Methods and devices for determining the resonance frequency of passive mechanical resonators

• US 20040211260A1
• Filed: 04/21/2004
• Published: 10/28/2004
• Est. Priority Date: 04/28/2003
• Status: Active Grant

• Current Assignee: MicroTech Medical Technologies Ltd.
• Original Assignee: Zuli Holdings, Ltd.
• Inventors: Girmonsky, Doron, Eisenberg, Ran, Avraham, Nissim
• Granted Patent: US 7,134,341 B2
• Time in Patent Office: Days
• US Class Current: 73/579
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• CPC Class Codes: A61B 5/036 by means introduced into body tracts A61B5/032 and A61B5/035 take precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 6/5217 extracting a diagnostic or physiological parameter from medical diagnostic data
• CPC Class Codes: A61B 8/08 Detecting organic movements or changes, e.g. tumours, cysts, swellings A61B8/02 - A61B8/06 take precedence
• CPC Class Codes: G01H 13/00 Measuring resonant frequency
• CPC Class Codes: G01L 9/0008 using vibrations
• CPC Class Codes: G01N 2291/02872 Pressure

Abstract

Methods and systems for determining the resonance frequency of a resonator, using the Doppler effect. An interrogating sonic beam including a carrier frequency and one or more resonator exciting frequencies is directed at a resonator disposed in a measurement environment. Resonator vibrations are excited by the resonator exciting frequencies. The carrier frequency is modulated by the vibrating part(s) of the resonator. The returning signal is received and analyzed to determine the amplitude of the Doppler shifted sideband frequencies. The resulting data is processed to determine the resonator'"'"'s resonance frequency. Using calibrated resonating sensors having a resonance frequency that varies as a function of a physical parameter in a measurement environment, the method and systems allow determining the value of the physical variable from the sensor'"'"'s resonance frequency. The methods and systems may be used, inter alia, to determine intraluminal blood pressure in various parts of a cardiovascular system, the pressure of intra-cranial fluids, the pressure of fluids in various bodily cavities by using implantable calibratable resonating pressure sensors. The methods and systems may also be used for determining the pressure in various industrial measurement environments and enclosures. Methods and systems are provided for detecting the sensor and for centering the interrogating beam on the sensor.

Claims

1. A method for determining the resonance frequency of a vibratable resonator, the method comprising the steps of:

subjecting said resonator to a sonic beam having one or more resonator exciting frequencies for exciting vibrations of said vibratable resonator and a carrier frequency capable of being frequency modulated by vibrations of said vibratable resonator, said carrier frequency is higher than said one or more resonator exciting frequencies;

receiving returning signals from said vibratable resonator; and

processing said returning signals to determine the resonance frequency of said vibratable resonator.

2. The method according to claim 1 wherein said resonator exciting frequencies are frequencies in the vicinity of the resonance frequency of said vibratable resonator.

3. The method according to claim 1 wherein said step of processing comprises the steps of:

processing said returning signals to determine for each exciting frequency of said one or more resonator exciting frequencies the amplitude of at least one Doppler shifted frequency component of said carrier frequency to obtain a set of amplitude and frequency data points; and

computing from said set of amplitude and frequency data points the resonance frequency of said vibratable resonator.

4. The method according to claim 3 further comprising the step of detecting the presence of said vibratable resonator within said sonic beam based on the amplitude of said at least one Doppler shifted frequency component of said carrier frequency.

5. The method according to claim 4 wherein said step of detecting comprises providing a signal indicating the presence of said resonator in said sonic beam when the amplitude of said at least one Doppler shifted frequency component exceeds a threshold value.

6. The method according to claim 5 wherein said step of detecting is performed automatically.

7. The method according to claim 4 wherein said resonator is a passive ultrasonic pressure sensor implanted within a cardiovascular system having a periodically varying blood pressure therein, and wherein said step of detecting comprises detecting the presence of said resonator in said sonic beam when the amplitude of said at least one Doppler shifted frequency component exceeds a threshold value.

8. The method according to claim 7 wherein said step of detecting further comprises detecting the presence of said resonator in said sonic beam when the amplitude of said at least one Doppler shifted frequency component periodically varies at a rate substantially similar to the rate of periodic varying of said blood pressure.

9. The method according to claim 4 wherein said resonator is a passive ultrasonic pressure sensor implanted within a cardiovascular system having a periodically varying blood pressure therein, and wherein said step of detecting comprises detecting the presence of said resonator in said sonic beam when the amplitude of said at least one Doppler shifted frequency component exceeds a threshold value and varies periodically at a rate substantially similar to the rate of periodic varying of said blood pressure.

10. The method according to claim 4 wherein said step of detecting comprises providing to a user performing said method a signal indicative of the amplitude of said at least one Doppler shifted frequency component.

11. The method according to claim 10 wherein the signal indicative of the amplitude of said at least one Doppler shifted frequency component is selected from, an auditory signal, a visual signal and combinations thereof.

12. The method according to claim 10 wherein the signal indicative of the amplitude of said at least one Doppler shifted frequency component is selected from,

a visual signal representing the real time variation of a frequency domain representation of said returning signals,

a visual signal representing the real time variation of the amplitude of said at least one Doppler shifted frequency component,

a visual signal displayed when the amplitude of said at least one Doppler shifted frequency component exceeds a threshold level,

an audio signal having a perceptible varying characteristic which is correlated to the variation of the amplitude of said at least one Doppler shifted frequency component, and

an audio signal initiated when the amplitude of said at least one Doppler shifted frequency component exceeds a threshold level.

13. The method according to claim 3 further comprising the step of centering said sonic beam on said vibratable resonator based on the amplitude of said at least one Doppler shifted frequency component of said carrier frequency.

14. The method according to claim 13 wherein said step of centering comprises redirecting said sonic beam to maximize the amplitude of said at least one Doppler shifted frequency component.

15. The method according to claim 14 wherein said redirecting comprises automatically redirecting said sonic beam to maximize the amplitude of said at least one Doppler shifted frequency component.

16. The method according to claim 1 wherein said step of processing comprises the steps of:

processing said returning signals to obtain a frequency domain representation of said returning signals comprising a plurality of amplitude peaks at a plurality of frequencies representing Doppler shifted frequencies of said carrier frequency;

determining the amplitude values of said plurality of amplitude peaks at said Doppler shifted frequencies to obtain a set of amplitude and frequency data points; and

computing from said set of amplitude and frequency data points the resonance frequency of said vibratable resonator.

17. The method according to claim 16 wherein said step of computing comprises fitting a curve to said set of amplitude and frequency data points, and computing the resonance frequency of said resonator as the frequency of said curve at which the amplitude of said curve has a maximum.

18. The method according to claim 16 wherein said step of computing comprises computing the resonance frequency of said resonator as the frequency of said set of amplitude and frequency data points having the maximal amplitude.

19. The method according to claim 16 wherein for each frequency of said one or more resonator exciting frequencies, the amplitude peak value is obtained from the amplitude of at least one frequency-domain sideband associated with the sensor exciting frequency by a step selected from the steps of,

computing the amplitude peak as the sideband amplitude of a single sideband selected from the pair of sidebands associated with each sensor exciting frequency,

computing the amplitude peak as a mean sideband amplitude by computing the arithmetic mean of the pair of sidebands associated with each sensor exciting frequency,

computing the amplitude peak as a mean sideband amplitude by computing the geometrical mean of the pair of sidebands associated with each sensor exciting frequency.

20. The method according to claim 1 wherein said sonic beam is selected from a continuous wave beam, a chirped beam, and a beam having at least one frequency burst.

21. The method according to claim 20 wherein said sonic beam comprises a plurality of sonic frequency bursts and wherein said frequency bursts are selected from a plurality of contiguous frequency bursts and a plurality of frequency bursts separated by silent time periods.

22. The method according to claim 20 wherein said sonic beam comprises a plurality of sonic frequency bursts and wherein said frequency bursts are selected from bursts having the same burst duration and a bursts having different burst durations.

23. The method according to claim 20 wherein said sonic beam comprises a plurality of sonic frequency bursts and wherein all the resonator exciting frequencies of said one or more resonator exciting frequencies are included in each burst of said plurality of sonic bursts.

24. The method according to claim 20 wherein said sonic beam comprises a sequential series of sonic frequency bursts and wherein each burst of said series of sonic frequency bursts comprises a different single resonator exciting frequency of said one or more resonator exciting frequencies, said series of sonic bursts includes all the resonator exciting frequencies of said one or more of resonator exciting frequencies required for performing a single measurement of said resonance frequency.

25. The method according to claim 24 wherein said carrier frequency of said sonic beam is selected from a continuously transmitted carrier frequency and a pulsed carrier frequency.

26. The method according to claim 20 wherein said sonic beam comprises a sequential series of sonic frequency bursts and wherein a single burst of said series of sonic frequency bursts comprises a subgroup of resonator exciting frequency of said one or more resonator exciting frequencies, said series of sonic bursts includes all the resonator exciting frequencies of said one or more resonator exciting frequencies required for performing a single measurement of said resonance frequency.

27. The method according to claim 26 wherein said carrier frequency of said sonic beam is selected from a continuously transmitted carrier frequency and a pulsed carrier frequency.

28. The method according to claim 20 wherein said sonic beam comprises a continuous wave at said carrier frequency and one or more sonic frequency bursts each burst of said one or more frequency bursts includes one or more sensor exciting frequencies.

29. The method according to claim 20 wherein said sonic beam comprises one or more sonic frequency bursts each burst having a burst duration including said carrier frequency and at least one sensor exciting frequency, and wherein said returning signals are sampled only within part of said burst duration.

30. The method according to claim 20 wherein said sonic beam comprises one or more sonic frequency bursts each burst having a burst duration including said carrier frequency and at least one sensor exciting frequency, and wherein said returning signals are sampled to obtain sampled data, wherein only a part of the sampled data corresponding to a portion of said burst duration is processed in said step of processing.

31. The method according to claim 20 wherein the measuring of a single pressure point comprises transmitting a single sonic frequency burst including said carrier frequency and said one or more resonator exciting frequencies.

32. The method according to claim 1 wherein said sonic beam is selected from a sound beam and an ultrasound beam.

33. The method according to claim 1 wherein said vibratable resonator is a resonating pressure sensor.

34. The method according to claim 1 wherein said vibratable resonator is a resonating pressure sensor disposed in a pressure measurement environment having a varying pressure therein, the resonance frequency of said pressure sensor varies with the pressure in said measurement environment.

35. The method according to claim 34, wherein said resonating pressure sensor is selected from a passive resonating pressure sensor, and a passive ultrasonic resonating pressure sensor.

36. The method according to claim 35, wherein said passive resonating pressure sensor, and said passive ultrasonic resonating pressure sensor are calibratable pressure sensors.

37. The method according to claim 34, wherein said step of processing further includes the step of determining the pressure in said measurement environment from the determined resonance frequency of said resonating pressure sensor.

38. The method according to claim 37, wherein said step of determining the pressure in said measurement environment comprises computing said pressure from said resonance frequency using calibration data of said resonating pressure sensor.

39. The method according to claim 38, wherein said calibration data is selected from,

a lookup table including resonance frequency values of said sensor and the corresponding pressure values at which said resonance frequency values where empirically determined, and

a computed calibration function for computing pressure values from determined values of said resonance frequency.

40. The method according to claim 34, further including the step of determining the external barometric pressure in the region in which the measurement is performed.

41. The method according to claim 40, further including the step of selecting from a plurality of sensors disposed in a measurement environment and having various different pressure working ranges, an appropriate sensor for performing a pressure measurement in said pressure measurement environment, based on said external barometric pressure.

42. The method according to claim 40, wherein said resonating pressure sensor is a wide range resonating pressure sensor, and wherein said method further includes the step of determining a set of sensor exciting frequencies to be used in said sonic beam, based on said external barometric pressure.

43. The method according to claim 40, further including the step of automatically selecting, based on said external barometric pressure, a set of sensor exciting frequencies to be used in said sonic beam.

44. The method according to claim 1, wherein said sonic beam comprises a plurality of measurement periods, each measurement period of said plurality of measurement periods comprises one or more frequency bursts, and wherein the plurality of the resonator exciting frequencies included in said one or more frequency bursts is identical in all of said measurement periods.

45. The method according to claim 1 wherein said sonic beam comprises a plurality of sequential measurement periods, each measurement period of said plurality of measurement periods comprises one or more frequency bursts, and wherein the plurality of the resonator exciting frequencies included in said one or more frequency bursts varies for different measurement periods of said plurality of measurement periods.

46. The method according to claim 45 wherein said vibratable resonator is a resonating pressure sensor disposed in a measurement environment having a varying pressure therein, the resonance frequency of said pressure sensor varies with the pressure in said measurement environment, and wherein the frequency values of the resonator exciting frequencies included in the current measurement period are determined based on a predicted value of the resonance frequency of said pressure sensor for the measurement period following the current measurement period.

47. The method according to claim 46 wherein said varying pressure is a periodically varying pressure having a plurality of cycles, and wherein said predicted value of said resonance frequency is determined based on test data obtained in measurements preceding the time of determining of said predicted value.

48. The method according to claim 47 wherein said test data comprises data obtained by measurements of the resonance frequency of said sensor in measurements preceding the time of determining of said predicted value.

49. The method according to claim 48 wherein said test data comprises data obtained by performing a plurality of measurements using a fixed set of sensor exciting frequencies prior to obtaining said predicted value of the resonance frequency of said pressure sensor.

50. The method according to claim 48 wherein said test data comprises data obtained from a plurality the sensor'"'"'s resonance frequency data cycles determined in a plurality of said cycles.

51. The method according to claim 50 wherein said test data comprises data selected from,

data representing the range of the sensor'"'"'s resonance frequency values obtained in measurements taken at similar time points within each cycle of said plurality cycles,

data representing the mean sensor'"'"'s resonance frequency obtained for all the measurements taken at similar time points within each cycle of said plurality of cycles, and

data representing the mean and the standard deviation of the sensor'"'"'s resonance frequency obtained for all the measurements taken at a similar time within each cycle of said plurality of cycles.

52. The method according to claim 47 wherein said measurement environment is a part of the cardiovascular system of a patient, said periodically varying pressure is the blood pressure within said part of said cardiovascular system, and wherein the time point of the resonance frequency determined by said current measurement is determined from an independently measured synchronizing signal.

53. The method according to claim 52 wherein said independently measured synchronizing signal comprises a biological signal associated with activity of said cardiovascular system or of a part thereof.

54. The method according to claim 52 wherein said independently measured synchronizing signal is associated with cardiac activity of said patient.

55. The method according to claim 52 wherein said independently measured synchronizing signal is selected from an electrocardiogram signal of said patient, and an acoustic signal associated with the mechanical beating of the heart of said patient.

56. The method according to claim 52 wherein the timing within the duration of the current resonance frequency cycle of the resonance frequency value determined by said current measurement is determined relative to a selected part of an electrocardiogram signal simultaneously recorded from said patient.

57. A system for determining the resonance frequency of a vibratable resonator, the system comprising:

transmitting means configured for directing at said vibratable resonator a sonic beam comprising one or more resonator exciting frequencies and a carrier frequency higher than said one or more exciting frequencies;

receiving means configured for receiving signals returning from said vibratable resonator; and

processing means operatively coupled to said transmitting means and to said receiving means, said processing means is configured for processing said signals to obtain data representing the amplitude of said signals at frequencies representing Doppler shifted frequency components of said carrier frequency and for determining the resonance frequency of said vibratable resonator from said data.

58. The system according to claim 57 wherein said processing means is configured for controlling the operation of said transmitting means and of said receiving means.

59. The system according to claim 57 wherein said vibratable resonator is a passive ultrasonic vibratable pressure sensor disposed in a measurement environment and wherein said processing means is configured for determining the pressure in said measurement environment from said resonance frequency.

60. The system according to claim 59 wherein said transmitting means comprises a at least one frequency generating unit operatively coupled to at least one transducer unit for generating said sonic beam.

61. The system according to claim 59 wherein said receiving means comprises at least one transducer unit for receiving signals returning from said vibratable resonator.

62. The system according to claim 61 wherein said processing means is selected from at least one processing unit, at least one controlling unit, and at least one processing and controlling unit.

63. The system according to claim 59 wherein said system further comprises pressure determining means for determining the external pressure level in the vicinity of said system.

64. The system according to claim 59 wherein said system further comprises interfacing means selected from means for allowing a user to control said system, means for presenting data to an operator or user of said system, and a combination thereof.

65. A system for determining the resonance frequency of a vibratable resonator, the system comprising:

a transmitter unit configured for directing at said vibratable resonator a sonic beam comprising one or more resonator exciting frequencies and a carrier frequency higher than said one or more resonator exciting frequencies;

a receiver unit configured for receiving signals returning from said vibratable resonator; and

a processing unit operatively coupled to said transmitter unit and to said receiver unit, said processing unit is configured for processing said signals to obtain data representing the amplitude of said signals at frequencies representing Doppler shifted frequency components of said carrier frequency and for determining the resonance frequency of said vibratable resonator from said data.

66. The system according to claim 65 wherein said vibratable resonator is a passive ultrasonic vibratable pressure sensor disposed in a measurement environment and wherein said processing unit is configured for determining the pressure in said measurement environment from said resonance frequency.

67. The system according to claim 65, wherein said processing unit is configured for determining the external pressure in the region in which the measurement is performed.

68. The system according to claim 67, wherein said processing unit is configured for selecting from a plurality of sensors disposed in a measurement environment and having various different pressure working ranges, an appropriate sensor for performing a pressure measurement in said pressure measurement environment, based on said external pressure.

69. The system according to claim 67, wherein said resonating pressure sensor is a wide range resonating pressure sensor, and wherein said processing unit is configured for determining a set of sensor exciting frequencies to be used in said sonic beam, based on said external pressure.

70. The system according to claim 67, wherein said processing unit is configured for automatically selecting, based on said external pressure, a set of sensor exciting frequencies to be used in said sonic beam.

71. The system according to claim 65 wherein said processing unit is configured for controlling the operation of said transmitter unit and said receiver unit.

72. The system according to claim 65 wherein said transmitter unit and said receiver unit are included in a transceiver unit operatively coupled to said processing unit.

73. The system according to claim 65 wherein said transmitter unit comprises,

a frequency generating unit for generating said carrier frequency and said one or more resonator exciting frequencies, and

a transducers unit operatively coupled to said frequency generating unit for transmitting said sonic beam.

74. The system according to claim 73 wherein said frequency generating unit comprises,

a high frequency generating unit for generating said carrier frequency, and

a low frequency generating unit for generating said one or more resonator exciting frequencies.

75. The system according to claim 73 wherein said transducers unit comprises one or more transducer units selected from, piezoelectric transducers, electromechanical transducers, electromagnetic transducers, capacitive transducers, electro-magneto-mechanical transducers and any combinations thereof.

76. The system according to claim 75 wherein said one or more transducer units comprise one or more piezoelectric transducers selected from, single-element piezoelectric transducers, multi-element piezoelectric transducers, nested piezoelectric transducers, coaxial concentric piezoelectric transducers, phased piezoelectric transducer arrays, and any combinations thereof.

77. The system according to claim 75 wherein said one or more transducer units comprise a wideband capacitive transducer for transmitting said carrier frequency and said one or more resonator exciting frequencies.

78. The system according to claim 75 wherein said one or more transducer units comprise a first piezoelectric transducer for transmitting said carrier frequency and a second piezoelectric transducer for transmitting said one or more resonator exciting frequencies.

79. The system according to claim 73 wherein said frequency generating unit is configured for generating any frequency selected from said carrier frequency and said one or more resonator exciting frequencies, in a form selected from a continuous wave frequency, one or more frequency pulses, one or more frequency bursts including a plurality of different frequencies and one or more chirped frequency sweeps.

80. The system according to claim 65 wherein said receiver unit comprises a frequency modulation receiver.

81. The system according to claim 65 wherein said frequency modulation receiver is selected from a baseband receiver unit and an intermediate frequency receiver unit.

82. The system according to claim 65 wherein said receiver unit comprises at least one receiving transducer for receiving said returning signals and for providing an output signal representing said returning signals.

83. The system according to claim 82 wherein said receiver unit further comprises an analog front end unit operatively coupled to said at least one receiving transducer for receiving said output signal from said at least one receiving transducer and for processing said output signal to provide a processed analog output signal, and an analog to digital converter unit operatively coupled to said analog front end unit and to said processing unit for digitizing said processed analog output signal and for providing a digitized signal to said processing unit.

84. The system according to claim 83 wherein said analog front end unit is configured for processing the output signal received from said at least one receiving transducer, wherein said processing is selected from, filtering the received signal to remove noise and undesired frequency components, amplifying the received signal to provide an amplified signal, mixing the signal with a reference signal to provide a mixed analog signal, filtering said mixed analog signal for removing undesired frequency components of said mixed analog signal to provide a down-converted analog signal, amplifying said down-converted analog signal, and combinations thereof.

85. The system according to claim 82 wherein said receiver unit further comprises an analog to digital converting unit operatively coupled to said at least one receiving transducer for digitizing the signal received from said at least one receiving transducer unit to provide a digitized signal.

86. The system according to claim 65 wherein said receiver unit is configured for down-converting the signal received from said at least one receiving transducer to provide a down converted signal.

87. The system according to claim 86 wherein said receiver unit is configured for processing said down converted signal to remove undesired frequency components therefrom to provide a filtered down-converted signal.

88. The system according to claim 87 wherein said receiver unit is configured for amplifying said filtered down-converted signal to provide an amplified filtered down-converted signal.

89. The system according to claim 65 wherein said system further comprises a synchronizing unit operatively coupled to said transmitting unit and said receiver unit, for synchronizing the operation of said transmitting unit and said receiver unit.

90. The system according to claim 89 wherein said synchronizing unit is operatively coupled to said processing unit.

91. The system according to claim 89 wherein said synchronizing unit is configured for receiving an external synchronizing signal.

92. The system according to claim 65 wherein said system is configured to condition said signals for providing said processing unit with a conditioned signal.

93. The system according to claim 92 wherein said system is configured to condition said signals by performing on said signals one or more operations selected from pre-amplification, band pass filtering, multiplication by a reference signal, low pass filtering, notch filtering, amplification, and combinations thereof.

94. The system according to claim 92 wherein said system is configured to condition said signals by performing on said signals the procedures of bandpass filtering, pre-amplification, bandpass filtering, multiplication by a reference signal, low pass filtering, notch filtering, and amplification.

95. The system according to claim 94 wherein said procedures are performed on said signals in the order recited in claim 94.

96. The system according to claim 65 wherein said system is configured to process said signals to obtain digitized data, and perform on said digitized data a digital Fourier transform to obtain frequency domain data representing signal amplitude as a function of frequency.

97. The system according to claim 65 wherein said processing unit comprises at least one unit selected from, a computer, a microcomputer, a microprocessor, a digital processor, a digital signal processor, a microcontroller unit, a controller unit, a personal computer, a workstation, a minicomputer, a networked computer, a mainframe computer, a distributed processor configuration, a computer cluster configuration, and combinations thereof.

98. The system according to claim 65 wherein said system is configured as part of a medical ultrasound imaging system.

99. The system according to claim 65 further comprising a high dynamic range analog to digital converting unit operatively connected to said receiver unit for receiving an analog signal from said receiver unit, said analog to digital converting unit is operatively connected to said processing unit and is configured for digitizing said analog signal to provide a digitized signal to said processing unit.

100. The system according to claim 65 wherein said system further comprises an analog front end unit and an analog to digital converting unit, said analog front end unit is operatively connected to said receiver unit to receive signals therefrom, said analog front end unit is operatively connected to said analog to digital converting unit and is configured for providing a conditioned analog output signal to said analog to digital converting unit, said analog to digital converting unit is operatively connected to said at least one processing unit to provide a digitized signal thereto.

101. The system according to claim 100 wherein said analog front end unit comprises a frequency down-converting unit for down-converting the signals received from said receiver unit.

102. The system according to claim 101 wherein said frequency down-converting unit comprises a mixer unit configured for receiving an analog signal, and a reference signal source operatively connected to said mixer unit for providing a reference signal to said mixer unit, said mixer unit is configured to mix said analog signal with said reference signal.

103. The system according to claim 102 wherein said analog front end unit comprises at least one signal conditioning unit operatively connected to said receiver unit for receiving signals from said receiver unit, said at least one conditioning unit is operatively connected to said mixer unit for providing a conditioned signal to said mixer unit.

104. The system according to claim 103 wherein said at least one signal conditioning unit comprises at least one filter unit for filtering the signals received from said receiver unit and at least one amplifier unit.

105. The system according to claim 104 wherein said at least one filter unit comprises a first band pass filter unit operatively connected to said receiver unit and to said at least one amplifier unit, and a second band pass filter unit operatively connected to said at least one amplifier unit for filtering the output of said at least one amplifier unit, said second band pass filter unit is operatively connected to said mixer unit.

106. The system according to claim 102 wherein said analog front end unit comprises a post mixing signal conditioning unit operatively connected to said mixer unit for receiving signals from said mixer unit, said post mixing signal conditioning unit is operatively connected to said analog to digital converting unit for providing a down-converted signal to said analog to digital converting unit.

107. The system according to claim 106 wherein said post mixing signal conditioning unit comprises a filter unit selected from a low pass filter, a notch filter, and a combination thereof.

108. The system according to claim 107 wherein said post mixing signal conditioning unit also comprises an amplifier operatively coupled to the filter unit of said down-converting unit.

109. The system according to claim 100 wherein said analog front end unit comprises,

a first filter unit operatively connected to said receiver unit for filtering signals received from said receiver unit to provide a first filtered signal,

a first amplifier unit operatively connected to said first filter unit for amplifying said first filtered signal to provide a first amplified signal,

a second filter unit operatively connected to said first amplifier unit for filtering said first amplified signal to provide a second filtered signal,

a high frequency source for providing a high frequency reference signal,

a mixer unit operatively connected to said second filter unit for receiving said second filtered signal therefrom, said mixer unit is operatively connected to said high frequency source for receiving said high frequency reference signal therefrom, said mixer is configured for mixing said second filtered signal with said high frequency reference signal to provide a down converted output signal,

a third filter operatively connected to said mixer unit for filtering said down converted signal for producing a third filtered signal,

a fourth filter unit operatively connected to said third filter unit for filtering said third filtered signal to provide a fourth filtered signal, and

a second amplifier unit operatively connected to said fourth filter unit for amplifying said fourth filtered signal, said second amplifier is operatively connected to said analog to digital converting unit to provide said conditioned analog output thereto.

110. The system according to claim 109 wherein said first filter and said second filter are band pass filters, said third filter is a low pass filter, and said fourth filter is a notch filter.

111. The system according to claim 65 wherein said system further comprises pressure determining means for determining the external pressure level in the vicinity of said system.

112. The system according to claim 65 wherein said system further comprises a barometer unit operatively coupled to said processing unit for determining the barometric pressure level and for providing said processing unit with a signal representative of said barometric pressure level.

113. The system according to claim 65 wherein said system further comprises a user interface.

114. The system according to claim 113 wherein said user interface is selected from at least one user interface for allowing a user to control said system, at least one user interface for presenting information to a user of said system, and a combination thereof.