# US 7,745,792 B2 · Terahertz detectors for use in terahertz inspection or imaging systems

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- Number: US 7,745,792 B2
- Document ID: US7745792B2
- Status: Granted
- Kind: B2
- Application number: 11/839,375
- Filed: 2007-08-15
- Published: 2009-02-19
- Granted: 2010-06-29
- Earliest claimed: 2007-08-15
- Assignees: Morpho Detection, Inc.
- Inventors: Michael Breit; Florian Krug
- Web page: https://patentgrep.com/patent/US7745792B2

## CPC

- G01J 3/42: Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry (beam switching arrangements G01J3/08)
- G01J 1/46: using a capacitor
- G01N 21/3581: using far infrared light; using Terahertz radiation
- G01N 21/3563: for analysing solids; Preparation of samples therefor
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A technique is provided for examining a subject. The technique includes illuminating at least a part of the subject with THz radiation and detecting THz radiation reflected and/or transmitted from the illuminated part and incident upon a detector array by measuring change in capacitance corresponding to the incident THz radiation.

## Claims

### Claim 1

A terahertz (THz) inspection or imaging system, comprising:
an electromagnetic radiation source configured to generate electromagnetic radiation at multiple discrete frequencies in the THz range; and
a detector array including a plurality of detector cells adapted to detect THz radiation, each of the plurality of detector cells comprising a gas-filled variable capacitor and configured to generate a detector output signal in response to a change in capacitance in the variable capacitor caused by thermal expansion of the gas, the change in capacitance corresponding to an intensity of the THz radiation incident upon the integrated detector cell.

### Claim 2 (depends on 1)

The system of claim 1, wherein the electromagnetic radiation source comprises a broadband electromagnetic radiation source and wherein the detector array comprises a two-dimensional broadband detector array.

### Claim 3 (depends on 1)

The system of claim 1, wherein the radiation source comprises a backward wave oscillator source, a quantum cascading laser source, a multiplier chain source, a gas laser source, or other high-power source.

### Claim 4 (depends on 1)

The system of claim 1, wherein each of the multiple discrete frequencies is selected based upon a known spectroscopic signature of an object of interest.

### Claim 5 (depends on 1)

The system of claim 1, comprising one or more optical devices configured to illuminate at least a part of a subject with the generated THz radiation.

### Claim 6 (depends on 5)

The system of claim 5, wherein the detector array is configured to detect THz radiation reflected and/or transmitted from the illuminated part.

### Claim 7 (depends on 5)

The system of claim 5, wherein the one or more optical devices are configured to focus on the illuminated part of the subject automatically.

### Claim 8 (depends on 1)

The system of claim 1, comprising a processor configured to at least one of:
generate an image based upon the detector output signal;
identify the presence or absence of an object of interest within the generated image; and
automatically calibrate the THz inspection or imaging system.

### Claim 9 (depends on 1)

The system of claim 1, comprising a processor configured to detect the presence or absence of an object of interest based upon the detector output signal.

### Claim 10 (depends on 9)

The system of claim 9, wherein the processor is configured to detect the presence of the object of interest by detecting the presence of a spectroscopic signature of the object of interest from the detector output signal.

### Claim 11 (depends on 1)

The system of claim 1, wherein the THz radiation is in a range of about 0.1 THz to about 10 THz.

### Claim 12 (depends on 1)

The system of claim 1, wherein the electromagnetic radiation source generates a selected narrow bandwidth of THz radiation at any particular point of time rather than generating electromagnetic radiation at continuous frequencies ranging a full spectrum.

### Claim 13 (depends on 1)

The system of claim 1, wherein the detector array detects an intensity of a broad bandwidth of incident THz radiation.

### Claim 14

A detector adapted to detect terahertz (THz) radiation, the detector comprising:
a plurality of detector cells arranged in an array and configured to receive the incident THz radiation, each of the plurality of detector cells comprising:
an enclosure containing a gas and comprising a flexible membrane having a conductive coating on one side; and
a fixed conductive plate facing the conductive coating on the flexible membrane to form a variable capacitor, wherein intensity of the incident radiation corresponds to a change in capacitance of the variable capacitor.

### Claim 15 (depends on 14)

The detector of claim 14, wherein the gas expands and exerts pressure on the flexible membrane upon receiving the incident radiation causing capacitance of the variable capacitor to change by bending the flexible membrane.

### Claim 16 (depends on 14)

The detector of claim 14, comprising a layer of absorbent disposed within the enclosure for absorbing the incident radiation and heating the surrounding gas.

### Claim 17 (depends on 14)

The detector of claim 14, comprising an entrance window for receiving the incident radiation.

### Claim 18 (depends on 17)

The detector of claim 17, wherein the entrance window comprises a material transparent to THz radiation.

### Claim 19 (depends on 14)

The detector of claim 14, comprising readout circuitry coupled to the plurality of variable capacitors for measuring change in capacitance of each of the plurality of variable capacitors and generating a detector output signal.

### Claim 20 (depends on 14)

The detector of claim 14, wherein the enclosure includes a heat insulating material configured to prevent a temperature change within a first detector cell of the plurality of detector cells from effecting a second detector cell of the plurality of detector cells.

### Claim 21

A method of inspecting or imaging a subject, comprising:
illuminating at least a part of the subject with a terahertz (THz) radiation of a first selected frequency;
detecting THz radiation reflected and/or transmitted from the illuminated part in response to the THz radiation of the first selected frequency at a detector array; and
generating a detector output signal in response to a change in capacitance in a variable capacitor of the detector array caused by thermal expansion of a gas included within the detector array, the change in capacitance corresponding to the THz radiation incident upon the detector array.

### Claim 22 (depends on 21)

The method of claim 21, further comprising generating the THz radiation.

### Claim 23 (depends on 21)

The method of claim 21, comprising generating an image of the illuminated part based upon the detected THz radiation.

### Claim 24 (depends on 23)

The method of claim 23, comprising identifying the presence or absence of an object of interest within the generated image.

### Claim 25 (depends on 21)

The method of claim 21, comprising detecting the presence or absence of an object of interest based upon the detected THz radiation by detecting the presence or absence of a spectroscopic signature of the object of interest from the detected THz radiation.

### Claim 26 (depends on 21)

The method of claim 21 further comprising:
illuminating at least a part of the subject with a THz radiation of a second selected frequency; and
detecting THz radiation reflected and/or transmitted from the illuminated part in response to the THz radiation of the second selected frequency at the integrated detector array.

### Claim 27

A method of manufacturing a terahertz (THz) detector, the method comprising:
forming a plurality of enclosures using microelectromechanical system (MEMS) techniques, each enclosure having a flexible membrane on one side such that each of the plurality of enclosures contains a gas;
coating a layer of a conductive material on one side of each of the flexible membrane membranes; and
disposing a conductive plate corresponding to each of the coated flexible membranes at a fixed distance from the flexible membrane to form a gas-filled variable capacitor, wherein an intensity of incident radiation corresponds to a change in capacitance of the variable capacitor.

### Claim 28 (depends on 27)

The method of claim 27, comprising disposing a layer of absorbent within each of the plurality of enclosures.

### Claim 29 (depends on 27)

The method of claim 27, comprising coupling an entrance window to the plurality of enclosures to receive the incident THz radiation.

### Claim 30 (depends on 27)

The method of claim 27, comprising electrically coupling a readout circuitry to the plurality of conductive plates and conductive coatings.

### Claim 31 (depends on 27)

The method of claim 27, wherein the plurality of enclosures include a heat insulating material configured to trap heat within each enclosure and to prevent a temperature change within a first enclosure of the plurality of enclosures from affecting a second enclosure of the plurality of enclosures.