WooCommerce Custom Product Loop by Category

<ul class="products">

                <?php
                    $args = array(
        'post_type' => 'product',
        'post_status' => 'publish',
        'meta_query' => array(
            array(
                'key' => '_visibility',
                'value' => array('catalog', 'visible'),
                'compare' => 'IN'
            )
        ),
        'tax_query' => array(
            array(
                'taxonomy' => 'product_cat',
                'terms' => 'permanent',
                'field' => 'slug',
                'operator' => 'IN'
            )
        )
    );

                    $loop = new WP_Query( $args );
                    while ( $loop->have_posts() ) : $loop->the_post(); global $product;

        if (!$product->is_visible()) continue;

        $woocommerce_loop['loop']++;?>

                <li class="product">

                <a href="<?php echo get_permalink( $loop->post->ID ) ?>" title="<?php echo esc_attr($loop->post->post_title ? $loop->post->post_title : $loop->post->ID); ?>">

                    <?php woocommerce_show_product_sale_flash( $post, $product ); ?>

                    <?php if (has_post_thumbnail( $loop->post->ID )) echo get_the_post_thumbnail($loop->post->ID, 'shop_catalog'); else echo '<img src="'.woocommerce_placeholder_img_src().'" alt="Placeholder" width="'.$woocommerce->get_image_size('shop_catalog_image_width').'px" height="'.$woocommerce->get_image_size('shop_catalog_image_height').'px" />'; ?>

                    <h3><?php the_title(); ?></h3>

                </a>

                <a href="<?php echo get_permalink($product->id); ?>" ><?php echo apply_filters('out_of_stock_add_to_cart_text', __('details', 'woocommerce')); ?></a> /
                <a href="<?php echo esc_url( $product->add_to_cart_url() ); ?>" ><?php echo apply_filters('add_to_cart_text', __('Buy Now >>', 'woocommerce')); ?></a>

            </li>

            <?php endwhile; ?>
            </ul><!--/.products-->