Abstract:
A SAW communication device has a main IDT mounted on an SAW substrate to receive an RF signal received by an antenna and convert the RF signal to an acoustic wave which travels along the SAW substrate in opposite directions from the main IDT. At least two secondary IDTs are mounted on the SAW substrate on opposite sides of and spaced from the main IDT to receive and reflect the acoustic wave in a modulated form such that the modulated acoustic wave from one secondary IDT is delayed relatively to the modulated acoustic wave from a secondary IDT on the opposite side of the main IDT to the one secondary IDT. The main IDT is also operable to receive and convert the reflected modulated acoustic waves to a further RF signal with a concatenated waveform corresponding to the two modulated acoustic waves and transmit the further RF signal from the antenna.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to multi-IDT SAW hybrid communication systems.  
         BACKGROUND OF INVENTION  
         [0002]    Remote passive wireless sensors or radio frequency identification devices (RFID) have typically primarily consisted of either all semiconductor or of all surface acoustic wave (SAW) components. The major disadvantage of semiconductor-based RFID devices is the high, typically 5 Watt RF power level which the base transceiver must emit to activate the device. Even at such a significant power level, the distance between the base and a remote sensor may be limited to 1 metre or less. The major advantage of semiconductor devices is their flexibility in programming and read/write memory capabilities. SAW sensors have somewhat opposite characteristics. Their major advantage is that they only require typically 5 mW of RF power to communicate 1 metre. Their disadvantages are that they currently have neither programming flexibility nor any write memory capabilities nor any read/write memory.  
           [0003]    It is therefore an object of the invention to provide a hybrid communication system which maximizes the advantages and minimizes the disadvantages of both semiconductor and SAW components.  
         SUMMARY OF INVENTION  
         [0004]    According to the invention, a SAW communication device has a main IDT mounted on an SAW substrate to receive an RF signal received by an antenna and convert the RF signal to an acoustic wave which travels along the SAW substrate in opposite directions from the main IDT, and at least two secondary IDTs mounted on said SAW substrate on opposite sides of and spaced from the main IDT to receive and reflect said acoustic wave in a modulated form such that the modulated acoustic wave from one secondary IDT is delayed relatively to the modulated acoustic wave from a secondary IDT on the opposite side of the main IDT to said one secondary IDT. The main IDT is also operable to receive and convert the reflected modulated acoustic waves to a further RF signal with a concatenated waveform corresponding to the two modulated acoustic waves and transmit said further RF signal from the antenna.  
           [0005]    This invention provides a hybrid system which captures the advantages of both SAW and semiconductor structures. With this system, it is possible to use a small battery or energy source rather than depending on RF signal conversion to derive energy for the semiconductor circuitry. The advantages of this hybrid system also include low RF complexity requirements for the transceiver and flexibility in programming with read/write memory abilities.  
           [0006]    The present invention provides a multi-IDT SAW hybrid communication system with a low power wireless radio frequency (RF) transceiver capable of exchanging information over distances ranging from less than one metre to tens of metres. The main radio transmitter and receiver components have passive surface acoustic wave (SAW) devices. Interdigital transducers (IDTs) are configured to replicate a given signal and then modulate each signal separately. This procedure eliminates the need, at the receiver, to generate a local reference signal from an on-board oscillator. Furthermore, due to the geometric nature of the IDTs during a transmit signal excitation process, a spreading of the signal spectrum occurs. Additionally, a processing gain is obtained during the reception and the detection process within the IDTs. Ancillary analogue and digital circuitry are associated with the IDTs to assist in the collection, processing and transfer of information between systems. This multi-IDT SAW hybrid communication system can be configured to allow for either Mbps of data between a few transceiver devices or Kbps of data between hundreds of transceiver devices.  
           [0007]    The multi-IDT SAW hybrid communication system in accordance with the invention is particularly suited for low power, low bit rate ZigBee type of applications such as sensors, read/write RFID tags, toys, wireless wallets, hearing aids, industrial and biomedical applications and automobile or other transportation apparatus and intelligent homes operating in the 400 MHz, 900 MHz or 2500 MHz frequency regions. Multi-IDT SAW hybrid communication devices in accordance with the invention are particularly suited for Ad-Hoc or mesh type networks where information is convened over large distances using strings of short-ranged devices. Wireless mesh networks have the positive attributes of being self-configuring, scalable and self-healing. Multi-IDT SAW hybrid communication devices in accordance with the invention are also ideal for such network applications because each device can behave either as a master and initiate a data transfer, or as a slave and respond to a data transfer. A multitude of such multi-IDT SAW hybrid communication devices can be distributed for data acquisition and control purposes. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0008]    Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which:  
         [0009]    [0009]FIG. 1 is a schematic view of a multi-IDT SAW hybrid wireless communication device,  
         [0010]    [0010]FIG. 2 is a similar view of a hybrid wireless communication system with four multi-IDT SAW hybrid communication devices of the kind shown in FIG. 1.  
         [0011]    [0011]FIG. 3 is a similar view of a five-IDT SAW hybrid communication device with external impedance and mixer,  
         [0012]    [0012]FIG. 4 is a similar view of the communication device indicating IDT lengths (L) and IDT distances (L B , L C , L D , L E ) with respect to IDT A,  
         [0013]    [0013]FIG. 5 is a similar view of the communication device indicating the electrical terminations of IDT B, IDT C, IDT D and IDT E,  
         [0014]    [0014]FIG. 6 is a similar view of the communication device indicating the steps to transmit and receive the signal between two such devices,  
         [0015]    [0015]FIG. 7 is a similar view of a demodulation circuit,  
         [0016]    [0016]FIG. 8 is a similar view of a switch arrangement for IDT B, and  
         [0017]    [0017]FIG. 9 is a similar view of a switch arrangement for IDT A, with a ganged switch in default receive mode.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0018]    Referring to the drawings, FIG. 1 is a schematic view of a multi-IDT SAW hybrid communication device. The device includes a digital signal processor (DSP), memory and logic control  110 , an external interface  120 , external transducers  125 , battery  130 , RF circuits  140 , SAW transceiver  150  and an antenna  160 . The purpose of this hybrid device is to exchange data via an RF signal  170 .  
         [0019]    An example of a hybrid wireless communication system using four such communication devices is shown in FIG. 2. Any of the communication devices can initiate a data transfer session. For a prearranged system which is dictated by a chosen protocol in which only two devices communicate with each other, the first device  210  initiates an RF interrogation signal  230  via its antenna  215  which propagates to the second device  220  and is detected by its antenna  225 . The communication sequence continues with data information within the second device  220  being modulated on to two separate acoustic waves which were originally excited by the RF signal  230 . Two concatenated data signals then leave the second device  220  via its antenna  225  and are propagated to the first device  210  via its antenna  215  for processing. A similar scenario would include third and fourth devices  240 - 250  and a chosen protocol among all devices which would implement frequency division, time division, or an encoding division multiple access scheme, or a combination thereof, to support numerous data transfer modes.  
         [0020]    Another possible configuration is to combine three or four multi-IDT SAW hybrid communication devices in a one-way multi-cast scenario. For example, one device  210  would broadcast simultaneously a predetermined RF signal  230  and a predetermined RF signal  260  to the other devices  220 ,  240  and  250 . The other devices would then detect the predetermined the RF signal  230  and  260  to decode data information using a detector circuit.  
         [0021]    One of the positive attributes associated with this hybrid system is that the SAW communication devices can transmit, receive and respond to a data stimulus by modulating an acoustic wave and retransmit an RF signal all passively on a piezoelectric substrate. FIG. 3 schematically demonstrates as an example a passive five interdigital transducer (5-IDT) SAW device  310  fabricated on a piezoelectric substrate  315  with some ancillary external circuitry such as an antenna  305 , external impulse and detector circuit  320 , impedance circuits  330  &amp;  335  and an RF mixer  340 . The impulse circuit  320  is activated when the SAW communication device functions as the initial inquiry transmitter, and the impedance circuits  330  &amp;  335  and RF mixer  340  are switched in during the receive mode. The positioning of the various SAW IDTs, IDT A  350 , IDT B  352  and IDT D  356  to allow for the correct time synchronization of both the reflected waves of the interrogated device and IDT C  354  and IDT E  358  acting as inputs to the mixer is very critical. A suitable dual track technique which enables the distribution of acoustic waves to achieve synchronization and minimize the device length is described in U.S. Provisional Patent Application No. 60/370,207 filed Apr. 8, 2002 and the subsequent complete application Ser. No. 10/400,656 filed Mar. 28, 2003. The contents of these applications are hereby incorporated herein by reference.  
         [0022]    SAW IDT  360  has two bus bars  362 ,  363  which run parallel to the acoustic wave propagation of the piezoelectric substrate  315  and fingers  364  which extend perpendicularly to the two bus bars  362  and  363 . One bus bar  362  is designated as electrically hot and the other bus bar  363  is electrically grounded. This configuration can be transposed to suit the nature of the device. The fingers  364  are alternately connected to the hot bus bar  362  or to the grounded bus bar  363 . The number of IDT fingers  364  will depend on the device and system parameters. Two adjacent fingers  364  constitute a finger pair Np. Two electrical connections  366  connect each bus bar  362 ,  363  to an external circuit  370  which varies depending upon the requirements of each separate IDT.  
         [0023]    To initiate a communication session, IDT B  352  of the first device  210  is excited by an impulse circuit  320  which is controlled by the DSP  110 . This impulse initiates an electrical-to-mechanical transformation within the IDT and causes a frequency selective acoustic wave to propagate towards IDT A  350 . The acoustic wave, as it propagates beneath the IDT, transforms to a frequency selected electrical RF signal  300  by a mechanical-to-electrical transformation. The RF signal  300  is then propagated by means of an antenna  305  which is connected to IDT A  350  of the first device  210 .  
         [0024]    The second 5-IDT communication device  220  is located within range of the first transmit device  210  and receives the RF signal  230  via the antenna  225  attached to IDT A of the second device  220 . A reciprocal electrical-to-mechanical transformation takes place with the excited IDT A  450  and produces an acoustic wave which propagates outwardly in opposite directions towards IDTs C  454  and D  456  as shown FIG. 4. These IDTs are configured during this period as reflectors at their acoustic ports by controlling the termination impedance  430 , 435  attached to their electrical ports. The acoustic reflection is governed by the acoustic reflection coefficient P 11 ′ defined by,  
               P11   ′     =     P11   -     P13P31       Y                 L     +   P33                 (   1   )                               
 
         [0025]    where P 11  is the reflection coefficient at acoustic port 1, P 13  is the transfer parameter from acoustic port 1 to the electrical port 3, P 31  is the transfer parameter from the electrical port 3 to the acoustic port 1, P 33  is the transfer parameter at the electrical port 3 and Y L  is the load admittance connected to the electrical port 3.  
         [0026]    The relationship between the load impedance ZL and load admittance, YL is,  
               Z                 L     =     1     Y                 L               (   2   )                               
 
         [0027]    The phase of P 11 ′, can then be controlled by the load impedance ZL such as when Z L  tends towards a short circuit, Z L =0 Ω the phase of P 11 ′, φ 1 ≈180° and when Z L  tends towards an open circuit, Z L &gt;10000 Ω the phase of P 11 ′, φ 2  approaches 90°.  
         [0028]    The acoustic wave reflected from IDT D  456  is then modulated with a phase shift of either φ 1  or φ 2  or, while the acoustic wave reflected from IDT C  454  is modulated with a constant phase shift of φ 2 .  
         [0029]    The reflected phase modulated acoustic wave from IDT C  454  returns back to IDT A  450  with the acoustic wave being converted to an RF signal  230  and is transmitted from the second device  220  via the antenna  225  attached to IDT A  450 . A time delayed second RF signal is also transmitted from the second device  220  which has also been phase modulated from IDT D  456 . The time delay is due to the longer acoustic path L D    466  between IDT A  450  and IDT D  456  when compared to the acoustic path L C    464  between IDT A  450  and IDT C  454 . The length of each IDT is also critical for the correct time synchronization of the acoustic waves and also impacts the overall bit rate of the system. Lengths LA  470 , LB  472 , LC  474 , LD  476  and LE  478  are calculated to optimise the impulse characteristics IDT B  452 , convolution processes IDT A  450  with IDT C  454  and IDT E  458  and the reflection properties of IDT C  454  and IDT D  456 .  
         [0030]    The two concatenated RF signals  400  transmitted from the second device  220  are then received at the first device  210  via the antenna  215  attached to IDT A  550  as shown in FIG. 5. The acoustic waves generated by IDT A  550  propagate in opposite directions towards IDT E  558  on one acoustic track and towards IDT C  554  on the other acoustic track. The acoustic waves at IDTs B  552  and IDT D  556  are not used as their termination impedances Z LB    553  and Z LD    557  minimize any reflections. The concatenated acoustic waves that interact with IDT C  554  and IDT E  558  do so simultaneously because of the acoustic distances L C    564  and L E    568 . The electrical outputs  555 ,  559  of IDT C  554  and IDT E  558  are used as the two inputs for the external active mixer  540  to produce an output signal V θ   545 .  
         [0031]    The steps to transmit and receive a signal between two 5-IDT hybrid communication devices are summarized as follows using FIG. 6 as a reference. Due to the convolution process as an acoustic wave passes through an IDT, there is an elongation of the original impulse waveform W B    662  emitting from IDT B  652 . The following steps assume an initial chip rate of 40 chips which transforms into 40 finger pairs for the structure of IDT B  652 .  
         [0032]    Steps to transmit and receive a signal between two 5-IDT devices:  
         [0033]    1. Impulse IDT B  652  on the first device which produces 40 chips.  
         [0034]    2. Acoustic wave W B    662  propagates from IDT B  662  to IDT A  650 .  
         [0035]    3. Convolution of acoustic wave W B    662  with IDT A  650  to produce 79 chips.  
         [0036]    4. RF signal  600  is radiated from antenna  605  that is electrically attached to IDT A  650 .  
         [0037]    5. RF signal  600  of chip length  79  arrives at the second device.  
         [0038]    6. Antenna  605  that is electrically attached to IDT A  650  of the second device receives RF signal  600  of chip length  79 .  
         [0039]    7. IDT A  650  is excited by RF signal  600  to produce acoustic waves W B    662 , W C    664 , W D    666  and W E    668  each with 118 chips in length.  
         [0040]    8. One acoustic wave W C    664  propagates towards IDT C  654  and the other acoustic wave W D    666  propagates a greater distance to IDT D  656 .  
         [0041]    9. Acoustic wave W C    664  reflects from IDT C  654  with a phase offset of φ 2 , due to the acoustic reflection coefficient P 11 ′, back to IDT A  650 .  
         [0042]    10. Acoustic wave W D    666  reflects from IDT D  656  with a phase offset of φ 1 , back to IDT A  650 .  
         [0043]    11. Acoustic wave W C    664  convolves with IDT A  650  to produce 157 chips.  
         [0044]    12. Acoustic wave W D    666  arrives slightly later and convolves with IDT A  650  to produce 157 chips.  
         [0045]    13. RF signal  600  that is comprised of two concatenated waveforms is radiated from the antenna  605  that is electrically attached to IDT A  650  of the second device.  
         [0046]    14. RF signal  600  arrives back at device #1 via the antenna  605  that is electrically attached to IDT A  650 .  
         [0047]    15. IDT A  650  is excited by RF signal  600  to produce an acoustic wave of 196 chips.  
         [0048]    16. Acoustic wave W C    664  of 196 chips propagates towards IDT C  654 , and the other acoustic wave W E    668  also of 196 chips travels a greater distance to IDT E  658 .  
         [0049]    17. The acoustic waves W B    662  and W D    666  propagating towards IDT B  662  and IDT D  656  respectively are not used, with the termination impedances Z LB    553  and Z LD    557  suitably chosen to minimize any reflections.  
         [0050]    18. The leading waveform of acoustic wave W C    664  convolves with IDT C  664  but the acoustic wave W E    668  has not arrived yet at IDT E  668 .  
         [0051]    19. The leading waveform of acoustic wave W E    668  convolves with IDT E  658  to produce an RF electrical signal  659  of 235 chips in length.  
         [0052]    20. The trailing waveform of acoustic wave W C    664  convolves with IDT C  664  to produce an RF electrical signal  655  of 235 chips in length.  
         [0053]    21. The two RF electrical signals  655  and  659  are the inputs to a mixer  640  configured as a phase detector.  
         [0054]    22. A signal V θ   645  contains both the sum (2fo) and difference (DC) components of the two RF electrical signals  655  and  659 .  
         [0055]    These steps enable data information to be exchanged from the second device back to the first device. A simple protocol implementing a time division access scheme enable the simple bi-directional transfer of data between two or more devices.  
         [0056]    The multi-IDT hybrid communication system implements certain active circuitry to realize and enhance its performance. Examples of this circuitry may include a mixer, filters, logic circuits, switches and amplifiers. FIG. 7 illustrates the key elements of the demodulation circuit. The two RF electrical signals  755  and  759  from the SAW IDTs are the inputs to the RF mixer  740 . The mixer  740  is configured as a phase detector whose voltage output V θ   745  contains both the DC component and the second harmonic of the fundamental frequency. This second harmonic is removed and the DC component is both amplified and level shifted as required by the low pass (LP) filter and conditioning circuit  750 .  
         [0057]    The DC component V θ   745  output of the mixer  740  is a result of the phase difference between the two input signals. The DC component V θ   745  of the output of the mixer  740  is a negative maximum when there is a minimum of phase difference (0°) or a positive maximum when there is a maximum of phase difference (180°) between the two input signals. Conversely, the DC component V θ   745  of the output of the mixer  740  reduces to a minimum (V θ =0 volts) as the phase difference approaches 90° between the two input signals. Depending on the value of the binary reference  757 , the logic gate  760  would produce a binary output  770  depending on the phase offset of the two RF electrical signals  755  and  759  from the SAW IDTs.  
         [0058]    The use of RF switches is significant in the function of the multi-IDT SAW hybrid communication system. FIG. 8 outlines an example of how a configuration of switches allows IDT B  852  to perform several multi functions such as an acoustic wave source when impulsed, a termination of acoustic waves when the reflector is configured with Γ=0 and also as a signal detector. A sequential communication event commences when the DSP control circuit  810  directs the switch SW 1   830  to move into a position to connect the impulse circuit  820  to IDT B  852 . An electrical impulse to the SAW IDT initiates the electrical-to-mechanical transformation which produces acoustic waves. In another scenario, IDT B  852  acts as an acoustic absorber by having the DSP control circuit  810  sequentially control switches SW 1   830  and SW 2   840  and the load Z LB    853  of IDT B  852  to produce a reflection coefficient Γ=0. This prevents any acoustic waves generated by IDT A  650  from reflecting from IDT B  852  back into IDT A  650  and causing self-interference. The default position for SW 1   830  and SW 2   840  electrically connects IDT B  852  with the diode detection circuit  821 . This configuration allows the communication device to sit idle for long periods of time. When queried by a similar communication device, it detects a predetermined RF signal sequence which initiates an internal progression of events which powers up and activates the device. This method is more power efficient than using a wake-up protocol to query any surrounding devices for missed data transfers.  
         [0059]    Another use of the diode detection circuit  821  is to combine three or more multi-IDT SAW hybrid communication systems in a multi-cast scenario. One device would send out a predetermined RF signal sequence to other similar devices. These other devices would then detect the predetermined RF signal to decode data information using the diode detection circuit  821 .  
         [0060]    Amplifier modules increase the link budget capabilities and when implemented in the antenna path increase the RF range of this system. The RF path losses for 400 MHz, 900 MHz and 2500 MHz frequencies are dictated by;  
             Gpathloss   =       -   20                     log        (       4      π                 d     λ     )                 (   3   )                               
 
         [0061]    where d=distance in metres and λ=wavelength at centre frequency fo.  
         [0062]    One of the distinctive features of this multi-IDT SAW hybrid communication system is that it requires that IDT A functions both as a transmit and receive transducer. FIG. 9 illustrates an example of IDT A  950  either transmitting or receiving an RF signal  900 . The default position of the double pole switch configuration SW 3   960  electrically connects IDT A  950  via the RX path  930  to the antenna  905  to receive the RF signal  900 . During the session sequence, the switch SW 3   960  is controlled by the DSP control circuit  910  and switched to the TX path  940  which electrically connects IDT A  950  to the RF amplifier  920 , which is electrically connected to the antenna  905 . This method provides a discontinuity at SW 3   960  for the RX path  930  and does not permit any of the RF signals at the output of the RF amplifier  920  to feedback to IDT A  950 .  
         [0063]    The usable bit rate potential of the multi-IDT SAW hybrid communication system, is dependent on several variables both at the device and system level. At the device level, one variable is the number of finger pairs Np to be used in the SAW IDTs. The larger the Np values, the greater the time duration of the corresponding acoustic wave and the longer the convolution interval. Another variable which affects both the device characteristics and system utilization is the centre frequency fo. As the centre frequency increases, the acoustic wavelength of the SAW device proportionally decreases. This allows the size of the SAW device to inversely scale with frequency. Therefore as the frequency increases the SAW size decreases, resulting in smaller time duration of the acoustic wave and a shorter convolution interval. These factors lead to a bit rate which scales with centre frequency. The system utilization of centre frequency determines which frequency band the system may operate in. Multi-IDT SAW hybrid communication systems in accordance with the invention may operate in, but not be limited to the 400 MHz, 900 MHz or 2500 MHz frequency regions.  
         [0064]    To illustrate the system variability of the possible usable bit rate, the following example is presented. For this example, it can be assumed that the acoustic velocity of the SAW substrate ν≈4000 m/s and the centre frequency fo=2.5 10 9  Hz. The acoustic wavelength is λ=ν/fo, λ=1.6 μm, and the number of IDT single finger pairs, Np=40, which is equivalent to 40 chips, is chosen to produce a transducer length L=40λ≈64 μm. The time t it takes for the acoustic wave to travel this length is t=L/ν, ≈16 ns. For this example, the acoustic lengths of the IDTs of FIG. 5; LA  570 , LB  572 , LC  574 , LD  576  and LE  578  are all equal and equal to 40λ≈64 μm. The distances between IDTs are L B    562 =20λ≈32 μm, L C    564 =80λ≈128 μm, L D    566 =200λ≈320 μm and L E    568 =320λ≈512 μm.  
         [0065]    Therefore the bit rate is ≈3.9 Mbps for the one-way exchange of data from the second device  220  to the first device  210  or in a multi-cast network where one device broadcasts to multiple devices. A time domain multiple access (TDMA) protocol may be implemented to allow for a full bi-directional rate of 1.95 Mbps between two multi-IDT SAW hybrid communication devices. Alternately, up to 64 devices could communicate with a bit rate of ≈50 Kbps using a TDMA protocol. More devices added to the network would further reduce the bit rate but still allow the useful transfer of low-data rate information.  
         [0066]    The acoustic distances between IDTs can be calculated to assure signal synchronization as the first segment of the concatenated signal arrives at IDT E and simultaneously as the second segment of the concatenated signal arrives at IDT C as follows:  
         [0067]    Total path of First Segment L B +2L C +L E    
         [0068]    Total path of Second Segment L B +2L D +L C    
         [0069]    resulting in L E =2L C +4(LB) and L D =1.5L C +2(LB); where L C ≧2(LB) and LB is the length of the impulsed IDT B.  
         [0070]    For a more optimum detection scheme with an increased processing gain, lengths LC  574  and LE  578  should be lengthened to ≈2.5 times that of the impulsed IDT B  552 . Therefore LC  574 =LE  578 =2.5LB  572 .  
         [0071]    By extending the lengths of LC and LE, the stretched signal that is caused by the convolution process “fits” under the extended IDT C and IDT E.  
         [0072]    It will thus be noted that particular advantages and features of the described embodiments are described as follows:  
         [0073]    1. The acoustic wave signal is replicated by taking advantage of the bi-directional propagation of the acoustic waves from an electrically excited IDT and then modulating each acoustic wave separately. One of the replicated waves may be used as an RF reference signal used for the demodulation of the data.  
         [0074]    2. RF Amplifier in the transmit (TX) branch which is switched on only when transmitting may be used, therefore reducing battery power. The default is for the amplifier to be bypassed to directly connect the antenna to an IDT for the reception and detection of RF signals. This permits the device to be readily available to receive RF signals without depending upon system wake-up protocols to turn on the radio.  
         [0075]    3. There is no requirement for a local oscillator in the receive portion of the transceiver. A reference signal can be provided in the demodulator circuit as both inputs to the mixer are derived from the replicated acoustic wave and then each separately modulated.  
         [0076]    4. The multi-IDT SAW hybrid communication system devices need not be master/slave based, so that any multi-IDT SAW hybrid device can initiate or respond to a data transfer session. This feature is advantageous for applications where a multi-cast network can provide any single multi-IDT SAW hybrid device to simultaneously broadcast the same data to all other devices that are in range.  
         [0077]    Other advantages and embodiments of the invention will now be readily apparent to a person skilled in the art, the scope of the invention being defined in the appended claims.