System for locating concealed underground objects using digital filtering
First Claim
Patent Images
1. A system for locating a concealed object comprising:
- transmitting means for transmitting an electromagnetic signal from said concealed object; and
receiving and processing means for receiving and processing said electromagnetic signal, said receiving and processing means includingantenna means for receiving said electromagnetic signal as an analog signal;
amplifying means for amplifying said received analog signal;
analog-to-digital converter means for converting said amplified analog signal to a digital signal, said analog-to-digital converter means sampling said amplified analog signal at a predetermined frequency;
digital filter means for filtering said digital signal, said digital filter means including a two-stage digital filter, the filter characteristics of said first stage of said two-stage digital filter being defined by parameters AO11 and AO12, and the filter characteristics of said second stage of said two-stage digital filter being defined by parameters AO21 and AO22, wherein
space="preserve" listing-type="equation">AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">AOx2=-(1-1/q).sup.2 *32768, whereinq=quality factor,fctr=center frequency,fsmpl=sampling frequency, andx=1 or 2; and
processing means for processing said filtered digital signal to provide an output signal indicative of the location of said concealed object.
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Abstract
A locating system has its performance enhanced by the use of digital filtering. The locating system may include a transmitter for transmitting an electromagnetic signal from a concealed object. The locating system may also use electromagnetic signals from existing electromagnetic sources unrelated to the locator system. A receiver is provided for receiving a selected electromagnetic signal. The signal is subsequently converted from an analog signal into a digital signal and subjected to digital filtering. The resulting digital signal is then processed to provide location information about the concealed object.
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Citations
27 Claims
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1. A system for locating a concealed object comprising:
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transmitting means for transmitting an electromagnetic signal from said concealed object; and receiving and processing means for receiving and processing said electromagnetic signal, said receiving and processing means including antenna means for receiving said electromagnetic signal as an analog signal; amplifying means for amplifying said received analog signal; analog-to-digital converter means for converting said amplified analog signal to a digital signal, said analog-to-digital converter means sampling said amplified analog signal at a predetermined frequency; digital filter means for filtering said digital signal, said digital filter means including a two-stage digital filter, the filter characteristics of said first stage of said two-stage digital filter being defined by parameters AO11 and AO12, and the filter characteristics of said second stage of said two-stage digital filter being defined by parameters AO21 and AO22, wherein
space="preserve" listing-type="equation">AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">AOx2=-(1-1/q).sup.2 *32768,wherein q=quality factor, fctr=center frequency, fsmpl=sampling frequency, and x=1 or 2; and processing means for processing said filtered digital signal to provide an output signal indicative of the location of said concealed object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of selecting a two-stage digital filter for use in a locating system including means for receiving a signal radiated from a concealed object as an analog signal, means for amplifying the received analog signal, means for converting the amplified analog signal to a digital signal, and a two-stage digital filter for filtering said digital signal, the means for converting said amplified analog signal to a digital signal sampling the amplified analog signal at a predetermined frequency, wherein the characteristics of said two-stage digital filter are defined by coefficients AO11, AO12, AO21 and AO22, the method comprising:
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calculating said coefficients AO11, AO12, AO21 and AO22 according to the following formulae;
space="preserve" listing-type="equation">AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">AOx2=-(1-1/q).sup.2 *32768wherein q=quality factor fctr=center frequency fsmpl=sampling frequency, and x=1 or 2; and performing a stabilization analysis of the digital filter defined by said coefficients. - View Dependent Claims (13, 14, 15)
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16. A receiver for receiving an electromagnetic signal radiated by a concealed object to indicate the location of said concealed object comprising:
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a. antenna means for receiving said electromagnetic signal as an analog signal; b. amplifying means for amplifying said analog signal; c. analog-to-digital converter means for converting said amplified analog signal to a digital signal, said analog-to-digital converter means sampling said amplified analog signal at a predetermined frequency; d. digital filter means for filtering said digital signal, said digital filter means including a two-stage digital filter, the filter characteristics of the first stage of said two-stage digital filter being defined by parameters AO11 and AO12, and the filter characteristics of the second stage of said two-stage digital filter being defined by parameters AO21 and AO22 wherein
space="preserve" listing-type="equation">AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">AOx2=-(1-1/q).sup.2 *32768,wherein q=quality factor, fctr=center frequency, fsmpl=sampling frequency, and x=1 or 2; and e. processing means for processing said filtered digital signal to indicate the location of said concealed object. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification