Microwave vibration sensors

A vibration sensor includes a probe body with a vibration isolator operatively connected to the probe body for isolation of the probe body from vibrations of a structure to be monitored for vibration. A waveguide is operatively connected to the probe body to convey microwaves to and from a surface for sensing vibration of the structure to be monitored for vibration.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to sensors, and more particularly to sensors for detecting vibrations such as in gas turbine engines.

2. Description of Related Art

A variety of sensor devices are known for detecting and monitoring vibrations. Piezoelectric sensors have often been used for this purpose. However, certain applications may preclude the use of piezoelectric sensors due to harsh conditions. For example, use of piezoelectric sensors in a gas turbine engine can be limited if the operating conditions are severe enough to shorten the sensor life, diminish the sensor reliability, or otherwise reduce the performance of the sensors. Temperature in particular is an important factor in shortening sensor life. Most sensors either have very short life at high temperatures or cannot operate at all. Additionally, piezoelectric sensors typically have relatively good sensitivity at higher frequencies, but in certain applications there may be a need for sensors to detect lower frequency vibrations than piezoelectric sensors are capable of detecting.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for methods and devices that allow for improved ruggedness and frequency range in vibration sensors. There also remains a need in the art for such methods and devices that are easy to make and use. The present invention provides a solution for these problems.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful vibration sensor. The vibration sensor includes a probe body with a vibration isolator operatively connected to the probe body for isolation of the probe body from vibrations of a structure to be monitored for vibration. A waveguide is operatively connected to the probe body to convey microwaves to and from a surface for sensing vibration of the structure to be monitored for vibration.

The mass of the probe body and at least one of a spring coefficient and a damping coefficient of the vibration isolator can be tuned to isolate the probe body from vibrations of a predetermined vibration frequency in the structure to be monitored for vibration. In certain embodiments, a cap is operatively connected to the vibration isolator with a space bounded by the probe body and cap for passage of microwaves to and from the wave guide. The cap can be configured and adapted to be mounted to a surface for sensing vibration thereof. A coaxial cable can be connected to the waveguide for conveyance of microwave signals to and from the waveguide.

In accordance with certain embodiments, a reflector is operatively connected to the probe body spaced apart from the waveguide for reflecting microwaves into the waveguide. The reflector can be operatively connected to a cap, such as the cap described above, within a space bounded by the probe body and cap. A pedestal can connect between the reflector and the cap. The mass of the reflector and at least one of a spring coefficient and a damper coefficient of the pedestal can be tuned to amplify vibration of the reflector in response to vibrations of a predetermined frequency in the structure to be monitored for vibrations.

These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a vibration sensor in accordance with the invention is shown inFIG. 1and is designated generally by reference character100. Other embodiments of vibration sensors in accordance with the invention, or aspects thereof, are provided inFIG. 2, as will be described. The systems and methods of the invention can be used for vibration detection in harsh environments such as in gas turbine engines.

Vibration sensor100includes a probe body102with a vibration isolator104operatively connected to probe body102for isolation of probe body102from vibrations of a structure to be monitored for vibration. For example, sensor100is mounted to surface106to monitor vibrations in the underlying structure. A waveguide108is operatively connected to probe body102to convey microwaves, indicated schematically inFIG. 1, to and from the interior surface of cap110for sensing vibration. Cap110is connected to vibration isolator104with an interior space112bounded by probe body102, vibration isolator104, and cap110for passage of microwaves to and from wave guide108. Cap110can be mounted to any suitable surface for sensing vibration thereof using an adhesive, fastener or the like, and serves to protect interior space112and vibration isolator104. Those skilled in the art will readily appreciate that cap110is optional, and that vibration isolator104can be mounted directly to a surface to be monitored in suitable applications. For example, if the surface being monitored has adequate reflective properties, vibration isolator104can be mounted directly to the surface without a cap therebetween.

The mass of probe body102and the spring and damping coefficients of vibration isolator104can be tuned to isolate probe body102from vibrations of a predetermined vibration frequency or range of frequencies. Frequencies of interest may include, for example, the frequencies of blades passing structures, and fundamental and harmonic frequencies of rotating parts such as gears shafts, high and low turbine rotors, and the like. For example, the materials and dimensions of probe body102and vibration isolator104can be tailored to isolate probe body102from a desired vibration frequency for a given application. In certain applications sensor100is generally tuned to reject frequencies, e.g., probe body102will not move, above a certain predetermined limit, so that sensor100will read frequencies above that predetermined limit. When the underlying structure vibrates at or above the predetermined frequency, vibration isolator104will isolate probe body102from the vibration. The underlying structure will therefore vibrate relative to probe body102and this relative vibration will be detectable as described below.

Coaxial cable114is connected to waveguide108for conveyance of microwave signals to and from waveguide108. Core116of coaxial cable114protrudes into waveguide108to serve as a microwave antenna. Waveguide108is otherwise hollow, and serves to deliver microwaves from coaxial cable114to cap110, and to return reflected microwaves from cap110to coaxial cable114. Cap110is mounted to surface106intimately so as to vibrate with surface106. As the interior surface of cap110vibrates relative to probe body102and waveguide108, the microwave signal returning to coaxial cable114can be interfered with the source signal to provide a modulated signal. As the modulated signal is monitored, vibration of surface106will manifest as changes in the modulated signal. Those skilled in the art will readily appreciate that interferometry is an exemplary way of producing a modulated signal, and that any other suitable method of monitoring microwaves can be used without departing from the scope of this disclosure. For example, another way to measure the vibration is simple phase variation over time of the incoming signal, relative to its average value.

With reference now toFIG. 2, another exemplary embodiment of a vibration sensor200includes a mechanism for amplifying vibrations. Vibration sensor200includes a probe body202, vibration isolator204, waveguide208, cap210, interior space212, coaxial cable214, and core216and is mounted to a surface206much as described above with respect toFIG. 1. A reflector218is operatively connected to probe body202spaced apart from waveguide208for reflecting microwaves into waveguide208, as indicated schematically inFIG. 2. Reflector218is connected to cap210by way of pedestal220and is situated within interior space212. The mass of reflector218and the spring and damper coefficients of pedestal220can be tuned, e.g., by selection of suitable materials and/or dimensions, to amplify vibration displacement of the reflector in response to vibrations of a predetermined frequency in the structure underlying surface206. This boosting of vibration displacement allows larger signals to be generated from microwave reflection from a target so tuned, than would be the case without such a target. For example, the spring mass damper system of reflector218can be tuned to amplify the same vibration frequency that the spring mass damper system of vibration isolator204is tuned to isolate from probe body202. This tuning increases sensitivity of vibration sensor200. Those skilled in the art will readily appreciate that the sensor components described above can be tuned to any suitable frequency as needed for particular applications without departing from the scope of this disclosure.

Potential advantages of the systems and methods described herein over traditional vibration sensors, such as piezoelectric sensors, include ruggedness to withstand harsh environments with better reliability. This can allow sensors as described herein to operate outside the temperature limits for traditional piezoelectric sensors, for example including high temperatures such as in gas turbine engines. Additionally, sensors as described herein can optionally be tuned to frequencies outside the practical limits of traditional piezoelectric sensors.

The methods and systems of the present invention, as described above and shown in the drawings, provide for vibration detection with superior properties. While the apparatus and methods of the subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention.