Wireless monitoring of temperature

Details Wireless monitoring of temperature Wireless monitoring of temperature

2000-04-12

2001-03-27

Lee, Benjamin C. (Department: 2736)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S572100, C340S572400, C340S870170, C374S100000, C374S141000, C324S200000, C324S201000, C324S224000

Reexamination Certificate

active

06208253

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to remote sensing of temperature, and in particular to wireless sensing.
BACKGROUND OF THE INVENTION
The need to monitor temperature occurs in a wide variety of automated applications, such as manufacturing and transportation of goods. For example, during various phases of a fabrication process, it may be important for the workpiece to remain within a limited temperature range, while food or medicine may be spoiled during shipment if exposed to temperatures above a particular maximum. While electronic temperature measurement is fast and accurate, traditional systems utilize temperature probes that are physically connected, via wires, to sensing circuitry. It is frequently not feasible or inconvenient to run wires to the desired measuring point.
In recognition of such environmental limitations, wireless temperature-monitoring systems have been developed. These typically involve associating both the temperature probe and measurement circuitry with the monitored items. Also associated with the measurement unit is a radio circuit that broadcasts the sensed temperature for remote reading. Obviously this arrangement involves considerable expense and bulk.
An alternative to these approaches is described in U.S. Pat. No. 6,025,725, which discloses an LC resonator package incorporating an electrically active material that responds to an external condition such as temperature. This response alters the resonant frequency and/or harmonic spectra of the package in a predictable fashion, thereby facilitating quantification of the external condition. While simple and inexpensive, the disclosed approach may encounter difficulties in electrically noisy or conductive environments. The LC resonators tend to operate at relatively high frequencies (>1 MHz), and are therefore easily shielded.
DESCRIPTION OF THE INVENTION
Brief Summary of the Invention
The present invention facilitates temperature sensing through observable, temperature-dependent effects on an interrogating magnetic field. This field is produced by transmitter antenna coils, and is effective within a zone representing the operating range of the sensing device. The interrogating magnetic fields used to operate the devices described herein may be relatively low-frequency (e.g., <100 kHz down to DC); the lower the frequency, the more resistant the signal will be to shielding. Moreover, DC magnetic fields will even penetrate most metals, so conductive environments will not prevent operation if a very low-frequency or DC measurement is employed.
The invention utilizes a “tag” or sensing module having, first, a signal element that interacts with the interrogation field to produce a remotely readable magnetic response; and disposed proximate to the signal element, a temperature-sensitive component. This latter component comprises at least one of (i) a modulation element having a magnetic permeability varying with temperature in the operating range, and (ii) a bias element comprising a magnet having a Curie temperature in the operating range. The temperaturesensitive component interacts magnetically with the signal element such that the remotely readable magnetic response is indicative of a temperature in the operating range. Significantly, this temperature-dependent magnetic response is an intrinsic function of the materials and structure of the tag, and thus requires no electronic circuitry on the tag. This results in significant cost reduction.
Depending on the embodiment, the response may be permanent—that is, the effect of exceeding a threshold temperature may be to irreversibly alter or fix the response of the sensing module to an interrogation field. Such embodiments thereby produce a permanent “heat signature” confirming exposure to the temperature threshold. Alternatively, the effect may be reversible, facilitating re-use of the sensor module (or sensing of temperature transitions from above to below the threshold).
Furthermore, the temperature sensitivity of the module may be abrupt or gradual. Modules exhibiting abrupt transitions are useful in registering threshold crossings, while more gradual transitions facilitate continuous monitoring of temperature within an operating range.
The invention is amenable to implementation not only as a thermometer, but in sensing applications for parameters that can be mapped to temperature; that is, if we can measure the temperature of an object subject to known a temperature-affecting influence, it is possible to determine the magnitude of the influence. For example, the invention may be employed as a bolometer to detect and measure electromagnetic radiation (e.g., infrared or RF), or heating due to strain, friction, or drag force (e.g., in an automobile tire).


REFERENCES:
patent: 3338100 (1967-08-01), Takami
patent: 4105971 (1978-08-01), Nevalainen
patent: 5392654 (1995-02-01), Boyle
patent: 5982282 (1999-11-01), Ryan, Jr.
patent: 6025725 (2000-02-01), Gershenfeld et al.
patent: 6067015 (2000-05-01), Lian et al.

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