Technical Field

The present disclosure relates to the field of wireless communication, associated methods and apparatus, and in particular concerns transmission of heat signals generated using phonons. Certain disclosed example aspects/embodiments relate to portable electronic devices, in particular, so-called hand-portable electronic devices which may be hand-held in use (although they may be placed in a cradle in use). Such hand-portable electronic devices include so-called Personal Digital Assistants (PDAs), smartwatches and tablet PCs.

The portable electronic devices/apparatus according to one or more described example aspects/embodiments may provide one or more audio/text/video communication functions (e.g. tele-communication, video-communication, and/or text transmission, Short Message Service (SMS)/ Multimedia Message Service (MMS)/emailing functions), interactive/non-interactive viewing functions (e.g. web-browsing, navigation, TV/program viewing functions), music recording/playing functions (e.g. MP3 or other format and/or (FM/AM) radio broadcast recording/playing), downloading/sending of data functions, image capture function (e.g. using a (e.g. in-built) digital camera), and gaming functions.

Background Signals may be transmitted between devices via wired or wireless communications. Commonly, wireless communication uses radio waves to transmit signals.

The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge. One or more aspects/embodiments of the present disclosure may or may not address one or more of the background issues.

Summary According to a first aspect, there is provided an apparatus comprising: a phononic filter configured to filter received phonons having a particular range of frequencies and output filtered phonons having frequencies within a sub-range of the particular range of frequencies; a phononic waveguide coupled to the phononic filter and configured to channel the filtered phonons away from the phononic filter; and at least one metallic carbon nanotube bundle coupled at one end to the phononic waveguide to receive channelled filtered phonons, wherein the at least one bundle has a length to exhibit surface plasmon resonance at a frequency corresponding to the frequency of the channelled filtered phonons to convert the channelled filtered phonons to heat wave signals for transmission. The apparatus may be considered to be a transmission-side apparatus/device, because it is configured to convert phonon-based signals to infrared/heat photon signals for transmission to a receiving apparatus/device.

Such an apparatus may advantageously be used for phonon generated wireless communications. The heat wave signals for transmission may also be referred to as THz waves or infra-red waves. The channelled filtered phonons received by the at least one metallic carbon nanotube bundle are used to create the signal, and are converted by the at least one bundle to (infra-red) heat photons having the same frequency as the phonons just prior to conversion. Transmission of the infra-red/heat signals may be through air in some examples, but may also be through infra-red transparent material in some examples.

The at least one metallic carbon nanotube bundle may be configured such that the end of the bundle opposing the coupled end is free.

The phononic filter may be configured to convert at least a portion of the generated phonons having frequencies outside the sub-range of frequencies to phonons having frequencies within the sub-range of frequencies. This may advantageously allow for improved efficiency by converting phonons outside a desired frequency range to phonons within a desired frequency range for use in signal transmission.

The phononic filter may comprise one or more of:

a phononic crystal comprising a periodic two-dimensional array of holes in the phononic crystal, wherein immediately neighbouring holes are separated by a particular distance, the particular distance in the range of 2 nm to 200 nm; a phononic crystal comprising an irregular two-dimensional arrangement of holes in the phononic crystal, wherein immediately neighbouring holes are separated by a particular distance, the particular distance in the range of between 2 nm to 200 nm;

two different materials with an interface therebetween, the interface configured to filter received phonons having the particular range of frequencies and output filtered phonons having frequencies within the sub-range of the particular range of frequencies; and

a phononic filter comprising a thermocrystal. Advantageously the phononic filter may be a phononic bandgap structure. The properties of the phononic filter, such as hole-hole separation or choice of material, may allow for phonon transmission in a desired frequency range. For a phononic filter comprising a thermocrystal, the thermocrystal may itself comprise impurity atoms, nanoparticles, dislocations and/or amorphism, for example, to tailor the phonon propagation properties of the thermocrystal.

The phononic waveguide may comprise:

a phononic crystal; and

a two-dimensional array of holes in the phononic crystal, the holes separated by between 2 nm and 200 nm, the array of holes configured to guide phonons towards the location of the at least one metallic carbon nanotube bundle. Again, advantageously, properties of the phononic waveguide, such as hole-hole separation or choice of material, may allow for efficient phonon channelling within a desired frequency range. The apparatus may comprise a phonon generator configured to generate phonons having the particular range of frequencies for filtering by the phononic filter. In some examples, the phonon generator may comprise a material which has both phononic and photonic bandgaps at substantially the same frequency. The apparatus may comprise at least one thermal diode between the phononic waveguide and the at least one metallic carbon nanotube bundle (mCNT), the thermal diode configured to inhibit the passage of heat from the at least one metallic carbon nanotube bundle back into the phononic waveguide. Advantageously, thermal diodes may improve the efficiency of the apparatus by increasing the temperature of the at least one mCNT bundle through prevention of heat loss back to the phononic waveguide. The apparatus may comprise a heat shield, the heat shield comprising: a negative differential thermal material with at least one aperture; the heat shield coupled to the apparatus such that the at least one aperture is aligned with the free end of the at least one metallic carbon nanotube bundle to: allow the passage of the heat wave signals from the free end of the at least one metallic carbon nanotube bundle for transmission; and inhibit the transmission of heat from the apparatus which is not associated with the heat wave signals. Use of such a heat shield may advantageously improve the signal to noise ratio of the received infra-red/heat wave signal by inhibiting the transfer of heat which is not related to the signal being transmitted from the mCNT ends.

The phononic filter may be configured to output filtered phonons having frequencies in the sub-range of 100 GHz to 30 THz. This range of frequencies lies in the upper hypersound and heat ranges of the sound spectrum. In some examples the filtered phonons may have frequencies in the sub-range of 300 GHz to 30 THz. Filtered phonons having a frequency above 300 GHz may allow for stronger resonances compared with filtered phonons having lower frequencies.

The phonons may be modulated using one or more of: on-off keying, binary phase shift keying, quadrature phase shift keying, frequency shift keying or amplitude shift keying to generate the signal for transmission. Advantageously, different modulation schemes may be used according to the signals to be transmitted.

The apparatus may comprise a plurality of bundles of metallic carbon nanotubes coupled at one end to the phononic waveguide. Using multiple bundles may advantageously provide for transmission of signals in more than one frequency range of different length mCNT bundles are used, or may advantageously allow for improved efficiency of signal transfer within one frequency range if similar mCNT bundles are used, for example. The apparatus may be one or more of an electronic device, a portable electronic device, a telecommunications device, a portable telecommunications device and a module for one or more of the same. According to a further aspect, there is provided a system comprising: an apparatus as described herein; and a receiver configured to receive heat transmitted waves from the apparatus and convert the received heat transmitted waves to electrical signals. The receiver may be a graphene based bolometric receiver. Such a receiver may advantageously work efficiency at room temperature through using graphene in the detector.

According to a further aspect, there is provided a method comprising: filtering, using a phononic filter, received phonons having a particular range of frequencies and output filtered phonons having frequencies within a sub-range of the particular range of frequencies; channelling, using a phononic waveguide coupled to the phononic filter, the filtered phonons away from the phononic filter; receiving the channelled filtered phonons by at least one metallic carbon nanotube bundle coupled at one end to the phononic waveguide, wherein the at least one bundle has a length to exhibit surface plasmon resonance at a frequency corresponding to the frequency of the channelled filtered phonons to convert the channelled filtered phonons to heat wave signals for transmission. The method may further comprise converting the channelled filtered phonons to heat wave signals for transmission, and transmitting the heat wave signals.

The method may further comprise receiving the transmitted heat wave signals at a receiver and converting the received heat wave signals to electrical signals.

According to a further aspect, there is provided a computer readable medium comprising computer program code stored thereon, the computer readable medium and computer program code being configured to, when run on at least one processor perform at least the following: control the generation of pulses for input to an apparatus as described herein for eventual transmission as infra-red/heat wave signals.

Corresponding computer programs (which may or may not be recorded on a carrier) for controlling the generation of pulses for input to an apparatus as described herein for eventual transmission as infra-red/heat wave signals are also within the present disclosure and encompassed by one or more of the described example embodiments. The present disclosure includes one or more corresponding aspects, example embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. Corresponding means for performing one or more of the discussed functions are also within the present disclosure.

The above summary is intended to be merely exemplary and non-limiting. Brief Description of the Figures

A description is now given, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 shows a schematic representation of the phononic spectrum;

Figure 2 shows an apparatus configured for phonon generation, filtering, channelling and conversion to heat signals according to the present disclosure;

Figure 3 shows a portion of an apparatus configured for phonon generation, filtering, channelling and conversion to heat signals using thermal diodes according to the present disclosure;

Figures 4a-4b show a portion of an apparatus comprising a heat shield having one or a plurality of apertures according to the present disclosure;

Figure 5 shows schematically a bundle of carbon nanotubes;

Figure 6 shows an example signal transmittable using apparatus according to the present disclosure;

Figure 7 shows a schematic multi-detector heat signal receiver according to the present disclosure;

Figure 8 shows two portable electronic devices communication using heat wave signals according to the present disclosure;

Figure 9 shows an example device comprising an apparatus according to the present disclosure;

Figure 10 shows a computer-readable medium comprising a computer program configured to provide a signal for transmission by apparatus according to the present disclosure; and

Figure 11 shows an example method according to the present disclosure. Description of Specific Aspects/Embodiments

This disclosure is generally directed to wireless communication, and in particular concerns transmission of heat signals generated using phonons.

Signals may be transmitted between devices via wired or wireless communications. Commonly, wireless communication uses radio waves to transmit signals, although other methods may be used, such as optical transmission, electromagnetic induction, and sound transmission.

Radio communication using wirelessly powered tags such as JEDEC (Joint Electron Device Engineering Council) JC64.9 Wireless Memory tags, which operate in a relatively short range (e.g., from about 1 cm to a few metres) require very power-efficient and simple signal modulation, such as on-off-keying (OOK).

Radio signalling equivalent isotropically radiated power (EIRP) spectral density is regulated very tightly below -41.3 dBm/MHz indoors and -70 dBm/MHz in outdoors in some countries, especially in the ultra-wide band (UWB) frequency range of 3.1 - 10.4 GHz. This limits use of the globally free UWB band to 7.25 - 8.5 GHz, enabling a maximum of around 1.25 Gbps bit rates with power efficient OOK modulation. In the 60 GHz band an approximately 5 GHz band is available globally with a very high allowed EIRP spectral density, enabling bit rates with simple OOK modulation up to about 5 Gbps within the regulatory emission mask. 20 Gbps bit rates using OOK may be possible if a bandwidth larger than 5 GHz is used, which limits such use mainly inside closed structures without outside emission.

A problem with using the 60 GHz band with simple OOK modulation for short-range links is that regulation for this band has not yet been well established. However, in the future, use of this band might be greatly limited, particularly for impulse radio applications.

Infrared links operating typically in the near-infrared band usually having a wavelength of between 850 nm to 1550 nm, and offer an alternative to radio signal communications. Such infra-red links typically employ vertical cavity surface-emitting laser (VCSEL) diodes to produce a signal from an electrical signal. However, components for use at such wavelengths are still relatively expensive compared to equivalent simple radio components.

The use of phonons for signal transmission is a relatively new field of study, and so far has been limited to mechanically connected interconnections. For wireless transmission, phonon signals have been converted into electromagnetic signals, for example using piezoelectric transducers.

There remains a need for apparatus and devices which are capable of improved wireless communication, for example using heat signals between devices to transmit information. Such devices may advantageously be manufactured with improved energy efficiency, at lower costs, and over much higher bandwidths, without the need for connection ports/connectors as communications may be effected wirelessly. Typically, Bluetooth and RFID communications take place over a relatively narrow bandwidth and the energy per transmitted bit is relatively high.

Figure 1 shows a schematic representation of the phononic spectrum. The infrasound range 102 lies below around 10 Hz. Sound waves 104, related to music and speech for example, lie in the frequency range between around 10 Hz and 10 kHz. Between around 10 kHz and 100 MHz sound waves are in the ultrasound frequency range 106, which may be used for ultrasonic imaging, for example. Sound waves in the range between around 100 MHz and 100 GHz may be called hypersound waves 108. High frequency sound waves, above around 100 GHz, may be considered to be heat/thermal waves 110, and may be used in thermal device applications.

The use of phonons in generating infra-red heat waves for wireless data transfer is possible without additional mechanical-to-electromagnetic transducers if the phonons lie in the sub-THz or THz frequency range. In this range, the mechanical energy of the phonons can be directly converted to infra-red/heat waves for signal transmission using metallic carbon nanotubes as phonon-photon converters as described herein.

Examples described herein relate to wireless communication using terahertz (THz) frequency sound waves and high frequency hypersound waves (in the frequency range of approximately 100 GHz to 1 THz). Hypersonic waves in the frequency range 100-300 GHz have a corresponding wavelength of λ=1 - 3 mm. Heat waves in the frequency range 0.3 - 30 THz have a corresponding wavelength of λ=10 - 1000 pm.

Figure 2 shows an apparatus 200 configured for generating heat/infra-red signals for transmission. The apparatus 200 comprises a phonon generator 202, a phononic filter 204, a phononic waveguide 206 and at least one metallic carbon nanotube (mCNT) bundle 208. The phonon generator 202 is coupled to the phononic filter 204. The phononic filter 204 is coupled to the phononic waveguide 206. The phononic waveguide 206 is coupled to the mCNT bundle 208.

Phonons may be generated at the phonon generator 202, filtered by the phononic filter 204 to a suitably narrow frequency bandwidth, and are then channelled to the mCNT bundle "antenna" 208 by the phononic waveguide 206. The phonon generator 202 is configured to generate phonons having a particular range of frequencies for filtering by the phononic filter 204. The phonon generator 202 may comprise a piezoelectric crystal. The piezoelectric crystal may have a fundamental or harmonic resonant frequency in the high GHz or THz range, suitable for downstream filtering and conversion to heat waves.

Phonons may be generated by optical pulse excitation or electrical pulse excitation at the phonon generator 202. Examples of piezoelectric crystals which may be employed as phononic generators include aluminium nitride (AIN), lead zirconate titanate (PZT, Pb[Zr(x)Ti(i _-X )]03), zinc oxide (ZnO), and other piezoelectric materials which may be used for phonon generation. Some piezoelectric materials may be used as thin films in a phonon generator.

The phononic filter 204 is configured to filter received phonons having a particular range of frequencies. In this example the phonons are received from the phonon generator 202. The phononic filter is also configured to output filtered phonons having frequencies within a sub-range of the particular range of frequencies. In this example the filtered phonons are output to the phononic waveguide 204. For example, phonons may be generated in the range 500 GHz to 5 THz, and the phononic filter may filter out phonons below 1 THz and above 2 THz to leave a 1 THz-wide sub-range of phonons having frequencies in the range 1-2 THz for onward transmission to the phonon waveguide. The phononic filter 204 may be configured to convert at least a portion of the generated phonons having frequencies outside the sub-range of frequencies to phonons having frequencies within the sub-range of frequencies. In this way the phononic filter 204 acts as a phononic converter. Phonon conversion may be considered to improve efficiency by converting phonons having frequencies outside the desired range to phonons having frequencies within the desired range, rather than simply filtering out and losing phonons outside the desired frequency range. Phonons having a frequency below the desired frequency range may be converted by upconversion, such as interfacial acoustic-optical upconversion. Two lower-frequency acoustic phonons may propagate towards a conversion interface. At the interface the two acoustic phonons may be converted to one higher frequency optical phonon. Similarly, a phonon having a frequency above the desired frequency range may be converted by downconversion, such as interfacial optical-acoustic downconversion. A higher- frequency optical phonon may propagate towards a conversion interface. At the interface the optical phonons may be converted to two lower frequency acoustic phonons.

For an example including both upconversion and downconversion, phonons may be generated in the range 1 THz to 3 THz, and the phononic filter may upconvert phonons in the range of 1 THz to 2 THz to phonons in the range 2 THz to 2.5 THz, and may downconvert phonons in the range 2.5 THz to 3 THz to phonons in the range 2 THz to 2.5 THz. This leaves phonons in the sub-range of 2 THz - 2.5 THz without "wasting" phonons which were generated outside this range by filtering them out and losing them. In another example the desired phonon frequency sub-range may be 20 - 25 THz.

The phononic filter may be configured to output filtered phonons having frequencies in the sub-range of 100 GHz to 30 THz. Phonons in this range are suitable for conversion to heat waves for transmission, for example through air. In certain examples it may be desirable to generate phonons of substantially one single frequency for downstream conversion to heat signals.

In this example the phononic filter 204 comprises a phononic crystal 216. The phononic crystal may be a phononic bandgap structure. The phononic crystal 216 in this example comprises a periodic two-dimensional array of holes 218. Such a crystal may be considered to be a nanomesh structure. The holes may be each separated from a neighbouring hole by a particular distance. The hole-hole separation distance may be in the range of 2 nm to 200 nm depending on the desired frequency of phonons to be retained. For example, the filter may comprise holes each separated from a neighbouring hole by 30 nm within an acceptable tolerance to filter out phonons having energies which cannot easily be transmitted along the phonon filter having this hole separation and to allow the passage of phonons having energies which can readily pass along the phonon filter having holes with this separation. In other examples, the phonon filter may have a hole-hole separation of between 15-140 nm, between 1 - 10 nm, between 10 - 50 nm, between 50 - 200 nm, of less than 300 nm, or of approximately 100 nm, depending on the required phonon frequency. The shape(s) and arrangements(s) of the holes also affect phonon filtering, although there may not be a straightforward relationship between, for example, hole size and frequencies filtered. Holes separated by distances in this range are configured such that phonon filtering can take place in the 100 GHz - THz range of frequencies. Larger hole separations are more suitable for lower frequency phonon filtering and smaller hole separations are more suitable for higher frequency phonon filtering. In certain examples such a phononic filter may provide up to 99% or better blocking of undesired "random heat" phonons outside the desired frequency range.

In other examples the phononic filter may comprise a phononic crystal comprising an irregular two-dimensional arrangement of holes in the phononic crystal, each hole separated by a particular distance from an immediately neighbouring hole. The hole-hole separation may be in the range of between 2 nm and 200 nm depending on the frequency required. For example, the filter may comprise holes each separated from a neighbouring hole by 50 nm within an acceptable tolerance.

In other examples the phononic filter may comprise two different materials with an interface therebetween. The interface may be configured to filter received phonons having the particular range of frequencies and output filtered phonons having frequencies within the sub-range of the particular range of frequencies.

In other examples the phononic filter may comprise a thermocrystal. The thermocrystal may itself comprise impurity atoms, nanoparticles, dislocations and/or amorphism to tailor the phonon propagation properties of the thermocrystal, for example to reduce the thermal conductivity of the material or increase the phononic bandgap.

In certain examples the phononic filter may comprise a phononic bandgap structure.

The phononic waveguide 206 is configured to channel the filtered phonons away from the phononic filter 204. In this example the phononic waveguide 206 is configured to channel the phonons received from the phononic filter 204 towards the bundle of mCNT 208. In this way the phonon energy is concentrated toward the point where the mCNT bundle 208 is located to increase efficiency.

In this example the phononic waveguide 206 comprises a phononic crystal 220 and a periodic two-dimensional array of holes 222 in the phononic crystal 206. Neighbouring holes 222 are separated by substantially the same distance of between 2 nm and 200 nm. Holes separated by distances in this range are configured such that phonon wave guiding/direction channelling can take place in the 100 GHz - THz range of frequencies. In this example the array of holes 222 form a "V" configuration such that holes to either side of the mounting site of the mCNTs are spaced further apart closer to the mCNT bundle mounting point. Such an arrangement is configured to guide phonons towards the location of the mCNT bundle 208 to channel the phonons towards the mCNTs 208. Of course other hole arrangements, such as a "U" configuration or a tapering configuration tapering towards the edge of the waveguide may also be used, provided the arrangement can act to guide phonons towards the location of a mCNT bundle mounted to the phononic waveguide.

Both the phononic filter/converter 204 and the phononic waveguide 206 may be considered to be narrow phononic bandgap structures in certain examples. How narrow the bandgap is depends generally on a (potentially complex) relationship between hole size and shape (both of the holes and the pattern of holes in the filter). A narrow bandgap structure required low losses, so that the structure oscillates with a high amplitude at a particular resonant frequency. By positioning the holes to form several- dimension structures, such as in a "snowflake" arrangement, there may be several resonant frequencies and the bandgap may broaden. A narrow bandgap structure may be made using a regular hole array of a single periodicity to resonate at a single resonant frequency. The at least one mCNT bundle 208 is coupled at one end 210 to the phononic waveguide 206 to receive channelled filtered phonons from the phononic waveguide 206. The mCNT bundle 208 has a length / 212 to exhibit surface plasmon resonance at a frequency corresponding to the frequency of the channelled filtered phonons. For example, a mCNT bundle 1000 nm in length may be used for transmitting signals at 1 THz.

The mCNT bundle 208 is configured to convert the channelled filtered phonons to heat wave signals for transmission. The incident phonon frequency should be matched to the resonant frequency of surface plasmons of the mCNTs 208 for efficient energy transmission to the free ends 214 of the mCNTs 208. Surface plasmon resonance in the current context may be described as the collective oscillation of electrons in a solid stimulated by an incident phonon. The resonance condition is met when the phonon frequency matches the natural frequency of surface electrons oscillating against the restoring force of positive nuclei in the mCNTs. Metallic CNTs may be used because these can exhibit surface plasmon resonances. However, semiconducting CNTs do not exhibit surface plasmon resonances and are not suitable for use in apparatus as described herein.

The mCNT bundle 208 is configured such that the end of the bundle 214 opposing the coupled end 210 is free and not coupled or bound directly to a supporting structure. The mCNT bundle may be considered a GHz THz frequency thermal antenna, as it is configured to receive phonon excitations in the high GHz and THz range and convert them to heat waves for transmission. The mechanical energy from the phonons can propagate along the mCNTs as surface plasmon resonances and the energy is then radiated as heat waves at the free ends 214. The thermal radiation generated at the free ends 214 of the mCNTs 208 may be enhanced, in some examples well above the black body radiation level, by matching the mCNT 208 length to support (i.e., match) the surface plasmon resonances.

Generally, the phonon frequency range over which an apparatus may currently practically operate is between 50 GHz and 30 THz. The minimum frequency at which mCNTs can support surface plasmon oscillations is around 50 GHz, so a minimum frequency of 50 GHz is required for the apparatus to function effectively. The upper frequency limit is determined at least in part by how the original phononic signal is generated and if this signal can propagate through the phononic filter and waveguide. Frequencies above around 20 - 30 THz would require, for example, a femtosecond laser pulse which currently cannot easily be implemented in a portable electronic device. In future it may be that phonon generation techniques and apparatus develop to allow phonons of 20 - 30 THz or higher to be generated in portable electronic devices using a femtosecond laser or another ultra-fast energy source.

The upper limit of phonons for use in apparatus described herein may also be limited by the phononic filter and waveguide operating frequency, because for a filter/waveguide comprising a periodic structure (wherein the period is the distance between adjacent holes in the filter/waveguide), the period must be half the phonon wavelength. Thus the periodicity and hole diameter of the filter should be in the nanometer range to block phonons having frequencies above 20 - 30 THz, and the periodicity and hole diameter of the waveguide should also be in the nanometer range otherwise phonon steering is less effective, resulting in loss of phonons guided towards the mCNTs.

Figure 3 illustrates the transmission side of an apparatus similar to that shown in figure 2. However in figure 3 the mCNT bundle 308 is coupled to the phononic waveguide 306 by a series of thermal diodes 324 connected between each mCNT in the bundle 308 and the phononic waveguide 306. The thermal diodes 324 are configured to inhibit the passage of heat from the mCNT bundle 308 back into the phononic waveguide 306, since they allow the passage of heat from the coupled end 310 of the mCNT bundle 308 to the free end 314, and inhibit the passage of heat from the free end 314 back to the coupled end 310 and the phononic waveguide 306. The thermal diodes 324 may be considered thermal rectifiers in this regard, allowing the passage of heat more favourably in one direction than the reverse direction.

By using thermal diodes 324 to mechanically load the mCNTs 308 at the mounting point 310 where the mCNT bundle 308 is coupled to the phononic waveguide 306, the efficiency of thermal rectification can be tuned to a particular value. The mechanical loading may be tuned such that the "dc'Vbackground level of heat is at an optimum level compared with the "ac'Ysignal heat level emitted from the free end 314 of the mCNT bundle 308. An example mechanical load may comprise a deposit of amorphous trimethylcyclopentadienyl platinum (CgHi ₆ Pt) at the mounting point of the mCNTs. In some examples, the temperature, either at the coupled end of the mCNT bundle 308 or elsewhere along the mCNT bundle 308, may be increased. The thermal diodes 324 may act to increase the temperature at the free ends 314 of the mCNTS 308. Increasing the temperature has the effect of increasing the efficiency of heat flow from the free end 314 of the mCNTs in the bundle 308, by increasing the thermal emission from the mCNTs 308. Thus the amount of energy emitted as heat waves is increased.

An example of a thermal diode is a two-segment bar wherein each segment has a different thermal conductivity (e.g., Cu/Cu02, aluminium/stainless steel, or asymmetric graphene ribbons.) In the example of a two-segment bar, a thermal current can be stopped or permitted to pass depending on the temperatures of the segments.

Increasing the temperature of the mCNT bundle 308 structure as a whole may lead to an increase in general thermal radiation, and thus may increase the noise present in the transmitted heat signal over a broad bandwidth.

Figure 4a shows a portion of an apparatus 400 as described in relation to figure 3 and a heat shield 430. Of course in other examples the apparatus 400 may not necessarily comprise thermal diodes 424 between the phononic waveguide 406 and the mCNT bundle 408. An example material which may be used as a heat shield is a vanadium dioxide (VO2) thin film.

The heat shield 430 in this example comprises a negative differential thermal material 432 with an aperture 434. The heat shield 430 is coupled to the apparatus 400 such that the aperture 434 is aligned with the free end 414 of the mCNT bundle 408.

The heat shield 430 is configured to allow the passage of heat wave signals from the free end 414 of the mCNT bundle 408 for transmission by allowing the heat signals to pass through the aperture 434. The heat shield 430 is also configured to inhibit the transmission of heat from the apparatus 404 which is not associated with the heat wave signals by blocking heat transmission not emanating from the free end of the mCNT bundle 408 via the negative differential thermal material 430. By reducing the heat emanating from the apparatus 400 which is not associated with the generated heat signal, the noise in the transmitted signal may be reduced. In other words, the thermal emittance of the apparatus 400 is reduced when the temperature is increase due to the heat shield 430.

Figure 4b shows a portion of an apparatus 450 comprising two mCNT bundles 408a, 408b and a heat shield 430 comprising two apertures 434a, 434b each aligned with a respective mCNT bundle 408a, 408b. Thus in certain examples, if more than one mCNT bundle 408 is present, there may be more than one aperture 434, each aperture being aligned with each free end of each mCNT bundle.

The heat shield 430 may be formed by laser drilling the apertures 434, 434a, 434b into the shield material, for example. The heat shield 430 may be aligned with the apparatus such that the heat shield apertures 434, 434a, 434b are aligned with the free ends of the at least one mCNT bundle 408, 408a, 408b. A typical mCNT bundle may comprise hundreds of mCNTs, and a heat shield aperture aligned with the end of such a bundle may be considered relatively large in relation to microelectronics processing lengthscales (e.g., several micrometers in diameter). Thus in some examples the heat shield 430 may be manufactured as an additional process in depositing/forming the mCNT bundle(s). For example, the mCNT bundle(s) may be deposited/formed in a CMOS process, and deposition of the heat shield material may be carried out using additional CMOS processing steps, by covering the surface (except aperture areas where the mCNT bundle end(s) are located) with Si0 ₂ or another dielectric material, then depositing a negative differential heat emission material on top.

In some examples the heat shield 430 may be separated from the end(s) of the mCNT bundle(s), in particular if the mCNTs are longer than 1000 nm. The heat shield may be connected to the apparatus in an area outside the location of the mCNT bundle(s) using, for example, large numbers of other CNT bundles. In some examples a typical area for the heat shield to cover may be 1 mm x 1 mm. In some examples the mCNTs in the bundle(s) configured for converting channelled filtered phonons to heat wave signals for transmission may be up to 10 pm long, after which resistive losses may become significant. Figure 5 illustrates schematically a bundle of metallic carbon nanotubes (mCNT). The length scale of approximately 200 nm across two separated nanotube diameters is approximate, and depends on the nanotube - nanotube separation and the diameter of each nanotube. CNT arrays may be readily manufactured, for example using standard complementary metal-oxide-semiconductor (CMOS) methods. The CNTs must be metallic to exhibit surface plasmon resonances. Single walled CNTs may be metallic or semiconducting, whereas multi-walled CNTs are metallic. Therefore if single walled CNTs are used, the CNTs must be treated/sorted to remove the semiconducting CNTs so that only metallic CNTs remain for use in the CNT bundle to improve efficiency.

Loose CNT bundles may be preferable to tightly packed CNT bundles, since packing the CNTs too tightly in the bundle inhibits the performance of the CNT bundle to amplify the received phonon excitations and convert them to heat waves. Tightly packed CNT bundles may behave more like a bulk metallic macrostructure, such as copper metal. Surface plasmon resonance based energy propagation may be much more efficient in a CNT-like material than in a macrometallic-like material.

Figure 6 illustrates a series of three "bits", whereby a "1" is transmitted as a damped sinusoidal excitation 602, 606, and a "0" is transmitted as an absence of excitation 604. One excitation is allowed to die away through damping before the following bit is transmitted. The "1" bit excitation 602, 606 may be created by transmitting a pulse excitation (electrical or optical) to a piezoelectric material or other material which can convert a pulse excitation to a damped mechanical oscillation. Damping can be high enough in a piezoelectric material that a string of bits may be generated without subsequent bits overlapping.

The pulsing scheme of figure 6 may be considered an example of "on-off keying" (OOK). OOK can be used up to bit rates of approximately 1 Gbps or 10 Gbps. Higher bit rates can be achieved by using other modulation schemes, such as using pulse amplitude modulation (PAM) with more than one amplitude level, time shifts, or phase shift keying such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), frequency shift keying (FSK) or amplitude shift keying (ASK). More complicated modulations may require several sources, and/or may require pulses to be handled by phononic waveguide and resonance cavity structures. Figure 7 illustrates a schematic representation of a detector 700 comprising a 2 x 2 array of detectors 702, 704, 706, 708 which may be used to detect heat waves transmitted by the apparatus described herein. Each detector may be a bolometric detector. Each detector may comprise graphene configured for use as a bolometric detection material.

The detector 700 is configured to receive infra-red/heat signals and convert the infrared/heat into electrical signals. Thus a voltage is generated as a function of absorbed power (heat), similarly to Joule heating and photon excitation. Electron-hole pairs are thermally generated in the detector 700 due to incident heat, and chemically or electrically biasing to the source and the drain electrodes causes the electrons and holes to drift to respective electrodes. Each cell 702, 704, 706, 708 may contain one source and one drain, or several of each. A preamplifier may be included in the detector circuit. After pre-amplification (if performed) the signals from multiple sources and multiple drains may be summed together to increase detector efficiency. An array of detectors 702, 704, 706, 708 may be used if the size of the received heat beam is larger than a single detector. In some examples a heat concentrator may be used to focus the received heat beam onto a detector or detectors.

Graphene may be incorporated into such detectors. Graphene is effective at detecting infra-red/heat frequencies, even at room temperature, because the timescale over which electron-hole pair recombination occurs in graphene is relatively long. Thus the timescale for conversion of the recombination to lattice vibrations is relatively long (rapid recombination is undesirable as the electronics and holes will not reach the source and drain to contribute to the received electrical signal). The effect of a longer recombination time in graphene allows a greater chance of the electrons and holes being directed to the source and drain for voltage generation before recombination, and therefore a greater detection efficiency.

Figure 8 illustrates schematically two portable electronic apparatus/devices 800, 802 in communication. Apparatus/device 800 comprises an apparatus 804 configured for transmitting signals as infra-red/heat waves such as those described in relation to figures 2-5. The apparatus 804 may be considered to be a transmission module. Apparatus/device 802 comprises a detector 806 configured for receiving heat wave signals such as those described in relation to figure 6. The apparatus 806 may be considered to be a receiver module. Such devices 800, 802 may each comprise both transmitting 804 and receiving 806 apparatus/modules. In other examples, a particular apparatus/device 800, 802 may be configured for transmission only, or reception only, of signals as heat signals. An apparatus/device 800, 802 may comprise both a transmission apparatus/module 804 and a receiver apparatus/module 806. In such a case the transmitter 804 and receiver 806 apparatus/modules may operate independently but be fabricated on the same silicon wafer separated by around 1 mm or more, for example. The transmitter 804 and receiver 806 on the Si wafer may typically function using time division multiplexing to inhibit coupling of the transmitted signal to the neighbouring receiver 806 through the silicon wafer/die.

The transmitter of one apparatus 800 may be aligned with the receiver of the other apparatus 802 for communication by heat signals. For example, the transmitter and receiver locations may be marked for alignment by eye by a user with corresponding visible markings on the two apparatus 800, 802. As another example, surfaces on each apparatus 800, 802 having corresponding raised/lowered profiles may be provided which mate when the surfaces are in contact, thereby aligning the transmitting and receiving apparatus 804, 806. Of course, any mechanism/method whereby the transmitting 804 and receiving 806 apparatus are aligned for signal transmission may be used.

Generally, by using a system of transmission and detection as described above, portable devices may be advantageously manufactured with increased energy efficiency, high bandwidth, and at low cost without the need for connectors/connector ports Wireless transmission may not need to be tightly regulated because the transmitted infra-red heat waves are not dangerous to the eyes. Infra-red/heat waves are regarded to be safe for eyes up to very power levels when the wavelength exceeds 1400 nm. In the above examples, the wavelength of the infra-red/heat radiation is in the range of approximately 10,000 nm - 1 mm, safely beyond the safe minimum wavelength. At very high power levels corneal burns may occur even at such long wavelengths, but the above apparatus may operate at power levels at advantageously low power/energy levels, below around 100 mW/cm ² , and therefore may be regarded as safe without time limitation.

Figure 9 shows an example of an apparatus/device 900 comprising an apparatus 908 configured for transmitting signals as infra-red/heat signals as described herein, such as the apparatus 802 described in relation to figure 8, and comprising a receiver 910 for receiving heat signals such as the receiver described in relation to figure 7. The transmission apparatus 908 in this example is protected by a heat shield 912 as described in relation to figures 4a-4b.

The apparatus/device 900 comprises a processor 902 and a storage medium 904 which are electrically connected to one another by a data bus 906. The apparatus/device 900 may be one or more of an electronic device, a portable electronic device, a telecommunications device, a portable telecommunications device and a module for any of the aforementioned devices.

The processor 902 is configured for general operation of the apparatus 900 by providing signalling to, and receiving signalling from, the other components to manage their operation. The processor 902 may be a microprocessor, such as an Application Specific Integrated Circuit (ASIC). The processor 902 may be configured to provide a signal as a (e.g., modulated) series of "1"s and "0"s for transmission by the apparatus 908.

The storage medium 904 is configured to store computer code configured to perform, control or enable operation of the apparatus 900. The storage medium 904 may also be configured to store settings for the other components. The storage medium 904 may comprise read-only memory (ROM), for example for storage of computer code/computer readable instructions, and random-access memory (RAM), for example for executing stored computer code/computer readable instructions. The processor 902 may access the storage medium 904 to retrieve the component settings in order to manage the operation of the other components. The storage medium 904 may be a temporary storage medium such as a volatile random access memory. In other examples the storage medium 904 may be a permanent storage medium such as a hard disk drive, a flash memory, or a non-volatile random access memory. The storage medium 904 may comprise computer program code for instructing the processor 902 to pass a particular signal onto the apparatus 908 for transmission.

Figure 10 illustrates schematically a computer/processor readable medium 1000 providing an example computer program configured to control the generation of pulses for input to an apparatus as described herein. For example, the computer program may control the generation of electrical or optical pulses provided to a phonon generator to encode a signal for transmission into a series of excitations for conversion to phonons.

In this example, the computer/processor readable medium 1000 is a disc such as a digital versatile disc (DVD) or a compact disc (CD). In other embodiments, the computer/processor readable medium 1100 may be any medium that has been programmed in such a way as to carry out an inventive function. The computer/processor readable medium 1100 may be a removable memory device such as a memory stick or memory card (SD, mini SD, micro SD or nano SD).

Figure 11 illustrates an example method 1100 comprising filtering, using a phononic filter, received phonons having a particular range of frequencies and output filtered phonons having frequencies within a sub-range of the particular range of frequencies 1102; channelling, using a phononic waveguide coupled to the phononic filter, the filtered phonons away from the phononic filter 1104; and receiving the channelled filtered phonons by at least one metallic carbon nanotube bundle coupled at one end to the phononic waveguide, wherein the at least one bundle has a length to exhibit surface plasmon resonance at a frequency corresponding to the frequency of the channelled filtered phonons to convert the channelled filtered phonons to heat wave signals for transmission 1106. In some examples the method may comprise the steps of converting the channelled filtered phonons to heat wave signals for transmission 1108, and/or transmitting the heat wave signals 1110 (for example through air). In some examples the method may comprise the steps of receiving the transmitted heat wave signals at a receiver and converting the received heat wave signals to electrical signals.

Other embodiments depicted in the figures have been provided with reference numerals that correspond to similar features of earlier described embodiments. For example, feature number 1 can also correspond to numbers 101 , 201 , 301 etc. These numbered features may appear in the figures but may not have been directly referred to within the description of these particular embodiments. These have still been provided in the figures to aid understanding of the further embodiments, particularly in relation to the features of similar earlier described embodiments.

It will be appreciated to the skilled reader that any mentioned apparatus/device and/or other features of particular mentioned apparatus/device may be provided by apparatus arranged such that they become configured to carry out the desired operations only when enabled, e.g. switched on, or the like. In such cases, they may not necessarily have the appropriate software loaded into the active memory in the non-enabled (e.g. switched off state) and only load the appropriate software in the enabled (e.g. on state). The apparatus may comprise hardware circuitry and/or firmware. The apparatus may comprise software loaded onto memory. Such software/computer programs may be recorded on the same memory/processor/functional units and/or on one or more memories/processors/functional units. In some embodiments, a particular mentioned apparatus/device may be preprogrammed with the appropriate software to carry out desired operations, and wherein the appropriate software can be enabled for use by a user downloading a "key", for example, to unlock/enable the software and its associated functionality. Advantages associated with such embodiments can include a reduced requirement to download data when further functionality is required for a device, and this can be useful in examples where a device is perceived to have sufficient capacity to store such pre-programmed software for functionality that may not be enabled by a user.

It will be appreciated that any mentioned apparatus/circuitry/elements/processor may have other functions in addition to the mentioned functions, and that these functions may be performed by the same apparatus/circuitry/elements/processor. One or more disclosed aspects may encompass the electronic distribution of associated computer programs and computer programs (which may be source/transport encoded) recorded on an appropriate carrier (e.g. memory, signal).

It will be appreciated that any "computer" described herein can comprise a collection of one or more individual processors/processing elements that may or may not be located on the same circuit board, or the same region/position of a circuit board or even the same device. In some embodiments one or more of any mentioned processors may be distributed over a plurality of devices. The same or different processor/processing elements may perform one or more functions described herein.

It will be appreciated that the term "signalling" may refer to one or more signals transmitted as a series of transmitted and/or received signals. The series of signals may comprise one, two, three, four or even more individual signal components or distinct signals to make up said signalling. Some or all of these individual signals may be transmitted/received simultaneously, in sequence, and/or such that they temporally overlap one another. With reference to any discussion of any mentioned computer and/or processor and memory (e.g. including RAM, ROM, CD-ROM etc), these may comprise a computer processor, Application Specific Integrated Circuit (ASIC), field-programmable gate array (FPGA), and/or other hardware components that have been programmed in such a way to carry out the inventive function.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole, in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that the disclosed aspects/embodiments may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the disclosure.

While there have been shown and described and pointed out fundamental novel features as applied to different embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. Furthermore, in the claims means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.