Note 7 — Intangible assets, net

Intangible assets, net consisted of the following (in thousands):

Amortization expense was $391,000, $160,000, $69,000 and $30,000 for the years ended December 31, 2017 and 2016, six months ended December 31, 2015 and the year ended June 30, 2015, respectively. The estimated aggregate amortization expense in respect of these assets for each of the five years ended 2022 is $585,000, $542,000, $467,000, $24,000 and $24,000, respectively.