Digital stethoscopes, and auscultation and imaging systems
Described embodiments include a system ( 74 ), including a garment ( 76 ), configured to cover at least a portion of a body of a subject, one or more sound transmitters ( 92 ) coupled to the garment, configured to transmit sound ( 128 ) through the body of the subject, and a plurality of sound detectors ( 22, 96 ) coupled to the garment. The sound detectors are configured to detect the transmitted sound following passage of the transmitted sound through the body of the subject, to detect body sound ( 25 ) emanating from the body of the subject, and to generate a plurality of sound-detector outputs in response to detecting the transmitted sound and the body sound. The system further includes a processor ( 98 ), configured to process the sound-detector outputs, and to generate a processor output in response thereto. Other embodiments are also described.
1. Apparatus for detecting sound waves emanating from a body of a subject, the apparatus comprising:
a housing;
a membrane, disposed at an opening of the housing, configured to deflect, when an outer face of the membrane contacts the body, responsively to the sound waves impinging on the membrane;
a piezoelectric microphone, disposed within the housing, configured to detect vibrations of air caused by the deflection of the membrane, and to generate a microphone output in response thereto;
an accelerometer, disposed on an inner face of the membrane, configured to deflect, along with the membrane, at frequencies below a minimum frequency that is detectable by the piezoelectric microphone, and to generate an accelerometer output in response thereto; and
a processor, configured to process the microphone output and the accelerometer output, and to generate, responsively to the processing, a sound signal that represents the impinging sound waves.
2. The apparatus according to claim 1 , wherein the membrane comprises a material having a specific acoustic impedance that is between 0.8 and 4.5 MPa·s/m.
3. The apparatus according to claim 2 , wherein the material is selected from the group consisting of: polyethylene, polyamide, and polymethyl methacrylate.
4. The apparatus according to claim 1 , further comprising a second microphone, disposed within the housing, configured to detect ambient noise that does not emanate from the body of the subject, and to generate a noise-detection output in response thereto,
wherein the processor is configured to generate the sound signal by adaptively filtering the microphone output, based on the noise-detection output.
5. The apparatus according to claim 4 , further comprising a printed circuit board (PCB) disposed within the housing, wherein the piezoelectric microphone is mounted on a face of the PCB that faces the membrane, and the second microphone is mounted on an opposite face of the PCB, facing away from the membrane.
6. The apparatus according to claim 1 , further comprising a printed circuit board (PCB) disposed within the housing, wherein the processor and the microphone are mounted on the PCB.
7. The apparatus according to claim 1 , further comprising a display coupled to the housing such that the display faces away from the membrane, wherein the processor is further configured:
to analyze the sound signal, and
to drive the display to display results of the analysis.
8. The apparatus according to claim 1 , further comprising earphones connected to the housing, wherein the processor is further configured to play the sound signal through the earphones.
9. The apparatus according to claim 8 , wherein the processor is configured to play infrasonic components of the sound signal, which represent infrasonic components of the sound waves, by translating the infrasonic components of the sound signal to a range of audible frequencies.
10. The apparatus according to claim 9 , wherein the processor is configured to translate the infrasonic components to the range of audible frequencies by:
computing a short-time Fourier transform (STFT) of the sound signal,
decimating the STFT of the sound signal, in a time domain of the STFT of the sound signal, by a factor R,
computing an inverse STFT of the decimated STFT of the sound signal, and
interpolating the inverse STFT by the factor R.
11. The apparatus according to claim 9 , wherein the range of audible frequencies is between 500 Hz and 4 kHz.
12. The apparatus according to claim 1 , further comprising a sound transmitter disposed within the housing, configured to transmit sound through the body of the subject.
13. The apparatus according to claim 12 , wherein the sound transmitter is configured to transmit the sound at a frequency between 25 kHz and 200 kHz.
14. The apparatus according to claim 12 , wherein the sound transmitter is configured to transmit the sound at a frequency between 500 Hz and 10 kHz.
15. The apparatus according to claim 12 , wherein the sound transmitter is configured to transmit the sound by transmitting a chirp signal.
16. A method for detecting sound waves emanating from a body of a subject, the method comprising:
by contacting the body of the subject with an outer face of a membrane that is disposed at an opening of a housing, causing the membrane to deflect responsively to the sound waves impinging on the membrane;
using a piezoelectric microphone disposed within the housing, detecting vibrations of air caused by the deflection of the membrane, and generating a microphone output in response thereto;
using an accelerometer that is disposed on an inner face of the membrane, detecting the deflection of the membrane at frequencies below a minimum frequency that is detectable by the piezoelectric microphone, and generating an accelerometer output in response thereto; and
using a processor, processing the microphone output and the accelerometer output, and generating, responsively to the processing, a sound signal that represents the impinging sound waves.
17. The method according to claim 16 , wherein the sound waves emanate from lungs of the subject.
18. The method according to claim 16 , further comprising, using the processor, playing the sound signal through earphones connected to the housing.
19. The method according to claim 18 , wherein playing the sound signal comprises playing infrasonic components of the sound signal, which represent infrasonic components of the sound waves, by translating the infrasonic components of the sound signal to a range of audible frequencies.
20. The method according to claim 19 , wherein translating the infrasonic components to the range of audible frequencies comprises:
computing a short-time Fourier transform (STFT) of the sound signal,
decimating the STFT of the sound signal, in a time domain of the STFT of the sound signal, by a factor R,
computing an inverse STFT of the decimated STFT of the sound signal, and
interpolating the inverse STFT by the factor R.
21. The method according to claim 19 , wherein the range of audible frequencies is between 500 Hz and 4 kHz.