# US 11,441,817 B2 · Photothermal trap

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- Number: US 11,441,817 B2
- Document ID: US11441817B2
- Status: Granted
- Kind: B2
- Application number: 17/048,205
- Filed: 2018-11-09
- Published: 2021-03-18
- Granted: 2022-09-13
- Earliest claimed: 2018-04-19
- Assignees: Massachusetts Institute of Technology
- Applicants: Massachusetts Institute of Technology
- Inventors: Kripa K. Varanasi; Susmita Dash; Jolet De Ruiter
- Web page: https://patentgrep.com/patent/US11441817B2

## CPC

- F24S 20/61: Passive solar heat collectors, e.g. operated without external energy source
- H10F 10/00: Individual photovoltaic cells, e.g. solar cells (electrolytic light-sensitive devices, e.g. dye-sensitised solar cells, H01G9/20)
- F24S 70/20: characterised by absorbing coatings; characterised by surface treatment for increasing absorption
- F24S 80/56: characterised by means for preventing heat loss
- F24S 80/60: Thermal insulation (transparent coverings F24S80/50)
- F28D 15/0275: {Arrangements for coupling heat-pipes together or with other structures, e.g. with base blocks; Heat pipe cores}
- F24S 2080/03: {Arrangements for heat transfer optimization}
- Y02E 10/50: Photovoltaic [PV] energy
- F24S: SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS (for producing mechanical power from solar energy F03G6/00)
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- F28D: HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT (fluid heaters having heat generating means and heat transferring means F24H; furnaces F27; details of heat-exchange apparatus of general)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

Articles, systems, and methods in which electromagnetic energy is converted to heat (e.g., for the purpose of inducing or inhibiting phase change of a material disposed over a surface) are generally described.

## Claims

### Claim 1

A photothermal trap, comprising:
a thermal spreader; and
an absorber over the thermal spreader, the absorber configured to absorb electromagnetic radiation;
wherein:
the photothermal trap is configured such that at least a portion of the electromagnetic radiation absorbed by the absorber is converted to heat that is transferred to the thermal spreader, and
the photothermal trap has a thermal response time constant of less than or equal to 800 seconds.

### Claim 2 (depends on 1)

The photothermal trap of claim 1, further comprising a thermal insulator under the thermal spreader.

### Claim 3 (depends on 1)

The photothermal trap of claim 1, further comprising a hydrophobic surface on or over the absorber.

### Claim 4 (depends on 1)

The photothermal trap of claim 1, wherein the thermal spreader is a thermally conductive solid.

### Claim 5 (depends on 1)

The photothermal trap of claim 1, wherein the thermal spreader is a heat pipe.

### Claim 6 (depends on 1)

The photothermal trap of claim 1, wherein the absorber has an absorptivity of at least 50% with respect to at least one wavelength of electromagnetic radiation within a band of wavelengths from 200 nm to 1 μm.

### Claim 7 (depends on 1)

The photothermal trap of claim 1, wherein the absorber has an emissivity of less than or equal to 50% at a temperature of 25° C. with respect to at least one wavelength of electromagnetic radiation within a band of wavelengths from 200 nm to 1 μm.

### Claim 8 (depends on 1)

The photothermal trap of claim 1, wherein the absorber has a broadband emissivity of less than or equal to 50% at a temperature of 25° C.

### Claim 9 (depends on 1)

The photothermal trap of claim 1, wherein the thermal spreader has a thermal conductivity in a lateral direction of at least 50 W m−1 K−1 at 25° C.

### Claim 10 (depends on 1)

The photothermal trap of claim 1, wherein there is a thermal transfer rate of at least 0.1 W between a first location and a second location in the thermal spreader separated in a lateral direction by a distance of at least 100 times the thickness of the thermal spreader, when the first and second locations have a difference in temperature of 1 Kelvin.

### Claim 11 (depends on 1)

The photothermal trap of claim 1, further comprising a material disposed over the absorber, wherein the material undergoes a phase change in the temperature range of from −20° C. to 50° C.

### Claim 12 (depends on 1)

The photothermal trap of claim 1, wherein the thermal spreader is in the form of a layer.

### Claim 13 (depends on 1)

The photothermal trap of claim 1, wherein the absorber is in the form of a layer.

### Claim 14

A photothermal trap, comprising:
a first region having a thermal conductivity in a lateral direction of at least 50 W m−1 K−1 at 25° C.; and
a second region, over the first region, the second region having an absorptivity of at least 50% with respect to at least one wavelength of electromagnetic radiation within a band of wavelengths from 200 nm to 1 μm;
wherein the photothermal trap has a thermal response time constant of less than or equal to 800 seconds.

### Claim 15 (depends on 14)

The photothermal trap of claim 14, further comprising a third region, under the first region, having a thermal conductivity in a transverse direction of less than or equal to 1 W m−1 K−1 at 25° C.

### Claim 16 (depends on 14)

The photothermal trap of claim 14, further comprising a hydrophobic surface on or over the second region.

### Claim 17 (depends on 14)

The photothermal trap of claim 14, wherein the first region is a solid.

### Claim 18 (depends on 14)

The photothermal trap of claim 14, wherein the first region is a heat pipe.

### Claim 19

A method of inducing or inhibiting a phase change of a material disposed over a photothermal trap comprising a thermal spreader, an absorber over the thermal spreader that is configured to absorb electromagnetic radiation, a thickness, and a lateral dimension perpendicular to the thickness, the method comprising:
exposing the photothermal trap to electromagnetic radiation such that the electromagnetic radiation is absorbed by a first area of the photothermal trap that is part of the absorber and converted to heat that is transported along the lateral dimension of the photothermal trap via the thermal spreader to a second area of the photothermal trap resulting in the inducing or inhibiting of the phase change of the material over the second area of the photothermal trap,
wherein the photothermal trap has a thermal response time constant of less than or equal to 800 seconds.