WO2010012035A1

WO2010012035A1 - A harmonics-based wireless transmission device and associated method

Info

Publication number: WO2010012035A1
Application number: PCT/AU2009/000970
Authority: WO
Inventors: Mehmet Yuce; Anthony Laskovski
Original assignee: Newcastle Innovation Limited
Priority date: 2008-07-31
Filing date: 2009-07-30
Publication date: 2010-02-04

Abstract

An embodiment of the device (1) has an external unit (2) that transmits a power signal to a wireless power receiver (7) in an implant (3). This received waveform provides the implant (3) with a sinusoidal input signal at a first frequency. This is fed to a rectifier (8) to provide a substantially direct current signal which is used as a power source for the implant (3). The sinusoidal input signal is also fed to a non-linear block (11), which modifies the input signal to provide a non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a second frequency different to the first frequency. The intermediate signal is fed to a filter (14) to provide an output signal substantially at the second frequency. The output signal may be used to transmit data to the external unit (2). In the event of a low quality communications link between the external unit (2) and the implant (3), the power signal may be modified so as to modify the output signal.

Description

A HARMONICS-BASED WIRELESS TRANSMISSION DEVICE AND ASSOCIATED METHOD

FIELD OF THE INVENTION The present invention relates to a new method and apparatus for signal generation and associated devices. Embodiments of the present invention find application, though not exclusively, in electronic sensors such as those utilized in bio- implantable medical telemetry devices, and the like.

BACKGROUND OF THE INVENTION

Many prior art electronic devices make use of a carrier signal for the purposes of data transmission. Typically, the carrier signal may be generated by a self oscillating device, such as a crystal or a voltage controlled oscillator. However, the use of such self oscillating devices may require compromises to be made with regard to the size of the circuitry required and the power usage rates.

Sensors are a type of electronic device that may be used in conjunction with a carrier signal for data transmission purposes. Sensors are utilized increasingly frequently across a vast array of contexts, such as in medical telemetry and other intelligent sensing systems. Such systems may be employed in fields as diverse as security, surveillance, air conditioning and power usage management, for example. With the increasing complexity of the sensors and the systems, it is generally advantageous to cater for higher data rates, lower power usage and smaller physical size.

The disclosure of United States Patent No. 6,553,260 provides an example of a medical implant in the form of a heart stimulator. The implant has working parameter status registers which are continuously updated with status information relating to parameters such as the battery status, the status of lead impedance or the status of the stimulation threshold. Upon detection of an externally generated interrogation signal, the device responds with an acoustic response signal, which is detectable by a stethoscope. The response signal indicates only whether the interrogated working parameter has a satisfactory or unsatisfactory value. In a similar manner to this heart stimulator, other recent implantable technologies such as bionic eyes, cochlear implants, implantable defibrillators and wireless endoscope devices also require status monitoring.

United States Patent No. 3,944,928 discloses a communication system in which a transmitter radiates a carrier frequency signal to a data station, which rectifies the received carrier signal to energy to the station elements. A harmonic generator produces harmonics of the carrier signal and the harmonic signal is modulated by a data signal and radiated to a receiver which demodulates the received signal to extract the data there from.

United States Patent No. 7,283,053 discloses a method of identifying an article of interest in which an RF antenna having a non-linear element is provided upon the article of interest. This antenna is interrogated with RF energy of a first frequency, which is converted into a reflected energy of a different frequency. The reflected energy is sensed and the different frequency effectively identifies the article of interest.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome, or substantially ameliorate, one or more of the disadvantages of the prior art, or to provide a useful alternative.

In one aspect of the present invention there is provided a harmonics-based wireless transmission device including: a wireless power receiver for providing a sinusoidal input signal at a first frequency; a rectifier responsive to the input signal so as to provide a substantially direct current signal; a non- linear block responsive to the input signal so as to provide a non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a second frequency different to the first frequency; a filter responsive to the intermediate signal so as to provide an output signal substantially at the second frequency; and a transmitter adapted to use the output signal for wireless transmission. Preferably the non-linear block includes at least one of: a non-linear device; an active circuit; an inverter; a comparator; a diode.

In an embodiment of the invention the intermediate signal has a plurality of harmonic components at a plurality of discrete frequencies each differing from the first frequency. In this embodiment the filter is responsive to the intermediate signal so as to provide a plurality of output signals substantially at said plurality of discrete frequencies.

In a typical embodiment the second frequency is higher than the first frequency. More particularly, the second frequency is typically an n^th harmonic of the first frequency, where n is an integral value greater than 1.

In an embodiment the device is bio-implantable. In this embodiment the device is a telemetry device having a sensor for data acquisition, the sensor being electrically connectable to the transmitter for wireless transmission of the data.

Preferably the output signal is used as a reference signal for the transmission of the data.

In an embodiment the non-linear block is a comparator adapted to compare the input signal to a reference point so as to provide a non-sinusoidal intermediate signal. Preferably the reference point is defined by the direct current signal.

Preferably the non-linear block is powered by the direct current signal.

According to another aspect of the invention there is provided a unit for use with a device according to the preceding aspect of the invention, the unit having a transmitter for transmitting a power signal and a receiver for receiving the output signal.

In one embodiment the unit includes a processor adapted to monitor the quality of a communications link between the unit and the device. Preferably the processor is adapted to modify a frequency of the power signal in dependence upon the quality of the communications link.

According to another aspect of the invention there is provided a harmonics- based wireless transmission method including the steps of: wirelessly receiving power so as to provide a sinusoidal input signal at a first frequency; applying the input signal to the non-linear block so as to provide a non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a second frequency different to the first frequency; filtering the intermediate signal so as to provide an output signal substantially at the second frequency; and using the output signal for wireless transmission.

In an embodiment the method includes the steps of: rectifying the input signal so as to provide a substantially direct current signal; and powering a non-linear block using the direct current signal.

An embodiment of the method may include the steps of: applying the output signal to the non-linear block so as to provide a further non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a further frequency different to the first and second frequencies; and filtering the further intermediate signal so as to provide a further output signal substantially at the further frequency.

In some embodiments it may be advantageous to include the step of applying the intermediate signal to a divider so as to lower the frequency of the intermediate signal. In other embodiments it may be advantageous to include the step of applying the intermediate signal to a multiplier so as to increase the frequency of the intermediate signal.

Preferably the shape of the intermediate signal may be selected from a group including: square waves, triangular waves and saw tooth waves.

Some embodiments of the invention include the step of tuning the wirelessly received power so as to tune the output signal. This feature is particularly advantageous if it is necessary to adjust the transmission frequency of the output signal from a problematic frequency to a frequency more suited to a specific environment.

In one embodiment the step of 'filtering the intermediate signal so as to provide an output signal substantially at the second frequency' is performed with a tunable filter. Preferably a processor is used to tune the tunable filter in response to the wirelessly received power.

Preferably a processor is operatively associated with a rectifier so as to control a received power level.

A multiple-device embodiment includes a unit having a transmitter for transmitting a power signal to a plurality of devices, each of the devices having a processor controlled tunable filter, the method including the step of configuring the processor on each of the devices to tune the tunable filter to a harmonic that is unique for each of the devices.

Another multiple-device embodiment includes a plurality of units each having a processor controlled transmitter for transmitting a power signal to a corresponding plurality of devices, the method including the step of configuring the processors such that the power signal transmitted by each of the units is at a frequency that is unique to the corresponding device.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in this specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of this application.

Throughout this specification the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The features and advantages of the present invention will become further apparent from the following detailed description of preferred embodiments, provided by way of example only, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 is a schematic block diagram of a preferred embodiment of the invention;

Figure 2 is a circuit diagram of the preferred embodiment shown in figure 1;

Figure 3 is a circuit diagram of a non-linear block in the form of an inverter that is utilized in the preferred embodiment;

Figure 4 is a circuit diagram of a data transmitter that is utilized in the preferred embodiment;

Figure 5 is a circuit diagram of a power transmitter that is utilized in the preferred embodiment;

Figure 6 is the voltage wave form in the time domain of the power transmitter of figure 5 ; Figure 7 is the voltage wave form in the time domain of the direct current signal provided by the rectifier of the preferred embodiment;

Figure 8 is a spectrum plot of the intermediate signal provided by the non-linear block of the preferred embodiment;

Figure 9 is a spectrum plot of the signal received by the external data receiver of the preferred embodiment;

Figure 10 is the signal of figure 9 shown in the time domain; and

Figure 11 is a schematic block diagram of another preferred embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

A preferred embodiment of the harmonics-based wireless transmission device 1 is depicted schematically in figure 1 and in somewhat more detail in figure 2. The device 1 may be used in a medical telemetry context and consists of two parts; an external unit 2 and an implant 3. As its name implies the external unit 2 remains external to the subject. It has a power transmitter 4 and a data receiver 5. The power transmitter 4 transmits a power signal to the implant 3. The power transmitter 4 is designed as a Class-E amplifier optimized at around 134 MHz and it is made in accordance with the circuit diagram of figure 5, where Lchoke is used to block noise from the DC power supply. The other inductor in the circuit, labeled L and having an inductance of 598nH, is a coil antenna 6 used to transmit a waveform that is shown in figure 6. It is a sinusoidal signal with a frequency of 134 MHz and a peak voltage of approximately 1.5V.

The implant is bio-implantable for insertion into the subject's body. It has a wireless power receiver 7, in the form of a coil antenna, which receives the power signal that was transmitted by the power transmitter 4 of the external unit 2. This received waveform provides a sinusoidal input signal at the first frequency, which is 134 MHz.

The 134 MHz sinusoidal input signal is fed to the rectifier 8 which comprises a diode 9 and a capacitor 10. The diode 9 provides half- wave rectification so as to minimize the diode bias voltage drop. The capacitor 10 stores charge and releases the energy during the diode's off -phase and has a value of 6.6 μF. The rectifier 8 as used in the preferred embodiment was chosen for its minimal number of components. As shown in figure 2, the sinusoidal input signal received by the rectifier 8 is diagrammatically represented to the left of the capacitor 10 and the direct current signal is diagrammatically represented to the right. The rectifier 8 provides a substantially direct current signal, as shown in more detail in figure 7. It can be seen that the direct current signal is, in fact, slightly variable. However, in practice, these minor voltage fluctuations do not inhibit the signal from being utilized as a power source and the term "direct current signal" as used in this specification, including in the claims, is to be construed sufficiently broadly so as to allow for such minor variations. The direct current signal is used as a power source for the implant 3 and in some embodiments may be used to charge a battery. The direct current signal powers the non-linear block 11, to which the 134 MHz sinusoidal input signal is fed.

The non-linear block 11 modifies the input signal so as to provide a non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a second frequency different to the first frequency. More particularly, the non- linear block 11 of the illustrated preferred embodiment is in the form of an inverter 12, which converts the 134 MHz sinusoidal input signal into a non-sinusoidal intermediate signal in the form of a square wave. A circuit diagram for the inverter 12 is shown in figure 3. The inverter 12 used in the preferred embodiment is a Fairchild 74LCX04 MOSFET chip. In figure 3, the sinusoidal input signal is shown diagrammatically on the left hand side of the inverter 12 and the resultant square wave intermediate signal is shown diagrammatically on the right hand side of the inverter.

As is known to those skilled in the art, a Fourier transform of a signal in the time domain produces a corresponding spectrum, which is a weighted sum of sinusoids of various frequencies, amplitudes and phases. The spectrum corresponding to the square wave intermediate signal is shown in figure 8. It can be seen that the Fourier transform of the intermediate signal has a number of characteristic harmonic components at varying frequencies . One or more of these harmonic components may be used by the preferred embodiment to create a carrier signal at the second frequency for data transmission purposes, as described in more detail below.

Typically the second frequency is an n harmonic of the first frequency, where n is an integral value greater than 1. For example, it can be seen in figure 8 that the third harmonic 13 is centered at about a frequency of 403 MHz. This third harmonic 13 is the harmonic used by the preferred embodiment to create the output signal because third harmonics typically have the highest power as compared to the other harmonics.

The intermediate signal is fed to the filter 14, for which a circuit diagram is provided in figure 4. The filter 14 is responsive to the intermediate signal so as to provide an output signal substantially at the second frequency. More particularly, the filter 14 is a tuned LCR band pass filter, with the pass band centered on 403 MHz. The filter 14 was designed mainly to reduce the two harmonics on either side of the 403 MHz signal. The chosen circuit parameters are R=30 Ω, C=O.6pF and L=180nH. The filter 14 allows the third harmonic to pass, however it reduces or completely filters out the other unwanted harmonic components. Hence, the output of the filter 14 is a near perfect sinusoidal waveform having a frequency of 403 MHz, which is used for wireless transmission as described below.

The inductor 15 (labeled sL in figure 4 and labeled L_f in figure 2) is a coil antenna functioning as a transmitter 18 from which a data signal is transmitted to the data receiver 5 of the external unit 2. It will be appreciated that the 403 MHz output signal is utilized as a carrier or reference signal for data transmission and various data modulation schemes may be employed. The preferred embodiment makes use of a 300 kHz On Off Keying (OOK) scheme by placing a transistor switch 16 in the series LCR circuit. The switching of the transistor 16 is controlled by a digital data signal. In a medical telemetry context, the digital data signal is provided by at least one sensor 17 within the implant. The sensor 17 acquires data and is electrically connectable to the transmitter 18 via the transistor 16 for wireless transmission of the data. The data transmission complies with the Medical Implant Communication Service (MICS) standard, which specifies a frequency range of between 402MHz and 405 MHz, with a maximum bandwidth of 30OkHz at any time and a maximum transmission power of 25 μW or -16dBm.

To minimize power and data transmission losses, the antennas of the external unit 2 and the implant 3 are typically respectively aligned closely with each other. In particular, the coil 6 of the power transmitter 4 of the external unit 2 is aligned for maximum transmission efficiency with the coil 19 of the power receiver 7 of the implant 3. Similarly, the coil 15 of the data transmitter 18 of the implant 3 is aligned for maximum transmission efficiency with the coil 20 of the data receiver 5 of the external unit 2.

The spectrum of the data signal as received by the data receiver 5 of the external unit 2 is shown in figure 9. The spectral component at 134 MHz is interference from the power signal transmission, and can be easily eliminated at the external data receiver 5 using a simple or complex filter. The signal as received by the data receiver 5 of the external unit 2 is shown in the time domain in figure 10. It can be seen that the 30OkHz OOK modulation is evident in the alternating higher and lower voltage amplitudes of the signal.

The illustrated embodiment makes use of inductive coils (6, 15, 19 and 20) for transmission and reception of both the power and data signals due to the typically close proximity between the external unit 2 and the implant 3. In a manner known to those skilled in the art, each of the inductive coils (6, 15, 19 and 20) is optimized to self resonate at the desired transmission frequency by selecting an appropriate internal capacitance. The 134MHz power coils (6 and 19) are 10mm in diameter with three turns of 0.5mm diameter copper wire. In use, they are separated by approximately lcm. The 403MHz data coils (15 and 20) are 6mm in diameter with five turns of lmm diameter wire. In use, they are separated by approximately 3cm. The power coils are positioned perpendicular to the data coils. In alternative embodiments other types of antennas, such as rod antennas, for example, may be used.

In summary, the steps performed by the implant 3 include the following:

1) using the power receiver coil 7 to wirelessly receive the power signal shown in figure 6 so as to provide a sinusoidal input signal at the first frequency;

2) using the rectifier 8 to rectify the input signal so as to provide a substantially direct current signal as shown in figure 7 ; 3) powering the non-linear block 11 using the direct current signal;

4) applying the input signal to the non-linear block 11 so as to provide a non- sinusoidal intermediate signal having a spectrum as shown in figure 8 with at least one harmonic component at a second frequency that is different to the first frequency;

5) using the filter 14 to filter the intermediate signal so as to provide an output signal substantially at the second frequency; and

6) using the output signal as a carrier for wireless transmission.

Hence, the preferred embodiment allows for data to be transmitted at a different frequency to that of the power signal. More particularly, the frequency used for data transmission is higher than the power transmission frequency, which is advantageous for transmitting data at high data rates. Advantageously, the preferred embodiment does not require the use of the power inefficient and often physically bulky self oscillating devices (such as oscillator blocks, phase locked loops, crystals or voltage controlled oscillators) that are typically used in the known prior art to generate the higher frequency carrier signal used for data transmission. This improves the size and power efficiency of the implant 3. This approach is elegant due to the dual role of the power signal not only to power the implant 3, but also to provide the input signal which is the starting point for the generation of the higher frequency output signal.

When selecting the power transmission frequency to use in order to obtain the desired data transmission frequency, it is possible to rely upon the known harmonic characteristics of commonly used wave forms. For example, in the preferred embodiment the intermediate signal is a square wave (also known as a periodic pulse signal). This signal has two voltage levels, low and high. It changes levels periodically, and the duty cycle of the signal represents the proportion of time that the signal is high compared to low within the signal period. A mathematical representation of the Fourier series for the periodic square pulse signal is as follows:

where τ is the pulse width in seconds, T is the period of the signal, A is the amplitude, k is the integer harmonic level and t is time. From this equation, it is evident that by manipulating the duty cycle (τ /T) the distribution of harmonics can be changed. Generally speaking, as the duty cycle decreases and the pulses become sharper, more sinusoidal harmonics exist at higher frequencies.

If it is desired to generate a further output signal at a different frequency to the above-mentioned output signal, one option involves taking the following additional steps:

7) applying the output signal to the non-linear block 11 so as to provide a further non-sinusoidal intermediate signal having a spectrum with at least one harmonic component at a further frequency different to the first and second frequencies; and

8) filtering the further intermediate signal so as to provide a further output signal substantially at the further frequency.

In other words, these additional steps involve treating the previously generated output signal as the new input signal for a further iteration of processing using the nonlinear block 11 and the filter 14. It will be appreciated, however, that for these additional steps to be performed, it must be possible for the filter 14 to pass not only the second frequency, but also the further frequency. This may be achieved by providing a filter with dual pass bands. Alternatively, it may be achieved with the use of a tunable filter. Yet other frequencies may be generated by yet further iterations of this process.

Another option for generating multiple output signals of differing frequencies involves ensuring that the spectrum of the intermediate signal has a plurality of harmonic components at a plurality of discrete frequencies each differing from the first frequency. For example, the spectrum shown in figure 8 has a number of other harmonic components in addition to the harmonic component centered on 403MHz. If necessary, each of these additional harmonic components may form the basis of additional output signals at differing frequencies. Once again, however, to implement these additional output signals, it must be possible for the filter to pass not only the second frequency, but also the further frequency or frequencies. In other words, the filter must be responsive to the intermediate signal so as to provide a plurality of output signals substantially at said plurality of discrete frequencies.

Embodiments in which a number of output signals are provided at differing frequencies are particularly useful for implementing an array of sensors. In such an array, the output of each sensor may be transmitted at a discrete pre-defined frequency.

Another embodiment makes provision for tuning of the frequency of the output signal. This involves using the power transmitter 4 on the external unit 2 to vary the frequency of the power signal that is wirelessly received by the implant 3. Remembering that the received power signal is used as the input signal, which is fed to the non-linear block 11, it follows that as the frequency of the power signal changes, so to does the frequency of the harmonic components of the intermediate signal. Hence, a tunable filter may be used to filter out the changing harmonic components to provide an output signal with a frequency that varies in dependence upon changes to the frequency of the power signal. This embodiment is useful in situations where a fixed output frequency may be unduly limiting. For example, in a medical telemetry context, a fixed output frequency may be subject to interference in certain environments, such as in a hospital due to other nearby electronic devices. If so, the frequency of the output signal may be easily varied by varying the power transmission frequency on the external unit whilst the implant remains implanted within the subject's body. In this way, it is possible to search for another data transmission frequency that is not subject to interference in a particular environment. For example, in one embodiment the default generated output signal is in the 13.56 ISM band. However, if this band is crowded in a particular environment in which the device is being used, it is possible to use this method to tune the output signal to a different frequency, such as 20 MHz, for example, that may be more likely to provide reliable communication.

In the embodiment illustrated in Figure 11 the external unit 23 includes a processor in the form of a microcontroller 21. This microcontroller 21 is used to manage the quality of the wireless communication between the external unit 23 and the implant 24. The microcontroller 21 in the external unit 23 senses the quality of the communications link between the external unit 23 and the implant 24. If the communication is poor (due, for example, to interference or other noise sources) the microcontroller 21 modifies the frequency of the power signal that is transmitted from the external unit 23. As outlined in the previous paragraph, this results in a modification of the frequency of the output signal that is transmitted from the implant 24. The microcontroller 21 modifies the power signal and continuously (or at least intermittently) monitors the quality of the communications link until a good quality communications link has been established.

A second processor, in the form of microcontroller 22, is utilized in the implant 24 to tune the tunable filter 25 in response to the modifications that are made to the frequency of the received power signal. This assists to optimize the filtering out of the changing harmonic components as required to provide an output signal with a modified frequency. The microcontroller 22 is also used to manage the rectifier/power supply 26 to control the received power level. Alternatively, or additionally, the microcontroller 21 on the external unit 23 may be used to control the amount of power that is transmitted from the external unit in the power signal, for example via modification of the amplitude of the power signal. A large range of commercially available processors may be used to provide the digital logics functionality required for microcontrollers 21 and 22. Some non-limiting examples include the Microchip Technology Inc. PIC18F87J93 and the Texas Instruments, Inc. MSP430FG43x. In other embodiments the digital logics functionality of the microcontrollers is integrated as part of a single custom designed digital logics computer chip.

In a medical telemetry context, a plurality of sensing devices 24 may be implanted into a single patient. One or both of the microcontrollers 21 and 22 may be used to manage the multi-device communication to ensure that the data signals transmitted by the multiple sensors 24 do not interfere with each other. In one multi- device application scenario a single external device 23 sends a power signal to a plurality of implants 24. In such a scenario interference may be avoided by configuring the microcontroller 22 on each of the implants 24 to tune to a harmonic that is unique for each of the implants 24.

In another multi-device scenario each implant 24 has a dedicated external power source 23. For such a scenario the avoidance of interference between the data signals of the multiple implants 24 may be achieved by configuring the microcontrollers 21 on each of the dedicated external power sources 23 to ensure that the power signal transmitted by each of the dedicated external power sources 23 is at a frequency that is unique to its corresponding implant 24. This results in unique data transmission frequencies for each of the implants 24.

In the embodiment illustrated in figure 2, the non- linear block 11 is provided by an inverter 12. However, it will be appreciated that the inverter 12 may be replaced with any component or arrangement capable of receiving a sinusoidal input signal and outputting a nonsinusoidal intermediate signal. Examples of other components that may be used to perform the function of a non-linear block include non-linear devices, active circuits, comparators and/or diodes.

In an embodiment in which the non-linear block is in the form of a comparator, the comparator receives both the input signal and the direct current signal as inputs. This is in addition to being powered by the direct current signal. Hence, the direct current signal defines a reference point against which the constantly changing value of the input signal is compared. The comparator compares which of the two inputs is greater at any point in time and outputs a square wave in dependence upon the outcome of this comparison. This square wave output is used as the intermediate signal.

Any non-sinusoidal waveform will suffice for the intermediate signal, provided its spectrum has a sufficiently well defined harmonic component at a frequency that is desirable for an output signal. In the above-described embodiment the waveform of the intermediate signal was a square wave, however in other embodiments the waveform of the intermediate signal may take other non- sinusoidal shapes, such as triangular waves, saw tooth waves, and so forth.

In the illustrated preferred embodiment the second frequency (i.e. 403 MHz) is higher than the first frequency (i.e. 134 MHz). However, in other embodiments, the second frequency may be lower than the first frequency. This may be achieved by applying the intermediate signal to a divider so as to lower the frequency of the intermediate signal. Similarly, the second frequency may be increased by applying the intermediate signal to a multiplier so as to increase the frequency of the intermediate signal.

It is anticipated that embodiments of the present invention utilized in implantable bio-telemetry systems may have reduced size and cost as compared to the larger and less power-efficient known prior art. It is also anticipated that intelligent sensing systems (such as those used in the security and surveillance industries, in the field of efficient air-conditioning control and in general power usage management, for example) may provide further examples of technical fields in which embodiments of the invention may be advantageously employed so as to allow for greater complexity and improved integrated systems. This is because it is anticipated that sensors made in accordance with the preferred embodiment of the invention may be smaller, cheaper and less power intensive.

While a number of preferred embodiments have been described, it will be appreciated that numerous variations and/or modifications may be made without departing from the spirit or scope of the invention as broadly described. Hence, the embodiments are to be considered in all respects as illustrative and not restrictive.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A harmonics-based wireless transmission device including: a wireless power receiver for providing a sinusoidal input signal at a first frequency; a rectifier responsive to the input signal so as to provide a substantially direct current signal; a non- linear block responsive to the input signal so as to provide a non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a second frequency different to the first frequency; a filter responsive to the intermediate signal so as to provide an output signal substantially at the second frequency; and a transmitter adapted to use the output signal for wireless transmission.

2. A device according to claim 1 wherein the non-linear block includes at least one of: a non-linear device; an active circuit; an inverter; a comparator; a diode.

3. A device according to claim 1 or 2 wherein the intermediate signal has a plurality of harmonic components at a plurality of discrete frequencies each differing from the first frequency.

4. A device according to claim 3 wherein the filter is responsive to the intermediate signal so as to provide a plurality of output signals substantially at said plurality of discrete frequencies.

5. A device according to any one of the preceding claims wherein the second frequency is higher than the first frequency.

6. A device according to claim 5 wherein the second frequency is an n^£ harmonic of the first frequency, where n is an integral value greater than 1.

7. A device according to any one of the preceding claims wherein the device is bio- implantable.

8. A device according to any one of the preceding claims wherein the device is a telemetry device having a sensor for data acquisition, the sensor being electrically connectable to the transmitter for wireless transmission of the data.

9. A device according to claim 8 wherein the output signal is used as a reference signal for the transmission of the data.

10. A device according to claim 1 wherein the non-linear block is a comparator adapted to compare the input signal to a reference point so as to provide a non-sinusoidal intermediate signal.

11. A device according to claim 10 wherein the reference point is defined by the direct current signal.

12. A device according to any one of the preceding claims wherein the non-linear block is powered by the direct current signal.

13. A unit for use with a device according to any one of the preceding claims, the unit having a transmitter for transmitting a power signal and a receiver for receiving the output signal.

14. A unit according to claim 13 including a processor adapted to monitor the quality of a communications link between the unit and the device.

15. A unit according to claim 14 wherein the processor is adapted to modify a frequency of the power signal in dependence upon the quality of the communications link.

16. A unit according to claim 14 or 15 wherein the processor is a microcontroller.

17. A harmonics-based wireless transmission method including the steps of: wirelessly receiving power so as to provide a sinusoidal input signal at a first frequency; applying the input signal to the non-linear block so as to provide a non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a second frequency different to the first frequency; filtering the intermediate signal so as to provide an output signal substantially at the second frequency; and using the output signal for wireless transmission.

18. A method according to claim 17 including the steps of: rectifying the input signal so as to provide a substantially direct current signal; and powering a non-linear block using the direct current signal.

19. A method according to claim 17 or 18 including the steps of: applying the output signal to the non-linear block so as to provide a further non- sinusoidal intermediate signal having a spectrum with at least one harmonic component at a further frequency different to the first and second frequencies; and filtering the further intermediate signal so as to provide a further output signal substantially at the further frequency.

20. A method according to any one of claims 17 to 19 including the step of applying the intermediate signal to a divider so as to lower the frequency of the intermediate signal.

21. A method according to any one of claims 17 to 20 including the step of applying the intermediate signal to a multiplier so as to increase the frequency of the intermediate signal.

22. A method according to any one of claims 17 to 21 wherein a shape of the intermediate signal is selected from a group including: square waves, triangular waves and saw tooth waves.

23. A method according to any one of claims 17 to 22 including the step of tuning the wirelessly received power so as to tune the output signal.

24. A method according to claim 23 wherein the step of 'filtering the intermediate signal so as to provide an output signal substantially at the second frequency' is performed with a tunable filter.

25. A method according to claim 24 wherein a processor is used to tune the tunable filter in response to the wirelessly received power.

26. A method according to any one of claims 17 to 25 wherein a processor is operatively associated with a rectifier so as to control a received power level.

27. A method according to any one of claims 17 to 26 including a unit having a transmitter for transmitting a power signal to a plurality of devices, each of the devices having a processor controlled tunable filter, the method including the step of configuring the processor on each of the devices to tune the tunable filter to a harmonic that is unique for each of the devices.

28. A method according to any one of claims 17 to 26 including a plurality of units each having a processor controlled transmitter for transmitting a power signal to a corresponding plurality of devices, the method including the step of configuring the processors such that the power signal transmitted by each of the units is at a frequency that is unique to the corresponding device.

Newcastle Innovation Limited, By Their Patent Attorneys,

ADAMS PLUCK