Electromagnetic sensor system and method

The determination of the presence and magnitude of electromagnetic radiation or whether an object of interest is being irradiated by electromagnetic radiation generally requires an absorbing sensor and electronic circuitry that is coupled to the object being considered. Typically, most systems for detecting electromagnetic radiation require that there be some defined relation between the dimensions of the sensor and the wavelength of the electromagnetic energy that is desired to be detected. However, there are some applications where it would be inconvenient to couple the sensor and electronic circuitry to the object. For example, for electromagnetic energy propagating inside radio frequency (“RF”) waveguides in a radar or communication system, a “T-shaped” waveguide must be inserted to extract a portion of the electromagnetic radiation to an absorbing sensor. Such a sensor and method are intrusive and not amenable with system maintenance or non-invasive in-situ performance monitoring. Alternative conventional techniques further require wire penetration through the RF waveguide to a sensor. Therefore, a need exists for a system and method for determining the presence and magnitude of electromagnetic radiation or whether an object is being irradiated by electromagnetic energy that does not require intrusion of the sensor within the propagating medium such as a waveguide.

An electromagnetic sensor system comprises an electromagnetic excitable structure that generates an acoustic signal when irradiated with electromagnetic energy; an acoustic energy transducer sensor for generating a first output signal that represents the acoustic signal in response to the acoustic energy transducer detecting the acoustic signal; and a processor for determining whether the electromagnetic excitable structure is being irradiated by the electromagnetic energy in response to the processor receiving the first output signal.

FIG. 1 shows an embodiment of an electromagnetic sensor system.

FIG. 2 shows another embodiment of an electromagnetic sensor system.

FIG. 3 shows an embodiment of an electromagnetic sensor system wherein an acoustic couplant is interposed between the acoustic transducer and the electromagnetic excitable structure.

FIG. 4 shows an oscilloscope trace of the output of acoustic energy transducer when the electromagnetic excitable sensor is being irradiated with electromagnetic energy and when it is not being so irradiated.

Throughout the several views, like elements are referenced using like references.

Referring to FIG. 1 there is shown an embodiment of an electromagnetic sensor system 10 for detecting electromagnetic energy 12 that may be in the microwave or radio frequency region of the electromagnetic spectrum (100 kHz to 100 Ghz), and which may be pulsed or continuous. Electromagnetic sensor system 10 includes an electromagnetic excitable structure 14 , an acoustic energy transducer 20 , and a processor 22 . Electromagnetic excitable structure 14 is a structure that resonates at acoustic wavelengths and thereby generates an acoustic energy signal 18 in response to being irradiated by electromagnetic radiation 12 . By way of example, the electromagnetic excitable structure may be implemented as a metallic structure such as an RF wave-guide, which may be made of aluminum or other types of metal and metal alloys. Typically, acoustic energy transducer operating wavelengths are in the range of about 1 kHz to 1000 kHz. However, it is to be understood that acoustic energy transducer 20 may be implemented for detecting wavelengths outside of the above stated range. Sources of electromagnetic energy include magnetrons, traveling wave tubes, klystrons, solid-state devices, or other devices that generate electromagnetic radiation or waves.

Still referring to FIG. 1 , acoustic energy transducer 20 may be positioned remotely from electromagnetic excitable structure 14 so that as acoustic energy signal 18 propagates through an acoustic propagating medium (or couplant) 15 , such as air, grease, or water, signal 18 is detected by acoustic energy transducer 20 . In another embodiment, the acoustic energy transducer 20 may be mounted directly onto electromagnetic excitable structure 14 , as shown in FIG. 2 . In response to detecting acoustic energy signal 18 , acoustic energy transducer 20 generates a first output signal 25 that represents the waveform of the acoustic energy signal 18 . Then, in response to receiving the first output signal 25 , a processor 22 determines whether electromagnetic excitable structure 14 is being irradiated with electromagnetic radiation 12 . Processor 22 may provide a second output signal 29 to a display device (not shown), such as a monitor, strip chart recorder, and the like, that represents such a determination. Alternatively, output signal 29 may be used as an input signal to another device (not shown). By way of example, processor 22 may be implemented as a personal computer (PC), microprocessor, analog processor, and the like.

By way of example, acoustic energy transducer 20 may be a piezoelectric transducer such as Physical Acoustics model R50, R80, S9208 or Digital Wave Corporation model B1025. The frequency response of these sensors is: 100 to 700 kHz; 200 to 1000 kHz; 20 to 1000 kHz; and 1 to 1.5 kHz, respectively. However, it is to be understood that electromagnetic sensor system 10 may employ acoustic energy transducers having a detection sensitivity anywhere in the range 1 kHz to 1000 kHz. The voltage output signal 25 from acoustic energy transducer 20 may be subjected to suitable signal processing, such as amplification and/or filtering by signal conditioning circuit (not shown) before being input into processor 22 .

In general, processor 22 may implement any of several well known mathematical techniques using suitable software routines for determining whether electromagnetic excitable structure 14 is being irradiated with electromagnetic energy 12 . For example, a software program such as the Integrated Condition Assessment System (ICAS) by the IDAX Corporation may be used for scaling or normalizing data, performing trend analysis, and the like.

One example of a mathematical technique that may be implemented by processor 22 is the integration of values representing the waveform of signal 25 over a period of time, where signal 25 represents the waveform of acoustic energy signal 18 . Sufficient deviations between the integrated values obtained from signal 25 and a set of reference values may be used to determine whether electromagnetic excitable structure 14 is being irradiated with electromagnetic energy 12 . In another embodiment, processor 22 may be employed to implement a suitable software routine that identifies and compares the maximum amplitude of signal 25 with the maximum amplitude of a reference value that corresponds to electromagnetic excitable structure 14 being irradiated by electromagnetic radiation 12 . The reference value is typically greater than the background noise level that would be present in signal 25 when electromagnetic excitable structure 14 is not being irradiated by electromagnetic radiation 12 . For example, if the maximum amplitude of signal 25 exceeds such a reference value, then processor 22 determines that electromagnetic excitable structure 14 is being irradiated by electromagnetic radiation 12 . If the maximum amplitude of signal 25 is less than such a reference value, then processor 22 determines that electromagnetic excitable structure 14 is not being irradiated by electromagnetic radiation 12 .

Another example of a mathematical technique for determining whether electromagnetic excitable structure 14 is being irradiated with electromagnetic radiation 12 is a fast Fourier transform (FFT) of a representation of the waveform of signal 25 , and hence the waveform characteristics of acoustic energy signal 18 . The FFT analysis performed by processor 22 may be used to identify frequency components in output signal 25 that are characteristic of irradiation of electromagnetic excitable structure 14 being irradiated by electromagnetic energy 12 . The FFT analysis performed by processor 22 may also be used to identify the the source of electromagnetic radiation 12 by the frequency components in signal 25 , where such frequency components are known to be characteristic of a particular source (not shown) of electromagnetic energy 12 .

Examples of suitable acoustic energy transducers include piezoelectric devices, surface acoustic wave devices, micro-electro mechanical systems (MEMS), and any other type of transducer that generates an output signal representing the waveform of a detected acoustic energy signal.

Another embodiment of electromagnetic sensor system 10 is shown in FIG. 3 to further include an acoustic couplant layer 30 interposed between the electromagnetic excitable structure 14 and the acoustic energy transducer 20 . Acoustic couplant layer 30 enhances the acoustic coupling between the electromagnetic excitable structure 14 and the acoustic energy transducer 20 to improve the signal to noise ratio of output signal 25 . Acoustic couplant layer 30 may be implemented as a silicone grease, acoustically conductive epoxies, and the like.

FIG. 4 shows an example of a signal 25 generated in an electromagnetic sensor system 10 wherein an R50 type of acoustic energy transducer 20 having a frequency range of 100 Khz to 700 kHz was affixed to a metallic RF waveguide using layer of General Electric MIL-S-8660B silicone grease having a thickness of less than 0.1 about mm. The silicone grease provided acoustic couplant layer 30 between acoustic energy transducer 20 and the metallic RF waveguide. The metallic RF waveguide served as electromagnetic excitable structure 14 . Signal 25 was connected to processor 22 through a Physical Acoustics Model 2/4/6 pre-amplifier and Physical Acoustics Model AE1A amplifier to a LeCroy Model 9354AM digital oscilloscope which served as a display device. Position 500 represents the amplitude of first output signal 25 when no electromagnetic radiation was passing through the RF waveguide. Position 550 shows the amplitude of voltage signal 25 when electromagnetic energy propagates through the RF wave-guide. As may be seen in FIG. 3 , the oscilloscope clearly indicates whether electromagnetic radiation is propagating through the RF waveguide.

Obviously, many modifications and variations of the invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.