Frequency modulation communication

Abstract

Methods and systems for low power communication using ultrasound are described herein. The method may include receiving, at one or more ultrasound transducers of the implantable device, ultrasound waves transmitted by an interrogator; and transmitting ultrasonic backscatter comprising encoded data from one or more ultrasonic transducers of the implantable device, where the data is encoded into the ultrasonic backscatter by modulating a frequency of the ultrasonic backscatter. In some embodiments, an apparatus may include an ultrasonic transducer configured to receive ultrasonic waves and emit ultrasonic backscatter; a switch configured to modulate a frequency of the emitted ultrasonic backscatter; and circuitry configured to operate the switch to encode data in the transmitted ultrasonic backscatter based on the frequency.

Description

[0001] priority

[0002] This application claims priority to U.S. patent application No. 63 / 322,987, filed on March 23, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Methods and systems for low power communication using ultrasound backscatter communication are described herein. Implantable devices using such methods and systems are also described. Background Art

[0004] Backscattered ultrasonic communication is a low-power communication method for transmitting data. This low-power method is preferred for communication between a device implantable in a patient and an external device (referred to herein as an interrogator). Typical communication between an interrogator and an implantable device may include the emission of backscattered ultrasonic pulses based on amplitude modulation at the implantable device. However, amplitude modulation is affected by noise problems (e.g., passive reflections from environmental structures), and therefore low signal-to-noise ratios (SNRs) cause digital communication errors between the interrogator and the implantable device. Alternatives to amplitude modulated backscattered communication include active transmission and elimination methods. However, as further described below, these alternatives may introduce significant disadvantages.

[0005] Active transmission typically relies on an internal battery to power the signal transmission outside the body. Active implants have an expanded read range, allow for more variation in transmitted information, and eliminate problems from passive reflections. While active transmission avoids the amplitude modulation problem, the introduction of a battery may increase the necessary size of the implant and introduce new challenges regarding battery recharging, safety, and cost.

[0006] Cancellation methods can be introduced to limit environmental interference passive reflections from environmental interference. Cancellation methods send a passive pulse to "learn" the reflective environment, and then send a calibrated active pulse to determine the modulation caused by the implant. Using the difference in these two reflections helps to limit the impact of environmental structure, which can also reflect ultrasound waves that cause passive reflections. Although this limits the problems caused by passive reflections, these cancellation methods do not take into account environmental interference and changes that occur after the training pulse during actual data transmission.

[0007] Therefore, there remains a challenge in overcoming passive reflections during ultrasound backscatter communications between an interrogator and an implantable device. Summary of the invention

[0008] Amplitude modulation can be used to encode data into ultrasonic backscatter in order to send information from an implantable device to an external device. However, as described in the previous section, communications based on amplitude modulation are affected by noise from passive reflections and other sources of reflection interference, which can negatively affect communications. Therefore, there remains a need to encode data into ultrasonic backscatter to enable low-power and low-noise communications between an implantable device and an interrogator.

[0009] Methods and systems for low-power communication using ultrasound are described herein. The method may include: receiving ultrasound transmitted by an interrogator at one or more ultrasound transducers of an implantable device; and transmitting ultrasound backscatter including encoded data from one or more ultrasound transducers of the implantable device, wherein the data is encoded into the ultrasound backscatter by modulating the frequency of the ultrasound backscatter. The device may include: an ultrasound transducer configured to receive ultrasound and transmit ultrasound backscatter; a switch configured to modulate the frequency of the transmitted ultrasound backscatter; and a circuit (which is optionally an integrated circuit) configured to operate the switch to encode data in the transmitted ultrasound backscatter based on the frequency.

[0010] A method for low-power communication using ultrasound may include: receiving ultrasound transmitted by an interrogator at one or more ultrasound transducers of an implantable device; and emitting ultrasound backscatter including encoded data from one or more ultrasound transducers of the implantable device, wherein the data is encoded into the ultrasound backscatter by modulating the frequency of the ultrasound backscatter. The method may include selecting a switching frequency from a plurality of different switching frequencies to modulate the frequency of the ultrasound backscatter, wherein the switching frequency is configured to encode the data into the ultrasound backscatter. In some embodiments, each switching frequency is associated with a different predetermined bit pattern. Modulating the frequency of the ultrasound backscatter may include switching a switch of the implantable device at the switching frequency.

[0011] In some implementations, each predetermined bit pattern includes two or more digital bits.In some implementations, the predetermined bit patterns associated with the plurality of different switching frequencies are Gray coded.

[0012] The switching frequency may be based at least on instructions received from the interrogator via ultrasound.

[0013] A plurality of different switching frequencies may be selected based at least on the strength of ultrasonic backscatter at a given frequency.

[0014] The method may also include detecting sensor information from one or more sensors of the implantable device, wherein the data includes the one or more sensor information, and the method includes selecting a switching frequency from a plurality of different switching frequencies based at least on the sensor information. The sensor information may include, for example, one or more of power level, pH, temperature, pressure, electrophysiological pulses, and analyte concentration. In some implementations, the analyte concentration includes an oxygen level.

[0015] The method may include determining operating state information of the implantable device, wherein the data includes the determined operating state information, and the method may include selecting the switching frequency from a plurality of different switching frequencies based at least on the determined operating state information.

[0016] The method may include selecting a sequence of two or more switching frequencies from a plurality of different switching frequencies to encode data, wherein each switching frequency is associated with a different predetermined bit pattern.

[0017] The method may also include decoding the received ultrasound backscatter at the interrogator, wherein decoding the ultrasound backscatter includes analyzing an incoming frequency of the received ultrasound backscatter at the interrogator to determine a calculated switching frequency of a switch that modulates the frequency of the ultrasound backscatter, matching the calculated switching frequency to a predetermined bit pattern, and recording the predetermined bit pattern as data transmitted from the implantable device. In some implementations, decoding the backscatter includes a bit error rate of up to 6%.

[0018] The method may include adjusting a parameter of an ultrasonic wave transmitted by the interrogator based on ultrasonic backscatter received from the implantable device.

[0019] In some implementations, modulating the frequency of ultrasound backscatter can include switching a switch of the implantable device between an open state and a closed state at a switching frequency from a plurality of different switching frequencies. For example, the closed state can short-circuit the ultrasound transducer. The open state can be a load configuration in which electrical energy is harvested from the ultrasound and maximum power is delivered from the ultrasound to the implantable device to power the implantable device.

[0020] The method may include switching a switch of the implantable device between an open state and a closed state configured to periodically (eg, sinusoidally) vary acoustic energy reflected by the implantable device.

[0021] The method may include instructing the implantable device, by the interrogator via the ultrasound wave, so that the implantable device performs one or more functions. For example, the one or more functions may include determining an average incident power from the ultrasound wave.

[0022] The method may further include transmitting an ultrasonic wave from the interrogator.

[0023] The method may further include receiving ultrasonic backscatter at the interrogator.

[0024] In some implementations of the method, the interrogator includes one or more transducers for transmitting ultrasonic waves and receiving ultrasonic backscatter.

[0025] A device for communicating via ultrasound may include: an ultrasonic transducer configured to receive ultrasound and transmit ultrasonic backscatter; a switch configured to modulate the frequency of the transmitted ultrasonic backscatter; and a circuit (which is optionally an integrated circuit) configured to operate the switch to encode data in the transmitted ultrasonic backscatter based on the frequency.

[0026] In some implementations of the device, the switch can be switched at a switching frequency from a plurality of different switching frequencies, and the data encoded in the transmitted ultrasonic backscatter is based on the switching frequency, wherein each switching frequency is associated with a different predetermined bit pattern. In some implementations, each predetermined bit pattern includes two or more digital bits. In some implementations, the predetermined bit patterns associated with the plurality of different switching frequencies can be Gray coded.

[0027] The interrogator may be configured to transmit ultrasonic waves including instructions, and the switching frequency may be based at least on the instructions received from the interrogator via the ultrasonic waves.

[0028] In some implementations, the switching frequency is based at least on a relative maximum intensity of ultrasonic backscatter receivable at the interrogator.

[0029] The device may also include one or more sensors configured to detect information (e.g., sensory information), wherein the data includes the detected information, and the switching frequency from a plurality of different switching frequencies may be based at least on the detected information. The information may include, for example, a power level of the device. In some implementations, the one or more sensors include one or more of a pressure sensor, a pH sensor, a temperature sensor, and an analyte sensor.

[0030] In some implementations, the device can include a status indicator, and the switching frequency from the plurality of different switching frequencies is based at least on one or more states of the status indicator.

[0031] In some implementations, the switches may be switched in a sequence of two or more switching frequencies from a plurality of different switching frequencies to encode data. Each switching frequency may, for example, be associated with a different predetermined bit pattern.

[0032] In some implementations, the interrogator is configured to receive ultrasonic backscatter, decode the ultrasonic backscatter by analyzing the incoming frequency of the ultrasonic backscatter to determine a calculated switching frequency of the switch, match the calculated switching frequency to a predetermined bit pattern, and record the predetermined bit pattern as data transmitted from the device. In some embodiments, the interrogator can analyze the ultrasonic backscatter with a bit error rate of up to 6% to decode the ultrasonic backscatter.

[0033] In some implementations, the ultrasonic wave is transmitted by the interrogator, and the interrogator is configured to adjust a parameter of the ultrasonic wave transmitted by the interrogator based on ultrasonic backscatter received from the device.

[0034] In some implementations, the switch can switch between an open state and a closed state at a switching frequency from a plurality of different switching frequencies. For example, the closed state can short-circuit one or more ultrasonic transducers of the device. In some implementations, the open state is a load configuration in which electrical energy is collected from the ultrasonic waves and maximum power is transmitted from the ultrasonic waves to the device to power the device. In some implementations, switching the switch between the open state and the closed state is configured to periodically (e.g., sinusoidally) vary the acoustic energy reflected by the device.

[0035] In some implementations of the device, the ultrasonic wave transmitted from the interrogator is configured to instruct the device to perform one or more functions. For example, the one or more functions may include determining the average incident power from the ultrasonic wave.

[0036] In some implementations, the interrogator includes one or more transducers configured to transmit ultrasonic waves and receive ultrasonic backscatter.

[0037] In some implementations, the device is an implantable device.

[0038] In some implementations, the device includes two or more electrodes that can transmit electrical pulses to tissue. In some implementations, the device includes two or more electrodes that can detect electrophysiological pulses.

[0039] Further described herein is a system for communicating via ultrasound, comprising: a device and an interrogator, the interrogator may include one or more ultrasonic transducers, the transducers are configured to receive emitted ultrasonic backscatter and transmit ultrasound to the device; and a processor, which is configured to decode the emitted ultrasonic backscatter. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0041] Figure 1An example is shown of how a switch of an implantable device can be operated to modulate the frequency of ultrasound backscatter according to some embodiments.

[0042] Figure 2 An example of modulating the frequency of ultrasonic backscatter based on the frequency of a carrier signal and the switching frequency of a switch is shown. The carrier signal is shown in the top panel, while the switch state is shown in the second panel. The backscatter signal generated by mixing the carrier signal with the switch state is shown in the third panel.

[0043] Figure 3 Examples of envelope extracted backscatter at different switching frequencies represented by Frequency 0 and Frequency 1 of Table 1 are shown in accordance with some embodiments.

[0044] Figure 4 A flow chart depicting a method 400 for detecting a signal at an interrogator is shown, in accordance with some embodiments.

[0045] Figure 5 A graph showing the bit error rate (BER) of individual transducer channels of an interrogator comprising sixteen channels in accordance with some embodiments.

[0046] Figure 6 An exemplary graph showing power levels read from frequency modulation based on piezoelectric voltage at an implantable device using the thresholds of Table 2 in accordance with some embodiments.

[0047] Figure 7 An example of the relationship between the ultrasonic backscatter amplitude received at the interrogator and the switching frequency calculated for the channel according to some embodiments is shown. As shown in this figure, different switching frequencies have higher or lower signal-to-noise ratios, which may depend on the physical properties of the ultrasonic transducer used (e.g., a piezoelectric crystal).

[0048] Figure 8 An example flow chart describing a manipulation method for a closed loop power delivery algorithm utilizing the communication methods described herein is shown in accordance with some embodiments.

[0049] Fig. 9 A flow chart describing a method 1000 for low power communication using ultrasound waves is shown in accordance with some embodiments.

[0050] Fig.10 An interrogator in communication with an implantable device is shown in accordance with some embodiments. DETAILED DESCRIPTION

[0051] Noise caused by passive reflections and other sources of reflection interference can change the accuracy and quality of data communications encoded by amplitude modulation of ultrasonic backscatter. This article describes an apparatus and system for implementing ultrasonic communication, which is more protected from passive reflections and other sources of reflection interference. A method for low-power and low-noise ultrasonic communication using the apparatus and system is further described. The apparatus and system include an ultrasonic transducer configured to receive ultrasonic waves and transmit ultrasonic backscatter, and include a switch for modulating the frequency of the transmitted ultrasonic backscatter. The switch can be operated to modulate the frequency of the ultrasonic backscatter so that data is encoded into the transmitted ultrasonic backscatter. Encoding data in the form of different frequencies or frequency sequences rather than in the form of different amplitudes provides a method of ultrasonic data communication that is more protected from passive reflections and other reflection interference.

[0052] Using ultrasound to operate and power implantable devices can be advantageous over other methods because biological tissue has a significantly lower absorption rate of ultrasound than other types of waves, such as RF waves. This property of ultrasound can allow the device to be implanted at greater depths in a subject while reducing tissue heating due to energy absorbed by the tissue.

[0053] As used herein, the singular form "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0054] Reference herein to "about" or "approximately" a value or parameter includes (and describes) variations involving the value or parameter itself. For example, a description referring to "about X" includes a description of "X".

[0055] It should be understood that the aspects and variations of the present invention described herein include "consisting of" and / or "consisting essentially of" the aspects and variations.

[0056] In the case of providing a range of values, it should be understood that each intermediate value between the upper and lower limits of the range, and any other specified or intermediate values ​​within the specified range, are included within the scope of the present invention. When the range includes an upper or lower limit, the range excluding any one of those included limits is also included in the present invention.

[0057] It should be understood that one, some, or all of the features of the various embodiments described herein may be combined to form further embodiments of the invention.The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0058] The features and preferences described above with respect to the "embodiment" are different preferences and are not limited to this particular embodiment; where technically feasible, they can be freely combined with features from other embodiments, and can form a preferred combination of features. This description is provided to enable a person of ordinary skill in the art to make and use the invention, and the description is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art, and the general principles herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the embodiments shown, but to be consistent with the widest scope consistent with the principles and features described herein.

[0059] The disclosures of all publications, patents, and patent applications cited herein are each hereby incorporated by reference in their entirety. To the extent any reference incorporated by reference conflicts with the present invention, the present invention controls.

[0060] As further described herein, a device for communicating via ultrasound may include an ultrasonic transducer, a switch, and a circuit (e.g., an integrated circuit) configured to operate the switch. The ultrasonic transducer can receive an ultrasonic wave (e.g., an ultrasonic wave transmitted by a separate device such as an interrogator) and transmit an ultrasonic backscatter (which can be received, for example, by an interrogator). Without intervention, the frequency of the ultrasonic backscatter depends on the frequency of the incident ultrasonic wave. However, the switch is configured to modulate the frequency of the transmitted ultrasonic backscatter. For example, the switch can short-circuit the ultrasonic transducer at a desired frequency, which causes modulation of the ultrasonic backscatter frequency. The circuit can operate the switch to encode data in the transmitted ultrasonic backscatter based on the frequency. For example, different frequencies can be used to transmit different bit patterns.

[0061] The data transmitted by the device may be information about the device (e.g., device status) or data collected by the device (e.g., sensor information, such as information indicating electrophysiological signals, pH, temperature, pressure, or other physiological information sensed by one or more sensors of the device). According to some embodiments, the implantable device may include two or more electrodes that may detect electrical pulses in the subject, such as electrophysiological pulses transmitted by nerves. According to some embodiments, the implantable device may include two or more electrodes that may transmit electrical pulses to body tissue.

[0062] According to some embodiments, the implantable device may include an ultrasonic transducer capable of receiving an ultrasonic wave emitted by an interrogator, converting the mechanical energy of the received ultrasonic wave into electrical energy to power the implantable device, and transmitting ultrasonic backscatter to the interrogator. The interrogator may include one or more transducers for transmitting ultrasonic waves and receiving ultrasonic backscatter. According to some embodiments, data may be encoded into the ultrasonic backscatter by modulating the frequency of the ultrasonic backscatter. Compared to communication protocols that rely on amplitude modulation to encode data into the ultrasonic backscatter, encoding data into the ultrasonic backscatter in this manner allows low-noise transmission through relatively noisy environments (e.g., in vivo). For example, encoding data using amplitude modulation suffers from noise problems, such as passive reflections that can change the amplitude of the ultrasonic backscatter. However, encoded data using frequency modulation cannot be changed by passive reflections, and thus eliminates the noise factor, and eliminates the need to calibrate the frequency modulation to address such environmental noise. According to some embodiments, the data encoded into the ultrasonic backscatter may be related to the instantaneous power of the ultrasonic transducer that hits the implantable device. According to some embodiments, the data encoded into the ultrasound backscatter may be, for example, related to sensor data from one or more sensors of the implantable device, any confirmation from the implantable device, and / or the operating state of the implantable device. The one or more sensors may be configured to detect power level, pH, temperature, pressure, electrophysiological pulses, and analyte concentrations (e.g., oxygen levels). Thus, the sensor data of the one or more sensors may include power level, pH, temperature, pressure, electrophysiological pulses, and analyte concentrations (e.g., oxygen levels).

[0063] The implantable device may include a switch for modulating the frequency of the ultrasonic backscatter so as to encode data into the ultrasonic backscatter emitted from the implantable device. The ultrasonic backscatter may include a pattern unique to the implantable device. According to some embodiments, the pattern may include a signature of the implantable device that may be used to distinguish the implantable device from other devices.

[0064] According to some embodiments, data can be encoded into ultrasonic backscatter by selecting the switching frequency of the switch of the implantable device. The switching frequency can be selected from a plurality of different switching frequencies, and each switching frequency can be associated with a predetermined bit pattern. The plurality of digital bits in any one predetermined bit pattern can be based on the binary logarithm of the plurality of switching frequencies in the plurality of different switching frequencies. The binary logarithm can be used to calculate the number of digital bits required to encode the message. For example, if sixteen different switching frequencies can be generated, the binary logarithm of sixteen (which is four) specifies that given sixteen different switching frequencies, each transmission can transmit four digital bits. By operating the switch to modulate the frequency of ultrasonic backscatter based on the selected switching frequency, the data associated with the selected switching frequency can be encoded into ultrasonic backscatter. According to some embodiments, the switching frequency can be a sequence of different frequencies.

[0065] According to some embodiments, at least four different switching frequencies are available. For example, 4 to 256 different switching frequencies are available (e.g., 4 to 8, 8 to 16, 16 to 32, 32 to 64, 64 to 128, or 128 to 256 different switching frequencies are available).

[0066] According to some embodiments, the selection of the switching frequency can be based on one or more of sensor data, the strength of ultrasonic backscatter at a given frequency, and the operating state of the implantable device. According to some embodiments, the operating state of the implantable device can indicate, for example, that the implantable device is powered by ultrasound from the interrogator, that the interrogator has interrogated the implantable device for data and the implantable device has responded to the interrogation, that a measurement made by the implantable device is complete, that a fault in the implantable device has been detected, and that the implantable device is receiving a particular power level from the interrogator.

[0067] According to some embodiments, the switching frequency is the frequency at which the switch of the implantable device short-circuits the ultrasonic transducer of the device. For example, the implantable device may include a switch and a digital logic component that determines the state of the switch (e.g., whether the switch should be open or closed). According to some embodiments, the closed state may be a short-circuit state. The switching frequency may be selected by switching the switch between the open state and the closed state at the selected switching frequency. According to some embodiments, when the switch is in the closed state, the implantable device cannot collect energy (e.g., store in an energy storage circuit) from the incoming ultrasonic wave because no energy flows into the implantable device. In the closed state, the implantable device may be configured so that at least some of the energy from the incoming ultrasonic wave is redirected. According to some embodiments, when the switch is in the open state, the implantable device may be in a load configuration, wherein electrical energy is collected from the ultrasonic wave and maximum power is transmitted from the ultrasonic wave to the implantable device to power the implantable device. The switching between the open and closed states of the switch may be configured to periodically (e.g., sinusoidally) change the acoustic energy reflected by the implantable device.

[0068] According to some embodiments, ultrasonic backscatter is transmitted at a frequency, and the one frequency can provide multiple bits of information by encoding multiple bits into one frequency. As described above, by selecting a switching frequency of an implantable device associated with multiple bits, and using the selected switching frequency to modulate a frequency transmitted from the implantable device, for example, multiple bits of data can be encoded into one frequency. For example, Table 1 below lists examples of different backscatter frequency symbols, each backscatter frequency symbol being associated with a different bit pattern. According to each backscatter frequency, the corresponding bit pattern is associated with the switching frequency. In the example of Table 1, the number of possible backscatter frequency symbols to be selected is sixteen, so the number of digital bits for each inquiry can be four. According to some embodiments, the possible number of backscatter frequency symbols can be up to 32 or 64.

[0069] Table 1: Example bit patterns associated with different switching frequencies

[0070] Bit Pattern frequency 0000 Frequency 0 0001 Frequency 1 0011 Frequency 2 0010 Frequency 3

[0071] In the example of Table 1, the association between the bit pattern and the frequency is Gray coded so that adjacent frequencies differ by only 1 bit. Alternative coding schemes are also possible, with the best scheme depending on the typical systematic errors of the frequency detector.

[0072] The selected switching frequency can be selected from a plurality of predetermined switching frequencies, which can be based on the frequency of the ultrasound waves received by the implantable device. For example, in some embodiments, the plurality of predetermined switching frequencies are within about 10%, within about 15%, within about 20%, within about 25%, or within about 30% of the frequency of the ultrasound waves received by the implantable device.

[0073] According to some embodiments, when the implantable device is energized by ultrasound received from an interrogator, ultrasonic backscatter encoded with data may be emitted from the implantable device. The ultrasonic backscatter emitted from the implantable device may be received and decoded at the interrogator. According to some embodiments, the interrogator may be configured to analyze the ultrasonic backscatter to determine the frequency or frequency change of the ultrasonic backscatter. According to some embodiments, the interrogator may be configured to determine the switching frequency of the switch of the implantable device. The determination may include calculating the switching frequency. Based on the determined switching frequency, the interrogator may be configured to associate the switching frequency with a predetermined digital bit pattern to decode the encoded data in the ultrasonic backscatter. According to some embodiments, the interrogator may be preprogrammed to associate the determined switching frequency with a corresponding predetermined digital bit pattern to decode the ultrasonic backscatter. According to some embodiments, the implantable device may be preprogrammed with one or more different switching frequencies, and each switching frequency may be associated with a different predetermined bit pattern. Similarly, the interrogator may be preprogrammed with one or more different switching frequencies to decode the ultrasonic backscatter.

[0074] According to some embodiments, decoding ultrasonic backscatter may include a bit error rate of at most 6%. According to some embodiments, decoding ultrasonic backscatter may include a bit error rate of at most 5%. According to some embodiments, decoding ultrasonic backscatter may include a bit error rate of at most 4%. According to some embodiments, decoding ultrasonic backscatter may include a bit error rate of at most 3%. According to some embodiments, decoding ultrasonic backscatter may include a bit error rate of at most 2%.

[0075] Ultrasonic communication between an implantable device and an interrogator can allow closed-loop communication. That is, the interrogator can change or adjust the parameters of the outgoing ultrasound in response to the encoded data received from the implantable device and decoded at the interrogator. For example, depending on the power level received at the implantable device, the frequency of the transmitted ultrasound backscatter can be associated with the power level received at the implantable device. In this way, the implantable device can inform the interrogator how much instantaneous power hits the implantable device via the frequency of the transmitted ultrasound backscatter. In response, the interrogator can turn to adjust and track how well the ultrasound from the interrogator hits the implantable device over time. Similarly, the implantable device can respond based on the ultrasound received from the interrogator at the implantable device. A given response may include selecting a switching frequency based at least on instructions received from the interrogator at the implantable device. According to some embodiments, the instructions may cause the implantable device to perform one or more functions. One or more functions may include determining the average incident power received from the ultrasound, detecting sensor information (e.g., electrophysiological pulse, pH, oxygen level), and performing one or more of a high sampling rate (rather than pulse detection) of a sensor data stream (e.g., an electrophysiological voltage time series).

[0076] According to some embodiments, the implantable device and the interrogator may be programmed with the same plurality of different switching frequencies. For example, the implantable device may be programmed with a plurality of different switching frequencies, from which one or more switching frequencies may be selected. Each switching frequency may be associated with a predetermined bit pattern that is configured to transmit a message to an external device, such as an interrogator. The interrogator may be configured to match a determined switching frequency with one of the plurality of different switching frequencies to determine a message from the implantable device. For example, if the determined switching frequency matches a first switching frequency of the plurality of different switching frequencies, the interrogator may be configured to interpret the predetermined bit pattern of the first switching frequency as a message from the implantable device. According to some embodiments, for each plurality of different switching frequencies, a different predetermined bit pattern associated with each different switching frequency is gray-coded.

[0077] The implantable device may include one or more piezoelectric crystals having different resonant operating modes. According to some embodiments, optimal signal-to-noise ratio transmission from the implantable device to the interrogator may be achieved by modulating the frequency of ultrasonic backscattering so that the frequency corresponds to the resonant operating mode of the one or more piezoelectric crystals. For example, a specific frequency of ultrasonic backscattering may achieve a specific backscattering intensity that is receivable at the interrogator. The intensity of the specific backscattering intensity may be a relative maximum intensity. According to some embodiments, the specific frequency may correspond to a characteristic (e.g., a relative minimum) of impedance data of the one or more piezoelectric crystals. According to some embodiments, the backscattering intensity and one or more characteristics of the impedance data may be used to determine a process for selecting a set of switching frequencies that may modulate the frequency of ultrasonic backscattering.

[0078] According to some embodiments, the implantable device may include an ultrasonic transducer configured to receive ultrasound waves from an interrogator and emit ultrasonic backscatter. The implantable device may also include a switch configured to modulate the frequency of the ultrasonic backscatter and a controller configured to transmit data to the interrogator using the ultrasonic backscatter, such as an application specific integrated circuit (ASIC). Typically, there is a limited amount of incoming acoustic energy originating from the interrogator that is then reflected back to the interrogator by the implantable device. When the ultrasonic transducer (e.g., a piezoelectric circuit) of the implant is short-circuited, the maximum amount of incoming acoustic energy is reflected. By adding a matching load to the piezoelectric circuit of the implantable device, electrical energy is collected and maximum power can be transmitted to the ASIC. According to some embodiments, the matching load can be a resistor.

[0079] Due to the conservation of energy, switching the load changes the reflected energy. Traditionally, changes in reflected energy can be detected and digital communication is achieved by making high amplitude reflected energy represent 1 and low amplitude reflected energy (when the energy is collected by the ASIC) represent 0. Although traditional amplitude modulation communication schemes work to transmit 1 and 0, there are limitations due to environmental interference and low data rates between the implant and the interrogator. Alternatively, the devices and systems described herein are configured to regulate the reflected energy by modulating the frequency of the reflected energy based on the frequency at which the piezoelectric circuit is shorted.

[0080] Rather than communicating via individual high and low amplitude 0s and 1s, the devices and systems described herein communicate by varying the frequency of the load variation at the piezoelectric circuit so that multiple bits of data can be transmitted via frequency modulated ultrasonic backscatter. For example, an ultrasonic signal can be transmitted from an interrogator to a piezoelectric circuit at 1.5 MHz. The piezoelectric circuit can then be switched between a short circuit configuration and a loaded configuration at a certain switching frequency such that the reflected acoustic energy varies periodically (e.g., sinusoidally). At the interrogator, rather than detecting the modulation amplitude at a certain threshold, a frequency analysis can be performed and the switching frequency of the piezoelectric circuit can be estimated by analyzing the ultrasonic backscatter signal, such as Figure 4 The switching frequency may represent a set number of bits, which may be recorded as data transmitted in response to an inquiry.

[0081] Figure 1 An example is shown of how a switch of an implantable device can be operated to modulate the frequency of ultrasound backscatter according to some embodiments. Figure 1 A graph showing the switching behavior of a switch with amplitude (voltage) on the y-axis and time (in microseconds) on the x-axis. The graph represents the voltage on the piezoelectric crystal of the implantable device as a result of the switching frequency imposed by the ASIC. The pattern on the piezoelectric crystal is reflected in the ultrasound backscatter emitted from the implantable device. Figure 1 In the example of FIG. 1 , the carrier frequency is 1.5 MHZ and the switch is configured to short the implantable device at a frequency of 125 kHz. When the switch is closed, such as in region A, the transmitted ultrasonic backscatter intensity has a minimum amplitude, indicating that the piezoelectric crystal of the implantable device is shorted. When the switch is open, such as in region B, the transmitted backscatter intensity is at a maximum amplitude. The ultrasonic backscatter received by the interrogator can identify the 125 kHz frequency segment and can decode (e.g., using a lookup table) a bit pattern associated with the 125 kHz frequency.

[0082] Figure 2 Another example of modulating the frequency of ultrasonic backscatter based on the frequency of the carrier signal and the switching frequency of the switch is provided in. Figure 2It shows what happens to the carrier signal (top panel) at the implantable device in the frequency domain based on the switch state of the implantable device (second panel). Specifically, the top panel represents the incoming signal that will be the input of the implantable device. The second panel ("implant switch state") represents the state of the switch of the implantable device determined by a digital logic controller configured to operate the switch. Examples of digital logic controllers can be application specific integrated circuits (ASICs), microcontrollers, field programmable gate arrays (FPGAs), or other similar components. Specifically, the second panel shows that the switch is operated to perform at a specific switching frequency between two states. The specific switching frequency of the switch affects how the ultrasonic backscatter (reflected acoustic energy) is modulated. The third panel ("mixed signal") shows an example of an ultrasonic backscatter signal generated by mixing the carrier signal (top panel) with the switch state (second panel). By switching the switch at the switching frequency, the frequency of the ultrasonic backscatter signal is modulated. This frequency modulation can be more robust than amplitude modulation because amplitude modulation can be corrupted by passive environmental interference.

[0083] Figure 2 The bottom panel of shows a different representation of the ultrasonic backscatter signal shown in the third panel. The graph shown in the bottom panel can be referred to as the frequency domain, and illustrates that different frequency content can be created by multiplying the carrier signal and the switch state signal together. In the example shown in the bottom panel, the frequency of the switch is a low frequency peak ("sw"), and the frequency of the carrier signal is a higher frequency ("x"). By multiplying the frequency of the switch with the frequency of the carrier signal, new frequency content can be generated and is shown in orange ("mixed x"). After mixing (orange signal in the bottom panel), the frequency of the ultrasonic backscatter signal is "mixed" or shifted + and - the switching frequency. The frequency content of the ultrasonic backscatter signal received at the interrogator remains centered at 1.5MHz, but the amplitude of the backscatter varies with a certain frequency. In this case, the frequency is detectable even if some amplitude changes are not detected due to typical amplitude modulation problems.

[0084] According to some embodiments, digital bits may be encoded by associating a specific bit (or bit pattern) with a backscatter frequency or (more preferably) with a switching frequency of a switch. For example, assume that an implantable device can backscatter one of 16 different backscatter frequencies, as shown in Table 1 above. Figure 3 Examples of envelope extracted ultrasound backscatter according to some embodiments are shown at different switching frequencies represented by Frequency 0 (300.0 kHz) and Frequency 1 (57.5 kHz) of Table 1. The y-axis is intensity proportional to the ultrasound pressure received by the interrogator and the x-axis is time in microseconds. Figure 3The curve of represents the backscattered frequency that can be received from the implantable device at the interrogator. Comparing the two frequencies shown, frequency 0 is a relatively high frequency, while frequency 1 is a relatively low frequency oscillation.

[0085] Figure 4 A flow chart describing a method 400 for detecting a signal at an interrogator is shown in accordance with some embodiments. The method 400 may be applied to receive different frequencies and separate the different frequencies. At step 410, the interrogator generates a signal. If it is a multi-element transducer, the signal may be focused at a specific point of a beamformer. At step 420, the original signal or the focused signal may be processed at the beamformer. The beamformer may be used to emphasize specific spatial regions of the received signal. At step 430, envelope extraction from the received signal may be performed. At step 440, spectral analysis of the envelope extraction may be performed. Spectral analysis may include decomposing the received signal frequency into different frequency components. Examples of such spectral analysis include Fast Fourier Transformation. At step 450, based on the output of the spectral analysis, the frequency may be determined.

[0086] According to some embodiments, the interrogator includes an ultrasonic transducer array. The transducer array may include channels that are configured to manipulate the focusing of the ultrasound waves and manipulate where the ultrasound backscatter signals are received. Each channel is a signal path that includes the physical elements (electronic components) of the transducer and the interrogator. Each channel can receive different information, for example, based on the location of each channel physically located on the transducer array. Each channel can also transmit different signals that focus the beam at different points. In this way, when you have a multi-element system, multiple channels can allow signal diversity, and you can choose to combine these signals, however it makes sense. For example, depending on the angle or distance of the implantable device to the transducer array, different vibrations can be received on each of the different channels. Different vibrations can be used to piece together a single picture of the communication received from the implantable device.

[0087] Figure 5 A graph of bit error rate (BER) for individual transducer channels of an interrogator including sixteen channels according to some embodiments is shown. The y-axis is a scale from 0 to 1, while the x-axis is the channel array of the transducer at the interrogator. Different channels of the interrogator are configured to receive ultrasonic backscatter at different locations in space. Figure 5 In the example of , a 16-element transducer is used to receive ultrasound backscatter. According to some embodiments, ultrasound backscatter may be acquired simultaneously across all channels, and therefore, performance variations across the transducer array may be due to spatial variations in backscatter characteristics. BER may be calculated by counting the number of received bits that do not match expected bits. Figure 5The low BER shown indicates that most decoded bits are decoded correctly. An example of a correct decode is a zero bit being sent to the interrogator and received by the interrogator and decoded as a zero bit.

[0088] In general, Figure 5 An example with relatively few errors in an ultrasound communication protocol is shown, where some channels (e.g., channel 1 and channel 2) have relatively high bit error rates. According to some embodiments, the relative bit errors may be due to the physical location of these elements relative to the implant. According to some embodiments, the signal quality may be based on the spatial geometry of the transducer and the channels.

[0089] Although channel 2 has a relatively high bit error rate compared to the other channels, one or more channels with relatively low bit error rates may be selected to view communication signals from the other channels. According to some embodiments, in order to compensate for one or more channels with relatively high bit error rates, in a multi-element system, you may select one or more other channels based on signal quality criteria. According to some embodiments, in order to compensate for one or more channels with relatively high bit errors, a beamformer may be used to combine information from all channels into a weighted average signal. The term "relatively high bit error rate" is intended to be relative to specific channels / frequencies that have no or very low bit error rates, and is not intended to indicate that the bit error rates of these channels are unusable or otherwise impair communications.

[0090] According to some embodiments, advantages of ultrasound communication described herein include low error rates for effective closed-loop communication (see Figure 5 ) and low power. Closed-loop communications can be used to power implantable devices that can be implanted deep in the body. According to some embodiments, the implantable device can backscatter depending on the input voltage to the piezoelectric crystal of the implantable device. In this way, an interrogator configured to determine how much power hits the implantable device can be electronically manipulated to compensate or adjust the power according to the requirements of the implantable device. Therefore, closed-loop communication can include transmitting power from the interrogator to the implantable device via ultrasound, emitting ultrasonic backscatter from the implantable device, and adjusting the frequency of the ultrasonic backscatter based on the voltage level input at the implantable device. Examples of closed-loop communications include charging the implantable device at a target rate based on the charge level of the implantable device.

[0091] Frequency modulation of ultrasonic backscatter can be applied to transmit information about changes in piezoelectric voltage at an implantable device. Changes in piezoelectric voltage indicate fluctuations in input power (current × voltage). Such changes can occur in a handheld ultrasound link. Table 2 below shows exemplary voltage range readings that can be associated with specific switching (or short-circuiting) frequencies of piezoelectric elements at an implantable device. At the interrogator, as described above, ultrasonic backscatter can be received and decoded by associating the frequency of ultrasonic backscatter and / or the switching frequency at the implantable device with a predetermined bit pattern. Each bit pattern can represent a power level that can be interpreted by the interrogator. For example, if the implantable device has an input voltage of less than half a volt, the implantable device can set the switching frequency to 50,000 Hz. The interrogator can be configured to calculate the switching frequency, and if it calculates the switching frequency to be any frequency less than 55,000, the interrogator can record that the voltage on the piezoelectric element on the implantable device is less than half a volt, and for discretization, it can be referred to as power level zero. Figure 6 An exemplary graph of the power level read from the frequency modulation based on the piezoelectric voltage at the implantable device using the threshold values ​​of Table 2 is shown. Figure 6 These data and correlations shown can be used to efficiently charge an implantable device based on the charging needs of the implantable device.

[0092] Table 2: Example correlation between voltage, frequency, and power levels

[0093]

[0094] According to some embodiments, plotting the amplitude of the ultrasound backscatter frequency versus the calculated switching frequency may show trends that may be indicative of the physical characteristics of the piezoelectric element at the implantable device. Figure 7 An example of the relationship between the ultrasonic backscatter amplitude received at the interrogator and the switching frequency calculated for the channel according to some embodiments is shown. As shown in this figure, different switching frequencies have higher or lower signal-to-noise ratios, which may depend on the physical properties of the ultrasonic transducer used (e.g., a piezoelectric crystal).

[0095] According to some embodiments, the switching frequency may be determined by a controller of the implantable device. The determination may be random, or may be based on the characteristics of the piezoelectric element at the implantable device. For example, suppose a high amplitude of ultrasound backscatter at the interrogator is desired. Figure 7 In the example of , there is a relative maximum in the backscatter amplitude around 60000 Hz. Therefore, in order to achieve high amplitude ultrasonic backscatter at the interrogator, the switching frequency can be selected to have a region including the relative maximum backscatter amplitude. That is, depending on the application, the switching frequency can be selected based at least in part on the amplitude of the ultrasonic backscatter at the interrogator.

[0096] According to some embodiments, a switching frequency close to the resonant characteristics of the piezoelectric crystal of the implantable device can potentially result in a relative maximum backscatter at the detector. According to some embodiments, a larger ultrasound backscatter amplitude at the detector can result in a lower bit error rate. According to some embodiments, the implantable device can be calibrated to select a switching frequency based on the amplitude received at the interrogator, and the selected switching frequency can correspond to a specific region of the impedance spectrum of the piezoelectric element.

[0097] According to some embodiments, a closed-loop power delivery algorithm may be implemented using the communication protocol described herein. Figure 8 An example flow chart describing a method 800 for closed loop communication according to some embodiments is shown. The method 800 outlines the processing of power level data in a closed loop system. That is, the method 800 describes how power level data can be communicated.

[0098] At step 810, electronic steering may be set at the interrogator. At step 820, the electronic steering is transmitted using a transducer array at the interrogator. The transducer array may transmit ultrasound waves to the implantable device. At step 830, the implantable device may receive the ultrasound waves, measure the incident power, and transmit ultrasound backscatter containing information. At step 840, one or more ultrasound transducers of the interrogator may receive ultrasound backscatter from the implantable device, and a processor of the interrogator may decode the ultrasound backscatter to determine the incident power received at the implantable device. At step 850, at the interrogator, new steering parameters may be calculated based on the determined incident power received at the implantable device.

[0099] Fig. 9 A flow chart describing a method 900 for low power communication using ultrasound waves is shown according to some embodiments. The method 900 may be implemented by an implantable device as described herein.

[0100] At step 910, one or more ultrasound transducers of an implantable device may receive ultrasound waves transmitted by an interrogator. The ultrasound waves may be transmitted by one or more ultrasound transducers of the interrogator.

[0101] At step 920, one or more ultrasound transducers of the implantable device may emit ultrasound backscatter including the encoded data. The data may be encoded into the ultrasound backscatter by modulating the frequency of the ultrasound backscatter.

[0102] According to some embodiments, the implantable device may include a switch configured to open and close a piezoelectric circuit of the implantable device. According to some embodiments, when the switch is closed, the circuit is short-circuited. The controller may be configured to operate the switch between an open state and a closed state, and to select a switching frequency at which the switch changes between the open state and the closed state. According to some embodiments, method 900 may include selecting a switching frequency from a plurality of different switching frequencies. As further described above, each switching frequency may be associated with a predetermined bit pattern that may include a plurality of bits. The association between each switching frequency and the predetermined bit pattern may be Gray coded.

[0103] According to some embodiments, the implantable device may include one or more sensors configured to detect sensor information, such as one or more of power level, pH, temperature, pressure, electrophysiological pulses, and analyte concentrations (e.g., oxygen levels). According to some embodiments, method 900 may include detecting sensor information by one or more sensors of the implantable device. The implantable device may include a status indicator configured to determine the operating state of the implantable device. The operating state may include, for example, whether the implantable device is on, off, in measurement mode, operating well, encountering an error, fully charged, or requires more power to reach a full charge level. According to some embodiments, the selection of the switching frequency may be based on one or more of an instruction from the interrogator, sensor information detected by one or more sensors of the implantable device, and the operating state of the implantable device.

[0104] According to some embodiments, method 900 may include decoding ultrasound backscatter at the interrogator. Decoding may include analyzing the incoming ultrasound backscatter to calculate the frequency of the ultrasound backscatter and the switching frequency of a switch of the implantable device. The calculated switching frequency may be matched to a predetermined bit pattern, which may be recorded as data transmitted from the device.

[0105] According to some embodiments, the implantable device may include one or more first electrodes configured to transmit electrical pulses to tissue. According to some embodiments, the implantable device may include one or more second electrodes configured to detect electrophysiological pulses. According to some embodiments, method 1000 may include transmitting electrical pulses and detecting electrophysiological pulses.

[0106] Fig.10An interrogator 1010 is shown communicating with an implantable device 1020. An external ultrasonic transceiver transmits an ultrasonic wave ("carrier wave") that can pass through tissue. The carrier wave induces mechanical vibrations on an ultrasonic transducer (e.g., a bulk piezoelectric transducer, a PMUT, or a CMUT). A voltage is generated across the ultrasonic transducer that applies a current that flows through a circuit (e.g., an integrated circuit) on the implantable device. The current flowing to the ultrasonic transducer causes the transducer on the implantable device to emit backscattered ultrasonic waves. In some embodiments, the circuit modulates the frequency of the ultrasonic transducer by shorting the circuit at a switching frequency to encode information, and the resulting ultrasonic backscattered wave encodes the information. The backscattered wave can be detected by the interrogator and can be analyzed to interpret the information encoded in the ultrasonic backscatter. According to some embodiments, the implantable device 1020 may include one or more sensors. According to some embodiments, the implantable device 1020 may include one or more electrodes.

[0107] For purposes of illustration, the foregoing description has been described with reference to specific embodiments. However, the above illustrative discussion is not exhaustive, nor is it intended to limit the invention to the precise form disclosed. In light of the above teachings, many modifications and variations are possible. The embodiments are chosen and described in order to best explain the principles of the technology and its practical application. Thus, others skilled in the art can best utilize the technology and various embodiments with various modifications suitable for the particular use under consideration.

[0108] Although the present invention and examples have been fully described with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications will be understood to be included within the scope of the present invention and examples as defined by the claims. Finally, the entire disclosures of the patents and publications cited in this application are incorporated herein by reference.

Claims

1. A method for communicating using ultrasonic waves, comprising: receiving, at one or more ultrasound transducers of the implantable device, ultrasound waves transmitted by the interrogator; as well as Ultrasonic backscatter comprising encoded data is emitted from the one or more ultrasonic transducers of the implantable device, wherein the data is encoded into the ultrasonic backscatter by modulating a frequency of the ultrasonic backscatter.

2. The method according to claim 1, comprising: A switching frequency is selected from a plurality of different switching frequencies to modulate the frequency of the ultrasonic backscatter, wherein the switching frequency is configured to encode the data into the ultrasonic backscatter.

3. The method according to claim 2, wherein: Each switching frequency is associated with a different predetermined bit pattern.

4. The method according to claim 2 or 3, wherein: Modulating the frequency of the ultrasound backscatter includes switching a switch of the implantable device at the switching frequency.

5. The method according to any one of claims 2 to 4, wherein: Each predetermined bit pattern includes two or more digital bits.

6. The method according to any one of claims 2 to 5, wherein: The predetermined bit patterns associated with the plurality of different switching frequencies are Gray coded.

7. The method according to any one of claims 2 to 6, wherein: The switching frequency is selected based at least on instructions received from the interrogator via the ultrasonic waves.

8. The method according to any one of claims 2 to 7, wherein: The plurality of different switching frequencies are selected based at least on the intensity of the ultrasonic backscatter at a given frequency.

9. The method according to any one of claims 1 to 8, comprising: detecting sensor information from one or more sensors of the implantable device, wherein the data includes the sensor information; and selecting the switching frequency from the plurality of different switching frequencies based at least on the sensor information.

10. The method according to claim 9, wherein: The sensor information includes one or more of power level, pH, temperature, pressure, electrophysiological pulses, and analyte concentration.

11. The method according to claim 10, wherein: The analyte concentrations include oxygen levels.

12. The method according to any one of claims 1 to 11, comprising: determining operating state information of the implantable device, wherein the data includes the determined operating state information; and selecting the switching frequency from the plurality of different switching frequencies based at least on the determined operating state information.

13. A method according to any one of claims 1 to 12, comprising selecting a sequence of two or more switching frequencies from a plurality of different switching frequencies to encode the data, wherein: Each switching frequency is associated with a different predetermined bit pattern.

14. The method according to any one of claims 1 to 13, comprising: receiving, at the interrogator, the ultrasonic backscatter including the encoded data; decoding the received ultrasound backscatter at the interrogator, wherein decoding the ultrasound backscatter comprises analyzing an incoming frequency of the received ultrasound backscatter at the interrogator to determine a calculated switching frequency of a switch that modulates the frequency of the ultrasound backscatter, matching the calculated switching frequency to a predetermined bit pattern, and recording the predetermined bit pattern as decoded data transmitted from the implantable device.

15. The method according to claim 14, wherein: The decoded data has a bit error rate of at most 6%.

16. A method according to any one of claims 1 to 15, comprising adjusting parameters of the ultrasonic wave transmitted by the interrogator based on the ultrasonic backscatter received from the implantable device.

17. The method according to any one of claims 1 to 16, wherein: Modulating the frequency of the ultrasound backscatter includes switching a switch of the implantable device between an open state and a closed state at a switching frequency from among a plurality of different switching frequencies.

18. The method according to claim 17, wherein: The closed state shorts the one or more ultrasound transducers of the implantable device.

19. The method according to claim 17 or 18, wherein: The off state is a load configuration in which electrical energy is harvested from the ultrasonic waves and maximum power is delivered from the ultrasonic waves to the implantable device to power the implantable device.

20. The method according to any one of claims 17 to 19, wherein: The switch that switches the implantable device between the open state and the closed state is configured to periodically vary acoustic energy reflected by the implantable device.

21. A method according to any one of claims 1 to 20, comprising transmitting ultrasound from the interrogator to the implantable device, wherein: The ultrasonic waves instruct the implantable device to perform one or more functions.

22. The method according to claim 21, wherein: The one or more functions include determining an average incident power from the ultrasound waves.

23. A method according to any one of claims 1 to 20, comprising transmitting the ultrasonic wave from the interrogator to the implantable device.

24. A method according to any one of claims 1 to 23, comprising receiving the ultrasonic backscatter at the interrogator.

25. The method according to any one of claims 1 to 24, wherein: The interrogator includes one or more transducers for transmitting the ultrasonic waves and receiving the ultrasonic backscatter.

26. An apparatus for communicating via ultrasound, comprising: an ultrasonic transducer configured to receive ultrasonic waves and emit ultrasonic backscatter; a switch configured to modulate the frequency of the transmitted ultrasonic backscatter; as well as Circuitry is configured to operate the switch to encode data in the transmitted ultrasonic backscatter based on the frequency.

27. The apparatus of claim 26, wherein: The switch is switchable at a switching frequency from a plurality of different switching frequencies, and the data encoded in the transmitted ultrasonic backscatter is based on the switching frequency, wherein each switching frequency is associated with a different predetermined bit pattern.

28. The apparatus of claim 27, wherein: Each predetermined bit pattern includes two or more digital bits.

29. The apparatus of claim 27, wherein: The predetermined bit patterns associated with the plurality of different switching frequencies are Gray coded.

30. Apparatus according to any one of claims 27 to 29, wherein: The switching frequency is based at least on a relative maximum intensity of ultrasonic backscatter receivable at the interrogator.

31. The apparatus of any one of claims 27 to 30, comprising one or more sensors configured to detect sensor information, wherein: The data includes detected sensor information, and the switching frequency from among the plurality of different switching frequencies is based at least on the detected sensor information.

32. The apparatus of claim 31, wherein: The sensor information includes a power level of the device.

33. Apparatus according to claim 31 or 32, wherein: The one or more sensors include one or more of a pressure sensor, a pH sensor, a temperature sensor, and an analyte sensor.

34. Apparatus according to any one of claims 27 to 33, comprising a status indicator, wherein: The switching frequency from among the plurality of different switching frequencies is based at least on one or more states of the state indicator.

35. An apparatus as claimed in any one of claims 27 to 34, the switch being switchable in a sequence of two or more switching frequencies from a plurality of different switching frequencies to encode the data.

36. The apparatus of claim 35, wherein: Each switching frequency is associated with a different predetermined bit pattern.

37. Apparatus according to any one of claims 26 to 36, wherein: The switch is switchable between an open state and a closed state at a switching frequency from among a plurality of different switching frequencies.

38. The apparatus of claim 37, wherein: The closed state short-circuits the ultrasonic transducer.

39. Apparatus according to claim 37 or 38, wherein The off state is a load configuration in which power is harvested from the ultrasonic waves and maximum power is delivered from the ultrasonic waves to the device to power the device.

40. The method according to any one of claims 37 to 39, wherein: Switching the switch between the open state and the closed state is configured to periodically change acoustic energy reflected by the device.

41. Apparatus according to any one of claims 26 to 40, wherein: The device is an implantable device.

42. A device according to any one of claims 26 to 41, comprising two or more electrodes configured to transmit electrical pulses to tissue.

43. A device according to any one of claims 26 to 42, comprising two or more electrodes configured to detect electrophysiological pulses.

44. A system for communicating via ultrasound, comprising: An apparatus according to any one of claims 26 to 43; as well as Interrogator, including: one or more ultrasonic transducers configured to receive the emitted ultrasonic backscatter and transmit the ultrasonic waves to the device; as well as A processor is configured to decode the transmitted ultrasonic backscatter.

45. The system of claim 44, wherein: The interrogator is configured to transmit the ultrasonic wave including instructions, and to select the switching frequency based at least on the instructions received by the device.

46. ​​A system according to claim 44 or 45, wherein: The interrogator is configured to decode the ultrasonic backscatter by analyzing its incoming frequency to determine a calculated switching frequency of the switch, match the calculated switching frequency to a predetermined bit pattern, and record the predetermined bit pattern as data transmitted from the device.

47. The system of claim 46, wherein: Decoding the ultrasonic backscatter results in a bit error rate of at most 6%.

48. A system according to any one of claims 44 to 47, wherein: The interrogator is configured to adjust a parameter of the ultrasonic wave transmitted by the interrogator based on the ultrasonic backscatter received from the device.

49. A system according to any one of claims 44 to 48, wherein: The ultrasonic waves transmitted from the interrogator are configured to instruct the device to perform one or more functions.

50. The system of claim 49, wherein: The one or more functions include determining an average incident power from the ultrasound waves.

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