connected in parallel, commonly referred to as an LC cavity circuit. The sensor's geometry allows the capacitor plates to deform as pressure increases. This deformation causes the plates to deflect, resulting in a change in the system's capacitance. The LC cavity circuit also generates an electronic resonant frequency. This resonant frequency is related to the circuit's inductance and capacitance values ​​and will change with the deflection of the capacitor plates under varying pressure. This emitted resonant frequency signal is received by an external wireless receiver or reader and decrypted into the associated pressure reading.

[0006] Such sensors can also include wireless data transmission capabilities. The device may not require a battery or internal power source. Instead, the sensor can be powered by an inductively coupled electromagnetic (EM) field directed towards its inductor coil. The receiver or reader can provide the electromagnetic field by generating a radio frequency (RF) burst or other signal. The sensor's inductor receives energy from the EM field, causing the sensor's LC cavity to resonate and store energy. When the external EM field is removed, the inductor and capacitor form a parallel resonant circuit, radiating energy through the inductor, which acts as an antenna. This oscillating circuit then generates an RF signal with a frequency proportional to the sensor's capacitance, which varies with pressure. The sensor's inductor coil can function both as an inductor generating an oscillating RF signal with a frequency proportional to the sensor's capacitance at a specific pressure, and as an antenna coil transmitting the RF signal generated by the LC cavity circuitry to provide the oscillating RF signal to the reader.

[0007] The pressure sensor may include an inductor / capacitor circuit system assembled in a parallel configuration. In other embodiments, it may include a piezoelectric, piezoresistive, or capacitive pressure sensor. In the inductor / capacitor circuit system, the resonant frequency of the excited circuit will vary with the patient's internal pressure. The sensor wirelessly transmits the sensed or detected pressure reading to an external system receiver via an RF signal, without requiring an internal power supply. In a particular embodiment, the sensor may be excited by an electromagnetic field directed at the circuit system of the sensor.

[0008] Wireless sensor readers for frequent use by patients at home are particularly useful for measuring vital parameters of interest to caregivers. However, to ensure consistent and accurate readings by patients, improvements to the system's functionality, particularly the reader's features and usability, are needed. Furthermore, it is essential to allow users to easily integrate the reader and related systems into their daily lives and to enhance the reader's reliability in the field to ensure functional, accurate, and secure data management.

[0009] Other existing technologies have proposed frequency sweep systems to achieve the same purpose. In these systems, multiple excitation pulses are transmitted from the reader to the sensor, each pulse having a different transmission frequency f. xmt And relative to the previous f of that parameter xmt The values ​​are observed to represent changes in system parameters. These changes can be the power delivered to the sensor by the reader, the amplitude or phase of the sensor response or 'ringing' signal, or other parameters. When a changed parameter is at or near its maximum or minimum value, it is assumed that the sensor is at its resonant frequency. The excitation frequency f used to induce a response at sensor resonance is assumed. xmt By matching the resonant frequency of the sensor, the physical parameters being measured can now be derived.

[0010] The reader application US Publication No. 20230072070 details the methods and systems for performing this measurement, the entire contents of which are incorporated herein by reference. However, these methods and systems do not use the frequency sweep method described above. Instead, a single excitation frequency f is pre-selected before the reading even begins. xmt The excitation frequency drives the sensor to resonate, then suddenly stops. The sensor will continue to resonate for a period of time, the duration of which is determined by f. xmt Signal strength, the physical distance between the reader and sensor antenna (referred to as the "link distance"), the transmitted signal and the sensor's RF quality (Q) factor, and f xmt and the resonant frequency f of the sensor res The increment between them determines the signal. When it resonates, the sensor transmits a response, or 'ringing-back' signal, that the reader can receive. The ringing-back signal can only be received at f. res The lower resonance is typically very weak and decays rapidly to zero. The reader must determine f before the response signal disappears. res This "fixed frequency" transmission method has advantages over the "frequency sweep" method. Its circuitry is typically smaller and less power-intensive, facilitating the design of handheld readers. Its control algorithms are generally simpler and less susceptible to interference from nearby non-sensor radiators or spurious locks with their own frequencies.

[0011] However, this fixed-frequency method has its own limitations. When the excitation frequency f xmt Equal to the sensor's resonant frequency f res At this time, the sensor's resonator stores the maximum RF energy, and the response signal it reflects back to the reader has a high signal strength (SS), providing the reader with a strong signal-to-noise ratio and a longer duration of response signal, thus enabling more accurate phase or frequency measurements. With f xmt Stay away from f res The sensor's response signal strength will rapidly decrease. At f xmt and f resAt some point between these intervals, the sensor response signal becomes too weak for the reader to detect. Therefore, a fixed-frequency system must be designed so that the reader's excitation signal frequency f is... xmt Always close enough to the sensor f res This generates a signal that is higher than the reader’s minimum signal strength (power amplitude) detection threshold, thereby providing more accurate phase or frequency measurements.

[0012] Such a design may impose other limitations on the system. The sensor must be designed to operate across its full range f. res The operating range is narrow enough, always within a certain bandwidth, which is the bandwidth of the reader's f xmt Centered on. For example, f xmt A fixed-frequency reader at 13.5 MHz can be used with sensors operating over a bandwidth spanning 13 MHz to 14 MHz, which corresponds to the pressure measurement range of 550 – 900 mmHg seen on the x-axis. The hash center arrow is f. xmt = 13.5 MHz is the narrowband excitation signal of the reader. The bell curve represents the sensor's transfer function, which indicates the sensor's response strength to the excitation signal at different frequencies. When the measured pressure is 737 mmHg, the sensor at f res Resonance occurs at 13.462 MHz, as indicated by the solid arrow to the left of the central arrow. According to the sensor's response curve, the amplitude of this arrow is very high, indicating a strong response signal far exceeding the reader's detection threshold, as shown by the scattering horizontal lines in the figure. In another measurement, when the pressure was 689 mmHg, f... res It becomes 13.602 MHz, located to the right of the center, at a distance of f xmt At a slightly greater distance, the signal may be slightly less accurate, but it is still strong enough to be detected. At pressures far from the center, such as 870 mmHg, f res = 13.120 MHz, which is too weak for the reader to detect.

[0013] The exemplary fixed-frequency system shown has a limited operating measurement range, confined to the space between the two points where the sensor response curve intersects the reader's detection threshold line, approximately 673–778 mmHg in this example. Designs of LC resonant cavity microsensors with wider operating ranges typically incur undesirable losses in size, accuracy, precision, and manufacturability. Therefore, a wireless LC resonant cavity sensor reader system is needed that retains the fixed-frequency range. xmt The architecture offers advantages, but allows for the detection of sensor frequencies f within a wide operating bandwidth. res . Summary of the Invention

[0014] The following is an overview of this disclosure to provide a basic understanding of certain aspects. This overview is not intended to identify key or essential elements, nor is it intended to define any limitations of the embodiments or claims. Furthermore, this overview provides a simplified overview of aspects that may be described in more detail in other parts of this disclosure. Any described aspect may be separated from or combined with other described aspects, and is not limited to having the same effect as when they are described individually and explicitly in every possible combination.

[0015] A wireless sensor reader configured to determine the resonant frequency of a sensor is disclosed. It may include a transmitting circuit and a receiver circuit. The transmitting circuit is configured to transmit a wireless excitation pulse to the sensor at a transmission frequency, thereby exciting a resonant circuit within the sensor to resonate at a frequency proportional to a measurement parameter. The receiver circuit is configured to receive a response signal from the sensor, the response signal being a continuous wave at the sensor's resonant frequency. The wireless sensor reader may further include circuitry for determining the frequency of the sensor response signal, wherein the reader selects the transmission frequency of the excitation pulse from a plurality of discrete narrowband frequencies, this selection occurring before determining the frequency of the sensor response signal. The reader acquires a plurality of samples of the sensor response signal within a measurement time interval, the frequency of each of the plurality of samples being determined by the circuitry for determining the frequency, and each of the plurality of samples of the sensor response signal being initiated by an excitation pulse at the same transmission frequency throughout the entire measurement time interval.

[0016] The described devices, systems, and methods can provide a wider operating range for LC resonant cavity sensors and microsensors without undesirable losses in size, accuracy, precision, and manufacturability. The devices, systems, and methods can provide a wireless LC resonant cavity sensor reader system that retains a fixed f... xmt The architecture offers advantages, but allows for the detection of sensor frequencies f over a wide operating bandwidth. res .

[0017] A wireless sensor reader is disclosed, configured to determine the resonant frequency of a sensor. In one embodiment, the reader may include a transmitting circuit configured to transmit a wireless excitation pulse to the sensor at a transmitting frequency, thereby exciting a resonant circuit within the sensor to resonate at a frequency proportional to a measured parameter. In another embodiment, the reader may include a receiver circuit configured to receive a response signal from the sensor, the response signal being a continuous wave at the sensor's resonant frequency. In yet another embodiment, the reader may include circuitry for determining the frequency of the sensor's response signal.

[0018] In one embodiment, the reader can select the transmission frequency of the excitation pulse from a plurality of discrete narrowband frequencies. In another embodiment, this selection can occur before the determination of the frequency of the sensor response signal. In another embodiment, the reader can acquire multiple samples of the sensor response signal within a measurement time interval. In another embodiment, the frequency of each of the plurality of samples of the sensor response signal can be determined by the circuitry used to determine the frequency. In yet another embodiment, each of the plurality of samples of the sensor response signal can be initiated by an excitation pulse at the same transmission frequency throughout the entire measurement time interval.

[0019] In one embodiment, the circuitry for determining the frequency of the sensor response signal may include a phase-locked loop (PLL) configured to lock an internal continuous wave signal to the response signal before the response signal disappears, such that the frequency of the internal signal matches the frequency of the sensor response signal. In another embodiment, the PLL may also be configured to maintain the internal signal at a constant frequency before the response signal disappears. In another embodiment, the constant frequency of the internal signal may be equal to the frequency of the sensor response signal. In yet another embodiment, the reader may further include circuitry for determining the frequency of the maintained internal signal while it is maintained at a constant frequency. In yet another embodiment, the circuitry for determining the frequency of the maintained internal signal may be configured to measure the elapsed time of one cycle of the internal signal.

[0020] In one embodiment, the selection of the emission frequency of the excitation pulse may occur before the determination of the frequency of the sensor response signal. In another embodiment, the reader may also be configured to select the initial emission frequency of the excitation pulse using previously measured data at the start of the measurement time interval. In this embodiment, the previously measured data may be selected from: past measurements of ambient pressure, mean gauge pressure, or pulmonary artery pressure, or calculated values ​​using these parameters.

[0021] In an embodiment, the reader may also be configured to measure the signal strength of the sensor response signal. In an embodiment, the reader may also be configured to determine whether the measured signal strength value is within a preset threshold window. In an embodiment, the window may have a lower limit and an upper limit, the lower limit defining the minimum signal strength required for the reader to perform frequency detection, and the upper limit defining the maximum signal strength allowed to prevent the receiver circuitry from saturating. In an embodiment, the reader may also be configured to provide an auditory, visual, or tactile cue to a user indicating whether the sensor response signal strength is within the window. In an embodiment, the reader may also be configured to select the transmission frequency by emitting a plurality of excitation pulses, each excitation pulse having a different frequency selected from the plurality of discrete narrowband frequencies, and the selection of the transmission frequency is based on the signal strength of the sensor response signal for each of the excitation pulses.

[0022] In an embodiment, the reader may also be configured to repeat a portion of its transmit frequency selection process when more than one of the plurality of discrete narrowband frequencies results in a sensor response signal that saturates the receiver circuitry. In an embodiment, the repeating portion may include repeating the following step: wherein the user repositions the reader in response to the tactile cue. In an embodiment, the reader may also be configured to use previously measured data to exclude a transmit frequency from the plurality of discrete narrowband frequencies when the transmit frequency is not the frequency closest to the sensor resonant frequency. In an embodiment, the reader may record data during each reading interval to include the previously measured data in future reading intervals.

[0023] In one embodiment, the reader may also be configured to analyze samples of the sensor response signal over a portion of the measurement time interval to determine whether the frequency of the samples is closer to a different narrowband frequency among the plurality of discrete narrowband frequencies than the current excitation signal frequency. In another embodiment, the reader may also be configured to change the current excitation signal frequency to the different narrowband frequency among the plurality of discrete narrowband frequencies for the remainder of the measurement time interval. In yet another embodiment, the plurality of discrete narrowband frequencies may be spaced along a spectrum spanning the full range of the sensor's resonant frequency.

[0024] In an embodiment, the transfer functions of the sensors at adjacent discrete narrowband frequencies on the spectrum can overlap to ensure that the sensor response signal at each frequency within the full range of the sensor resonant frequency has at least one reader transmission frequency capable of exciting the sensor to provide a sensor response signal with sufficient energy for the reader to determine the frequency of the response signal. In an embodiment, the reader can also be configured to select an excitation signal transmission frequency from adjacent frequencies when the intensity of the response signal is equal for two adjacent frequencies. In an embodiment, the selection of the excitation signal transmission frequency can be performed by an algorithm selected from the group consisting of: selecting the transmission frequency closest to the estimated sensor resonant frequency based on measurement parameters; selecting the transmission frequency based on past readings of the sensor resonant frequency; selecting the transmission frequency closest to the center of the full range; selecting the transmission frequency most frequently used in past readings; selecting the transmission frequency based on data from the patient's medical history; and selecting the transmission frequency based on the patient's posture measured by a tilt sensor on the reader.

[0025] In an embodiment, the plurality of samples of the sensor response signal on the measurement time signal may include the output waveform of the measurement parameters. In an embodiment, the plurality of samples of the sensor response signal may be processed to obtain the output parameters, the sample processing being selected from: averaging, low-pass filtering, band-pass filtering, weighted averaging, rolling window averaging, Fourier transform, wavelet transform, differentiation, integration, curve fitting, area under the curve calculation, trend analysis, correlation with other datasets, standard deviation, analysis of variance, minimum and maximum value detection, rise and fall times, or other mathematical data processing. In an embodiment, the sensor resonant frequency may be proportional to cardiac pressure, and the sample processing is further selected from: heart rate detection, respiratory rate detection, peak systolic detection, minimum diastolic detection, cardiac output estimation, flow rate estimation, arrhythmia detection, irregular breathing detection, vascular compliance estimation, patient posture, patient activity, patient health status, and comparison of any of these parameters with a predetermined threshold. In an embodiment, the patient health status may include one or more of vital signs, comorbidities, medications, age, and weight.

[0026] In an embodiment, the reader may also be configured to calculate a rate-of-change trend of the sensor resonant frequency during the measurement time interval, and to automatically switch the excitation emission frequency to the new value if the rate-of-change trend indicates that the sensor resonant frequency may remain closer to the new value for the remainder of the time interval. In an embodiment, the sensor resonant frequency may be proportional to cardiac pressure. In an embodiment, the automatic switching of the excitation frequency may occur each time the cardiac pressure approaches its systolic maximum or diastolic minimum. In an embodiment, the circuitry for determining the frequency may be configured to determine the emission frequency independently of the excitation pulse.

[0027] The following description and figures disclose various illustrative aspects. Some improvements and novel aspects may be clearly identified, while others may be apparent from the description and figures. Attached Figure Description

[0028] The object, advantages, and operation of the present invention can be better understood by referring to the following detailed description in conjunction with the following figures, wherein:

[0029] Figure 1 A graph depicting the prior art sensor response curve intersecting with the reader detection threshold line is shown;

[0030] Figure 2 A graph depicting the transmission and sensor response curves for four fixed frequency bands is shown, identifying the frequency and pressure;

[0031] Figure 3 A flowchart of the fixed-frequency transmission control algorithm is shown;

[0032] Figure 4 This is an example of a wireless sensor system.

[0033] This invention may be embodied in various forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, not in the preceding detailed description. Therefore, all embodiments falling within the equivalent meaning and scope of the claims are intended to be covered by the claims. Detailed Implementation

[0034] Reference will now be made in detail to exemplary embodiments of this teaching, examples of which are illustrated in the accompanying drawings, wherein aspects with the same number denote common features throughout. It should be understood that other embodiments may be utilized, and structural and functional changes may be made without departing from the corresponding scope of this teaching. Furthermore, features of various embodiments may be combined or modified without departing from the scope of this teaching. Therefore, the following description is presented by way of illustration only and should not in any way limit the various alternatives and modifications that may be made to the illustrated embodiments, which remain within the spirit and scope of this teaching.

[0035] Throughout this disclosure, numerous specific details provide for a thorough understanding of the subject matter. It should be understood that aspects of this disclosure may be practiced in conjunction with other embodiments, and not necessarily all aspects set forth herein.

[0036] As used herein, the terms “example” and “exemplary” refer to instances or illustrations. The terms “example” or “exemplary” do not indicate key or preferred aspects or embodiments. Unless the context otherwise requires, the word “or” is intended to be inclusive rather than exclusive. As an example, the phrase “A uses B or C” includes any inclusive permutation (e.g., A uses B; A uses C; or A uses both B and C). On the other hand, unless the context otherwise requires, the articles “a” and “one” generally mean “one or more”.

[0037] A wireless sensor reader is disclosed. In an embodiment, the wireless sensor reader can be configured to determine the resonant frequency of a sensor and can include a transmitting circuit and a receiving circuit. The transmitting circuit is configured to transmit a wireless excitation pulse to the sensor at a transmitting frequency, thereby exciting the resonant circuit within the sensor to resonate at a frequency proportional to the measured parameters. The receiving circuit is configured to receive a response signal from the sensor, the response signal being a continuous wave at the sensor's resonant frequency.

[0038] The wireless sensor reader may also include circuitry for determining the frequency of the sensor response signal, wherein the reader selects the transmission frequency of an excitation pulse from a plurality of discrete narrowband frequencies, the selection occurring before determining the frequency of the sensor response signal, wherein the reader acquires a plurality of samples of the sensor response signal during a measurement time interval, the frequency of each of the plurality of samples of the sensor response signal being determined by the circuitry for determining the frequency, and each of the plurality of samples of the sensor response signal being initiated by an excitation pulse at the same transmission frequency throughout the entire measurement time interval.

[0039] Wireless sensor systems typically include reader units or devices configured to be in a state of use, reading from sensors, and in a state of rest, not communicating with sensors. For example, the disclosed reader may be handheld or battery-powered and adapted for use for a few minutes each day. For example, the disclosed reader may be handheld or battery-powered and adapted for use over discrete or preset time periods, including, for example, during a scheduled physical activity such as exercise, walking, cycling, etc. For example, the disclosed reader may be handheld or battery-powered and adapted for use during exercise, and the reader may be programmed to dynamically change the Tx band as needed during a walking test (e.g., a 9-minute walking test). The disclosed reader may also be configured to sit at a charging station or connection station when not in use. It should be noted that the disclosed sensor and reader systems can incorporate many types of wireless technologies, including, for example, active and passive sensors, continuous wave (CW) and modulated data transmission, analog and digital systems, etc.

[0040] The illustrated parameter values ​​demonstrate the operational concept of this system. Here, the reader is designed to transmit excitation pulses at multiple discrete narrowband fixed frequencies, four in this example. Note that any number of transmission bands can be used, including two, three, four, five, six, seven, eight, nine, ten, or more transmission bands and f. xmt Frequency. In the example, the reader can transmit more than one, more than two, multiple, or several transmission bands and f. xmt frequency. Figure 2 The four f shown xmt Each frequency is located at the center of a frequency spectrum 'band', labeled A to D. The sensor's f... res Depending on the value of the parameter being measured (pressure in this example), and can be anywhere on the 13-14 MHz spectrum shown, or in other embodiments on alternative spectra such as 15-16 MHz, 11-12 MHz, 12-13 MHz, or 14-15 MHz, this reader can now be selected to have the closest value to f. res f xmt The frequency band of the value is optimized to improve energy transfer to the sensor during excitation and provide a strong and persistent ringing signal to promote f res This measurement can be used to determine the pressure at sensor locations, such as the pulmonary artery.

[0041] from Figure 2 As can be seen, each frequency in the sensor's full-range spectrum has at least one band where the transfer function is higher than the reader's detection threshold. As shown in the figure, adjacent frequency bands overlap, providing an intermediate region between two adjacent transmission frequencies, in which f... xmtThis will cause the excitation sensors to produce equal or nearly equal ringing response strengths. In actual field use, factors such as ambient noise, reader location, and manufacturing tolerances may cause asymmetry, resulting in one of the overlapping frequency bands providing a better signal strength in the sensor's returned signal than the other.

[0042] When the return signal strength (SS) between adjacent frequency bands is equal or nearly equal, the system will follow an algorithm to select one or the other frequency band and its corresponding f. xmt Such algorithms can include:

[0043] Choose the one closest to P. amb The estimated f res f xmt Regardless of whether there is a deviation from the mean pulmonary artery pressure (mPAP) of historical readings;

[0044] Select the frequency band closest to the center of the total bandwidth; and

[0045] Frequency bands are selected based on historical data (data that was more commonly used in the past).

[0046] The diagram shown graphically illustrates how a reader determines the optimal f for a given reading from a discrete number of available frequencies. xmt The algorithm. Figure 3 The example shown is a 20-second reading from an LC resonant cavity pressure sensor located in a patient's pulmonary artery. The details and parameter values ​​provided in this application are merely exemplary and can be substituted with other values ​​without altering the system.

[0047] In step 1, at the top left corner or "Start", the reader selects its discrete transmit frequency f. xmt The first one in the equation is used for sensor excitation. Generally, it is based on the sensor's current f. res This value is chosen based on a rough estimate. For the specific case illustrated, the reader measures the ambient air pressure P in its surrounding environment. amb A small amount (typically 5-50 mmHg) is added to account for the pulmonary artery pressure exerted by the body, and this pressure is converted to frequency based on a pressure-frequency calibration lookup table or formula stored in its memory. This table or formula can be specific to a single sensor or generalized to all sensors of this type. Since a patient's pulmonary artery typically produces a small offset from the current atmospheric station pressure, this method can provide a starting point for finding the optimal frequency from among these available. xmt Using P, etc. amb The general concept of adapting the reader to the measurement parameters is described in detail in U.S. Patent No. 8,570,186, the entire contents of which are incorporated herein by reference.

[0048] In step 2, the first selected f based on environmental pressure is transmitted. xmt The signal strength (SS), or the amplitude of the ringing signal from the implant, is measured. The signal strength should be high, but not so high that it saturates the receiver amplifier circuitry used to measure it, because if different signals are saturated, their strengths cannot be compared. To achieve the desired signal strength (SS), the patient may need to move the handheld reader in response to audible or visual signals from the reader (or, in the case of a pillow-type reader, move the body relative to the reader). For example, the reader may emit a series of audible tones that vary in volume, pitch, or pulse frequency as it approaches or moves away from the optimal SS position. Different sounds may be emitted when an acceptable SS is achieved. This may take several seconds. Alternatively, a self-adjusting gain amplifier, which can be logarithmic or other types of amplifier circuitry, can be used. In this example, the SS value is converted to a digital code between 0 and 4096, where 3800-4000 is considered an acceptable SS for home mode and 3200-4000 is considered an acceptable SS for clinical mode.

[0049] If all other parameters, such as link distance, antenna tilt angle, frequency-dependent circuit parameters, and electrical characteristics of the intervening medium, remain constant, then when the sensor's f... res Closer to f xmt At that time, the sensor's return signal will always have a larger SS value.

[0050] Once SS is in the first f xmt Within the specified range, the patient is instructed not to move the reader relative to their body. The system proceeds to step 3, and while the reader remains in place, uses an excitation signal from all f... xmt The values ​​(four in the example shown) are used to obtain SS readings. Typically, these SS measurements are performed quickly over 5-20 ms to be completed before the patient moves their hand.

[0051] Step 4: Determine the first f xmt Whether to provide the highest SS. If so, the remainder of the reading process will continue using the first f. xmt (Step 9).

[0052] If not, the system proceeds to steps 5 and 6, at the highest f xmt A 'reasonableness check' is performed on the readings when the excitation signal (frequency band D shown) provides the highest signal strength. At f xmt In the case of frequency band D, we expect the environmental pressure P to be... amb The value is relatively low because the measured pulmonary artery pressure is P. ambThis is in addition to the sum of the smaller pressures (typically 5-50 mmHg) applied by the body. Because the reader provides P... amb Direct measurement, so the system can evaluate P. amb Is it low enough that band D can reasonably be expected to provide optimal SS? For example, if the reader's onboard pressure sensor measures P... amb A reading above 700 mmHg would correspond to a measured pulmonary artery pressure of 705–750 mmHg, as expected. In this example, 705–750 mmHg corresponds to an fi of 13.429–13.557 MHz. res The tests shown indicate that when f is selected from band B or band C instead of band D... xmt At that time, this frequency range will provide the strongest SS. If the reader determines P amb > 700 mmHg and frequency band D f xmt Providing the strongest SS indicates a clear measurement error, and the system ignores the frequency band Df before proceeding to step 7. xmt And select f from the frequency band with the next highest SS. xmt Note that in this example, this concept is applied to the other direction (when P). amb At very low frequencies (band A having the highest SS), this may be undesirable because some patients with conditions such as pulmonary hypertension may have very high pulmonary pressures, up to 300 mmHg. In such cases, even if P... amb At a lower frequency, band A may also have the best SS.

[0053] In the example steps described above, the expected frequency value corresponds to a fixed assumption that the body increases its pressure to ambient pressure by 5-50 mmHg. In alternative embodiments, weighted or other types of learning algorithms can be used to make different assumptions based on learned values ​​from the patient's past pulmonary artery pressure measurements. The concept of using past data to inform assumptions about future measurements can be applied to any type of measurement and is not limited to pulmonary artery pressure. In a particular example embodiment, the reader can record the gauge pulmonary pressure (pressure above ambient pressure) for a given patient daily. In step 1, a rolling window average (e.g., the average of the previous 5 days) can be added to P. amb Then the average and P amb The sum is converted into frequency, thus providing the current f. res The reader then selects the estimated value f that is closest to the estimated value of the first excitation pulse. xmt .

[0054] After the 'reasonableness check' in step 6, proceed to step 7. Here, the reader considers the possibility that at least one of the four SS values ​​measured in step 3 would saturate the receiving circuit. If so, the value of f that caused saturation in step 8 can be selected. xmt One of the values ​​is selected, and the process returns to step 2. An audio prompt from the reader guides the patient again to the optimal reader location, this time using the new f... xmt And repeat the process. If there is more than one f in step 3 xmt If the excitation pulse causes saturation, then step 7 selects the pulse closest to P. amb The corresponding frequency is determined, and the cycle is repeated. Finally, step 7 or step 9 will determine the excitation f that provides the ringback signal with the highest SS. xmt .

[0055] Now select f from the path leading to step 9 or step 10. xmt The system can then continue reading itself. In step 11, the reader reads the selected f during a portion of the total reading interval (5 seconds in this example). xmt An excitation pulse is emitted at the location, and the sensor's f is determined using a method described in the prior art. res In a typical embodiment, the reader stimulates the sensor 1000 times per second with excitation pulses, directly sampling the sensor's frequency each time. One embodiment achieves this by using a phase-locked loop (PLL) to lock the internal reader signal to the received sensor response signal. The reader opens the PLL and maintains the frequency of its output signal stable after a preset time interval, which is selected to be slightly shorter than the expected duration of the rapidly decaying sensor response signal. While the PLL remains stable at a frequency matching the now-disappearing sensor signal, the reader has time to determine that frequency using a zero-crossing timer or other methods known in the art. This embodiment and other embodiments are described in detail in the referenced prior art.

[0056] In an embodiment, the excitation signal transmission frequency can be selected from an algorithm chosen from the group consisting of: selecting the transmission frequency closest to the estimated sensor resonant frequency based on measurement parameters; selecting the transmission frequency based on past readings of the sensor resonant frequency; selecting the transmission frequency closest to the center of the full range; selecting the transmission frequency most frequently used in past readings; selecting the transmission frequency based on data from the patient's medical history; and selecting the transmission frequency based on the patient's posture measured by a tilt sensor on the reader. For example, a patient's medical history may indicate that their PAP is typically higher than the ambient value. The reader can use this information to determine the patient's possible initial f xmtIt is known in the art that when a patient is lying down, their PAP typically increases by a certain amount, usually around 5-15 mmHg, compared to when they are in an upright (sitting or standing) position. The reader may include an accelerometer or other tilt sensor to determine the patient's posture and use this information to predict optimal posture. xmt The input. For example, the initial f xmt The PAP can be derived from environmental stress plus the patient's typical physical PAP, plus the offset caused by the patient's posture measured during a clinical calibration visit, in which the patient uses a reader to measure the PAP increment between the supine and upright positions.

[0057] In this embodiment, the sensor resonant frequency may be proportional to cardiac pressure, and sample processing may also be selected from: heart rate detection, respiratory rate detection, peak systolic pressure detection, minimum diastolic pressure detection, cardiac output estimation, flow rate estimation, arrhythmia detection, irregular breathing detection, vascular compliance estimation, patient posture, patient activity, patient health status, and comparison of any of these parameters with predetermined thresholds. In this example, patient activity may be measured using an onboard accelerometer that determines step rate or steps. In this example, health status may include vital signs, comorbidities, medications, age, weight, etc.

[0058] In one embodiment, the circuitry for determining the frequency determines the emission frequency, independent of the excitation pulse. In another embodiment, the reader does not need to "know" the emission frequency of the excitation signal in order to determine the sensor's resonant frequency.

[0059] Returning to the example shown, step 12 simply checks if the full time interval for the reading has elapsed. In our pulmonary artery pressure example, this interval is 20 seconds long to allow for several respiratory cycles. Throughout the interval, the reader provides audio cues to the patient to ensure the device is securely held against the chest. During this interval, each f res Each sample may have its own SS reading, and individual SS readings below the selected threshold may be rejected. Rolling window weighted averaging or other filtering methods can be used to filter the measured f. res Perform low-pass filtering. Many other low-pass filtering and spurious signal suppression methods can be used to obtain the most accurate f. res reading.

[0060] If the interval has not yet elapsed, the system can proceed to step 13. This step checks the average measurement f. res The case where the reader moves from one transmitter band to another within a previous 5-second interval. The reader's maximum and minimum f... res From this interval, select the midpoint. If the midpoint has been moved closer to a different f...xmt If the reader changes to the new value in step 14 and returns to step 2, it can signal the patient to reposition the reader so that SS is within range. (Not shown in the figure, the reader can limit the change of f in this manner to a given measurement interval.) xmt The number of reads is adjusted to avoid excessively long read times and user relocation. In addition, besides the minimum and maximum f... res Beyond the midpoint, other methods can be used to extract the full pressure waveform within the measurement interval into a single value. Examples include averaging, mean, mode, or weighted average.

[0061] If we start from step 13, the filtered measurement f res It did not move to a position closer to the currently used f xmt Different f xmt The system then proceeds to step 15, which is a repetition of the 'reasonableness check' that began in step 5. If the system selects an f value corresponding to a pressure much lower than the ambient pressure... xmt If the reasonableness check fails, then in step 16, all f values ​​at or above that frequency are ignored. xmt The value is then returned to step 2. In the diagram shown, step 15 instructs that f be... xmt With P amb The comparison is made as shown in step 5, but in an alternative embodiment, it can be compared with the measurement f calculated in step 13. res Compare the midpoints. If f xmt If the value is still within a reasonable range and passes the reasonableness test in step 15, the process returns to step 11 for another measurement interval with an exemplary value of 5 seconds.

[0062] After the measurement interval, the system determines in step 12 whether a complete measurement time has elapsed. Figure 3 (20 seconds in the middle). If not, control proceeds to step 13. If yes, the excitation pulse stops, and f is no longer acquired. res Sample. In step 17, the reader's processor calculates the mean pulmonary artery pressure (mPAP) for the entire 20-second reading. (Not shown in the flowchart, the processor can also process data rejected throughout the process due to insufficient SS, readings outside the expected range, or any other reason.) res The number of samples is counted. If the cumulative number of rejected samples exceeds a preset threshold, such as 10% of the samples, the reader can reject the entire read, return to step 1, and start again. Alternatively, it can send a read failure message to the user and wait until a new read is initiated, or suggest that the user take action, such as contacting customer support.

[0063] In step 18, the reader calculates the meter pressure mPAP, i.e., P.amb The above is mPAP. It stores this value and can be used with other historical values ​​to predict the possible f at the start of the next read. res This prediction can be performed using machine learning and artificial intelligence algorithms known in the field.

[0064] Although the parameters shown include those specific to pulmonary artery pressure (PAP) measurements, they can be easily generalized to any wireless sensor measurement based on a passive LS resonant cavity excited by an external reader. To achieve this generalization, it is only necessary to... Figure 3 The specific parameters in the code are converted into the following general parameters:

[0065] P amb It can be any measured parameter

[0066] The 'reasonableness check' in steps 5 and 15 can be applied to any combination of parameter values ​​that are physically unlikely to occur in a given application; for example, in applications where the system reduces pressure below ambient pressure, we would reject f. xmt and P amb All low rather than high

[0067] In step 17, other parameters besides the final parameter average can be calculated.

[0068] In steps 17 and 18, the sensed parameters can be any parameters other than PAP.

[0069] Steps 17 and 18 are optional and depend on the application.

[0070] Specific numerical quantities (four f) xmt (e.g., 20-second read interval, 5-second sub-interval) can be replaced with any value.

[0071] implement Figure 3 Other embodiments of the system in the middle step may include the following variations:

[0072] The system can skip some steps, execute them in a different order, repeat them, or add more steps.

[0073] P amb It can be any sensed parameter; some other known values ​​used for initial value estimation and reasonableness checks can be used to help the system select its excitation frequency.

[0074] f xmt The interval does not need to be as Figure 2 The intervals shown are uniform; the intervals may vary for different patients or readings.

[0075] All time intervals in the example can be changed.

[0076] The 5-second interval can be omitted before f. xmt The re-evaluation. In other words, step 11 shown can cover the entire reading interval and will continue to step 17. Steps 12, 13, 14, 15, and 16 can be omitted.

[0077] The reader implementation can continuously monitor the midpoint or average value of the PAP and determine its trend over time. It can use this trend to predict the optimal time to switch to a new frequency band and can perform f at the optimal time. xmt The conversion, ideally, occurs before signal strength is lost.

[0078] The reader implementation can monitor the pulse pressure (PAPmax–PAPmin) for each heartbeat and can predict when the next minimum or maximum value will occur. If the pulse pressure is high enough to cross between adjacent frequency bands, the algorithm uses the rate of change of pressure relative to time (dP / dt) to predict the future pulse pressure. xmt The optimal point for switching from one frequency band to the next and then back again. The reader can change the frequency band twice during each heartbeat to optimize the frequency band closest to the implant and the patient's systolic (PAPmax) and diastolic (PAPmin) frequencies. xmt In other embodiments, the reader can rapidly dither between two frequency bands. xmt The output is then averaged to obtain a quasi-static PAP reading. Jitter can be detected by averaging the two f values. xmt The values ​​are alternated, one value per sample. Alternatively, it can be achieved by alternating two values ​​in each single-sample burst of excitation.

[0079] Go to Figure 4 This illustration shows an embodiment of a wireless sensor system that can be used in conjunction with this disclosure. A wireless system 10 is typically provided. The wireless system 10 may include a wireless reader 12 and a wireless sensor 14. The wireless sensor 14 may be a passive device, such as a device including a capacitor 16 and an inductor 18, or an active device. The wireless sensor 14 may be implantable, such as implantable within a living organism. For example, the wireless sensor 14 may be implanted within a human body to monitor conditions or parameters within the body.

[0080] The reader 12 can be configured to emit an excitation pulse 20 to excite the sensor 14. The excitation pulse 20 can cause the sensor 14 to ring at its resonant frequency or emit a ringing signal 22. The resonant frequency of the sensor 14 can vary based on parameters sensed by the sensor 14. The reader 12 can measure the frequency of the ringing signal 22 and determine the sensed parameters. For example, the reader 12 can use formulas, lookup tables, or calibration tables to determine the sensed parameters.

[0081] Reader 12 may include a receiver for receiving ringing signal 22 from sensor 14. The receiver may include antenna 24 or any other signal receiving device. The receiver may also include one or more filters, such as analog or digital filters, to filter the signal 22 received from sensor 14. The filters may be tuned to a passband to allow reader 12 to receive the desired frequency bandwidth. In an embodiment, the reader may include sensor 25.

[0082] It should be understood that the systems and methods described herein can be applied to any measured or sensed parameter, such as pressure, temperature, or any other parameter.

[0083] The embodiments of this disclosure have been described above. It is obvious that modifications and alterations will be made by others after reading and understanding this specification. The following claims are intended to cover all modifications and alterations, provided they are within the scope of the claims or their equivalents.

Claims

1. A wireless sensor reader configured to determine the resonant frequency of a sensor, comprising: A transmitting circuit is configured to transmit wireless excitation pulses to the sensor at a transmitting frequency, thereby exciting a resonant circuit within the sensor to resonate at a frequency proportional to the measurement parameters. A receiver circuit is configured to receive a response signal from the sensor, the response signal being a continuous wave at the sensor's resonant frequency. as well as Circuit used to determine the frequency of the sensor's response signal; The reader selects the emission frequency of the excitation pulse from a plurality of discrete narrowband frequencies, and the selection occurs before the determination of the frequency of the sensor response signal; The reader acquires multiple samples of the sensor's response signal within a measurement time interval; The frequency of each of the plurality of samples of the sensor response signal is determined by the circuit used to determine the frequency; and Each of the plurality of samples of the sensor response signal is initiated by an excitation pulse at the same emission frequency throughout the entire measurement time interval.

2. The wireless sensor reader according to claim 1, wherein, The circuitry used to determine the frequency of the sensor response signal includes a phase-locked loop configured to lock an internal continuous wave signal to the response signal before the response signal disappears, such that the frequency of the internal signal matches the frequency of the sensor response signal.

3. The wireless sensor reader according to claim 2, wherein, The phase-locked loop is also configured to maintain the internal signal at a constant frequency until the response signal disappears, the constant frequency of the internal signal being equal to the frequency of the sensor response signal.

4. The wireless sensor reader according to claim 3, wherein, The reader also includes a circuit system for determining the frequency of the held internal signal when it is maintained at a constant frequency.

5. The wireless sensor reader according to claim 4, wherein, The circuitry used to determine the frequency of the held internal signal is configured to measure the elapsed time of one cycle of the internal signal.

6. The wireless sensor reader according to claim 1, wherein, The selection of the emission frequency of the excitation pulse occurs before the determination of the frequency of the sensor response signal.

7. The wireless sensor reader according to claim 1, wherein, The reader is also configured to use previously measured data to select the initial emission frequency of the excitation pulse at the start of the measurement time interval.

8. The wireless sensor reader according to claim 7, wherein, The previously measured data were selected from past measurements of ambient pressure, mean gauge pressure, and pulmonary artery pressure, or calculated values ​​using these parameters.

9. The wireless sensor reader according to claim 1, wherein, The reader is also configured to measure the signal strength of the sensor's response signal.

10. The wireless sensor reader according to claim 9, wherein, The reader is also configured to determine whether the signal strength measurement is within a preset threshold window, the window having a lower limit and an upper limit, the lower limit defining the minimum signal strength required for the reader to perform frequency detection, and the upper limit defining the maximum signal strength allowed to prevent the receiver circuit from saturating.

11. The wireless sensor reader according to claim 10, wherein, The reader is also configured to provide the user with auditory, visual, or tactile cues indicating whether the sensor response signal strength is within the window.

12. The wireless sensor reader according to claim 11, wherein, The reader is also configured to select the transmission frequency by emitting a plurality of excitation pulses, each excitation pulse having a different frequency selected from the plurality of discrete narrowband frequencies, and the selection of the transmission frequency is based on the signal strength of the sensor response signal of each of the excitation pulses.

13. The wireless sensor reader according to claim 12, wherein, The reader is also configured to repeat a portion of its transmit frequency selection process when more than one of the plurality of discrete narrowband frequencies causes a sensor response signal that saturates the receiver circuitry. The repeated portion includes repeating the following steps: wherein the user repositions the reader in response to the tactile cue.

14. The wireless sensor reader according to claim 7, wherein, The reader is also configured to use the previously measured data to exclude the selection of a transmission frequency from the plurality of discrete narrowband frequencies when the transmission frequency is not the frequency closest to the resonant frequency of the sensor.

15. The wireless sensor reader according to claim 7, wherein, The reader records data during each reading interval to include the previously measured data in future reading intervals.

16. The wireless sensor reader according to claim 1, wherein, The reader is further configured to analyze samples of the sensor response signal over a portion of the measurement time interval to determine whether the frequency of the samples is closer to a different narrowband frequency among the plurality of discrete narrowband frequencies than the current excitation signal frequency, and wherein the reader is further configured to change the current excitation signal frequency to the different narrowband frequency among the plurality of discrete narrowband frequencies for the remainder of the measurement time interval.

17. The wireless sensor reader according to claim 1, wherein, The plurality of discrete narrowband frequencies are spaced along a spectrum spanning the full range of the sensor's resonant frequency.

18. The wireless sensor reader according to claim 17, wherein, The transfer functions of the sensors at adjacent discrete narrowband frequencies on the spectrum overlap with each other to ensure that the sensor response signal at each frequency within the full range of the sensor resonant frequency has at least one reader transmission frequency that can excite the sensor to provide a sensor response signal with sufficient energy for the reader to determine the frequency of the response signal.

19. The wireless sensor reader according to claim 18, wherein, The reader is also configured to select an excitation signal transmission frequency from the adjacent frequencies when the intensity of the response signal is equal for two adjacent frequencies.

20. The wireless sensor reader according to claim 19, wherein, The selection of the excitation signal transmission frequency is performed by an algorithm selected from the group consisting of: selecting the transmission frequency closest to the estimated sensor resonant frequency based on measurement parameters; selecting the transmission frequency based on past readings of the sensor resonant frequency; selecting the transmission frequency closest to the center of the full range; and selecting the transmission frequency most frequently used in past readings. The transmission frequency is selected based on data from the patient's medical history; and the transmission frequency is selected based on the patient's posture measured by a tilt sensor on the reader.

21. The wireless sensor reader according to claim 1, wherein, The multiple samples of the sensor response signal on the measurement time signal include the output waveform of the measurement parameters.

22. The wireless sensor reader according to claim 1, wherein, The plurality of samples of the sensor response signal are processed to obtain output parameters, wherein the sample processing is selected from the following: averaging, low-pass filtering, band-pass filtering, weighted averaging, rolling window averaging, Fourier transform, wavelet transform, differentiation, integration, curve fitting, area under the curve calculation, trend analysis, correlation with other datasets, standard deviation, analysis of variance, minimum and maximum value detection, rise and fall time, or other mathematical data processing.

23. The wireless sensor reader according to claim 22, wherein, The sensor resonant frequency is proportional to cardiac pressure, and the sample processing is further selected from: heart rate detection, respiratory rate detection, peak systolic value detection, minimum diastolic value detection, cardiac output estimation, flow rate estimation, arrhythmia detection, irregular breathing detection, vascular compliance estimation, patient posture, patient activity, patient health status, and comparison of any of these parameters with a predetermined threshold.

24. The wireless sensor reader according to claim 22, wherein, The patient's health status includes one or more of the following: vital signs, comorbidities, medications, age, and weight.

25. The wireless sensor reader according to claim 1, wherein, The reader is also configured to calculate the rate of change trend of the sensor resonant frequency during the measurement time interval, and to automatically switch the excitation emission frequency to the new value if the rate of change trend indicates that the sensor resonant frequency may remain closer to the new value for the remainder of the time interval.

26. The wireless sensor reader according to claim 25, wherein, The sensor's resonant frequency is proportional to cardiac pressure, and the automatic switching of the excitation frequency occurs each time the cardiac pressure approaches its maximum systolic value or minimum diastolic value.

27. The wireless sensor reader according to claim 1, wherein, The circuitry used to determine the frequency determines the emission frequency, which is independent of the excitation pulse.

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