FULL-DUPLEX ULTRASONIC THROUGH-WALL COMMUNICATION AND POWER DELIVERY SYSTEM WITH FREQUENCY TRACKING

• US 20150049587A1
• Filed: 03/21/2013
• Published: 02/19/2015
• Est. Priority Date: 03/29/2012
• Status: Active Grant

• Current Assignee: Rensselaer Polytechnic Institute
• Original Assignee: Rensselaer Polytechnic Institute
• Inventors: Lawry, Tristan J., Saulnier, Gary J., Wilt, Kyle R., Ashdown, Jonathan D., Scarton, Henry A., Gavens, Andrew
• Granted Patent: US 9,455,791 B2
• Time in Patent Office: Days
• US Class Current: 367/87
• CPC Class Codes: H04B 11/00 Transmission systems employing sonic, ultrasonic or infrasonic waves
• CPC Class Codes: H04L 5/14 Two-way operation using the same type of signal, i.e. duplex
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and apparatus provide simultaneous bi-directional communications through a barrier using a pair of piezoelectric transducers. Outside-to-inside transmission of differentially encoded binary data is only sampled at the inside when a known repeated bit in a Barker sequence is transmitted in the other direction. Differentially encoded data is translated based on the absolute value of differences between each signal envelope sample and the previous signal envelope sample. Inside-to-outside data is transmitted by varying an electrical load on the inside transducer to vary the proportion of a continuous wave signal it reflects. The reflected portion of the continuous wave changes the electrical impedance of the outside transducer and this change is measured and interpreted as binary data. Two frequency selection algorithms select minimally sufficient and then optimal frequencies for power and data transmission by a frequency stepping process.

Claims

1. A method for simultaneous bi-directional communication through a metallic wall using a single pair of piezoelectric transducers, the method comprising the steps of:

providing a metallic wall having an inner side and an outer side;

providing coaxially aligned inside and outside piezoelectric traducers mounted on respective opposite sides of the metallic wall;

communicating a differentially encoded binary command word from the outer side of the metallic wall to the inner side of the metallic wall by a first sub-process comprising the steps of;

selecting a command word;

translating the command word to binary bits;

configuring the binary bits of the command word as part of a binary outside packet, the outside packet also comprising an incoming Barker sequence,

translating the binary bits of the outside binary packet into differentially encoded bits using an algorithm comprising modulo-2 addition of each binary bit with the most recently transmitted differentially encoded bit;

applying a carrier signal (25) to the outer side of the wall using the outside transducer, and modulating the amplitude of the carrier signal to communicate the differentially encoded bits of the outside packet, wherein the carrier signal is also adapted to transmit power to one or more devices on the inside of the wall;

receiving the carrier signal at the inner side of the wall with the inside transducer;

determining an envelope of the carrier signal received by the inside transducer, called a carrier signal envelope, using an inside envelope detector circuit;

periodically sampling the carrier signal envelope using an analog-to-digital converter (ADC), the periodic sampling being timed to coincide with a periodic transmission of a selected bit from the inner side to the outer side of the wall, wherein the selected bit falls within an outgoing Barker sequence, and wherein the periodic transmission of the selected bit have a consistent amplitude;

translating a plurality of consecutive envelope samples into a plurality of translated binary bits using a complex programmable logic device (CPLD);

wherein the translating step comprises determining whether an absolute value of the difference between each envelope sample and an immediately preceding envelope sample is above a threshold value, interpreting the envelope sample as a translated binary bit having the same binary value as an immediately preceding translated binary bit when said absolute value is below the threshold value, and interpreting the envelope sample as a translated binary bit having a different binary value than the immediately preceding translated binary bit when said absolute value is above the threshold value;

determining the command word using the plurality of translated binary bits; and

using the command word to control electronics;

wherein an initial frequency and a minimum power level for the carrier signal (25) are selected using an initial frequency selection algorithm, the algorithm comprising the steps of;

applying a carrier signal having a power level and a frequency at the outer side (21) of the wall (20), and stepping through a range of carrier signal frequencies at the same power level while searching for a Barker Sequence in a data envelope sent back from the inner side (22) to the outer side (21) of the wall;

terminating the initial frequency selection algorithm if a Barker sequence is detected, the detected Barker signal indicating that the power level and frequency used most recently used were adequate to send power and communications through the wall; and

increasing the carrier signal power level and stepping through the range of carrier signal frequencies again if no Barker sequence is detected, and repeating the steps of increasing the carrier signal power level and then stepping through the range of carrier signal frequencies until an initial frequency and minimum power level are found which result in detection of a Barker sequence sent from the inner side (22) of the wall;

wherein after the initial frequency and minimum power level are determined, the frequency of the carrier signal (25) is optimized and periodically adjusted to maximize power transfer from the outside transducer (10) to the inside transducer (11) using an optimization algorithm, the optimization algorithm comprising the steps of;

applying a carrier signal having said initial frequency and said minimum power level to the outer wall;

sampling and quantifying a voltage level of a power harvesting capacitor (36) on the inside (13) of the wall (20) and sending a digital representation of the voltage level, called a voltage reading, to the outside (12) within a data packet for use in the optimization algorithm;

stepping the carrier signal (25) frequency a small step in a first direction, the first direction being selected from one of up and down, and comparing the voltage level of the next new voltage reading with the voltage level of the previous old voltage reading;

stepping the carrier signal (25) frequency an additional step in the first direction if the new voltage reading is higher than the old voltage reading;

stepping the carrier signal (25) frequency a step in a second direction opposite the first direction if the new voltage reading is lower than the old voltage reading; and

repeating the process of stepping the carrier signal frequency in the same direction when the previous step resulted in a higher voltage reading, and stepping the carrier signal in the opposite direction when the previous step resulted in a lower voltage reading;

the method for simultaneous bi-directional communication further comprising communicating binary inside data from the inside (13) of the metallic wall to the outside (12) by a second sub-process comprising the steps of;

providing a metal oxide semiconductor field-effect transistor which is linked to the inside transducer, the metal oxide semiconductor field-effect transistor having an on position corresponding to a binary value 1 and an off position corresponding to a binary value 0;

applying a continuous wave carrier to the outer side (21) of the wall via the outside transducer (10), the continuous wave carrier (45) traveling through the wall to the inside transducer (11), a fraction of the continuous wave being reflected by the inside transducer back towards the outer side of the wall, the reflected fraction being called a reflected wave (47);

altering an electrical load on the inside transducer by turning the metal oxide semiconductor field-effect transistor on and off, thereby modulating the acoustic impedance of the inside transducer and changing the strength of the reflected wave;

wherein the reflected wave interacts with the outside transducer, and thereby modifies the electrical input impedance of the outside transducer, so that the electrical input impedance of the outside transducer varies in response to the varying strength of the reflected wave;

monitoring variations in the amplitude of a voltage applied across the outside transducer, said variations corresponding to variations in the electrical input impedance of the outside transducer, and thereby also corresponding to the binary inside data from the inner side of the wall;

determining the envelope of the voltage applied across the outside transducer, termed a reflected signal envelope, using an outside envelope detector circuit;

sampling the reflected signal envelope using an analog to digital converter;

adjusting at least one of the reflected signal envelope and samples of the reflected signal envelope to correct for overlay between the reflected wave and the carrier signal from the first sub process; and

processing reflected signal envelope samples with a digital signal processor to recover the binary inside data.

2. A method for simultaneous bi-directional communication through a metallic wall using a single pair of piezoelectric transducers, the method comprising the steps of:

providing a wall having an inner side and an outer side;

providing inside and outside traducers mounted on respective opposite sides of the wall;

communicating a differentially encoded binary outside signal from the outer side of the metallic wall to the inner side of the metallic wall by a first sub-process comprising the steps of;

selecting an outside signal;

translating the outside signal to binary bits;

configuring the binary bits of the outside signal as part of a binary outside packet, the outside packet also comprising an incoming Barker sequence,

translating the binary bits of the outside binary packet into differentially encoded bits using an algorithm comprising modulo-2 addition of each binary bit with the most recently transmitted differentially encoded bit;

applying a carrier signal to the outer side of the wall using the outside transducer, and modulating the amplitude of the carrier signal to communicate the differentially encoded bits of the outside packet, wherein the carrier signal is also adapted to transmit power to one or more devices on the inside of the wall;

receiving the carrier signal at the inner side of the wall with the inside transducer;

determining an envelope of the carrier signal received by the inside transducer, called a carrier signal envelope, using an inside envelope detector circuit;

periodically sampling the carrier signal envelope using an analog-to-digital converter, the periodic sampling being timed to coincide with a periodic transmission of a selected bit from the inner side to the outer side of the wall, wherein the selected bit falls within an outgoing Barker sequence, and wherein the selected bit has a consistent amplitude;

translating a plurality of consecutive envelope samples into a plurality of translated binary bits using a logic device;

wherein the translating step comprises determining whether an absolute value of the difference between each envelope sample and an immediately preceding envelope sample is above a threshold value, interpreting the envelope sample as a translated binary bit having the same binary value as an immediately preceding translated binary bit when said absolute value is below the threshold value, and interpreting the envelope sample as a translated binary bit having a different binary value than the immediately preceding translated binary bit when said absolute value is above the threshold value;

determining the outside signal using the plurality of translated binary bits;

the method for simultaneous bi-directional communication further comprising communicating binary inside data from the inside (13) of the wall to the outside (12) by a second sub-process comprising the steps of;

providing a signal toggling arrangement which is linked to the inside transducer, the signal toggling arrangement having a first position corresponding to a binary value 1 and an second position corresponding to a binary value 0;

applying a continuous wave carrier to the outer side (21) of the wall via the outside transducer (10), the continuous wave carrier (45) traveling through the wall to the inside transducer (11), a fraction of the continuous wave being reflected by the inside transducer back towards the outer side of the wall, the reflected fraction of the continuous wave carrier being called a reflected wave;

altering an electrical load on the inside transducer by switching the signal toggling arrangement between its first and second positions, thereby modulating the acoustic impedance of the inside transducer and changing the strength of the reflected wave;

wherein the reflected wave interacts with the outside transducer, and thereby modifies the electrical input impedance of the outside transducer, so that the electrical input impedance of the outside transducer varies in response to the varying strength of the reflected wave;

monitoring variations in the amplitude of a voltage applied across the outside transducer, said variations corresponding to variations in the electrical input impedance of the outside transducer, and also corresponding to the binary inside data from the inner side of the wall;

determining the envelope of the amplitude of the voltage across the outside transducer, termed a reflected signal envelope, using an outside envelope detector circuit;

sampling the reflected signal envelope;

adjusting at least one of the reflected signal envelope and samples of the reflected signal envelope to correct for overlay between the reflected wave and the carrier signal from the first sub process; and

processing reflected signal envelope samples to recover the binary inside data.

3. The method of claim 2, wherein the signal toggling arrangement comprises a metal oxide semiconductor field-effect transistor.

4. The method of claim 2, wherein the outside signal comprises a command word for controlling a device on the inside.

5. The method of claim 2, wherein the transducers are piezoelectric transducers.

6. The method of claim 2, wherein the carrier signal (25) has an envelope of no less than 100 megavolts.

7. A method of optimizing the frequency and power level of the carrier signal (25) of claim 2, wherein an initial frequency and a minimum power level for the carrier signal (25) are selected using an initial frequency selection algorithm, the algorithm comprising the steps of:

applying a carrier signal having a power level and a frequency at the outer side (21) of the wall (20), and stepping through a range of carrier signal frequencies at the same power level while searching for a Barker Sequence in a data envelope sent back from the inner side (22) to the outer side (21) of the wall;

terminating the initial frequency selection algorithm if a Barker sequence is detected, the detected Barker signal indicating that the power level and frequency used most recently used were adequate to send power and communications through the wall; and

increasing the carrier signal power level and stepping through the range of carrier signal frequencies again if no Barker sequence is detected, and repeating the steps of increasing the carrier signal power level and then stepping through the range of carrier signal frequencies until an initial frequency and minimum power level are found which result in detection of a Barker sequence sent from the inner side (22) of the wall;

wherein after the initial frequency and minimum power level are determined using the initial frequency selection algorithm, the frequency of the carrier signal (25) is optimized to maximize power transfer from the outside transducer (10) to the inside transducer (11) using an optimization algorithm, the optimization algorithm comprising the steps of;

applying a carrier signal having said initial frequency and said minimum power level to the outer wall;

sampling and quantifying a voltage level received by a power harvesting arrangement on the inside, and sending a digital representation of the voltage level, called a voltage reading, to the outside (12);

stepping the carrier signal (25) frequency a small step in a first direction, the first direction being selected from one of up and down, and comparing the voltage level of a subsequent new voltage reading with the voltage level of the previous old voltage reading;

stepping the carrier signal (25) frequency an additional step in the first direction if the new voltage reading is higher than the old voltage reading;

stepping the carrier signal (25) frequency a step in a second direction opposite the first direction if the new voltage reading is lower than the old voltage reading; and

repeating the process of stepping the carrier signal frequency in the same direction when the previous step resulted in a higher voltage reading, and stepping the carrier signal in the opposite direction when the previous step resulted in a lower voltage reading.

8. The method of claim 7, wherein the optimization algorithm runs continuously to continuously adjust the carrier signal frequency to maximize power transfer efficiency from the outside transducer (10) to the inside transducer (11).

9. The method of claim 7, wherein the optimization algorithm automatically runs periodically to update the carrier signal frequency to maximize power transfer efficiency from the outside transducer (10) to the inside transducer (11).

10. The method of claim 7, wherein the optimization algorithm ends when the new voltage reading and old voltage reading are equal.

11. The method of claim 7, wherein the optimization algorithm ends when the algorithm reaches a frequency where increasing the frequency of the carrier signal by one step and decreasing the frequency of the carrier signal by one step both result in lower voltage readings.

12. The method of claim 2, wherein the step of monitoring variations in the amplitude of a voltage applied across the outside transducer is accomplished including by monitoring a voltage divider comprising a power amplifier.

13. The method of claim 2, wherein the wall is a metallic hull of a water craft.

14. The method of claim 2, wherein for the step of translating a plurality of envelope samples into a plurality of translated binary bits using a logic device, the logic device is a complex programmable logic device.

15. The method of claim 2, wherein an outside-to-inside data rate is a sub-multiple of an inside-to-outside packet rate.

16. The method of claim 2, wherein an inside clock is derived from the carrier signal applied to the outer side of the wall for outside-to-inside communication, the inside clock being derived including by using a comparator.

17. The method of claim 16, wherein an inside-to-outside data rate is selected by frequency dividing the clock.

18. The method of claim 17, wherein the wherein the carrier signal has a carrier frequency, and wherein the inside-to-outside data rate is a sub-multiple of the carrier frequency.

19. The method of claim 18, wherein the inside-to-outside data rate is determined by dividing down the carrier frequency by a power of two.

20. The method of claim 2, wherein an inside-to-outside data rate can be dynamically changed while the transducers are in operation, and wherein and outside-to-inside data rate is automatically adjusted in response to such changes.

21. The method of claim 2, wherein an inside-to-outside data rate can be dynamically changed while the transducers are in operation, wherein an outside-to-inside data rate is left constant when the inside-to-outside data rate is changed, and an inside envelope sample rate is changed to compensate for the change in the inside-to-outside data rate.