Systems for Detecting Cracks in Windows

Abstract

A system such as a vehicle may have windows with one or more conductive layers. The conductive layers may form part of an infrared-light-blocking layer or other layer. The infrared-light-blocking layer or other layer may be formed as a coating on a transparent structural window layer such as an outer or inner glass layer in a laminated window or may be embedded in a polymer layer between the outer and inner layers. Segmented terminals and elongated terminals that may extend past two or more segmented terminals may be coupled to the edges of the conductive layers. Using these terminals, control circuitry can apply localized ohmic heating currents and can make resistance measurements on the conductive layers to detect cracks.

What is claimed is: 
     
         1 . A vehicle, comprising:
 a body;   a vehicle window in the body having a thin-film conductive layer and at least first and second terminals coupled to the thin-film conductive layer; and   control circuitry configured to apply signals to the thin-film conductive layer through the first and second terminals to ohmically heat different regions of the thin-film conductive layer by different amounts.   
     
     
         2 . The vehicle defined in  claim 1  wherein the first terminal is located along a first edge of the thin-film conductive layer and the second terminal is located along a second opposing edge of the thin-film conductive layer. 
     
     
         3 . The vehicle defined in  claim 2  further comprising additional terminals coupled to the thin-film conductive layer. 
     
     
         4 . The vehicle defined in  claim 3  wherein the additional terminals are located along third and fourth opposing edges of the thin-film conductive layer. 
     
     
         5 . The vehicle defined in  claim 1  wherein the thin-film conductive layer comprises an infrared-light-blocking layer. 
     
     
         6 . The vehicle defined in  claim 1  wherein the control circuitry is configured to make electrical measurements on the thin-film conductive layer. 
     
     
         7 . The vehicle defined in  claim 6  wherein the electrical measurements comprise resistance measurements and wherein the control circuitry is configured to detect a crack in the vehicle window based on the resistance measurements. 
     
     
         8 . The vehicle defined in  claim 1  wherein the first and second terminals are located along a first edge of the thin-film conductive layer. 
     
     
         9 . The vehicle defined in  claim 1  wherein the first and second terminals are elongated terminals that each extend entirely across a respective edge of the thin-film conductive layer. 
     
     
         10 . The vehicle defined in  claim 1  wherein the control circuitry is configured to apply the signals to the thin-film conductive layer through the first and second terminals to defrost a driver-side area of the vehicle window before defrosting other areas of the vehicle window. 
     
     
         11 . A vehicle, comprising:
 a body;   a vehicle window in the body having a conductive layer that forms an infrared-light-blocking filter and having segmented terminals coupled to at least first and second edges of the conductive layer; and   control circuitry configured to apply a current to the conductive layer through the segmented terminals to ohmically heat a localized portion of the vehicle window.   
     
     
         12 . The vehicle defined in  claim 11  wherein the conductive layer comprises a thin-film conductive layer and wherein the segmented terminals are coupled to third and fourth edges of the conductive layer. 
     
     
         13 . The vehicle defined in  claim 11  wherein the control circuitry is configured to apply the current to the conductive layer through the segmented terminals to locally defrost a driver-side area of the vehicle window before defrosting other areas of the vehicle window. 
     
     
         14 . The vehicle defined in  claim 11  wherein the infrared-light-blocking filter comprises a thin-film interference filter. 
     
     
         15 . The vehicle defined in  claim 14  wherein the infrared-light-blocking filter comprises an additional conductive layer and additional terminals through which the control circuitry applies a current to the additional conductive layer. 
     
     
         16 . The vehicle defined in  claim 15  wherein the additional terminals comprise an elongated terminal that extends past the segmented terminals. 
     
     
         17 . A vehicle, comprising:
 a body;   a vehicle window in the body having a thin-film interference filter with at least first and second conductive layers and having terminals coupled to the first and second conductive layers; and   control circuitry configured to apply a current to the first and second conductive layers through the terminals to ohmically heat only a portion of the vehicle window.   
     
     
         18 . The vehicle defined in  claim 17  wherein the terminals comprise segmented terminals that are distributed along different edges of the first and second conductive layers. 
     
     
         19 . The vehicle defined in  claim 17  wherein the portion of the vehicle window comprises a driver-side portion of the vehicle window. 
     
     
         20 . The vehicle defined in  claim 17  wherein at least one of the terminals extends across an entire edge of the first conductive layer.