Electricity: measuring and testing – Conductor identification or location – Inaccessible
Patent
1987-11-19
1989-08-01
Strecker, Gerard R.
Electricity: measuring and testing
Conductor identification or location
Inaccessible
324 61R, 324329, G01R 3300, G01R 2726, G01V 311
Patent
active
048536172
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a device for detecting objects behind a surface.
Concealed metal objects behind surfaces may be investigated by metal detectors that work by magnetic induction between associated transmitter and receiver coils, e.g. on the so-called balanced inductor principle. Metal detectors that work in this way include those described in U.S. Pat. Nos. 2,451,596 (Wheeler), 2,547,407 (Nelson), 2,557,994 (Ostlund), 2,772,394 (Bradley), 3,882,374 (McDaniel) and 4,255,711 (Thompson) and in German Patent Specification No. 2718132 (Reiners).
Inhomogeneities in the dielectric properties of surfaces may also be investigated by capacitance sensing, in order to detect moisture, concealed voids or concealed objects as described in U.S. Pat. Nos. 2,718,620 (Howe), 2,885,633 (Cook), 3,043,993 (Maltby), 3,046,479 (Mead et al), 3,230,519 (Metz et al), 3,493,854 (Zurbrick), 3,515,987 (Zurbrick et al), 3,694,742 (Berginanis), 3,967,197 (Anderson) and 4,099,118 (Franklin) and UK Patent Specification Nos. 1052194 (Associated Electrical Industries) and 1403720 (Fisons).
A problem in the production of a compact device that can investigate surfaces both capacitively and by magnetic induction is that these two kinds of sensors interfere one with another.
The present invention provides a device for detecting objects behind a surface comprising a support intended in use to be held adjacent and traversed over the surface, transmitter and receiver plate means of stray field capacitor means responsive to alterations in dielectric constant of the surface resulting from the presence of concealed objects and transmitter and receiver coils of metal detector means located behind the plates of the stray field capacitor means, wherein electrostatic screen means is positioned between the plates of the stray field capacitor means and the coils of the metal detector means and connected to a steady reference potential, and the plates of the stray field capacitor means and electrostatic screen means have a combination of electrical conductivity and area perpendicular to the magnetic field from said metal detector means providing continuous conductive paths such that circulating currents induced therein by a magnetic field from the metal detector means are small and the plates of the stray field capacitor means and electrostatic screen means do not prevent operation of the metal detector means.
One approach to shield and plate design is to use a resistive non-metallic material. Thus the plates of the stray field capacitor means and the electrostatic screen means may be derived from conductive ink and have a surface resistance that permits electrostatic charging and discharging thereof whilst not responding to magnetic field from the metal detector means by having large circulating currents induced therein. Alternately the shield and plates could be of metal or other conductive material but divided into narrow strips to minimise the area perpendicular to the magnetic field from the metal detector means and enclosed by continuous conductive paths.
The invention also provides a device for detecting objects behind a surface comprising a support intended in use to be held adjacent and traversed over the surface, a multiplicity of capacitor plate means at intervals along the support, circuit means for sensing for each plate means for alterations in dielectric constant of a local region of the surface and a plurality of display elements arranged at intervals along display means and each associated with a plate means so that each element changes in appearance depending upon the dielectric constant of the local region of the associated plate means so that as the support is traversed past an object the display elements change appearance according to the positions of their associated plate means relative to the object and edges of the object are imaged on the elements.
The invention enables a multiplicity of capacitor sensor plates disposed in an array to provide a pictorial image of an object concealed behind a surface such as a wall by means
REFERENCES:
patent: 3609735 (1972-09-01), Dauterman et al.
patent: 3764819 (1973-10-01), Muller
patent: 4464622 (1984-08-01), Franklin
patent: 4686454 (1987-08-01), Precukonis
patent: 4743902 (1988-05-01), Andermo
Douglas Keith
Meyer Mark Q.
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