Abstract:
A sensing system comprises a corner-cube reflector that has three reflective surfaces wherein at least one of the reflective surfaces is a surface of a bimaterial cantilever. The reflective surface of the bimaterial cantilever undergoes a change between a substantially planar shape and a curved shape upon direct exposure to an agent of interest. Such a change is perceived by a suitable detector.

Description:
BACKGROUND 
   The ensuing description relates generally to sensing systems for detecting environmental conditions. 
   SUMMARY 
   A sensing system comprises a corner-cube reflector that has three reflective surfaces wherein at least one of the reflective surfaces is a surface of a bimaterial cantilever. The reflective surface of the bimaterial cantilever undergoes a change between a substantially planar shape and a curved shape upon direct exposure to an agent of interest. Such a change is perceived by a suitable detector. 
   Other objects, advantages and new features will become apparent from the following detailed description when considered in conjunction with the accompanied drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a prior art corner cube reflector. 
       FIG. 2  is a representative view of a sensor according to the description herein. 
       FIG. 3  is a representative view of another sensor according to the description herein. 
       FIG. 4  depicts a utilization of a sensor according to the description herein. 
   

   DESCRIPTION 
   Referring to  FIG. 1 , a prior art corner cube reflector  10  is illustrated. Reflector  10  is shown to include three planar reflective surfaces  12 ,  14  and  16  that in this figure are arranged to be mutually orthogonal and that cumulatively form a right-angle concave mirror. 
   Such corner cube reflectors may, for example, be fabricated via the emerging technology known as MEMS (Micro Electro Mechanical Systems). The term MEMS broadly encompasses many different kinds of devices fabricated on the micron scale, such as sensors, actuators, and instruments. These devices are usually fabricated with integrated circuit technology on a silicon substrate. Such MEMS technology allows the fabrication of microsensors that are very small in size and that are easily transitioned into standard Integrated Circuit (IC) technology facilities manufacturing. 
   Referring again to  FIG. 1 , it is well-known that a light ray  18  incident upon the corner cube reflector from direction A will result in a reflected-back ray  20  from direction—A, i.e. toward light source  22 . This is the case when the light reflects off the three plano-reflective surfaces of the corner cube reflector. See for example, Scholl, “Ray Trace Through a Corner-Cube Reflector With Complex Reflection Coefficients”, Journal of the Optical Society of America A, Vol. 12, No. 7, pp. 1589–1592 (1995). 
   Microcantilevers, such as those used in atomic force microscopy, are known to undergo bending due to forces involved in molecular adsorption. Adsorption induced forces can be so large that on a clean surface they can rearrange the lattice locations of surface and subsurface atoms, producing surface reconstructions and relaxations. An analogous transduction process is found in biology, where the interaction of membrane molecules modifies the lateral tension of a lipid bilayer. The resulting curvature of the membrane is responsible for mechanically triggering membrane protein function. See Zhiyu Hu, T. Thundat, and R. J. Warmack from Oak Ridge National Laboratory reported their “Investigation of adsorption and absorption-induced stresses using microcantilever sensors” in Journal of Applied Physics, Vol 90, Number 1. See also J. Fritz, M K Baller and H P Lang titled “Translating biomolecular recognition into nanomechanics”, Science; Volume 288, Issue 5464, Pg. 316–318. 
   Specialized coatings, such as polymer coatings, may be added to the microcantilevers to react to specific agents of interest. Such coatings permit selected chemical/biological adsorption or absorption to take place at the cantilever. See the references by J. Fritz, M K Baller and H P Lang titled “Translating biomolecular recognition into nanomechanics”, Science; Volume 288, Issue 5464, Pg. 316–318. 
   Referring now to  FIG. 2 , a bimaterial cantilever  24  is made part of a corner cube reflector  26  having reflective surfaces  28 ,  30  and  32 . Reflector  26  as shown in  FIG. 2  is identified herein as being in a first sensing condition characterized by reflective surface  32  of bimaterial cantilever  24  being substantially planar. When reflective surface  32  is substantially planar, the three reflecting surfaces  28 ,  30  and  32  of the reflector are mutually orthogonal as shown. Though reflector  26  is illustrated to include a single bimaterial cantilever, two or three such cantilevers may be used. Electromagnetic radiation  34 , such as thermal, infrared, light or other, is projected from source  36  and is received in a first electromagnetic radiation state  38  by a detector  40 . The first state of the electromagnetic radiation corresponds to reflected radiation when reflector  26  is in the first sensing condition as described above and as shown in  FIG. 2 . 
   Cantilever  24  may be comprised of a variety of material, examples of which can be found, for example, in the atomic force microscopy field. This field is known to employ cantilevers having a base of Si or Si3N4 and a thin reflective surface of either gold or palladium. 
   Referring now to  FIG. 3 , another embodiment is shown wherein an agent sensitive coating  42  is suitably disposed on bimaterial cantilever  24 . When positioned as shown in  FIG. 3 , such a coating is selected to be thin enough (suitable transparent) so that the reflectivity of the underlying material is not obstructed or is selected to be reflective itself. Such a coating, for example a polymer coating, is chosen to selectively bond to an agent of interest, such as a chemical or biological species. 
   Referring now to  FIG. 4 , a second sensing condition of reflector  26  is shown wherein bimaterial cantilever  24  has deflected as a function of molecular interactions. The cantilever transforms from a substantially planar shape, as shown in  FIG. 2 , to a curved shape upon encountering an agent of interest. Reflective surface  32  will likewise undertake this curved shape as well as any agent sensitive coating  42  placed upon the reflective surface, whether the coating itself is also reflective or is transparent as indicated above. When cantilever  24  deflects, it disrupts the alignment of the corner cube reflector. Electromagnetic energy  34  from source  36  takes on a second state  38 ′ upon being reflected from the reflector in the condition shown and is then received at detector  40 . In this process, the second sate of the electromagnetic energy ( 38 ′) has experienced a shift from the first state of the electromagnetic energy ( 38 ) as received at detector  40 . The change in the received electromagnetic energy, due to the deflection of cantilever  24 , may be measured at detector  40  in terms of intensity, angular direction or phase change, and is equated with a change in the presence of an agent of interest, such as a chemical or biological agent species. 
   In the figures, for simplicity, the associated substrate on which the cantilever is formed is not shown. This substrate, however, may contain control circuitry, alternate sensors, etc. as desired for specific applications. 
   The method of fabricating the corner cube chemical-biological agent sensor is analogous to the steps carried out in prior art MEMS corner cube fabrication, with the exception that one or more bimaterial cantilevers are used and that an optional agent sensitive coating is formed on the cantilever or cantilevers. It is suitable to form the coating prior to the assembly of the corner cube. Piezoelectric transducers, as practiced in the art, could be integrated to self-assemble the corner cube reflector. 
   The sensor described herein is miniaturizable, allows remote (non-contact) read-out, requires no electrical bias (power), and is immune to electromagnetic interference. 
   Though a sensor employing a corner cube retroreflector has been described, the concept of utilizing a bimaterial cantilever is considered extendable to other retroreflectors, such as a penta-prism. 
   Obviously, many modifications and variations are possible in light of the above description. It is therefore to be understood that within the scope of the claims the invention may be practiced otherwise than as has been specifically described.