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Intangible assets, net (Tables)
12 Months Ended
Dec. 31, 2021
Intangible assets, net  
Schedule of intangible assets, net

    

December 31, 

    

December 31, 

2021

2020

Software

$

30,838

$

25,957

Land use rights*

 

314,456

 

307,241

Patents

 

4,707,000

 

4,599,000

Subtotal

 

5,052,294

 

4,932,198

Less: Accumulated amortization

 

(4,846,323)

 

(4,268,165)

Intangible assets, net

$

205,971

$

664,033

*There is no private ownership of land in China. Land is usually owned by the local government and the government grants land use rights for specified terms. The Company acquired land use rights from the local government in December 2002 for period of 50 years. As of December 31, 2021 and 2020, land use rights with net book value of $200,204 and $201,755, respectively, were pledged as collateral for bank loans (Note 12).