Ferroelectric Radiation Detector Employing Frequency Modulated Readout

• US 20100264325A1
• Filed: 04/21/2009
• Published: 10/21/2010
• Est. Priority Date: 04/21/2009
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Inventors: Potrepka, Daniel, Tidrow, Steven C., Crowne, Frank, Rod, Bernard J.
• Granted Patent: US 8,143,578 B2
• Time in Patent Office: Days
• US Class Current: 250/394
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: H01L 31/09 Devices sensitive to infrared, visible or ultraviolet radiation H01L31/101 takes precedence

Abstract

A detector for electromagnetic radiation such as millimeter wave and infrared employs a ring-shaped ferroelectric element having a temperature affected by an absorber for the radiation. The dielectric constant of the ferroelectric material is a strong function of the temperature near its Curie temperature. The resonant frequency of the ferroelectric element is detected by applying a swept-frequency signal to the circuit and detecting the frequency which enhances the energy of the pulse. A two-dimensional camera for the radiation employs a two-dimensional array of these ferroelectric resonant circuits and a system for rapidly interrogating their resonant frequencies on a sequential basis.

Claims

1. A detector for electromagnetic radiation, comprising:

an absorber for the electromagnetic radiation;

a ferroelectric element in thermal contact with the absorber so that the temperature and the dielectric constant of the ferroelectric element is shifted as a function of the incoming radiation received by the absorber;

a resonant circuit including the ferroelectric element; and

means for detecting the resonant frequency of the ferroelectric element which is a function of the incoming radiation.

2. The radiation detector of claim 1 further including a constant temperature chamber enclosing the radiation absorber and the ferroelectric element.

3. The radiation detector of claim 2 further including a window in the chamber exposing the radiation absorber to radiation external of the chamber.

4. The radiation detector of claim 1 wherein said means for determining the resonant frequency of the circuit including the ferroelectric element includes means for applying a swept-frequency to the circuit and determining the frequency at which the circuit resonates.

6. The electromagnetic energy detector of claim 1 in which the ferroelectric element is a ring.

7. The electromagnetic energy detector of claim 6 where the ring is formed of barium strontium titanate.

8. The electromagnetic energy detector of claim 7 wherein the ferroelectric element is maintained in a constant temperature chamber having a temperature close to the Curie temperature of the ferroelectric element.

5. The radiation detector of claim 5 wherein the means for determining the frequency at which the circuit resonates includes a comparator which receives the output of the resonant circuit and the instantaneous applied frequency of the swept-frequency.

9. A system for imaging electromagnetic radiation, comprising:

an array of ferroelectric elements each forming an element of a resonant circuit, the array consisting of N rows of M elements;

radiation absorbers associated with each ferroelectric element;

a constant temperature chamber surrounding the ferroelectric elements and absorbers;

a window in the chamber exposing the said absorbers to incident electromagnetic radiation;

circuitry for applying a swept-frequency signal sequentially to each of the resonant circuits to determine each resonant frequency; and

a means for generating a two-dimensional image based upon the resonant frequencies of the individual ferroelectric elements.

10. The system of claim 9 where each element in a row has a different resonant frequency with no incident radiation.

11. The system of claim 10 including a template representing the resonant frequencies of the circuits with a base line radiation and a comparator for comparing the values in the template with the detected resonant frequencies of the circuits.

12. A method for constructing a resonant frequency electromagnetic radiation detector comprising the following steps:

providing a planer ground plane;

placing a dielectric layer on said planer ground plane;

placing a metal microstrip transmission line on said dielectric strip;

building up a mesa formed of dielectric material on said dielectric layer;

forming a ferroelectric ring on top of said mesa; and

placing a radiation absorbing layer on top of said ferroelectric ring.

13. The method of claim 12 wherein said planer ground plane is capable of supporting a resonate mode.

14. The method of claim 12 wherein said planer ground plane is formed of copper.

15. The method of claim 12 wherein said mesa is formed in a substantially cylindrical shape.

16. The method of claim 15 wherein said ferroelectric ring is formed to have a substantially similar diameter as that of said mesa.

17. The method of claim 12 wherein said ferroelectric ring is formed of Barium Strontium Titanate.

18. The method of claim 12 wherein said ferroelectric ring has a thickness in the range of 0.1-100 microns.