Methods and apparatus for improved vibration cancellation in acoustic sensors

• US 10,156,472 B2
• Filed: 11/04/2014
• Issued: 12/18/2018
• Est. Priority Date: 11/04/2014
• Status: Active Grant

• Current Assignee: Raytheon BBN Technlogies Corp. (Rtx Corporation)
• Original Assignee: Raytheon BBN Technlogies Corp. (Rtx Corporation)
• Inventors: Coleman, Ronald Bruce
• Primary Examiner(s): Kim, Paul S
• Assistant Examiner(s): SUTHERS, DOUGLAS JOHN
• Application Number:
  US14/532,379
• Publication Number:
  US 20170023401A1
• Time in Patent Office: 1,505 Days
• Field of Search: 381 949, 381169
• CPC Class Codes: G01H 3/005 Testing or calibrating of detectors covered by the subgroups of G01H3/00 calibrating geophysical instruments, e.g. seismic receivers G01V13/00
• CPC Class Codes: G01H 3/08 Analysing frequencies present in complex vibrations, e.g. comparing harmonics present acoustic presence detection G01V1/001
• CPC Class Codes: H04R 2410/03 Reduction of intrinsic noise in microphones
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453

Abstract

Acoustic sensing systems having improved vibration cancelation, and methods of achieving improved vibration cancelation. In one example, an acoustic sensing system includes an acoustic sensor configured to produce a sensor output signal representative of a response of the acoustic sensor to acoustic excitation and vibration excitation, at least one accelerometer configured to provide an acceleration signal responsive to the vibration excitation, and a controller, including an adaptive digital filter, coupled to the acoustic sensor and to the at least one accelerometer, and configured to receive the acceleration signal and to adjust coefficients of the adaptive digital filter so as to minimize coherence between a residual signal and the acceleration signal, the residual signal being a difference between the sensor output signal and a filter output signal from the adaptive digital filter.

Claims

1. An acoustic sensing system comprising:

an acoustic sensor configured to produce a sensor output signal representative of a response of the acoustic sensor to acoustic excitation and a rocking vibration excitation, the rocking vibration excitation being about an axis perpendicular to an acoustic sensing axis of the acoustic sensor, wherein the rocking vibration excitation is based on movement of a housing of the acoustic sensor,

wherein the acoustic sensor includes a sensing crystal and a plurality of compensation crystals coupled together, the plurality of compensation crystals including;

a top compensation crystal having a first top surface with a first polarity and a first bottom surface with a second polarity,

a lower compensation crystal having a second top surface and a second bottom surface, each of the second top surface and the second bottom surface being split between a first portion thereof having the first polarity and a second portion thereof having the second polarity, and

a middle compensation crystal interposed between the top compensation crystal and the lower compensation crystal, the middle compensation crystal having a third top surface and a third bottom surface, each of the third top surface and the third bottom surface being split between a third portion thereof having the first polarity and a fourth portion thereof having the second polarity;

at least one accelerometer mounted to the housing of the acoustic sensor and configured to measure the movement of the housing and to provide an acceleration signal responsive to the rocking vibration excitation; and

a controller, including an adaptive digital filter, coupled to the acoustic sensor and to the at least one accelerometer, and configured to receive the acceleration signal and to adjust coefficients of the adaptive digital filter so as to minimize coherence between a residual signal and the acceleration signal and thereby minimize a portion of the residual signal that is correlated with the rocking vibration excitation, the residual signal being a difference between the sensor output signal and a filter output signal from the adaptive digital filter, the controller being configured to output the residual signal as a vibration compensated output.

2. The acoustic sensing system of claim 1 wherein the controller is configured to implement a least-mean-square algorithm to minimize the portion of the residual signal that is correlated with the rocking vibration excitation, thereby minimizing the coherence.

3. The acoustic sensing system of claim 1, wherein the sensor output signal is further representative of a response of the acoustic sensor to an axial vibration excitation, and the sensing crystal and the plurality of compensation crystals are connected together to provide at least partial cancellation of the axial vibration excitation.

4. The acoustic sensing system of claim 1 wherein the controller is further configured to receive the residual signal.

11. The acoustic sensing system of claim 1, wherein the first polarity is a positive polarity and the second polarity is a negative polarity.

5. An acoustic sensing system comprising:

an acoustic sensor including a sensing crystal and a compensation crystal stack each mounted inside a housing of the acoustic sensor, the sensing crystal providing a sense output signal in response to an acoustic excitation and a rocking vibration excitation, the rocking vibration excitation being about an axis perpendicular to an acoustic sensing axis of the acoustic sensor, and the compensation crystal stack providing a compensation output signal in response to the acoustic excitation and the rocking vibration excitation, wherein the rocking vibration excitation is based on movement of the housing,

wherein the compensation crystal stack includes a plurality of compensation crystals coupled together, the plurality of compensation crystals including;

a top compensation crystal having a first top surface with a first polarity and a first bottom surface with a second polarity,

a lower compensation crystal having a second top surface and a second bottom surface, each of the second top surface and the second bottom surface being split between a first portion thereof having the first polarity and a second portion thereof having the second polarity, and

a middle compensation crystal interposed between the top compensation crystal and the lower compensation crystal, the middle compensation crystal having a third top surface and a third bottom surface, each of the third top surface and the third bottom surface being split between a third portion thereof having the first polarity and a fourth portion thereof having the second polarity; and

a controller, including an adaptive digital filter, coupled to the acoustic sensor and configured to receive the compensation output signal and to adjust coefficients of the adaptive digital filter so as to minimize coherence between a residual signal and the compensation output signal and thereby minimize a portion of the residual signal that is correlated with the rocking vibration excitation, the residual signal being a difference between the sense output signal and a filter output signal from the adaptive digital filter, the controller being configured to output the residual signal as a vibration compensated output.

6. The acoustic sensing system of claim 5 wherein the controller is configured to implement a least-mean-square algorithm to minimize the portion of the residual signal that is correlated with the rocking vibration excitation, thereby minimizing the coherence.

7. The acoustic sensing system of claim 5 wherein the acoustic sensor further includes a tuning mass coupled to the sensing crystal and to the compensation crystal stack, the tuning mass being selected such that a response of the compensation crystal stack is dominated by an axial vibration excitation rather than the acoustic excitation.

10. The acoustic sensing system of claim 5, wherein the first polarity is a positive polarity and the second polarity is a negative polarity.

8. A method of providing vibration cancelation in an acoustic sensing system, the method comprising:

providing an acoustic sensor including a sensing crystal and a plurality of compensation crystals coupled together, the plurality of compensation crystals including;

a top compensation crystal having a first top surface with a first polarity and a first bottom surface with a second polarity,

a lower compensation crystal having a second top surface and a second bottom surface, each of the second top surface and the second bottom surface being split between a first portion thereof having the first polarity and a second portion thereof having the second polarity, and

a middle compensation crystal interposed between the top compensation crystal and the lower compensation crystal, the middle compensation crystal having a third top surface and a third bottom surface, each of the third top surface and the third bottom surface being split between a third portion thereof having the first polarity and a fourth portion thereof having the second polarity;

receiving a sensor output signal from the acoustic sensor, the sensor output signal being representative of a response of the acoustic sensor to acoustic excitation and a rocking vibration excitation, the rocking vibration excitation being about an axis perpendicular to an acoustic sensing axis of the acoustic sensor, wherein the rocking vibration excitation is based on movement of a housing of the acoustic sensor;

receiving, at an input to an adaptive digital filter, an acceleration signal from at least one accelerometer mounted to the housing of the acoustic sensor, the acceleration signal being responsive to the rocking vibration excitation;

producing a residual signal as a vibration compensated output by taking a difference between the sensor output signal and a filter output signal from the adaptive digital filter; and

adjusting coefficients of the adaptive digital filter so as to minimize coherence between the residual signal and the acceleration signal and thereby minimize a portion of the residual signal that is correlated with the rocking vibration excitation.

9. The method of claim 8 wherein adjusting the coefficients includes applying a least-mean-square algorithm to minimize the portion of the residual signal that is correlated with the rocking vibration excitation, thereby minimizing the coherence between the residual signal and the acceleration signal.